GALACTIC NOISE AND PASSIVE MICROWAVE ... - Semantic Scholar
-?_t, c _ _
GALACTIC
NOISE
_"_
AND PASSIVE MICROWAVE FROM SPACE AT L-BAND David
Goddard
M. Le Vine
Space
Flight
REMOTE
SENSING
and Saji Abraham
Center,
Greenbelt,
dmlevine@priamgsfc,
MD
20771
nasa.gov
ABSTRACT The spectral window at L-band (1.4 GHz) is important for passive remote sensing of soil moisture and ocean salinity from space, parameters that are needed to understand the hydrologic extraterrestrial background,
and ocean circulation. At this frequency, galactic) sources is strong and, unlike the
this radiation
map of the portion derived
cycle (mostly
celestial
is spatially
sky at L-band
variable.
This paper
and a solution
presents
radiation constant
a modern
for the problem
from cosmic
radiometric
of determining
what
of the sky is seen by a radiometer in orbit. The data for the radiometric map is from recent radio astronomy surveys and is presented as equivalent brightness
temperature
suitable
representative
for remote
of those
salinity
from
space
galactic
plane,
sensing
contemplated
are presented
the contribution
applications. for remote
to illustrate can exceed
Examples
sensing
orbits
of soil moisture
the signal
several
using
levels
and antennas
and sea surface
to be expected.
Near
the
Kelvin.
I. INTRODUCTION The spectral important
window
for measuring
1.400-1.427
parameters
GHz
&the
salinity that are needed for understanding with the atmosphere. Being able to make microwave
spectrum
wavelengths
increase
the vegetation salinity, long dependence
surface
is a good
reflector
celestial concern
sky, being in the case
contributes
such
for passive
use only is
as soil moisture
the hydrological cycle and energy observation at the long wavelength
measurements.
and ocean exchange end of the
In the case of soil moisture, effects
of surface roughness. the sensitivity to
of attenuation
In the case salinity and
long
through
of sea surface minimize the
and roughness. from
the brightness
extraterrestrial
and the salinity
sources
temperature
radiation that is reflected from is of particular concern for remote
is exacerbated
addition,
radiation
to know
reserved
surface
into the soil and mitigate
temperature
at L-band
one needs
problem
that
penetration
on surface
down-welling contribution
to these
canopy and the effects wavelengths increase
However, example,
is critical
(L-band)
Earth
is not negligible.
of the celestial
sky to correct
For for
the surface into the receiver [1, 2]. This sensing of sea surface salinity because the
signal
by the fact the down-welling
itself
is relatively
radiation
small
[3, 4, 5].
is not a constant
across
The the
significantly stronger in the galactic plane [4, 6]. This is a particular of remote sensing from space because the portion of the celestial sky
radiation
changes
the orbit itself may change
rapidly
as the
its orientation
sensor with
moves respect
through
its orbit.
to the celestial
In
sky as is
the case with sun-synchronous keep
the orientation Previous
orbits
that precess
of the orbit with respect
estimates
as the Earth
rotates
around
of the magnitude
and distribution
of galactic
radiation
in remote sensing [4, 6, 7] have been rather course. However, recent surveys sky at 1.4 GHz [8, 9, 10, 11, 12, 13] have made it possible to produce sufficient
spatial
and radiometric
This paper present a modern problem of determining the orbit.
The
data
applications. for remote
sensing
illustrate
the signal
lI.
RADIO
THE
There
as equivalent
using
orbits
of soil moisture levels
are three
are discussed Cosmic
details
cosmic
in a "big of its spatial
applications remote
important
by thermal
sources
such
sensing
microwave bang".
for
remote
of those
from
within
space
sensing
contemplated
are presented
the L-band
solar system: The cosmic (mostly) neutral hydrogen The latter
background
Although
distribution as remote
applications,
to
window
at 1.413
microwave background and continuum emission
two are the subject
of this paper
but all
radiation
the recent
[14], these variations sensing
is a remnant
cosmological
of the origin
of the
(milli-Kelvin)
of soil moisture
the cosmic
research
background
or ocean radiation
a value of about 2.7 K. This with a down-looking radiometer
has
focussed
are not important
salinity
from
is essentially background in a direct
space.
on for For
constant
in
radiation can manner if, for
has side lobes above the horizon. It also can contribute radiation off the surface [1]. The latter is especially
in remote sensing of the ocean surface where the reflection large. The cosmic background will be included in the examples over the spectral [1, 7].
window,
coefficient is to be presented
it is relatively
easily
Emission: The window
original galaxy
salinity
of radiation
here; but, since it is uniform and constant included in radiometer retrieval algorithms
emission
temperature
representative
and sea surface
sources.
example, the radiometer antenna via reflection of down-welling
B. Line
brightness
and antennas
for completeness.
both space and time with contribute to a measurement
important relatively
applications.
Background:
The universe
sensing
SKY AT L-BAND
such as is emitted
A.
to remote
of the radio maps with
to be expected.
GHz that originate outside of our (CMB), discrete line emission from three
to be relevant
for use
map of the radiometric sky at L-band and a solution to the portion of the sky seen by a'down-looking radiometer in
is presented
Examples
accuracy
the Sun (to
to the sun constant).
from
at 1.413 GHz was protected
a hyperfine
proposal that such is attributed to Oort
transition
in neutral
for passive hydrogen
use because
that occurs
of the interest
in this window.
in The
radiation could be detected from neutral hydrogen in our and van de Hulst, and the first observations were made by
Ewen and Purcell in 1951 [12]. This radiation provides information on the temperature, density and motion of hydrogen. The radiation is concentrated around the plane of the
galaxy,but cloudsof hydrogenarewidespreadandnodirectionis observedwithout some suchradiation. Severalsurveysof this sourceof radiationhavebeenmade[15, 16, 17, 18, 19, 20]. Recently,HartmanandBurton [12] motivatedby the high quality, all-sky surveys beingmadeat otherwavelengths,reporteda new survey. The Leiden/Dwingeloosurvey (TableI) useda 25-meterradiotelescopeandcoveredthe sky abovedeclinationof-30 °. This surveywasrecentlycomplementedby datacollectedwith the 30 meterdish antenna at theInstitutoArgentinode Radioastronomia (IAR) andreportedby Arnal et al [13]. The IAR survey (Table I) covereddeclinationssouth of-25 degreesfilling in the missing portions of the southernsky. The resultis datawith sufficient spatialresolution(0.5° x 0.5°) andradiometricresolution(AT < 0.1 K) to be applicableto remotesensingat Lbandfrom space,includinghigh-resolutionsensorsproposedfor the future (e.g.a spatial resolutionof 0.5° x 0.50corresponds to an apertureof about25 meters). C. Continuum Radiation In addition to the discrete spectra associatedwith atomic transitions as in hydrogenabove,thereis a continuumof radiationfrom extra-terrestrialsources. This radiationcan be dividedinto thermalandnon-thermalsources.Thermalsourceshavea spectrum(amplitudeversusfrequency)similar to thatof blackbodyradiation. At L-band, the Rayleigh-Jeanslaw appliesand the power increaseswith frequency as f2. Nonthermal sources are sources whose spectra behave differently. An example is synchrotronradiationfrom relativistic electrons,in which casethe spectrumat L-band decreaseswith frequencyroughly as f-0.7s[21]. The sourceof continuumradiationmay belocalizedin space(discretesources)or may be of a spatiallycontinuousnature(diffuse or unresolveddiscretesources). The sourceof the radiationis mostly galacticbecause thesesourcesare closest,but there are also strong extra-galacticsourcessuch as the "radio galaxy"CygnusA [21]. There havebeenseveralsurveysof the continuumradiationat 1.4GHz [22, 23, 24, 25, 26, 27]. None of thesesurveyscoveredthe entire sky and they use different bandwidthsandthe measurements were madewith differing sensitivity. For the most part, they consistof a map of discretesources. However,for applicationsto remote sensingof the Earth, it is desirableto have the integratedsignal from a particular direction in the sky (i.e. power from all sources,discrete and continuous),because antennaslikely to be employedin spacein the foreseeablefuture will not resolve individual sources.The recentsurveywith the StockerttelescopeatBonnUniversity [8], [9] providesdatain this format. The antennahada half-powerbeamwidth of about0.5 degrees.The sensitivity of these measurementsis about 0.05 K and the absolute calibration (zerolevel accuracy)is 0.5 K. This survey(Stockertsurvey;TableI) covers all of the northernsky andthe southernsky to -19° declination. The data includesall sourcesexceptfor a region aroundCassiopiaA which was too strong. Recently,the surveyof the southernskywascompletedusingthe 30-mradio telescopeof the Instituto ArgentinodeRadioastronomia [10], [11]. The IAR continuumsurvey(TableI) coversthe
3
southernsky for declinationbelow-10 ° with spatialresolutionandsensitivity similar to thatof theStockertsurvey. III.
DATA
Sensing
Format
It is common practice in passive microwave remote sensing to treat the scenes as sources and the receivers as narrow bandwidth devices [7, 21]. In the Rayleigh-
thermal Jeans
in Remote
limit,
this permits
one
equivalent
"brightness"
temperature emissivity
is the product is a function
parameters
of interest.
surface
salinity
to describe
temperature.
For sources
This
is the
approach
changes
In the sections
below,
to measure
and salt change
temperature
in terms
the brightness
soil moisture
the emissivity
the
Doppler
line emission
sea
astronomy
surveys
will be presented
temperature. The data will be presented as an such that total power is P = kTBAB. For this
has a relatively
at the frequency
line
spread
and
a reasonable
Emission The
occurs
The the
sufficiently
purpose, a bandwidth, AB = 20 MHz, has been assumed. This represents maximum for the window at 1.413 GHz after allowances for filter shape. A. Line
of an
can be detected.
the data from the radio
in the form of an equivalent blackbody equivalent thermal source normalized
scenes
and emissivity of the surface. surface, hopefully including
proposed
case water
in brightness
and
that are not blackbodies,
of the physical temperature of the properties of the
[4, 28, 29] in which
that the resulting
the measurements
is shifted
by
by thermal
associated motion
energy
shift and thermal
For example,
narrow
spectrum
with the hyperfine
of hydrogen
of the
gas
broadening,
relative
(collisions
to the and
the spectrum
the Leiden/Dwingeloo
survey
[21]. For hydrogen
transition
at 21.106
observer
vibrations).
However,
(doppler But,
of this radiation
[12] and IAR survey
at rest, it
cm.
shift)
even
with
is relatively [13] cover
and large
narrow.
the velocity
range from -450 to +400 km/s (Table I) which corresponds to a frequency range of less than _+2.2 MHz about the center (at rest) frequency of 1.42 GHz. The two surveys both report km/s.
power
integrated
To convert K-MHz Then,
using this
over the spectrum
into a format
the standard
value
was
useful
form
divided
of the line. The integrated
for remote
for Doppler by
20 MHz
sensing,
shift:
power
in K-
this data was first converted
v = Vo (1 - v/c)
to convert
is given
it into
where
to
v is velocity.
an effective
brightness
temperature. The brightness temperature, TB, is the temperature of a blackbody that observed with an ideal receiver with a bandwidth of AB = 20 MHz, will give the power (P = kTBAB) reported in the radio astronomy surveys. with receivers with other bandwidth with the obvious
The data can be converted for use re-normalization. (Of course, this
only makes
on the line and is greater
sense if the receiver
bandwidth
is centered
than _+2.2
MHz.) The
data in the above
the plot is in celestial
form
coordinates.
is shown
in Figure
The "U'
shape
1 (top).
region
The units
of high brightness
are Kelvin
and
temperature
is the plane of the galaxy (which is tilted with respectto an observerin the celestial coordinatesystem).The effective brightnesstemperatureis small almost everywhere exceptin the galacticplanewhereequivalentblackbodytemperatures on the orderof 3 K canoccur. B. Continuum
Radiation
For the continuum
radiation,
the data used here was the Stockert
survey
[9] for the
northern sky together with the more recent IAR survey [10] for the southern sky (Table I). In both cases, the data are in the form of total power over the bandwidth of the receiver
with the exception
that the line emission
from hydrogen
with a narrow filter at the line center). The power represents within the beam, discrete and unresolved and includes thermal However,
Cassiopeia
a small region
A, which
was too strong
of the sky around
Cassiopeia
to be included
A is excluded
was excluded
(removed
radiation from all sources and non-thermal sources. in the Stockert
survey,
and
from the data.
For both surveys, the data are in the form of power integrated over the pass-band of the radiometer receiver. The effective bandwidth was about 18 MHz and 13 MHz for the Stockert and Villa Elisa surveys, respectively (after correction for the filter to remove line emission). The Villa Etlisa antenna (30 m) was under-illuminated to match the resolution
of 25 m antenna The
data
from
used in the Stockert
the Stockert
survey
survey
[10, 11 ].
[9] normalized
to a bandwidth
of 20 MHz
is
shown in celestial coordinates in bottom panel of Figure 1. (All of data in Figure 1 has been converted to celestial coordinates using the J2000 epoch [21, 32]). As in the case of the line emission galaxy right
from hydrogen,
as is evident (Declination
the strongest
on the far right hand 60 o and
Right
Ascension
Cassiopeia However,
A. Data exists for the this data (IAR continuum
resolution
shown
resolution
[30] and is presented
in Figure
radiation
side.
tends
the white
355 °) which
portion survey;
of the Reich,
1. The data has been and discussed
to lie along
Also notice
is the
the plane
of the
spot at the upper
data
missing
around
southern sky missing in Figure 1. 2001) has not been released at the
provided
in Sections
for use in this paper
at lower
IV-V.
C. Examples
more
Figure 2 shows examples of the magnitude and spatial detail. The data shown are cuts through the color-coded
declination brightness function
of 0 °, 200 and temperature due of right ascension
temperature for the curves are associated the
continuum
40 °.
On
the
left
side
2 is shown
to line emission from hydrogen (from and on the right side is shown the
continuum radiation (from with crossing the galactic
is considerably
of Figure
distribution of the data in maps in Figure 1 at fixed
larger
than
from
Figure plane.
the
effective
Figure 1; top) as a effective brightness
1; bottom). The peaks in these Notice that the contribution from
the line
emission
from
hydrogen.
In
particular, peak values of effective brightness temperature from line emission are on the order of 2 K whereas the peak value due to continuum radiation is nearly 20 K. Also,
notice that the distribution is quite complexwith the obviouspeakat the galacticplane but with levelsthatdependon wherethe intersectionswith the galacticplaneoccur. IV.
Effect
of Antenna
The apparent will depend radiation values
Beam brightness
on the antenna
and, as a result, in Figure
relatively
temperature
employed. the observed
1. This is especially
value
seen
antenna
in a remote
smoothes
can be significantly
true in the vicinity
sensing
of the celestial
with the power to perform contributing
the incident
different
from
of the galactic
the peak
plane,
which
is
the
effect
sky contributing
pattern
of the antenna
of the
antenna,
one
to the measurement. (e.g. Section
could
integrate
over
the
That is, take the convolution
3.4 of [21]).
However,
it is equivalent
the convolution over the entire sky first and then locate the portion of the sky to the measurement. This approach has the advantage of presenting the
smoothed data done here.
in its entirety
independent
of the particular
application.
This
The data is presented in Figure 3 for an antenna with a Gaussian at half maximum (FWHM) of 10 °. The details of the integration
width
application
(integrates)
narrow. In order to understand
portion
actually The
has
been
beam with a full are presented in
Appendix A. The choice of 10 ° beam width was made to indicate the effect of smoothing but to remain conservative and not overly smooth the data for remote sensing applications. Figure 3 (top) shows the smoothed data for line emission and Figure 3 (bottom) is the smoothed data for the continuum radiation. In the case of the continuum radiation,
the
data
from
the
Stockert
survey
(Table
I) was
smoothed
Appendix A and the data for the southern sky (IAR continuum us with the 10 degree smoothing (courtesy of P. Reich [30]). features
of the high-resolution
maps
remain
in the smoothed
survey) Notice
as outlined
was provided to that the general
data.
Figure 4 shows detail for cuts through the data at fixed declination 40 o. The smoothed line emission is shown on the left and the continuum the right.
Notice
remain,
although
continuum peak
that the general the
at 40 degrees
in the continuum
galactic
large
plane,
is much radiation
the continuum
features
difference
evident
in the
reduced.
radiation
(-
value
This reflects
on the galactic
of 0 °, 20 ° and radiation is on
in the high-resolution
peak plane.
between the very
Also,
1 K) is greater
in
than
notice
data line
(Figure
emission
narrow
nature
that away
from line emission
2) and
of the
from
the
(- 0.05
K). Figure contributions:
5 is an example at 20 degrees declination of the total Cosmic background, line emission and continuum. Shown
original and smoothed data for the line emission. smoothed data for the continuum radiation. The components
(smoothed
line emission,
smoothed
together with the sum. Notice that the plane contribution of the continuum and line emission
In the bottom
continuum
middle panel
from the three at the top is the
is the shows
and the cosmic
original and each of the background)
of the galaxy is evident and that is clearly important and comparable
the to
the CMB. The peakaroundthe galacticplanedependson declinationand,for example, would bemuchlargerif a declinationof 40 degreeswereshown(seeFigures2 and4). It is clearfrom Figures1-5 that the backgroundradiationis spatially complex. Large valuesarepossiblealongthe galacticplane. On the otherhand,thereareregions nearthe galacticpole wheretheline emissionandcontinuumradiationaresmall (< 1 K) andthe cosmicbackgrounddominates. Clearly, it is importantto know whatportion of the "sky" is contributingto a particular measurement.This problem is addressedin SectionV. V. REMOTE
SENSING
The radiation
data can
applications
from
be
the
radio
significant
and
it is important
particular orbit
PROBLEM
measurement.
circling
from
to know To
the Earth
contribution
the
astronomy highly what
address
with
sky
portion
this
its antenna
radio
surveys
variable.
indicates
that
Consequently, of the celestial
problem,
imagine
pointing
down.
(down-welling
the
for
background
remote
sky is contributing
a radiometer The
radiation
sensing
goal that
to a
at L-band
in
is to determine
is reflected
the
into
the
antenna), which must be taken into account at each position in this orbit. The input is the data given in Figure 1 (or Figure 3) normalized to the radiometer bandwidth, plus a constant
of 2.7 K that is added The
solution
to account
can be found
for the cosmic
by tracing
rays
microwave
from
background.
the antenna
to the
surface
and
computing how they are reflected toward the sky. For example, a flat, specular surface behaves like a mirror and the solution can be obtained by placing the antenna at its conjugate
point
reflected
ray.
behind The
the
surface
and
pattern
is unchanged,
antenna
change of symmetry (i.e. right power reflected into the antenna
solution
that looks At
the
surface).
left
are
the
smoothed
direction
but it does
of the
undergo
specularly
a mirror
image
computes the over the sky.
procedure to solve the problem for a curved earth. The B and solved for an ideal case (spherical earth, circular
Examples
to the side in a plane
out in the
hand symmetry becomes left hand). One by integrating the mirrored antenna pattern
One can follow a similar is outlined in Appendix
orbit and specular
looking
are shown
perpendicular data
in Figure
6 for the case of an antenna
to the orbit (e.g.
describing
the
radio
as in a cross
sky
track
at L-band
in
scan).
celestial
coordinates (sum of line emission and continuum) seen by the antenna (Gaussian power pattern with a 10 degree beam width). Shown on the smoothed data is the locus traced by the reflected circular
ray at bore-sight
orbit with inclination
for an antenna
looking
angle is 95 degrees
to the right
(angle
at 0i = 30 degrees
3I in Equations
4B).
in a
It is possible
to plot orbits on the original mentioned above, it is more
data and then integrate over the antenna beam. However, as efficient to integrate first and then plot the orbits. This what
has
Figure
been
done
in creating
6.
The
panels
on
the
right
show
temperature along this locus as a function of declination. Four values line emission, continuum emission, CMB (the straight line) and the total.
the
brightness
are plotted:
The
The and
the
shape
of the loci in Figure
inclination
determined
of the
orbit.
by the intersection
is illustrated
by
intersection
the
two
of the plane
6 depends
The
position
of the plane examples
on the incidence
of the locus
angle
(i.e.
of the orbit with the plane
shown
in Figure
of the orbit has been
rotated
6 that
of the antenna
center
of the curve)
of the equator.
differ
by 90 degrees.
only
These
below
moisture
using
from
the orbit
space.
coordinate
system
to celestial
coordinates
VI.
The
the
called
in Appendix
is presented This
here
for
is an orbit
HYDROSTAR
on the Earth
of
choice
observation
for
pole)
In order
[28].
sees
two examples
ago
as seen
can be in the
to measure
soil
in an earth-centered
of longitude
and
local
time)
C.
a sun-synchronous
commonly
remote
the
to remain
local
remote
a 6am/6pm
sensing
of soil
soil moisture
oriented
such
from that all
local
time.
It is the
applications
because
the
local
time
generally
has a high
crossing
in the same
with
at the same
this orbit
equatorial
for
to measure
orbit is one
overhead
sensing
In practice,
and
pass
orbit
selected proposed
A sun-synchronous
the satellite
many
is constant.
close to the value.
orbit
years
as a function
[28], [31] and was the orbit for a sensor
observers orbit
of relating
several
the
Orbit
crossing.
moisture
proposed
intersection
is discussed
example
equatorial
problem
(e.g. equatorial
HYDOSTAR
An
space
The
for a mission
This
in that
show that keeping track of changes in the orbit, for example due to precession, important for determining the background radiation. This is illustrated further section
is
time
precesses
orientation
inclination
a bit about
with respect
of
(passes
the
nominal
to the sun, the orbit
must precess in celestial about 1 degree per day.
coordinates As a result
as the earth rotates about the sun. The change is of the precession, the position of the locus of the
reflected
coordinates
(Figure
rays in celestial
change
of 360 degrees
celestial astronomy
in right
ascension
6) will drift
each year.
across
The problem
the sky going of locating
through
a
the orbit in
coordinates given the local time of equatorial crossing is the problem in of transforming local time into sidereal time. The solution used here is given
in Appendix
C.
Once
the orbit is located
in celestial
coordinates,
the procedure
outlined
in Section V above is followed to plot the locus of the reflected rays on the sky. (This amounts to neglecting changes of the orbital plane during one period, about 90 minutes.) Figure year
starting
(10 ° Gaussian degrees.
7 shows
examples
with March beam)
The curves
with the HYDROSTAR
15, 2002.
looking
right
on the left show
Thecalculation at 5 degrees
orbit
for several
is for the antenna (0i = 5).
the orbit in celestial
The
orbit
coordinates.
times
described inclination The
curves
of the above is 95 on the
right show the total effective background radiation, the sum of the three terms, line emission, continuum and CMB. Notice that the total varies from a little less than 4 K to nearly over
11 K.
The
values
the orbit varies
if the incidence
angle,
change
seasonally 0i, where
over the orbit (i.e. in one period). (i.e. with the time of year). changed.
Also,
The values
the distribution
would
also change
VII.
CONCLUSION In addition
radiation into
to the uniform
(line emission
account
radiation
for
background
from hydrogen
remote
is spatially
cosmic
sensing
varying
and a continuum
at L-band.
and
radiation
there
background)
In contrast
strongest
(CMB),
to the
in the direction
is additional
that must be taken CMB,
this
of the plane
additional
of the galaxy.
The effective brightness temperature of down-welling radiation from these sources that is reflected from the surface into the radiometer depends on the antenna beam width and surface
conditions.
For
antenna
with a beam
width
a perfectly on the order
other than the CMB is on the order and orbit. The fact that this signal the sensor
in its orbit
Earth.
The
surface
conditions.
sensing
of soil moisture
(on the order
of 0.3).
(on the order
where
careful
VII.
REFERENCES
[1] C. T. Swift,
Meteorol.,
[2] H-J. C. Blume
[3] H-J. C. Blume, and salinity 308, 1978.
radiation
depends
on the
where
the reflectivity
(on the order radiation
remote
an
sources
sensing applications
small
applications
such
of the surface
of 0.5 K per psu).
of the ocean-
and
as the remote
at the surface
sensing
will be an important
sensing
of the
is large
In the latter
issue.
A review,"
Bound.
1980. "Passive
IEEE
B. M. Kendall
and
from
such
and the reflectivity
salinity
and B. M. Kendall, zones,"
for applications
is small
microwave
via microwave
for remote
for remote
vol. 18, pp. 25-54,
and salinity in coastal 394-404, 1982.
contribution
important
of the down-welling
"Passive
of unity)
issue
is large
it is more
of sea surface
mapping
the peak
it is less an issue
the signal
However,
(reflectivity
an important
background
of 0.7) and the signal
case,
of 10 degrees,
its presence
of the
surface
of 1 - 6 K, varying with the orientation of the sensor can change both seasonally and with the location of
For example,
as the measurement
Layer
makes
importance
reflecting
microwave
Trans.
Geosci.
and J. C. Fedors,
radiometry,"
measurements Remote
"Measurement
Boundary-Layer
of temperature
Sensing,
vol. GE-20,
of ocean
Meteorol.,
pp.
temperature
vol.
13, pp. 295-
[4] C. T. Swift and R. E. McINTOSH, "Considerations for Microwave remote sensing of ocean-surface salinity," IEEE Trans. Geosci. Remote Sensing, vol. GE-21, No. 4, 480-491,
1983.
[5] E. G. Njoku, microwave sensing,"
W. J. Wilson,
S. H. Yueh,
radiometer-scatterometer IEEE
[6] H. C. Ko, "The 46, pp. 208-215,
Trans.
Geosci.
distribution
and
concept
Remote
Sensing,
of cosmic
radio
1958.
9
Y. Rahmat-Samii, for
ocean
salinity
vol. 38, pp. 480-491, background
radiation,"
"A large-antenna and
soil
moisture
2000. Proc.
IRE,
vol.
[7] F. T. Ulaby, and
R. K. Moore
radiometry,
Wesley
publishing
[8] W. Reich,
[9] P. Reich
and W. Reich,
- Part II," Astronomy
pp. 861-877, [11]
[14]
sensing
Passive,
series,
"A radio
The atlas of contour
maps,"
J. A. Bava,
Astronomy
"A radio continuum
survey
Astronomy
and W. 1997.
B. Burton,
Atlas
E. Bajaja,
G. Hauser,
L37-IAO,
- Part
sky at 1420
survey
of the
Larrarte,
1986.
E. E. Hurrel, of the southern
of Galactic
R Morras
J. J. Larrarte,
Neutral
sky at 1420
MHz:
vol. 368, pp.
1123-
Hydrogen.
and W G L P6ppel,
W.
Cambridge
"A high sensitivity
and Astrophysics
Supplement
Series,
2000.
M.
Janssen,
T. Kelsall,
R. F. Silverberg, of the Explorer
P. M.
G. F. Smoot
cosmic (COBE)
microwave satellite,"
and
Lubin, D.
T.
S. S. Meyer, R. A. E. Dwek, S. Gulkis,
S. H. Moseley, Wilkinson,
"A
Jr.,
T.
L.
preliminary
background spectrum by the Cosmic The Astrophysical Journal, vol. 354, pp.
1990.
F. R. Colomb,
W.
G.
L. Poppel
and
C. Heiles,
"Galactic
HI
[17] G. Westerhout,
G. L. Mader
and R. H. Harten,
"Telescope
beam
data,"
Astronomy
characteristics
scale of the Maryland-Green Bank 21-cm line survey," Supplement series, vol. 49, pp. 137-141, 1982.
10
in HI,"
at Ibl _> 10% II.
Photographic presentation of the combined southern and northern and Astrophysics Supplement Series, vol. 40, pp. 47-55, 1980.
temperature Astrophysics
MHz
vol. 376,
[15] M. N. Cleary, C. Heiles and C. G. T. Haslam, "A synoptic view of the galaxy Astronomy and Astrophysics Supplement Series, vol. 36, pp. 95-127, 1979. [16]
1,"
southern
& Astrophysics,
and Astrophysics,
of the sky at 6 < -25°, '' Astronomy
measurement Background
MHz
vol. 63, pp. 205-292,
continuum
F. R. Colomb,
reduction,"
142, pp. 35-40,
Murdock,
1. Addison-
1982.
of the northern
supplement
and W. Reich,
sky at 1420
J. C. Mather, E. S. Cheng, R. E. Eplee, Jr., R. B. Isaacman, Shafer, R. Weiss, E. L. Wright, C. L. Bennett, N. W. Boggess, M.
fundamentals
vol.
vol. 48, pp. 219-297,
survey
and data
[13] E. M. Arnal, vol.
series,
and Astrophysics
and A. J. Sanz,
HI survey
and
of the northern
"A radio continuum
P. Reich,
Observations 1132, 2001. [12] D. Hartmann Univ. Press,
remote
Active
2001.
J. C. Testori, Reich
survey
supplement
J. C. Testori
sky at 1420 MHz,
Microwave
sensing:
1981.
continuum
and Astrophysics
[10] P. Reich,
remote
company,
"A radio
Astronomy
and A. K. Fung,
Microwave
Astronomy
and and
[18] F. J. Kerr, P. F. Bowers, P. D. Jacksonand M. Kerr, "Fully sampledneutral hydrogen survey of the southern milky way," Astronomy and Astrophysics supplement
series,
[19] W. B. Burton,
Galactic
K. I. Kellerman, [20] W.
[21]
maps
and Extragalactic
The Galactic
Springer-Verlag,
J. J. Condon
1986.
eds.), Springer-Verlag,
B. Burton,
eds.),
vol. 66, pp. 373-504,
Radio New
Interstellar
Heidelberg,
Astronomy.
York,
(G. L. Verschuur
and
1988.
Medium.
(D. Pfenniger
and
P. Bartholdi,
1992.
and J. J. Broderick, "A 1400 MHz sky survey. I. Confusion-limited 7h30 m < O_< 19 i130 m, _5 ° < 8 < +82o, ', The Astronomical Journal, vol.
covering
90, p. 2540,
1985.
[22] J. D. Kraus,
Radio
[23] R. S. Dixon,
Astronomy.
"A master
McGraw-Hill
list of radio
Inc, 1966.
sources,"
Astrophys.
J. Suppl.
Ser, vol 20, No.
180, 1970. [24]
A. E. Wright Australia
and
R. Otrupcek,
Telescope
[25] W. Reich,
National
P. Reich
the Galactic Supplement [26] R. L. White
and
Astrophysical
Facility,
and E. Ftirst,
plane Series,
Parkes
Radio
Sources
Catalogue,
Journal
"The
Effelsberg
"A new
Supplement
1.Ol.
1990. 21 cm radio
continuum
between I= 357 ° and 1= 95.5°, '' Astronomy vol. 83, pp. 539-568, 1990. R. H. Becker,
Version
Series,
Catalog
of 30,239
and
of
Astrophysics
1.4 GHz
vol. 79, pp. 331-467,
survey
sources,"
The
1992.
[27] B. Uyaniker, E. Ftirst, W. Reich, P. Reich, and R. Wielebinski, "A 1.4 GHz radio continuum and polarization survey at medium Galactic latitudes," Astronomy & Astrophysics
Supplement
[28] D. M. Le Vine, surface
Series,
vol.
138, pp. 31-45,
J. B. Zaitzeff,
E. J. D'Sa,
Toward
an operational
salinity:
Oceanography and Society. (D. Halpern, Series #63, Elsevier Science, 2000. [29]
P.
Waldteufel,
characteristics L-band
concept,"
Sulface Netherlands, [30]
P. Reich,
E.
and
Anterrieu,
J.
M.
of a 2-D interferometric in Microwave
Atmosphere. pp. 467-475,
Private
Ed.),
ll
and
Y.
Elsevier
Kerr,
as illustrated and and
Remote S.
M. Goodberlet,
system,"
pp. 321-335,
Goutoule
P.
2002.
C. Swift,
remote-sensing
Radiometry
2000.
Communication,
J. L. Miller,
antenna,
(Pampaloni
1999. "Sea
in Satellites, Oceanography
"Field
of
view
by the MIRAS/SMOS Sensing
Paloscia,
of the
Eds.),
Earth's
VSP,
The
[31]
Y. H.
Kerr,
Goutoule,
P. Waldteufel,
C. Tabard
an overview,"
in Microwave
and Atmosphere. 467-475, 2000. [32]
D.
A.
Table
h
and
Parameters
W.
of the
D.
HPBW (effective) Effective
-19 °
-35' 50 mK
and Remote S. Paloscia,
McClain,
survey
Stockert Continuum
8>
J. M. Martinuzzi,
soil moisture
B. Lazard,
and ocean
Sensing
Eds.),
VSP,
Fundamentals
of
J.-M.
salinity
mission:
of the Earth's
Smface
The
Netherlands,
Astrodynamics
pp.
and
1997.
Survey 0°< c_ < 360 °
Coverage
"The
P. and
McGraw.Hill,
Summary
Wigneron,
Radiometry
(Pampaloni
Vallado
Applications.
J.-P.
and A. Lannes,
parameters
IAR Continuum
Leiden/Dwingeloo Hydrogen Survey
IAR Hydrogen
Survey
Survey 0°< ot __360 °
0°< _z < 360 °
0°< c_ _5.0
(bottom)
K
as equivalent
brighmess
20 OECLINAT;OH DECLINATION
4{] Degree
40 Degree
_18
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300
350
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100
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4
II
05
5
2: Line
emission
and 40 degrees
(bottom
150
200
ASCENSION
(left)
250
300
00
350
50
100
and continuum
to top). Notice
150
#IGHT
(Degreel
background
that the vertical
20
(right) scale
200
ASCENSION
250
300
350
(Degree,)
at constant
of the upper
declination
right panel
of 0, 20
is 0-20 K.
5O
z
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0
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Figure
3: Smoothed
0.05
200 ASCENSION
0.1
0.25
data.
Line
0.5
300 (Degree)
200 ASCENSION
1.0
emission
300 (Degree)
2.0
3.0
(top)
and
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continuum
background
(bottom)
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21
with
as a
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Figure 4: Smoothed data. Line emission (left) and continuum 3 but at constant declination of 0, 20 and 40 degrees (bottom
22
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20
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23
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Figure 6: Examples of the background polar orbit with inclination 95 degrees. in the equatorial crossing. smoothed with a Gaussian
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40
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The data on the left is the net background (line emission plus continuum) as beam with a 10 degree beam width (FWHM). The two panels on the fight
temperature
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24
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MARCH 15, 2002, 00:00:00 10
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ASCENSION
using
(Degree]
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temperature
(the
The values
DECLINATION
the HYDROSTAR
projection CMB).
:,o
300
total
are for a sensor
coordinates contribution
orbit.
The antenna
is shown from
line
with 20 MHz bandwidth
25
points
(Degree)
at 5 degree
on the left. On the right and
continuum
and a 10 degree
emission Gaussian
look angle. are the values together beam.
with
The of the
GALACTIC
NOISE
_"_
AND PASSIVE MICROWAVE FROM SPACE AT L-BAND David
Goddard
M. Le Vine
Space
Flight
REMOTE
SENSING
and Saji Abraham
Center,
Greenbelt,
dmlevine@priamgsfc,
MD
20771
nasa.gov
ABSTRACT The spectral window at L-band (1.4 GHz) is important for passive remote sensing of soil moisture and ocean salinity from space, parameters that are needed to understand the hydrologic extraterrestrial background,
and ocean circulation. At this frequency, galactic) sources is strong and, unlike the
this radiation
map of the portion derived
cycle (mostly
celestial
is spatially
sky at L-band
variable.
This paper
and a solution
presents
radiation constant
a modern
for the problem
from cosmic
radiometric
of determining
what
of the sky is seen by a radiometer in orbit. The data for the radiometric map is from recent radio astronomy surveys and is presented as equivalent brightness
temperature
suitable
representative
for remote
of those
salinity
from
space
galactic
plane,
sensing
contemplated
are presented
the contribution
applications. for remote
to illustrate can exceed
Examples
sensing
orbits
of soil moisture
the signal
several
using
levels
and antennas
and sea surface
to be expected.
Near
the
Kelvin.
I. INTRODUCTION The spectral important
window
for measuring
1.400-1.427
parameters
GHz
&the
salinity that are needed for understanding with the atmosphere. Being able to make microwave
spectrum
wavelengths
increase
the vegetation salinity, long dependence
surface
is a good
reflector
celestial concern
sky, being in the case
contributes
such
for passive
use only is
as soil moisture
the hydrological cycle and energy observation at the long wavelength
measurements.
and ocean exchange end of the
In the case of soil moisture, effects
of surface roughness. the sensitivity to
of attenuation
In the case salinity and
long
through
of sea surface minimize the
and roughness. from
the brightness
extraterrestrial
and the salinity
sources
temperature
radiation that is reflected from is of particular concern for remote
is exacerbated
addition,
radiation
to know
reserved
surface
into the soil and mitigate
temperature
at L-band
one needs
problem
that
penetration
on surface
down-welling contribution
to these
canopy and the effects wavelengths increase
However, example,
is critical
(L-band)
Earth
is not negligible.
of the celestial
sky to correct
For for
the surface into the receiver [1, 2]. This sensing of sea surface salinity because the
signal
by the fact the down-welling
itself
is relatively
radiation
small
[3, 4, 5].
is not a constant
across
The the
significantly stronger in the galactic plane [4, 6]. This is a particular of remote sensing from space because the portion of the celestial sky
radiation
changes
the orbit itself may change
rapidly
as the
its orientation
sensor with
moves respect
through
its orbit.
to the celestial
In
sky as is
the case with sun-synchronous keep
the orientation Previous
orbits
that precess
of the orbit with respect
estimates
as the Earth
rotates
around
of the magnitude
and distribution
of galactic
radiation
in remote sensing [4, 6, 7] have been rather course. However, recent surveys sky at 1.4 GHz [8, 9, 10, 11, 12, 13] have made it possible to produce sufficient
spatial
and radiometric
This paper present a modern problem of determining the orbit.
The
data
applications. for remote
sensing
illustrate
the signal
lI.
RADIO
THE
There
as equivalent
using
orbits
of soil moisture levels
are three
are discussed Cosmic
details
cosmic
in a "big of its spatial
applications remote
important
by thermal
sources
such
sensing
microwave bang".
for
remote
of those
from
within
space
sensing
contemplated
are presented
the L-band
solar system: The cosmic (mostly) neutral hydrogen The latter
background
Although
distribution as remote
applications,
to
window
at 1.413
microwave background and continuum emission
two are the subject
of this paper
but all
radiation
the recent
[14], these variations sensing
is a remnant
cosmological
of the origin
of the
(milli-Kelvin)
of soil moisture
the cosmic
research
background
or ocean radiation
a value of about 2.7 K. This with a down-looking radiometer
has
focussed
are not important
salinity
from
is essentially background in a direct
space.
on for For
constant
in
radiation can manner if, for
has side lobes above the horizon. It also can contribute radiation off the surface [1]. The latter is especially
in remote sensing of the ocean surface where the reflection large. The cosmic background will be included in the examples over the spectral [1, 7].
window,
coefficient is to be presented
it is relatively
easily
Emission: The window
original galaxy
salinity
of radiation
here; but, since it is uniform and constant included in radiometer retrieval algorithms
emission
temperature
representative
and sea surface
sources.
example, the radiometer antenna via reflection of down-welling
B. Line
brightness
and antennas
for completeness.
both space and time with contribute to a measurement
important relatively
applications.
Background:
The universe
sensing
SKY AT L-BAND
such as is emitted
A.
to remote
of the radio maps with
to be expected.
GHz that originate outside of our (CMB), discrete line emission from three
to be relevant
for use
map of the radiometric sky at L-band and a solution to the portion of the sky seen by a'down-looking radiometer in
is presented
Examples
accuracy
the Sun (to
to the sun constant).
from
at 1.413 GHz was protected
a hyperfine
proposal that such is attributed to Oort
transition
in neutral
for passive hydrogen
use because
that occurs
of the interest
in this window.
in The
radiation could be detected from neutral hydrogen in our and van de Hulst, and the first observations were made by
Ewen and Purcell in 1951 [12]. This radiation provides information on the temperature, density and motion of hydrogen. The radiation is concentrated around the plane of the
galaxy,but cloudsof hydrogenarewidespreadandnodirectionis observedwithout some suchradiation. Severalsurveysof this sourceof radiationhavebeenmade[15, 16, 17, 18, 19, 20]. Recently,HartmanandBurton [12] motivatedby the high quality, all-sky surveys beingmadeat otherwavelengths,reporteda new survey. The Leiden/Dwingeloosurvey (TableI) useda 25-meterradiotelescopeandcoveredthe sky abovedeclinationof-30 °. This surveywasrecentlycomplementedby datacollectedwith the 30 meterdish antenna at theInstitutoArgentinode Radioastronomia (IAR) andreportedby Arnal et al [13]. The IAR survey (Table I) covereddeclinationssouth of-25 degreesfilling in the missing portions of the southernsky. The resultis datawith sufficient spatialresolution(0.5° x 0.5°) andradiometricresolution(AT < 0.1 K) to be applicableto remotesensingat Lbandfrom space,includinghigh-resolutionsensorsproposedfor the future (e.g.a spatial resolutionof 0.5° x 0.50corresponds to an apertureof about25 meters). C. Continuum Radiation In addition to the discrete spectra associatedwith atomic transitions as in hydrogenabove,thereis a continuumof radiationfrom extra-terrestrialsources. This radiationcan be dividedinto thermalandnon-thermalsources.Thermalsourceshavea spectrum(amplitudeversusfrequency)similar to thatof blackbodyradiation. At L-band, the Rayleigh-Jeanslaw appliesand the power increaseswith frequency as f2. Nonthermal sources are sources whose spectra behave differently. An example is synchrotronradiationfrom relativistic electrons,in which casethe spectrumat L-band decreaseswith frequencyroughly as f-0.7s[21]. The sourceof continuumradiationmay belocalizedin space(discretesources)or may be of a spatiallycontinuousnature(diffuse or unresolveddiscretesources). The sourceof the radiationis mostly galacticbecause thesesourcesare closest,but there are also strong extra-galacticsourcessuch as the "radio galaxy"CygnusA [21]. There havebeenseveralsurveysof the continuumradiationat 1.4GHz [22, 23, 24, 25, 26, 27]. None of thesesurveyscoveredthe entire sky and they use different bandwidthsandthe measurements were madewith differing sensitivity. For the most part, they consistof a map of discretesources. However,for applicationsto remote sensingof the Earth, it is desirableto have the integratedsignal from a particular direction in the sky (i.e. power from all sources,discrete and continuous),because antennaslikely to be employedin spacein the foreseeablefuture will not resolve individual sources.The recentsurveywith the StockerttelescopeatBonnUniversity [8], [9] providesdatain this format. The antennahada half-powerbeamwidth of about0.5 degrees.The sensitivity of these measurementsis about 0.05 K and the absolute calibration (zerolevel accuracy)is 0.5 K. This survey(Stockertsurvey;TableI) covers all of the northernsky andthe southernsky to -19° declination. The data includesall sourcesexceptfor a region aroundCassiopiaA which was too strong. Recently,the surveyof the southernskywascompletedusingthe 30-mradio telescopeof the Instituto ArgentinodeRadioastronomia [10], [11]. The IAR continuumsurvey(TableI) coversthe
3
southernsky for declinationbelow-10 ° with spatialresolutionandsensitivity similar to thatof theStockertsurvey. III.
DATA
Sensing
Format
It is common practice in passive microwave remote sensing to treat the scenes as sources and the receivers as narrow bandwidth devices [7, 21]. In the Rayleigh-
thermal Jeans
in Remote
limit,
this permits
one
equivalent
"brightness"
temperature emissivity
is the product is a function
parameters
of interest.
surface
salinity
to describe
temperature.
For sources
This
is the
approach
changes
In the sections
below,
to measure
and salt change
temperature
in terms
the brightness
soil moisture
the emissivity
the
Doppler
line emission
sea
astronomy
surveys
will be presented
temperature. The data will be presented as an such that total power is P = kTBAB. For this
has a relatively
at the frequency
line
spread
and
a reasonable
Emission The
occurs
The the
sufficiently
purpose, a bandwidth, AB = 20 MHz, has been assumed. This represents maximum for the window at 1.413 GHz after allowances for filter shape. A. Line
of an
can be detected.
the data from the radio
in the form of an equivalent blackbody equivalent thermal source normalized
scenes
and emissivity of the surface. surface, hopefully including
proposed
case water
in brightness
and
that are not blackbodies,
of the physical temperature of the properties of the
[4, 28, 29] in which
that the resulting
the measurements
is shifted
by
by thermal
associated motion
energy
shift and thermal
For example,
narrow
spectrum
with the hyperfine
of hydrogen
of the
gas
broadening,
relative
(collisions
to the and
the spectrum
the Leiden/Dwingeloo
survey
[21]. For hydrogen
transition
at 21.106
observer
vibrations).
However,
(doppler But,
of this radiation
[12] and IAR survey
at rest, it
cm.
shift)
even
with
is relatively [13] cover
and large
narrow.
the velocity
range from -450 to +400 km/s (Table I) which corresponds to a frequency range of less than _+2.2 MHz about the center (at rest) frequency of 1.42 GHz. The two surveys both report km/s.
power
integrated
To convert K-MHz Then,
using this
over the spectrum
into a format
the standard
value
was
useful
form
divided
of the line. The integrated
for remote
for Doppler by
20 MHz
sensing,
shift:
power
in K-
this data was first converted
v = Vo (1 - v/c)
to convert
is given
it into
where
to
v is velocity.
an effective
brightness
temperature. The brightness temperature, TB, is the temperature of a blackbody that observed with an ideal receiver with a bandwidth of AB = 20 MHz, will give the power (P = kTBAB) reported in the radio astronomy surveys. with receivers with other bandwidth with the obvious
The data can be converted for use re-normalization. (Of course, this
only makes
on the line and is greater
sense if the receiver
bandwidth
is centered
than _+2.2
MHz.) The
data in the above
the plot is in celestial
form
coordinates.
is shown
in Figure
The "U'
shape
1 (top).
region
The units
of high brightness
are Kelvin
and
temperature
is the plane of the galaxy (which is tilted with respectto an observerin the celestial coordinatesystem).The effective brightnesstemperatureis small almost everywhere exceptin the galacticplanewhereequivalentblackbodytemperatures on the orderof 3 K canoccur. B. Continuum
Radiation
For the continuum
radiation,
the data used here was the Stockert
survey
[9] for the
northern sky together with the more recent IAR survey [10] for the southern sky (Table I). In both cases, the data are in the form of total power over the bandwidth of the receiver
with the exception
that the line emission
from hydrogen
with a narrow filter at the line center). The power represents within the beam, discrete and unresolved and includes thermal However,
Cassiopeia
a small region
A, which
was too strong
of the sky around
Cassiopeia
to be included
A is excluded
was excluded
(removed
radiation from all sources and non-thermal sources. in the Stockert
survey,
and
from the data.
For both surveys, the data are in the form of power integrated over the pass-band of the radiometer receiver. The effective bandwidth was about 18 MHz and 13 MHz for the Stockert and Villa Elisa surveys, respectively (after correction for the filter to remove line emission). The Villa Etlisa antenna (30 m) was under-illuminated to match the resolution
of 25 m antenna The
data
from
used in the Stockert
the Stockert
survey
survey
[10, 11 ].
[9] normalized
to a bandwidth
of 20 MHz
is
shown in celestial coordinates in bottom panel of Figure 1. (All of data in Figure 1 has been converted to celestial coordinates using the J2000 epoch [21, 32]). As in the case of the line emission galaxy right
from hydrogen,
as is evident (Declination
the strongest
on the far right hand 60 o and
Right
Ascension
Cassiopeia However,
A. Data exists for the this data (IAR continuum
resolution
shown
resolution
[30] and is presented
in Figure
radiation
side.
tends
the white
355 °) which
portion survey;
of the Reich,
1. The data has been and discussed
to lie along
Also notice
is the
the plane
of the
spot at the upper
data
missing
around
southern sky missing in Figure 1. 2001) has not been released at the
provided
in Sections
for use in this paper
at lower
IV-V.
C. Examples
more
Figure 2 shows examples of the magnitude and spatial detail. The data shown are cuts through the color-coded
declination brightness function
of 0 °, 200 and temperature due of right ascension
temperature for the curves are associated the
continuum
40 °.
On
the
left
side
2 is shown
to line emission from hydrogen (from and on the right side is shown the
continuum radiation (from with crossing the galactic
is considerably
of Figure
distribution of the data in maps in Figure 1 at fixed
larger
than
from
Figure plane.
the
effective
Figure 1; top) as a effective brightness
1; bottom). The peaks in these Notice that the contribution from
the line
emission
from
hydrogen.
In
particular, peak values of effective brightness temperature from line emission are on the order of 2 K whereas the peak value due to continuum radiation is nearly 20 K. Also,
notice that the distribution is quite complexwith the obviouspeakat the galacticplane but with levelsthatdependon wherethe intersectionswith the galacticplaneoccur. IV.
Effect
of Antenna
The apparent will depend radiation values
Beam brightness
on the antenna
and, as a result, in Figure
relatively
temperature
employed. the observed
1. This is especially
value
seen
antenna
in a remote
smoothes
can be significantly
true in the vicinity
sensing
of the celestial
with the power to perform contributing
the incident
different
from
of the galactic
the peak
plane,
which
is
the
effect
sky contributing
pattern
of the antenna
of the
antenna,
one
to the measurement. (e.g. Section
could
integrate
over
the
That is, take the convolution
3.4 of [21]).
However,
it is equivalent
the convolution over the entire sky first and then locate the portion of the sky to the measurement. This approach has the advantage of presenting the
smoothed data done here.
in its entirety
independent
of the particular
application.
This
The data is presented in Figure 3 for an antenna with a Gaussian at half maximum (FWHM) of 10 °. The details of the integration
width
application
(integrates)
narrow. In order to understand
portion
actually The
has
been
beam with a full are presented in
Appendix A. The choice of 10 ° beam width was made to indicate the effect of smoothing but to remain conservative and not overly smooth the data for remote sensing applications. Figure 3 (top) shows the smoothed data for line emission and Figure 3 (bottom) is the smoothed data for the continuum radiation. In the case of the continuum radiation,
the
data
from
the
Stockert
survey
(Table
I) was
smoothed
Appendix A and the data for the southern sky (IAR continuum us with the 10 degree smoothing (courtesy of P. Reich [30]). features
of the high-resolution
maps
remain
in the smoothed
survey) Notice
as outlined
was provided to that the general
data.
Figure 4 shows detail for cuts through the data at fixed declination 40 o. The smoothed line emission is shown on the left and the continuum the right.
Notice
remain,
although
continuum peak
that the general the
at 40 degrees
in the continuum
galactic
large
plane,
is much radiation
the continuum
features
difference
evident
in the
reduced.
radiation
(-
value
This reflects
on the galactic
of 0 °, 20 ° and radiation is on
in the high-resolution
peak plane.
between the very
Also,
1 K) is greater
in
than
notice
data line
(Figure
emission
narrow
nature
that away
from line emission
2) and
of the
from
the
(- 0.05
K). Figure contributions:
5 is an example at 20 degrees declination of the total Cosmic background, line emission and continuum. Shown
original and smoothed data for the line emission. smoothed data for the continuum radiation. The components
(smoothed
line emission,
smoothed
together with the sum. Notice that the plane contribution of the continuum and line emission
In the bottom
continuum
middle panel
from the three at the top is the
is the shows
and the cosmic
original and each of the background)
of the galaxy is evident and that is clearly important and comparable
the to
the CMB. The peakaroundthe galacticplanedependson declinationand,for example, would bemuchlargerif a declinationof 40 degreeswereshown(seeFigures2 and4). It is clearfrom Figures1-5 that the backgroundradiationis spatially complex. Large valuesarepossiblealongthe galacticplane. On the otherhand,thereareregions nearthe galacticpole wheretheline emissionandcontinuumradiationaresmall (< 1 K) andthe cosmicbackgrounddominates. Clearly, it is importantto know whatportion of the "sky" is contributingto a particular measurement.This problem is addressedin SectionV. V. REMOTE
SENSING
The radiation
data can
applications
from
be
the
radio
significant
and
it is important
particular orbit
PROBLEM
measurement.
circling
from
to know To
the Earth
contribution
the
astronomy highly what
address
with
sky
portion
this
its antenna
radio
surveys
variable.
indicates
that
Consequently, of the celestial
problem,
imagine
pointing
down.
(down-welling
the
for
background
remote
sky is contributing
a radiometer The
radiation
sensing
goal that
to a
at L-band
in
is to determine
is reflected
the
into
the
antenna), which must be taken into account at each position in this orbit. The input is the data given in Figure 1 (or Figure 3) normalized to the radiometer bandwidth, plus a constant
of 2.7 K that is added The
solution
to account
can be found
for the cosmic
by tracing
rays
microwave
from
background.
the antenna
to the
surface
and
computing how they are reflected toward the sky. For example, a flat, specular surface behaves like a mirror and the solution can be obtained by placing the antenna at its conjugate
point
reflected
ray.
behind The
the
surface
and
pattern
is unchanged,
antenna
change of symmetry (i.e. right power reflected into the antenna
solution
that looks At
the
surface).
left
are
the
smoothed
direction
but it does
of the
undergo
specularly
a mirror
image
computes the over the sky.
procedure to solve the problem for a curved earth. The B and solved for an ideal case (spherical earth, circular
Examples
to the side in a plane
out in the
hand symmetry becomes left hand). One by integrating the mirrored antenna pattern
One can follow a similar is outlined in Appendix
orbit and specular
looking
are shown
perpendicular data
in Figure
6 for the case of an antenna
to the orbit (e.g.
describing
the
radio
as in a cross
sky
track
at L-band
in
scan).
celestial
coordinates (sum of line emission and continuum) seen by the antenna (Gaussian power pattern with a 10 degree beam width). Shown on the smoothed data is the locus traced by the reflected circular
ray at bore-sight
orbit with inclination
for an antenna
looking
angle is 95 degrees
to the right
(angle
at 0i = 30 degrees
3I in Equations
4B).
in a
It is possible
to plot orbits on the original mentioned above, it is more
data and then integrate over the antenna beam. However, as efficient to integrate first and then plot the orbits. This what
has
Figure
been
done
in creating
6.
The
panels
on
the
right
show
temperature along this locus as a function of declination. Four values line emission, continuum emission, CMB (the straight line) and the total.
the
brightness
are plotted:
The
The and
the
shape
of the loci in Figure
inclination
determined
of the
orbit.
by the intersection
is illustrated
by
intersection
the
two
of the plane
6 depends
The
position
of the plane examples
on the incidence
of the locus
angle
(i.e.
of the orbit with the plane
shown
in Figure
of the orbit has been
rotated
6 that
of the antenna
center
of the curve)
of the equator.
differ
by 90 degrees.
only
These
below
moisture
using
from
the orbit
space.
coordinate
system
to celestial
coordinates
VI.
The
the
called
in Appendix
is presented This
here
for
is an orbit
HYDROSTAR
on the Earth
of
choice
observation
for
pole)
In order
[28].
sees
two examples
ago
as seen
can be in the
to measure
soil
in an earth-centered
of longitude
and
local
time)
C.
a sun-synchronous
commonly
remote
the
to remain
local
remote
a 6am/6pm
sensing
of soil
soil moisture
oriented
such
from that all
local
time.
It is the
applications
because
the
local
time
generally
has a high
crossing
in the same
with
at the same
this orbit
equatorial
for
to measure
orbit is one
overhead
sensing
In practice,
and
pass
orbit
selected proposed
A sun-synchronous
the satellite
many
is constant.
close to the value.
orbit
years
as a function
[28], [31] and was the orbit for a sensor
observers orbit
of relating
several
the
Orbit
crossing.
moisture
proposed
intersection
is discussed
example
equatorial
problem
(e.g. equatorial
HYDOSTAR
An
space
The
for a mission
This
in that
show that keeping track of changes in the orbit, for example due to precession, important for determining the background radiation. This is illustrated further section
is
time
precesses
orientation
inclination
a bit about
with respect
of
(passes
the
nominal
to the sun, the orbit
must precess in celestial about 1 degree per day.
coordinates As a result
as the earth rotates about the sun. The change is of the precession, the position of the locus of the
reflected
coordinates
(Figure
rays in celestial
change
of 360 degrees
celestial astronomy
in right
ascension
6) will drift
each year.
across
The problem
the sky going of locating
through
a
the orbit in
coordinates given the local time of equatorial crossing is the problem in of transforming local time into sidereal time. The solution used here is given
in Appendix
C.
Once
the orbit is located
in celestial
coordinates,
the procedure
outlined
in Section V above is followed to plot the locus of the reflected rays on the sky. (This amounts to neglecting changes of the orbital plane during one period, about 90 minutes.) Figure year
starting
(10 ° Gaussian degrees.
7 shows
examples
with March beam)
The curves
with the HYDROSTAR
15, 2002.
looking
right
on the left show
Thecalculation at 5 degrees
orbit
for several
is for the antenna (0i = 5).
the orbit in celestial
The
orbit
coordinates.
times
described inclination The
curves
of the above is 95 on the
right show the total effective background radiation, the sum of the three terms, line emission, continuum and CMB. Notice that the total varies from a little less than 4 K to nearly over
11 K.
The
values
the orbit varies
if the incidence
angle,
change
seasonally 0i, where
over the orbit (i.e. in one period). (i.e. with the time of year). changed.
Also,
The values
the distribution
would
also change
VII.
CONCLUSION In addition
radiation into
to the uniform
(line emission
account
radiation
for
background
from hydrogen
remote
is spatially
cosmic
sensing
varying
and a continuum
at L-band.
and
radiation
there
background)
In contrast
strongest
(CMB),
to the
in the direction
is additional
that must be taken CMB,
this
of the plane
additional
of the galaxy.
The effective brightness temperature of down-welling radiation from these sources that is reflected from the surface into the radiometer depends on the antenna beam width and surface
conditions.
For
antenna
with a beam
width
a perfectly on the order
other than the CMB is on the order and orbit. The fact that this signal the sensor
in its orbit
Earth.
The
surface
conditions.
sensing
of soil moisture
(on the order
of 0.3).
(on the order
where
careful
VII.
REFERENCES
[1] C. T. Swift,
Meteorol.,
[2] H-J. C. Blume
[3] H-J. C. Blume, and salinity 308, 1978.
radiation
depends
on the
where
the reflectivity
(on the order radiation
remote
an
sources
sensing applications
small
applications
such
of the surface
of 0.5 K per psu).
of the ocean-
and
as the remote
at the surface
sensing
will be an important
sensing
of the
is large
In the latter
issue.
A review,"
Bound.
1980. "Passive
IEEE
B. M. Kendall
and
from
such
and the reflectivity
salinity
and B. M. Kendall, zones,"
for applications
is small
microwave
via microwave
for remote
for remote
vol. 18, pp. 25-54,
and salinity in coastal 394-404, 1982.
contribution
important
of the down-welling
"Passive
of unity)
issue
is large
it is more
of sea surface
mapping
the peak
it is less an issue
the signal
However,
(reflectivity
an important
background
of 0.7) and the signal
case,
of 10 degrees,
its presence
of the
surface
of 1 - 6 K, varying with the orientation of the sensor can change both seasonally and with the location of
For example,
as the measurement
Layer
makes
importance
reflecting
microwave
Trans.
Geosci.
and J. C. Fedors,
radiometry,"
measurements Remote
"Measurement
Boundary-Layer
of temperature
Sensing,
vol. GE-20,
of ocean
Meteorol.,
pp.
temperature
vol.
13, pp. 295-
[4] C. T. Swift and R. E. McINTOSH, "Considerations for Microwave remote sensing of ocean-surface salinity," IEEE Trans. Geosci. Remote Sensing, vol. GE-21, No. 4, 480-491,
1983.
[5] E. G. Njoku, microwave sensing,"
W. J. Wilson,
S. H. Yueh,
radiometer-scatterometer IEEE
[6] H. C. Ko, "The 46, pp. 208-215,
Trans.
Geosci.
distribution
and
concept
Remote
Sensing,
of cosmic
radio
1958.
9
Y. Rahmat-Samii, for
ocean
salinity
vol. 38, pp. 480-491, background
radiation,"
"A large-antenna and
soil
moisture
2000. Proc.
IRE,
vol.
[7] F. T. Ulaby, and
R. K. Moore
radiometry,
Wesley
publishing
[8] W. Reich,
[9] P. Reich
and W. Reich,
- Part II," Astronomy
pp. 861-877, [11]
[14]
sensing
Passive,
series,
"A radio
The atlas of contour
maps,"
J. A. Bava,
Astronomy
"A radio continuum
survey
Astronomy
and W. 1997.
B. Burton,
Atlas
E. Bajaja,
G. Hauser,
L37-IAO,
- Part
sky at 1420
survey
of the
Larrarte,
1986.
E. E. Hurrel, of the southern
of Galactic
R Morras
J. J. Larrarte,
Neutral
sky at 1420
MHz:
vol. 368, pp.
1123-
Hydrogen.
and W G L P6ppel,
W.
Cambridge
"A high sensitivity
and Astrophysics
Supplement
Series,
2000.
M.
Janssen,
T. Kelsall,
R. F. Silverberg, of the Explorer
P. M.
G. F. Smoot
cosmic (COBE)
microwave satellite,"
and
Lubin, D.
T.
S. S. Meyer, R. A. E. Dwek, S. Gulkis,
S. H. Moseley, Wilkinson,
"A
Jr.,
T.
L.
preliminary
background spectrum by the Cosmic The Astrophysical Journal, vol. 354, pp.
1990.
F. R. Colomb,
W.
G.
L. Poppel
and
C. Heiles,
"Galactic
HI
[17] G. Westerhout,
G. L. Mader
and R. H. Harten,
"Telescope
beam
data,"
Astronomy
characteristics
scale of the Maryland-Green Bank 21-cm line survey," Supplement series, vol. 49, pp. 137-141, 1982.
10
in HI,"
at Ibl _> 10% II.
Photographic presentation of the combined southern and northern and Astrophysics Supplement Series, vol. 40, pp. 47-55, 1980.
temperature Astrophysics
MHz
vol. 376,
[15] M. N. Cleary, C. Heiles and C. G. T. Haslam, "A synoptic view of the galaxy Astronomy and Astrophysics Supplement Series, vol. 36, pp. 95-127, 1979. [16]
1,"
southern
& Astrophysics,
and Astrophysics,
of the sky at 6 < -25°, '' Astronomy
measurement Background
MHz
vol. 63, pp. 205-292,
continuum
F. R. Colomb,
reduction,"
142, pp. 35-40,
Murdock,
1. Addison-
1982.
of the northern
supplement
and W. Reich,
sky at 1420
J. C. Mather, E. S. Cheng, R. E. Eplee, Jr., R. B. Isaacman, Shafer, R. Weiss, E. L. Wright, C. L. Bennett, N. W. Boggess, M.
fundamentals
vol.
vol. 48, pp. 219-297,
survey
and data
[13] E. M. Arnal, vol.
series,
and Astrophysics
and A. J. Sanz,
HI survey
and
of the northern
"A radio continuum
P. Reich,
Observations 1132, 2001. [12] D. Hartmann Univ. Press,
remote
Active
2001.
J. C. Testori, Reich
survey
supplement
J. C. Testori
sky at 1420 MHz,
Microwave
sensing:
1981.
continuum
and Astrophysics
[10] P. Reich,
remote
company,
"A radio
Astronomy
and A. K. Fung,
Microwave
Astronomy
and and
[18] F. J. Kerr, P. F. Bowers, P. D. Jacksonand M. Kerr, "Fully sampledneutral hydrogen survey of the southern milky way," Astronomy and Astrophysics supplement
series,
[19] W. B. Burton,
Galactic
K. I. Kellerman, [20] W.
[21]
maps
and Extragalactic
The Galactic
Springer-Verlag,
J. J. Condon
1986.
eds.), Springer-Verlag,
B. Burton,
eds.),
vol. 66, pp. 373-504,
Radio New
Interstellar
Heidelberg,
Astronomy.
York,
(G. L. Verschuur
and
1988.
Medium.
(D. Pfenniger
and
P. Bartholdi,
1992.
and J. J. Broderick, "A 1400 MHz sky survey. I. Confusion-limited 7h30 m < O_< 19 i130 m, _5 ° < 8 < +82o, ', The Astronomical Journal, vol.
covering
90, p. 2540,
1985.
[22] J. D. Kraus,
Radio
[23] R. S. Dixon,
Astronomy.
"A master
McGraw-Hill
list of radio
Inc, 1966.
sources,"
Astrophys.
J. Suppl.
Ser, vol 20, No.
180, 1970. [24]
A. E. Wright Australia
and
R. Otrupcek,
Telescope
[25] W. Reich,
National
P. Reich
the Galactic Supplement [26] R. L. White
and
Astrophysical
Facility,
and E. Ftirst,
plane Series,
Parkes
Radio
Sources
Catalogue,
Journal
"The
Effelsberg
"A new
Supplement
1.Ol.
1990. 21 cm radio
continuum
between I= 357 ° and 1= 95.5°, '' Astronomy vol. 83, pp. 539-568, 1990. R. H. Becker,
Version
Series,
Catalog
of 30,239
and
of
Astrophysics
1.4 GHz
vol. 79, pp. 331-467,
survey
sources,"
The
1992.
[27] B. Uyaniker, E. Ftirst, W. Reich, P. Reich, and R. Wielebinski, "A 1.4 GHz radio continuum and polarization survey at medium Galactic latitudes," Astronomy & Astrophysics
Supplement
[28] D. M. Le Vine, surface
Series,
vol.
138, pp. 31-45,
J. B. Zaitzeff,
E. J. D'Sa,
Toward
an operational
salinity:
Oceanography and Society. (D. Halpern, Series #63, Elsevier Science, 2000. [29]
P.
Waldteufel,
characteristics L-band
concept,"
Sulface Netherlands, [30]
P. Reich,
E.
and
Anterrieu,
J.
M.
of a 2-D interferometric in Microwave
Atmosphere. pp. 467-475,
Private
Ed.),
ll
and
Y.
Elsevier
Kerr,
as illustrated and and
Remote S.
M. Goodberlet,
system,"
pp. 321-335,
Goutoule
P.
2002.
C. Swift,
remote-sensing
Radiometry
2000.
Communication,
J. L. Miller,
antenna,
(Pampaloni
1999. "Sea
in Satellites, Oceanography
"Field
of
view
by the MIRAS/SMOS Sensing
Paloscia,
of the
Eds.),
Earth's
VSP,
The
[31]
Y. H.
Kerr,
Goutoule,
P. Waldteufel,
C. Tabard
an overview,"
in Microwave
and Atmosphere. 467-475, 2000. [32]
D.
A.
Table
h
and
Parameters
W.
of the
D.
HPBW (effective) Effective
-19 °
-35' 50 mK
and Remote S. Paloscia,
McClain,
survey
Stockert Continuum
8>
J. M. Martinuzzi,
soil moisture
B. Lazard,
and ocean
Sensing
Eds.),
VSP,
Fundamentals
of
J.-M.
salinity
mission:
of the Earth's
Smface
The
Netherlands,
Astrodynamics
pp.
and
1997.
Survey 0°< c_ < 360 °
Coverage
"The
P. and
McGraw.Hill,
Summary
Wigneron,
Radiometry
(Pampaloni
Vallado
Applications.
J.-P.
and A. Lannes,
parameters
IAR Continuum
Leiden/Dwingeloo Hydrogen Survey
IAR Hydrogen
Survey
Survey 0°< ot __360 °
0°< _z < 360 °
0°< c_ _5.0
(bottom)
K
as equivalent
brighmess
20 OECLINAT;OH DECLINATION
4{] Degree
40 Degree
_18
_2o_ 214 I:g _12
NlO _8
15
LIJ _
6
2 /
0
50
100
150
200
R_GHT ASCENSION
DECUNATION
25o
300
350
50
100
{Degree)
150
RIGHT
200
ASCENSION
250
30°
350
[Degree)
20 Degree g
25
DECUNATIOH
20'3_egree
8
2
7
< 6 5 4
_E 05
00_
50
100 RIGHT
150
200
ASCENSION
2':;0
3(jO
?.50
,3
50
100
{Degree)
150
_IGHT
200
ASCENSION
250
300
350
(Degree)
25 DECLINATION
0 Degree
9 - DECUNATI©tJ uJ
[J Degree
8
2.0 7 6 ILl
_°
==
... _
0
50
100 RIGHT
Figure
4
II
05
5
2: Line
emission
and 40 degrees
(bottom
150
200
ASCENSION
(left)
250
300
00
350
50
100
and continuum
to top). Notice
150
#IGHT
(Degreel
background
that the vertical
20
(right) scale
200
ASCENSION
250
300
350
(Degree,)
at constant
of the upper
declination
right panel
of 0, 20
is 0-20 K.
5O
z
I O0 RIGHT
0
I C)O RIGHT
>0.0
Figure
3: Smoothed
0.05
200 ASCENSION
0.1
0.25
data.
Line
0.5
300 (Degree)
200 ASCENSION
1.0
emission
300 (Degree)
2.0
3.0
(top)
and
4.0
>5.0 K
continuum
background
(bottom)
equivalent brightness temperature in 20 MHz bandwidth as seen by an antenna Gaussian beam with a 10 degree beam width (full width at half maximum).
21
with
as a
5O DECLINt, _" I 0 I|DECLINATION
TION
40 Degree
A45
4D Degree
_"o 81. '
_40 235
I
.!
30
._15
02 05 00 0
50
100 RIGHT
150
200
ASCENSION
250
300
50
350
100
150
RIGHT
(Degree}
200
ASCENSION
250
300
350
300
350
(Degree)
50
10
osr
OECLINATION
DECLli'LAT_ON 20 Degree
20 Degnee
_45
_4o 235
_3o w
w25
_o4
_
20
_15
g 02
02
,I O0
50
100 RIGHT
150
200
ASCENSION
250
300
0%
350
50
100
150
PlGHT
(Degree)
200
ASCENSION
_0 (Degree)
1
50
_"
1 01
DECLINAltON
O Degree
_.45
_4o
i°sI
_3o _gs _go Z15 •
_z 10 m 05l
0%
00 50
100 RIGHT
150
200
ASCENSION
250
300
50
350
100
150
RIGHT
(DeQ[ee)
Figure 4: Smoothed data. Line emission (left) and continuum 3 but at constant declination of 0, 20 and 40 degrees (bottom
22
200
ASCENSION
220
300
350
(Degree)
background to top).
(right)
from Figure
20
1 8
UNE
EMISSION
uJ16 rw _- 14 < rr uJ12 O.. ORIGINAL UJ t--
DATA -----m
10
tu
50
100 RIGHT
150
200
250
ASCENSION
300
350
300
350
(Degree)
40
C oKrFII,4UUM
EMISSION
_35
ORIGINAL
DATA
uJ 30 i--< 25 n
_2o Io') 15
10 rm m
0.5 i 00
6[
_1"_4 l _5t
.4o 16o 4o
260 2;o
RIGHT
(Degree)
SMOOTHED
CMB _
+ LINE
ASCENSION
DATA
EMISSION
f
+
CONTINUUM
_3
'
JEMISSIOJ
CMB
09 LU
_2
CONTINUUM
I L0
0
so
_oo RIGHT
components
(smoothed)
/
,
0
Figure 5: Total background emission is shown at the
EMISSION
_5o
2oo
ASCENSION
-. 250
300
350
(Degree)
radiation at a constant declination of 20 degrees. The line top and continuum background in the middle. Each of the
and the CMB
is shown
at the bottom
23
together
with the total.
_5 5O
2 LU Q. :E LU3
v
CMB
O3 b3 LIJ Z2 k-r
-'i
--5O
[
Continuum
"_
.
•
une
Emission_
_mls_lllon
.,r
0
3OO
-20
-40
0
DECLINATION
uJ _5
5O
l
,
20
40
l 6o
{Degree)
i
J
,
,
pry LIJ eL :E LtJ
v
CMB O3 CO UJ Z
_E
@
.
i3 ,,'\
-5O _
r,rm
"--
.....
"7..... _'_ 0
100
200 RIGHT
ASCENSION
show
the brightness
-40
(Degree)
Continuum
_--20 DECLINATION
Figure 6: Examples of the background polar orbit with inclination 95 degrees. in the equatorial crossing. smoothed with a Gaussian
_0
300
_
Emission
_,o._ ...._o ,
O
20
40
6o
(Degree)
radiation seen by a sensor at look angle 30 degree in a circular, The two cases are identical except for a change of 90 degrees
The data on the left is the net background (line emission plus continuum) as beam with a 10 degree beam width (FWHM). The two panels on the fight
temperature
along
the locus
of the projected
24
beam
(solid
line) shown
on the left.
,_
MARCH 15, 2002, 00:00:00 10
E
•
9
uJ 8 uJ 7
6
d,
L_ Z 5
4
IO0
3-80
2O0
RIOHT/LSCENSION
-(_0
-4'0
-20
(_
2'0
DECUNA'RON
(Degr._)
4'0
610
8'0
(Degree)
JULY 15, 2002, 00:00:00 10
9 ILl O_ 8 or"
6
=.
_1-8'0 -_0 -4'0 -2'0 0
20 40
DECLINATION
6'0 8'0
(Degree)
NOVEMBER 15, 2002, 00:00:00
0
100
200
R18HT
Figure
7: Examples
ASCENSION
using
(Degree]
of the beam
on celestial
brighmess
temperature
(the
The values
DECLINATION
the HYDROSTAR
projection CMB).
:,o
300
total
are for a sensor
coordinates contribution
orbit.
The antenna
is shown from
line
with 20 MHz bandwidth
25
points
(Degree)
at 5 degree
on the left. On the right and
continuum
and a 10 degree
emission Gaussian
look angle. are the values together beam.
with
The of the
