4032 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 45, NO. 12, DECEMBER 2007
Focused 70-cm Wavelength Radar
Mapping of the Moon
Bruce A. Campbell,Member,IEEE, Donald B. Campbell, J. L. Margot, Rebecca R. Ghent,
Michael Nolan, John Chandler, Lynn M. Carter, and Nicholas J. S. Stacy
Abstract?We describe new 70-cm wavelength radar images of
the lunar near-side and limb regions obtained via a synthetic-
aperture-radar patch-focusing reduction technique. The data are
obtained by transmitting a circularly polarized pulsed waveform
from the Arecibo telescope in Puerto Rico and receiving the echo
in both senses of circular polarization with the Robert C. Byrd
Green Bank Telescope in West Virginia. The resultant images in
both polarizations have a spatial resolution as fine as 320 m ?
450 m near the lunar limb. The patch-focusing technique is
a computationally efficient method for compensating for range
migration and Doppler (azimuth) smearing over long coherence
times, i.e., 983 s, which is needed to achieve the required Doppler
resolution. Three to nine looks are averaged for speckle reduction
and to improve the signal-to-noise ratio. At this long wavelength,
the radar signal penetrates up to several tens of meters into the
dry lunar surface materials, thus revealing details of the bulk
loss properties and decimeter-scale rock abundance not evident
in multispectral and other remote-sensing data. Application of
the new radar images to the analysis of basalt flow complexes in
Mare Serenitatis shows that the long-wavelength radar data are
sensitive to differences in both flow age and composition, and may
be particularly useful for studies of smaller deposits that do not
have robust crater statistics. The new 70-cm lunar radar data are
archived at the National Aeronautics and Space Administration
Planetary Data System.
Index Terms?Moon, radar imaging.
I. INTRODUCTION
E
ARTH-BASED remote-sensing studies of the Moon in-
clude observations of ultraviolet, visible, and infrared (IR)
reflectance; thermal IR properties during eclipse; and scattering
or emission in the microwave region. Radar studies are of
particular interest as the only method for probing to depths
beyond a few centimeters (the range of thermal IR variations)
and for their sensitivity to the bulk geochemical properties and
rock abundance of the lunar regolith. Synoptic data sets for the
Manuscript received November 13, 2006; revised July 9, 2007. This work
was supported in part by a grant from NASA?s Planetary Astronomy Program.
B. A. Campbell and L. M. Carter are with the Center for Earth and Planetary
Studies, Smithsonian Institution, Washington, DC 20013-7012 USA (e-mail:
campbellb@si.edu).
D. B. Campbell and J. L. Margot are with the Department of Astronomy,
Cornell University, Ithaca, NY 14853 USA.
R. R. Ghent is with the Department of Geology, University of Toronto,
Toronto, ON M5S 3B1, Canada.
M. Nolan is with the Arecibo Observatory, Arecibo, PR 00612, Puerto Rico.
J. Chandler is with the Smithsonian Astrophysical Observatory, Cambridge,
MA 02138 USA.
N. J. S. Stacy is with the Defence Science and Technology Organization,
Edinburgh, S.A. 5111, Australia.
Digital Object Identifier 10.1109/TGRS.2007.906582
Moon, which cover most of the visible near side, have been
collected at wavelengths of 3.8 cm (2- to 4-km resolution)
[1], 70 cm (4- to 8-km resolution) [2], and 7.5 m (10- to
30-km resolution) [3]. Selected areas have been mapped at
spatial resolutions of 20?150 m using wavelengths of 3?4 cm
[4]?[6] and 12.6 cm [7]?[9].
The 70-cm wavelength radar data have been proven to
be particularly useful in probing the upper several meters
of the regolith. Backscatter variations at this wavelength are
correlated with the local and regional geologic properties,
such as varying titanium content in mare basalts [10], [11],
block-size distribution in ejecta from large craters and impact
basins [12], [13], changes in bulk regolith loss tangent due
to buried ancient mare basalt units [14], and rock-poor re-
gional pyroclastic deposits formed by volcanic fire fountains
[15]?[18]. There are strong reasons to conduct geologic studies
at finer spatial resolution and to extend the 70-cm radar image
coverage to areas near the poles and limbs that have previously
not been investigated. To this end, we have collected data for a
new 70-cm radar backscatter map of the Moon?s near side with
horizontal spatial resolution of 450?900 m.
Because of the large distances and relatively low resolution,
the imaging of planetary bodies using Earth-based radars nor-
mally only requires unfocused processing of the data, which
is usually referred to in the field of planetary radar astronomy
as delay-Doppler mapping [19]. The 9-arcmin beamwidth of
the Arecibo antenna is about 30% of the angular diameter of
the Moon, so a single observation reveals a large field of view
on the lunar surface. At the desired resolution of a few hun-
dred meters, there is significant range migration and Doppler
smearing at the edges of the field of view, which requires a
focused reduction of the data. To minimize the computational
effort, a simple focusing scheme [7] is implemented in which
an unfocused delay-Doppler analysis followed by a coordinate
transformation into selenographic coordinates is used to image
a ?patch? centered on a target location, i.e., the geographic
point on the Moon for which the changing range and the range
rate are compensated over the integration period (983 s). The
patch size is dictated by the area over which the range and
range?rate changes result in smearing of more than one-half
of a resolution cell. A new target location is then chosen, and
its computed range and phase history relative to the initial
target location are used to focus the data at this point. Another
delay-Doppler analysis is performed to obtain an image over
the patch, and this process is repeated until the entire field
of view is imaged. Sections II?V discuss the radar mapping
and calibration methodology, while Section VI describes how
0196-2892/$25.00 ? 2007 IEEE
CAMPBELLetal.: FOCUSED 70-cm WAVELENGTH RADAR MAPPING OF THE MOON 4033
Fig. 1. Unfocused 70-cm wavelength delay-Doppler (range?rate) image of
the Moon showing the radar illumination pattern on the surface. The dark curve
marked in part by a white dashed curve is the first null of the Arecibo antenna
beam pattern. The radar beam was centered on Mare Orientale (the dark region
at the center of the Orientale basin).
radar echo information complements the estimation of mare
basalt titanium content and age from multispectral and photo-
graphic data.
II. DATA COLLECTION
We transmit a left circularly polarized (LCP) radar signal
at 430 MHz (radar wavelength ? of 0.7 m) from the 305-m
National Science Foundation?s (NSF?s) Arecibo Telescope in
Puerto Rico. The transmitted waveform is a 3-?s-long pulse
at a pulse repetition period (PRP) of 15 ms, which yields
a range resolution ?r of 450 m. The pulse repetition fre-
quency (PRF) and its inverse (i.e., the PRP) must satisfy
two conditions: 1) sample the frequency-broadened echo from
the Moon at the relevant Nyquist frequency and 2) not ex-
ceed the delay depth of the Moon to avoid time ambiguity
between successive pulses. The roundtrip time delay depth
of the Moon (radius of 1738 km) is 11.59 ms, while the
maximum apparent limb-to-limb bandwidth at 430 MHz is
approximately 12 Hz. A PRF of 66.67 Hz (15-ms PRP) easily
satisfies the ambiguity constraints and also provides data sam-
ples of a region ?off the Moon? for system noise calibration
measurements.
The reflected echoes in both circular polarizations are re-
ceived at the 100-m NSF Robert C. Byrd Green Bank Telescope
(GBT) in West Virginia and quadrature mixed to baseband
(there are several mixing and filtering stages), and the resultant
complex voltages are sampled at a 1-MHz rate [20] (Fig. 1).
The GBT is used as the receiving station because the Arecibo
430-MHz monostatic radar system cannot receive the echo in
both senses of circular polarization for nearby solar system
targets such as the Moon, which has a roundtrip light time
of about 2.5 s. Echoes polarized in the same circular sense
as that transmitted (here LCP) are termed ?SC? and often
referred to as ?depolarized? since they arise from effects such as
multiple scattering or scattering from sharp edges. Echoes in the
opposite circular sense (i.e., right circularly polarized) to that
transmitted, i.e., the one expected for a mirror-like reflection,
are termed ?OC? or ?polarized.?
The GBT is not equipped to compensate in real time for
changes in the range and range?rate (Doppler shift) to the target
location (the beam center on the Moon), so these operations
are performed at the transmitter in Arecibo. The echo from the
target location thus arrives at the GBT at 430 MHz and with a
PRP of 15 ms. The range and range?rate corrections are applied
by simply Doppler shifting the transmitted signal and the
20-MHz clock that drives the timing generator. New values are
applied at 1.0-ms intervals based on ephemerides, which are
generated at the Smithsonian Astrophysical Observatory and
predict the range and Doppler shift to the target location, plus
the pointing information for the antennas, at 1-min intervals. A
seventh-order polynomial is fitted to the Doppler shift values
spanning the anticipated observation time and evaluated each
time that the Doppler shifts are updated. A frequency offset of
a few hertz (f
o
) is added to the incoming signal at the GBT
to move the center frequency of the lunar echoes away from
0 Hz to avoid problems related to DC level errors. During
data acquisition, each quadrature channel is digitized using
four-bit analog-to-digital conversion, and the resultant data
stream is stored on a disk. The initial data analysis converts the
four-bit samples to floating-point values and sums the 1-?s-
spaced samples in pairs, which yields seven thousand five
hundred 2-?s ?range bins? per PRP. This retains a 50% over-
sampling of the 3-?s pulse. We further coherently sum groups
of four individual PRPs, which yield an effective PRP of
60 ms (PRF of 16.67 Hz). Each radar coherence interval T
coh
or ?look? is 983 s long, which gives a frequency resolution of
1.017 mHz. Since the maximum limb-to-limb bandwidth of the
Moon is approximately 12 Hz, there is a comfortable margin
to avoid frequency aliasing. The presumming step introduces a
sinc
2
variation in echo power with increasing frequency, which
we correct in the subsequent mapping.
III. FOCUSED MAPPING
Each bistatic radar observation is made by tracking a partic-
ular target location on the Moon specified by a latitude ?
t
and
a longitude ?
t
over a coherence interval sufficient to yield the
required frequency resolution. As described in Section II, the
time-varying range and range?rate for this point are corrected
for in the transmitted signal so that the echo from the target
arrives at the GBT at a fixed delay relative to the PRP and
without a Doppler offset from 430 MHz. For all the other
points on the Moon, however, the range and range?rate are
changing with respect to the target point, with the rate of change
increasing with distance from (?
t
,?
t
). A simple unfocused
mapping of the radar echoes from the delay-Doppler coordinate
system to a selenographic coordinate system will therefore lead
to increased smearing in resolution with distance from the target
point. We employ a ?patch-focusing? algorithm to achieve the
best possible spatial resolution across the region of the Moon
illuminated by the 430-MHz Arecibo beam.
For almost all planetary radar observations, the beamwidths
of the transmitting and receiving antennas (normally the same)
are larger than the angular size of the solar system body being
studied. This results in a north?south ambiguity; every location
in one hemisphere of a rotating spherical body has a symmetric
4034 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 45, NO. 12, DECEMBER 2007
Fig. 2. Relationship between the lunar cartographic coordinate system (x,y,z) and the lunar range and range rate (?Doppler?) coordinate system. (a) Diagram
showing the two coordinate transformations discussed in the text. The first transformation places the x
prime
axis along the line between the Moon?s COM and the
observer. After this rotation, the y
prime
and z
prime
axes define the ?plane of the sky.? A second rotation about the x
prime
axis by the angle ? orients the z
primeprime
axis to match
the direction of the Moon?s apparent spin vector. (b) Diagram showing the projection of delay and Doppler shift variations onto the lunar surface. The line from
the COM through the SRP defines the delay axis x
primeprime
.They
primeprime
axis corresponds to changes in the apparent range rate or Doppler shift. The Doppler ?equator? lies
in the x
primeprime
?y
primeprime
plane; there is an ambiguity between delay and Doppler coordinates of points north and south of this plane. The radar incidence angle ? is defined
with respect to the x
primeprime
axis.
location in the other hemisphere that has the same distance and
velocity relative to the radar [19]. For a single observation, the
echo powers from each pair of locations cannot be separated.
For our lunar observations, the 9-arcmin beamwidth of the
Arecibo antenna at 430 MHz is smaller than the 28-arcmin
angular diameter of the Moon, thus allowing the ambiguity
problem to be largely avoided by limiting the illuminated area
to one lunar hemisphere.
The relative motion of an observer on the Earth and a point
on the Moon has components due to the intrinsic rotations of the
two bodies, the librations of the Moon, and the geometry of the
observer?target line with respect to these components (Fig. 2).
The subradar point (SRP), which is denoted by coordinates
(?
srp
,?
srp
), lies at the intersection of the lunar surface with
a line between the observer and the Moon?s center of mass
(COM). The SRP moves on the surface of the Moon throughout
an observation period, and a plane containing two successive
SRP vectors and the COM defines the instantaneous ?Doppler
equator.? The vector perpendicular to this plane at the COM
represents the apparent instantaneous rotation axis or ?Doppler
axis? of the Moon.
Contours of equal radar time delay form concentric circles
about the SRP, which are also contours of equal incidence
angle for a spherical reference surface [Fig. 2(b)]. The Doppler
shifts across the surface are well modeled by a spherical solid-
body rotation for which the apparent rate and axial tilt vary
with time. We may therefore express the Doppler shift for any
given lunar surface point as a function of the instantaneous
SRP, apparent plane-of-sky rotation angle for the Doppler
axis ? [Fig. 2(a)], and apparent maximum Doppler shift at the
limbs (in hertz) w.
Fig. 3. Observed GBT 430-MHz system temperature (K), including lunar
surface emission and background sky contributions, versus incidence angle
for targets on the Moon. System temperature of about 166 K at the center of
Moon and about 113 K at the limb. There is little dependence of lunar physical
temperature on lunation at this wavelength. The solid line shows the best-fit
power-law function of incidence angle for angles > 25
?
. The scatter in the
data may be due to the radio-frequency interference at GBT, which varies in
strength with time.
We can compute detailed range and frequency (phase) his-
tories for any individual surface location relative to the target
point, but carrying this out for thousands of surface locations to
achieve focused mapping would be computationally intensive.
One solution is to use range and range?rate information as a
function of time for several points on the Moon. From these
values, we determine a best-fit set of ?spin? parameters at
1-min intervals (?
srp
, ?
srp
, w, and ?) and fit a second-order
polynomial to their variation with time. The spin parameters
are also used to set up the coordinate transformation between
range and range?rate values, and the lunar latitude?longitude
CAMPBELLetal.: FOCUSED 70-cm WAVELENGTH RADAR MAPPING OF THE MOON 4035
Fig. 4. Seventy-centimeter wavelength same-sense polarization radar image mosaics of the near-side and limb regions of the Moon. Radar echoes are normalized
to a cosine variation of power with incidence angle. Logarithmic scaling with black?white dynamic range of 45 dB. Horizontal spatial resolution averaged to about
1.2 km per pixel. Simple cylindrical projection used for equatorial regions. (a) 70
?
S?0
?
N latitude; 100
?
W?0
?
W longitude.
grid. The interpolation errors introduced by using the spin
parameters are below the values needed to create a one-pixel
offset in the final selenographic maps.
The radar echoes are recorded as a time series of complex
voltages denoted by V(m,n), where m is the range bin, and n
denotes the particular pulse record. The target point echo occurs
at a fixed range bin m
t
in all records and has zero frequency (or
whatever arbitrary small offset value we introduce). To produce
a delay-Doppler image about this point, we simply take the
Fourier transform of the data along the columns (n) and re-
sample to selenographic coordinates using the spin parameters
(Section IV). No range compression is needed due to the use
of a pulsed signal. As the distance from the target location
increases, the range migration and Doppler offset over the
983-s coherence interval also increase. The distance over which
this offset becomes comparable to the range and/or frequency
resolution defines a ?patch size? [7].
We build up the output map of a particular illuminated
region by carrying out the frequency-transform operation and
selenographic resampling for constituent patches after applying
a time-varying correction to the raw data array for delay and
frequency variations between the original target point (?
t
,?
t
)
and the center of the patch (a method suggested in [7]). The
focusing operation is applied in four steps. 1) An interpolation
of each range record (along the m time samples) is used to
correct the time-varying delay offset. These delay errors vary
slowly with time, so we can apply a single correction to each
pulse record. 2) The cumulative phase difference between the
pointing target and the patch center, i.e., the primary source
of image smearing, is compensated at each pulse record of
the complex voltage array based on the spin state of the
Moon at the start of the pulse. 3) The array is Fourier trans-
formed along the frequency lines to yield a delay-Doppler
array. 4) The relative backscatter intensity is mapped to se-
lenographic coordinates across the patch, as detailed in the next
section.
IV. RELATIONSHIP OF DELAY-DOPPLER AND
SELENOGRAPHIC COORDINATES
The mapping between delay-Doppler and selenographic co-
ordinates requires a transform between the Cartesian (x,y,z)
location of a point on the lunar reference grid with latitude ?
and longitude ?
?
?
x
y
z
?
?
= r
moon
?
?
cos?cos?
cos?sin?
sin?
?
?
(1)
and the (x
primeprime
,y
primeprime
,z
primeprime
) coordinates along the axes that define the
apparent (plane of sky) orientation and spin state of the Moon
(Fig. 2). The radius of the Moon at this location is given by
r
moon
. For most mapping, we assume a single mean radius for
the Moon, but a more detailed topography (if available) could
be used to orthorectify the final image. The transformation is
represented by
[D][S]
?
?
x
y
z
?
?
=
?
?
x
primeprime
y
primeprime
z
primeprime
?
?
(2)
where [S] rotates the coordinate system to place the SRP along
the x
prime
= x
primeprime
axis as
[S]=
?
?
cos?
srp
cos?
srp
sin?
srp
cos?
srp
sin?
srp
?sin?
srp
cos?
srp
0
?cos?
srp
sin?
srp
?sin?
srp
sin?
srp
cos?
srp
?
?
.
(3)
The [D] matrix rotates the coordinates about the x
prime
= x
primeprime
axis
by the Doppler angle (defined as positive clockwise) ? as
[D]=
?
?
10 0
0cos? ?sin?
0sin? cos?
?
?
. (4)
4036 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 45, NO. 12, DECEMBER 2007
Fig. 4. (Continued.) Seventy-centimeter wavelength same-sense polarization radar image mosaics of the near-side and limb regions of the Moon. Radar echoes
are normalized to a cosine variation of power with incidence angle. Logarithmic scaling with black?white dynamic range of 45 dB. Horizontal spatial resolution
averaged to about 1.2 km per pixel. Simple cylindrical projection used for equatorial regions. (b) 70
?
S?0
?
N latitude, 0
?
E?100
?
E longitude.
Delay variations arise due to differences in the range of a
surface point R
T
at (x
primeprime
,y
primeprime
,z
primeprime
) with respect to the SRP range
R
srp
. This difference in range is given by
?r =R
T
?R
srp
=
bracketleftbig
R
2
srp
+2r
2
moon
+2R
srp
r
moon
? 2x
primeprime
(R
srp
+r
moon
)]
1/2
?R
srp
(5)
and the appropriate delay bin is
n_delay = m
o
?
2?r
?tc
(6)
wherecis the speed of light, and ?tis the delay resolution. The
value of x
primeprime
must be > 0 in order for the desired point to be on
the radar-visible hemisphere of the Moon. The radar incidence
angle ? is [Fig. 2(b)]
? =cos
?1
(x
primeprime
/r
moon
). (7)
The frequency bin in the transformed data array for a surface
point at (x
primeprime
,y
primeprime
,z
primeprime
) is
n_freq= T
coh
(f
o
+y
primeprime?
w/r
moon
)
(R
srp
+r
moon
)
R
T
. (8)
We reproject the radar data by solving for the appropriate delay
and frequency bin in the Fourier-transformed array for each
(latitude, longitude) cell in the output map. These output values
may be complex valued, if we wish to later form a Stokes?
vector representation of the echo, or converted to relative power
by taking the squared magnitude of the complex values.
The surface horizontal resolution along the range axis is a
function of the incidence angle
?s
range
=?r/sin? =
c?t
2
radicalbigg
1 ?
parenleftBig
x
primeprime
r
moon
parenrightBig
2
(9)
and for our 3-?s observations, it varies from 450 m at the limbs
to 900 m at 30
?
incidence. The horizontal resolution along the
axis perpendicular to the range direction (?azimuth?) ?s
azimuth
is best when the image area is close to the Doppler axis
(y
primeprime
=0)
s
azimuth
=
r
moon
wT
coh
radicalbigg
1 ?
parenleftBig
y
primeprime
r
moon
parenrightBig
2
. (10)
The surface area A contributing to the echo in a given delay-
Doppler cell is thus
A =
r
moon
c?t
2wT
coh
radicalbigg
1 ?
parenleftBig
x
primeprime
r
moon
parenrightBig
2
radicalbigg
1 ?
parenleftBig
y
primeprime
r
moon
parenrightBig
2
. (11)
For the 983-s looks, the finest possible azimuth horizontal
resolution is about 320 m. Farther from the axis, the azimuth
resolution cells increase in size, and at the Doppler equator
(where the azimuth and range axes are parallel), there is no use-
ful frequency mapping capability. The final maps are produced
at 400-m resolution to limit undersampling of the frequency-
resolved cells.
V. C ALIBRATION AND MULTILOOK AVERAGING
One advantage of our 70-cm radar mapping relative to
shorter-wavelength observations using the same antennas is
the large illuminated region on the Moon. This permits the
CAMPBELLetal.: FOCUSED 70-cm WAVELENGTH RADAR MAPPING OF THE MOON 4037
Fig. 4. (Continued.) Seventy-centimeter wavelength same-sense polarization radar image mosaics of the near-side and limb regions of the Moon. Radar echoes
are normalized to a cosine variation of power with incidence angle. Logarithmic scaling with black?white dynamic range of 45 dB. Horizontal spatial resolution
averaged to about 1.2 km per pixel. Simple cylindrical projection used for equatorial regions. (c) 0
?
N?70
?
N latitude, 0
?
E?100
?
E longitude.
acquisition of full near-side coverage (with three or more looks)
in about 20 runs (one run is a 2- to 2.5-h passage of the
Moon above Arecibo) with different target locations. There is
however a variation in effective gain across the illuminated
region (Fig. 1), which must be removed to mosaic data for
adjacent target areas. The true beam pattern varies with time
during a run because the Arecibo 430-MHz line feed illumi-
nates a toroidal region of the dish and progressively spills off
the edge of the fixed reflector as the elevation angle decreases.
The GBT antenna has a fixed sensitivity pattern as it tracks
the target point. The net roundtrip power beam pattern P(?),
which represents the product of the individual Arecibo and
GBT patterns for a summed set of looks, can be represented
by a Bessel function with an ?effective width? parameter W as
P(?)=[J
1
(2W?sin?)/(W?sin?)]
4
(12)
where ? is the angle between the pointing target and a chosen
surface point [21]. In the case of a fully illuminated aperture at
Arecibo (i.e., when pointing at the zenith), the net beam pattern
is well represented by W = 170. Lower values correspond to
wider beams as the illuminated area of the Arecibo antenna
decreases with decreasing elevation angle. The beam angle
may be defined from the plane-of-sky offsets in the rotated
coordinate system and the observer?target distance R
T
as
? = tan
?1
?
?
radicalBig
parenleftbig
y
primeprime
?y
primeprime
target
parenrightbig
2
+
parenleftbig
z
primeprime
?z
primeprime
target
parenrightbig
2
R
T
?
?
. (13)
The average beam pattern for the Arecibo?GBT 70-cm data is
given by W = 155 based on the analysis of overlap regions
between images collected for different pointing centers. The
resulting correction factor (12) is used to normalize the ?
?
values for their distance from the beam center.
Every 15-ms data record includes a 3.41-ms interval that
contains no reflections from the Moon. For this interval, the
measured power equals the product of the net system gain in
each channel (G
1
and G
2
) and the net thermal noise from
the receiver system, Moon, and background sky. The degree
to which the Moon fills the GBT beam varies with the target
location on the lunar surface. The lunar and sky emissions are
assumed to be the same in the two circular polarizations. Where
lunar echoes are present, the measured power contains both the
noise and the lunar echo power. The dimensionless backscat-
ter coefficient ?
?
may be expressed in terms of the average
transmitted power P
T
, thermal noise power P
N
, scattering area
A, gain of the transmitting and receiving antennas G
AO
and
G
GBT
, range between the target and the observer R
T
, and
ratio of the observed echo power (i.e., after the off-Moon noise
power has been subtracted) at some location in the radar image
S
image
to that in the off-Moon region S
o?-Moon
?
o
=
S
image
S
o?-Moon
parenleftbigg
P
N
P
T
parenrightbiggparenleftbigg
1
A
parenrightbiggbracketleftbigg
64?
3
R
4
T
?
2
G
AO
G
GBT
bracketrightbigg
. (14)
The noise power is given by kT
B
B
N
, where k is Boltzmann?s
constant,T
B
is the system temperature of the GBT at 430 MHz,
and B
N
is the noise bandwidth.
The system temperature varies with the degree to which the
Moon fills the GBT beam, so we measured this parameter as
a function of incidence angle for the center of the pointing
region (i.e., from the center of the Moon to the limbs). We
also observed a sky source of known flux at 430 MHz to
calibrate the GBT system temperature. As expected, the system
temperatures were very similar between the left and right
circular polarization receivers, and the average value is 166 K
when the GBT is pointed at the center of the Moon. Since
none of our mapping observations have a target incidence angle
less than about 30
?
, we did not fully characterize the slow
change in system temperature between ? =0
?
and ? =25
?
.At
4038 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 45, NO. 12, DECEMBER 2007
Fig. 4. (Continued.) Seventy-centimeter wavelength same-sense polarization radar image mosaics of the near-side and limb regions of the Moon. Radar echoes
are normalized to a cosine variation of power with incidence angle. Logarithmic scaling with black?white dynamic range of 45 dB. Horizontal spatial resolution
averaged to about 1.2 km per pixel. Simple cylindrical projection used for equatorial regions. (d) 0
?
N?70
?
N latitude, 0
?
W?100
?
W longitude.
higher angles, the beam is partially off the Moon, and a good
approximation to the GBT system temperature is
T
GBT
system
= 415?
?0.289
(?>25
0
). (15)
Targets very close to the limb thus have a noise temperature of
about 113 K (Fig. 3).
The noise bandwidth is very close to the frequency resolution
of 1.017 MHz. The gain of the GBT at 430 MHz is a fixed value
(51.5 dB), but the dependence of the illuminated area on the
Arecibo primary reflector on zenith angle leads to a reduction
in gain with zenith angle ? in degrees (P. Perillat, personal
communication), i.e.,
G
AO
=
parenleftbigg
11044?
?
2
parenrightbigg
[18.67 ? 0.5414?]. (16)
Using these corrections, the derived ?
?
values in spatially
overlapping regions of observations with different target loca-
tions differ by ?3 dB. Our greatest uncertainty in calibrating
the backscatter coefficient is the transmitted power, which is not
well measured at Arecibo. These differences between different
observation runs can be compensated to produce mosaics of
large areas (Fig. 4), but the absolute backscatter coefficient
remains uncertain by about 50%. The relative cross sections
between the two circular polarizations are known with much
higher accuracy.
To decrease speckle noise in the final radar maps, we collect
three or more independent looks at each target area. Each
look is mapped using the patch-focusing method. Slight image
distortions between looks are corrected by selecting a single
look as a reference image and choosing widely spaced tie points
within this image. For each succeeding look, we determine
through cross correlation the best offset (?x,?y) for each
tie point, apply a rubbersheet transformation, and sum the
data. The standard deviation of the relative power values due
to speckle is reduced by incoherent summation as 1/
?
N,
where N is the number of averaged looks. While three or
more summed looks yield a geologically useful radar map, we
typically require a higher degree of local averaging (100 looks
or more) to reduce the uncertainties in the circular polarization
ratio (CPR) (SC/OC power).
The 70-cm radar maps are archived at the National Aeronau-
tics and Space Administration (NASA) Planetary Data System
(PDS) in two formats. The ?NASA Level 1? data (PDS Level 4)
are in the form of backscattered power (in each of the two
received senses of circular polarization) normalized to the
thermal noise in each look and the scattering area of every
resolution cell on the surface, projected to a latitude?longitude
grid, and averaged over three to nine looks. Maps of the equa-
torial and midlatitudes are presented in a sinusoidal equal-area
projection. Areas at higher latitude are shown in polar stereo-
graphic projection. The ?NASA Level 2? data (PDS Level 5)
are calibrated to our best estimate of the absolute backscat-
ter coefficient, normalized to the measured 68-cm scattering
functions in [22] to reduce the strong dependence of echo
brightness on incidence angle, and geometrically warped to
match the Clementine 750-nm lunar image base produced by
the U.S. Geological Survey. Level 2 products also include a
CPR data set formed after averaging the echo data for the
two circular polarization channels to 2-km resolution (at least
75 total averaged looks per pixel).
VI. RELATIONSHIP OF RADAR ECHOES TO MARE
BASALT AGE AND ILMENITE CONTENT
Basins on the lunar near side, which are formed by giant
impacts more than 2.8 billion years (b.y.) ago, are largely
filled by basaltic lava flows called maria. These flow complexes
formed as low relief plains and have been subsequently covered
by an impact-produced mixture of rocky debris and dust called
the regolith. Considerable work has been done to understand
mare composition and age, since these reveal the thermal and
CAMPBELLetal.: FOCUSED 70-cm WAVELENGTH RADAR MAPPING OF THE MOON 4039
Fig. 4. (Continued.) Seventy-centimeter wavelength same-sense polarization radar image mosaics of the near-side and limb regions of the Moon. Radar echoes
are normalized to a cosine variation of power with incidence angle. Logarithmic scaling with black?white dynamic range of 45 dB. Horizontal spatial resolution av-
eraged to about 1.2 km per pixel. Simple cylindrical projection used for equatorial regions. (e) Polar stereographic projection of the north polar region (60
?
?90
?
N
latitude). Zero longitude is toward the right. (f) Polar stereographic projection of the south polar region (60
?
?90
?
S latitude). Zero longitude is toward the left.
Note that the Moon?s libration during the period 2002?2006 predominantly favored viewing of the southern hemisphere from Arecibo. As a result, the spatial
coverage of the northern hemisphere is more limited in longitude.
chemical history of the magma reservoirs that supplied the
eruptions. There are two principal sources of remote-sensing
information on mare flow composition: near-IR multispectral
properties and orbital gamma-ray/neutron spectroscopy. Rel-
ative dating is accomplished by studying the abundance and
degradation state of impact craters, with absolute dating by
reference to population curves for areas surrounding samples of
known age. As a general rule, crater?population age estimates
are most robust where large regions are studied, and have
greater possible errors for smaller areas. Two recent studies
[23], [24] applied these techniques to spectroscopically defined
units across most near-side maria.
Long-wavelength radar data can play a complementary role
in these investigations. Schaber et al. [10] noted that the
70-cm radar echoes for lava flows in Mare Imbrium were
typically lower for flows that are ?blue,? or higher in their
abundance of the mineral ilmenite (FeTiO
3
). This mineral
has a higher microwave loss tangent than other species in
mare basalts and much higher loss than the generally feldspar-
rich rocks that form the lunar highlands; work on returned
lunar samples confirmed that the loss properties of basalts are
correlated with the total iron and titanium content [25]. Since
much of the 70-cm radar return comes from scattering within
the regolith, an increased loss tangent leads to lower echoes by
attenuating the incident signal [26].
Comparison of the 4- to 8-km-resolution 70-cm radar images
with FeO and TiO
2
abundance estimated from multispectral
data showed that the TiO
2
(i.e., ilmenite) content appears to be
the principal driver of basalt loss tangents, with the other iron-
bearing minerals playing a much less significant role [11]. This
same study identified differences in overall radar brightness be-
tween the maria in major basins for any given TiO
2
abundance
and suggested that such variations might be linked to relative
age. In this model, supported by measurements of the thermal
properties of the maria during eclipse, younger mare units have
a thin (2?3 m) regolith cover, which permits relatively small
Fig. 5. Cartoon representation of the mare regolith thickness and rock abun-
dance variations with age. The younger mare regolith is thinner (2?3 m) and has
a larger population of suspended and surface decimeter-scale rocks. The older
mare regolith is thicker (5?8 m) and has fewer 10-cm and larger-diameter rocks
capable of supporting 70-cm radar scattering.
impacts to excavate fresh blocky debris from the underlying
bedrock. With greater age, the regolith thickens to 5?8 m,
and small impacts simply break down the existing suspended
boulders. As a result, a younger mare unit will have a higher
radar brightness (more surface and suspended rocks to permit
volume scattering) than an older unit of the same TiO
2
content
(Fig. 5). Our new 70-cm radar maps permit a more detailed
comparison between echo properties, inferred composition, and
crater?statistic age estimates.
We selected Mare Serenitatis [Fig. 6(a)] for a preliminary
study as the entire basin is contained within a single beam
pattern of the 70-cm system [Fig. 6(b)]. This avoids any issues
of relative calibration between images collected with different
target centers. Serenitatis basalts were mapped based on dif-
ferences in IR reflectance by Pieters [27] and in an early form
by Thompson etal. [28]. We mapped the FeO [Fig. 6(c)] and
TiO
2
[Fig. 6(d)] abundance using Clementine data (available
from the PDS) and the techniques of Lucey et al. [29] and
Gillis et al. [30]. The ages of mare units within Serenitatis
(based on crater statistics) range from 2.44 to 3.81 b.y. For com-
parison, the basalts across the near side of the Moon range from
4040 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 45, NO. 12, DECEMBER 2007
Fig. 6. (a) Clementine 750-nm mosaic of Mare Serenitatis. The region cov-
ered is 12.8
?
?39.8
?
N, 3.1
?
?35.3
?
E. (b) Seventy-centimeter SC-polarized
radar image of Mare Serenitatis. (c) Map of TiO
2
content across Serenitatis
using Clementine multispectral data and the technique of Gillis etal. [2003].
The black?white stretch corresponds to values of 0%?15%. (d) Map of FeO
content across Serenitatis using Clementine multispectral data and the tech-
nique of Luceyetal.[2000]. The black?white stretch corresponds to values of
0%?25%.
a minimum age of about 1.2 b.y. to a maximum age of just over
3.9 b.y. [24].
Mare Serenitatis is characterized by an inner area of lower
titanium and iron basalts, and surrounded by a concentric ring
of moderate to high titanium flows. Many of the abrupt changes
in TiO
2
between flow complexes are accompanied by changes
in the same sense radar echo, which is consistent with our
expectation that ilmenite modulates the regolith loss tangent.
However, a comparison of the radar image and TiO
2
map also
shows some dramatic differences. Most striking is a ?finger?
of radar-bright material extending northward from the area
of Bessel crater. This higher radar return is not accompanied
by a change in the iron or titanium maps. In the area north-
west of Posidonius crater, a relatively homogenous region of
moderate TiO
2
flows comprises distinct areas of moderate and
very low radar return. Across the entire Serenitatis basin, the
radar echoes appear to trace ?unit? boundaries that are often
somewhat different from those that are readily noted in the TiO
2
map or in earlier multispectral characterizations [27].
To illustrate these differences, we compared the average
same-sense radar brightness to the average TiO
2
abundance
for 25 sample areas with relatively uniform properties (Fig. 7).
Based on earlier studies and a model for the dependence of
70-cm echoes on the ilmenite content of the regolith, we expect
about a 0.3-dB decline in echo power for each 1% rise in TiO
2
content. This corresponds to about one-half of the echo power
arising from within the regolith?if all of the echoes come from
the subsurface, we expect about 0.6 dB of change per weight
percent TiO
2
[14]. The data shown in Fig. 7 are best fit by a
linear function with slope of ?0.24 dB per 1% TiO
2
, but there
is a range in backscatter of about ?5 dB about this line for any
given titanium content.
Fig. 7. Plot of radar backscatter versus TiO
2
content for basalts in Mare
Serenitatis. The solid line shows the best-fit trend for all sites. The slope of
the trend line is ?0.24 dB per weight percent TiO
2
.
Fig. 8. Lunar Orbiter IV view of the area that is north of Posidonius crater
(95-km diameter), and (inset) 70-cm same-sense radar image of similar area,
which shows a very low backscatter from an apparently older mare flow unit.
White arrows connect crater locations in both images for reference.
Some of the spread in echo power with respect to the best-fit
line is likely related to the differences in age and the associated
variation in regolith thickness and rock abundance (Fig. 5)
relative to the average age across all of the sampled areas (about
3.4 b.y.). A feature that may be older than the average is north of
Posidonius (Fig. 8). This radar-dark area has an echo strength
that is 5 dB lower than the neighboring deposit (termed as S8
by Hiesinger etal. [23] and dated to 3.63 b.y.) of similar TiO
2
content. A possible area with younger age than expected is part
of unit S15, which was estimated at 3.44 b.y. [23] [labeled in
Fig. 6(a)]. In the southeastern portion of this unit, the radar
echo is 5 dB higher than predicted from the TiO
2
content, which
suggest that materials near the basin rim are younger than the
more interior deposits of similar spectral properties.
Our preliminary analysis of the differences in radar backscat-
ter between units of similar TiO
2
content with ages based on
crater statistics [23] did not show a strong correlation of greater
age with lower backscatter. However, such a test is not robust
for two reasons. First, the 25 sites chosen for the radar versus
TiO
2
study (Fig. 7) often do not overlap the limited areas
chosen for crater counting in [23], so there could be differences
in age between our sites not resolved by that study. For example,
the two extreme cases noted above were not sampled for statis-
tical analysis in [23]. Second, some radar-identified units within
CAMPBELLetal.: FOCUSED 70-cm WAVELENGTH RADAR MAPPING OF THE MOON 4041
Mare Serenitatis are not matched by changes in spectroscopic
properties (Fig. 6), which suggests that larger crater-count sam-
ple boxes could mix terrains of different age. It is also possible
that discrepancies in radar return from a simple trend with TiO
2
may arise from mineralogic differences that cause significant
variations in the microwave loss tangent among rocks with
similar FeO and TiO
2
abundance. At present, we have no strong
evidence for such a mineralogical mechanism based on lab
studies of lunar rocks [25], but the sample collection is not nec-
essarily complete with regard to possible basalt compositions.
Further work is needed to examine crater counts in relatively
large areas of uniform TiO
2
content and to compare these with
the average radar echo behavior to 1) define a relationship
between ?
?
,TiO
2
, and age, and 2) identify basalt deposits that
appear to have anomalous mineralogy. If this technique proves
valid, then the radar data and inferred composition could be
used to define relative ages for mare outcrops too small for
robust crater statistics.
VII. CONCLUSION
The new 70-cm wavelength radar maps have application to
studies of lunar geologic history; the resource potential of mare
basalts, pyroclastic deposits, and polar cold traps [31]; and
the search for safe landing areas. These data are archived at
the NASA PDS to make them available to the lunar science
community [32].
ACKNOWLEDGMENT
The authors would like to thank the staff at the Arecibo
Observatory and the GBT for invaluable assistance in collecting
the lunar radar data, in particular, F. Ghigo of the GBT and
A. Hine of the Arecibo Observatory. The Arecibo Observatory
is part of the National Astronomy and Ionosphere Center,
which is operated by Cornell University under a cooperative
agreement with the NSF. The GBT is part of the National Radio
Astronomy Observatory, which is a facility of the NSF operated
under cooperative agreement with Associated Universities, Inc.
The comments of two anonymous reviewers helped to improve
the manuscript.
REFERENCES
[1] S. H. Zisk, G. H. Pettengill, and G. W. Catuna, ?High-resolution radar
maps of the lunar surface at 3.8-cm wavelength,? EarthMoon,Planets,
vol. 10, no. 1, pp. 17?50, May 1974.
[2] T. W. Thompson, ?High-resolution lunar radar map at 70-cm wavelength,?
EarthMoon,Planets, vol. 37, no. 1, pp. 59?70, Jan. 1987.
[3] T. W. Thompson, ?High resolution lunar radar map at 7.5 m wavelength,?
Icarus, vol. 36, pp. 174?188, Nov. 1978.
[4] S. H. Zisk, B. A. Campbell, G. H. Pettengill, and R. Brockelman, ?Alphon-
sus crater: Floor fracture and dark-mantle deposit distribution from new
3.0-cm radar images,? Geophys. Res. Lett., vol. 18, pp. 2137?2140,
Nov. 1991.
[5] J. L. Margot, D. B. Campbell, R. F. Jurgens, and M. A. Slade, ?Topog-
raphy of the lunar poles from radar interferometry: A survey of cold trap
locations,?Science, vol. 284, no. 5420, pp. 1658?1660, Jun. 1999.
[6] J. L. Margot, D. B. Campbell, R. F. Jurgens, and M. A. Slade, ?Digi-
tal elevation models of the Moon from Earth-based radar interferome-
try,? IEEETrans.Geosci.RemoteSens., vol. 38, no. 2, pp. 1122?1133,
Mar. 2000.
[7] N. J. S. Stacy, ?High-resolution synthetic aperture radar observations of
the moon,? Ph.D. dissertation, Cornell Univ., Ithaca, NY, 1993.
[8] N. J. S. Stacy, D. B. Campbell, and P. G. Ford, ?Arecibo radar mapping
of the lunar poles: A search for ice deposits,?Science, vol. 276, no. 5318,
pp. 1527?1530, Jun. 1997.
[9] D. B. Campbell, B. A. Campbell, L. M. Carter, J. L. Margot, and
N. J. S. Stacy, ?Lunar polar ice: No evidence for thick deposits at the
South Pole,?Nature, vol. 443, pp. 835?837, 2006.
[10] G. G. Schaber, T. W. Thompson, and S. H. Zisk, ?Lava flows in Mare
Imbrium: An evaluation of anomalously low Earth-based radar reflectiv-
ity,?Moon, vol. 13, pp. 395?423, 1975.
[11] B. A. Campbell, B. R. Hawke, and T. W. Thompson, ?Long-wavelength
radar studies of the lunar maria,? J.Geophys.Res., vol. 102, pp. 19 307?
19 320, 1997.
[12] T. W. Thompson, W. J. Roberts, W. K. Hartmann, R. W. Shorthill, and
S. H. Zisk, ?Blocky craters: Implications about the lunar megaregolith,?
EarthMoon,Planets, vol. 21, no. 3, pp. 319?342, Nov. 1979.
[13] R. R. Ghent, D. W. Leverington, B. A. Campbell, B. R. Hawke, and
D. B. Campbell, ?Earth-based observations of radar-dark crater haloes
on the Moon: Implications for regolith properties,?J.Geophys.Res.,vol.
110, no. E2, E02005, 2005. DOI:10.1029/2004JE002366.
[14] B. A. Campbell and B. R. Hawke, ?Radar mapping of lunar cryptomaria
east of Orientale basin,?J.Geophys.Res., vol. 110, no. E9, E09002, 2005.
DOI:10.1029/2005JE002425.
[15] S. H. Zisk, C. A. Hodges, H. J. Moore, R. W. Shorthill, T. W. Thompson,
E. A. Whitaker, and D. E. Wilhelms, ?The Aristarchus?Harbinger region
of the moon: Surface geology and history from recent remote sensing
observations,?EarthMoon,Planets, vol. 17, no. 1, pp. 59?99, Sep. 1977.
[16] L. R. Gaddis, C. M. Pieters, and B. R. Hawke, ?Remote sensing of
lunar pyroclastic mantling deposits,? Icarus, vol. 61, no. 3, pp. 461?489,
Mar. 1985.
[17] B. A. Campbell, N. J. S. Stacy, D. B. Campbell, S. H. Zisk, and
T. W. Thompson, ?Estimating lunar pyroclastic deposit depths from imag-
ing radar data: Applications to lunar resource assessment,? in ?Proc.
WorkshopNewTechnol.LunarResourceAssessment,? pp. 16?17, 1992.
LPI Tech. Rep. 92-06.
[18] B. A. Campbell, D. B. Campbell, J. L. Margot, R. R. Ghent, M. Nolan,
L. M. Carter, and N. J. S. Stacy, ?Looking below the Moon?s surface with
radar,?EOSTrans.AGU, vol. 88, no. 2, pp. 13?18, 2007.
[19] G. H. Pettengill, S. H. Zisk, and T. W. Thompson, ?The mapping of
lunar radar scattering characteristics,?EarthMoon,Planets, vol. 10, no. 1,
pp. 3?16, May 1974.
[20] J. L. Margot, ?A portable fast sampling system for astronomical applica-
tions,? inProc.URSIGen.Assembly. Maastricht, The Netherlands, 2002.
[21] M. L. Skolnik,IntroductiontoRadarSystems. New York: McGraw-Hill,
1980.
[22] T. Hagfors, ?Remote probing of the Moon by infrared and microwave
emissions and radar,?RadioSci., vol. 5, pp. 189?227, 1970.
[23] H. Hiesinger, R. Jaumann, G. Neukum, and J. W. Head, ?Ages of mare
basalts on the lunar nearside,? J. Geophys. Res., vol. 105, no. E12,
pp. 29 275?29 329, Dec. 2000.
[24] H. R. Hiesinger, J. W. Head, U. Wolf, R. Jaumann, and G. Neukum, ?Ages
and stratigraphy of mare basalts in Oceanus Procellarum, Mare Nubium,
Mare Cognitum, and Mare Insularum,?J.Geophys.Res., vol. 108, no. E7,
1, 2003. DOI:10.1029/2002JE001985.
[25] W. D. Carrier, G. R. Olhoeft, and W. Mendell, ?Physical properties of the
lunar surface,? inLunarSourcebook. New York: Cambridge Univ. Press,
1991.
[26] T. W. Thompson, J. B. Pollack, M. J. Campbell, and B. T. O?Leary, ?Radar
maps of the Moon at 70-cm wavelength and their interpretation,? Radio
Sci., vol. 5, no. 2, pp. 253?262, 1970.
[27] C. M. Pieters, ?Mare basalt types on the front side of the moon,? inProc.
LunarPlanet.Sci.Conf.9, 1978, pp. 2825?2849.
[28] T. W. Thompson, R. W. Shorthill, E. A. Whitaker, and S. H. Zisk, ?Mare
Serenitatis: A preliminary definition of surface units by remote observa-
tions,?EarthMoon,Planets, vol. 9, no. 1/2, pp. 89?96, Mar. 1974.
[29] P. G. Lucey, D. T. Blewett, and B. D. Joliff, ?Lunar iron and titanium abun-
dance algorithms based on final processing of Clementine UV?visible
images,?J.Geophys.Res., vol. 105, pp. 20 297?20 306, 2000.
[30] J. J. Gillis, B. L. Joliff, and R. C. Elphic, ?A revised algorithm for calcu-
lating TiO
2
from Clementine UVVIS data: A synthesis of rock, soil, and
remotely sensed TiO
2
concentrations,?J.Geophys.Res., vol. 108, no. E2,
2003. DOI:10.129/2001JE001515.
[31] B. A. Campbell and D. B. Campbell, ?Regolith surface properties in the
south polar region of the moon from 70-cm radar polarimetry,? Icarus,
vol. 180, no. 1, pp. 1?7, Jan. 2006.
[32] B. A. Campbell and J. Ward, Dual-PolarizationCalibratedRadarMap
of the Moon. NASA Planetary Data System, 2007. ARCB/NRAO-L-
RTLS/GBT-4/5-70CM-V1.0.
4042 IEEE TRANSACTIONS ON GEOSCIENCE AND REMOTE SENSING, VOL. 45, NO. 12, DECEMBER 2007
Bruce A. Campbell (S?87?M?91) received the B.S. degree in geophysics from
Texas A&M University, College Station, in 1986, and the Ph.D. degree in
geology and geophysics from the University of Hawaii, Honolulu, in 1991.
Since 1992, he has been with the Center for Earth and Planetary Studies,
Smithsonian Institution, Washington, DC. From 1996 to 1998, he was the
Discipline Scientist for NASA?s Planetary Instrument Definition and Develop-
ment Program. His research interests focus on the applications of radar remote
sensing to the understanding of volcanism, impact cratering, weathering, and
other processes on terrestrial planets. Much of this work has emphasized the
relationship of surface roughness to radar observations of volcanic surfaces,
which remains a key element in interpreting data for Venus, the Moon, and
Mars. Fieldwork in support of this includes the collection of a large database
of high-resolution topographic profiles for lava flows in Hawaii and the desert
southwest. More recent projects have expanded this effort to include radar pen-
etration and polarization signatures of Mars-like sand, dust, and ash deposits.
He is a team member for the SHARAD shallow radar sounder on the 2005 Mars
Reconnaissance Orbiter. This instrument probes the upper kilometer of the
martian crust to identify geologic layering and possible water or ice deposits.
Donald B. Campbell is currently a Professor of astronomy with Cornell
University, Ithaca, NY. He has been using radar for over 30 years to study the
surfaces of terrestrial planets, satellites, and smaller bodies in the solar system.
He carried out some of the first detailed studies of the surface of Venus using
the Arecibo radar system and was a coinvestigator on the Magellan mission.
With colleagues, he discovered the unusual radar reflection properties of the
surfaces of the icy Galilean satellites. Working with his graduate students, he
has used the polarization properties of radar echoes to study the lunar regolith
and mantling deposits on Venus, studied the wavelength dependence of radar
reflections from the icy Galilean satellites to derive parameters of the scattering
layer, and used radar interferometric techniques to measure the topography of
the lunar poles. His current work includes radar studies of the surface of Titan
and the icy midsized saturnian satellites, and high-resolution polarimetric radar
studies of the surface of the Moon.
J. L. Margot, photograph and biography not available at the time of
publication.
Rebecca R. Ghent, photograph and biography not available at the time of
publication.
Michael Nolan, photograph and biography not available at the time of
publication.
John Chandler, photograph and biography not available at the time of
publication.
Lynn M. Carter received the B.S. degree in astronomy and physics from the
University of Illinois, Urbana, in 1999 and the Ph.D. degree in astronomy from
Cornell University, Ithaca, NY, in 2005.
She is currently a Postdoctoral Researcher with the Center for Earth and
Planetary Studies, Smithsonian Institution, Washington, DC. Her primary
research interest is in planetary geology, particularly the composition and
structure of the surface and subsurface of Venus, Mars, Titan, the Moon, and
asteroids. Her current research projects include ground-based radar studies
of lunar pyroclastic deposits, using radar polarimetry to study the surface
properties of asteroids, analysis of Cassini RADAR data of Titan to investigate
the surface-scattering behavior, and using the SHARAD sounding radar on
the Mars Reconnaissance Orbiter to study the extent and internal layering of
martian volcanic deposits.
Nicholas J. S. Stacy, photograph and biography not available at the time of
publication.