Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.naic.edu/vscience/schedule/tpfiles/SimpsontagR2223tp.ps Äàòà èçìåíåíèÿ: Wed Mar 8 21:14:40 2006 Äàòà èíäåêñèðîâàíèÿ: Sat Dec 22 22:49:12 2007 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: ice cap

Proposal Identification No.: R2223 Date Received: 2006­Feb­28 16:12:13
Technical Page
Proposal Type: Urgent
General Category: Planetary Radar
Observation Category: Solar System
Total Time Requested: 3 Hours
Proposal Title: Bistatic Mars Express­Arecibo Radar Observations of the ``Stealth'' Region of
Mars
ABSTRACT:
The ``Stealth'' area was identified by Muhleman et al (SCIENCE, 253, 1508­1513, 1991) as being unique on Mars
because it returns NO backscattered echo when illuminated by Earth­based radar. Surface models suggest that the
material is very loosely compacted ash or other fine­grained volcanic debris. The loose compaction allows matching
of centimeter­wavelength radar signals into the regolith where they are eventually absorbed. The fact that there is
no echo at all requires that there be no embedded rocks or other discrete scatterers in the ''dust'' within one
absorption length (perhaps meters); otherwise, there would be di#use echoes at moderate to high incidence angles
as is the case elsewhere on Mars. Starting in 2005, a series of bistatic radar experiments was begun using the Mars
Express spacecraft. Radio signals at 3.6 and 13.1 cm wavelengths are beamed from the spacecraft toward the
(moving) specular point on Mars' surface; echoes are captured with dual­polarization receivers at each wavelength
at 70­m antennas of the NASA Deep Space Network. The forward specular scattering expected in these
experiments complements the backscattering results from entirely Earth­based radar systems. Experiments have
already been conducted over Mars' Residual South Polar Ice Cap (RSPIC), which appears usually BRIGHT to
Earth­based radar. The MEX RSPIC results show a surface with ``normal'' scattering properties ­ except that the
inferred dielectric constant is too high to be solid CO2, the main constituent assumed in LIMITED areas (perhaps
smaller than the MEX footprint) from other data (Simpson et al., 2005 Fall AGU). The S­Band MEX bistatic
radar experiment is 30 dB less sensitive than the companion X­Band experiment because of lower transmitter
power and lower antenna gain on both ends. The addition of 10 dB in gain provided by Arecibo could be the
di#erence between no detection and a usable signal in this area already expected to be a di#cult target.
Name Institution E­mail Phone Student
Richard Simpson Stanford University rsimpson@magellan.stanford.edu 650­723­3525 no
Service Observing Request Remot e Observing Request
X None X No
All of the observing run. Maybe
Part of the observing run. Yes
Queue Observing
1

Instrument Setup
S­band receiver
Atmospheric Observation Instruments:
Special Equipment or setup: none
RFI Considerations
Frequency Ranges Planned
2280­2310
2