Computer Science – Sound
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003eaeja....13449b&link_type=abstract
EGS - AGU - EUG Joint Assembly, Abstracts from the meeting held in Nice, France, 6 - 11 April 2003, abstract #13449
Computer Science
Sound
Scientific paper
The SHARAD (SHAllow RADar) is a radar sounder that will be used to explore the surface and subsurface and surface of Mars in the context of the Mars Reconnaissance Orbiter 2005 mission. This instrument is a nadir-looking pulse limited radar sounder and altimeter, which uses synthetic aperture techniques to isolate subsurface reflections. SHARAD can be effectively operated at any altitude reached by the MRO spacecraft. The instrument consists of one antenna assembly and an electronics assembly. The antenna assembly consists of a dipole antenna, parallel to the surface and perpendicular to the direction of motion, used to receive echoes reflected by the Martian surface and subsurface. The bandwidth is10 MHz centred at 20 MHz and can be split in two bandwidths of 5 MHz in order to estimate the dielectric properties of the subsurface detected interfaces and for further reduction of the surface clutter (in this case the vertical resolution will decrease accordingly to the reduced transmitted frequency bandwidth). The selected frequencies will be able to penetrate the ionosphere and will be used to estimate the dielectric properties of the surface. A chirp signal, with a bandwidth of 10 MHz, will be generated and transmitted at the operating frequency for a period of 85 microseconds. The instrument then switches to a receive mode and records the echoes from the surface and subsurface for the expected duration. The total transmit-receive cycle lasts in the order of a few milliseconds. The received signals are down-converted, passed to an analog-to-digital converter, and compressed in range and azimuth. The azimuth integration (multi-look focused SAR processor implemented on ground using the on board pre-elaborated data) accumulates up to 2 seconds of pulses, resulting in an along-track space resolution of 300 m. The cross-track footprint size is on the order of 3 to 7 km. The data rate is variable depending on the degree of on-board pre-processing performed, and shall be approximately in the range of few or fraction of Mbps. The instrument has been designed to fulfil the mass and power constraints of the spacecraft: the SHARAD total mass allocation is 15 kg, including both the antenna and the electronic assembly. The total power consumption will not exceed 60 W, while the standby power will be approximately 10 W. Various figures of data volume can be achieved depending on the MRO mission timeline.
Biccari Daniela
Lorenzoni L. V.
Masdea Arturo
Orosei Roberto
Picardi Giovanni
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