SHARAD, a shallow radar sounder to investigate the red planet

摘要

SHARAD is a sounder provided by ASI, which is participating as a facility instrument to 2005 NASA’s Mars Reconnaissance Orbiter mission. SHARAD is, together with MARSIS, the only sounding instrument that orbits around Mars. It has a higher vertical resolution than MARSIS, however the latter has a greater penetration capability. Goal of this nadir-looking Altimeter with synthetic aperture capabilities is to investigate surface and subsurface of Mars and subsequently provide radar data that supply unique information concerning dielectric interfaces. The sounder’s low-frequency and wideband features, meaning respectively a carrier band of 20 MHz and a bandwidth of 10 MHz, give the opportunity to achieve a theoretical vertical resolution of 15 meters in free space, maintaining an acceptable penetration capability of approximately 1500 meters. The instrument is composed of two main subsystems: the antenna (a 10 meter foldable dipole) and the SHARAD Electronic Box. In order to maximize the signal’s received power and increase the quality of the data acquired, a certain number of calibration measurements on-ground and in-flight have been executed. The calibration outcome is part and parcel of the on ground processing of the radar. The processing method through which Planetary Data System compliant products are generated at the SHARAD operational center (SHOC) includes both range compression for the vertical resolution and synthetic aperture processing to achieve along-track resolution. To discern surface and subsurface echoes from clutter and thus support the scientific analysis of the data, the SHOC team developed an incoherent simulator for surface echoes [1].