1. G. Picardi 1, J. Plaut 2, R. Seu 1, R. Phillips 3, Ali Safaeinili 2, R.Orosei 4, R. Mecozzi 5, R. Croci 5, C. Catallo 5, G. Alberti 6, E. Flamini 7 and the MARSIS and SHARAD Teams 1 INFOCOM Department, University of Rome “La Sapienza” Via Eudossiana 18, 00184, Rome, Italy 2 Jet Propulsion Laboratory California Institute of Technology 3 Washington University in St.Louis 4 INAF – Istituto Nazionale di Astrofisica 5 Thales Alenia Space Italia S.p.A., Business Unit Observation Systems & Radar,Via Saccomuro 24, 00131, Rome, Italy 6 CO.RI.S.T.A.Viale J. F. Kennedy 5, 80125, Naples, Italy 7 Italian Space Agency – ASI,Viale di Villa Grazioli 23, 00198 Rome Italy MARSIS and SHARAD: Radar Sounding from Orbit at Mars MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) is a low frequency nadir looking sounding radar selected by ESA as a payload of the Mars Express mission. The Mars Shallow Radar Sounder (SHARAD), a facility instrument provided by the Italian Space Agency (ASI), is embarked on board the NASA Mars Reconnaissance Orbiter spacecraft. Primary Scientific Objective of these two instrument is to map the distribution of water both solid and liquid, at global scale on the Martin crust. MARSIS-SHARAD System Parameters SHARAD Image Generation After A-to-D conversion, the only processing applied to the received signal is a presuming, with variable presuming-factors: 1 (no presuming), 2, 4, 8, 16, 28 and 32, to reduce the output data rate SHARAD Architecture - Functional Diagram Flow Diagram of the ground processing The CSA is applied to SHARAD data after a preliminary processing. During this phase different operations are performed: Data decompression and quality check; Base Band Conversion; Remove Bias; Remove spurious signals; Compensate amplitude and phase distortion of the Rx/Tx chain; Range Compression; Compensate for ionosphere distortions (PGA technique); Compensate the Receive Window position; Compensate the Radial Velocity of the spacecraft SHARAD Experimental Results Example of SHARAD result : (1) MOLA map of the zone covered by the radar during the observation. The line at zero kilometers is the ground-track of the radar; (2) Topography profile corresponding to the ground-track of the radar; (3) Focused SHARAD image. MARSIS Image Generation MARSIS Functional Block Diagram Input echoes are fast Fourier transformed Doppler filtering is operated in the frequency domain by coherently presumming the echoes before applying the reference function. Azimuth processing, in essence foresees the coherent summation of the radar returns by adjusting their phase. Example of MARSIS result : (1)Unfocused MARSIS image @ carrier frequency 4 MHz. (2)Unfocused MARSIS image @ carrier frequency 2 MHz. (3)MOLA map of the zone covered by the radar during the observation. MARSIS-SHARAD Mars north pole coverage One of the MARSIS observations (Orbit 3749) is very close to orbit 2026 and it can be compared with the SHARAD image. The SHARAD orbit 2026 doesn’t match perfectly with the MARSIS one, however some Mars zones are covered by both the sounder. In these zones, we can compare perfectly the radar-grams of MARSIS and SHARAD. SHARAD Orbit 2026: Marsis Orbit 3749: Images generated by SHARAD and MARSIS in an area covered by both the sensor. SHARAD radar-grams are more detailed than the MARSIS ones (pixel size in SHARAD image 10 times less than the pixel size in MARSIS image) in the first kilometers below the Mars’s surface, but SHARAD has not visibility down to 2Km (weak penetration capability) according to the different value of the transmitted wavelength. By a preliminary analysis it is evident that MARSIS detects signals from subsurface interfaces at 3Km of depth, while the signals received by SHARAD in the same zone and at the same depth are very weak compared with the background noise. However, SHARAD radar-grams show subsurface interfaces at 100-200m of depth: these interesting targets can not be discriminated by MARSIS because of its coarse vertical resolution. MARSIS Experimental Results MARSISSHARAD Carrier Frequency 1.8, 3, 4, 5 MHz20 MHz Vertical Resolution 150 mfree space 10-20m Penetration Depth from ~0.5 km to ~5 km Lessthen2Km Horizontal Resolution 5-9 km300-500m Pulsewidth250µs (baseline) 85µs PRF130Hz700 Hz, 670Hz, 775 Hz Pulse Bandwidth 1MHz10MHz MARSISSHARAD Carrier Frequency 1.8, 3, 4, 5 MHz20 MHz Vertical Resolution 150 mfree space 10-20m Penetration Depth from ~0.5 km to ~5 km Lessthen2Km Horizontal Resolution 5-9 km300-500m Pulsewidth250µs (baseline) 85µs PRF130Hz700 Hz, 670Hz, 775 Hz Pulse Bandwidth 1MHz10MHz