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SHARAD
SHARAD (Mars SHAllow RADar sounder) is a subsurface sounding radar embarked on the Mars Reconnaissance Orbiter (MRO) probe. It complements the MARSIS radar on Mars Express orbiter, providing lower penetration capabilities (some hundred meters) but much finer resolution (15 metres - untapered - in free space).[citation needed]
SHARAD was developed under the responsibility of the Italian Space Agency (ASI, Agenzia Spaziale Italiana), and provided to JPL for use on board NASA's Mars Reconnaissance Orbiter spacecraft in the frame of a NASA/ASI agreement which foresees exploitation of the data by a joint Italian/US team. The INFOCOM dept. of the University of Sapienza University of Rome is responsible for the instrument operations, while Thales Alenia Space Italia (formerly Alenia Spazio) designed and built the instruments. SHARAD operations are managed by INFOCOM from the SHARAD Operation Centre (SHOC), located within the Alcatel Alenia Space facilities in the suburbs of Rome.
SHARAD is intended to map the first kilometer below the Mars surface,[citation needed] providing images of subsurface scattering layers with high vertical resolution (15 m), with the intent to locate water/ice deposits and to map the vertical structure of the upper subsurface layers.
SHARAD operates on a carrier frequency of 20 MHz, transmitting a "chirped" signal with a bandwidth of 10 MHz. Pulsewidth is 85 μs and the nominal Pulse Repetition Frequency is 700.28 Hz. Transmitted power is 10 W peak. The antenna is a 10 m dipole. A synthetic aperture is generated on-ground to reduce the unwanted surface returns from off-nadir scatterers at the same range of the subsurface echoes.
SHARAD is physically divided into two elements:
The instrument operates at fixed PRF (700.28 Hz) and the echo is received in rank 1 (i.e., after the second transmitted pulse). Two alternate (higher and lower) PRF are available to deal with the extended mission orbit range. An open-loop tracking system, based on a prior knowledge of the surface topography, is the nominal means to position the 135 μs receive window on the expected echo position (a closed-loop tracker is available as backup).
The instrument on-board signal processing is minimal, and consists of a coherent presumption of the received echoes (programmable between 1 and 32 in power of 2 steps) to reduce the generated data rate, with programmable number of bits (8, 6, 4).
The chirp signal is generated directly on the 20 MHz carrier by a digital chirp generator and fed to the power amplifier, followed by a Transmit/Receive switch and the matching network. The receiver provides amplification, filtering and digital gain control directly at RF, and the digitised using an undersampling technique at a rate of 26.6 MHz. A single digital signal processor provides both the control and processing function.
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SHARAD
SHARAD (Mars SHAllow RADar sounder) is a subsurface sounding radar embarked on the Mars Reconnaissance Orbiter (MRO) probe. It complements the MARSIS radar on Mars Express orbiter, providing lower penetration capabilities (some hundred meters) but much finer resolution (15 metres - untapered - in free space).[citation needed]
SHARAD was developed under the responsibility of the Italian Space Agency (ASI, Agenzia Spaziale Italiana), and provided to JPL for use on board NASA's Mars Reconnaissance Orbiter spacecraft in the frame of a NASA/ASI agreement which foresees exploitation of the data by a joint Italian/US team. The INFOCOM dept. of the University of Sapienza University of Rome is responsible for the instrument operations, while Thales Alenia Space Italia (formerly Alenia Spazio) designed and built the instruments. SHARAD operations are managed by INFOCOM from the SHARAD Operation Centre (SHOC), located within the Alcatel Alenia Space facilities in the suburbs of Rome.
SHARAD is intended to map the first kilometer below the Mars surface,[citation needed] providing images of subsurface scattering layers with high vertical resolution (15 m), with the intent to locate water/ice deposits and to map the vertical structure of the upper subsurface layers.
SHARAD operates on a carrier frequency of 20 MHz, transmitting a "chirped" signal with a bandwidth of 10 MHz. Pulsewidth is 85 μs and the nominal Pulse Repetition Frequency is 700.28 Hz. Transmitted power is 10 W peak. The antenna is a 10 m dipole. A synthetic aperture is generated on-ground to reduce the unwanted surface returns from off-nadir scatterers at the same range of the subsurface echoes.
SHARAD is physically divided into two elements:
The instrument operates at fixed PRF (700.28 Hz) and the echo is received in rank 1 (i.e., after the second transmitted pulse). Two alternate (higher and lower) PRF are available to deal with the extended mission orbit range. An open-loop tracking system, based on a prior knowledge of the surface topography, is the nominal means to position the 135 μs receive window on the expected echo position (a closed-loop tracker is available as backup).
The instrument on-board signal processing is minimal, and consists of a coherent presumption of the received echoes (programmable between 1 and 32 in power of 2 steps) to reduce the generated data rate, with programmable number of bits (8, 6, 4).
The chirp signal is generated directly on the 20 MHz carrier by a digital chirp generator and fed to the power amplifier, followed by a Transmit/Receive switch and the matching network. The receiver provides amplification, filtering and digital gain control directly at RF, and the digitised using an undersampling technique at a rate of 26.6 MHz. A single digital signal processor provides both the control and processing function.