SARAL instruments (Credits ISRO)



AltiKa is a Ka-band altimeter (35 GHz) developed by CNES that can be flown on a microsatellite or as an auxiliary passenger on other missions. Signal frequencies in the Ka-band enable better observation of ice, rain, coastal zones, land masses (forests, etc.) and wave heights.

AltiKa is aiming to observe the ocean in as much detail and as accurately as current missions, only at lower cost, by flying the altimeter on a microsatellite that is cheaper to design, build and launch. Experience has shown that an altimetry platform must comprise an altimeter, radiometer and precise orbit determination system, with sufficient redundancy, as well as enough fuel to keep the satellite orbiting on a repeating ground track – at least with a ‘conventional’ altimetry mission.

The AltiKa altimeter is a single-frequency Ka-band altimeter (operating at 35.75 GHz, weighing less than 20 kg and consuming less than 50 Watts). Alcatel Space developed a Ka-band altimeter between 1998 and 2000 which was based on the same technologies as those used for the Poseidon-1 and Poseidon-2 altimeters.

Dual frequency microwave radiometer

The bi-frequency (23.8 GHz / 37 GHz) radiometer is used to correct altimetry measurements from wet troposphere crossing effects. The 23.8 GHz channel is the primary water vapour sensing channel, meaning higher water vapor concentrations will lead to larger 23.8 GHz brightness temperature values. The addition of the 37 GHz channel, which has less sensitivity to water vapour, facilitate the removal of the contributions from cloud liquid water, which also act to increase the 23.8 GHz brightness temperature

Illustration of the AltiKa & Radiometer antenna (CAD model), image credit: CNES

DORIS System

The complete DORIS system includes the DORIS on-board package, a network of approximately 60 beacons located around the world and a ground system. The on-board package includes the electronic box hosting the receiver itself and the ultra stable oscillator and an omnidirectional antenna. The DORIS on-board package is of the same version as the one embarked on Jason-2. It includes a 7-beacon receiving capability and an on-board real time function (DIODE for Détermination Immédiate d’Orbite par DORIS Embarqué) to compute the orbit ephemeris in real time.The DORIS on-board package is dual string (in cold redundancy), each DORIS chain is automatically connected to the single antenna through a switching box inside the DORIS unit. Each receiver is connected to its own ultra-stable oscillator.

SARAL/AltiKa DORIS Receiver Antenna and Instrument

Laser Reflector Array LRA

It is used for precise calibration of other POD instruments, through analysis of laser shots from the ground then reflected by the LRA mirrors. The laser reflector array is placed on the nadir face of the satellite. It consists of several quartz corner cubes arrayed as a truncated cone with one in the center and the others distributed azimuthally around the cone.

SARAL/AltiKa Laser Reflector Array

Argos-3 (Data Collection System)

The objective is to collect data from remote terminals in the ground segment referred to as PPTs (Platform Transmitter Terminals).

The Argos-3 onboard package represents the newest generation of the Argos system. The major improvement of the new Argos-3 system is that it will now be able to send orders to its terminals whereas before the onboard instruments were only capable of receiving data (up to Argos-2 inclusive). The MetOp-A spacecraft of EUMETSAT (launch Oct. 19, 2006) is carrying the first Argos-3 instrument demonstrator package. In comparison to previous generations, system performance is enhanced via a unique downlink and a high data uplink (4800 bit/s versus 400 bit/s), while ensuring complete compatibility with existing systems in the ground segment. Thanks to digital processing, the new instrument is lighter and more compact than its predecessors on analog basis. Argos-3 is capable of receiving messages from over 1000 PTTs (Platform Transmitter Terminal) simultaneously within the satellite’s FOV (Field of View).


SARAL UHF antenna

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