SMOS mission payload
The biggest challenge the SMOS mission faces is to fly and demonstrate a completely new type of instrument – a radiometer that operates between 1400-1427 MHz (L-band).
In order to achieve the required spatial resolution for observing soil moisture and ocean salinity a huge antenna would normally be necessary. For the SMOS mission, however, the antenna aperture has been cleverly synthesized through a multitude of small antennae. After more than 10 years of research and development, with the aim of demonstrating key instrument performance such as antenna deployment and image validation, the innovative SMOS instrument, called MIRAS (Microwave Imaging Radiometer using Aperture Synthesis) has been realised.
MIRAS consists of a central structure and three deployable arms, each of which has three segments. During launch, these arms are folded-up, but soon after separation from the launch vehicle they are gently deployed via a system of spring-operated motors and speed regulators.
There are 69 antenna elements – the so-called LICEF receivers, which are equally distributed over the three arms and the central structure. Each LICEF is an antenna-received integrated unit that measures the radiation emitted from the Earth at L-band. The acquired signal is then transmitted to a central correlator unit, which performs interferometry cross-correlations of the signals between all possible combinations of receiver pairs. By pre-processing the calculations on-board, the amount of data that has to be transmitted to the ground is significantly reduced.
Last update: 11 February 2009
SMOS: ESA's water mission 
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