The instrument
Biomass carries the first P-band synthetic aperture radar in space. It operates in side-looking geometry with full polarimetric and interferometric capabilities. To penetrate the forest canopy, a large wavelength is necessary (around 70 cm) and means a large antenna of more than 10 m across. The instrument therefore comprises a large deployable reflector with a 12 m diameter projected aperture with an offset feed array and a single-beam.
This use of a single beam simplifies the feed array concept and is compensated by a limited roll steering of the satellite to achieve global coverage of the Earth.
To fit into Vega rocket fairing, the length of the reflector boom has been minimised, which impacted the focal length (7.8 m). The feed array has therefore been designed to compensate for this short focal length while still providing good polarimetric performance.
To generate and provide the input signal to the feed, the instrument includes several electronics such as the digital control unit that generates the signal at P-band and the power amplifier subsystem amplifies this signal which is routed to the feed array. In reception, the same reflector antenna collects the backscattered signal from ground.
The received amplifier subsystem amplifies the received signal, which is then digitised and stored in the satellite mass memory.
