A rotating, range-gated, fanbeam spaceborne scatterometer concept

A new, simple scatterometer concept combines the advantages of both the fixed, multiple beam, side-looking radar such as AMI-Wind (ERS-1/2) and NSCAT (ADEOS), and the conically scanning pencil-beam radar such as SeaWinds. A wide, fanbeam antenna is rotated around a vertical axis with a slow rotation rate. For a satellite at an altitude of 725 km, the antenna footprint sweeps a circular donut of 1500 km diameter. Such a slow conical scan combined with the motion of the satellite at ~7 km/s ground-speed results in highly overlapping successive sweeps such that an image pixel is revisited up to 10 times during an overpass. The pixels in the radial direction are resolved by range-gating the radar echo. Depending on the across-track position of the imaged pixel, the measurement acquisitions during an overpass consist of a set of σ⁰ at different combinations of the azimuth and incidence angles. A preliminary optimisation of the system resulted in a C-band radar concept with a 15 km multiple-look spatial resolution and global coverage in two days. A sketch of the developed concept, preliminary system design and predicted performance are described