An analysis of a rotating, range-gated, fanbeam spaceborne scatterometer concept

A new simple scatterometer concept combines the advantages of both the fixed, multiple beam, sidelooking 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∼11 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 σ° at different combinations of the azimuth and incident angles. A preliminary optimization 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.