scatterometer

A scatterometer is a microwave radar instrument designed to measure the roughness of the sea surface by observing the backscatter of radar signals. From these measurements, it provides estimates of ocean surface wind speed and direction over large areas.

Operating as an active remote sensing sensor, a scatterometer transmits microwave energy and records the energy scattered back to the instrument (the backscatter or sigma0). The returned signal depends on sea surface roughness, which is driven by wind, as well as the incidence angle and polarization of the radar. By collecting data at multiple incidence angles and polarizations, a model function relates sigma0 to wind parameters, yielding wind vectors.

Spaceborne scatterometers typically produce gridded wind fields with spatial resolutions on the order of tens of kilometers and sweep wide swaths across the oceans. Revisit times range from daily to several days, depending on the satellite constellation. The primary outputs are wind speed and wind direction, often provided relative to true north or to the satellite’s viewing geometry.

Prominent platforms include SeaWinds on NASA’s QuikSCAT and ASCAT on the European MetOp series. The technology traces back to SEASAT-1 in 1978, which carried an early scatterometer. Airborne scatterometers are used for field experiments and calibration campaigns.

Applications include weather forecasting, tropical cyclone analysis, climate research, and oceanography. Limitations involve reduced accuracy near coastlines, under heavy rain, and for extreme wind conditions. Data require calibration and validation with buoy and ship measurements to maintain reliability.