# Radar scatterometry
*sensing . methodologies*

Real-aperture radar that measures normalized radar cross-section from multiple azimuth angles to retrieve ocean surface wind vectors (speed and direction) over wide swaths at ~12-25 km resolution. Distinct from SAR: non-imaging, coarse-resolution, optimised for global daily wind fields.

## Specifications
- **family**: SAR processing
- **requirements envelope**: {"kind":"geometric","gsd_max":25000,"repeat_pass_geometry":false,"polarisation_modes":["C-band multi-azimuth sigma0","Ku-band multi-azimuth sigma0"],"swath_min_km":500,"daylight_required":false,"cloud_tolerant":true}
- **entity type**: methodology
- **last verified date**: 2026-06-08
- **verified by**: agency-doc
- **claim status**: agency-sourced
- **subtype**: sensing
- **attributes**: {"family":"SAR processing","kind":"sensing","summary":"Real-aperture radar that measures normalized radar cross-section from multiple azimuth angles to retrieve ocean surface wind vectors (speed and direction) over wide swaths at ~12-25 km resolution. Distinct from SAR: non-imaging, coarse-resolution, optimised for global daily wind fields.","requirements_envelope":"{\"kind\":\"geometric\",\"gsd_max\":25000,\"repeat_pass_geometry\":false,\"polarisation_modes\":[\"C-band multi-azimuth sigma0\",\"Ku-band multi-azimuth sigma0\"],\"swath_min_km\":500,\"daylight_required\":false,\"cloud_tolerant\":true}"}
- **technology**: radar
- **relevance**: in-scope

## Editorial
Radar scatterometry is the operational coarse-resolution radar method for ocean surface wind vectors. It measures normalised radar backscatter from multiple azimuth and incidence-angle looks, then retrieves wind speed and direction with a geophysical model function rather than forming a fine-resolution image.[^noaa-ascat] It serves ocean-surface winds, numerical weather prediction, marine forecasting, and storm monitoring where wide swath and frequent coverage matter more than local detail.

The method needs a dedicated real-aperture scatterometer geometry, stable calibration, multi-look ambiguity removal, land and ice masks, and quality control against rain and coastal contamination. It fails as a fine coastal mapper: conventional products are around 12.5-25 km, rain can bias wind retrievals, and land proximity or sea ice can contaminate the wind vector cell.[^osi-saf-ascat]

Demonstrated implementations include ASCAT on Metop and SeaWinds on QuikSCAT. OSI SAF ASCAT products provide operational Level-2 wind direction and speed from Metop ASCAT at 25 km sampling, with a long operational series beginning in 2007.[^osi-saf-ascat] QuikSCAT's SeaWinds instrument was a microwave radar designed for ocean near-surface wind speed and direction and provided global ocean coverage every two days.[^nasa-quikscat]

## Sources
- [osi-saf-ascat] | Metop-C ASCAT 25 km Winds | https://osi-saf.eumetsat.int/products/osi-102-c | tier=agency-doc | accessed=2026-06-08 | author=EUMETSAT OSI SAF
- [noaa-ascat] | ASCAT - Advanced Scatterometer | https://www.ospo.noaa.gov/products/atmosphere/ascat/ | tier=agency-doc | accessed=2026-06-08 | author=NOAA OSPO
- [nasa-quikscat] | Quick Scatterometer | https://www.nasa.gov/image-article/quick-scatterometer/ | tier=agency-doc | accessed=2026-06-08 | author=NASA | published=2010-01-07

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Source: https://eo-atlas.org/methodologies/radar-scatterometry
Maintainer: SpectraWorks B.V. (CC-BY 4.0)