# SAR backscatter imaging
*sensing . methodologies*

Synthetic-aperture radar amplitude imaging: measures the surface normalized radar cross-section (sigma-nought) at high spatial resolution, day-night and cloud-independent. The base SAR sensing method underlying ocean wind retrieval, wave-mode spectra, flood mapping, and change detection.

## Specifications
- **family**: SAR processing
- **requirements envelope**: {"kind":"geometric","gsd_max":100,"repeat_pass_geometry":false,"polarisation_modes":["HH","HV","VH","VV","single-pol or dual-pol SAR amplitude"],"swath_min_km":20,"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":"Synthetic-aperture radar amplitude imaging: measures the surface normalized radar cross-section (sigma-nought) at high spatial resolution, day-night and cloud-independent. The base SAR sensing method underlying ocean wind retrieval, wave-mode spectra, flood mapping, and change detection.","requirements_envelope":"{\"kind\":\"geometric\",\"gsd_max\":100,\"repeat_pass_geometry\":false,\"polarisation_modes\":[\"HH\",\"HV\",\"VH\",\"VV\",\"single-pol or dual-pol SAR amplitude\"],\"swath_min_km\":20,\"daylight_required\":false,\"cloud_tolerant\":true}"}
- **technology**: radar
- **relevance**: in-scope

## Editorial
SAR backscatter imaging is the base active-radar method for all-weather surface imaging. It uses a synthetic-aperture radar payload to form calibrated amplitude images of surface backscatter at metre-to-tens-of-metres scale, independent of daylight and most cloud conditions.[^esa-s1-instrument] It serves flooding, sea ice, oil spill screening, maritime surveillance, and the downstream SAR wind and wave methods that start from SAR image products.

The method needs radiometric calibration, incidence-angle metadata, polarisation metadata, and enough antenna, power, downlink, and processing margin for imaging modes. Interpretation fails when geometry dominates the target signal: layover, shadow, foreshortening, speckle, wind roughening, wet-surface effects, and incidence-angle variation can all look like real surface change unless the product is terrain-corrected and normalised.

Demonstrated implementations include Sentinel-1 C-SAR, ALOS-2 PALSAR-2, and ICEYE X-band SAR. C-SAR provides C-band SAR modes including Interferometric Wide swath imaging at 250 km swath and 5 x 20 m ground resolution.[^esa-s1-instrument] PALSAR-2 adds L-band SAR with spotlight, stripmap, and ScanSAR modes plus single, dual, compact, and full-polarisation options.[^jaxa-palsar2] ICEYE provides X-band SAR imaging modes for repeat commercial monitoring, with sub-metre tasking modes and day-night, all-weather operation.[^iceye-sar-data]

## Sources
- [esa-s1-instrument] | Sentinel-1 Instrument | https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-1/Instrument | tier=agency-doc | accessed=2026-06-08 | author=European Space Agency
- [jaxa-palsar2] | ALOS-2 Sensor: PALSAR-2 | https://www.eorc.jaxa.jp/ALOS/en/alos-2/a2_sensor_e.htm | tier=agency-doc | accessed=2026-06-08 | author=JAXA EORC
- [iceye-sar-data] | ICEYE SAR data | https://www.iceye.com/sar-data | tier=operator-engineering | accessed=2026-06-08 | author=ICEYE

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