Sentinel-1 GRD IW

Sentinel-1 GRD IW is the Level-1 Ground Range Detected product derived from the Interferometric Wide Swath (IW) acquisition mode of the ESA Copernicus Sentinel-1 C-band SAR constellation^[1][2]. The IW mode uses TOPSAR burst scanning to achieve a 250 km swath at a 10 m pixel spacing; the product is available in High Resolution (HS, 10 m pixel spacing) and Medium Resolution (MD, 40 m pixel spacing) variants, with HS the dominant distributed form^[3]. The actual SAR spatial resolution of the IW GRD HS product is approximately 20x22 m after multi-looking (5 range looks x 1 azimuth look), giving an equivalent number of looks of approximately 4.4^[3]; the 10 m pixel spacing is finer than the resolution and is the operationally standard grid for downstream processing.

GRD processing removes the phase component of the SAR signal, retaining amplitude backscatter intensity. The product is therefore not suitable for interferometric analysis; Sentinel-1 Single Look Complex (SLC) data must be used for InSAR applications^[3][4]. TOPSAR burst-mode processing can produce scalloping artefacts at sub-swath boundaries if multi-look filtering is insufficient. Speckle is inherent to SAR imagery and is reduced but not eliminated by GRD multi-looking.

From June 2023, the product is additionally distributed in COG_SAFE format (Cloud Optimized GeoTIFF within the SAFE container), complementing the original SAFE/JPEG2000 packaging^[2]. Both formats are available from the Copernicus Data Space Ecosystem under the Copernicus Sentinel Data Legal Notice, which permits free and open use^[5].

The revisit cadence has varied with fleet state: the Sentinel-1A+B dual-satellite configuration before August 2022 provided a 6-day repeat; the retirement of Sentinel-1B extended the interval to 12 days; and the commissioning of Sentinel-1C (launched December 2024) restored the nominal 6-day repeat as of mid-2025^[2][1].

Published applications include tropical deforestation monitoring (as the SAR input to the RADD alert system^[6]), open-ocean ship detection via VV backscatter change, emergency response mapping for floods and landslides, and land cover change analysis^[4].