Sentinel-1A/B Combined Product Geolocation Accuracy

Abstract

Sentinel-1A and -1B are twin spaceborne synthetic aperture radar (SAR) sensors developed and operated by the European Space Agency under the auspices of the Copernicus Earth observation programme. Launched in April 2014 and April 2016, Sentinel-1A and -1B are currently operating in tandem, in a common orbital configuration to provide an increased revisit frequency. In-orbit commissioning was completed for each unit within months of their respective launches, and level-1 SAR products generated by the operational SAR processor have been geometrically calibrated. In order to compare and monitor the geometric characteristics of the level-1 products from both units, as well as to investigate potential improvements, products from both satellites have been monitored since their respective commissioning phases. In this study, we present geolocation accuracy estimates for both Sentinel-1 units based on the time series of level-1 products collected thus far. While both units were demonstrated to be performing consistently, and providing SAR data products according to the nominal product specifications, a subtle beam-and mode-dependent azimuth bias common to the data from both units was identified. A method for removing the bias is proposed, and the corresponding improvement to the geometric accuracies is demonstrated and quantified.

Rapid Detection of Windthrows Using Sentinel-1 C-Band SAR Data

“…In IW mode, S-1 acquires data at nominal incident angles between 31 • and 46 • , with a swath width of 250 km [36]. GRDH products have a pixel spacing of 10 m; the geolocation accuracy has been shown to be well within the product specification of 7 m [39].…”

Characterizing Tropical Forest Cover Loss Using Dense Sentinel-1 Data and Active Fire Alerts

“…Individual image pre-processing using ESA's (European Space Agency) Sentinel Application Platform (SNAP) toolbox [36] consisted of data import and format conversion, multi-looking (2 × 2 pixel), radiometric calibration (gamma-naught), topographic normalization [37] and geocoding to 20 m pixel resolution (WGS84, Latitude/longitude). Geocoding was done automatically, using ESA Precise Orbits with an estimated absolute geolocation accuracy of below 5 m [38]. The output was geocoded and topographically normalized gamma-naught backscatter images at 20 m resolution.…”

Using Multitemporal Sentinel-1 C-band Backscatter to Monitor Phenology and Classify Deciduous and Coniferous Forests in Northern Switzerland

“…Furthermore, the high temporal and spatial resolutions offered by Sentinel-1 allow a much denser sampling of data. Since the end of the commissioning phase of Sentinel-1B in September 2016 [56], the number of products has been high enough to generate LRW composites with over twice the temporal resolution of those used in this study. An LRW composite every six days would offer even more insights into the temporal evolution of the backscatter of forests.…”

“…The low number of available acquisitions in summer 2015 (2 acquisitions) and 2016 (3 acquisitions) were caused by the DLR campaign. A gradual increase to a maximum of 18 acquisitions towards the end of the investigated time period was due to a (a) ramp-up of the production by the European space agency (ESA) payload data ground segment and (b) the addition of Sentinel-1B acquisitions in September 2016 [56]. Figure 5.…”