The Extended Timing Annotation Dataset for Sentinel-1—Product Description and First Evaluation Results

Abstract

This paper introduces the extended timing annotation dataset (ETAD) product for Sentinel-1 (S-1) which was developed in a joint effort of German Aerospace Center (DLR) and the European Space Agency (ESA). It allows to correct range and azimuth timing of S-1 images for geophysical effects as well as for inaccuracies in synthetic aperture radar (SAR) image focusing. In combination with the precise orbit solution, these effects determine the absolute geolocation accuracy of S-1 SAR images and the relative collocation accuracy of repeat pass image stacks. ETAD contains the gridded timing corrections for the tropospheric and ionospheric path delays, the tidal-based surface displacements, and the SAR processing effects, all of which are computed for each data take using standard models from geodesy and auxiliary atmospheric data. The ETAD product helps S-1 users to significantly improve the geolocation accuracy of the S-1 SAR products to better than 0.2 m and offers a potential solution for correcting large scale interferometric phase variations. The product layout and the product generation are described schematically. The paper also reports first results for different SAR techniques: first, the improvement in geolocation accuracy down to a few centimeters by verification of accurately surveyed corner reflector positions in the range-azimuth plane; second, the well-established offset-tracking technique, that is used for systematic ice velocity monitoring of ice sheets and glaciers, where ETAD can reduce velocity biases down to subcentimetric values; and third, the correction of atmospheric phase contributions in wide-area interferograms used for national and European ground motion services. These early results proof the added value of the ETAD corrections and that the product design is well suited to be integrated into the processing flows of established SAR applications such as absolute ranging of targets, speckle/feature tracking and interferometry.

InSAR‐Derived Horizontal Velocities in a Global Reference Frame

“…The list of factors influencing u az is not comprehensive (Gisinger et al., 2022; Yunjun et al., 2022). We limited our experiments to general models of solid‐earth tides and ionosphere, the latter of which primarily affects ascending (dusk) frames, especially at lower latitudes.…”

InSAR-derived horizontal velocities in a global reference frame

“…We did not implement an approach to reduce the error propagation as in (Fattahi, Agram, & Simons, 2017). The list of factors influencing u az is not comprehensive (Gisinger et al, 2022;Yunjun et al, 2022). We limited our experiments to general models of solid-earth tides and ionosphere, the latter of which primarily affects ascending (dusk) frames, especially at lower latitudes.…”

An Advanced Quality Assessment and Monitoring of ESA Sentinel-1 SAR Products via the CyCLOPS Infrastructure in the Southeastern Mediterranean Region

“…Such a response is useful for estimating the limit of the expected location measurement accuracy, as outlined in Equation (22). The SCR of the point target is multiplied by both the slant range and azimuth resolution parameters, according to product specifications, as reported by [26,[50][51][52].…”

“…These coordinates are associated with the zero-Doppler geometry. The latter is essential for accurate SAR imagery interpretation and is governed by the range-Doppler equation [26,52]. The S-1 SLC image products, specifically, adhere to this zero-Doppler geometry convention.…”

“…These influences can introduce apparent displacement shifts, occasionally reaching several metres. Mitigating the abovementioned influences requires several post-processing steps and external data for accurate correction [16]. Determining the geolocation accuracy of SAR products entails empirically assessing the system's inherent biases in both range and azimuth timing.…”