Sentinel-1 processing with GAMMA software
be generated). The geocoding is done using the program gc_map (and not gc_map_grd which
would be for data in ground-range geometry).
For GRD data products the geocoding quality achieved based on the state vectors and DEM is
of the same high quality as for the SLC products. Note that typically meter scale quality is
achieved even without refinement of the geocoding lookup table.
4.4. Offset tracking
TOPS mode S1 GRD products can be used for offset tracking (program
offset_pwr_trackingm) to map displacements. For this it is highly recommended to use the
imported multi-look intensity image in slant range geometry (and not the ground-range
product that can also be generated which may result in anomalies in the offset field). In order
to apply a co-registration of the data considering the terrain topography before the
determination of the offsets it is recommended to use the co-registration procedure using
rdc_trans. Furthermore, supportive programs e.g. to calculate the look vector direction or to
convert the LOS displacement component to other components are available for the MLI in
slant range geometry.
As compared to offset tracking with SLC data a reduced quality is expected for the range
offsets because of the multi-looking applied in the generation of the GRD products.
Nevertheless, this may be acceptable as the quality of the range offsets will still be higher than
the quality of the azimuth offsets.
Considering that the GRD and SLC product based MLI geometries are identical means that it
is also possible to do offset tracking between a GRD product and an SLC product.
4.5 Other functionality
After the importing, the GRD data (even if acquired in TOPS mode) is in the normal MLI
slant range geometry and format used in the GAMMA software, making all functionality of
the software available (e.g. multi-temporal analysis or terrain correction of backscattering
coefficients using the pixel_area approach).
4.6 Sentinel-1 Extended Wide-Swath (EWS) GRD products
The functionality for Sentinel-1 GRD products is also applicable for the Sentinel-1 Extended
Wide-Swath (EWS) GRD products. An example of a geocoded S1 EWS offset field over
Svalbard is shown in Figure 2. The result confirms that EWS GRD products can be used for
offset tracking, nevertheless the quality of the results is lower than for IWS data because of
the lower spatial resolution.