# Analysis of Sentinel-1 Radiometric Stability and Quality for Land Surface Applications
## 2 Dataset Description  
In this study, 154 S-1A images of both Ascending and Descending modes acquired between October 2014 and February 2016 over France (two different places) and Gabon (the southern region) were used. All of the images used the IW imagining mode with VH and VV polarizations. Moreover, all of the images were generated from the high-resolution Level-1 Ground Range Detected (GRD) product. Other image products were less accessible. The GRD product consists of focused SAR data that have been detected, multi-looked (5 and 1 looks according to slant ranges and azimuthal directions, respectively), and projected to a ground range based on an Earth ellipsoid model. The high-resolution GRD product uses roughly square resolution pixels of 20 m \(\times\) 22 m. The Sentinel-1 Toolbox [5] was used to calibrate and geocode images. The calibration aims to convert digital number values of the raw images into backscattering coefficients (\(\sigma^{\circ}\)). Our geocoded S-1A images have pixel sizes of \(\sim\)10 m \(\times\) 10 m.  
Moreover, three SAR images acquired from Radarsat-2 (RS-2) (C-band \(\sim\) 5.3 GHz) at the fine quad-polarization mode (HH, HV, VH, VV) and at incidence angles of 38\({}^{\circ}\) (one image) and 43\({}^{\circ}\) (two images) were used. These images were acquired 12 June 19 and 2014 and on 6 July 2014 at a spatial resolution of 12.5 m. The PolSARPro v4.2.0 software program [6] was used to calibrate RS-2 images. A 7 \(\times\) 7 boxcar filter was used to reduce image speckle effects. These images were then geocoded using the MapReduce 2.3 software program [7]. Our geocoded RS-2 images include pixels of \(\sim\)8 m \(\times\) 8 m.  
Three invariant targets were chosen to assess the radiometric stability of returned S-1A signals (Figure 1). The first target is an asphalt racetrack located in southeastern France (43\({}^{\circ}\)34\({}^{\prime}\)47\({}^{\prime\prime}\)N, 04\({}^{\circ}\)57\({}^{\prime\prime}\)53\({}^{\prime\prime}\)E) that covers an area of 14.7 ha (1561 and 2406 pixels for S-1A and RS-2, respectively). The second target is a forest situated in Southern France referred to as the \"Mende forest\". Austrian Pine is the main species found in this forest, which is located at 43\({}^{\circ}\)30\({}^{\prime}\)04\({}^{\prime\prime}\)N and 03\({}^{\circ}\)30\({}^{\prime}\)41\"E. The forest covers an area of approximately 8.1 ha (856 pixels in S-1A). Finally, the third target represents a dense evergreen tropical forest located south of Gabon (01\({}^{\circ}\)08\({}^{\prime}\)19\({}^{\prime\prime}\)N and 11\({}^{\circ}\)50\({}^{\prime}\)07\({}^{\prime\prime}\)E) that is referred to as the \"Gabon forest\". Gabon forest covers an area of approximately 635.2 ha (63882 pixels in S-1A images). Both the Mende and Gabon forests have evergreen canopies that retain foliage throughout the year. The S-1A images cover all of the invariant targets, whereas the RS-2 images only cover the racetrack target.  
For the racetrack, hourly temperature and precipitation data acquired from a meteorological station located 8 km away from the racetrack were available. For the Mende forest, hourly temperature and precipitation data were also available. Meteorological data for the Gabon forest were not available.