# Independent System Calibration of Sentinel-1B
## 3 Internal Calibration
### TRM Characterization
At the beginning, the instrument was brought to its hot case with a temperature around 25 \({}^{\circ}\)C. No imaging data were acquired during the 24 h of RFC campaign to make sure the instrument cools down until about 0 \({}^{\circ}\)C. Instrument temperatures over this period have been extracted from the HK values in the Level-0 products and are depicted in Figure 11.  
A total of 79 RFC acquisitions acquired during this period were selected to perform the analysis (42 H-pol and 37 V-pol). Figure 12 shows the deviation results over the 24 h campaign for the selected 42 RFC data sets acquired with H polarization on transmit. Amplitude deviation values are depicted on the left-hand side, phase deviations on the right. Every group of points at a certain position on the time axis gives the deviation values for the 280 H-pol TRMs in the front-end which result from the analysis of one single RFC measurement; each individual TRM is represented by a different color. Concentrating on one color representing one TRM, all TRMs show a very stable behavior over time and under different temperature conditions, with variations of about 0.25 dB for the amplitude and of about 4 \(deg\) for the phase. These results are very good considering Sentinel-1B instrument temperature variation of about 25 \({}^{\circ}\)C during the 24-h RFC campaign (hot and cold cases). Note that the two striking TRMs in tile number 5 have not been considered in the plot and that the reference values used in this first analysis are still the ones defined on-ground, better results are expected when using in-flight reference values. Figure 10: Tx/Rx chain settings measured for individual Sentinel-1B front-end TRMs between June and August 2016. The blue curve represents the mean value of 76 RFC pairs per TRM for the V polarization. The second analysis performed concerns the stability of the front-end TRMs over longer periods of time. Figure 13 represents each individual TRM by a different color over the three months of the commissioning phase. Concentrating again on one color, all modules show a very stable behavior over time with variations of about 0.2 dB for the amplitude and of about 3 _deg_ for the phase. These are very good results considering the observation period of 3 months in which the instrument was working in  
Figure 11: Sentinel-1B front-end mean temperature during the 24 h of continuous RFC acquisitions, as part of the 24 h RFC campaign performed on 15 May 2016. Figure 12: Sentinel-1B amplitude and phase deviations for a total of 42 H-pol RFC measurements acquired during the 24 h RFC campaign in May 2016. The two top plots show the deviations for the Tx-chain (amplitude and phase); the two bottom plots show the deviations for the Rx chain. conditions similar to the ones of the operational phase. Note that the representation of the failed TRMs in tile 5 number has not been considered in the plots and that in-flight reference values have been used to derive the deviations. Further details on the analysis of RFC measurements acquired during the Sentinel-1B commissioning phase can be found in [14].