## 5 Results and Discussion
### Single-Pass Interferometry and Polarimetry  
Interferometric and polarimetric applications, as well as DBF imaging, rely on phase consistency among data in several channels simultaneously acquired by the SAR sensor. This section presents results that illustrate how propagation direction independent phase consistency is achieved by the baseline calibration approach described in Section 4.4. The results in this section pertain to data acquired with the X-band polarimetric across track interferometer of F-SAR in 2014.  
Figure 13: Similar to the analysis of Figure 12, but with an emphasis on the azimuth dimension. The top row shows the absolute residual phase \(\delta\chi^{s}_{pq}(az)\) variation as a function of the squint angle, after the mean phase has been subtracted from each response. The second row shows the reference target azimuth position error as measured in focused SAR imagery.  
The impact of the baseline calibration process on the inter-channel phase differences of the interferometer is illustrated in Figure 14. The polar plots show phase differences between the range histories of reference targets deployed in the calibration site. The underlying raw data was acquired during the calibration campaign _OP14 AF_. The evaluation covers all unique interferometric pairs among the co-polar channels acquired simultaneously by the interferometer. These are four channels corresponding to the two antennas, X1 and X2. The top and the bottom halves of the figure juxtapose interferometric phase errors before and after baseline calibration. The results clearly show that systematic trends are effectively removed from the two independent interferometric calibration data acquisitions considered. The evaluation shows that the errors addressed are, indeed, systematic across independent acquisitions and that the proposed baseline correction model is able to simultaneously explain residual errors in all possible channel combinations of a multi-channel SAR acquisition.  
Table 1 lists the position refinements corresponding to the results of Figure 14. Baseline calibration shifts the phase centers of the interferometer on the order of 1 mm. To further validate this correction, Figure 15 summarizes results obtained during the scientific measurement campaign _ICESAR_, which included acquisitions over the Rhone Glacier in Switzerland that were carried out days after the calibration acquisitions of _OP14 AF_ in September 2014. The results show how the baseline corrections of Table 1 significantly improve the consistency of digital surface models (DSMs) derived from F-SAR acquisitions with opposing look directions. The original DSM difference shown in the bottom left of Figure 15 is dominated by a clear trend. The result after calibration, on the other hand, appears to be free of systematic errors. Instead, it shows differences that may be of scientific interest: they could be related to variations in the penetration depth of the radar signal that depend on the local incidence angle.  
Figure 14: Residual interferometric phase errors along the range histories of reference targets in two independent polarimetric, interferometric X-band acquisitions. The top and the bottom halves of the figure show interferograms before and after baseline calibration, respectively. Each half comprises six plots that correspond to all possible combinations of four channels. The channels in this example are the four co-polar channels that are acquired, simultaneously, by the two polarimetric antennas in the F-SAR X-band across track interferometer.