# Independent System Calibration of Sentinel-1B
## 6 In-Flight Antenna Model Verification
### Verification in Elevation  
The acquisition of StripMap, IW and EW data takes used for the in-flight verification of the antenna elevation pattern was performed over different areas within the Amazon calibration test site between late June and late August 2016. The in-flight verification of the antenna elevation patterns is also based on the calculation of range gamma profiles as used for the verification of the elevation pointing described in Section 5.2, now using nominal imaging acquisitions. Moreover, the same restrictions apply with respect to the homogeneity of the observed scenes used for analysis. However, in contrast to the notch measurements considered in Section 5.2, starting from a processed SLC product, non-homogeneous areas of the rainforest, such as rivers and clear cuts, can now be masked by a specific masking algorithm. Next, the antenna pattern compensation which has been applied by the SAR processor is reversed (i.e., the antenna reference pattern annotated in the product is subtracted from the data). Then, the azimuth-averaged gamma profile is calculated for each scene based on the measurement data and the result is compared to the reference calculated by the Sentinel-1 antenna model. This section is concentrated on the results for the IW and EW TOPS modes and discusses the verification of (i) the antenna pattern shape for each sub-swath and (ii) the beam-to-beam gain offsets, i.e., the relative gain variation (in the maximum of the beam) from beam to beam. Having subtracted the predicted antenna patterns from the data, ideally one would expect a flat pattern shape over elevation for each (sub-)swath. In addition, beam-to-beam offsets for IW and EW are expected to be largely removed, if predicted correctly by the antenna model. In contrast, monotonous slopes in the difference between data and model can be observed, which indicates a potential antenna mispointing in roll. Hyperbolically (parabolically) shaped differences of a hyperbolically shaped beam indicate an under- (over-) estimation of the width of the measured hyperbola. The analysis starts with the IW mode, which is the most commonly used data acquisition mode for Sentinel-1A/B. Absolute gain values are shown in Figure 19 for both co- and cross-polarized channels, comparing the mean measured values (solid lines) with the corresponding antenna model prediction (dashed lines). As expected from rainforest data, the gain values for H-Pol are on average lower than for V-Pol. Figure 20 shows the corresponding differences between data and the model, normalized to the mean of IW3. As a result, beam-to-beam offsets of up to 0.2 dB for VV data (most notably IW1/IW2) and up to 0.5 dB in VH data (IW1/IW2) have been identified. For DH polarizations, the observed IW-gamma profile is largely flat, varying only 0.06 dB (1\(\sigma\)) over elevation with negligible beam-to-beam offsets. Figures 21 and 22 show the corresponding analysis for all available EW data take slices. Since these data takes have been acquired before the star tracker realignment, an antenna mispointing as derived from the first set of elevation notch measurements has been corrected for before calculating the measured-model difference as shown in Figure 22. Especially for EW1, the antenna model cannot represent the measured beam shape very well which results in a clear variation in the differences over elevation. For EW2-5 (DH), there are no significant gain slopes visible within each sub-swath. However, the actual observed beam-to-beam offsets at the edge of the subswath