## 7 Results and Discussion  
Using the methods described in the previous sections, the ALE was estimated for all SM products acquired over the Swiss test sites after 4 June 2014 (41 acquisitions, each processed to SLC and GRDF products). Since the _Torny-le-Grand_ products had two CRs visible in each image, their individual ALE values were averaged so that the values would not be statistically over-weighted in comparison with those from the _Dubendorf_ site, where only one CR per product was visible. During the time series analysis, the individual ALE values for CR pairs over _Torny-le-Grand_ were periodically compared, and observed to be generally very similar (often agreeing to \(<0.1\) samples). Since their DGPS positions were independently surveyed, a small difference in the individual ALE estimates based on the two reflectors would be expected, purely due to small differences in survey error. In fact, no such biases were observed. Instead, their differences varied randomly about zero, presumably caused by noise in the estimation of their image positions. The high inter-reflector consistency was therefore considered a confirmation of the validity of the estimates overall and justified the use of their combined (mean) ALE values. In Figure 6, the ALE is shown for three scenarios as a scatterplot for the SM SLC time series over both test sites combined. The slant range ALE is the horizontal axis; azimuth ALE is the vertical axis. For all SM mode ALE plots, the scale and axis extents are the same to facilitate easy comparison. Each green point is a mean ALE value for the CR pair in the case of _Torny-le-Grand_; each black point represents a single product over _Dubendorf_. Up-pointing symbols are from ascending-orbit acquisitions, down-pointing symbols from descending products. The mean and standard deviation of the point cloud is given for each plot in the inset box. In Figure 6a, no atmospheric PD and no bistatic residual corrections were applied. The large spread in range is caused by a variation in the path delay error from product to product, while the azimuth spread largely reflects the variations in the CR positions relative to the scene mid-range (_i.e._, the bistatic residual correction). Note that no products from SM beam S1 were available for inclusion in the analysis. The range spread would be expected to be even greater if such products were added to the mix, since the atmospheric path length difference is greatest between beams S1 and S6. Additionally, the diversity of bistatic residual values would increase. Figure 6b shows the same scatterplot, but includes the PD correction. The range standard deviation has improved six-fold, highlighting the importance of this correction. Figure 6c includes the bistatic residual correction as well, with a corresponding \(\sim\)two-fold reduction of the spread. Figure 6c represents the best geolocation result achieved during the calibration phase for S1A: it reflects the extraordinarily high ranging accuracy of the sensor, and an azimuth consistency that is very good as well, although not as consistent as the range. This may partly be due to the coarser azimuth sample spacing in comparison with the slant range sampling. For the S2 beam, the range spacing  
Figure 6: StripMap SLC ALE estimates based on precise state vectors; each point represents a single product over _Torny-le-Grand_ (green) or _Dubendorf_ (black); (**a**) no path delay or bistatic residual corrections; (**b**) path delay correction but no bistatic residual correction; (**c**) path delay and bistatic residual corrections applied. (a) no PD, no bistatic; (b) PD, no bistatic; (c) PD, bistatic. is \(\sim\)1.8 m while S6 products have a range spacing of \(\sim\)3.2 m. In all cases, the azimuth spacing is nearly constant at \(\sim\)4.1 m. This suggests that the measurement of the CR peak position could be less accurate in the azimuth dimension, as less information might be available for oversampling the raster.