# On-Board Wind Scatterometry
## 4 Experiment and Results
### Results and Analysis  
In this part, L1 products from on-board preprocessing are displayed, and then on-board wind inversion with a full resolution of the LUTs described in Section 3. When apply theseLUTs, that more time is required in the proposed on-board processing chainis illustrated. The resampling of LUTs to a half and a quarter number of samples LUTs for geo-locating and the X-factor were applied to obtain the LUTs of fewer samples. The resampled dimensions of the LUTs were latitude and antenna azimuth angles. Comparisons were made with the full and smaller sample of LUTs. Figure 5 illustrates the ground L1 product and the on-board NRCS distributions of the track of data used in the experiment. Figure 6 illustrates a randomly selected pulse from data in Figure 5. The horizontal axes of both figures are longitudes in degrees, the vertical axes are latitudes in degrees, and color indicates amplitudes of the NRCS in dB. In both figures, the (a) sections are from ground products, the (b) sections are from  
Figure 4: Wind inversion procedures of a wind vector cell (WVC) for on-board processing. on-board procedures in full resolution LUTs, and the (c) and (d) sections are from on-board products obtained in half and a-quarter sample numbered LUTs, respectively. From Figure 6, the differences in geo-locating and NRCS amplitude derivation differences are not obvious, though the (d) sections in Figures 5 and 6 appear much noisier than the (a) and (b) groups. Taking the positions of L1 ground products as references, the root-mean-square error (RMSE) of the on-board results in the (b) of Figure 5 is 0.93 m, and the half number of sampling LUT results in (c) is 2.81 m, and 4.81 m for (d). Figure 5: Ground level 1 (L1) product (**a**) and on-board normalized radar cross section (NRCS) distributions in LUTs for geolocating and X-factors in full resolution (**b**); half number resampled (**c**) and a quarter number resampled (**d**). Color indicates NRCS values in dB. Figure 6: _Cont._  
Figure 7 shows correlations with error bars for the slice NRCS of ground and on-board products. The horizontal axis represents the NRCS from the ground L1 products, and the vertical axis represents the NRCS from on-board procedures. The color represents sample number density in dB. The on-board obtained NRCS in (a) are from LUTs in the original resolution, and those in (b) and (c) are in a half and a quarter number resampled LUTs. Specific values are listed in Table 2. It can be observed that when the on-board results were with large differences from ground products, the resampled LUTs also tended to give large differences. There was a similar trend in the standard deviations (stdev.). However, when the stdev. reaches largests or smallest values, it is not not necessarily that the corresponding differences in mean also reach the largest or the smallest values. Figure 6: A randomly selected rotating circle of observations. (**a**)–(**d**) are labelled in the same order as Figure 5. Color indicates NRCS values in dB and is of the same scale of that in Figure 5.  
Figure 7: Correlation and error bars of NRCS for ground products (vertical axis) and on-board products (horizontal axis). Color indicates sample number density in dB. (**a**) illustrates results from LUTs in full resolution, and in in a half (**b**) and a quarter (**c**) number resampled LUTs. In Figure 7a, it can also be observed that the ground products and on-board NRCS had a good consistency. When on-board results were obtained in coarser LUTs, as shown in (b) and (c), more random noise was aroused. The biases of (b) and (c) to the eground products were similar to those from the on-board, full resolution LUTs. In Figure 7, due to the more random noise expressed in dB, the regions in (b) and (c) with denser samples (deeper red) have a larger slope towards the negative direction of the vertical axis in (c) than (b), while in (a), such a feature is not shown. This is consistent with the conclusion that when the coarser LUTs were used, noisier products were obtained.