# On-Board Wind Scatterometry
## 4 Experiment and Results
### Results and Analysis
Specific effects on wind products are provided later in this section. Figures 5-7 were derived from VV (transmitted and received in vertical polarization) observations. HH (transmitted and received in horizontal polarization) observations shared similar features and are not listed. For the wind inversion procedure, both polarized observations were applied with a resampled GMF LUT in both polarizations. The wind inversion for CFOSCAT is based on the National Aeronautics and Space Administration Scatterometer GMF version 4 (NSCAT-4) [8]. The results are illustrated in Figures 8-11. Figure 8 shows the wind speed from the ground L2 products in (a), and the on-board wind inversion results were obtained in procedures described in Section 3. For (b) of Figure 8, resampled GMF LUTs in on-board inversion procedures were used for generating wind speeds. The horizontal axis is longitude, and the vertical axis is latitude. The resolution of the resampled GMF was of 0.4 m/s in the wind speed dimension. The other dimensions were the same as those at full resolution, as the step length in the incidence angles is 0.1\({}^{\circ}\), in the wind directions is 0.5\({}^{\circ}\), and 0.1 m/s in the wind speeds. The color in Figure 8 indicates wind speed amplitude in m/s. It can be observed that the wind speeds were of similar features for the three products. A randomly selected region from Figure 8 is shown in Figure 9. The horizontal and vertical axes, color bar, and products corresponding to (a), (b), and (c) are the same as those of Figure 4:0 The black arrows in Figure 9 indicate wind directions. Figure 4:1 Wind speed of ground the L2 product (**a**) and that of on-board procedure in a full resolution geophysical modelling function (GMF) LUT (**b**) and a desampled GMF LUT (**c**). Color indicates wind speed in m/s. Figure 4:2 Wind speed of the ground L2 product (**a**) and that of the on-board procedure in a full resolution GMF LUT (**b**) and a desampled GMF LUT (**c**). Color indicates wind speed in m/s. Figure 10 shows correlation and error bars between the ground L2 product wind speed and the on-board wind speeds, Figure 11 demonstrates the mean differences and error bars of the ground L2 product wind direction and on-board wind directions. Statistics came from the results of the whole dataset, as in Figure 4:3 Ground winds were used as references. The statistics of wind speed were obtained in a bin size of 2 m/s. Mean differences and stdev. in wind direction were calculated for different wind speed bins via the same procedure that was used for wind speed error analysis. In Figure 10, the horizontal axis represents the wind speeds from the ground L2 products, and the vertical axis represents the on-board wind speeds derived from a full-resolution GMF LUT (a) and that from a resampled GMF LUT (b). The mean absolute average differences of (a) and (b) are 0.14 and 0.17 m/s, respectively. The lowest and highest wind speed values were obtained from the 0 m/s and 28 m/s in wind speed, and these extremally low and high speeds are of higher noise level in wind inversion and GMF themselves. For most wind speeds, (b) had slightly larger average differences than (a). The smallest average differences for both (a) and (b) were both at 18 m/s. The largest stdev. of (a) and (b) also appeared at 24 m/s when mean differences were the largest at 0.84 and 1.55 m/s, respectively. The smallest stdev. values for (a) and (b) were all at 2 m/s as 0.55 and 0.56 m/s, respectively. It can be noted that the average differences of the ground L2 product wind direction and on-board wind directions are much smaller than the average differences of the ground L2 product wind direction. Figure 4:4 Mean differences and error bars of the ground L2 product wind direction and on-board wind directions derived from a full GMF LUT (**a**) and a desampled GMF LUT (**b**). Figure 4:5 Correlation and error bars between the ground L2 product wind speed and the on-board wind speeds derived from a full GMF LUT (**a**) and a desampled GMF LUT (**b**).