# Sea Ice Detection Based on Differential Delay-Doppler Maps from UK TechDemoSat-1
## 3 Experimental Results
### Case Study  
In order to illustrate the proposed sea ice detection methods, a dataset collected over sea ice and water field is selected to depict the detailed process of distinguishing between sea ice and water. Some basic information about tested dataset is shown in Table 1 and the specular points (SP) ground-track is shown in Figure 7.  
The sea ice detection scheme is applied to 131 GNSS-R DDMs and hence 130 dDDMs. For illustration purpose, 30 dDDMs (dDDM 45 to dDDM 74) are displayed in Figure 8. \begin{table}
\begin{tabular}{c|c} \hline
**Start time** & 17:29:01 26 October 2015 \\
**End time** & 17:31:11 26 October 2015 \\
**Start point** & \(13^{\circ}58^{\prime}48.05^{\prime\prime}\) E \(77^{\circ}09^{\prime}55.70^{\prime\prime}\) N \\
**End point** & \(19^{\circ}24^{\prime}48.51^{\prime\prime}\) W \(78^{\circ}10^{\prime}31.35^{\prime\prime}\) N \\
**No. Of DDM** & 131 \\
**Ground-track length** & 793 km \\ \hline \end{tabular}
\end{table} 
Table 1: Information for the tested dataset. Figure 7: GNSS-R Specular Points (SP) ground-track (green and red line) of TDS-1 signal related to the tested dataset collected over Greenland Sea on 26 October 2015 at 17:29 UTC to 17:31 UTC. The track goes from the East to the West. dDDMs corresponding to SP ground-track in red line are presented in Figure 8. The location of DDM 45 (\(3^{\circ}23^{\prime}35.44^{\prime\prime}\) E, \(77^{\circ}57^{\prime}5.44^{\prime\prime}\) N) and DDM 75 (\(4^{\circ}26^{\prime}20.72^{\prime\prime}\) W, \(78^{\circ}14^{\prime}11.77^{\prime\prime}\) N) are marked with a blue line and purple line, respectively. The three rows of dDDMs presented in Figure 8 depict three different transition cases, respectively. However, in order to analyze a large amount of data automatically by software, PS-D and PN-D methods described in Section 2.4 are employed to obtained dDDMs. Results of PS-D and PN-D under five different power value thresholds are shown in Figure 9a,b, respectively. Both PS and PN of dDDMs show an abrupt change at dDDM 62 from variation to almost a constant value, so this location provides the basis of determining the boundary between water and sea ice. According to the proposed approach, the first 61 dDDMs are identified as water-water transition, while the 62 th dDDM is determined as water-ice transition and the next 67 dDDMs are determined as ice-ice transition. Therefore, the first 62 DDMs were collected over sea water field, while the remaining 69 DDMs were collected over sea ice field. There is a large variability in PS and PN from dDDM 1 to dDDM 37, then a relatively stable variability from dDDM 38 to dDDM 58, and again large change from dDDM 59 to dDDM 61. This phenomenon may be associated with the sea wave height (WH) over the studied area. The significant wave height data (shown in Figure 10) of 26 October 2015 was retrieved from the European Centre for  
Figure 8: Examples of processed dDDMs (dDDM 45 to dDDM 74) obtained from DDM 45 to DDM 75 of water-water transition, water-ice transition and ice-ice transition. Figure 9: (**a**) PS-D method results and (**b**) PN-D method results for five different thresholds (\(DDM_{T}\) = 0.36, \(DDM_{T}\) = 0.38, \(DDM_{T}\) = 0.40, \(DDM_{T}\) = 0.42 and \(DDM_{T}\) = 0.44). Medium-Range Weather Forecasts (ECMWF, available online: [[https://www.ecmwf.int](https://www.ecmwf.int)]([https://www.ecmwf.int](https://www.ecmwf.int))) for validating our results. The SP ground-track of 57 DDMs (DDM 1 to DDM 57) is marked in the WH map with a red line, while there is no valid WH data from DDM 58 to DDM 131. The WH of these 57 SP was retrieved through a 2-D linear interpolation according to the SP locations. The values of WH were scaled down as we only concentrate on the variability, which may explain the variability of dDDMs.