# Sea Ice Detection Based on Differential Delay-Doppler Maps from UK TechDemoSat-1
## 3 Experimental Results
### Overall Experimental Results  
As introduced in Section 3.1, a number of datasets containing a large number of DDMs spanning over twelve months (March 2015, June 2015, October 2015, January 2016 and March 2016) were employed in this section to validate the proposed sea ice detection approach. Only DDMs collected over sea ice and water field are used and DDMs over land are excluded based on the position of specular point and geographic information. Moreover, datasets collected over sea water far from Arctic center region are also excluded. In order to assess the performance of the proposed methods, another two observables (power summation of normalized DDM (PS-N) [30], pixel number of normalized DDM (PN-N) [31]) and a matcher filter (MF) approach proposed by [PERSON] et al. [42] were also used to detect sea ice. Thresholds for best detection results are used for each methods and the probability of false detection of the four methods are presented in Table 2. The sea ice edge data provided by OSI SAF are used as the ground-truth data to examine the detection results. The probability of false detection results for five methods are illustrated in Figure 12. The PS-D and PN-D methods achieve similar performance with a detection probability of 99.72% and 99.69%, respectively, while the detection probabilities of the PS-N, PN-N and MF methods are 96.38%, 96.45% and 98.16%, respectively. Compared to the proposed method PS-D and PN-D, the computation complexity of MF is about 10% lower than that of PS-D and PN-D, but the detection probability of MF is about 1.5% less than that of PS-D and PN-D. The results retrieved by MF show about 97.9% agreement with those obtained by PS-D and PN-D. Moreover, the performance of MF presented in this paper shows good agreement with that presented in [42]. It is useful and interesting to illustrate sea ice detection results directly on a geographical map. Figure 13 shows the sea ice detection results based on the PS-D method using data collected over six periods (24 March 2015, 4 June 2015, 23 August 2015, 26 October 2015, 21 January 2016 and 26 March 2016). \begin{table}
\begin{tabular}{l l l l l l l l} \hline \hline
**Date of Dataset** & **Number of Dataset** & **Number of Tested DDM** & **PS-D** & **PN-D** & **PS-N** & **PN-N** & **MF** \\ \hline
24 March 2015 & 22 & 2815 & 0.28 & 0.36 & 3.20 & 3.48 & 1.88 \\
4 June 2015 & 25 & 2906 & 0.34 & 0.41 & 3.99 & 3.92 & 1.72 \\
23 August 2015 & 20 & 2668 & 0.22 & 0.30 & 3.67 & 3.37 & 1.95 \\
26 October 2015 & 22 & 3411 & 0.29 & 0.23 & 3.28 & 3.34 & 1.91 \\
21 January 2016 & 21 & 2764 & 0.22 & 0.29 & 4.12 & 3.98 & 1.77 \\
26 March 2016 & 20 & 2782 & 0.29 & 0.29 & 3.52 & 3.24 & 1.83 \\ \hline Total & 130 & 17346 & 0.28 & 0.31 & 3.62 & 3.55 & 1.84 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Probability of false detection for four observables using GNSS-R DDM. Figure 12: Sea ice detection probability of four different detection methods. PS-D (blue bar) and PN-D (cyan bar) based methods show better performance than PS-N (yellow bar), PN-N (magenta bar) and MF (red bar) based approaches. Figure 13: Sea ice detection results based on PS-D using differential and normalized DDM observables in six different days: (**a**) 24 March 2015, (**b**) 4 June 2015, (**c**) 23 August 2015, (**d**) 26 October 2015, (**e**) 21 January 2016, (**f**) 26 March 2016. Lines in green and red represent detected sea ice and water respectively. Three areas marked with blue rectangles are defined as A, B and C respectively. The area marked with magenta rectangle is regarded as D. The white and gray area depicts the ground-truth sea ice coverage (sea ice edge product of the EUMETSAT Ocean and Sea Ice Satellite Application Facility, OSI SAF, www.osi-saf.org). There was a significant decline in the coverage of sea ice over Arctic region from March to August 2015 due to the increase of temperature. On the other hand, as the temperature decreased from August 2015 to March 2016, the coverage of sea ice increased up to almost the same coverage of March 2015.