## 2 Requirements Specifications and Measurements Gaps
### Wind Speed
\begin{table}
\begin{tabular}{l l l} \hline
**Technology Type** & **Measurements** & **Instrument Limitations** \\ \hline \multirow{4}{*}{GNSS-R} & Sea ice thickness \({}^{a}\) & Accuracy (\(\sim\)20 cm) [12; 20] \\ \cline{2-3}  & Dominant wave direction \({}^{b}\) & Coarse spatial resolution (\(\sim\)25 km) [21] \\ \cline{2-3}  & Wind speed over the sea surface (horizontal) \({}^{a}\) & Coarse spatial resolution (\(\sim\)25 km) \\  & Accuracy (2 m /s) [12] \\ \cline{2-3}  & Significant wave height \({}^{b}\) & \\  & Sea ice cover \({}^{b}\) & No specific limitation [22] \\  & ocean surface currents \({}^{b}\) & \\ \hline Microwave sounder (50-60 GHz) & Atmospheric pressure (over sea surface) \({}^{c}\) & Coarse spatial resolution (20 km, at 400 km altitude) [23] \\ \hline \multirow{4}{*}{Microwave radiometer (X-, K-, Ka-, W-bands)} & Wind speed over sea surface (horizontal) \({}^{b}\) & Coarse spatial resolution (\(\sim\)25 km) [24] \\  & Sea ice cover \({}^{b}\) & Accuracy: (1.5-m/s ocean wind speed) [25] \\  & Sea ice drift \({}^{a}\) & (0.5 K for 871) [25] \\  & Sea surface temperature \({}^{a}\) & (from 10\%-20\%\) for sea ice data) [26] \\ \hline \multirow{4}{*}{L-band microwave radiometer} & Sea ice cover \({}^{b}\) & Coarse spatial resolution \\ \cline{2-3}  & Soil moisture at the surface \({}^{c}\) & Coarse spatial resolution \\ \cline{2-3}  & Sea ice thickness \({}^{a}\) & Accuracy [27; 28] \\ \hline AIS decoder & Monitoring system: vessels \({}^{c}\) & No specific limitation [5] \\ \hline Cloud radar (oxygen band) & Atmospheric pressure (over sea surface) \({}^{c}\) & Narrow swath (2 km) [29; 30] \\ \hline \multirow{4}{*}{Radar scatterometer} & Wind speed over sea surface (horizontal) \({}^{c}\) & Accuracy: \\  & Sea ice type \({}^{a}\) & Wind speed (\(<\)2 m/s) [31] \\ \hline \multirow{4}{*}{Radar altimeter (SAR)} & Ocean surface currents\({}^{3}\) & \\  & Significant wave height \({}^{b}\) & \\  & Dominant wave direction \({}^{b}\) & Narrow coverage (nadir-pointing) \\  & Sea ice type \({}^{b}\) & Long-term analysis and narrow coverage \\  & Sea ice cover \({}^{b}\) & \\  & Wind speed over sea surface (horizontal) \({}^{a}\) & \\ \hline \multirow{4}{*}{LiDAR} & Ocean surface currents \({}^{c}\) & \\  & Iceberg tracking \({}^{c}\) & \\  & Sea ice drift \({}^{c}\) & \\  & Sea ice extent \({}^{c}\) & \\  & Sea ice type \({}^{a}\) & Narrow coverage (\(<\)600 km) \\  & Sea ice cover \({}^{c}\) & Long-term analysis and narrow coverage [32] \\  & Dominant wave direction \({}^{b}\) & Long-term analysis and narrow coverage [32] \\  & Dominant wave period \({}^{b}\) & \\  & Significant wave height \({}^{b}\) & \\  & Sea ice thickness \({}^{a}\) & \\  & Wind speed over sea surface \({}^{a}\) & \\ \hline \multirow{4}{*}{LiDAR} & Sea ice thickness \({}^{b}\) & Long-term analyses, narrow coverage, \\  & Cloud sensitive & \\ \hline \multirow{4}{*}{Multispectral radiometer VIS/NIR/TIR} & Ocean chlorophyll concentration \({}^{c}\) & \\  & (\(\lambda\) center: 42.5, 490, 510, 560 nm) & \\  & Ocean imagery and water leaving radiance \({}^{c}\) & \\  & (\(\lambda\) Centre: 485, 560, 660, 2100 nm) & \\ \cline{1-1}  & Color Dissolved Organic Matter (CDM) \({}^{c}\) & Cloud sensitive, \\ \cline{1-1}  & (\(\lambda\) center: 42.5, 490, 510, 560, 665 nm) & Daylight only \\ \cline{1-1}  & Sea surface temperature \({}^{c}\) & \\ \cline{1-1}  & (\(\lambda\) center: 37.5, 495, 855, 11, 12 nm) & \\ \cline{1-1}  & Sea ice cover \({}^{a}\) & \\ \cline{1-1}  & (\(\lambda\) center: 640, 1610 nm) & \\ \hline \multirow{4}{*}{Hyperspectral radiometer (VIS/NIR)} & CDOM \({}^{c}\) & Cloud sensitive, \\ \cline{1-1}  & Sea ice cover \({}^{b}\) & Daylight only \\ \hline \multirow{4}{*}{Spectrometer/sounder IR} & Sea ice cover \({}^{c}\) & Cloud sensitive, \\ \cline{1-1}  & Sea surface temperature \({}^{c}\) & Daylight only \\ \hline \end{tabular}
\end{table} 
Table 3: Mapping of the potential technologies to cover measurements with gaps. The technology limitations from the perspective of the measurement requirements are presented.