# A Review of Irrigation Information Retrievals from Space and Their Utility for Users
## 6 Synthesis and Future Perspectives
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Irrigation Mapping** & **Irrigation Quantity** & **Irrigation Timing** \\ \hline Products at & & Up to 10–100 m with & & With SAR and \\ local/field scale in & With SAR and & SAR data and 30 m & & thermal and optical \\ support of water & thermal data (up to & with visible and & & data depending on \\ management and & 30 m with Landsat and S2-S3, 10–100 m & Accuracy limited by & & the location. Limited \\ agriculture (approx. \textless{}100 m) & with SAR SI data) & the temporal & & to temporal \\  & & with SAR & resolution of the & \\  & & sensors and noise. & & a day. \\ \hline Products at & With SAR (e.g., S1) & With SAR (e.g., S1) & & Daily with thermal \\ Products at & and thermal data & & and thermal data & \\ national/basin scale & (e.g., MODIS, S2–S3) & & & sub-weekly with SAR \\ in support of water & and their & their combination. & & location and other \\ management & combination. Suitable & Accuracy depends & & visible and \\ (500 m–1 km) & for relatively large & upon satellite revisit & & near-infrared \\  & agricultural areas & time and noise. Cloud & & observations such as \\  & & cover can be an issue. & & S2 and S3 depending \\  & & & on the cloud cover. \\ \hline  & With active and & & & \\  & passive coarse-scale & & & \\  & microwave & & & \\  & observations limited & & observations, limited & With coarse-scale \\  & to large and intensive & & & microwave \\ Products at & irrigated areas much & & & observations, \\ regional/global level & larger than the & & & potentially daily if the \\ (\textgreater{}10 km) & product spatial & & resolution. Noise can & signal is sufficiently \\  & resolution (large and & be an issue. & & strong with respect to \\  & intensively irrigated & & With any visible and & \\  & areas of India, USA, & near-infrared sensor. & & thermal data. \\  & any optical, & & Gravimetric & \\  & near-infrared sensor & & & \\  & & & (GRACE). \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Potential of satellite-based remote sensing observations to detect irrigation information from space as a function of the scale of application. planned to be launched in 2022 and 2028, and that should provide improved soil moisture estimates over vegetated areas and from a deeper soil layer compared to C-Band (S1) products at higher spatial resolutions. In addition, higher temporal resolution can be achieved with a constellation of low-cost CubeSats with a GNSS reflectometer onboard. Other missions such as TRISHNA and ESA LSTM missions already mentioned above will provide enhanced high spatial-temporal resolution measurements of land surface temperature, which would be helpful to map small irrigated fields. These missions, among others already planned, should cover the majority of the users' requirements at scales identified in Table 2, and that should bring important progress to the land and water management with significant benefits for food and water security. The following is available online at [[https://www.mdpi.com/article/10.3390/rs13204112/s1](https://www.mdpi.com/article/10.3390/rs13204112/s1)]([https://www.mdpi.com/article/10.3390/rs13204112/s1](https://www.mdpi.com/article/10.3390/rs13204112/s1)). Conceptualization, C.M., S.M., J.D., P.Q.-S. and A.G.; methodology, C.M., S.M., J.D., P.Q.-S., A.G.; writing--original draft preparation, C.M., S.M., J.D., A.G, G.J.M.D.L., P.Q.-S., M.G., L.J., M.L.P., M.V., M.Z., L.Z. ; writing--review and editing, all authors. All authors have read and agreed to the published version of the manuscript. * _[PERSON] et al. (2020)_ [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] Climate change impacts on water resources in the Mediterranean. _Reg. Environ. Chang._**2020**, _20_, 83. [CrossRef]
* _[PERSON] et al. (2020)_ [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] Potential for sustainable irrigation expansion in a 3 \({}^{\circ}\)C warmer climate. _Proc. Natl. Acad. Sci. USA_**2020**, _117_, 29526-29534.