Challenges and benefits of quantifying irrigation through the assimilation of Sentinel-1 backscatter observations into Noah-MP

[摘要] In recent years, the amount of water used foragricultural purposes has been rising due to an increase in food demand.However, anthropogenic water usage, such as for irrigation, is still not orpoorly parameterized in regional- and larger-scale land surface models (LSMs). By contrast, satellite observations are directly affected by, and hence potentially able to detect, irrigation as they sense the entire integrated soil–vegetation system. By integrating satellite observations and fine-scalemodelling it could thus be possible to improve estimation of irrigationamounts at the desired spatial–temporal scale. In this study we tested the potential information offered by Sentinel-1backscatter observations to improve irrigation estimates, in the frameworkof a data assimilation (DA) system composed of the Noah-MP LSM, equippedwith a sprinkler irrigation scheme, and a backscatter operator representedby a water cloud model (WCM), as part of the NASA Land Information System(LIS). The calibrated WCM was used as an observation operator in the DAsystem to map model surface soil moisture and leaf area index (LAI) intobackscatter predictions and, conversely, map observation-minus-forecastbackscatter residuals back to updates in soil moisture and LAI through anensemble Kalman filter (EnKF). The benefits of Sentinel-1 backscatter observations in two differentpolarizations (VV and VH) were tested in two separate DA experiments,performed over two irrigated sites, the first one located in the Po Valley(Italy) and the second one located in northern Germany. The results confirmthat VV backscatter has a stronger link with soil moisture than VHbackscatter, whereas VH backscatter observations introduce larger updates in the vegetation state variables. The backscatter DA introduced bothimprovements and degradations in soil moisture, evapotranspiration andirrigation estimates. The spatial and temporal scale had a large impact onthe analysis, with more contradicting results obtained for the evaluation at the fine agriculture scale (i.e. field scale). Above all, this study sheds light on the limitations resulting from a poorly parameterized sprinkler irrigation scheme, which prevents improvements in the irrigation simulation due to DA and points to future developments needed to improve the system.

[学科分类] 妇产科学