**6. Conclusions**

Based on multisource remote sensing data, including SMAP, MODIS, and an irrigation map, the 5-point moving average method was used to detect irrigation signals in southern Hebei. Then, irrigation record data were used to validate the accuracy of the irrigation signal detection results. The accuracies of the four WW samples used for validation are 50.00%, 100.00%, 75.00%, and 83.33%, and the overall accuracy is 77.08%. The consistency analysis of 55 WW growth samples showed that the growth consistency of WW reached 82.72% in two large-scale surface water irrigation areas. Based on a consistency analysis, the downscaling method can be used to downscale the WW irrigation signal detected by the SMAP data. The proposed irrigation signal detection and downscaling method are more suitable for the detection of large-scale surface water irrigation signals. Limited by the spatial resolution of SMAP data and continuous in situ measured SM data, small-scale groundwater irrigation signal detection is difficult to establish. In future research, small-scale groundwater irrigation signal detection will be further studied.

**Author Contributions:** Z.H. and H.Z. designed the experiment; C.Z. and Y.J. provided revisions to the paper; H.W. and H.Z. provided financial support; and Z.H. wrote the manuscript.

**Funding:** National Key R&D Program of China (Grant No. 2018YFC0407705), Fundamental Research Funds for the China Institute of Water Resources and Hydropower Research (WR0145B012017), and Fundamental Research Funds for the China Institute of Water Resources and Hydropower Research (WR0145B272016).

**Conflicts of Interest:** The authors declare no conflict of interest.
