A Deep Learning Approach to Mapping Irrigation Using Landsat: IrrMapper U-Net

Accurate maps of irrigation are essential for understanding and managing water resources. We present a new method of mapping irrigation based on an ensemble of convolutional neural networks that use reflectance information from Landsat imagery to classify irrigated pixels. The methodology does not rely on extensive feature engineering and does not condition the classification with land-use information from existing geospatial datasets. The ensemble does not need exhaustive hyperparameter tuning, and the analysis pipeline is lightweight enough to be implemented on a personal computer. Furthermore, the proposed methodology provides an estimate of the uncertainty associated with the classification. We evaluated our methodology and the resulting irrigation maps using a highly accurate novel spatially explicit ground-truth dataset, using county-scale United States Department of Agriculture (USDA) surveys of irrigation extent, and using cadastral surveys. We demonstrate the accuracy of the method by mapping irrigation over the state of Montana from 2000 to 2019. We found that our method outperforms other methods that use satellite remote-sensing information in terms of overall accuracy (OA) and precision. We found that our method agrees better statewide with the USDA National Agricultural Statistics Survey estimates of irrigated areas compared to other methods and has far fewer errors of commission in rainfed agriculture areas. This methodology has the potential to be applied across the entire United States and for the complete Landsat record.