National-scale soybean mapping and area estimation in the United States using medium resolution satellite imagery and field survey

• Published in: Remote sensing of environment Vol. 190; pp. 383 - 395
• Main Authors: Song, Xiao-Peng, Potapov, Peter V., Krylov, Alexander, King, LeeAnn, Di Bella, Carlos M., Hudson, Amy, Khan, Ahmad, Adusei, Bernard, Stehman, Stephen V., Hansen, Matthew C.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.03.2017
• Subjects: Agriculture; Classification; Cropland; Decision tree; Image time-series; Landsat; Remote sensing; Sample; Cropland; Image time-series; Sample; Landsat; Classification; Agriculture; Decision tree; Remote sensing
• DOI: 10.1016/j.rse.2017.01.008
• ISSN: 0034-4257

Reliable and timely information on agricultural production is essential for ensuring world food security. Freely available medium-resolution satellite data (e.g. Landsat, Sentinel) offer the possibility of improved global agriculture monitoring. Here we develop and test a method for estimating in-season crop acreage using a probability sample of field visits and producing wall-to-wall crop type maps at national scales. The method is illustrated for soybean cultivated area in the US for 2015. A stratified, two-stage cluster sampling design was used to collect field data to estimate national soybean area. The field-based estimate employed historical soybean extent maps from the U.S. Department of Agriculture (USDA) Cropland Data Layer to delineate and stratify U.S. soybean growing regions. The estimated 2015 U.S. soybean cultivated area based on the field sample was 341,000km2 with a standard error of 23,000km2. This result is 1.0% lower than USDA's 2015 June survey estimate and 1.9% higher than USDA's 2016 January estimate. Our area estimate was derived in early September, about 2months ahead of harvest. To map soybean cover, the Landsat image archive for the year 2015 growing season was processed using an active learning approach. Overall accuracy of the soybean map was 84%. The field-based sample estimated area was then used to calibrate the map such that the soybean acreage of the map derived through pixel counting matched the sample-based area estimate. The strength of the sample-based area estimation lies in the stratified design that takes advantage of the spatially explicit cropland layers to construct the strata. The success of the mapping was built upon an automated system which transforms Landsat images into standardized time-series metrics. The developed method produces reliable and timely information on soybean area in a cost-effective way and could be applied to other regions and potentially other crops in an operational mode. •A new method for national-scale crop-specific area estimation and wall-to-wall mapping.•Field-based stratified sample soybean area estimate 1–2% different from USDA estimates.•Soybean map calibrated to match sample estimated area had 84% overall accuracy.•Methodology suitable for operational use for other regions and crops.