Near real-time detection of winter cover crop termination using harmonized Landsat and Sentinel-2 (HLS) to support ecosystem assessment

Authors: Gao, Feng; Jennewein, Jyoti; Hively, Wells - Dean; SOROKA, ALEXANDER - Us Geological Survey (USGS); THIEME, ALISON - Collaborator; BRADLEY, DAWN - Maryland Department Of Agriculture; KEPPLER, JASON - Maryland Department Of Agriculture; Mirsky, Steven; Akumaga, Uvirkaa

Submitted to: Science of Remote Sensing
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2022
Publication Date: 12/27/2022
Citation: Gao, F.N., Jennewein, J.S., Hively, W.D., Soroka, A., Thieme, A., Bradley, D., Keppler, J., Mirsky, S.B., Akumaga, U. 2022. Near real-time detection of winter cover crop termination using harmonized Landsat and Sentinel-2 (HLS) to support ecosystem assessment. Science of Remote Sensing. 7. Article 100073. https://doi.org/10.1016/j.srs.2022.100073.
DOI: https://doi.org/10.1016/j.srs.2022.100073

Interpretive Summary: Cover crops are planted to reduce soil erosion, increase soil fertility, and improve watershed management. The cost-share program has been created to encourage the use of cover crops to achieve conservation objectives. This program required winter cover crops to be planted and terminated within a specified time window. Usually, program participants report cover crop termination dates for each enrolled field, and conservation district staff confirm the reported termination with field visits within two weeks of termination. This verification process is labor-intensive and time-consuming. Remote sensing imagery provides time-series information for detecting cover crop terminations on a timely basis. The results show that the WIST-estimated remote sensing termination dates agreed with roadside surveys and grower-reported termination dates from the Maryland Department of Agriculture database for the 2020-2021 cover crop season. Our approach offers quick and valuable support for the cover crop program and saves staff field visit time.

Technical Abstract: Cover crops are planted to reduce soil erosion, increase soil fertility, and improve watershed management. In the Delmarva Peninsula of the eastern U.S., winter cover crops are essential for reducing nutrient and sediment losses from farmland. Cost-share programs have been created to incentivize cover crops to achieve conservation objectives. This program required that cover crops be planted and terminated within a specified time window. Usually, farmers report cover crop termination dates for each enrolled field (~28,000 per year), and conservation district staff confirm the report with field visits within two weeks of termination. This verification process is labor-intensive and time-consuming and became restricted in 2020-2021 due to the COVID-19 pandemic. This study used Harmonized Landsat and Sentinel-2 (HLS, version 2.0) time-series data over the Delmarva Peninsula and the within-season termination (WIST) algorithm to detect cover crop termination dates. The estimated remote sensing termination dates were compared to roadside surveys and to farmer-reported termination dates from the Maryland Department of Agriculture database for the 2020-2021 cover crop season. The results show that the WIST algorithm using HLS detected 94% of terminations for the enrolled fields (n = 28,190). Among the detected terminations, about 49%, 72%, 84%, and 90% of remote sensing detected termination dates were within one, two, three, and four weeks of farmer-reported dates, respectively. A real-time simulation showed that the termination dates could be detected one week after termination operation using routinely available HLS data, but termination dates detected after mid-May are more reliable than those from early spring when NDVI was low. We conclude that HLS imagery and the WIST algorithm provide a fast and consistent approach for generating near-real-time cover crop termination maps over large areas, which can be used to support cost-share program verification.