Limitations of Interpreting Orbiting Satellite-Based Fire Detection for Crop Residue Burning: Has Agricultural Burning in North-West India Decreased in Recent Years?

Abstract

In the Punjab region of northwest India, large quantities of rice straw are burned after the harvest. These fires are typically extinguished within an hour, meaning that the active fires detected by orbiting satellites represent only a small fraction of the daily total. Many fires go undetected due to cloud cover, further compromising the reliability of fire detection data in terms of quantity. In this study, we aimed to demonstrate the limitations of satellite observations of straw burning. We carefully investigated the effects of cloud cover, estimated the number of fires obscured by clouds, and explored potential fires occurring outside the satellite's observation time. The analysis involved FDC data from MODIS and VIIRS on multiple orbiting satellites, as well as aerosol data from MODIS and the INSAT-3D geostationary satellite over India. Our findings indicate that the rapid decrease in FDC after 2022 cannot be attributed to cloud effects. However, INSAT-3D smoke data shows elevated values several hours after the satellite's orbital pass at 13:30 LT, suggesting that burning occurs more frequently at other than the time of the orbit passage. This interpretation, which posits that fires occurring outside the 13:30 observation window increased, is supported by interviews with local farmers and in-situ measurements. These findings are expected to help policymakers better interpret the year-to-year variation in the fire detected counts observed by polar orbiting satellites to track the effectiveness of straw burning mitigation policies.

Keywords: satellite observation, MODIS, VIIRS, INSAT-3D, fire detection, crop residue burning, north-west India