India, Nov. 11 -- The most widely quoted count of farm fires in Punjab and Haryana is taken by Nasa satellites that pass overhead. For years, the method was reliable: the MODIS and VIIRS instruments on Nasa's satellites can pick out a fire on a patch of ground as small as 1 km and 375 metres across, respectively. Since 2022, that has changed. Several analyses have established that the drop in detections, from 84,240 fires in the 2021 season to 4,824 in 2025, is largely because farm fires now happen after the Nasa satellites have passed.

An HT analysis of fire detections by INSAT-3DS, India's own weather satellite, now shows how much of this season's Diwali surge that count missed. By HT's estimate, the satellite's daily fire count in Pun...