Approaches for synergistically exploiting VIIRS I- and M-Band data in regional active fire detection and FRP assessment: A demonstration with respect to agricultural residue burning in Eastern China

Abstract

We demonstrate a new active fire (AF) detection and characterisation approach for use with the VIIRS spaceborne sensor. This includes for the first-time joint exploitation of both 375m I-Band and 750m M-Band data to provide both AF detections and FRP (fire radiative power) retrievals over the full range of fire and FRP magnitudes. We demonstrate the value of our VIIRS-IM ‘synergy’ product in an area of eastern China dominated by numerous small agricultural residue burns, which contribute significantly to regional air quality problems but which are often difficult to identify via standard (e.g. MODIS 500m resolution) burned area mapping. We show that the highly ‘fire sensitive’ VIIRS I-Band data enables detection of the ‘small’ active fires (FRP≤1MW), but this sensitivity can lead to false alarms, often associated with manmade structures. We help avoid these via use of 30m resolution global land cover data and an OpenStreetMap mask. Comparisons to near-simultaneous Aqua-MODIS AF detections, and the existing VIIRS I-Band AF global product, highlight our VIIRS algorithm's ability to more reliably detect the lowest FRP pixels, associated with the type of agricultural burning dominating eastern China. Our algorithm delivers typically 5 to 10× more AF pixels than does simultaneous-collected MODIS AF data (notwithstanding differences in spatial resolution), and importantly with a AF detection sensitivity that remains much more constant across the swath due to VIIRS' unique pixel aggregation scheme. The VIIRS I4-Band saturates over higher FRP fires, but by combining use of I- and M-Band data our algorithm generates reliable FRP records for all fires regardless of FRP magnitude. Using the VIIRS-IM methodology we find regionally summed FRP's up to 4× higher than are recorded by MODIS over the same fire season, highlighting the significance of the formally undetected low FRP active fires and indicating that current MODIS FRP-based emissions inventories for areas dominated by agricultural burning may be underestimating in a similar way to burned-area based approaches. FRP generation from VIIRS that takes into account both low- and high-FRP fires via use of both the I- and M-Band data should therefore enable significant improvements in global fire emissions estimation, particularly for regions where smaller types of fire are especially dominant.