A method to retrieve subpixel fire temperature and fire area using MODIS data

Abstract

Methods for retrieving subpixel fire temperature and fire area have been developed over several years, but the retrieval accuracies of these methods require further improvement. In this study, a channel of the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor centred at 2.1 μm and associated with the MODIS 4.0 2.1 μm channel is used to retrieve the temperature and area of fires. To test the feasibility of using the 2.1 μm channel for retrieval, the fire contribution ratios of MODIS 2.1, 4.0 and 11.0 μm channels are first examined using simulated surface radiance. Considering the difficulties in obtaining real-time validation data and in evaluating the retrieval accuracies, simulated MODIS data are used for this study. A modified method, which combines MODIS 2.1 and 4.0 μm channels, is introduced and described in detail. Compared with the traditional method, which utilizes a combination of 4.0 and 11.0 μm channels (Dozier 1981), the results show that the 2.1 μm channel is more sensitive to active fires and the large area of fires than the 11.0 μm channel, but is less sensitive to smouldering fires and small fires. The modified method that we propose has better performance and higher accuracy in active fires (temperature ≥ 800 K) and in large fires (area ≥ 0.5%). However, the traditional method is more accurate for smouldering fires and small fires. Finally, a sensitivity analysis is performed to estimate the uncertainty in assessing fire temperature and area. Experimental results indicate that under realistic conditions (fire temperatures of approximately 1000 K and a fire fractional area greater than 0.005), the retrieval errors for fire temperature and fire area are ±35 K and 20%, respectively.