Wildfires release large amount of green house gas

smoke and aerosols which strongly impact on global climate.In China

wildfire in steppe area caused greatly economic loss.Remote sensing is a powerful tool to monitor fire and estimate burn scar area.Based on GEMI（Global Environment Monitoring Index） and spectral characteristics of burn scar in short wave region

a new index GEMI-B（Global Environment Monitoring Index-Burn scar） is proposed to extract burn scar in steppe area.In order to avoid the daily disturbance of cloud

aerosol

sensor zenith and sunglint

new multi-temporal composite methods based on maximal GEMI-B are proposed in the study to composite time series MODIS data.Based on active fire（hotspot） map

an automated extraction procedure has also been developed.A case study is carried out for the wildfire occurred in May

2003 on the border area between China and Mongolia.It is suggested by the results that the GEMI-B index

compositing algorithm and automated extraction method have potential to be applied on burn scar mapping in the semi-arid or arid areas.