Abstract：In order to detect the scope and intensity of sand and dust storm quantificationally by using MODIS data，the spectrum characteristics
of sand and dust storm，cloud and snow were analyzed in detail using several MODIS data，bands that can distinguish sand and dust from cloud and surface were detected，two indices for determining the scope and intensity of sand and dust storm were found out and tested in several cases. Our study shows：1）The spectrum characteristic of sand and dust in solar wavelengths is that the reflectance increases with the wavelength，this is similar to soil，and the reflectance of large size dusts increases faster than small size dusts. 2）Small size dusts show typical characteristic of aerosol，which are sensitive to blue band of 0. 46 μm and insensitive to short- wave infrared bands of 1. 6 and 2. 1 μm. 3）Large size dusts do not have aerosol characteristic，they are insensitive to blue band and sensitive to short - wave infrared bands. 4）Dusts are sensitive to bands of 3. 7 μm and 8. 5 μm ，and the difference of the two bands can be used to identify sands and dusts and reflect the intensity to certain extent. 5）The two indices are very effective to monitor sands and dusts，and the method is simple and easy for operational use.

Using the EOS/MODIS data of six forest and grassland fires which occurred during 2002,12~2003,5 in Gansu province,
the relation of the brightness temperature in channel 20 and 31 was analyzed, including fire area, fire influencing area and normal
environment, and an approximate threshold was found.The results indicate the normal environment always on condition of (T20-
T31)/T20<0.08,fire influencing area always on condition of 0.08<(T20-T31)/T20<0.093,and the fire area always on condition
of(T20-T31)/T20>0.093. By quantitatively distinguishing the“4.15”forest fire in Diebu with this method, it has proved that
the threshold has a good effect on the fire region’s identifying and fire area’s estimating. This method can be applied in the operation
for forest and grassland fire mornitoring.