An assessment of brightness temperature data quality of MSMR of IRS-P4 satellite

摘要

Frequency dependence of brightness temperature (T_B) in the range 6-21 GHz is studied as a function of surface roughness, vegetation cover and soil moisture using theoretical models. Frequency dependence of T_B is plotted from Multichannel Scanning Microwave Radiometer (MSMR) T_B data of Indian Remote Sensing Satellite (P-series) IRS-P4 for different target types such as ocean, desert, forest, agricultural and snow regions. MSMR responds to the variations of the target parameters; however, it is noticed that the T_B data at 18 GHz deviate from the theoretically predicted trend. The effect of atmosphere (water vapour) is taken into account in the theoretical trend. However, the frequency dependence of T_B plots from Scanning Multi-channel Microwave Radiometer (SMMR) of Nimbus-7 closely resemble the theoretical trend. This indicates that the relative calibration of 18 GHz T_B of IRS-P4 has some problem and needs to be looked into. Approximate offset values for each land type are computed and presented here. A general comparison of T_B of MSMR and SMMR indicates that T_B of MSMR is higher by 4 K, which needs to be further investigated.