Global Simplified Atmospheric Radiative Transfer Model at L-Band

A simplified atmospheric radiative transfer model at L-band has been developed for the Soil Moisture Active/Passive (SMAP) forward brightness temperature (level 1) simulator. The upwelling and downwelling brightness temperatures and the total loss factor of the atmosphere are modeled as polynomial functions of pressure, temperature, and water vapor density near the Earth's surface, as well as incidence angle. The model has been developed and verified by using global radiosonde data, and the model error is within the 0.1 K error budget (atmosphere portion) of the SMAP brightness temperature (Level 1B) product.