Land surface temperature from Ka band (37 GHz) passive microwave observations

TLDR

The 37 GHz channel offers a balance between reduced soil sensitivity and high atmospheric transmissivity. The study proposes an alternative to thermal infrared satellite sensors for measuring land surface temperature, offering a complementary approach especially under clouded conditions. Ts is derived from 37 GHz vertical‑polarized brightness temperatures, deemed the most suitable microwave frequency for temperature retrieval. A simple linear relationship between 37 GHz brightness temperature and Ts yields bias within 1 K for 70 % of vegetated land, with precision better than 2.5 K for forests and 3.5 K for low vegetation, though barren and sparsely vegetated areas are less accurate, yet the method can capture diurnal temperature cycles with surprising accuracy.

Abstract

An alternative to thermal infrared satellite sensors for measuring land surface temperature ( T s ) is presented. The 37 GHz vertical polarized brightness temperature is used to derive T s because it is considered the most appropriate microwave frequency for temperature retrieval. This channel balances a reduced sensitivity to soil surface characteristics with a relatively high atmospheric transmissivity. It is shown that with a simple linear relationship, accurate values for T s can be obtained from this frequency, with a theoretical bias of within 1 K for 70% of vegetated land areas of the globe. Barren, sparsely vegetated, and open shrublands cannot be accurately described with this single channel approach because variable surface conditions become important. The precision of the retrieved land surface temperature is expected to be better than 2.5 K for forests and 3.5 K for low vegetation. This method can be used to complement existing infrared derived temperature products, especially during clouded conditions. With several microwave radiometers currently in orbit, this method can be used to observe the diurnal temperature cycles with surprising accuracy.