Microwave Radiometers

Synonyms

Passive microwave radiometer (PMR)

Definition

The microwave radiometer is a calibrated receiver that measures properties of the natural emission from the environment as picked up by an antenna system.

Introduction: what is radiometry about?

All bodies at a temperature above the absolute zero (0 K = −273 °C) radiate power, according to Planck’s law. At microwave frequencies the Rayleigh-Jeans approximation holds, and the radiation is proportional to physical temperature. Actually, this is only true for the so-called blackbodies, which are perfect emitters. Natural bodies radiate less, and we introduce the term emissivity (ε) which is a number between 0 and 1 describing how well the body radiates relative to a blackbody. Within radiometry the radiated power is expressed as the so-called brightness temperature, T_B, so that T_B = ε · T_phys. The brightness temperature of a blackbody is thus equal to its physical temperature, while all natural bodies will have brightness...