Remote sensing of lightning by a ground-based microwave radiometer

• Emissions from a super-heated air cylinder generated by lightning can be observed with a ground-based microwave radiometer in 51-59 GHz for atmospheric temperature profiling.
• The TB response of the radiometer is proportional to both the increment of temperature in the discharging area and the atmospheric transmittance to the radiometer, and the proportional factor is the emissivity of the lightning-heated air cylinder.
• The TB response of the radiometer is inversely proportional to the distance between the radiometer and the cylinder.
• The distance and features of the lightning-heated air cylinder can be estimated from TB observations with the radiometer.

Based on the theory of thermal radiation and its transfer in the atmosphere, the response of a ground-based microwave radiometer to a lightning-superheated cylinder in the atmosphere is studied and the theoretical expressions are given for the relationship between brightness temperatures and parameters such as distance, size, duration and temperature of the lightning-superheated cylinder. The results from simulated calculations show that it is quite possible for a lightning-superheated cylinder to be observed by a microwave radiometer working in the 50–60 GHz band with a sensitivity of 0.3 K, typically used for atmospheric temperature profiling. The brightness temperature observed with any one of the channels in the band increases as the distance between the lightning and the radiometer decreases. Lightning at a short distance would make the brightness temperature observed by the channels near to 60 GHz increase more while distant lightning would make the brightness temperature observed by the channels near to 50 GHz increase more. This feature could be used to retrieve lightning distance and features of the lightning-heated air cylinder from brightness temperature observations. One lightning observation by a ground-based radiometer, the challenge of such observations, and a theoretical analysis are presented. Additional observations are needed for more thorough exploration of this unique remote sensing capability.