Improving the radiance retrieval accuracy in limb sounding by utilizing a similarity model correcting the internal thermal radiation for an infrared radiometer.

For commercially available infrared radiometers with a small volume and a light weight and without an independent cooling system for the optical structure, thermal sensitivity is a key constraint for their application to high-precision limb observations. In this research, the response law of a medium wave (3.7-4.8 µm) infrared radiometer with different thermal states is investigated, and emphasis is placed on the background gray variability caused by different thermal states. We construct a similarity model to describe the response difference. Utilizing the very small radiance of the upper atmosphere and the similarity model, we can correct the deviation caused by the thermal fluctuation of the sounder with high accuracy. The method of improving the retrieval accuracy is validated by simulating the limb-sounding scenarios with ground experiments. When the target radiance is 2.27 × 10^-7 Wcm^-2sr^-1, a temperature difference of 2.5°C causes a 918% deviation in the retrieved radiance, which can be reduced to 23% after correction with the similarity model proposed in this paper. This method can facilitate the application of portable radiometers in the field of high-precision detection.