Feasibility of a specialized ground light source for night-time low-light calibration

ABSTRACT

The day/night band (DNB) of the Visible Infrared Imaging Radiometer Suite can not only identify surface characteristics when illuminated by moonlight, but can also detect night-time radiation from ground active light sources. Accordingly, the low-light sensor can be calibrated by comparing upward active radiation with actual observed digital counts, which has attracted new research interest. In this article, the first attempt to calibrate the high-gain stage of the DNB using a specialized ground light source was introduced. The DNB imaging rule of the target pixel at various observation geometries was analysed based on the long-term monitoring of a light source set in Dunhuang, Gansu Province, China. The radiance caused by emissive radiation varied greatly over time in a 16-day cycle. To solve the major problem of the Dunhuang light source when used for low-light calibration, a light source that emits homogenous radiation intensity in most upward directions was custom designed. Based on this device, a comprehensive low-light calibration scheme was proposed and three verification experiments were performed in Mingguang, Anhui Province, China. The predicted in-band DNB at-aperture radiance values of the 3-day experiments were 3.86 × 10⁻⁹, 4.38 × 10⁻⁹, and 5.27 × 10⁻⁹ W cm⁻² sr⁻¹, respectively, while the actual observed DNB radiance values were 4.53 × 10⁻⁹, 5.06 × 10⁻⁹, and 5.57 × 10⁻⁹ W cm⁻² sr⁻¹, respectively. With deviations of 14.8%, 13.4%, and 5.4%, respectively, the calibration result based on the specialized light source was generally in good agreement with the operational calibration result, and thus the feasibility of the device for low-light calibration had been preliminarily verified.

KEYWORDS:

• NPP
• DNB/HGS
• calibration
• specialized light source
• verification experiment

Acknowledgments

The authors thank Professor Muqing Liu and Dr. Xiaolin Zhang of Fudan University for their help with the measurements of the device. We also thank NOAA CLASS for making DNB products publicly available. This work was supported by National Natural Science Foundation of China (Grants 41575028, 41705007, 41605016, and 41475019)

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China [Grants 41475019, 41575028, 41605016, 41705007];