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

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ABSTRACTThe 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.