Spaceborne Relative Radiometer: Instrument Design and Pre-Flight Test

In order to simultaneously determine the values of total solar irradiance (TSI) and the Earth's radiation at the top of the atmosphere (TOA) on board the Fengyun-3F satellite, a spaceborne relative radiometer (SRR) was developed. It adopts a dual-channel structure, including a solar radiometer channel (SR) with an unobstructed field of view (FOV) of 1.5 & DEG; and an Earth radiometer channel (ER) with a wide field of view (WFOV) of 95.3 & DEG; and a diameter of about 1900 km on the ground. Before the launch, both the SR and ER were calibrated. The SR, installed on the inner frame of the solar tracker of the SIM-II (solar irradiance monitor-II), is used to observe rapid changes in solar radiance with the SIAR (solar irradiance absolute radiometer), an electrical-substitution radiometer, on orbit. The ER is mounted on the U-shaped frame of the solar tracker, directly pointing in the nadir direction. Additionally, a dark space observation mode is used to determine the on-orbit background noise and lunar observation mode for on-orbit calibration. In this article, the instrument design and working principle of the SRR is first introduced, and an analysis of the measurement model of the ER, the WFOV channel of the SRR, is focused on. Finally, ground test results of the SRR are introduced.

Automated summary

To determine TSI and Earth's radiation at TOA on the Fengyun-3F satellite, a dual-channel SRR was developed and calibrated. The SR observes solar radiance changes with the SIAR on orbit, while the ER directly points in the nadir direction. Dark space and lunar observation modes are used for background noise and on-orbit calibration. This article introduces the SRR design and working principle, focusing on the measurement model of the ER, and presents ground test results.