Inter‐Calibration of Geostationary Imager Infrared Bands Using a Hyperspectral Sounder on the Same Platform

• Published in: Geophysical research letters 2023-02, Vol.50 (3), p.n/a
• Main Authors: Di, Di, Liu, Yue, Li, Jun, Zhou, Ronglian, Li, Zhenglong, Gong, Xinya
• Format: Article
• Language: English
• Subjects: Angles (geometry); Bias; Calibration; Climate monitoring; Diurnal; Earth orbit; Earth orbits; geostationary; hyperspectral IR sounder; imager; inter‐calibration; Low earth orbits; Meteorological satellites; Radiance; Radiation; Satellites; Viewing; Weather forecasting
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2022GL101628

Geostationary (GEO) imager Infrared (IR) bands are often intercalibrated with hyperspectral IR sounders onboard low earth orbit (LEO) satellites. Due to viewing geometry and time differences between GEO and LEO, the inter‐calibration is limited to certain viewing angles and times. When a GEO hyperspectral IR sounder and GEO imager are on the same platform, the inter‐calibration can be conducted from all angles and at all times. In this study, the Geostationary Interferometric Infrared Sounder (GIIRS) is used to inter‐calibrate the Advanced Geosynchronous Radiation Imager (AGRI), both onboard FengYun‐4A. Radiance inter‐comparisons between GIIRS and AGRI under homogeneous scenes, including both clear and cloudy situations, indicate that the differences are within 1 K. The differences have obvious dependence on scene radiance, less dependence on the cloudy situation, and the local zenith angle when it is less than 70°. However, they exhibit significant diurnal characteristics. Plain Language Summary Inter‐calibration is an important way to monitor, improve and harmonize the quality of observations from operational weather and environmental satellites. It aims to ensure consistent accuracy among space‐based observations worldwide for climate monitoring, weather forecasting, and environmental applications. Usually, geostationary (GEO) imager infrared (IR) bands are inter‐calibrated with a hyperspectral IR sounder onboard a low earth orbit (LEO) satellite. Due to viewing geometry differences between GEO and LEO, the inter‐calibration is limited to certain viewing angles and LEO overpass times. When a GEO hyperspectral IR sounder and GEO imager are on the same platform, the inter‐calibration is more accurate, and the calibration bias can be well understood for applications. In particular, the angle and scene dependence, and the diurnal characteristics of GEO imager radiance observations can be well quantified. This study analyzes GEO imager IR band calibration bias characteristics when the hyperspectral IR sounder is on the same platform. Because GEO hyperspectral IR sounders have been developed in China and are being planned in Europe, U.S., and Japan, this study provides scientific evidence of the importance of placing an advanced imager and sounder together in the same GEO orbit. Key Points Geostationery (GEO) hyperspectral IR sounder has the unique advantage to inter‐calibrate GEO imager infrared (IR) bands at the same observation time and geometry Geostation