Evaluation and adjustment of the radiometric degradation of HY-1B satellite COCTS via a stable marine site

ABSTRACT

The Chinese Ocean Color and Temperature Scanner (COCTS) on-board the Chinese second ocean color satellite, HY-1B, obtained approximately 6 years of data between 2007 and 2013 in China coastal seas and the adjacent waters. However, its radiometric performance has hardly been analyzed, which confuses its applicability in ocean remote sensing. This study tracked the long-term radiometric responsivity trend of HY-1B COCTS based on a stable marine target. Firstly, we identified a temporally stable maritime site of 12° ~ 15°N and 116°~119°E according to the water and atmospheric optical properties using Aqua MODIS products. Then, the time-series of top-of-atmosphere (TOA) reflectance was obtained for each band of HY-1B COCTS and Aqua MODIS over this site according to the criteria of sun-target-view geometry. Finally, exponential or linear degradation models were built and used to adjust the radiometric levels of HY-1B COCTS. Results indicate that the radiometric performance exhibited continuous degradation for all bands at varying levels between 0.4% and 8.1% yr⁻¹. The worst degradation occurred at 412 nm, with an annual average rate of 8.1%. The degradation at 443 nm reached 5.5% yr⁻¹ following 412 nm. The radiometric performance at 490 nm, 520 nm, and 565 nm was relatively stable with a drift of ~3% yr⁻¹. The 670 nm, 750 nm, and 865 nm bands remain most stable with the degradation of ~1% yr⁻¹. Taking Terra MODIS as a reference, the temporal consistency of HY-1B COCTS was significantly improved for each band after radiometric adjustment. Cloud-free imageries between 2007 and 2013 showed relatively high spatial consistency. The bias of TOA reflectance was ~5% in visible bands and ~10% in near-infrared bands after degradation correction. These improvements confirm the application potentials of HY-1B COCTS in ocean remote sensing.

KEYWORDS:

• HY-1B COCTS
• radiometric degradation
• stable marine site

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The HY-1B COCTS data are available on application from the National Satellite Ocean Application Service (http://www.nsoas.org.cn/). The MODIS L1B data can be obtained from the Level-1 and Atmosphere Archive and Distribution System (https://ladsweb.modaps. eosdis.nasa.gov/). The MODIS level-3 data can be obtained from Ocean Color Level 3 browser (https://oceancolor.gsfc.nasa.gov/l3/).

Correction Statement

This article has been corrected with minor changes. These changes do not impact the academic content of the article.

Additional information

Funding

This work was supported by the National Key R&D Program of China [grant numbers 2018YFB0504900 and 2018YFB0504904], the National Natural Science Foundation of China [grant numbers. 42071325 and 42176183], LIESMARS Special Research Funding, the “985 Project” of Wuhan University, and Special funds of State Key Laboratory for equipment.

Notes on contributors

Wenkai Li

Wenkai Li is currently pursuing a PhD. Degree with Wuhan University. His current research interests include the applications of remote sensing.

Guangping Xia

Guangping Xia is a postgraduate at Wuhan University. Her research interests focus on applications of remote sensing.

Qingjun Song

Qingjun Song is a researcher with the National Satellite Ocean Application Service, Ministry of Natural Resources, Beijing, China, and works on HY-1 and HY-2 series satellite instrument calibration and ocean remote sensing product validation. His research interests include remote sensing and the absolute radiometric calibration of optical instruments.

Ruqing Tong

Ruqing Tong is a postgraduate at Wuhan University. Her research interests focus on applications of remote sensing.

Liqiao Tian

Liqiao Tian is a professor at Wuhan University. His current research interest is the application of remote sensing and radiometric calibration of optical instruments.