Out-of-Band Response for the Coastal Zone Imager (CZI) Onboard China's Ocean Color Satellite HY-1C: Effect on the Observation Just above the Sea Surface.

Tingwei Cui,Fujuan Jia,Bing Mu,Jie Zhang,Jianqiang Liu,Pengmei Xu,Rongjie Liu,Jing Ding

doi:10.3390/s18093067

Abstract

The out-of-band (OOB) response is one of the key specifications for satellite optical sensors, which has important influences on quantitative remote sensing retrieval. In this paper, the effect of OOB response on the radiometric measurements made just above the sea surface is evaluated for the three broad visible bands (i.e., blue, green, and red) of the Coastal Zone Imager (CZI) onboard China’s ocean satellite HY-1C to be launched in September 2018. For the turbid coastal (Case 2) waters whose optical properties are mainly dominated by suspended sediment and colored dissolved organic material, the OOB effect can be neglected (<2%) for all three CZI visible bands. For the phytoplankton-dominated (Case 1) waters which are mainly distributed in the clear open ocean, a significant (>2%) OOB effect was found in the green band over oligotrophic waters (chlorophyll a concentration ≤~0.1 mg/m3), and accordingly a model based on the CZI blue-green band ratio is proposed to correct this effect. The OOB influence on the CZI ocean color retrieval is discussed. This research highlights the importance of the comprehensive pre-launch radiometric characterization and the OOB effect correction for the broad band space-borne sensor, in order to achieve a high-quality quantitative ocean product.

Highlights

The international ocean satellite family will soon have two new members, HY-1C in 2018 and HY-1D in 2019, which will constitute China’s optical satellite constellation for global ocean monitoring
Our results indicate that the green band had significant response in the addition, a 3% OOB response would lead to the positive bias in the derived Chla for the Case oligotrophic the highly for the quantitative
Based on the sensor-observed signals just above the sea surface, the OOB response was evaluated for the three visible bands of the two Coastal Zone Imager (CZI) sensors onboard the HY-1C

Summary

Introduction

The international ocean satellite family will soon have two new members, HY-1C in 2018 and HY-1D in 2019, which will constitute China’s optical satellite constellation for global ocean monitoring (one in the morning and the other in the afternoon). Zone Imager (CZI), which can provide four broad band (i.e., blue, green, red, and near infrared) optical images with a wide swath of 950 km and moderate spatial resolution (50 m), for the coastal environment and resources monitoring from space. CZI will aid coastal zone management by providing key information on reclamation [1], wetlands [2], land cover/use [3], mangroves [4], coral reef [5], and Sensors 2018, 18, 3067; doi:10.3390/s18093067 www.mdpi.com/journal/sensors. The quantitative information inversion from CZI images may be expected to retrieve key parameters of aquatic environments (including turbidity, suspended sediment concentration, transparency, and water depth) [7,8,9], natural resources (such as wetland biomass) [10], and abnormal ecological phenomena [11,12]. In order to achieve this goal, the comprehensive optical characterization of CZI is of high importance, including the radiometric accuracy, signal-to-noise ratio, out-of-band (OOB) response, etc

Methods

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Discussion

Conclusion