The Operational Inflight Radiometric Uniform Calibration of a Directional Polarimetric Camera

Feinan Chen,Shule Ge,Donggen Luo,Benyong Yang,Jin Hong,Liang Sun,Shuang Li

doi:10.3390/rs13193823

Abstract

The directional polarimetric camera (DPC) on-board the GF-5A satellite is designed for atmospheric or water color detection, which requires high radiometric accuracy. Therefore, in-flight calibration is a prerequisite for its inversion application. For large field optical sensors, it is very challenging to ensure the consistency of radiation detection in the whole field of view in the space environment. Our work proposes a vicarious in-flight calibration method based on sea non-equipment sites (visible bands) and land non-equipment sites (all bands). Combined with environmental parameters and radiation transmission calculations, we evaluated the radiation detection accuracy of the 0° to 60° view zenith angle of the DPC in each band. Our calibration method is based on the single-day normalized radiance data measured by the DPC. Through data selection, enough calibration samples can be obtained in a single day (the number of desert samples is more than 5000, and the number of calibration samples of the ocean is more than 2.8×106). The measurements are compared with the simulation of 6SV VRT code or look-up tables. The massive amount of data averages the uncertainty of a single-point calculation. Although the uncertainty of a single sample is significant, the final fitting of the curve of the variation in the radiometric calibration coefficient with the observation angle can still keep the root mean squared error at approximately 2–3% or even lower, and for visible bands, the calibration results for both ocean sites and desert sites are in good agreement regarding the non-uniformity of the sensor.

Highlights

Polarization remote sensing is becoming an international research hotspot
+ H3i,j where DN is the digital number with no unit; k denotes the sequence of the band; i, j denote the pixel number of the sensor; G is the gain of the CCD; t is the integral time; Ak is the k is the absolute calibration coefficient; T k, a is the relative transmittance of the polarizer; Pi,j k, H2k and H3k are polarization effect relative transmittance of the optical system; H1i,j i,j i,j k, Qk and U k are parameters which correspond to the polarization rate of the optics ε; Ii,j i,j i,j
We used the bidirectional reflectance distribution function (BRDF) product of moderate-resolution imaging spectroradiometer (MODIS) because it can be obtained from NASA and input into the Py6S module [24]

Summary

Introduction

The directional polarimetric camera (DPC) of atmospheric aerosols on-board the Gaofen (GF)-5A satellite developed by the Optical Remote Sensing Center of the Anhui Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences is based on the global operational atmosphere aerosol monitoring load. The working principle and scientific target of the DPC are the same as those of POLDER Reflectance), which has eight observation bands in the visible and near-infrared (NIR). Due to its ±50◦ wide-angle observation range and the continuous working method of the rotating filter, it can measure the polarization radiation of the target reflectance from nine directions during a single pass (Figure 1). For more detailed technical characteristics of the sensor, please refer to the DPC laboratory calibration and review materials [1,2,3,4]

Methods

Results

Conclusion