The Directional Polarimetric Camera (DPC), developed by Anhui Institute of Optics and Fine Mechanics (AIOFM), Hefei Institutes of Physical Science (HFIPS) and loaded on Gao Fen-5 Satellite, is a satellite sensor with the aim to observe the polarization and directionality of the earth’s reflectance. The multi-angle polarization information is helpful to obtain the spatial distribution of target radiation.
Recently, a research group led by Professor HONG Jin from AIOFM realized the non-uniformity calibration of space-borne area charge coupled device (CCD) for DPC based on multi-parameters.
Non-uniformity consists of many factors such as lens, detector assembly, etc. As for DPC, non-uniformity is reflected in the high frequency difference in the rapid change of adjacent pixels, and the low frequency difference in the overall slow change of different field of view, which is hard to be distinguished by the single correction method effectively.
In this research, scientists proposed new method basing on multi parameters. Through the electro-optical performance measurement system of the CCD detector, they obtained the sensitive factors such as temperature, dark current, exposure time and spectral response.
After a series of preprocessing of the image including removal of dark signal and smearing effect, the low-frequency unbalanced response difference of the image surface is eliminated, and the high-frequency difference is effectively suppressed.
"The non-uniformity of single picture is reduced from 2.86% to 0.36%”, said YAO Pingping excitedly, a member of the research team, “after correction, the data noise is shown as shot noise, and the detector has good ability of dynamic range adjustment.”
This research offered data support for the instrumental calibration and in-flight fast calculation, and provided effective reference for the subsequent polarization remote sensing instruments.
This work was supported by Major special project of high resolution earth observation system (civil part) (Grant No. 30-Y20A19-9007-15/17), and the Satellite Data Simulation Technology (Grant No.50-Y20A38-0509-15/16).
DOI: Non-uniformity calibration method of space-borne area CCD for directional polarimetric camera
Fig.1 Schematic of the Directional Polarimetric Camera (Image by YAO Pingping)
Fig.2 Comparison of single frame image before and after PRNU correction (Image by YAO Pingping)
Contact:
ZHAO Weiwei
Hefei Institutes of Physical Science (http://english.hf.cas.cn/)
Email: annyzhao@ipp.ac.cn