Assessment of Image Sharpness Evaluation Methods and Image Sharpness Changes in GF-4 Satellite Time-Series Data

The Gaofen-4 satellite (GF-4) is the first Chinese remote sensing satellite to be placed in a geosynchronous orbit, which has a wide range of application prospects. The image sharpness evaluation method is a key step to quickly, accurately and automatically obtain the quality of a large number of GF-4 remote sensing data and understand the changes of the in-orbit satellite. Moreover, the assessment of image sharpness changes is the verification of the stability of the satellite operation, and can also provide reference for the follow- up satellite planning. Taking the time-series GF-4 panchromatic images of Zhengzhou and Chifeng from May 2016 to July 2020 as the data source, we use the block standard deviation sharpness evaluation method based on spatial domain and the power spectrum sharpness evaluation method based on frequency domain to calculate four kinds image sharpness evaluation values and carry out the correlation analysis from the same day and the same month, considering whether to remove the influence of image brightness. We analyze the influence of image brightness on the sharpness evaluation, and explores the applicability of these two methods for GF-4 image, so as to select the best sharpness evaluation method. The results show that the image power spectrum that has been normalized by the average image brightness is the most suitable image sharpness evaluation method for GF-4 image. This method is used to evaluate the image quality of 208 GF-4 panchromatic images in Zhengzhou and Chifeng. The results show that: since the delivery of GF-4 in orbit test satellite, the image sharpness is stable. At the same time, some suggestions are given for the planning of subsequent geosynchronous orbit satellites. It is necessary to improve the anti- interference ability of the camera to the atmospheric conditions, platform jitter and other external conditions.