| Radiometric calibration is the basis and premise of satellite quantitative application,which provides guarantee for reliable application of data.The lunar surface has no atmosphere,smooth spectral curve,stable reflectance and emissivity,and is a good radiation source for satellite stability monitoring.Carrying a multispectral imager,the JL-1 spectral satellite had made long-term continuous lunar phase observations and obtained hyperspectral data from 19 spectral segments in the wavelength range of 4501350 nm.However,the bias coefficients of B5 and B6 bands varyed greatly in laboratory calibration coefficients,and B1 band was on the high side while B8 band was on the low side.There was a great jitter in the lunar spectrum,which was quite different from the actual smooth lunar spectrum,indicating that the laboratory calibration coefficients needed to be improved.In this paper,the moon was used as the radiation source to study the absolute radiometric calibration of JL-1 spectral satellite in orbit.Specific research results include the following three aspects:(1)Preprocess the data of JL-1 satellite.A program for automatic extraction of lunar regions from satellite images was developed.The extracted lunar images retain more lunar information and reduce the influence of stray light around them.The geometric information query program is developed to match the geometric information data of different satellite data and find the same name point data with similar observation geometry.(2)To carry out lunar calibration research on JL-1 satellite.Considering the timeliness of calibration coefficients,observation data were divided into two groups of calibration according to time.The ROLO model was used to calculate the lunar irradiance at satellite observation time,and the relationship between ROLO model values and satellite observation values was constructed and linear fitting was carried out,so as to obtain two groups of calibration coefficients of 19 spectral segments,the fitting effects were all greater than 0.99.The uncertainty of calibration coefficients of the two groups was 1.72%and 1.24%,respectively.In terms of spectral shape,the lunar spectral shape is improved greatly by using the smooth lunar spectral curve and the spectral shape is consistent with the lunar radiation characteristics after lunar calibration.(3)The lunar calibration results were compared and verified with MT2009 model,GF-4 data and M3 data.Compared with MT2009 model,the average error of all bands is 5.655%,and the average error of all bands is less than 10%.Compared with GF-4 data,the mean relative error of lunar irradiance is 8.1%,and the error is about 8%compared with the same image point of M3 data.The relationship between the reflectivity of the lunar disk during two optical cycles of M3 data is consistent with previous studies.Compared with three different data,the accuracy of the lunar calibration result of JL-1 is verified quantitatively.This paper is an attempt of lunar calibration,which improves the data quality of JL-1 satellite and is more conducive to scientific application.In addition,important load parameters related to radiometric calibration,such as stray light,bias and dark current,frame transfer,and response nonlinearity,are difficult or even impossible to obtain from earth observation,but can be obtained from lunar observation of black sky background.Therefore,it has many advantages to use the moon(and other extraterrestrial bodies)for in-orbit evaluation and attenuation monitoring of satellites,and it is suggested that satellites launched in the future should increase their lunar observation function as much as possible. |
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