Research on an Absolute Radiometric Calibration Method Based on a Point Source Array

Factors such as the optical point spread function (PSF), intrapixel sensitivity (IPS), and interpixel crosstalk of an imaging system can cause the response to point sources to vary with position, directly affecting the absolute radiometric calibration accuracy of the remote sensor. This paper investigates an absolute radiometric calibration method based on a multilevel point source array and quantitatively evaluates the differences in response stability between a single point source and a point source array as a function of position. The method improves the stability and accuracy of point source response acquisition through subpixel sampling and averaging, and obtains the calibration coefficients of the imaging system by linear regression on multilevel data, thereby achieving wide-dynamic-range calibration based on the point source array. The test results indicate that the stability of the point source response using a 6 × 6 array is better than 0.21%, while the stability of the calibration coefficient is better than 0.3%. The relative difference between the point source calibration coefficient and the results calculated using conventional extended source calibration methods is within 1.5%, thereby validating the effectiveness of the point source array calibration method. Further optimization based on on-orbit application requirements indicates that a point source array ranging from 2 × 2 to 3 × 3 can reduce response fluctuations in the imaging system by a factor of 6 to 10; point source arrays within this range offer high engineering feasibility while maintaining calibration accuracy. Following an uncertainty analysis, the laboratory measurement uncertainty of the calibration method using a multilevel point source array was found to be 3.2%; when the method was applied to on-orbit absolute radiometric calibration, the estimated uncertainty was approximately 3.9%. The multilevel point source array effectively enhances calibration accuracy while ensuring response stability and accuracy, thereby providing technical support for point-source-based on-orbit absolute radiometric calibration.