V.A. Zenin – Ph.D.(Eng.), Leading Research Scientist, 

Aerospace Image Processing Research Institute of Ryazan State Radio Engineering University E-mail: foton@rsreu.ru

Algorithms of relative radiometric calibration of remote sensing systems (ERS) of scanner type are considered. The proposed algorithms are based on the formation of uniform brightness images on the materials of shooting natural objects of the earth's surface. According to the generated images, the calculation of calibration coefficients is performed to ensure high quality of processing. A comparative analysis of the proposed algorithms. Experimental studies of the developed algorithms using real images are performed. The proposed algorithms were used for the first time in Russia.

Scanning type imaging systems have a technological variation of characteristics. As a result, the brightness images in the form of banding are observed on the generated images. Each column of the image is formed by a separate well-defined photodetector element. Each column of the image is formed by a separate well-defined photodetector element. The article describes the model of the photodetector element and gives a mathematical description of the correction functions of the distortion under consideration. The task of radiometric calibration is to find the parameters of these functions. The most important issue in solving the problem is the formation of a reference image with a constant level of brightness of the observed scene. According to the brightness nonuniformity of the formed image, the radiometric calibration parameters are estimated. The article discusses two approaches that allow the formation of such an image without the use of additional equipment.

The first approach involves shooting sufficiently long sections of the earth's surface with constant brightness. This allows to level the inevitable heterogeneity of the plot. The most suitable are sand and snow deserts and the surface of the oceans. It is possible to combine calibration results across multiple images. The calibration of the calibration data by the operator is mandatory. This allows you to exclude the effect of random objects significantly different in brightness from the background. Then the calibration process is performed automatically. Evaluation of calibration parameters is performed by comparing the average brightness of each column of the image with the average brightness in the field of view.

To improve the automation of the calibration process, a new approach is proposed. It is necessary to deploy the device with a scanning device along the flight direction. Thus, each photodetector element will register the same objects of the earth's surface. As a result, it is possible to refuse detailed control of images by the operator. The required duration of reference images is also reduced. All this leads to a reduction in the time required to perform a relative radiometric calibration. But this approach imposes non-standard requirements for the spacecraft motion control system.

The considered algorithms are implemented in the form of software calibration systems for imaging equipment. These complexes are successfully used in processing data from domestic Earth observation devices Resurs-P. The proposed algorithms in Russia are used for the first time.

1. Zenin V.A., Kuznetsov A.E., Pobaruev V.I. Algoritm radiometricheskoi korrektsii izobrazhenii s neodnorodnym syuzhetom, poluchennykh ot kosmicheskogo apparata «Resurs-DK». Vestnik Ryazanskogo gosudarstvennogo radiotekhnicheskogo universiteta. 2008. № 23. S. 43−48.
2. Eremeev V.V., Zenin V.A. Radiometricheskaya normalizatsiya izobrazhenii ot mnogomatrichnykh skaniruyushchikh ustroistv. Tsifrovaya obrabotka signalov. 2009. № 3. S. 31−35.
3. Cosnefroy H., Leroy M., Briottet X. Selection and characterization of Saharian and Arabian desert sites for the calibration of optical satellite sensors. Remote Sens. Environ. 1996. V. 58. № 1. P. 101−114.
4. Martin V., Blanchet G., Kubik P., Lacherade S., Porez-Nadal F. PLEIADES-HR 1A&1B image quality commissioning: innovative radiometric calibration methods and results. Proceedings of SPIE. The International Society for Optical Engineering 8866: 10 September 2013.
5. Eremeev V.V., Zenin V.A. Modeli korrektsii dinamicheskikh strukturnykh iskazhenii na kosmicheskikh izobrazheniyakh. Vestnik Ryazanskogo gosudarstvennogo radiotekhnicheskogo universiteta. 2010. № 33. S. 3−7.