Radiometric Calibration
- The Paper
Lunar calibration method through attitude maneuver of low-earth-orbit and high-resolution remote sensing satellites
Abstract：As an ideal calibration source, the moon has stable spectral characteristics and light intensity within the dynamic range of the detector. Thus, lunar calibration on-orbit is one of the important means to improve the efficiency of radiometric calibration and monitor the imaging stability of remote sensing satellites. Targeting low earth orbit and high-resolution remote sensing satellites, an on-orbit lunar calibration method, which includes imaging time, satellite attitude, imaging parameters of lunar observation, etc., is proposed in this paper. Lunar observation experiments on a low-orbit optical remote sensing satellite were successfully conducted 15 times in July, 2019, under the conditions of satellite attitude angular velocity of 0.06 (°)/s and integration time of 0.293 8 ms. The lunar phase angle covered the range of -79.872° to 89.236°. The results suggest that the satellite attitude of the actual implementation is in accordance with that of the design. Moreover, the lunar calibration method has high observation efficiency, which takes only 1 500 s and will not affect the normal earth observation mission. Furthermore, the texture of 15 acquired images of the moon has a better distribution hierarchy of image DN value, and the spatial resolution is better than 1.18 km. The calculated lunar irradiance distribution trend is consistent with that of the RObotic Lunar Observatory (ROLO) model published internationally. The experimental results verified the correctness and rationale of the proposed method. Multiple lunar phase angle observation has been realized for the first time in China though the attitude maneuver of a low-orbit remote sensing satellite, which can provide a reliable basis for long-term monitoring of the imaging stability of the senor and accumulating a large amount of lunar calibration data to establish a lunar radiation model independently in China.Keywords：low-earth-orbit satellite;high resolution;attitude maneuver;lunar calibration;lunar radiation model635|1731|8
<HTML><L-PDF><Meta-XML>Updated：2020-09-28Cross-calibration of FY-3C medium resolution spectral imager in reflective bands
Abstract：To ensure absolute calibration of the solar band of the Medium Resolution Spectral Imager (MERSI), a cross-calibration algorithm utilizing Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) instrument over six Pseudo-invariant Targets (PTs) is developed and used to calibrate FY-3CMERSI data. The technique involves three key steps:Capturing the actual Bi-directional Reflectance Distribution Function (BRDF) characteristics using the well-calibrated SeaWiFS radiance data; Parameterizing the Spectral Band Adjustment Factors (SBAF) between SeaWiFS and MERSI sensor; and Cross-calibrating each screened MERSI observation based on the above two modules. The employed BRDF model can accurately predict ρTOA as observed by SeaWiFS with small biases (within approximately 3% for most cases). Furthermore, the fitted SBAF are nearly unbiased estimations of the simulated values. The time series of the cross-calibration result is very stable and exhibits no obvious trend, which is consistent with the characteristic of long-term stability and regular change of radiation signal of PTs. Hence, there is a systematic deviation from the calibration result of L1. This method fully considers and solves the uncertainty due to orbit drift, i.e., the difference between observed geometric conditions and spectral response in cross-calibration, and can effectively monitor and correct the radiation performance of satellites in orbit.Keywords：spectral imager;cross-calibration;spectral band adjustment factor;bi-directional reflectance distribution function534|650|3<HTML><L-PDF><Meta-XML>Updated：2020-08-13Combined radiometric calibration of ground-based large-aperture infrared photoelectric systems
Abstract：When infrared standard stars are used in radiation calibration for a ground-based large-aperture infrared photoelectric system, it can not determine the radiance responsivity of each pixel and shows a poor adaptability for non-uniformity of the system. To solve this problems, a combined radiometric calibration method based on infrared standard stars and the small-aperture blackbody was proposed. The infrared standard stars were taken as an outer reference source to calibrate the radiance responsivity of the Keywords：infrared photoelectric system;combined radiometric calibration;infrared standard stars;small-aperture blackbody;infrared radiation feature646|1218|2<HTML><L-PDF>Updated：2020-08-13Self-calibrated spectral radiance standard source
Abstract：Aiming at the demand of high-precision space-based optical quantitative remote sensing, a self-calibrated spectral radiance standard source which employs Digital Micromirror Device (DMD) was developed. The light source has two working modes. In narrow-band mode, it is calibrated by CAS spectroradiometer and Gershun radiometer. In broad-band mode, it is used for calibration of the spectral radiance responsivity of ground-based or space-based remote sensing instruments. An spectral radiance standard source co Keywords：radiometry;remote sensing;radiance calibration;source;Digital Micromirror Device(DMD)503|907|4<HTML><L-PDF>Updated：2020-07-07Radiometric calibration of photographic camera with a composite plane array CCD in laboratory
Abstract：To eliminate the serious vignetting phenomenon and to solve the difficulty of choosing a relatively positioning target value problems among CCDs during the radiometric calibration of the whole image plane of the photographic camera with a composite plane array CCD, a method for radiometric calibration of multi-CCDs was proposed. After the dark signal calibration on each pixel, the gray value of the pixel in the vignetting area was revised, and by choosing the appropriate relative calibration target gray val Keywords：radiometric calibration;non-uniformity;vignetting;composite plane array CCD623|582|0<HTML><L-PDF>Updated：2020-07-07Radiation calibration of EUV space cameras
Abstract：There are no proper radiation calibration methods and devices for EUV space cameras, so this paper proposes a small target imaging radiation calibration method suitable for the EUV band and establishes a radiation calibration device based on the method in a lab. This method uses a standard transfer detector to calibrate the radiance of the small target. Then, a EUV space camera is used to take the small target's image in its center Field of View(FOV) and to get its radiance responsivity. Finally, by adjusting the motion platform, the small target's images in different FOVs are taken by the EUV camera, and the radiance responsivity in different FOVs are obtained. The developed radiation calibration device consists of a light source system, standard transfer detectors, a vacuum tank and a four-dimensional motion platform fixed in the camera. The light source system consists of a hollow cathode light source, an extreme ultraviolet grazing incidence monochromator, and a collimating mirror generating a parallel monochromatic beam. The standard transfer detectors are used to calibrate the beam's photon flux and small target's radiance and the motion platform enables the camera to take the small target's images in different FOVs and to get camera's responsivity in different FOVs. A EUV camera has been calibrated by this device, and the error sources are analyzed. The calibration results indicate that its accuracy is better than 15% and implements the radiation calibration for whole bands.Keywords：space camera;radiation calibration;small target imaging;standard transfer detector;extreme ultraviolet band366|984|0<HTML><L-PDF><Meta-XML>Updated：2020-08-13Establishment of image model for on-board space camera
Abstract：The concept of on-board imaging model for a space camera was proposed, and the method to establish the imaging model of the space camera was researched. On the basis of the solar elevation angle and the reflection of earth surface, the radiance at the entrance pupil of space camera was calculated using the MODTRAN software. Then the radiometric calibration data were analyzed and the responsibility, radiance range and the integration time for each image model were acquired. Meanwhile, the relation between the responsibility and the integration time was obtained for scroll image and standard image and the radiance ranges at each image model was calculated at every scroll angle. Finally, according to the radiance range at each image model and the maximum objective at sensor radiance from the earth surface, an imaging model table was established under the scroll angle and solar elevation angle. When the space camera worked on board, one could choose a corresponding imaging model by looking up the table and could achieve better images. The method has been used in space camera imaging for several times, high quality remote images have been acquired. The image satisfaction improves from 65% to 99.9%. According to the method, the remote image's quality has been improved obviously. The image not only includes all scene information, but also has abundant levels.Keywords：space camera;radiometric calibration;image model308|683|0<HTML><L-PDF><Meta-XML>Updated：2020-08-12Spectral and radiometric calibrations for mapping satellite-1 camera
Abstract：The spectral calibration and radiometric calibration were performed for every waveband of the Mapping Satellite-1 camera to validate its spectral and radiometric performance. In spectral calibration, a collimated monochromatic light source was provided by wavelength scan using a monochrometer and a collimator. Meanwhile, the camera acquired calibration images, and then compared image's digital number and the output of calibrated standard reference detector to obtain relative spectral responsive curve by data analysis and processing. Furthermore, spectral characteristics were acquired. In radiometric calibration, the nearest emitting source method was used to perform the end to end relative and absolute radiometric calibrations with irradiating the whole aperture and the field of view. In the on-orbit inner calibration, the aged and picked up LEDs were employed as on-orbit inner calibration light sources to monitor the changes and status of focal plane detector array and its imaging electric circuit at post launch, and they were corrected in necessary conditions. Spectral calibration and radiometric calibration results indicate that all the spectral performance and radiometric performance of the Mapping Satellite-1 camera meet design requirements, non-uniformity of the camera is decreased from 1.93% to 0.22% after relative radiometric calibration. The typical Signal to Noise ratios(SNRs) of panchromatic and multispectral cameras are beyond 90 times and 180 times respectively. The compared results from the on-board inter calibration after launching and the tested data from a laboratory before launching show that radiometric responsive performance of the camera has not changed during this period, and not need to be corrected.Keywords：mapping camera;spectral calibration;radiometric calibration;on-orbit inner calibration366|863|0<HTML><L-PDF><Meta-XML>Updated：2020-08-12Cross-calibration of VIRR/FY-3A split-window channels with AIRS/AQUA and IASI/METOP-A data
Abstract：Some practical applications indicate that there is calibration deviation in the on-orbit radiometric calibration of the two split-window channels(IR4,~10.8 μm;IR5,~12.0 μm) on the Visible and Infrared Radiometer(VIRR) mounted in FY-3A. Therefore, this paper applies high-spectral convolution method to implementation of the cross radiometric calibration for the two spilt-window channels of VIRR/FY-3A based on the observation data from the Infrared Atmospheric Sounding Interferometer/METOP-A(IASI/METOP-A)and the Atmospheric Infrared Sounder/AQUA(AIRS/AQUA). According to the characteristics of the satellite orbit, the Arctic region (60°N-90°N,180°W-180°E) was chosen as the research area, and June, September, December 2010 and March 2011 were selected as the research satellite orbit spectral response functions of the 4th and 5th channels of VIRR/FY-3A. Then, the Planck blackbody radiation formula was used to achieve the conversion between radiation value and brightness temperature. On the basis on the corresponding matching conditions, the matching observation points between the 4th and 5th channesl of VIRR/FY-3A and AIRS/AQUA, the 4th and 5th channels of VIRR/FY-3A and IASI/METOP-A were extracted, respectively. Finally, the regression of matching observation point pairs was analyzed to obtain the cross radiometric calibration coefficients. The experimental results show that the proposed high-spectral convolution method with IASI/METOP-A and AIRS/AQUA for the cross calibration has the same calibration results. By using IASI/METOP-A and AIRS/AQUA as the standard, the brightness temperature biases for the 4th channel of VIRR/FY-3A are 2.39 K and 2.06 K; and those for the 5th channel of VIRR/FY-3A are 0.59 K and 0.44 K. This work indicates that calibration deviation is related to the brightness temperature.Keywords：Visible and Infrared Radiometer/FY-3A;split-window channel;Atmospheric Infrared Sounder/AQUA;Infrared Atmospheric Sounding Inter ferometer/METOP-A;cross-calibration;high-spectral convolution method423|569|0<HTML><L-PDF><Meta-XML>Updated：2020-08-12FY-3C/MERSI caliration for solar band using multi-reflectance stable targets
Abstract：The calibration accuracy of solar bands for Fengyun-3C/Moderate Resolution spectral Imager(FY-3C/MERSI) from January 2014 to October 2014 is assessed based on multi-reflectance stable targets, such as deserts and salt lakes with different reflectances in a globe. In combination of ground surface and atmospheric parameters of Moderate Resolution Imaging Spectroradiometer(MODIS) products and the atmospheric radiation transfer model, the band reflectances of the satellite when it transits into the pupil are calculated and then they are taken as the reference true values for validation of the absolute radiation calibration accuracy. The validation experiments on radiation calibration accuracy of the FY-3C/MERSI for reflective solar bands are performed for the dates mentioned above. The results show that the calibration accuracy of most solar bands of FY-3C/MERSI is different for the targets with different reflectances. For some bands, the calibration accuracy is lower for larger reflectance targets, and higher for lower reflectance targets. For other bands, the calibration accuracy is lower for larger and lower reflectance targets, and higher for targets with moderate reflectances. Bands 1~4, 9~11, 15~16 and band 19 of FY-3C/MERSI can maintain a calibration accuracy of 5% during one year after its launching. The time series of the calibration accuracy of each band show that the variation of the calibration accuracy for the whole study period is within 5% except for the blue band and the water vapor absorption bands,. It concludes that it is effectively to acquire a good knowledge of the radiometric calibration accuracy over a wider dynamic range for FY-3C/MERSI by using the deserts and salt Lakes simultaneously.Keywords：radiometric calibration;FY-3C/Moderate Resolution Spectral Imager (MERSI);stable target;solar band402|652|0<HTML><L-PDF><Meta-XML>Updated：2020-08-12
