In order to meet the requirements of high precision automatic measurement of surface brightness temperature, which is used for in-orbit calibration and product verification of infrared remote sensor, the design and verification of field thermal infrared brightness temperature radiometer are studied. The difference and compensation method is used to obtain the radiance of the ground target. First, the thermopile detector is used to measure the target and the background respectively for difference, and then the standard platinum resistance is used to improve the measurement accuracy. The optical spectrum of 8~14 μm, 8.2~9.2 μm, 10.3~ 11.3 μm, 11.5~l2.5 μm is achieved by the optical spectrum and rotation of the filter wheel, and the photoelectric amplification and acquisition are realized by the high-precision pre-amplification and acquisition circuit. After the radiometer is developed, radiation calibration based on the surface source blackbody is carried out, and the temperature measurement is compared with the laboratory water blackbody. The deviation of measurement is less than 0.14K. The field thermal infrared bright temperature radiometer was compared with thermal infrared radiometer CE312 in the field, and the average deviation of the two devices was less than 0.12K, which verified the feasibility and rationality of the temperature measurement method.
In order to meet the needs of on-orbit radiometric calibration of remote sensors, an infrared channel field radiometer (ICFR) was developed for on-site measurement. The working principle, optical system design and mechanical structure design of ICFR were expounded, the ICFR laboratory radiometric calibration and calibration uncertainty analysis were carried out. The results show that the received radiance of each ICFR channel has a high linear relationship with the response DN value, and the radiometric calibration uncertainty is better than 0.18 K. The ICFR thermal shock resistance and working environment temperature adaptability tests were carried out. The results show that ICFR has strong thermal shock resistance and can be applied to the working environment of -20℃~50℃, It has an important application prospect in the field calibration of remote sensor thermal infrared band.
Spectral calibration accuracy of solar irradiance spectrometer plays an important role in the measurement of the absolute solar spectral irradiance. The solar irradiance spectrometer uses fèry prism to disperse composite light and linear CCD to control the scan of spectrum. The solar irradiance spectrometer has a spectral range of 380 nm ~ 2500 nm. In order to ensure the spectral response efficiency of different bands, three detectors are used to achieve spectral detection of different bands respectively. Single wavelength lasers distributed in different bands are used as the light source in the spectral calibration experiment, and the relationship between wavelength and CCD pixel is obtained through spectral scanning. The actual equivalent angle of fèry prism and spectral calibration equation are calculated. In this paper, two methods of calculating spectral calibration equation are studied. In the experiment, method one uses two characteristic wavelength points of visible near-infrared band to calculate the actual equivalent angle, which is taken as the common prism angle of the whole band. Method two uses the same two characteristic wavelength points as method one in the visible near-infrared band, and uses another characteristic wavelength point in the visible and short-wave infrared bands, respectively. Experimental analysis and calculation show that the pixel deviation of method two is 7.44 pixels and 23.78 pixels less than that of method one in visible and short-wave infrared bands, respectively. Therefore, calculating the actual equivalent angle of the prism in different wavebands can improve the accuracy of wavelength calibration.
In this Letter, we present the automated observation radiometric calibration (AORC) approach for vicarious calibration to determine the surface reflectance for any arbitrary test site in the absence of ground personnel. It has successfully operated at Dunhuang test site for 4 months, with a suite of instruments including an automated test-site radiometer, a precision solar radiometer, and a visible and short-wave infrared hyper-spectral irradiance meter. The predicted top-of- atmosphere (TOA) radiance are in good agreement with those obtained from the on-board calibration system of Terra Moderate Resolution Imaging Spectrometer (MODIS), the average percent difference less than 3.10% in nine bands except 5.14% in band 5. It enable us to improve the calibration frequency, currently once a year in situ, to 1~2 times every month and maintain radiometric accuracy on par with manned field campaigns which making it possible to establish long-term trends in sensor performance.
Solar reflection band of typical in-orbit payload was calibrated by the use of the Dunhuang site automatic observation radiometric calibration operational system (DARCOS) in 2018. Several automatic observation instruments were installed at Dunhuang site. DARCOS integrated product generation, acquisition, archiving, publishing, retrieval, downloading, user hierarchical management and performance monitoring functions together. Automatic calibration algorithm for AQUAMODIS, JPSS1VIIRS, FY2GVISSR, FY3CVIRR and FY4AAGRI were developed. How to accurately measure the surface reflectance without human intervention and correct it to the payload viewing angle is an important subject needs to be solved. A surface reflectance algorithm based on surface radiance and total sky radiation was developed. The directionality calibration was performed using the micro-facet cosine linear kernel-driven (MICOKE) BRDF model. The reflectance was corrected by the site vicarious calibration campaign on August 7-9, 2018. The site correction factor exhibits two variations rules with increasing wavelength, which corresponds to the HIM detector design. The calibration results for 5 payloads between August 13 and December 31, 2018 were analyzed. Ratio of the apparent reflectance from space and ground base was used to judging the agreement. AQUAMODIS (1.02-1.15), JPSS1VIIRS (1.07-1.15), and FY3CVIRR(1.10 to 1.19) are in good agreement with the automatic observation products of the site. FY2GVISSR (1.25) and FY4AAGRI (1.07-1.31) show differences changing by time. As an efficient independent calibration method, automatic calibration could be an effective supplement to the in-orbit calibration.
As the most commonly used hyperspectral data source, the acquisition method of Hyperion hyperspectral reflectance became more and more important. In this study, a batch atmospheric correction method based on Second Simulation of a Satellite Signal in the Solar Spectrum radiative transfer code (6SBAC) has been presented. The 6SBAC was used MODIS synchronous atmospheric data products to obtain meteorological parameters, and set up automatic input-output parameter module to obtain Hyperion reflectance data. At the same time, using Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH), Quick Atmospheric Correction(QUAC) atmospheric correction methods on Hyperion satellite images, the results was compared with the synchronous hyperspectral data measured in Dunhuang test site. The authenticity of the obtained hyperspectral reflectance was verified by MODIS surface products. The results showed that the hyperspectral reflectance obtained by the three kinds of atmospheric correction methods were consistent with the measured reflectance in trend. Despite the compromises in different wavelength regions 6SBAC is found to be a better corrector method for the Hyperion hyperspectral reflectance acquisition. The precision of the 6SBAC obtained hyperspectral reflectance can meet the application requirements and improve the acquisition efficiency of Hyperion hyperspectral reflectance data.
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