Preliminary Selection and Characterization of Pseudo-Invariant Calibration Sites in Northwest China

Abstract

Pseudo-invariant calibration sites (PICS) have been used for the radiometric calibration and stability monitoring of satellite optical sensors. Several stable PICS, such as those in the Sahara Desert in North Africa, were selected for the vicarious calibration of earth remote sensing satellites. However, the selection procedure of PICSs in the whole of Northwest China has not been fully explored before. This paper presents a novel technique for selecting PICS in Northwest China by combined using the coefficient of variation (CV) and the iteratively reweighted multivariate alteration detection (IR-MAD) technique. IR-MAD, which calculates the differences between two multispectral N-band images from the same scene acquired at different times, is used to identify no-change pixels (NCPs) of the scene through one image pair. The NCPs from IR-MAD using the long-term data of FY-3 visible infrared radiometer (VIRR) and aqua Moderate Resolution Imaging Spectroradiometer (MODIS) were aggregated into the contiguously stable sites. The traditional spatial uniformity and temporal stability from MODIS surface products were used to select the potential PICS. By combining the results of both methods, over thirty PICSs with a wider brightness range of the scene types were selected. To confirm and characterize these PICSs over Northwest China, Landsat operational land imager (OLI) high-spatial-resolution images were used to check the spatial uniformity of the selected site to determine the specific location and the size of these sites. Additionally, the surface spectral reflectance and bidirectional reflectance distribution function (BRDF) were obtained from the field campaign at Chaidamu Basin, 2018. To demonstrate the practical utilization and usability of these PICSs, they were employed in the multi-site top of atmosphere (TOA) reflectance simulation to validate the operational calibration performance of Aqua/MODIS and FY-3D/MERSI-II (Medium Resolution Spectral Imager II). The simulation results showed good consistency compared with the observations from both MODIS and MERSI-II, with a relative bias and root mean square error (RMSE) of <5% and <0.05%, respectively. These sites provide prospects for multi-site vicarious calibrations of solar reflective bands, which may help to evaluate or characterize instrumental nonlinear responses using a wider signal dynamic from the sites in different seasons.

A Novel Intercalibration Method for Fengyun(FY)-3 VIRR Using MERSI Onboard the Same Satellite Based on Pseudo-Invariant Pixels

“…An iteratively re-weighted modification of the MAD transformation (IR-MAD) has been introduced [37] and was extended to radiometric normalization with substantial improvement [38]. This method was later applied to the selection of pseudo-invariant calibration sites in Northwest China [39]. In this study, the IR-MAD technique is used to statistically selected pixel-level targets for intercalibration.…”

Evaluation of Temporal Stability in Radiometric Calibration Network Sites Using Multi-Source Satellite Data and Continuous In Situ Measurements

“…CV is a dimensionless value that provides a standardized measure of reflectance variability within a defined area of an image. The CV has been widely used to estimate spatial homogeneity of vicarious calibration sites [4,7,48,49]. The CV is defined as follows:…”

BRDF modeling and analysis of the pseudo-invariant calibration site in northwest China

“…Pseudo-invariant calibration sites exist in the Tengger Desert, the Badain Jaran Desert, and the Gobi of Qinghai in northwest China, and 32 quasi-invariant calibration sites suitable for remote sensor calibration were selected based on the IR-MAD method [9] . Based on this, pseudo-invariant calibration sites with different surface types of desert, Gobi, and saline land are selected as experimental sites in this paper, and the details of the experimental sites are shown in Table 1.…”