Abstract
A high-spatial resolution aerosol optical depth (AOD) dataset is critically important for regional meteorology and climate studies. Chinese Huanjing-1 (HJ-1) A/B charge-coupled diode (CCD) data are a suitable data source for retrieving AODs. However, AOD cannot be retrieved based on the dark target method due to the absence of a shortwave infrared band. In this study, an AOD estimation method based on the relationships between visible bands of HJ-1 A/B CCDs is proposed. The Polarization and Directionality of the Earth's Reflectances (POLDER) Bidirectional Reflectance Distribution Function (BRDF) dataset was used to construct a lookup table for interband regression coefficients that varied by solar/view angle and land cover type. Finally, high-spatial resolution AODs could be retrieved with the aerosol lookup table and constraints. The results showed that the AODs retrieved from the HJ-1 A/B CCD data had the same range of distribution and trends as a visual interpretation of the images and Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol products did. The validation results using four sites of the Aerosol Robotic Network (AERONET) in Beijing showed that the value of the correlation coefficient R was 0.866, the root mean square error (RMSE) was 0.167, the mean absolute error (MAE) was 0.131, and the expected error (EE) was 53.9%. If the measurements of an AERONET site were used as prior knowledge, AOD retrieval results could be much more accurately obtained by this method (R is 0.989, RMSE is 0.052, MAE is 0.042, and EE is 96.7%).
Highlights
Aerosol optical depth (AOD) is considered an important geophysical parameter for atmospheric pollution, aerosol radiation, and atmospheric correction studies [1]
If the AOD measurements of an Aerosol Robotic Network (AERONET) site were used as prior knowledge to get optimal offset step i, and the measurements of other AERONET sites were used for validation, the AOD of the entire image could be much more accurately obtained by this method (R is 0.989, root mean square error (RMSE) is 0.052, mean absolute error (MAE) is 0.042, and expected error (EE) is 96.7%; Figure 11b)
The results showed that the AOD estimation results of the Moderate Resolution Imaging Spectroradiometer (MODIS) aerosol product were lower than the AODs retrieved from the HJ-1 A/B charge-coupled diode (CCD) data for a relatively low AOD case, with an R2 of 0.859 and an RMSE of 0.131 (Figure 14a)
Summary
Aerosol optical depth (AOD) is considered an important geophysical parameter for atmospheric pollution, aerosol radiation, and atmospheric correction studies [1]. Wang et al [12,17] and Sun et al [5,18] used the deep blue algorithm on bright surfaces such as cities, applied the MODIS surface reflectance product to establish a surface reflectance database in the blue band, obtained AOD by inversion, and conducted atmospheric correction based on the obtained AOD. These methods ignored the angular effects on the interband correlations. An improved dark target method is proposed to retrieve high-spatial resolution AODs based on interband regression coefficients that vary with the solar/view angle and land cover type
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