研究目的
To improve the retrieval of aerosol optical depth (AOD) over land by utilizing polarimetric measurements at 1640 nm, demonstrating the utility of additional 1640-nm observations for measuring AOD over land.
研究成果
The study demonstrates the capacity of 1640-nm polarized measurements to evaluate surface polarization and improve AOD retrievals over land. An average AOD error of approximately 0.03 at 865 nm is obtained, with maximum uncertainties ranging from 0.01 to 0.06. Further observations over various surface types and higher polluted conditions are needed to explore the robustness of the aerosol retrieval using additional polarized 1640-nm measurements.
研究不足
The study is limited to vegetated surfaces and clear sky conditions. The applicability to other surface types and higher polluted conditions (larger AOD) needs further investigation. The spectral neutrality hypothesis of surface reflected polarization is inapplicable to cases where the scattering angle is larger than 145°.
1：Experimental Design and Method Selection:
The study employs an improved aerosol retrieval algorithm based on the Advanced Multi-angular Polarized Radiometer (AMPR) using look-up table approaches. Spectral neutrality of the polarized surface reflectance is verified, and 1640-nm measurements corrected for atmospheric effects are used to estimate polarized surface reflectance at shorter wavelengths.
2：Sample Selection and Data Sources:
AMPR measurements over the Beijing-Tianjin-Hebei region in north China are used. Ground-based Sun-sky radiometer measurements from the Sun-sky Radiometer Observation Network (SONET) are used for validation.
3：List of Experimental Equipment and Materials:
AMPR instrument with spectral bands centered at 490, 555, 670, 865, 960, and 1640 nm. Ground-based CE318 Sun-sky radiometers for validation.
4：Experimental Procedures and Operational Workflow:
AMPR measurements are corrected for atmospheric effects to estimate polarized surface reflectance. AOD is retrieved using 670-nm and 865-nm band measurements, with 1640-nm measurements used to estimate surface reflectance.
5：Data Analysis Methods:
A cost function is defined to compare measured and calculated polarized reflectance, with AOD retrieved by minimizing this function.
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