As aerospace detection technology evolves, limb optical detection is increasingly becoming a focal point of research, attributed to its high spatial coverage and elevated vertical resolution. Based on the SCIATRAN limb atmospheric radiation model, simulation analyses of limb radiation transmission characteristics in the middle and upper atmosphere were conducted for both clear and cloudy conditions in the visible to near-infrared spectrum. The study results indicate that observational tangent height and solar zenith angle are important parameters affecting limb radiation brightness in the middle and upper atmosphere, with limb radiation brightness showing a decreasing trend as tangent height increases; in the visible light spectrum, it gradually weakens with increasing solar zenith angle, but in the near-infrared spectrum, it first decreases and then increases. The presence of aerosols and cirrus clouds significantly affects the mid-to-high altitude atmospheric limb radiation brightness. Under stratospheric aerosol conditions, radiation brightness can increase up to 2744.31% compared to background conditions, and under cirrus clouds with an optical thickness of 1, the increase in radiation brightness can be up to 13.78 times compared to clear sky conditions. The study delves into and analyzes the impact of particle optical properties on limb atmospheric background radiation, offering theoretical and data foundations for comprehending its spectral characteristics and designing limb detectors.
The total atmospheric transmittance of the South China Sea was measured using a Fourier Transform Infrared Spectroradiometer. After measuring the direct solar spectrum data in 1.1-2μm using the Spectroradiometer, the Langley method was employed to extract the atmospheric spectral transmittance of the South China Sea. The Langley method was utilized to extract atmospheric spectral transmittance at different altitudes and angles, and the variation in atmospheric transmittance over the South China Sea was analyzed extensively. The Combined Atmospheric Radiative Transfer (CART) model was used on the above data, to simulate the atmospheric transmittance under similar circumstances and draw a comparison with the previously obtained results. The data obtained from the Spectroradiometer indicates that the slant path atmospheric transmittance is in coherence with the model simulation results, with a negligible absolute error of less than 2.3%. Furthermore, as the solar zenith angle increases, there is a gradual decrease in the transmittance of the entire measurement band. The short-wave atmosphere attenuates rapidly; however, the long-wave attenuation is slow.
Aerosol optical depth (AOD) is one of the basic parameters used to analyze physical properties of regional aerosols, but the in-situ observation or remote sensing AOD dataset could be scarce especially in ocean area. The Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA-2) reanalysis has the longest temporal span, and its accuracy in China sea area is to be evaluated. This study provides a validation of MERRA-2 AOD products’ applicability in the eastern and southern China sea based on Aerosol Robotic Network (AERONET). The results indicated that the MERRA-2 AOD with 1-hour temporal resolution agreed with the time averaged AERONET AOD well, for its correlation coefficient is 0.887, root mean square error (RMSE) is 0.096, and mean absolute error (MAE) is 0.056. Presented analysis also revealed a systematic underestimation of AOD that MERRA-2 made, and that deviation tended to increase in higher AOD which demonstrated a slope of -0.26 when utilized linear fitting technics, but the mean bias (MB) of test dataset was only -0.001 because the AOD concentrated on lower than 0.2. These results illustrated the suitability of using MERRA-2 AOD product in aerosol researches of the China sea area.
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