Research on the Influence of Aerosol Optical Thickness Distribution on Apparent Brightness Contrast Under Vertical Non-Uniformity

The vertical non-uniform distribution of aerosol optical thickness is a core element in regulating atmospheric radiative transmission and influencing the apparent brightness contrast between the target and background. However, current research mainly focuses on the macroscopic effects of the aerosol optical thickness, and the mechanism by which vertical variations in aerosol distribution regulate apparent brightness contrast remains inadequately understood. Therefore, in this study, a layered superposition aerosol model is established using extinction coefficient profiles from ground-based lidar observations with an ideal Gaussian or rectangular aerosol layer. An apparent brightness contrast model is then developed using the SBDART radiative transfer model. The influences of center height, vertical width, and peak intensity on contrast are analyzed, and their effects are quantified using maximum contrast and slant visibility. The results show that the closer the aerosol layer center height is to the observation height, the larger the vertical width, or the stronger the peak intensity, the faster the visual contrast decays with vertical distance. The influence of center height is the most significant, with slant visibility variations for Gaussian and rectangular distributions reaching up to 164.9% and 187.3%, respectively. The influence of vertical width gradually saturates as the width increases, while the influence of peak intensity is the weakest, with almost no effect on near-range contrast. Moreover, the regulatory characteristics of the Gaussian and rectangular distributions are distinctly different: the rectangular distribution exhibits a stronger local step effect, whereas the influence of the Gaussian distribution is more global and persistent.