A Simple Empirical Equation to Calculate Cloud Optical Thickness Using Shortwave Broadband Measurements

Abstract

In this paper, an empirical equation is presented that can be used to estimate shortwave cloud optical thickness from measurements and analysis of shortwave broadband irradiances. When applied to a time series of broadband observations, this method can predict cloud optical thickness distributions that are very similar to those obtained using the algorithm of Min and Harrison (henceforth the Min algorithm). For a given site, medians of the Min algorithm-derived and empirically derived distributions differ by less than 10%. This level of agreement holds over a wide geographical range of sites. The equation is designed for fully overcast skies, surface albedos less than 0.3, and a cosine of the solar zenith angle greater than 0.15.

A Focus On Mixed-Phase Clouds

“…3e and 4g) in addition to the vertical integrals of the extinction retrievals. Broadband SW irradiance measurements provide an estimated effective layer optical depth via an empirical expression that incorporates information on sun angle, surface albedo, an equivalent clear-sky SW irradiance, and an assumed asymmetry parameter (Barnard and Long 2004). In this case, it is assumed that all SW obscuration is solely due to the cloud liquid.…”

Wavelength dependence of the effective cloud optical depth

“…The use of radiative transfer models is of great interest, as it allows us to obtain values where no experimental data are available and to get the possibility of modelling the atmosphere under various conditions (Barnard and Long, 2004;Mateos et al, 2011). Existing radiative transfer models propose different approaches to solve the radiative transfer equation.…”

“…Therefore, one-dimensional radiative transfer simulations with SBDART (Santa Barbara Disort Atmospheric Radiative Transfer) model on the version 2.4 (Ricchiazzi et al, 1998) and LibRadtran (Library for Radiative Transfer) model, version 1.7 (Mayer and Kylling, 2005) are used to explain the observations. This approach is a practical way of dealing with non-homogeneous clouds and it was used in other studies such as , Min and Harrison (1996), Barker et al (1998), Barnard and Long (2004), Binyamin et al (2010), Antón et al (2012), Serrano et al (2014) and amongst others. Therefore, the obtained results refer to statistics of effective cloud optical depth and the term "effective"…”

Estimation of photosynthetically available radiation (PAR) from OCEANSAT-I OCM using a simple atmospheric radiative transfer model

“…From the previous literature it was evident that, COD was estimated from the transmitted radiance data by ground-based observations at 415 nm, 440 nm, 675 nm, 870 nm wavelength (Min and Harrison, 1996;Barnard and Long, 2004;Chiu et al, 2010). To estimate COD from space based observation, reflectance at 443 nm , 645 nm, 670 nm, 750 nm, 858 nm, 865 nm and 1.24 lm over earth surface features were used for different sensors (MODIS, MERIS, POLDER) using various approaches (Nakajima and King, 1990;Fischer et al, 2000;Parol et al, 2000).…”