Combining visible and infrared radiometry and lidar data to test simulations in clear and ice cloud conditions

Abstract

Abstract. Measurements taken during the 2003 Pacific THORPEX Observing System Test (P-TOST) by the MODIS Airborne Simulator (MAS), the Scanning High-resolutionInterferometer Sounder (S-HIS) and the Cloud Physics Lidar (CPL) are compared to simulations performed with a line-by-line and multiple scattering modeling methodology (LBLMS). Formerly used for infrared hyper-spectral data analysis, LBLMS has been extended to the visible and near infrared with the inclusion of surface bi-directional reflectance properties. A number of scenes are evaluated: two clear scenes, one with nadir geometry and one cross-track encompassing sun glint, and three cloudy scenes, all with nadir geometry.CPL data is used to estimate the particulate optical depth at 532 nm for the clear and cloudy scenes and cloud upper and lower boundaries. Cloud optical depth is retrieved from S-HIS infrared window radiances, and it agrees with CPL values, to within natural variability. MAS data are simulated convolving high resolution radiances. The paper discusses the results of the comparisons for the clear and cloudy cases. LBLMS clear simulations agree with MAS data to within 20% in the shortwave (SW) and near infrared (NIR) spectrum and within 2 K in the infrared (IR) range. It is shown that cloudy sky simulations using cloud parameters retrieved from IR radiances systematically underestimate the measured radiance in the SW and NIR by nearly 50%, although the IR retrieved optical thickness agree with same measured by CPL.Correspondence to: R. Rizzi (rolando.rizzi@unibo.it) MODIS radiances measured from Terra are also compared to LBLMS simulations in cloudy conditions, using retrieved cloud optical depth and effective radius from MODIS, to understand the origin for the observed discrepancies. It is shown that the simulations agree, to within natural variability, with measurements in selected MODIS SW bands.The impact of the assumed particles size distribution and vertical profile of ice content on results is evaluated. Sensitivity is much smaller than differences between measured and simulated radiances in the SW and NIR. The paper dwells on a possible explanation of these contradictory results, involving the phase function of ice particles in the shortwave.

Cloud identification and classification from high spectral resolution data in the far infrared and mid-infrared

“…Cirrus clouds properties in the tropics and at midlatitudes are mostly based on what was found by Veglio and Maestri (2011), while Antarctic cloud properties are obtained from several sources (i.e. Adhikari et al, 2012;Bromwich et al, 2012;Lachlan-Cope, 2010). In Table 1 the range of variability of some key cloud properties is reported.…”

Antarctic Ice Cloud Identification and Properties Using Downwelling Spectral Radiance From 100 to 1,400 cm−1

“…Radiative transfer computation are performed with the RTX code (Rizzi et al, ) that is an extension of the RT3 doubling and adding code introduced by Evans and Stephens (). RTX is a plane parallel, line‐by‐line multiple scattering radiative transfer algorithm used as a reference tool for faster radiative codes (Bozzo et al, ), for validation/calibration experiments (Maestri et al, ), for theoretical studies (Harries et al, ), for cloud properties studies (Bozzo et al, ), and in support of cloud properties retrievals (i.e., in Maestri et al, ).…”

Cloud identification and classification from high spectral resolution data in the far and mid infrared

“…1. The computational methodology is similar to the one described by Bozzo et al (2010) and the radiative transfer equation is solved through an adding-doubling algorithm for a plane-parallel geometry and simulating the FORUM satellite nadir view.…”