Bulk Scattering Properties for the Remote Sensing of Ice Clouds. Part I: Microphysical Data and Models

Abstract

This study reports on the use of in situ data obtained in midlatitude and tropical ice clouds from airborne sampling probes and balloon-borne replicators as the basis for the development of bulk scattering models for use in satellite remote sensing applications. Airborne sampling instrumentation includes the twodimensional cloud (2D-C), two-dimensional precipitation (2D-P), high-volume precipitation spectrometer (HVPS), cloud particle imager (CPI), and NCAR video ice particle sampler (VIPS) probes. Herein the development of a comprehensive set of microphysical models based on in situ measurements of particle size distributions (PSDs) is discussed. Two parameters are developed and examined: ice water content (IWC) and median mass diameter D m . Comparisons are provided between the IWC and D m values derived from in situ measurements obtained during a series of field campaigns held in the midlatitude and tropical regions and those calculated from a set of modeled ice particles used for light-scattering calculations. The ice particle types considered in this study include droxtals, hexagonal plates, solid columns, hollow columns, aggregates, and 3D bullet rosettes. It is shown that no single habit accurately replicates the derived IWC and D m values, but a mixture of habits can significantly improve the comparison of these bulk microphysical properties. In addition, the relationship between D m and the effective particle size D eff , defined as 1.5 times the ratio of ice particle volume to projected area for a given PSD, is investigated. Based on these results, a subset of microphysical models is chosen as the basis for the development of ice cloud bulk scattering models in Part II of this study.

Influence of ice particle model on satellite ice cloud retrieval: lessons learned from MODIS and POLDER cloud product comparison

“…The theoretically derived ice water content and median mass diameter based on the Baum05 mode agrees closely with the in-situ measurements. More than 1000 ice particle size distributions are used to derive not only the mean values, but also the variability of ice cloud parameters (Baum et al, 2005). The former is used to retrieve the expected cloud optical thickness and effective radius; the latter is needed for the assessment of retrieval uncertainty.…”

“…For this reason, the ice particle model has a significant influence on the retrieval. An ice particle model advanced by Baum et al (2005) (hereafter referred to as the "Baum05 model") is employed in the MODIS operational retrieval algorithm, while POLDER retrieval is based on a so-called IHM (Inhomogeneous Hexagonal Monocrystal) model . The two models are substantially different in many aspects.…”

“…Over the last two decades, several major ice cloud measurement campaigns have been carried out (Cox et al, 1987;Jensen et al, 2004;Gallagher et al, 2005). Based on the in-situ and remotely-sensed data obtained from these campaigns, a number of ice particle models have been developed and used for ice cloud retrievals (e.g., McFarquhar and Heymsfield, 1996;Baran et al, 2001;McFarquhar, 2001;McFarquhar et al, 2002;Baum et al, 2005;Baran and Labonnote, 2007). Unfortunately, as will be shown hereafter, these models generally differ substantially from one another.…”

Effects of atmospheric light scattering on spectroscopic observations of greenhouse gases from space. Part 2: Algorithm intercomparison in the GOSAT data processing for CO2 retrievals over TCCON sites

“…The four airborne particle types chosen are water cloud, ice cloud, and two different types of aerosol, corresponding to the aerosol types "2b" and "3b" of Kahn et al [2001]. The liquid water cloud has a Gamma size distribution [Hansen and Travis, 1974] of spherical drops with an effective radius of 8 mm, while the ice water cloud optical properties are taken from the model of Baum et al [2005aBaum et al [ , 2005b, assuming an effective particle radius of 70 mm. Type "2b" Kahn aerosol is a mixture of sulfate, sea salt, and course and fine-mode dust, while type "3b" Kahn aerosol is a mixture of sulfate and sea salt, and carbonaceous particles.…”

Effect of particle size distributions on the retrieval of ice cloud properties

“…For example, Mitchell [2002] reveals that neglecting shapes of crystal size distributions leads to large uncertainties in single scattering albedo (48%) and extinction efficiencies (100%). Baum et al [2005] presented significant scatters in the relation of effective diameter and single scattering properties based on hundreds of size distributions from aircraft measurements for MODIS channels. The results of these studies cast a question about the adequacy of the ad hoc choice of various measured size distributions characterized only by effective diameter in different satellite retrieval algorithms.…”