HR: 1330h
AN: H32B-0553    [PDF]
TI: Above-Cloud Precipitable Water Retrievals Using the MODIS 0.94 $\mu$m Band With Applications for Multi-Layer Cloud Detection
AU: * Platnick, S
EM: steven.platnick@nasa.gov
AF: NASA, Goddard Space Flight Center Code 913, Greenbelt, MD 20771 United States
AU: Wind, G
EM: wind@climate.gsfc.nasa.gov
AF: L-3 Communications GSI, 1801 McCormick Dr. #170, Largo, MD 20774 United States
AB: In order to perform satellite retrievals of cloud properties, it is important to account for the effect of the above-cloud atmosphere on the observations. The solar bands used in the operational MODIS Terra and Aqua cloud optical and microphysical algorithms (visible, NIR, and SWIR spectral windows) are primarily affected by water vapor, and to a lesser extent by well-mixed gases. For water vapor, the above-cloud column amount, or precipitable water, provides adequate information for an atmospheric correction; details of the vertical vapor distribution are not typically necessary for the level of correction required. Cloud-top pressure has a secondary effect due to pressure broadening influences. For well-mixed gases, cloud-top pressure is also required for estimates of above-cloud abundances. We present a method for obtaining above-cloud precipitable water over dark ocean surfaces using the MODIS 0.94 $\mu$m vapor absorption band. The retrieval includes an iterative procedure for establishing cloud-top temperature and pressure, and is useful for both single layer water and ice clouds. Knowledge of cloud thermodynamic phase is fundamental in retrieving cloud optical and microphysical properties. However, in cases of optically thin cirrus overlapping lower water clouds, the concept of a single unique phase is ill-defined and depends, at least, on the spectral region of interest. We will present a method for multi-layer and multi-phase cloud detection which uses above-cloud precipitable water retrievals along with several existing MODIS operational cloud products (cloud-top pressure derived from a CO2 slicing algorithm, IR and SWIR phase retrievals). Results are catagorized by whether the radiative signature in the MODIS solar bands is primarily that of a water cloud with ice cloud contamination, or visa-versa. Examples in polar and mid-latitude regions will be shown.
DE: 0320 Cloud physics and chemistry
DE: 0322 Constituent sources and sinks
DE: 0350 Pressure, density, and temperature
DE: 0394 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting