Microwave radiometry of snow-covered grasslands for the estimation of land-atmosphere energy and moisture fluxes.

Abstract

This thesis presents a snowpack model and experimental data that link land-atmosphere interactions and microwave emission from snow-covered terrain. Energy and moisture fluxes between terrain and atmosphere are the boundary conditions for atmospheric dynamics and composition. As both computer capabilities and the understanding of land-atmosphere interactions improve, numerical models of weather and climate are using more sophisticated soil-vegetation-atmosphere transfer (SVAT) models as boundary conditions. The goal of this research is the use of space-based microwave radiometry to verify atmosphere-SVAT model dynamics. Original results from a seven month study of terrain radiobrightness in the northern Great Plains are presented. The data include: (a) continuous ground-based observations of terrain radiobrightness at a site near Sioux Falls, South Dakota, (b) micrometeorological observations at the same site, and (c) coincident antenna temperature measurements from the Special Sensor Microwave/Imager, a space-borne radiometer. The micrometeorological data drive a SVAT model that generates a 60 day snowpack simulation including moisture and energy flux estimates. The simulated snowpack in turn drives a simulation of snowpack radiobrightness. Comparisons are made between radiometric measurements from the ground-based and space-borne instruments, and between SVAT-linked predicted brightnesses and the measurements. The conclusions are that ground-based observations of terrain radiobrightness can simulate space-based observations when the field-of-view of the space-borne instrument is homogeneous; that a SVAT-linked emission model for snowpack radiobrightness simulations is feasible; and that radiobrightness predictions from such a model can be compared with radiometric measurements to improve the land-atmosphere transfer elements of the combined model.