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UBC Theses and Dissertations

Development of a nighttime cooling model for remote sensing thermal inertia mapping Leckie, Donald Gordon


The capabilities of remote sensing can be utilized to map the thermal inertia of a surface. Thermal inertia is a property governing the temperature response of a medium to a heat flux at its surface and is beneficial to geologic mapping and soils stud ies. It is hypothesized that a method using only nighttime cooling will give a simple thermal inertia model requiring a minimum of input. Albedo and topographic slope and aspect data are not required. Since latent heat flux is commonly small at night the model should be applicable over surfaces of varying moisture content. The objective of this thesis is to develop a nighttime cooling model for remote sensing thermal inertia mapping. Three models (I, II, and III) are presented. They are based on solutions to the one-dimensional heat conduction equation for a semi-infinite homogeneous solid with isothermal initial temperature and time dependent boundary conditions of heat flux at the surface. Tests of the models on several soil types using ground based data indicate that all three models give meaningful relative relationships between thermal inertias and that model III often yields accurate quantitative results. For the remote sensing implementation of the model ground heat flux is determined as the residual of the energy balance of the surface. Thus, a procedure for determining net radiation using remotely sensed temperature is discussed. Also, aerodynamic heat transfer theory is used to develop a remote sensing method of estimating sensible heat flux. Corrections for the surface sublayer are necessary. Results for vegetated surfaces are expected to be unreliable. Latent heat flux is assumed to be zero or the average of several sites. Tests of these methods using ground based data give good results. An error analysis approach is used to estimate the errors resulting from a remote sensing implementation of Model III. Airborne thermal line-scan data and ground based micrometeorological observations are used to determine typical errors in the input parameters of the model. Errors in determining the energy balance components are also analyzed in detail. With good input, model III gives reasonable results (generally less than 50 percent probable error) at low thermal inertias (< 2000 J m⁻² C⁻¹ s⁻[sub ½] ). For surfaces of high thermal inertia, errors are large. The limitation of the model is not in the model itself, but in the accuracy of remotely sensed surface temperature as determined from thermal infrared line-scan surveys. For surfaces of low thermal inertia model III provides a simple thermal inertia mapping method which requires a minimum of input and is applicable over a wide variety of terrain and ground moisture conditions. The model is most suitable for the investigation of soils and may provide a useful model for planetary studies.

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