Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)


Plant Science


About 70% of the water that falls on the Continental United States is utilized, not as most of us would expect, by drainage into our vast rivers and lakes, but by direct evaporation from our soil surface or by transpiration from plants. It is estimated that three thousand billion gallons of water per day are returned to the atmosphere from the soil and plants in the United States. As weather modification and water management become more practical in the Great Plains Region, it is going to be more and more important and necessary for us to be able to predict rapidly and' accurately the water, nutritional, and thermal properties of soil and plants. Presently the only feasible methods for determining the physical conditions of soils and plants require ground truth observations. Determining the conditions over a large area is difficult if not impossible without large numbers of people and equipment utilizing much time and expense. With recent developments and improvements in aircraft and satellite capabilities, it is now possible to view remote sensing imagery taken from many different spectral passbands, representing large land areas. In order for imagery to be of practical importance, adequate information for analyzing and interpreting the imagery is necessary. During the growing season radiation in the infrared spectrum does not penetrate deeply into a crop canopy, therefore, imagery in this spectral/passband is imagery of the crop canopy. To properly interpret: canopy imagery, knowledge of the interaction between the crop and its environment must be known. I assert that the status of crop transpiration rate and viability, which are closely associated with soil water, nutrition, and meteorological conditions, can be determined as a function of the deviation of the crop canopy temperature from the ambient air temperature. In order to determine the manner in which the crop canopy temperature responds to meteorological conditions, a study was initiated with the following objectives: 1. Evaluate the departure of surface temperature from ambient temperature for various soil, plant, and weather conditions. 2. Test the applications of surface temperature-evapotranspiration equations against other well-known evapotranspiration equations. 3. Develop a reliable evapotranspiration equation based on the temperature of the evaporating surface.

Library of Congress Subject Headings

Plants -- Transpiration
Evaporation control
Sorghum -- Climatic factors



Number of Pages



South Dakota State University