Thesis (Ph. D.)--University of Melbourne, 1983. / Includes bibliographical references (leaves 297-311).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1964. / Typescript. Vita. Description based on print version record. Includes bibliographical references (leaves 65-68).

A system for the energy balance/Bowen ratio measurement of evaporation was designed and tested. The system produces eight channels of integrated meteorological data for evaporation calculation. The various voltages required to operate the meteorological sensors are produced internally by a bank of regulated power supplies. Control signals are generated by a quartz crystal -clock. The data in a selected channel and the time of day are displayed on the front panel of the data logger. All eight channels of data and the time are printed on a paper tape every 15 or 30 minutes as desired. The output circuitry was designed to be compatible with microprocessor components. The data logger is contained in a 60 cm x 50 cm x 40 cm metal cabinet and is powered by 110 VAC. The laboratory and field tests of the system were successful. / Land and Food Systems, Faculty of / Graduate

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In the arid southwestern United States, where water is a limiting factor in agricultural and industrial development, a sizeable portion of the annual precipitation may be lost through evapotranspiration. In Arizona such losses account for approximately 95 per cent of the annual precipitation. Tamarisk (Tamarix pentandra Pall.) is estimated to occupy over one million acres of the flood plains and streambanks in the southwest. Although reported to use a large quantity of water, accurate estimates of evapotranspiration are unknown. Evapotranspiration processes are complex and depend on many interrelationships of the soil-plantatmosphere system. Although, water use by tamarisk has been intensively studied, evapotranspiration measurements under different climatic and hydrologic conditions are not available. The evapotranspiration tent was selected to measure evapotranspiration rates of tamarisk under varying climatic and hydrologic conditions. Intensive investigations of the enclosure effect of the tent were performed. Modifications of the tent reduced serious enclosure effects of the original tent. Evapotranspiration rates measured by the tent agreed favorably with rates computed by Penman's equation. Evapotranspiration rates for an area where the water table depth was approximately 20-feet was greater than an area where the Water table depth was 14-feet. This deviation, which may be attributed to salinity, led to a laboratory investigation of the effects of salinity on transpiration rates of tainarisk. An intensive laboratory study was conducted to determine the effect of salinity on transpiration rates of tamarisk at different vapor pressure deficits. Results indicated that the effect of salinity is dependent on vapor pressure deficit. Transpiration rates were linearily related to vapor pressure deficits at low salinity levels, but a curvilinear relationship was obtained at high salinity levels. An estimate of saturation deficit of the mesophyll cells was determined by extrapolation of transpiration and vapor pressure deficit relationships. These data indicate minimial increases in salt concentrations in the stomatal cavities as indicated by small increases in the mesophyll saturation deficits as the salinity of the root substrate was increased. Root permeability tests were conducted on plants subjects to varying salinity and vapor pressure deficit levels. Results indicated a significant reduction only at the highest salinity and vapor pressure deficit levels.

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The research described in this dissertation is predicated on the hypothesis that remotely sensed information from climatological satellites can be used to estimate the actual evapotranspiration from agricultural crops to improve irrigation scheduling and water use efficiency. The goal of the enabling research program described here was to facilitate and demonstrate the potential use of satellite data for the rapid and routine estimation of water use by irrigated crops in the Yaqui Valley irrigation scheme, an extensive irrigated area in Sonora, Mexico. The approach taken was first, to measure and model the evapotranspiration and crop factors for wheat and cotton, the most common irrigated crops in the Yaqui Valley scheme. Second, to develop and test a high-resolution (4 km x 4 km) method for determining cloud cover and solar radiation from GOES satellite data. Then third, to demonstrate the application of satellite data to calculate the actual evaporation for sample crops in the Yaqui Valley scheme by combining estimates of potential rate with relevant crop factors and information on crop management. Results show that it is feasible to provide routine estimates of evaporation for the most common crops in the Yaqui Valley irrigation scheme from satellite data. Accordingly, a system to provide such estimates has been established and the Water Users Association, the entity responsible for water distribution in Yaqui Valley, can now use them to decide whether specific fields need irrigation. A Web site (tekapucemitson. mx) is also being created which will allow individual farmers to have direct access to the evaporation estimates via the Internet.

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