Technical Memorandum Report No. 8
Leonard A. Palmer
Ground water springs near the shoreline discharge a large portion of the Ghyben-Herzberg fresh water lens in the Hawaiian Islands. Conventional methods are applicable to measurement of rainfall, evaporation and runoff, but the irregular distribution and size of holes in the volcanic rock through which most Hawaiian water flows make accurate ground water flow measurements difficult (Fig. 1). More precise information on the rates of ground water losses through coastal spring discharge are important to the understanding and planning for future Hawaiian water supply. Numerous infrared sensing instruments and infrared sensitive films have recently been developed. A variety of reliable and economical methods of utilizing infrared radiation and reflection are being successfully applied to the study of rocks, plants, sea water and other material (Fischer, 1964; Gates and Tantraporn, 1952; Gates, 1959; Smith, 1956). Specifically, infrared radiation has been shown to be an effective indicator of fresh and sea water temperatures (Clark and Frank, 1963). A side result of infrared radiation studies of Hawaiian volcanoes with imaging radiometers was the detection of coastal springs ground water into the sea around the island of Hawaii. The temperature contrast between cool or warm ground water and sea water was detected showing 219 springs on the periphery of that island (Fischer et al, 1964 and 1966). (Fig. 2). Such springs have long been known to exist and were utilized even by ancient Hawaiian settlements. Many of the larger springs are easily recognized, and some have been developed for use, as in the Pearl Harbor area. However the smaller and more diffuse flows are not easily recognized. Infrared measurements potentially permit much better recording of the locations and relative strengths of the coastal springs. The imaging radiometers utilized by Fischer et all are “temperamental and difficult to operate without thorough training” and are expensive to procure and operate (Fischer, personal communication, 1966). More reliable and economical infrared sensors are available but their adaptation to Hawaiian coastal spring detection has not previously been attempted although they have been used by the U. S. Geological Survey in other areas (Brown, personal communication, 1966). A joint federal and state project funded for the year 1966-67 through the Water Resources Research Center at the University of Hawaii in part will investigate the applicability of various sensors to the measurement of thermal contrast in and around coastal ground water springs wasting into the sea (Office of Water Resources Research Project No. B-005-HI, “Geophysical Exploration for Hawaiian Ground Water”). Studies will include the examination of infrared radiation spectra at various wavelengths by films and thermistor instrumentation. Surface and underwater temperatures will be compared with radiometer measurements to determine the accuracy and water penetration of radiation sensors. From thermal radiation characteristics and their measurement, analysis will be made of the techniques for their application to coastal spring detection and to other ground water research.