| Abstract |
The shallow ground temperature measurement surveys most commonly used to monitor for and characterise surface thermal changes are extremely time consuming, expensive, necessarily incomplete and, in some cases, impractical. Aerial thermal infrared investigations of New Zealand geothermal areas conducted from 1968 to 1975 illustrated their usefulness for identifying and locating thermal features as well as estimating heat flows. Unfortunately, these studies were not continued. The recent availability of advanced thermal IR instrumentation and powerful image processing facilities in New Zealand, and the continuing need for a comprehensive, economic geothermal surface activity monitoring technique, led to the present investigation of helicopter-borne thermal IR video scanner methods. Thermal IR imagery of several thermal areas associated with the Rotorua geothermal field was obtained with an Inframetrics 525 thermal IR video scanner mounted in a helicopter. Simultaneous visible video imagery was also obtained to assist with interpretation. Preliminary visual examination of the imagery shows that several different thermal feature types, including hot seepages, hot streams and pools and warm ground, are easily identifiable. Manmade features such as roads, cars and buildings are also clearly visible. An incorrect instrument phase adjustment produced an imagery banding problem, however, techniques for defining and correcting the data have been developed and are demonstrated. A methodology for obtaining, processing and analysing comprehensive thermal IR and visible video imagery for geothermal surface activity monitoring purposes has been developed. Use of the video data capture method avoids all the photographic processing problems and provides the ability to easily store vast quantities of data, examine it at a basic level as it is being collected and easily digitize and analyse data of specific interest using powerful computer image processing techniques. As a result of the success of this study, a comprehensive baseline survey of the surface thermal activity at Broadlands geothermal field is scheduled for late 1988. |