Infra—red line scanning, a tool in engineering geology?

Abstract

1. Theoretical approach Infra red line scanning is a remote sensing technique, a non-conventional method of gathering information from an aeroplane about the earth surface and the top soil layer. To investigate the possibilities of the application of this technique in relation to Earth and Agricultural Sciences is one of the aims of the NIWARS (Interdepartmental Working community for the Applications of Remote Sensing techniques). IRLS, or “heat” images, show the distribution of radiation temperatures on the soil surface. The phenomena governing the thermal behaviour of the soil will be discussed briefly. A large number of parameters play a role in this research. This makes the empirical interpretation of the heat images a precarious task. To solve this problem a more fundamental approach is necessary. Therefore a mathematical model (RADMOD) has been constructed. This model simulates the transport processes of heat, water and vapour at both sides of the surface of a bare soil during the daily cycle. The surface temperature and water content will be found from the condition of the continuity of heat and total water flux at the soil surface. The results of some computer calculations show the sensibility of the surface temperature for several parameters, such as soil type and soil humidity. These parameters may play an important role in engineering geology in deltaic areas. Finally, objects for future research in relation to the application will be discussed. 2. Experimental approach Within 24 hours four IRLS flights were performed over certain parts of Zeeuws Vlaanderen (Holland). Simultaneously, a field experiment was executed in a pilot area. During three days meteorological and soil physical parameters were continuously registrated at both sides of the dividing line between Pleistocene sand and Holocene clay. Measuring procedures and instruments will be discussed briefly. The thermal behavior of the two soils will be compared on the basis of the measuring results. Four IRLS-images, made of the same area at different hours, will be compared. From these images conclusions will be drawn about the daily surface temperature cycle at various points in the area. These temperature cycles will be compared with measured cycles and those obtained by model simulation. Interesting phenomena in the images will be shown and their possible interpretation will be discussed and compared with local geology and soil conditions.