The thermal behaviour of a three-dimensional object placed in the open field

In this thesis the energy-exchange between the atmosphere and a three-dimensional obstacle, placed in the open field is studied.This problem is part of a research program carried out by the infrared group of the Physics Laboratory TNO and is mainly concerned with the discrimination of objects and backgrounds in the infrared region.After a short introduction and a definition of the problem, chapter 3.0 is dealing with the heat exchange processes involved i.e. short- and longwave radiation, conduction and convective heat exchange. It is checked to what extent existing (empirical) relations can be used for such an obstacle.Because it appeared not possible to measure all terms in the heat balance equation, a number of instruments has been developed and built and will be discussed in chapter 4.0. These instruments are:a. a sky-radiance distribution scanner ('HDS'); this instrument measures the short- and longwave radiance distribution of the sky with a spatial resolution of 15° x 15°. From these measurements the irradiance at a horizontal and vertical surface is determined.b. an elevation scanner ('ELSCA'); located on a platform this instrument measures the apparent emittance of the obstacle and the surrounding terrain.c. an infrared reflectometer; this instrument measures the infrared reflectivity of a surface in different wave length bands. Measuring time 1 minute.d. to observe the scene from the air, two airborne scanners were used, a line scanner ('FLORIS') and a scanner having a circular scan pattern ('CIRCLE'). Both are mounted in the airplane of the International Training Centre (ITC) located at Enschede.To test the instruments individually as well as in rela tion to the others, an experiment was carried out at the airfield 'De Peel', located in the province of Limburg. The results of the system performance and of the first measurements are given in chapter 5.0.Conclusions and recommendations are given in chapter 6.0.