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photos taken during the radar trials. 
The following organizations and individuals cooperated in this project: 
Minister of Agriculture, Costa Rica 
The Administration of San José Airport 
Instituto de Cartografia, San José 
Organization for Tropical Studies, San José 
Tropical Science Centre, San José 
Canadian Embassy in Costa Rica 
National Research Council 
GTW Resource Inventory Radar 
Capital Air Surveys 
Forest Management Institute 
Description of the system 
Technical details were given by Nielsen (1974) and Westby (1967 and 1975). 
The most important change incorporated after 1975 into the new prototype is the 
capability of changing, mostly during flight, the characteristics of the key factors 
influencing performance. These include transmitter pulse length, pulse integration and 
antenna beam width. ^ Also, a new capability, which provides a second profile 
corresponding to the tree tops, was added. 
Description of the experiment site 
The requirements were similar to those of the earlier experiments, i.e. the 
terrain had to be rolling and covered by typical and undisturbed virgin high tropical 
forest. The forest around the field station "La Selva" belonging to the Organization for 
Tropical Studies met these requirements. 
"La Selva", with an average rainfall of over 3500 mm, is located close to the 
junction of the rivers Sarapiqui and Puerto Viejo at 10?26'N in the Atlantic lowlands. In 
this 730 ha area 320 different tree species exist, 120 of which belong to the dominant and 
codominant canopy. The forest is very lush and the crown density very high. Two 200 by 
200 m established research plots were of particular interest because of the large amount 
of data available on them. Topography was mapped to 1 and 2 m contours, the position 
of individual trees was indicated with circles of size proportional to the tree diameters, 
and trees in the field were tagged. Figure 1 gives an impression of the conditions in the 
field. 
Two transects cutting across the test site and the two established plots were 
selected and surveyed by a local contractor. One line was about 1 km in length the other 
2.) km. A 1 m contour map was made for the longer, 120-m-wide strip. Cross profiles 
were taken at every 20 m mark on the shorter profile. 
Flight operations 
The aircraft was based at San José's International Airport, about 65 km south 
of the test area. To reach the area, the mountain range had to be crossed, which 
sometimes was difficult due to low clouds. Although it rained every day over the test 
area and there was not a single day with "photographic weather" it was possible to obtain 
good large-scale photography — including colour — on 10 out of the 16 days available for 
flying.