The Anglo-Netherlands Norwegian Collaboration Project (1959 – 1970)
In 1959, the Anglo-Netherlands-Norwegian Collaboration Project (ANNCP) was established within NATO.
The collaborative project ANCP I-11 “low-level air reconnaissance” was a collaboration between the British Royal Radar Establishment (RRE) and the TNO Defence Research Physics Laboratory. In January and February 1960, mutual visits were made. TNO learned for the first time about the side-looking radar concept.
In the UK, two side-looking airborne radar (SLAR) systems were developed at EMI and RRE for the TSR-2 fighter. The TSR-2 fighter was a UK development that was later dropped. One radar system (3 cm) was intended for navigation and one for reconnaissance (8 mm).
A SLAR system for navigation means that the opponent does not immediately see you coming. The images from an SLAR are also much easier to interpret because they have a much higher signal/noise ratio (SNR) due to the much higher number of hits per scan (pulses per observation). This provides a significantly better image than with a rotating scanning radar. The image became available to the navigator directly on film with the help of a fast processor. He was then able to compare the image with a ‘stripe map’ of the overflown area. He did that verification at fixed distances and for a short time. This would make the aircraft less detectable. The 8 mm radar was housed in a pod under the aircraft together with a Thermal Infrared system (TIR). This pod was later offered to NATO by the UK (‘P391 system’).
The British were very interested in the TNO radar observations at low altitudes. It was agreed that the RRE would be able to use Dutch official low-flight routes for flights of interest to both countries with their experimental aircraft, which contained both radar systems. The Netherlands is very flat, which makes flying very low possible. For example, on 8 and 10 November 1960 the first flights with 8 mm SLAR took place over the province of Zeeland and the major rivers (Exercise Buzzard). The flight of November 8 had to do with rough weather, which meant that the results on film were not in a straight line at many places. The fixed antenna could not compensate for the movements of the aircraft, as can be seen in the images of Goes and the Oosterschelde with the Galgeplaat and Vondelingeplaat (areas of no-show) below. The waters are cluttering up and were interpreted as ‘land’ by the RRE. The flight was repeated with good results under better weather conditions on November 10.
Parallel to this, thermal imaging equipment was also developed at the Physics Laboratory. In the early fifties equipment with pneumatic detectors (the Golay detector) and later with indium antimonide detectors. In 1966 the first TNO infrared scanner flew with the Royal Netherlands Navy.
At the end of the fifties, the first contacts with employees of the International Institute for Aerial Mapping and Geography (ITC) had been established. These contacts were initially entirely informal and ad hoc. Then there was a discussion about the respective fields. At the ITC, the photogrammetrists regarded conventional radar images as aerial photographs taken with a camera with a very short focal length (1 mm and smaller). TNO also experimented with stereo recordings. On the TV towers, you could get a base of 12.5 m and on the roof of the Physics laboratory, a base of 50 m was possible. It was not a resounding success, but it did broaden the understanding of the ITC and TNO: what radar can and does for the ITC. For the TNO researchers, the insight was that you can observe the earth’s surface with it. The latter has civil as well as military applications.
In parallel, the Physics Laboratory worked on developing thermal imaging equipment: in the early fifties, equipment with pneumatic detectors (the Golay detector) and later with indium-antimonite detectors. In 1966, the first TNO infrared scanner flew with the Royal Netherlands Navy.
For example, in the early 1960s, both a SLAR and a thermal imaging camera were available to the RRE for conducting tests over the Netherlands. At that time, these were still pure image production machines. The images provided nice, but physically completely uncontrolled, images on photographic material. However, they weren’t photos.
It should be noted that at that time there were no computers involved in image interpretation.
How to use the recorded images Like everyone who starts with Remote Sensing, we also thought that it was only a matter of good image interpretation. That is why we at TNO sought cooperation with others who were better at it: the ITC. One problem was that the images were classified. Around 1962 the cooperation with the ITC was formalised despite this hurdle. A small group of ITC employees was allowed to study the classified footage. This also allowed the ITC to develop new ideas, which resulted in Remote Sensing research in Limburg, Saeftinge (radar) and the Alblasserwaard (TIR).
In July 1962, the ANCP exercise Humming Bee followed in which Q-band SLAR was tested at a low flying height of 300 to 500 ft.
To make the currents and salt marshes of Zeeland visible, a higher gain setting of the SLAR equipment was required. That is why Zeeland was flown twice (scale 1:50,000). The currents were clearly visible as rubbish, the mudbanks did not show. A series of points on the images turned out to be poles (with a diameter on the order of the radar wavelength) used to mark oyster beds.
In October, a very high altitude SLAR flight (approximately 40,000 ft) using the official air corridors followed to compare SLAR with photogrammetry. Analysis showed that SLAR enables small-scale mapping for inventory purposes (landforms and soil properties).
Finally, there was also a collaboration with the Institute for Sensory Physiology TNO (IZF) in Soesterberg. The investigation then went in different directions. First of all, we worked on getting familiar with the newly recorded images. This happened at the ITC. In addition, means were sought to properly define the images physically. For example, the IZF investigated the influence of blur and noise. That project was called “photo-interpreter performance“.
The RRE was able to provide large groups of photo interpreters for the experiments set up by the IZF in close collaboration with photo interpreters from the School Military Intelligence (SMID). In this research, the aspect of good physical image definition was essential.
Television was also busy opening up new possibilities in this area. The ITC, therefore, worked on the use of the modulation transfer function. Currently; a standard technique, but in the early sixties still absolutely new and unknown. The results of the research on “photo-interpreter performance” were concluded with publications in Photogrammetric Engineering . One result was that blur in an image is worse than noise. A result that sparked a whole discussion with the TV people who had found the opposite. The results both turned out to be true: TNO worked with still images (photos) and the TV world with moving images.
In addition to SLAR, several TIR flights were also performed above the Alblasserwaard. This was done in 1966 by the RRE and in 1968 by the Royal Netherlands Navy with the TIR scanner of the Physics Laboratory.
Dr.rr. G.P. de Loor gave a lecture on 7 June 1988 on the occasion of the 10th anniversary of the “Kring voor Remote Sensing” on 17 August 2009. He wrote down the basis for this text. His lecture also appeared in an interim version in the Remote Sensing Newsletter no.95 of December 2000 at the closing of the NRSP.
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