As improved photogrammetric equipme

As improved photogrammetric equipment was introduced in the 1920 's and 1930 's, vertical aerial photography became the standard information source for the compilation of topographic maps. Aerial photography was used to a limited extent by geologists, foresters and planners in Europe and North America and by cartographers and geographers for small-scale geographic studies in Africa and South America. Colour film was first developed during this period, although it saw little aerial application until the Second World War. Several areas of scientific research were also initiated which would later form the foundation of modern remote sensing techniques.
World War II provided another catalyst for rapid technological development inthe field of remote sensing. Once again the acquisition of reconnaissance photography for military intelligence was the primary application. Photo interpretation techniques became highly sophisticated. One aspect of value to later coastal zone studies was the use of aerial photography inplanning amphibious assaults. The water penetration capability of aerial film, particularly colour film, made it possible to obtain reliable information on bathymetry and bottom materials when navigational charts were inaccurate or non-existent. The first colour infrared films were also developed during the war for camouflage detection. Large radar networks were erected in the 1940's to provide an early warning system for aircraft detection. Advances in radar technology permitted the development of smaller transmitting and receiving equipment appropriate for airborne use. Included in this class were plan position indicator (PPI) radars which provided an image of the terrain below the aircraft, independent of weather conditions or light availability. The PPI radar, which was used mainly for target detection during nighttime bombing missions or high altitude bombing through cloud cover, also proved useful for coastal navigation.