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Under the Colombo Plan, in the early 1960s, Canadian surveyors used aerial photography to produce detailed and widely used topographic maps of the Lower Mekong Basin. Much of the original film is still held at the MRC. Also available for that time period are the now de-classified American CORONA satellite images; they are available over the internet. Both sources can serve as useful historic documents for environmental study. However, in many cases the 1:50,000 topographic maps derived from the aerial photographs are out-of-date as there have been many changes to roads, settlements and land cover in the last 40 years. Other satellite imagery, notably Landsat images, have only been available since 1972, when the first satellite in that series was launched. The acquisition of aerial photography is a fairly expensive proposition, particularly when large areas have to be covered for detailed mapping. Hence, coverage is intermittent and infrequent throughout the Mekong Basin. Today, commercial Earth observation satellites with a spatial resolution of 1 metre or less are providing a viable alternative to aerial photography.
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