Abstract
Often discussed, the spatial extent and scope of the Khmer Rouge irrigation network has not been previously mapped on a national scale. Although low resolution, early Landsat images can identify water features accurately when using vegetation indices. We discuss the methods involved in mapping historic irrigation on a national scale, as well as comparing the performance of several vegetation indices at irrigation detection. Irrigation was a critical component of the Communist Part of Kampuchea (CPK)’s plan to transform Cambodia into an ideal communist society, aimed at providing surplus for the nation by tripling rice production. Of the three indices used, normalized difference, corrected transformed, and Thiam’s transformed vegetation indexes, (NDVI, CTVI, and TTVI respectively), the CTVI provided the clearest images of water storage and transport. This method for identifying anthropogenic water features proved highly accurate, despite low spatial resolution. We were successful in locating and identifying both water storage and irrigation canals from the time that the CPK regime was in power. In many areas these canals and reservoirs are no longer visible, even with high resolution modern satellites. Most of the structures built at this time experienced some collapse, either during the CPK regime or soon after, however many have been rehabilitated and are still in use, in at least a partial capacity.
Highlights
It is well established that Landsat and other remotely sensed imagery can be used to study land use change [1,2], agriculture [3], the impacts of climate change [4], and many other physical characteristics of the Earth’s surface
The goal of this research was to determine the nature, extent, and relative success of all irrigation features built through forced labor during the Khmer Rouge regime, which existed in Cambodia from 1975 to 1979
Pol Pot, the leader of the Communist Part of Kampuchea (CPK), envisioned a canal network arranged in 10-km grids, each with smaller 1 × 1 km canal grids nested inside them (Figure 1a,b) and each again with 100 m × 100 m grids nested inside them
Summary
It is well established that Landsat and other remotely sensed imagery can be used to study land use change [1,2], agriculture [3], the impacts of climate change [4], and many other physical characteristics of the Earth’s surface. Landsats 1–3 differ from more recent satellites in spatial, spectral, and temporal resolution, as well as data quality and bit depth [9,10] This presents challenges for remote sensing applications, the data from earlier Landsats are still useful for many analyses and should not be overlooked. The goal of this research was to determine the nature, extent, and relative success of all irrigation features built through forced labor during the Khmer Rouge regime, which existed in Cambodia from 1975 to 1979. By comparing the early and later imagery we identified the water features that were built during the Khmer Rouge period. Many of the smaller canal networks cannot be detected in existing satellite imagery, indicating that this tally is certainly an undercount of the features that were built at the time
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