Extracting Khmer Rouge Irrigation Networks from Pre-Landsat 4 Satellite Imagery Using Vegetation Indices

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.

Critical Physical Geography and the Study of Genocide: Lessons from Cambodia

“…How large of an increase was this in comparison to pre‐Khmer Rouge Cambodian irrigation networks? What was the relative success or sustainability of these irrigation features?” (Coakley et al, 2019, p. 2). To answer these questions, we undertook a full geospatial inventory of the irrigation structures built between 1975 and 1979, an activity not previously undertaken in any study of the Cambodian Genocide.…”

“…The corpus of work we have undertaken in recent years, which provides the basis for section four here, demonstrates the important collaborative potential embedded in the discipline and inherent to geographical ways of thinking and knowing the world. Our work on the Cambodian genocide begins by assessing the materiality of human-environment relations and utilises contemporary geophysical methods and technology to empirically reconstruct how these relations have changed over time (Coakley et al, 2019;Rice & Tyner, 2017;Rice et al, 2016Rice et al, , 2020Tyner et al, 2018aTyner et al, , 2014Tyner et al, , 2018bTyner & Rice, 2016b;Tyner & Will, 2015). That this critical physical geographic work can enhance genocide studies at large further demonstrates the significant role that thinking spatially and critically can provide, and presents an ongoing example of what Castree (2012), and Barnes and Sheppard (2010) term "engaged pluralism.…”

“…Two myths in the STV narratives—both involving landscape transformations to increase rice production and therefore situated at the nexus of the relations between water, agriculture, and violence in Democratic Kampuchea—are effectively countered with our grounded critical physical geography approach. First, empirically documenting the scale and scope of Khmer Rouge irrigation schemes, and the resulting ability to classify them based on the spatial forms they took relative to the landscapes in which they were constructed, allows us to offer corrections to STV narratives (Coakley et al, 2019, pp. 18–19; Tyner et al, 2018b, pp.…”

“…From these questions and research, we documented thousands of kilometres of canals, dikes, and reservoirs built by forced labour, and developed a six‐class typology of the spatial forms that Khmer Rouge irrigation schemes took (Coakley et al, 2019, pp. 13–15; Tyner et al, 2018b, pp.…”

From Air Survey to GIS-Aided Mapping, Photogrammetry-Based 3D Modelling and the Virtual Reconstructions of Czech Lowland Crop-Marked Archaeological Sites / Od leteckého průzkumu a mapování k tvorbě digitálního výškopisného modelu a 3D virtuálních rekonstrukcí lokalit identifikovaných prostřednictvím porostových příznaků v nížinných oblastech Čech

“…Agapiou et al (2013) addressed the issue of the identifiability of vegetation marks (specifically in the Mediterranean) on a set of multi-and hyperspectral satellite data in connection with the spectral band and on the results of terrestrial spectroradiometer phenological cycle measurements (performed in 2001-2012). Attention is paid to the identifiability of archaeological sites from phenological information on satellite data (Kirk et al 2016;Agapiou et al 2012), data collection using artificial/machine intelligence or automatic classification (Davis 2020;Stott -Kristiansen -Sindbaek 2019;Luo et al 2019b), and procedures related to the visibility of defunct immovable relics (Verhoeven 2016;Agudo et al 2018;Coakley 2019;Gojda 2017). The results of the Czech project contributed to clarifying issues concerning the differences in the chemical composition of the topsoil and subsoil between features visible by the effect of vegetation marks and the surrounding (archaeologically sterile) environment, and in the height and chemical composition of barley growing above and away from sunken features of prehistoric origin.…”