Automated identification of tile lines from remotely sensed data

American Society of Agricultural and Biological Engineers ISSN 01/2008; 51:1937-1950.

ABSTRACT Although subsurface drainage provides many agronomic and environmental benefits, extensive subsurface drainage systems have important implications for surface water quality and hydrology. Due to limited information on subsurface drainage extent, it is difficult to understand the hydrology of intensively tile‐drained watersheds. In order to address this problem, a methodology was developed to use image processing techniques for automated detection of tile drains from multiple dates of aerial photography at the Agronomy Center for Research and Education (ACRE), West Lafayette, Indiana. A stepwise approach was adopted to first identify potential tile‐drained fields from the GIS‐based analysis of land use class, soil drainage class, and surface slope using decision tree classification. Based on preliminary classification of potential tile‐drained area from the decision tree classifier, a combination of image processing techniques such as directional edge enhancement filtering, density slice classification, Hough transformation, and automatic vectorization were used to identify individual tile lines from images of 1976, 1998, and 2002. Accuracy assessment of the predicted tile line maps (Hough transformed and untransformed) was accomplished by comparing the locations of predicted tile lines with the known tile lines mapped through manual digitization from historic design diagrams using both a confusion matrix approach and drainage density. Forty‐eight percent of tile lines were correctly predicted for the Hough transformed map and 58% for the untransformed map based on the producer accuracy. Similarly, 73% of non‐tile area was correctly predicted for Hough transformed and 68% for untransformed lines. Based on drainage density calculation, 60% of tile lines were predicted from the aerial image of 1976 and 50% from the aerial image of 2002 for both techniques, while 72% of tile lines were predicted from the aerial image of 1998 for untransformed and 50% for Hough transformed lines. The Hough transformation provided the best results in producing a map without discontinuity between lines. The overall performance of the image processing techniques used in this study shows that these techniques can be successfully applied to identify tile lines from aerial photographs over a large area. Keywords. Aerial photography, Decision tree, Edge detection, Hough transformation, Tile lines. n the Midwestern U.S., the main purpose of subsurface drainage systems is to control waterlogging in agricul‐ tural fields by installing a series of drainage pipes below the soil surface. Traditionally, subsurface drainage pipes were made from ceramic clay tiles; later, clay tiles were replaced with corrugated polyvinyl chloride (PVC) tubes, generally still referred to as tile lines. Tile lines can be installed at different spacings and depths depending on physi‐ cal properties of the soil, crop type, and climate condition (Varner et al., 2002). Typically, subsurface drainage pipes are placed at a depth of 70 to 130 cm and at a spacing of 6 to 244m (Zucker and Brown, 1998). To reduce cost, earlier systems were more likely to target specific wet spots in the fields. However, with improved mechanization, more uniform pat‐ terns of installation have increased. Lateral lines are usually installed on higher elevations and connected with the main tile lines at low elevations in the field. This network of sub‐ surface drainage empties either into an open ditch or stream.

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    ABSTRACT: Detailed location maps of tile drains in the Midwestern United States are generally not available, as the tile lines in these areas were laid more than 75 years ago. The objective of this study is to map individual tile drains and estimate drain spacing using a combination of GIS-based analysis of land cover, soil and topography data, and analysis of high resolution aerial photographs to within the Hoagland watershed in west-central Indiana. A decision tree classifier model was used to classify the watershed into potentially drained and undrained areas using land cover, soil drainage class, and surface slope data sets. After masking out the potential undrained areas from the aerial image, image processing techniques such as the first-difference horizontal and vertical edge enhance filters, and density slice classification were used to create a detailed tile location map of the watershed. Drain spacings in different parts of the watershed were estimated from the watershed tile line map. The decision tree identified 79% of the watershed as potential tile drained area while the image processing techniques predicted artificial subsurface drainage in approximately 50% of the Hoagland watershed. Drain spacing inferred from classified aerial image vary between 17 and 80 m. Comparison of estimated tile drained areas from aerial image analysis shows a close agreement with estimated tile drained areas from previous studies (50% versus 46% drained area) which were based on GIS analysis and National Resource Inventory survey. Due to lack of sufficient field data, the results from this analysis could not be validated with observed tile line locations. In general, the techniques used for mapping tile lines gave reasonable results and are useful to detect drainage extent from aerial image in large areas. These techniques, however, do not yield precise maps of the systems for individual fields and may not accurately estimate the extent of tile drainage in the presence of crop residue in agricultural fields and/or existence of other spatial features with similar spectral response as tile drains.
    Agricultural Water Management. 01/2009;


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