Peer-Reviewed Articles
755 A Spatial Filter for the Removal of Striping
Artifacts in Digital Elevation Models
Marco Albani and Brian Klinkenberg
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Elongated topographic artifacts, such as the striping production artifacts
described for USGS 7.5-minute DEMs, can result in globally biased estimates
of slope and aspect. As such, developing methods to reduce these artifacts
and their resulting biases is important. This study presents an algorithm
for the mitigation of these artifacts, using Terrain Resource Information
Management (TRIM) digital elevation models (DEMs) of the Fort St. John Forest
District, in British Columbia, Canada, as the test bed. The algorithm uses
a theoretical error model, where elevation measurement errors are assumed
to be autocorrelated along the collection lines of the photogrammetric model,
and takes advantage of the entry order of DEM points to apply a sequence
of spatial filters to the elevation. A probability function is used to constrain
the elevation changes to an acceptable range. The algorithm is effective
in mitigating the artifacts' effects on slope and aspect while preserving
the original topographic detail.
767 A Fast Algorithm for Approximate Viewshed
Computation
David Izraelevitz
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Given a terrain model, the viewshed from a viewpoint is computed as the set
of X-Y positions of a point target such that the target is visible. We introduce
a novel approach to the computation of accurate viewshed approximations.
Our algorithm relies on the computation of an approximation to the so-called
line-of-sight (LOS) function. This function is defined over target X-Y positions,
and is the highest elevation of a target so that it is still occluded from
the viewpoint. The LOS function summarizes intervisibility information and
per- mits reuse of previous intervisibility computations, resulting in computational
efficiencies. Our algorithm gives results very close to the traditional sightline
ray method at a substantially smaller computational cost, and is a generalization
of the approach developed by Franklin and Ray for the same problem. We describe
in detail the application to gridded terrain models, but the approach is
similarly applicable to other elevation models.
775 Urban Subsidence Monitoring Using Radar
Interferometry: Algorithms and Validation
Michele Crosetto, Manuel Castillo, and Roman Arbiol
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The differential interferometric SAR (DInSAR) technique has proved its capability
to detect small surface deformations in several types of applications. In
this paper, its use as a quantitative subsidence monitoring tool is addressed
to. A complete procedure is described, giving emphasis to the algorithms
that have a major impact on the quality of the DInSAR results: the calibration
of the InSAR geometry based on ground control points, which guarantees a
high accuracy of the InSAR geometric model; a filtering procedure suitable
to reduce the atmospheric effects in small-scale subsidences; and a data
fusion procedure for multiple observations, which represents a key step to
improve the quality of the DInSAR products. The procedure was used in the
analysis of a small-scale urban subsidence located in Catalonia, northeastern
Spain. The validation of the results, which was based on the comparison with
precise and independent reference data, is discussed in detail.
785 Impact of Topographic Normalization
on Land-Cover Classification Accuracy
Stephen R. Hale and Barrett N. Rock
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For pixel classifying algorithms to perform effectively, effects of topographic
relief must be minimized or removed. In areas of high topographic relief,
problems arise when spectral variations in ground target illumination and
radiance, owing to differences in incident radiation and non-Lambertian reflectance
behavior, respectively, cause identical land-cover types to reflect differently,
or different cover types to reflect similarly. A Landsat Enhanced Thematic
Mapper image was processed using band ratios, the Minnaert Correction, aspect
partitioning, and combinations of these treatments to generate independent
land-cover classifications. Treatment classification accuracy was determined
using error matrices and the Kappa statistic. Producer's and User's Accuracies
were examined to determine if treatments were superior at producing greater
class-specific accuracy. None of the treatments produced a significantly
more accurate classification; however, assessment of class-specific accuracies
indicated accuracy gains using aspect partitioning alone or in combination
with the Minnaert Correction.
793 Land-Cover Change Monitoring with Classification
Trees Using Landsat TM and Ancillary Data
John Rogan, Jennifer Miller, Doug Stow, Janet Franklin, Lisa Levien,
and Chris Fischer
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We monitored land-cover change in San Diego County (1990-1996) using multitemporal
Landsat TM data. Change vectors of Kauth Thomas features were combined with
stable multitemporal Kauth Thomas features and a suite of ancillary variables
within a classification tree classifier. A combination of aerial photointerpretation
and field measurements yielded training and validation data. Maps of land-cover
change were generated for three hierarchical levels of change classification
of increasing detail: change vs. no-change; four classes representing broad
increase and decrease classes; and nine classes distinguishing increases
or decreases in tree canopy cover, shrub cover, and urban change. The multitemporal
Kauth Thomas (both stable and change features representing brightness, greenness,
and wetness) provided information for magnitude and direction of land-cover
change. Overall accuracies of the land-cover change maps were high (72 to
92 percent). Ancillary variables representing elevation, fire history, and
slope were most significant in mapping the most complicated level of land-cover
change, contributing 15 percent to overall accuracy. Classification trees
have not previously been used operationally with remotely sensed and ancillary
data to map land-cover change at this level of thematic detail.
805 Settlement Design, Forest Fragmentation,
and Landscape Change in Rondônia, Amazônia
Mateus Batistella, Scott Robeson, and Emilio F. Moran
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Deforestation and colonization in Amazônia have attracted substantial attention.
This article focuses on an area of 3,000 km2 within the Brazilian State of
Rondônia. Two adjacent settlements were compared to assess the role of their
different designs in landscape change. Anari was planned following an orthogonal
road network. Machadinho was designed with attention to topography in laying
out roads and farm properties, while including communal reserves. Field research
was undertaken in conjunction with multi-temporal classifications of remotely
sensed data (1988, 1994, and 1998) and landscape ecology methods. The results
indicate that large patches of communal reserves play an important role in
maintaining lower levels of fragmentation. Analyses of landscape structure
confirmed that forest patches in Machadinho are less fragmented, more complex,
and preserve more interior habitat. By comparing the effects of different settlement
designs on landscape change and forest fragmentation, this article contributes
to the debate about colonization strategies in Amazônia.
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