Peer-Reviewed Articles
1245 Recognition of Fiducial Surfaces in Lidar Surveys of Coastal Topography
John C. Brock, Asbury H. Sallenger, William B. Krabill, Robert
N.
Swift, and C. Wayne Wright
Abstract
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A new method for the recognition and mapping of surfaces in coastal
landscapes that provide accurate and low variability topographic
measurements with respect to airborne lidar surveys is described
and demonstrated in this paper. Such surfaces are herein termed "fiducial" because
they can represent reference baseline morphology in studies of coastal
change due to natural or anthropogenic causes. Non-fiducial surfaces
may also be identified in each separate lidar survey to be used in
a given geomorphic change analysis. Sites that are non-fiducial in
either or both lidar surveys that bracket the time period under investigation
may be excluded from consideration in subsequent calculations of
survey-to-survey elevation differences to eliminate spurious indications
of landscape change. This new analysis method, or lidar fiducial
surface recognition (LFSR ) algorithm, is intended to more fully
enable the non-ambiguous use of topographic lidar in a range of coastal
investigations. The LFSR algorithm may be widely applied, because
it is based solely on the information inherent in the USGS/NASA/NOAA airborne
topographic lidar coverage
that exists for most of the contiguous U.S. coastline.
1261 Land Subsidence Monitoring with Differential SAR Interferometry
Tazio Strozzi, Urs Wegmüller, Luigi Tosi, Gabriele Bitelli,
and Volker Spreckels
Abstract
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The potential of differential SAR interferometry for land subsidence
monitoring is reported on. The principle of the technique and the
approach to be used on a specific case are first presented. Then
significant results using SAR data from the ERS satellites for various
sites in Germany, Mexico, and Italy, representing fast (m/year) to
slow (mm/year) deformation velocities, are discussed. The SAR interferometric
displacement maps are validated with available leveling data. The
accuracy of the subsidence maps produced, the huge SAR data archive
starting in 1991, the expected continued availability of SAR data,
and the maturity of the required processing techniques lead to the
conclusion that differential SAR interferometry is suitable
for operational monitoring of land subsidence.
1271 Remote Sensing of Clear-Water, Shallow, Gravel-Bed Rivers Using
Digital Photogrammetry
Richard M. Westaway, Stuart N. Lane, and D. Murray Hicks
Abstract
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The digital elevation model (DEM) quality that can be obtained from
a digital photogrammetric survey of a reach of the clear water, shallow,
gravel-bed North Ashburton River, New Zealand is assessed. An automated
correction procedure is used to deal with point errors associated
with submerged topography, based on a correction for refraction at
an air-water interface. The effects of collection parameter variation
upon DEM quality are also considered. The accuracy and precision
of DEMs of submerged topography are evaluated using an independent
data set.
Results show that digital photogrammetry, if used in conjunction with image
analysis techniques, can successfully be used to extract high-resolution DEMs
of gravel riverbeds, but that the quality of submerged topographic representation
is heavily dependent upon the water depth at the time of image acquisition.
It is suggested that differences between the digital photogrammetric surface
and the "actual" riverbed surface (as determined by terrestrial ground survey)
will, in part, reflect the problem of defining what is the true elevation of
a gravel-covered surface. A digital photogrammetric survey will generally see
the tops of gravel cobbles, while a hand-held survey staff will tend to record
the elevation between stones. The nomenclature of errors is also discussed,
and it is concluded that the measure of surface quality adopted should be consistent
with the application for which the DEM
is to be used.
1283 Robust Surface Matching for Automated Detection of Local Deformations
Using Least-Median-of-Squares Estimator
Zhilin Li, Zhu Xu, Minyi Cen, and Xiaoli Ding
Abstract
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Automated detection of the local deformation of a surface involves
the detection of the differences between an original and a deformed
digital surface model without the aid of control points. The process
is normally automated by matching two digital surface models. This
technique is desirable for many industrial applications.
With the existence of local deformation, conventional surface matching algorithms
with least-squares conditions will fail because the estimated parameters are
influenced by local deformation. As a result, some robust estimators can be
applied to robustify surface matching algorithms. In addition to a re-evaluation
of the performance of the M-estimator, two other robust estimators-the GM-estimator
and the LMS-estimator (least median of squares)-have been explored in this
study for the purpose of detecting local deformation. Test results show that
the LMS-estimator is superior to both the M-estimator and the GM-estimator
for detecting local deformation in three respects: (1) it is not sensitive
to the location of local deformation; (2) the largest tolerable deformation
percentage is improved to a level of almost 50 percent; and (3) when the deformation
percentage is less than 40 percent, deformations of very small magnitude can
be detected. It has also been found that the largest tolerable deformation
percentage is related to the magnitude of the deformation.
1293 An Accuracy Assessment of Various GIS-Based Viewshed Delineation
Techniques
Mark A. Maloy and Denis J. Dean
Abstract
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Actual viewsheds from 11 viewpoints were field surveyed and compared
to predicted viewsheds generated using various commonly used elevation
data sets, various data models, and various visibility criteria.
It was found that some data sets produced predicted viewsheds that
mimicked surveyed viewshed much more accurately than other data sets,
and that some combinations of data models and visibility criteria
produced much greater matching accuracies than other combinations.
However, none of the combinations of data source, data model, and
visibility criteria produced predicted viewsheds that matched surveyed
viewsheds with much more than 50 percent accuracy. Some possible
reasons for this lack of accuracy are proposed.
1299 An Airborne Direct Digital Imaging System
Don Light
Abstract
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Solid state digital cameras are finding their place in the aerial imaging
market; a market heretofore dominated by film mapping cameras. Emerge
teamed with Landcare Aviation, Inc., has eight Cessna 172 aircraft
equipped with state-of-the-art digital cameras, dual-channel Global
Positioning Systems (GPS) receivers, and inertial measurement units
(IMU). This trio of sensors collects imagery with position and attitude
data that permits geopositioning of each frame without the use of
ground surveyed control points. Also, two Piper Aztec aircraft are
available
where flying above 10,000 feet is required. The cameras are Kodak DCS 460 frame
cameras with a CCD array of 3072 by 2048 pixels in each frame. The cameras
collect either natural color or color infrared imagery, depending on the filter
used. The output products are 1-, 2-, or 3-foot ground sampled distance (GSD)
orthorectified frames or mosaics on CD-ROM, photo paper, or transparencies.
Applications for the imagery are in agriculture, forestry, geology, water resources,
floods and disaster assessment, and pollution detection, as well as orthorectified
image maps for a variety of land-use planning activities. The collection system
and its technology are highlighted in order to describe today's airborne direct
digital imaging technology.
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