Peer-Reviewed Articles
573 Potential for Calibrating Airborne Video Imagery Using
Preflight Calibration Coefficients
A. Edirisinghe, J.P. Louis, and G.E. Chapman
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The low-cost Multispectral Airborne Video System (MAVS), developed using off-the-shelf
components, is predominantly being used for agricultural and environmental
monitoring applications in Australia. In order to guarantee quality of operational
imagery, regular radiometric calibration checks, under both preflight and
in-flight environments, are a necessity. While preflight calibration is conducted
in the field with relative ease, to conduct in-flight calibration checks
during operational missions is difficult, especially when onboard calibration
instrumentation is not available. The calibration of MAVS imagery in flight
requires a radiative transfer code such as the 6S to simulate the radiation
signal at the operational altitude. A comparison of the simulated in-flight
calibration equation with the corresponding preflight calibration equation
showed a statistically significant agreement for every MAVS band, demonstrating
the stability of response of the instrument in the air. This MAVS response
stability indicates a potential for calibrating operational airborne imagery
using preflight calibration equations. A few simulated in-flight calibration
checks, in addition to regular preflight calibrations, could still be carried
out during the flight season to verify system radiometric response in the
air.
581 Assessment of Bidirectional Effects over Aquatic
Macrophyte Vegetation in CIR Aerial Photographs
Kirsi Valta-Hulkkonen, Petri Pellikka, and Jouni Peltoniemi
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Radiometric effects hamper the use of airborne remote sensing data for quantitative
studies of biophysical environments. The effect of bidirectional reflectance
is evaluated in four areal samples from three lakes in the Vuoksi drainage
basin in Finland. It is shown statistically that the relationship between
measured upwelling radiation and the sun-target-sensor geometry is weak for
an aquatic macrophyte species, the common reed (Phragmites australis), but
strong for birch (Betula pubescens) and mixed birch-spruce (Picea abies)
forest. The density and phenotype of the common reed vegetation seem to have
an effect on the strength of the bidirectional reflectance in the images.
When the effect of bidirectional reflectance over common reed vegetation
is statistically significant, an empirical normalization method can be used,
after which the brightness of the test areas is no longer statistically dependent
on the sun-target-sensor geometry.
589 Seeing the Trees in the Forest: Using Lidar
and Multispectral Data Fusion with Local Filtering and Variable Window Size
for Estimating Tree Height
Sorin C. Popescu and Randolph H. Wynne
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The main study objective was to develop robust processin and analysis techniques
to facilitate the use of small-footprint lidar data for estimating plot-level
tree height by measuring individual trees identifiable on the three-dimensional
lidar surface. Lidar processing techniques included data fusion with multispectral
optical data and local filtering with both square and circular windows of
variable size. The lidar system used for this study produced an average footprint
of 0.65 m and an average distance between laser shots of 0.7 m. The lidar
data set was acquired over deciduous and coniferous stands with settings
typical of the southeastern United States. The lidar-derived tree measurements
were used with regression models and cross-validation to estimate tree height
on 0.017-ha plots. For the pine plots, lidar measurements explained 97 percent
of the variance associated with the mean height of dominant trees. For deciduous
plots, regression models explained 79 percent of the mean height variance
for dominant trees. Filtering for local maximum with circular windows gave
better fitting models for pines, while for deciduous trees, filtering with
square windows provided a slightly better model fit. Using lidar and optical
data fusion to differentiate between forest types provided better results
for estimating average plot height for pines. Estimating tree height for
deciduous plots gave superior results without calibrating the search window
size based on forest type.
605 A Complete High-Resolution Coastline of Antarctica
Extracted from Orthorectified Radarsat SAR Imagery
Hongxing Liu and Kenneth C. Jezek
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A complete, high-resolution coastline of Antarctica, extracted from an orthorectified
mosaic of Radarsat-1 synthetic aperture radar (SAR) images through a sequence
of automated image processing algorithms, is presented. A locally adaptive
thresholding method is used to segment the orthorectified SAR images, while
image-object formation and labeling, and edge-tracing techniques are used
to process the segmented images into vector-based cartographic products of
coastline, defined here as the boundary between continental ice or rock exposures
and sea ice covered ocean. The absolute accuracy of planimetric positioning
of the resultant coastline is estimated to better than 130 m, and its spatial
resolution (25 m) is adequate for supporting cartographic and scientific
applications at 1:50,000 scale. This radar-image-derived coastline gives
an accurate description of geometric shape and glaciological characteristics
of the Antarctic coasts and also provides a precise benchmark for future
change-detection studies.
617 An Integrated Approach for Landslide Susceptibility
Mapping Using RemoteSensing and GIS
S. Sarkar and D.P. Kanungo
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A methodology for landslide susceptibility mapping using an integrated remote
sensing and GIS approach is presented. A part of the Darjeeling Himalaya
was selected for the model execution. IRS satellite data, topographic maps,
field data, and other informative maps were used as inputs to the study.
Important terrain factors, contributing to landslide occurrences in the region,
were identified and corresponding thematic data layers were generated. These
data layers represent the geological, topographical, and hydrological conditions
of the terrain. A numerical rating scheme for the factors was developed for
spatial data analysis in a GIS. The resulting landslide susceptibility map
delineates the area into different zones of four relative susceptibility
classes: high, moderate, low, and very low. The susceptibility map was validated
by correlating the landslide frequencies of different classes. This has shown
a close agreement with the existing field instability condition. The effectiveness
of the map was also confirmed by the high statistically significant value
of a chi-square test.
627 Thematic Map Comparison: Evaluating the Statistical
Significance of Differences in Classification Accuracy
Giles M. Foody
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The accuracy of thematic maps derived by image classification analyses is often
compared in remote sensing studies. This comparison is typically achieved
by a basic subjective assessment of the observed difference in accuracy but
should be undertaken in a statistically rigorous fashion. One approach for
the evaluation of the statistical significance of a difference in map accuracy
that has been widely used in remote sensing research is based on the comparison
of the kappa coefficient of agreement derived for each map. The conventional
approach to the comparison of kappa coefficients assumes that the samples
used in their calculation are independent, an assumption that is commonly
unsatisfied because the same sample of ground data sites is often used for
each map. Alternative methods to evaluate the statistical significance of
differences in accuracy are available for both related and independent samples.
Approaches for map comparison based on the kappa coefficient and proportion
of correctly allocated cases, the two most widely used metrics of thematic
map accuracy in remote sensing, are discussed. An example illustrates how
classifications based on the same sample of ground data sites may be compared
rigorously and highlights the importance of distinguishing between one-and
two-sided statistical tests in the comparison of classification accuracy
statements.
635 A Raster Image Re-Projection Web Service Prototype
Nadine Alameh
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Full Article
A prototyping effort pertaining to the design and development of a
raster image re-projection web service is summarized. The goal of the effort
is to identify the complexities of interoperable service design and the feasibility
of service chaining in a GIS Web Services architecture. A description of a
preliminary web interface and the implementation options considered for the
prototype are described. The experience of chaining this service with the Open
GIS Consortium (OGC) Web Mapping Services is also summarized. In the process,
the difficulties arising from the lack of standards in the areas of projection
systems representation and georectified raster imagery encodings are highlighted.
The limitations of legacy GIS systems in accommodating the requirements of
a generic reprojection service are also discussed. Lessons learned about basic
requirements for efficient service chaining are presented in the areas of performance
and reliability of services, ease of access to services and their capabilities,
and the need for simple solutions.
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