Peer-Reviewed Articles
565 Accuracy of Rectification Using Topographic Map versus GPS Ground
Control Points
David P. Smith and Samuel F. Atkinson
Abstract
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Reliable assessments of landscapes are needed for natural resource
conservation and preservation efforts and for understanding the impacts
humans are having upon those resources. Remotely sensed data provide
an integrated view of the landscape and are nicely suited for temporal
change studies. Reliable interpretation of Earth surface characteristics
relies largely on accurate rectification of the remote sensing imagery
to a map projection and on subsequent thematic classification. For
rectification, we found that control points acquired using the Global
Positioning System (GPS) were superior to those acquired from digitized
topographic maps. Differentially corrected GPS locations provided
for the optimum rectification of SPOT satellite imagery while marginally
better rectifications were obtained for Landsat MSS imagery using
uncorrected GPS positions. Accuracy of ground control point sources
for rectification should match the resolution of the digital image.
Shifts in pixel digital number locations following the resampling
procedure
in rectification indicate a substantial amount of change might erroneously
be attributed to change when, in fact, it might simply be due to differing
methods of determining cartographic coordinates of ground control points. This
has important implications in change detection studies and should be explored
further.
571 On Statistical Band Selection for Image Visualization
M. Beauchemin and Ko B. Fung
Abstract
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We show that two often-cited statistical band selection methods for
image visualization provide significantly different results when
applied to the same data set. The cause of the difference is first
identified. Then, an alternative method based on the minimization
of redundant information between bands is presented. The new measure
is robust against the existence of multicollinearity. A procedure
to help determine an appropriate band subset size is also proposed.
575 Appropriate Plot Size and Spatial Resolution for Mapping Multiple
Vegetation Types
Guangxing Wang, George Gertner, Xiangyun Xiao, Steven Wente, and Alan B.
Anderson
Abstract
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For mapping multiple vegetation types at large scale, determining appropriate
plot size and spatial resolution is very important. However, this
can be difficult because of spectral mixtures, low correlation of
remote sensing and field data, and high cost to collect field data
at a high density. This paper presents a method to determine appropriate
plot size and spatial resolution for mapping multiple vegetation
types using remote sensing data for a large area. This method is
based on field data and geo-statistics theory. The method accounts
simultaneously for within-support and regional spatial variability
by modeling both within-support and regional semi-variograms. The
range parameters of the within-support semi-variograms implied the
maximum range of the appropriate plot sizes. Using the regional semi-variograms,
the support size was considered appropriate when the ratio of the nugget variance
to sill variance stabilized. The method is assessed using field data and satellite
TM data by developing the semi-variograms by vegetation type and TM band; and
by cross validation of vegetation classification. A possible improvement for
remote sensing to aid mapping is suggested.
585 High-Resolution DEMs for Urban Applications from NAPP Photography
Curt H. Davis and Xiangyun Wang
Abstract
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Digital elevation models (DEMs) are widely used in many GIS and resource
management applications. Increased use of DEMs has led to greater
demand for higher resolution and higher accuracy digital elevation
data. Here we demonstrate that digitally scanned 1:40,000-scale NAPP
aerial photography, used in conjunction with precision ground control,
can be used to generate DEMs with horizontal resolutions of 1 to
3 m. The vertical accuracies of the DEMs were evaluated using more
than 50,000 check points derived from a precision kinematic GPS survey. The
results indicate that the DEMs have RMS vertical accuracies on the order of
1.8 to 2.5 m. The DEMs reveal very fine-scale features in an urban test area.
The horizontal resolution and vertical accuracy of the NAPP DEMs are many times
better than those currently derived from satellite remote sensing platforms.
Moreover, the NAPP imagery is an inexpensive source of data that are readily
available throughout most of the United States. The exploitation of the NAPP
data could make high-resolution / high accuracy DEMs available to smaller cities
and counties that would otherwise be unable to afford more expensive commercial
datasets of comparable resolution and accuracy.
593 Analysis of GAC NDVI Data for Cropland Identification and Yield
Forecasting in Mediterranean African Countries
Fabio Maselli and Felix Rembold
Abstract
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The utilization of NOAA-AVHRR NDVI data for crop yield forecasting
is of particular importance in semiarid regions where there are strong
inter-year yield fluctuations due to meteorological vagaries. The
present work deals with the use of monthly GAC NDVI data for the
early estimation of cereal crop yield in Mediterranean African countries.
A preliminary analysis showed that relatively high correlations were
present between crop yield and mean NDVI values of specific months
computed at national levels. The stratification of the countries
according to the USGS global land-cover map brought only marginal
correlation increases. Greater improvements were instead reached
by a statistical method which allows the estimation of the per-pixel
fractions of agricultural and non-agricultural vegetation. When compared
to available independent maps, the areas identified in this way were
confirmed to be mainly covered by crop and forest land, respectively.
The methodology for cropland identification and yield forecasting
was finally evaluated for operational applications.
603 Operational Monitoring of Green Biomass Change for Forest Management
Pol Coppin, Kris Nackaerts, LLoyd Queen, and Ken Brewer
Abstract
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Forest managers are in constant need of accurate, up-to-date resource
information. A first attempt towards an operational, quantitative,
remote-sensing-based change detection system is described. The change
information derived from this system can then be used either to "flag" those
areas that require additional detailed investigation, or to monitor
conditions to determine if changes occur as expected. The digital
change detection system described is based on standardized differences
of Kauth-Thomas transformations. Minimum-distance, maximum-likelihood,
and Mahalanobis-distance classifiers were tested with field data
and compared. The maximum-likelihood and Mahalanobis-distance classifiers
produced the more accurate results. They were able to detect small
amounts of change resulting from forest thinnings, which are the
most difficult to discriminate. Overall results of this work demonstrated
the high potential value of an operational, digital, quantitative
change detection system to support forest management decisions across
large geographic extents.
613 Applying Spatial Autocorrelation Analysis to Evaluate Error in
New England Forest-Cover-Type Maps Derived from Landsat Thematic
Mapper Data
Scott A. Pugh and Russell G. Congalton
Abstract
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A spatial autocorrelation of error analysis was performed to compare
the patterns of error in a classified Landsat Thematic Mapper (TM)
forest-cover-type image for two forested areas - one public and one
private. TM data were classified to generate a detailed forest type
map, and intensive ground reference data covering approximately 3600
ha were collected for both study areas. Two difference images were
produced by comparing the reference inventory with the classified
data, pixel by pixel. The subsequent spatial autocorrelation analysis
indicated that concentrated blocks of error were more pronounced
in the public lands study area than in the private lands study area,
where error was more evenly distributed. The results indicated that
systematic sampling is not always suitable for assessing error in
TM data.
621 Two-Medium Photogrammetry for Bottlenose Dolphin Studies
A.K. Chong and K. Schneider
Abstract
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In this research we determined the significance of the external physiology
between a unique pod of bottlenose dolphins in Doubtful Sound, Fiordland,
New Zealand and their cousins elsewhere. To do this, we introduced
an in situ digital stereophotogrammetric technique to measure these
cetaceans' body dimensions accurately at sea without having to capture
the individuals. The technique involved the use of a wooden model
to determine the size of measurement error of a prototype stereocamera
system for measuring objects under the surface of seawater. A linear
regression model was used to correct for the measurement error. The
model utilized the stereophotogrammetric depth measurement of an
object under the water surface. Body dimensions of stranded dolphins
from the Texas coast were used to estimate growth parameters of Doubtful
Sound dolphins. These growth parameters were used to estimate the
age of the stereoscopically measured Doubtful Sound dolphins. We
found that the Doubtful Sound bottlenose dolphins are larger and
longer than their Texas cousins by 28 percent and their flippers
and the flukes are longer by 22 percent and 17 percent, respectively.
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