Peer-Reviewed Articles
681 Viewing Geometry of AVHRR Image Composites Derived Using Multiple Criteria
David M. Stains, Michael J. Buena, and Frank W Davis
Abstract
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The US Geological Survey currently generates composites of AVHRR imagery based
on a single objective - maximizing the Normalized Difference Vegetation Index
(NDVI) - as a means of reducing cloud contamination. This research supports
the findings of others that, in some cases, NDVI is maximized at the expense
of optimal viewing geometry; that is, satellite zenith angles are often further
off- nadir than necessary to ensure cloud-free viewing. The authors explore
various compositing methods by systematically varying weights on NDVI, satellite
zenith angle, and maximum apparent temperature. A test composite of California
from September 1990 appears to be superior to the maximum NDVI and maximum
apparent temperature composites in several respects. First, the satellite zenith
angle distribution is more closely clustered about nadir, which minimizes atmospheric
path length, spatial distortion, and bidirectional reflectance effects. Second,
neighboring pixels are more frequently selected with similar viewing geometry
and atmospheric conditions.
691 Fusion of Satellite Images of Different Spatial Resolutions: Assessing
the Quality of Resulting Images
Lucien Wald, Thierry Ranchin, and Marc Mangolini
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Methods have been proposed to produce multispectral images with enhanced
spatial resolution using one or more images of the same scene of better spatial
resolution. Assuming that the main concern of the user is the quality of the
transformation of the multispectral content when increasing the spatial resolution,
this paper defines the properties of such enhanced multispectral images. It
then proposes both a formal approach and some criteria to provide a quantitative
assessment of the spectral quality of these products. Five sets of criteria
are defined. They measure the performance of a method to synthesize the radiometry
in a single spectral band as well as the multispectral information when increasing
the spatial resolution. The influence of the type of landscape present in the
scene upon the assessment of the quality is underlined, as well as its dependence
with scale. The whole approach is illustrated by the case of a Spot image and
three different standard methods to enhance the spatial resolution.
701 Spectral Reflectance with Varying Suspended Sediment Concentrations in
Clear and Algae-Laden Waters
Luoheng Han
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The objective of the study was to characterize and compare the relationship
between suspended sediment concentration (SSC) and reflectance in clear and
algae-laden waters. A controlled experiment was conducted outdoors in a 7510-litre
water tank using natural sunlight. A red loam soil was added and suspended
in the tank filled with clear and algae-laden waters, respectively. A total
of 20 levels of SSC (from 25 to 500 mg l-1) were created for
each type of treatment. The same amount of suspended sediment generated higher
reflectance between 400 and 700 nm in clear water than in algae-laden water
due to the blue and red absorption of chlorophyll. The effect of chlorophyll
on the SSC- reflectance relationship was minimum at wavelengths between 700
and 900 nm. For both clear and algae-laden waters, the linearity in the SSC-reflectance
relationship increased with wavelength between 400 and 900 nm. A near-linear
relationship between SSC and reflectance was found between 720 and 900 nm.
707 Mapping Desert Shrub Rangeland Using Spectral Unmixing and Modeling Spectral
Mixtures with TM Data
Youngsinn Sohn and Roger M. McCoy
Abstract
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Spectral unmixing experiments were done to explore the applcability
of linear unmixing models, especially the basic
least-squares method for mapping sparse vegetation in
rangeland. Some important theoreticaI and technical issues
involved in physical inversion problems were addressed.
Based on the field reference spectra of image components, a
constrained least-squares method was applied to Landsat
Thematic Mapper data over an area in Long Valley, Nevada
to caIculate vegetation abundance in a pixel.
A method for formulating a well-conditioned spectral mixture by calculating the cosine of the angles between the candidate surface components was presented. This method provides a way to measure the separability of candidate endmembers quantitatively and derive spectral endmembers objectively. The results of this study suggest that the ambiguity or uncertainty in physical inversion problems arises from the inability to provide a complete set of representative reference spectra and to formuIate a well-conditioned spectral mixture, not from the least-squares method itself. Some of import implications of the study include the following: (1) the unmixing techniques can provide moderate estimates of vegetation fractions in arid rangeland, where vegetation is sparse, with TM data; and (2) the degree of spectral pureness of endmembers should be consistent between endmember spectra that are used for unmixing.
717 Subpixel Classification of Bald Cypress and Tupelo Gum Trees in Thematic
Mapper Imagery
Robert L. Huguenin, Mark A. Karaska, Donald Van Blariconi, and John R.
Jensen
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A subpixel spectral analytical process was used to classify
Bald Cypress and Tupelo Gum wetland in Landsat Thematic
Mapper imagery in Georgia and South Carolina. The subpixel
process enobled the detection of Cypress and Tupelo
trees in mixed pixels. Two-hundred pixels were field verified
for each tree species to independently measure errors of
omission and commission. The cypress total accuracy was 89
percent and the tupelo total accuracy wes 91 percent. Field
investigations revealed that both cypress and tupelo trees
were succcessfully classified when they occurred both as pure
stands and when rnixed with other tree species and water. In
a comparison with traditional cIassification techniques (ISODATA clustering, maximum likelihood, end minimum distance)
the subpixel classification of cypress and tupelo
yielded improved results. Large areas of wetland where cypress
was heavily mixed with other tree species were correctly
classified by the subpixel process and not classified by
the traditional classifiers.
727 Mapping City Lights with Nighttime Data from the DMSP Operational Linescan
System
Christopher D. Elvidge, Kimberly E. Baugh, Eric A. Kihn, Herbert W Kroehl,
and Ethan B. Davis
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The Defense Meteorological Satellite Program (DMSP) Operational Linescan System
(OLS) has a unique capability to detect low levels of visible and near-infrared
(VNIR) radiance at night. With the OLS 'VIS' band data, it is possible to detect
clouds illuminated by moonlight, plus lights from cities, towns, industrial
sites, gas flares, and ephemeral events such as fires and lightning illuminated
clouds. This paper presents methods which have been developed for detecting
and geolocating VNIR emission sources with nighttime DMSP-OLS data and the
analysis of image time series to identify spatially stable emissions from cities,
towns, and industrial sites. Results are presented for the United States.
735 Statistical Significance and Normalized Confusion Matrices
Perry J. Hardin and I. Matthew Shumway
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In this research, the procedure for estimating the sampling distribution of
normalized cell values is described. Three methods for determining the standard
error of normalized cell value sampling distributions are also outlined. Using
these sampling distributions and their attendant standard error, the statistical
comparison of cell values from two normalized confusion matrices is illustrated.
One illustrated method requires a mild parametric assumption, whereas the other
is completely nonparametric. Nevertheless, the two distinct bootstrap methods
produce nearly identical results.
741 A Large-Scale Aerial Photoghraphic Technique for Measuring Tree Heights
on Long-Term Forest Installations
Miklos Kovats
Abstract
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Provides a feasible alternative to the conventional clinometer and tape technology.
The system uses large-scale aerial photographs (LSP) with permanent ground
control points. Test results indicate that, by the second assessment in installations
containing 456 trees or more, the cumulative cost of LSP-measured tree heights
will be less, and be as accurate as and more precise than clinometer-measured
heights. By the 10th assessment in installations containing 3000 trees or more,
the LSP system can offer 80% cumulative savings over the clinometer and tape
method.
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