Peer Reviewed Articles
263-265 An Examination of Measuring Selected Water Quality
Trophic Indicators with SPOT Satellite HRV Data
Stefan H. Cairns, Kenneth L. Dickson, and Samuel F. Atkinson
Abstract
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Concurrent in situ water quality and SPOT satellite data were obtained for
three reservoirs located in north Texas. In situ data included measurement
of chlorophyll a, pheophytin a, total suspended solids, total dissolved solids,
and turbidity. The SPOT data from locations of water samples were subset
and digital data were examined in their raw states as well as numerous transformations.
Low but significant correlations were observed between digital numbers and
both turbidity and chlorophyll a. The degree of correlation was not as great
as in previously reported studies using SPOT and Landsat data. To be useful
for reservoir scale monitoring in north Texas, the techniques still need
to be refined sufficiently to detect differences within the range of water
quality typically found in the area under study.
267-271 The Role of Spatial Resolution in Quantifying
SSC from Airborne Remotely Sensed Data
Jay Gao and Stephen M. O'Leary
Abstract
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Suspended solids concentration (SSC) was measured at 90 positions when aerial
photographs were being taken. The aerial photographs were scanned at 300
dpi, geometrically and radiometrically rectified, and mosaicked. The mosaicked
image was resampled from 1 m to 5 m, 10 m, and 20 m, from which the digital
numbers (DN) at the SSC sampling positions were obtained. There was a significant
linear relationship between SSC and DN at all four resolution levels. The
regressed relationship between SSC and its DN is the most accurate at a spatial
resolution of 10 m.
273-279 Flood-Tide Deltaic Wetlands: Detection
of Their Sequential Spatial Evolution
Qizhong Guo and Norbert P. Psuty
Abstract
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Techniques to detect evolution of marsh islands in Great Egg Harbor Bay, New
Jersey are presented in this paper. Aerial photographs and topographic maps
were digitized. A geographic information system (GIS) was subsequently established
with the digitized data. A computer program was also written to carry out
necessary computations. Through these efforts, change in area, shift of centroid,
and rotation of marsh islands were quantified.
281-291 Monitoring South Florida Wetlands Using
ERS-1 SAR Imagery
Eric S. Kasischke and Laura L. Bourgeau-Chavez
Abstract
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This study evaluates the utility of synthetic aperture radar (SAR) imagery
collected by the ERS-1 satellite for monitoring wetland vegetation communities
in southwestern Florida. The range of image intensity values from the different
test sites varied by a factor of 6.2 (7.9 dB) on a dry season ERS-1 SAR image
and by a factor of 2.6 (4.1 dB) for a wet season ERS-1 SAR image. The results
of this study illustrate that radar imagery is uniquely suited to detect
and monitor changes in soil moisture, flooding, and aboveground biomass in
these wetland ecosystems.
293-297 AVHRR Imagery Used to Identify Hurricane
Damage in a Forested Wetland of Louisiana
Elijah W. Ramsey III, Dal K. Chappell, and Dan G. Baldwin
Abstract
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On 26 August 1992, Hurricane Andrew passed through Louisiana, impacting a large
area of forested wetlands. One response to the widespread defoliation resulting
from the hurricane impact was an abnormal bloom of new leaves and new growth
in the underlying vegetation between September and October. To capture this
atypical phenology, a time sequence of AVHRR images was transformed into
a normalized difference vegetation index, NDVI, as an indicator of vegetation
changes in the forest impacted by the passage of a hurricane. Using geogrpahic
information system functions, three sites in the impacted forest were vectorized
as polygons, and the inclusive pixels were extracted for subsequent graphical
and univariate statistical analysis. Temporal curves of mean NDVIs for the
three sites for before, during, and after the hurricane passage, and aggregate
curves of the impacted forest to an undisturbed forest, were compared. These
comparisons corraborated the atypical phenology of the impacted forested
wetland and directly related the cause to the hurricane passage.
299-306 Assessing Corn Yield and Nitrogen Uptake
Variability with Digitized Aerial Infrared Photographs
M.D. Tomer, J.L. Anderson, and J.A. Lamb
Abstract
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Methods for large-scale mapping of crop variability are needed for precision
farming applications. The authors hypothesized that aerial-infrared photographs
can predict corn yield and N uptake variability. A 2.6-ha area in Minnesota
was cropped with corn in 1991 and 1992. Photographs of bare soil and of the
mature crops were color scanned. Corn yield and N uptake were determined
at 58 locations, and were related to phototone data using multiple regression.
Spatial analysis of imagery showed that the crop canopy was more influenced
by soil conditions in 1991 than in 1992. This is attributed to the cooler
climate in 1992. Consequently, harvest data were better predicted in 1991
than in 1992. In 1991, 65 percent of yield and 59 percent of N-uptake variability
were captured by phototones; respective values for 1992 data were 47 percent
and 37 percent. Use of aerial photographs for spatial modeling of crop growth
can work, but multi-year studies are recommended.
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