Peer-Reviewed Articles
801 Effects of Sensor Resolution on Mapping In-Stream
Habitats
Carl J. Legleiter, W. Andrew Marcus, and Rick L. Lawrence
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Effects of spatial, spectral, and radiometric resolution on remote mapping
of fourth-order in-stream habitats were evaluated by comparing hyperspectral
imagery to simulated multispectral data. Spectral resolution was more important
than spatial or radiometric resolution in improving classification accuracies,
although overall accuracies never exceeded 62 percent. Overall accuracies
were significantly greater for (1) hyperspectral data (7.2 percent) compared
to simulated multispectral imagery, (2) 1-m pixels (4.7 percent) compared
to 2.5-m pixels, and (3) 11-bit data (0.8 percent) compared to 8-bit data.
Higher spatial resolution also enabled removal of transitional areas between
units by using interior buffers, improving accuracy by up to 15.6 percent.
We believe low overall accuracies were primarily due to the subjective and
oversimplified nature of the polygon-based field maps used as ground reference
data, and high-resolution imagery might provide a more detailed representation
of in-stream habitats. Improved methods of collecting ground reference data,
utilizing a point-based approach, should be developed for assessing the accuracy
of classifications derived from fine spatial resolution (less than 5-m) imagery.
809 Monitoring Wetland Ditch Water Levels Using
Landsat TM and Ground-Based Measurements
D.H.A. Al-Khudhairy, C. Leemhuis, V. Hoffmann, I.M. Shepherd, R. Calaon,
J.R. Thompson, H. Gavin, D.L. Gasca-Tucker, G. Zalidis, G. Bilas, and D.
Papadimos
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A methodology which makes use of Landsat Thematic Mapper (TM) data to indirectly
provide remotely sensed observations of water levels within channels and
ditches in wetlands is
presented. Using multi-temporal Landsat TM imagery and simultaneous ground-based
measurements of water levels, statistical relationships are established between
satellite-derived effective wet-ditch widths and measured water levels in the
drainage systems of three European wetlands. These relationships can thereafter
be used to estimate historical ditch water levels and to monitor contemporary
ditch water levels in the wetlands. The study shows that satellite imagery
has much to offer in providing a historical perspective of wetland hydrology
that otherwise would not be available, in monitoring changes in the hydrological
regime of wetlands, and in providing complimentary approaches to field monitoring.
821 Photogrammetric Retrieval of Cloud Advection
and Top Height from the Multi-Angle Imaging Spectroradiometer (MISR)
Jia Zong, Roger Davies, Jan-Peter Muller, and David J. Diner
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This article describes a stereo-photogrammetric method for simultaneous retrieval
of cloud advection and cloud-top height fields using multi-angle imagery
from the MISR instrument. Although stereoscopy has been widely used for topographic
surface retrieval, its application to dynamic cloud elevations has been very
limited. This article shows theoretically that, by using multiple MISR camera
look angles from satellite altitudes, cloud advection and cloud-top height
can be separated stereoscopically, thus enabling their simultaneous retrieval.
A completely automatic retrieval algorithm was designed and implemented,
including steps for multi-angle image registration on a reference Earth ellipsoid
surface, mesoscale cloud advection derivation employing stereoscopic retrieval,
and simultaneous stereoscopic reduction of high-resolution cloud-top heights.
Before instrument launch, numerical simulations were implemented to demonstrate
the feasibility of the retrieval, and to derive estimates of the algorithm
errors. Since launch, stereo cloud reduction from MISR has been routinely
processed for global climatological studies.
831 Testing the Sensitivity of a MODIS-Like Daytime
Active Fire Detection Model in Alaska Using NOAA;shAVHRR Infrared
Data
C.A. Seielstad, J.P. Riddering, S.R. Brown, L.P. Queen, and W.M. Hao
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A MODIS-like daytime active fire detection model was tested in Alaskan biomes
using NOAA-AVHRR infrared data, and its performance was assessed across a
range of channel 3 (3.8 ;ZMm) brightness temperature and contextual standard
deviation thresholds. Absolute thresholding of channel 3 (T;i3) and the channel
3;sh4 difference (T;i3;i4) was more effective than contextual analysis in
minimizing false detections, although detection sensitivity to actual fire
pixels was lower. The contextual analysis became more effective in terms
of fire
detections as the T;i3 and standard deviation thresholds were loosened. However,
enhanced fire detection capabilities were achieved at the expense of increased
false detections associated primarily with cloud edges. False detections increased
exponentially and detections of active fires increased linearly as thresholds
were loosened. Furthermore, T;i3 and standard deviation thresholds suggested
for the MODIS global fire detection product appear too high for Alaska. An
optimal T;i3 threshold between 314K and 315K and a standard deviation threshold
between 2.5 and 3.5 are proposed. These results suggest that each biome or
region may require different thresholds to optimize algorithm performance,
recognizing
that optimization of the model depends upon user goals. Effective cloud removal
is clearly the most significant issue facing this type of fire detection method.
839 Evaluation of SAR-Optical Imagery Synthesis
Techniques in a Complex Coastal Ecosystem
Floyd M. Henderson, Robert Chasan, Jamie Portolese, and Thomas Hart, Jr.
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Coastal areas comprise some of the world's most important and sensitive ecosystems.
Although optical remote sensing systems have demonstrated an ability to map
land cover in
many coastal environments, spectral confusion has also been reported. The parameters
of SAR imagery suggest that combinations of SAR and optical data may improve
land-cover
classification accuracy. Seven satellite SAR data sets were merged with TM
data using four techniques. These were tested by classifying 11 upland and
wetland land covers in a rapidly
urbanizing coastal area of the northeast United States. Not all SAR;shTM combinations
bettered the accuracy obtained using TM data alone. In general, simple techniques
improved accuracy more than did complex image merge methods. Although one SAR
image proved superior overall, improvement in detection accuracy varied among
individual land-cover categories and SAR data. The results point to the possible
benefits of hierarchical;shlayered classifications.
847 Effects of JPEG Compression on the Accuracy
of Photogrammetric Point Determination
Zhilin Li, Xiuxiao Yuan, and Kent W.K. Lam
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An empirical investigation into the effects of JPEG compression on the accuracy
of photogrammetric point determination (PPD) is described. A pair of black-and-white
aerial photographs of a city, taken at a scale of 1:8000, was selected and
scanned at a resolution of 25 ;ZMm. Eighteen image points were measured with
the ISDM module of an Intergraph digital photogrammetric workstation (DPW),
and the bundle adjustment of a single model was performed using WuCAPS;zS;zG;zP;zS
(Wuhan GPS supported bundle block adjustment software). In processing various
JPEG compressed images with Q-factors from 1 to 100, the accuracy of the
3D coordinates of the pass points was assessed and compared with that obtained
from the original images (i.e., without compression). The empirical results
show that, when the compression ratios are under 10, the compressed image
is near-lossless. In other words, the visual quality of JPEG compressed images
is still excellent and the accuracy of manual image mensuration is essentially
not influenced. However, no indication can be found from the results that
a compression of 10 is the critical value or the optimum compression level
for PPD. Indeed, it is clear that the degradation of accuracy in PPD is almost
linear
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