Peer-Reviewed Articles
297 A Basis for Estimating Digital Camera Parameters
Don Light
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Matching the diffraction-limited optical resolution with the appropriate detector
size is a fundamental design requirement for digital imaging systems. A useful
Design Function based on the Airy disk is λF/p = 0.82. Where λ is the average
wavelength, F is the camera F-number, and p is the detector sampling pitch
(pixel size). A second metric, attributed to Schade and reported by Holst
(1999), produces an often used Design Function: λF/p = 1. Examples demonstrate
the use of the Design Functions to determine basic parameters, F-number,
focal length, aperture diameter, and pixel size for an imaging system. Pixel
size is selected from commercially available arrays and the other parameters
are estimated given the required ground sampled distance (GSD) with either
of the two Design Functions. One of the primary uses for the Design Functions
is to provide optical systems engineers with a simple, fast, and proven means
of arriving at first-order estimates for electro-optical camera designs.
It follows that estimating costs for building large space camera systems
should be less complicated. Mobile Digital Cameras for As-Built Surveys of
Roadside Features
301 Mobile Digital Cameras for As-Built Surveys of Roadside
Features
Kandiah Jeyapalan
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A method for determining the three-dimensional locations of roadside features
appearing on multiple sequential images captured using a mobile video-logging
system without any ground control is described. The digital camera was calibrated
using a special three-dimensional calibration range and Calib software to
simultaneously determine the interior and exterior orientation elements on
a local system. The software was then used to determine the local three-dimensional
coordinates of roadside features using the sequential imagery from the mobile
video-logging system captured along a highway at highway speed. The relative
locations were transformed to the absolute locations using the locations
of the camera's exposure stations from the Global Positioning System. The
relative accuracy of the locations obtained was 5 cm, and absolute accuracy
using the code phase kinematic Global Positioning System was 2 m. This paper
also shows the two-dimensional geographic information system, three-dimensional
geographic information system, and virtual reality created for three test
sites using the imagery from the mobile video-logging system. NASA's Global
Orthorectified Landsat Data Set
313 NASA’s Global Orthorectified Landsat Data Set
Compton J. Tucker, Denelle M. Grant, and Jon D. Dykstra
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NASA has sponsored the creation of an orthorectified and geodetically accurate
global land data set of Landsat Multi-spectral Scanner, Thematic Mapper,
and Enhanced Thematic Mapper data, from the 1970s, circa 1990, and circa
2000, respectively, to support a variety of scientific studies and educational
purposes. This is the first time a geodetically accurate global compendium
of orthorectified multi-epoch digital satellite data at the 30- to 80-m spatial
scale spanning 30 years has been produced for use by the international scientific
and educational communities. We describe data selection, orthorectification,
accuracy, access, and other aspects of these data.
323 Mapping Snowpack Depth Beneath Forest Canopies Using
Airborne Lidar
Chris Hopkinson, Mike Sitar, Laura Chasmer, and Paul Treitz
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An evaluation of airborne lidar (Light Detection And Ranging) technology for
snow depth mapping beneath different forest canopy covers (deciduous, coniferous,
and mixed) is presented. Airborne lidar data were collected for a forested
study site both prior to and during peak snowpack accumulation. Manual field
measurements of snow depth were collected coincident with the peak snowpack
lidar survey, and a comparison between field and lidar depth estimates was
made. It was found that (1) snow depth distribution patterns can be mapped
by subtracting a "bare-earth" DEM from a "peak snowpack" DEM,
(2) snow depth estimates derived from lidar data are strongly related to
manual field measures of snow depth, and (3) snow depth estimates are most
accurate in areas of minimal understory. It has been demonstrated that airborne
lidar data provide accurate snow depth data for the purpose of mapping spatial
snowpack distribution for volume estimations, even under forest canopy conditions.
331 Accuracy of Airborne Lidar-Derived Elevation: Empirical
Assessment and Error Budget
Michael E. Hodgson and Patrick Bresnahan
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As part of a countywide large-scale mapping effort for Richland County, South
Carolina, an accuracy assessment of a recently acquired lidar-derived data
set was conducted. Airborne lidar (2-m nominal posting) was collected at
a flying height of 1207 meters above ground level (AGL) using an Optech ALTM
(Airborne Laser Terrain Mapper) 1210 system. Unique to this study are the
reference point elevations. Rather than using an interpolation approach for
gathering observed elevations at reference points, the x-y coordinates of
lidar points were located in the field and these elevations were surveyed.
Using both total-station-based and rapid-static GPS techniques, observed
vertical heights were measured at each reference lidar posting. The variability
of vertical accuracy was evaluated for six land-cover categories. Root-mean-squared
error (RMSE) values ranged from a low of 17 to 19 cm (pavement, low grass,
and evergreen forests) to a high of 26 cm (deciduous forests). The unique
error assessment of lidar postings also allowed for the creation of an error
budget model. The observed lidar elevation error was decomposed into errors
from lidar system measurements, horizontal displacement, interpolation error,
and surveyor error. A cross-validation approach was used to assess the observed
interpolated lidar elevation error for each field-verified reference point.
In order of decreasing importance, the lidar system measurements were the
dominant source of error followed by interpolation error, horizontal displacement
error, and surveyor error. Observed elevation error in steeper slopes (e.g.,
25°) was estimated to be twice as large as those on low slopes (e.g.,
1.5°).
341 Automating the Analysis of Remotely Sensed Data
Chris Skelsey, A.N.R. Law, Mark Winter, and J.R. Lishman
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Land cover is a complex phenomenon, its appearance and transition influenced
by the soil, topography, climate, politics, ecology, and other aspects of
land use. An operational study of land-cover change must consider such factors,
and, if automation is to be employed, a new approach to software architecture
and reasoning is required. The Macaulay Institute has developed the concept
of task orientation as a means of supporting such work, and is currently
investigating its utility in the update of the Land Cover of Scotland (1988)
dataset. This paper describes the motivation behind the development of ETORA-II,
an operational toolkit providing a task-orientated capability, and SYMOLAC-II,
a proof-of-concept application. The final aim of this work is to produce
an environmental information system for Scotland's land cover.
351 Individual Tree-Crown Delineation and Treetop Detection
in High-Spatial-Resolution Aerial Imagery
Le Wang, Peng Gong, and Gregory S. Biging
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The cost of forest sampling can be reduced substantially by the ability to
estimate forest and tree parameters directly from aerial photographs. However,
in order to do so it is necessary to be able to accurately identify individual
treetops and then to define the region in the vicinity of the treetop that
encompasses the crown extent. These two steps commonly have been treated
independently. In this paper, we derive individual tree-crown boundaries
and treetop locations under a unified framework. We applied a two-stage approach
with edge detection followed by marker controlled watershed segmentation.
A Laplacian of Gaussian edge detection method at the smallest effective scale
was employed to mask out the background. An eight-connectivity scheme was
used to label the remaining tree objects in the edge map. Subsequently, treetops
are modeled based on both radiometry and geometry. More specifically, treetops
are assumed to be represented by local radiation maxima and also to be located
near the center of the tree-crown. As a result, a marker image was created
from the derived treetop to guide a watershed segmentation to further differentiate
touching and clumping trees and to produce a segmented image comprised of
individual tree crowns. Our methods were developed on a 256- by 256-pixel
CASI image of a commercially thinned trial forest. A promising agreement
between our automatic methods and manual delineation results was achieved
in counting the number of trees as well as in delineating tree crowns. Landscape
Dynamics and Risk Modeling of Human Alveolar Echinococcosis
359 Landscape Dynamics and Risk Modeling of Human Alveolar
Echinococcosis
F. Mark Danson, Philip S. Craig, Wai Man, Dazhong Shi, and Patrick Giraudoux
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Human alveolar echinococcosis (AE) is a rare but fatal liver disease caused
by a parasitic tapeworm. Between 1994 and 1997 a medical survey in a rural
area in central China revealed the highest incidence rate of the disease
recorded in the world to date, with 15.8 percent of the population infected
in one village. Hypotheses on the nature of the transmission mechanisms from
the natural to human environment focused on the effects of recent landscape
change from forest to agricultural land. Archived Landsat MSS and TM data
were used to examine relationships between landscape and human AE prevalence
in 31 villages. The results showed a significant positive correlation between
AE and the proximity of villages to forest, grassland, and shrubland vegetation,
and a negative correlation with the area of cultivated land. A predictive
model, based on spatial characteristics of the landscape, is now being developed
with the aim of designing management tools for disease control.
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