Peer-Reviewed Article Abstracts
709 Radar and Optical Data Integration for Land-Use/Land-Cover
Mapping
Barry N. Haack, Nathaniel D. Herold, and Matthew A. Bechdol
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This study evaluated the advantages of combining traditional spaceborne
optical data from the visible and infrared wavelengths with the longer
wavelengths of radar. East African landscapes, including areas of
settlements, natural vegetation, and agriculture, were examined.
For three study sites, multisensor data sets were digitally integrated
with training data and ground-truth information derived from field
visits. The primary methodology was standard image processing, including
spectral signature extraction and the application of a statistical
decision rule to classify the surface features. The relative accuracy
of the classifications was established by comparison to ground-truth
information. In all sites, the merger of optical and radar sensors
improved the ability to map surface features over either sensor independently,
although different manipulations of the radar data were necessary
to obtain the most useful results. Those manipulations included measures
of texture, spatial filtering, and despeckling prior to texture extraction.
717 Applications of Orbital Imaging Radar for Geologic Studies
in
Arid Regions: The Saharan Testimony
Mohamed G. Abdelsalam, Cordula Robinson, Farouk El-Baz, and Robert
J. Stern
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The multi-frequency and multi-polarization Shuttle Imaging Radar (SIR)-C/X Synthetic
Aperture Radar (SAR) data collected in 1994 aboard two flights of the Shuttle
Endeavour constitute a milestone in imaging of deserts from space. The data
are here used to explore the eastern Sahara, including lithological and structural
mapping, geomorphological studies, and mineral exploration. The SIR-C/X-SAR images
in this environment are generally found to be (1) less useful for lithological
mapping than orbital visible and near infrared (VNIR) images, except where
rock types weather differently to produce varying roughness levels; (2) superior
to orbital VNIR images for structural mapping in areas of subdued relief or
where structures are partially covered by dry sand, as well as in tectonically
active mountainous terrains; (3) superior to orbital VNIR images for mapping
surface and sub-surface geomorphological features such as paleo-channels; and
(4) useful in delineating geologic controls on mineral deposits, but inferior
to orbital VNIR images for direct identification of these.
727 Use of Argon, Corona, and Landsat Imagery toAssess 30 Years of Land
Resource Changes in West-Central Senegal
G. Gray Tappan, Amadou Hadj, Eric C. Wood, and Ronald W. Lietzow
Abstract
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Over the past 35 years, an agricultural area of west-central Senegal has experienced
rapid population growth, fast expansion of agricultural lands, a decline
in rainfall, and degradation of vegetative and soil resources. Although such
changes have not escaped the attention of Senegal's people, its government,
and the scientific community, the ability to monitor and quantify land resource
trends of recent decades has been difficult. Recently available high-resolution
satellite photographs from the American Argon and Corona Programs provide
coverage of Senegal back to 1963. The photographs make it possible to study
and map land resources at the beginning of the Space Age. In this study,
we characterize the changes that have occurred in the region from the early
1960s to the mid-1990s. Early Argon and Corona photographs are used to reconstruct
the historical land use and land cover; comparisons are made with assessments
from recent Landsat images. Field studies and aerial surveys provide additional
insight. The forces of change, driven primarily by population growth and
unsustainable agricultural practices, are examined.
737 Generalizing El Nino Effects Upon Maasai Livestock Using Hierarchical
Clusters of Vegetation Patterns
Randall B. Boone, Kathleen A. Galvin, Nicole M. Smith, and Stacy
J. Lynn
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Cultural anthropologists often use household-level interviews to understand
components of land-use patterns and their effects upon human welfare. These
results are extrapolated to some broader areas, usually without description.
We present a method to make this extrapolation more rigorous. Evidence suggests
that high precipitation in 1997/1998, associated with El Nino/Southern Oscillation,
affected livestock belonging to the Maasai differently in two regions of
northern Tanzania. We used cluster analysis of vegetation biomass, as represented
by Advanced Very High Resolution Radiometry-based Normalized Difference Vegetation
Indices, to divide the region into hierarchically related, non-overlapping
regions. These regions were used to generalize household interviews, where
possible. When the difference in small livestock sold from 1997 to 1998 was
generalized, we found that the Maasai in the Ngorongoro region sold many
more animals (e.g., 10 to 17) during the dry 1997 year than those in Loliondo
region (e.g., 0 to 5). During the wet 1998 year, the Maasai at higher elevations
of both Ngorongoro and Loliondo sold more animals than those at lower elevations.
745 Use of Radar Data to Delineate Palaeodrainage Flow Directions in
the Selima Sand Sheet, Eastern Sahara
Cordula Robinson, Farouk El-Baz, Mutlu Ozdogan, Michael Ledwith, Daniel Blanco,
Susan Oakley, and Jennifer Inzana
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Palaeodrainage directions in the Selima Sand Sheet (centered on 22.5;dg N,
29;dg E) were determined using high-resolution, multi-wavelength, multi-polarization
Spaceborne Imaging Radar (SIR-C) data and the Global Land One-km Base Elevation
(GLOBE) Project Digital Elevation Model (DEM). The combined use of these
two data sets shows that both large flood features and later superimposed
drainage channels of variable morphology all drain NE and ENE from
northwest Sudan toward the Kharga depression in southern Egypt. This is supported
by drainage directions deduced from the USGS Global Topography (GTOPO)
DEM . These directions are opposite to those of the Trans-African Drainage
System (TADS) model in which the large flood features are considered to flow
southwest across northeastern Africa into the Chad Basin. Instead, the results
show that an internal drainage basin operated in the gently undulating terrain
of the Selima Sand Sheet (probably during the Cenozoic period), and that
the slope of the North African plate remained generally northeastward during
those times. Further, the northeastern parts of the Selima Sand Sheet are
likely to be the primary area for ground-water accumulation in southern Egypt.
755 Remote Sensing and GIS Modeling for Selection of a Benchmark Research
Area in theInland Valley Agroecosystems of West and Central Africa
Prasad S. Thenkabail, Christian Nolte, and John G. Lyon
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This paper presents and illustrates a methodology for rational selection of
benchmark research areas (or benchmark watersheds) for technology development
research activities in the inland valley (IV) agroecosystems of West and
Central Africa. This was done through a two-tier characterization approach.
The Level 1 characterization involved macro-scale sub-continental-level secondary
agroclimatic and soil datasets to produce 18 agroecological and soil zones
(AESZ), each of over10 million hectares, spread across West and Central Africa.
The Level II characterization involved the use of Landsat TM or SPOT high-resolution
visible (HRV) "windows" within each Level I AESZ, as well as other spatial
datasets to determine locations of the representative benchmark research
areas. The focus here is a methodology for Level II characterization for
benchmark research-area selection using SPOT HRV data, secondary GIS datasets,
and detailed ground-truth data with GPS locations. The spatial datalayers
were analyzed in a GIS modeling framework. The study was conducted
in an area of 0.39 million hectares around Gagnoa, southwestern Cote d'Ivoire
which is located in AESZ number 16 (humid forests with acrisols). A
toposequence oriented land-use/land-cover mapping was suggested and implemented.
The spatial distribution of the 16 land-use classes was mapped across toposequence:
uplands (40.1 percent of total geographic area), valley fringes (40.3 percent),
valley bottoms (18 percent), and others (1.6 percent). The broad land-use/land-cover
classes as a percentage of total geographic area (393112 hectares) comprised
(1) 58.2 percent of areas in pristine humid forests, (2) 23 percent of areas
in humid forest-cropland mosaic, and (3) 15.4 percent of areas in significant
farmlands in humid forests. Expert knowledge was incorporated through an
appropriate weighting criterion for classes in various land-use/land-cover
datalayers and other spatial datalayers. GIS modeling was then performed
on various spatial datalayers leading to the selection of representative
benchmark research areas. It is expected that the research conducted or technologies
developed in these benchmark research areas can then be extrapolated or transferred
to other areas within the same agroecological and soil zones like AESZ number
16.
769 Mapping Land Rights in Mozambique
Paul S. Anderson
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Mapping of land rights in Third World areas can be done by modestly trained
and assisted local residents using highly enlarged (1:5000 or larger) aerial
photography. Three technical challenges are discussed: (1) cartographic quality
attained from non-standard methods, (2) image enlargement (8x to 40x) accomplished
with photo-digital techniques, and (3) implementation methods using pre-literacy
and distance education techniques. Examples of images and GIS-cartography
results of two pilot studies are shown and discussed in the context of Mozambique's
recent and highly progressive land-rights laws. Implications for improving
local education and for collection of additional geography-based data (soils,
biodiversity, demographics, etc.) are discussed.
777 Satellite Observations of the Interplay between Wind and Water Processes
in the Great Sahara
Farouk El-Baz
Abstract
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Images of the Great Sahara of North Africa obtained by the Advanced Very High
Resolution Radiometer (AVHRR), manned missions, and Landsat show regional
linear patterns of sand dunes resulting from wind action. These patterns
trend southward in the northern part and southwestward in the center of the
desert. Radar data from the Spaceborne Imaging Radar (SIR-C) and Radarsat
reveal sand- buried courses of palaeo-channels that lead to depressions,
which enclose major sand accumulations. Interpretation of these data suggests
that the sand originated in the southern part of the Sahara and was carried
northward in river courses during past wet climates to be deposited within
inland lakes. Prior to the onset of dryness, and the resulting aeolian forms,
much of the water would have seeped into the substrate through primary (rock)
and/or secondary (fault-induced) porosity to be stored as ground water. Therefore,
the exploration for ground water in the Sahara should consider depressions
with large accumulations of sand.
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