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ABSTRACT: Archaeology can provide insight into interactions of climate change and human activities in sensitive areas such as the Sahara, to the benefit of both disciplines. Such analyses can help set bounds on climate change projections, perhaps identify elements of tipping points, and provide constraints on models. The opportunity exists to more precisely constrain the relationship of natural solar and climate interactions, improving understanding of present and future anthropogenic forcing. We are beginning to explore the relationship of human occupation of the Sahara and long-term solar irradiance variations synergetic with changes in atmospheric-ocean circulation patterns. Archaeological and climate records for the last 12 K years are gaining adequate precision to make such comparisons possible. We employ a range of climate records taken over the globe (e.g. Antarctica, Greenland, Cariaco Basin, West African Ocean cores, records from caves) to identify the timing and spatial patterns affecting Saharan climate to compare with archaeological records. We see correlation in changing ocean temperature patterns ~ contemporaneous with drying of the Sahara ~6 K years BP. The role of radar images and other remote sensing in this work includes providing a geographically comprehensive geomorphic overview of this key area. Such coverage is becoming available from the Japanese PALSAR radar system (Palliou, et. al., 2007), which can guide fieldwork to collect archaeological and climatic data to further constrain the climate change chronology and link to models. Our initial remote sensing efforts concentrate on the Gilf Kebir area of Egypt.
Radar Conference, 2009 IEEE; 06/2009
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K. L. Mitchell,
S. D. Wall,
E. R. Stofan,
R. M. C. Lopes,
M. Janssen,
B. Stiles,
P. Paillou,
G. Mitri,
J. Lunine,
S. Ostro,
R. D. Lorenz, T. G. Farr,
R. L. Kirk,
J. Radebaugh,
Cassini RADAR Science Team
LPI Contributions. 07/2007; 1357:97-98.
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ABSTRACT: Global-scale topographic data are of fundamental importance to
many Earth science studies, and obtaining these data is a priority for
the Earth science community. Several groups have considered the
requirements for such a data set, and a consensus assessment is that
many critical studies would be enabled by the availability of a digital
global topographic model with accuracies of 2 and 30 m in the vertical
and horizontal directions, respectively. Radar interferometric
techniques have been used to produce digital elevation models at these
accuracies and are technologically feasible as the centerpiece of a
spaceborne satellite mission designed to map the world's land masses,
which we denote TOPSAT. A radar interferometer is formed by combining
the radar echoes received at a pair of antennas displaced across-track,
and specialized data processing results in the elevation data. Two
alternative implementations, one using a 2 cm-λ radar, and one
using a 24 cm-λ radar, are technologically feasible. The former
requires an interferometer baseline length of about 15 m to achieve the
required accuracy, and this could be built on a single spacecraft with a
long extendible boom. The latter necessitates a kilometers long
baseline, and would thus be best implemented using two spacecraft flying
in formation. Measurement errors are dominated by phase noise, due
largely to signal-to-noise ratio considerations, and attitude errors in
determining the baseline orientation. For the 2-m accuracy required by
TOPSAT, the orientation must be known to 1 arc-second. For the
single-spacecraft approach, where attitude would be determined by star
tracking systems, this performance is just beyond the several arc-second
range of existing instruments. For the dual-spacecraft systems, though,
differential global positioning satellite measurements possess
sufficient accuracy. Studies indicate that similar performance can be
realized with either system
Proceedings of the IEEE 01/1995; · 6.81 Impact Factor
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ABSTRACT: Remote sensing data collected from orbital satellites can provide
global coverage at regular intervals at moderate to high spatial
resolutions in broad spectral bands. Airborne instruments, such as the
Jet Propulsion Laboratory Airborne Visible/Near-Infrared Imaging
Spectrometer (AVIRIS), can provide high spatial resolution in narrow
spectral bands. High spectral resolution information is potentially
useful for identifying and mapping such things as mineralogy and plant
communities. However, airborne systems cannot easily provide periodic
coverage nor can they provide global coverage of any sort. The logical
outgrowth of this problem is to use airborne and satellite data
synergistically. In this study, data from the AVIRIS airborne
instrument, the Landsat MultiSpectral Scanner (MSS), and the ex-Soviet
RESOURCE satellite have been combined into a co-registered temporal
dataset covering the period from 1972 to 1991. The data cover the Manix
Basin Area of the Mojave Desert, which is located NE of Barstow,
California. This area has been cultivated with center-pivot irrigation
systems. Beginning in 1973, a series of fields has been abandoned
producing a sequence of abandoned fields at different stages of
evolution. The remote sensing data shows that the vegetation cover on
recently abandoned fields typically exceeds that in the surrounding
desert for a few years. This is followed by a rapid decline in
vegetation cover leading to the abandoned fields becoming more barren
than the adjoining desert. The effects of wind erosion on vegetation
cover can be easily seen in the temporal data The time series of data
allows quantitative measurements of the area covered by active sand.
On-site investigations have confirmed the relative barrenness of old
abandoned fields and the relatively high vegetation cover on recently
abandoned fields. Regions that have been identified in the remote
sensing data as areas undergoing sand mobilization show evidence of wind
erosion when observed on the ground. This study shows that the
abandonment of irrigated fields in arid regions leads to land
degradation which may not be evident from a single on-site or remote
sensing observation
Geoscience and Remote Sensing Symposium, 1994. IGARSS '94. Surface and Atmospheric Remote Sensing: Technologies, Data Analysis and Interpretation., International; 09/1994
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Combined Optical, Microwave, Earth and Atmosphere Sensing, 1993., Proceedings of IEEE Topical Symposium on; 04/1993
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ABSTRACT: Radar remote sensing data provide a unique perspective on the
Earth's crust and the processes that have influenced its evolution.
Physically based models are required, however, to relate the geophysical
quantities being measured by the radar sensor to useful geologic
information. Synthetic aperture radar (SAR) data over the Cima volcanic
field in the Mojave Desert of California are quantitatively connected
with microtopography through inversion of a radar backscatter model.
Changes in surface roughness inferred from the derived microtopography
are modeled and found to be consistent with aeolian mantling as surfaces
age. Estimated rates of aeolian deposition for the Cima area are
compared to the Lunar Crater volcanic field in Nevada. Rates of
deposition appear to be higher at Cima volcanic field, most likely
because of its proximity to Soda Lake, the main source of the aeolian
material
IEEE Transactions on Geoscience and Remote Sensing 04/1992; · 2.89 Impact Factor
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Geoscience and Remote Sensing Symposium, 1992. IGARSS '92. International; 02/1992
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ABSTRACT: Acquisition of ground truth data for use in microwave interaction modeling requires measurement of surface roughness sampled at intervals comparable to a fraction of the microwave wavelength and extensive enough to adequately represent the statistics of a surface unit. Sub-centimetric measurement accuracy is thus required over large areas, and existing techniques are usually inadequate. A technique is discussed for acquiring the necessary photogrammetric data using twin film cameras mounted on a helicopter. In an attempt to eliminate tedious data reduction, an automated technique was applied to the helicopter photographs, and results were compared to those produced by conventional stereogrammetry. Derived root-mean-square (RMS) roughness for the same stereo-pair was 7.5 cm for the automated technique versus 6.5 cm for the manual method. The principal source of error is probably due to vegetation in the scene, which affects the automated technique but is ignored by a human operator.
09/1991;
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ABSTRACT: Geologic analyses of spaceborne radar images of Earth are reviewed and summarized with respect to detecting, mapping, and interpreting impact craters, volcanic landforms, eolian and subsurface features, and tectonic landforms. Interpretations are illustrated mostly with Seasat synthetic aperture radar and shuttle-imaging-radar images. Analogies are drawn for the potential interpretation of radar images of Venus, with emphasis on the effects of variation in Magellan look angle with Venusian latitude. In each landform category, differences in feature perception and interpretive capability are related to variations in imaging geometry, spatial resolution, and wavelength of the imaging radar systems. Impact craters and other radially symmetrical features may show apparent bilateral symmetry parallel to the illumination vector at low look angles. The styles of eruption and the emplacement of major and minor volcanic constructs can be interpreted from morphological features observed in images. Radar responses that are governed by small-scale surface roughness may serve to distinguish flow types, but do not provide unambiguous information. Imaging of sand dunes is rigorously constrained by specific angular relations between the illumination vector and the orientation and angle of repose of the dune faces, but is independent of radar wavelength. With a single look angle, conditions that enable shallow subsurface imaging to occur do not provide the information necessary to determine whether the radar has recorded surface or subsurface features. The topographic linearity of many tectonic landforms is enhanced on images at regional and local scales, but the detection of structural detail is a strong function of illumination direction. Nontopographic tectonic lineaments may appear in response to contrasts in small-surface roughness or dielectric constant. The breakpoint for rough surfaces will vary by about 25 percent through the Magellan viewing geometries from low to high Venusian latitudes. Examples of anomalies and system artifacts that can affect image interpretation are described.
01/1990;
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Geoscience and Remote Sensing Symposium, 1989. IGARSS'89. 12th Canadian Symposium on Remote Sensing., 1989 International; 08/1989
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Geoscience and Remote Sensing Symposium, 1989. IGARSS'89. 12th Canadian Symposium on Remote Sensing., 1989 International; 08/1989
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Geoscience and Remote Sensing Symposium, 1989. IGARSS'89. 12th Canadian Symposium on Remote Sensing., 1989 International; 08/1989
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ABSTRACT: A common problem in acquiring ground truth data for use in microwave interaction modelling is the capture of surface roughness data that are both sampled at distances comparable to a fraction of the microwave wavelength and extensive enough to represent the surface statistics in at least one resolution cell of the microwave remote sensor employed. This leads to a requirement for height measurements with sub-centimeter accuracy and tedious d a t a reduction. Existing techniques such as electronic transits are usually inadequate for this purpose. C o n t a c t d e v i c e s such a s p r o f i l o m e t e r s (templates) are by nature one-dimensional and cannot span the required distances. Aerial photogrammetry and interferometric methods suffer from a lack of the necessary resolution. A technique has been developed for acquiring the necessary photogrammetric data using twin 70-mm film cameras mounted on a helicopter boom. The apparatus will be described and an estimate of the accuracy with which ground surface roughness can be characterized using this device will be given. In order to facilitate the tedious data reduction process, either standard stereogrammetric techniques must be employed or new techniques developed. For this study both standard and c r o s s c o r r e l a t i o n m e t h o d s w e r e u s e d . Stereogrammetry will be compared with a c o m p l e t e l y a u t o m a t e d i m a g e m a t c h i n g technique. Dense disparity images were generated from the helicopter stereo pairs. Using interior orientation parameters supplied by the camera manufacturers, and assuming that exterior orientation p a r a m e t e r s remained constant between control target and test field photography, an extremely dense DEM for a test field has been derived. Results will be compared and accuracy estimates will be presented.
Geoscience and Remote Sensing Symposium, 1989. IGARSS'89. 12th Canadian Symposium on Remote Sensing., 1989 International; 07/1989
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ABSTRACT: A common problem in acquiring ground-truth data for use in microwave interaction modeling is the capture of surface roughness data that are both sampled at distances comparable to a fraction of the wavelength and extensive enough to represent the surface statistics in at least one resolution cell of the microwave remote sensor used. A technique has been developed for acquiring the necessary photogrammetric data using twin 70-mm film cameras mounted on a helicopter boom. The apparatus is described, and the accuracy with which ground surface roughness can be characterized using this device is estimated. Both standard and cross-correlation methods were used for data reduction. Stereogrammetry is compared with a completely automated image-matching technique. Dense disparity images were generated from the helicopter stereo pairs. Using interior orientation parameters supplied by the camera manufacturers, and assuming that exterior orientation parameters remain constant between control target and test field photography, an extremely dense DEM (digital elevation model) for a test field has been derived. Results are compared, and accuracy estimates are presented.
02/1989;
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ABSTRACT: The authors have developed several techniques to analyze
polarimetric radar data from the NASA/JPL airborne SAR for Earth science
applications. The techniques determine the heterogeneity of scatterers
with subregions, optimize the return power from these areas, and
identify probable scattering mechanisms for each pixel in a radar image.
These techniques are applied to the discrimination and characterization
of geologic surfaces and vegetation cover, and it is found that their
utility varies depending on the terrain type. It is concluded that there
are several classes of problems amenable to single-frequency
polarimetric data analysis, including characterization of surface
roughness and vegetation structure, and estimation of vegetation
density. Polarimetric radar remote sensing can thus be a useful tool for
monitoring a set of Earth science parameters
IEEE Transactions on Geoscience and Remote Sensing 12/1988; · 2.89 Impact Factor
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Geoscience and Remote Sensing Symposium, 1988. IGARSS '88. Remote Sensing: Moving Toward the 21st Century., International; 10/1988
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Geoscience and Remote Sensing Symposium, 1988. IGARSS '88. Remote Sensing: Moving Toward the 21st Century., International; 10/1988
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ABSTRACT: The results of inferring geologic parameters such as rms surface height, correlation length, and dielectric constant of rough surfaces by fitting observed polarization signatures with those predicted by the second order Rice model are discussed. The inferred results are compared to measured values of rms height and correlation length. The rms height values inferred are in good agreement with in situ measurements. The inferred correlation lengths generally do not agree with measured values. The results allow the separation of the effects of surface roughness and dielectric constant on the overall backscatter from rough surfaces.
09/1988;
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ABSTRACT: A procedure is presented to discriminate and characterize regions of uniform image texture. The procedure utilizes textural features consisting of pixel-by-pixel estimates of the relative emphases of annular regions of the Fourier transform. The utility and derivation of the features are described through presentation of a theoretical justification of the concept followed by a heuristic extension to a real environment. Two examples are provided that validate the technique on synthetic images and demonstrate its applicability to the discrimination of geologic texture in a radar image of a tropical, vegetated area.
IEEE Transactions on Geoscience and Remote Sensing 10/1986; · 2.89 Impact Factor
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ABSTRACT: Receivers buried in the Nevada desert were used with the Shuttle Imaging Radar to measure microwave attenuation as a function of soil moisture in situ. Results agree closely with laboratory measureements of attenuation and suggest that penetration of tens of centimeters in desert soils is common for L-band (1.2-GHz) radar.
IEEE Transactions on Geoscience and Remote Sensing 08/1986; · 2.89 Impact Factor
