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Radar remote sensing is a tool of increasing importance in the study of volcanic sites. Synthetic aperture radar (SAR) is a high‐resolution imaging tool used to survey areas which are not practical or safe to be directly inspected. With the introduction of the across‐track SAR interferometry (IFSAR) technique, digital elevation models (DEM) can be produced. The usefulness of such interferometric products depends on the ability to extract information that can be used for geological interpretation. We analyzed the shuttle imaging radar C (SIR‐C)/X‐SAR multifrequency multipass interferometry mission over Mount Etna, Sicily, and we performed a supervised geological interpretation of the coherence maps and a fractal‐based analysis of the IFSAR DEMs. The first permits us to recognize different volcanic terrain and to distinguish between vegetated and unvegetated areas, while the second allows us to validate the IFSAR DEMs and to detect large‐scale geological features. This latter analysis, performed over the photogrammetric DEM, enabled us to recognize artifacts caused by digitizing and resampling. Obviously, IFSAR DEMs are not affected by these problems. As a consequence, IFSAR products are a valuable aid in geological interpretation.

The Imager for Mars Pathfinder (IMP) acquired more than 16,000 images and provided panoramic views of the surface of Mars at the Mars Pathfinder landing site in Ares Vallis. This paper describes the stereoscopic, multispectral IMP imaging sequences and focuses on their use for digital mapping of the landing site and for deriving cartographic products to support science applications of these data. Two‐dimensional cartographic processing of IMP data, as performed via techniques and specialized software developed for ISIS (the U.S. Geological Survey image processing software package), is emphasized. Cartographic processing of IMP data includes ingestion, radiometric correction, establishment of geometric control, coregistration of multiple bands, reprojection, and mosaicking. Photogrammetric processing, an integral part of this cartographic work which utilizes the three‐dimensional character of the IMP data, supplements standard processing with geometric control and topographic information [Kirk et al., this issue]. Both cartographic and photogrammetric processing are required for producing seamless image mosaics and for coregistering the multispectral IMP data. Final, controlled IMP cartographic products include spectral cubes, panoramic (360° azimuthal coverage) and planimetric (top view) maps, and topographic data, to be archived on four CD‐ROM volumes. Uncontrolled and semicontrolled versions of these products were used to support geologic characterization of the landing site during the nominal and extended missions. Controlled products have allowed determination of the topography of the landing site and environs out to ∼60 m, and these data have been used to unravel the history of large‐ and small‐scale geologic processes which shaped the observed landing site. We conclude by summarizing several lessons learned from cartographic processing of IMP data.

Vegetation phenology has a strong influence on the timing and phase of global terrestrial carbon and water exchanges and is an important indicator of climate change and variability. In this study we tested the application of inexpensive digital visible‐light cameras in monitoring phenology. A standard digital camera was mounted on a 45 m tall flux tower at the Lägeren FLUXNET/CarboEuropeIP site (Switzerland), providing hourly images of a mixed beech forest. Image analysis was conducted separately on a set of regions of interest representing two different tree species during spring in 2005 and 2006. We estimated the date of leaf emergence based on the levels of the extracted red, green and blue colors. Comparisons with validation data were in accordance with the phenology of the observed trees. The mean error of observed leaf unfolding dates compared with validation data was 3 days in 2005 and 3.6 days in 2006. An uncertainty analysis was performed and demonstrated moderate impacts on color values of changing illumination conditions due to clouds and illumination angles. We conclude that digital visible‐light cameras could provide inexpensive, spatially representative and objective information with the required temporal resolution for phenological studies.

A technique for routinely determining the velocity structure of the sediment column with an average error of less than 100/m sec during normal reflection profiling is described. An expendable passive sonobuoy is launched while the ship is underway. A variable angle reflection profile is recorded on one channel of the seismic profiler, and a vertical reflection profile is obtained on the other, providing dip and topographic corrections for the variable angle data. The velocity structure is determined by means of a modified T2/X2 solution programmed for a digital computer. The sonobuoy system has the advantage of being free of towing noise, permitting the use of lower frequencies, which in some areas results in greater penetration than is possible with a towed array. The accuracy and reliability of the system and the problems relating to velocity gradients are discussed. The examples discussed cover a wide range of conditions and geographic locations.

Digital topographic contours from four 1:250000 scale maps have been gridded to produce a digital elevation model for part of Ellesmere and Axel Heiberg islands in the Canadian Arctic Islands. Gradient calculations were used to define both east and west dipping slopes defining a pattern of lineaments that have been compared with mapped geological structures. In ice‐covered areas, where geological mapping was not possible, well‐defined topographic lineaments have been identified and are correlated to extensions of major structural features. The northeast‐southwest patterns of both topographic lineaments and mapped structures are strongly unimodal and support a single compressive event oriented at 67° west of north. This orientation is coincidental with the convergence direction calculated from the kinematic poles of rotation for Greenland relative to North America between 56 and 35 Ma. A minor secondary peak at 70° east of north is observed for thrust and normal fault solutions and is not directly related to the predicted convergence direction. Whether this represents a unique phase of deformation or is a subcomponent of a single event is not known. The agreement of structural components, lineament orientations, and convergence direction suggests an overwhelming overprint of Eurekan deformation on any preexisting structural fabric. This study confirms, for the first time, an excellent compatibility between geological and geophysical constraints for the timing and geometry of the Eurekan orogeny.

This report revisits the very early high‐frequency slab phases from earthquakes in the Kermadec slab (between −25°S and −37°S) that arrive as a precursor to the P wave onset at stations in New Zealand. The analysis of short‐period digital records for station SNZO (South Karori New Zealand) for the time period between 1980 and 1986 involved 4 times as many data as in previous studies. We confirm most of the earlier observations, in particular the relationship between source region and observed waveform. Numerical waveform modeling using two‐dimensional slab models confirm that the high‐frequency precursor can be explained by P wave propagation in a thin (8–10 km) high‐velocity layer (HVL). The sensitivity of the high‐frequency phase to source position in the slab is investigated, and we demonstrate that the slab phase does not survive interruptions or strong lateral variations of the HVL. Assuming the shape of the slab from tomographic images and continuity of the HVL, we infer that the large negative travel time residuals can be explained if P wave propagation is 4 to 5% faster than in the ambient mantle for depths to 300 km and about 2% faster for depths between 300 and 600 km. Rather than resorting to regional differences in structure and composition of the HVL, we argue that specific source‐receiver configurations and the shape of the slab explain the observed regional variation in the character of the high‐frequency slab phases.

Digital computer techniques for Mars surface imagery systematic video data distortions quantification and correction onboard Mariner 6 and 7

A vibrating string accelerometer (VSA) sea gravity meter with electronics for digital readout has been assembled, tested, and used by the Woods Hole Oceanographic Institution. The VSA meter is installed in a portable van laboratory that also contains a digital computer for automatic logging of gravity, magnetic, and ship's velocity information. Two years of testing and use of the VSA gravity meter at sea are summarized. Tares and remaining sensitivity to variations in ambient temperature and supply voltage are inferred to be due primarily to the oscillator amplifiers. Improved oscillator amplifiers will be installed. During December 1969, the VSA meter, together with a gyrostabilized LaCoste and Romberg (L&R) sea gravity meter, were operated aboard the RV Atlantis 2. The values from the VSA and L&R gravity meters were both reduced using identical navigational information. Resulting profiles of free-air anomalies derived from both meters differed by up to 15 mgal and led to the identification of a malfunction in the cross-coupling circuitry of the L&R meter. Identical malfunctions have been subsequently identified in three other L&R sea gravity meters.

A method is presented for calculating the gravitational attraction of three-dimensional bodies of arbitrary shape within a spherical or ellipsoidal earth. The sphericity of the earth is treated exactly by developing the formulas in a spherical coordinate system and the ellipticity is treated approximately by including only first-order terms in the flattening of the earth. The three-dimensional body is specified by giving its shape and density at a number of successive depths. The method is well suited for evaluation on a digital computer, and calculations are presented for a couple of examples that demonstrate in a quantitative manner the relative effects of sphericity and ellipticity.