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Both MAGSAT data and preliminary results emphasizing Africa, Latin America, and the Caribbean were presented to geologists in Jamaica, Guyana, Brazil, and Argentina. Preliminary interpretations were discussed. A synopsis tectonic map of South America was completed. Semi-final modeling of northern South America was initiated.
A wide spectrum of technology pertaining to the inventory of crops using LANDSAT without in situ training data is addressed. Methods considered include Bayesian based through-the-season methods, estimation technology based on analytical profile fitting methods, and expert-based computer aided methods. Although the research was conducted using U.S. data, the adaptation of the technology to the Southern Hemisphere, especially Argentina was considered.
A differential equation describing the temporal behavior of greenness, G(t), with time was developed. The basic equation, dG(t)/dt=k(t)(1-G/G sub m) where G sub m is the saturation value of greenness at time, t sub p. It demonstrated that k(t) is linearly proportional to the rate of change of leaf area index. It was also demonstrated that G sub m, t sub p and profile width, are the key to vegetation identification and that the inflection points of the profile are related to the ontogenic state of the plant. These profile features were shown to hold not only throughout the United States corn/soybean growing area, but for the first time in Argentina. A mathematical technique that maximizes the sensitivity of spectral transformation to Leaf Area Index and simultaneously minimizes the sensitivity to all other variables was formulated. Initial results on corn and wheat were obtained.
Current knowledge and theories of large scale Andean tectonics as they relate to site planning for the NASA Crustal Dynamics Program's proposed high precision geodetic measurements of relative motions between the Nazca and South American plates are summarized. The Nazca Plate and its eastern margin, the Peru-Chile Trench, is considered a prototype plate marked by rapid motion, strong seismicity and well defined boundaries. Tectonic activity across the Andes results from the Nazca Plate subducting under the South American plate in a series of discrete platelets with different widths and dip angles. This in turn, is reflected in the tectonic complexity of the Andes which are a multitutde of orogenic belts superimposed on each other since the Precambrian. Sites for Crustal Dynamics Program measurements are being located to investigate both interplate and extraplate motions. Observing operations have already been initiated at Arequipa, Peru and Easter Island, Santiago and Cerro Tololo, Chile. Sites under consideration include Iquique, Chile; Oruro and Santa Cruz, Bolivia; Cuzco, Lima, Huancayo and Bayovar, Peru; and Quito and the Galapagos Islands, Ecuador. Based on scientific considerations, Santa Cruz, Huancayo (or Lima), Quito and the Galapagos Islands should be replaced by Isla San Felix, Chile; Brazilia or Petrolina, Brazil; and Guayaquil, Ecuador. If resources permit, additional important sites would be Buenaventura and Villavicencio or Puerto La Concordia, Colombia; and Mendoza and Cordoba, Argentina.
Evaluations of remote sensing procedures developed specifically to estimate non-U.S. spring small grains area show accuracies of less than 10 percent relative difference to reference statistics for North Dakota in 1978 and good comparison with 9000 square miles of observations over four states and Saskatchewan, Canada during the years 1976-79. Processing a 5 x 6-nautical-mile sample site requires a few minutes manual time and a few minutes central processing unit time on an AS-3000 computer. Evaluations of summer crop, corn, and soybeans area estimates show unbiased summer crops estimates in the U.S. central corn belt but significant bias in one of two years for area estimates of corn and soybeans. Based on results to date, a highly automated corn/sorghum/soybean area estimation procedure should be achieved that is applicable to Argentina.
Preliminary results on the radargrammetric processing of SIR-A and SIR-B data are presented. Radargrammetric processing was applied to images of the Trinity National Forest in Northern California, the islands of Cephalonia, Ithaka, and Sardegna, Mt. Shasta, and Cordon La Grasa, Argentina. The preliminary processing of the SIR-A and SIR-B data has produced digital elevation models, stereo models, and a contour map.
The use of signature-extendable technology to improve the efficiency of machine processing of remotely sensed data is examined. Temporal profile technology is employed to automatically recognize crops; the technique uses the Kauth and Thomas (1976) transform of Landsat, multidata, and parameters derived from a model of each crop's greenness-time trajectory. The basic characteristics of temporal profile technology and the U.S. based labeling algorithm are described. Consideration is given to signature extension, signature-extendable spaces, and signature-extendable features. The greenness and brightness parameters used in temporal profile technology are derived. The signature extendability of the parameters is evaluated by applying them to the analysis of corn and soybean crops in the U.S. and Argentina. It is noted that the technique is an affordable and efficient method for deriving data on crops on a global basis.
Analysis of moisture availability, determined from GOES IR surface temperature measurements and a boundary layer model, and antecedent precipitation are presented for data taken over Texas and Argentina. Correlations between antecedent precipitation and moisture availability are high where the spatial variation in moisture availability is much larger than an inherent uncertainty in the method, which is judged to be about + or - 0.2 for the moisture availability parameter. In regions where there are large gradients of precipitation, the IR method can provide useful information on variations in soil moisture availability and, by implication, in precipitation.
The LANDSAT Thematic Mapper (TM) studies of 2.2 my old ignimbrites in a test area around the Cerro Galan Caldera, N. W. Argentina, show that the ignimbrites exhibit a remarkable range of spectral characteristics dependent both on intrinsic and extrinsic properties resulting from aeolian weathering processes. Spectral profiles of the ignimbrite in four contrasted environments were constructed using 6 TM bands. The textural and structural characteristics of ignimbrites on Mars were evaluated.
This paper focuses on the use of a high resolution digital elevation model (DEM) to aid in rectifying and enhancing synthetic aperture radar images. Using a synthetic backscatter image, the SIR-B images are manually rectified and resampled to remove geometric distortions caused by topography. In a second step, an improved reflectance function of incidence angle is derived from the DEM and the rectified image and this function is used to reduce radiometric effects of topography yielding an albedo image which clearly shows the thematic, as opposed to topographic content of the image. The procedure is tested on four SIR-B images of a scene in Argentina (crossover point) that is imaged under different azimuth and incidence angles. The similarity of the resulting images indicates that the procedure effectively reduces artefacts from the images that are dependent on topography.
A particularly detailed set of observations in the vicinity of an intraplate, thrust earthquake (M 7.4) in Argentina, indicate a cyclic pattern of deformation very similar to that reported previously for interplate earthquakes. This deformation cycle, which may be characteristic of many seismically active areas, consists of: (1) steady strain accumulation, possibly punctuated by strain reversals; (2) coseismic strain release; (3) a period of continued strain release due to afterslip (persisting for perhaps a year or so); and (4) rapid postseismic strain accumulation which decreases exponentially and grades into steady strain accumulation. Deformation associated with three earthquakes in the U.S. (1940, M7.1 Imperial Valley California; 1964, M8.4 Alaska; 1959, M7.5 Hebgen Lake, Montana) are interpreted in light of this general earthquake cycle and are used to investigate the mechanics of strain release for these events. These examples indicate that large postseismic movements can occur for strike-slip, thrust, and normal fault events, and both viscoelastic relaxation and postseismic after-slip must be incorporated in models of earthquake related deformation. The mechanics of the strain release process revealed by these examples has implications for estimating earthquake repeat times from geodetic observations near active faults.
Observations of an interplate, thrust earthquake in Argentina are used to characterize a cyclic pattern of earthquake deformation. The cycle consists of steady strain accumulation, coseismic strain release, a period of continued strain release due to afterslip, and rapid postseismic strain accumulations which decrease exponentially and grade into steady strain accumulation. The cycle is used to interpret the deformation of three earthquakes in California, Alaska, and Montana, focusing on the mechanics of strain release. The results suggest that large postseismic movements can occur for strike-slip, thrust, and normal fault events. It is found that viscoelastic relaxation and postseismic afterslip should be incorporated in models of earthquake-related deformation. The use of these results for estimating earthquake repeat times from geodetic observations near active faults is considered.
Local network data from San Juan, Argentina, provides new information about crustal seismicity in the Andean foreland above a horizontal segment of the subducted Nazca Plate. Two areas of foreland seismicity are found, one associated with the Sierras Pampeanas basement uplifts, and the other beneath, but not within, the Precordillera foreland fold-thrust belt. The Precordillera seismicity provides direct evidence for basement deformation beneath the sediments of the thrust belt and supports the idea that its eastern part is significantly modified by underlying basement deformation. In both areas, events are concentrated between 15 and 35 km depth and have volumetric, rather than planar, faultlike distributions. The depth distribution is unusually deep for intraplate earthquakes and suggests a brittle-ductile transition near 30-35 km.
Periodic variations in Comet Halley's production of gas and dust during its 1910 apparition were searched for using measurements from a homogeneous set of photographic plates obtained at the National Observatory of Argentina at Cordoba. After applying corrections to the observations to compensate for geometric and heliocentric distance effects, the data, spanning the two months immediately following perihelion, were split into two sections for analysis. Of the possible periods indicated in either half of the dataset, only those in the range of 7.3-7.8 days were present in both halves. The additional constraint of similarity in the shape of the resulting, phased light curves further constrained the period from about 7.35 to 7.60 days. Allowing for the inherent limitations of the 1910 data, comparison of these light curves to the equivalent 1986 light curve indicates that a match in features between the two apparitions is made possible by utilizng one of two phase shifts. While not conclusive, this ability to match features suggests long-term stability in many aspects of Halley's intrinsic activity.
An overview of space flight STS-41 is presented, including personal observations and comments by the mission astronauts. The crew deployed the Ulysses spacecraft to study the polar regions of the sun and the interplanetary space above the poles. Environmental observations, including those of Lake Turkana, Lake Chad, biomass burning in Madagascar and Argentina, and circular features in Yucatan are described. Observations that include landforms and geology, continental sedimentation, desert landscapes, and river morphology are discussed.
Quantitative use of remote multispectral measurements to study and map land surface evapotranspiration has been a challenging issue for the past 20 years. Past work is reviewed against process physics. A simple two-layer combination-type model is used which is applicable to both vegetation and bare soil. The theoretic analysis is done to show which land surface properties are implicitly defined by such evaporation models and to assess whether they are measurable as a matter of principle. Conceptual implications of the spatial correlation of land surface properties, as observed by means of remote multispectral measurements, are illustrated with results of work done in arid zones. A normalization of spatial variability of land surface evaporation is proposed by defining a location-dependent potential evaporation and surface temperature range. Examples of the application of remote based estimates of evaporation to hydrological modeling studies in Egypt and Argentina are presented.
During our participation in the NASA Crustal Dynamics Project under NASA contract NAS-27339 and grant NAG5-814 for the period 1982-1991, we published or submitted for publication 30 research papers and 52 abstracts of presentations at scientific meetings. In addition, five M.I.T. Ph.D. students (Eric Bergman, Steven Bratt, Dan Davis, Jeanne Sauber, Anne Sheehan) were supported wholly or in part by this project during their thesis research. Highlights of our research progress during this period include the following: application of geodetic data to determine rates of strain in the Mojave block and in central California and to clarify the relation of such strain to the San Andreas fault and Pacific-North American plate motions; application of geodetic data to infer post seismic deformation associated with large earthquakes in the Imperial Valley, Hebgen Lake, Argentina, and Chile; determination of the state of stress in oceanic lithosphere from a systematic study of the centroid depths and source mechanisms of oceanic intraplate earthquakes; development of models for the state of stress in young oceanic regions arising from the differential cooling of the lithosphere; determination of the depth extent and rupture characteristics of oceanic transform earthquakes; improved determination of earthquake slip vectors in the Gulf of California, an important data set for the estimation of Pacific-North American plate motions; development of models for the state of stress and mechanics of fold-and-thrust belts and accretionary wedges; development of procedures to invert geoid height, residual bathymetry, and differential body wave travel time residuals for lateral variations in the characteristic temperature and bulk composition of the oceanic upper mantle; and initial GPS measurements of crustal deformation associated with the Imperial-Cerro Prieto fault system in southern California and northern Mexico. Full descriptions of the research conducted on these topics may be found in the Semi-Annual status Reports submitted regularly to NASA over the course of this project and in the publications listed.
Initial analyses of the geologic setting, petrology, and geochemistry of glasses recovered from within and around the elongate Rio Cuarto (RC) craters in Argentina focused on selected samples in order to document the general similarity with impactites around other terrestrial impact craters and to establish their origin. Continued analysis has surveyed the diversity in compositions for a range of samples, examined further evidence for temperature and pressure history, and compared the results with experimentally fused loess from oblique hypervelocity impacts. These new results not only firmly establish their impact origin but provide new insight on the impact process.