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It had been a long, productive trip. Launched in 1977, the two Voyager spacecraft had visited three giant planets, a dozen major Moons, three ring systems with thousands of rings composed of a myriad of tiny Moonlets. The spacecraft had returned 5 trillion bits of data and over 100,000 photographs. The last encounter in our Solar System by Voyager 2 with Neptune was to be a spectacular finale to the 12-year drama.
In 1977, the United States launched two unmanned Voyager spacecraft that were to take part in an extensive reconnaissance of the outer planets over a 12-year period visiting the environs of Jupiter, Saturn, Uranus, and Neptune. Their first encounter was with the complex Jupiter planetary system 400 million miles away. Sweeping by Jupiter and its five moons in 1979, the two spacecraft have sent back to Earth an enormous amount of data that will prove to be vital in understanding our solar system. Voyager 1 is scheduled to fly past Saturn on November 13 of this year; Voyager 2, in August of the following year.
The gross topography in southern Mare Imbrium and northern Oceanus Procellarum correlates with the buried structure and deposits of the Imbrium Basin and its rim, and many of the mare slopes may be depositional and reflect the pre-existing major features of the basin. Post-depositional, local distortion of the mare surface, however, is present and in many places associated with mare ridges. Many mare ridges are concentric to the Imbrium Basin suggesting that they are influenced by basin structures. Morphologic diversity of mare ridges suggests that not all have the same origin, and volcanic activity took place along some of them. Most mare ridges are associated with faults. The faults could be reverse and associated with a shrinking of the moon, however, some ridges parallel slopes and could be interpreted as decollement thrust faults along gliding horizons or as vertical faults caused by differential gravitational settling along lines that separate areas that are thinly flooded on topographic highs from areas that are thickly flooded in adjacent lows.
The population of Apollo, Amor and Mars crossing asteroids is studied. With the 18-inch Schmidt camera of the Hale Observatories at Mt. Palomar, four new planet crossing asteroids were discovered. A formal theory relating the probability of discovery of asteroid of a given orbital class to condition of search has been developed. From the estimated populations the flux of the Apollo objects to magnitude 18 near the Earth is of the order of (0.4 ± 0.2) 10 -14 km -2 yr -1 . During 3.3 b.y. this flux produces an estimated 60 ± 20 craters of 10 km in diameter and larger per 10 6 km 2 on the Moon. This number seems to be consistent with the observed crater densities on 3. 3 b.y. old mare surfaces in the eastern Oceanus Procellarum and Mare lmbrium.
Surveyor VI landed on the lunar surface at 01:01:05 GMT on day 314 (November 10, 1967) in the southwestern part of Sinus Medii near the center of the visible face of the Moon. Over 30,000 pictures were transmitted from the spacecraft during the first lunar day of operation. The number of pictures taken by Surveyor VI almost equals the total number of pictures returned from the previous Surveyor missions combined. The pictures were received at the Goldstone, California, Canberra, Australia, and Madrid, Spain, tracking stations of the Deep Space Network.
Surveyor VII, the last spacecraft of the Surveyor series, successfully landed at 01:05:36 GMT, January 10, 1968, on the outer rim flank of the large crater Tycho, in the southern part of the Moon. The spacecraft landed about 30 hours after local lunar sunrise and transmitted about 21,000 pictures during the remainder of the first lunar day of operation. On January 22, after local sunset, almost 700 pictures were taken of the Earth, the Sun's corona and parts of the lunar surface illuminated by earthlight. On February 12, Surveyor VII was revived for operation on the second lunar day approximately 120 hours after local lunar sunrise. The camera was then operated in the 200-line (low-resolution) mode because of loss in horizontal sweep in the 600-line (high-resolution) mode. About 45 pictures were taken in the 200-line mode during the second lunar day before loss of power caused suspension of camera operation.
Surveyor V landed on the lunar surface at 00:46:44 GMT on Day 254 (September 11), 35 hr after local sunrise on the moon. Between the time of landing and lunar sunset, 13 days later, it transmitted more than 18,000 high-quality television pictures of the lunar surface and parts of the spacecraft. The Surveyor V camera was operated extensively from the Goldstone, California, and Canberra, Australia, Tracking Stations of the Deep Space Network; some pictures were also received at the Madrid, Spain, Tracking Station.
Whereas the previous Surveyor missions were undertaken to examine mare surfaces as potential landing areas for the Apollo Program, the primary objective of the Surveyor VII mission, based on purely scientific motivations, was to explore a contrasting highland region and, specifically, to determine the chemistry of the highland material for comparison with the Surveyor V and VI chemical analyses at the mare sites. Site selection was limited to some extent by Surveyor operational constraints, but primarily by the requirements of 10-m-resolution photographs from the Lunar Orbiter Program for landing site certification. None of the nine sites studied in detail appeared capable of providing an unambiguous answer to the highland chemistry. The final selection of a site to the north of Tycho was based on the belief that the youthful character of the structure implied a minimum of contamination to the surface layers by foreign material via meteoritic processes. Moreover, the selection of a site near the rim of a major lunar crater promised insight into the “microscale” properties of a structure that represents the dominant morphologic feature on the moon.
Geologic mapping of the limbs and far side of the Moon has demonstrated the desirability of subdividing the pre-Imbrian rocks. A convenient datum is the Janssen Formation, the ejecta blanket of the Nectaris basin. A new system, herein named the Nectarian System, extends from the base of the Janssen Formation up to, but not including, the Fra Mauro Formation, which is the ejecta blanket of the Imbrium basin and the basal unit of the Imbrian System. As all rocks older than the Janssen Formation are informally called pre-Nectarian, the name "pre-Imbrian" is superseded by Nectarian and pre-Nectarian where rocks of these ages can be recognized.
The 2022 Crustal Deformation Modeling Workshop was held June 20–24 at the Colorado School of Mines in Golden, Colorado. The workshop included two days of tutorials on the use of the open-source software PyLith for crustal deformation modeling followed by three days of science talks and discussions. The workshop focused on three primary themes: (1) Earthquake cycle modeling; (2) Inversions for fault slip; and (3) Faulting, fluids, and surface loading. The talks highlighted how computational models provide insight into intriguing observations of Earth and planetary behavior. These included (1) earthquake synchronization of rupture patches due to their close proximity to each other, (2) the influence of fault geometry and damage zones on hypocenter depth and rupture propagation, (3) a lack of steady-state faulting behavior due to long time scales for grain size evolution in the mid-crust, (4) crustal deformation due to tidal, hydrological, and atmospheric loads, and (5) plumes of gas and icy particles due to tidal driven faulting on Enceladus (one of Saturn’s moons). The talks also described new computational modeling capabilities for incorporating complex geologic structure into Bayesian inversions for fault slip and efficient implementation of earthquake cycle models using a symmetric interior discontinuous Galerkin method. The complete agenda is available on the Computational Infrastructure for Geodynamic (CIG) website.
Rare Earth Elements (REEs) are increasingly attracting attention globally due to their pivotal role in enhancing the performance of various hightech devices. Small amounts of these elements greatly improve the performance of materials, making magnets stronger, lenses clearer, lights brighter, batteries last longer, etc. Here we examine the notion that REEs from the Moon might compete with mining on Earth.
The Great Lakes region, as defined here, includes the Great Lakes and their drainage basins in Minnesota, Wisconsin, Illinois, Indiana, Ohio, Pennsylvania, and New York. The region also includes the portions of Minnesota, Wisconsin, and the 21 northernmost counties of Illinois that lie in the Mississippi River drainage basin, outside the floodplain of the river. The region spans about 9º of latitude and 20º of longitude and lies roughly halfway between the equator and the North Pole in a lowland corridor that extends from the Gulf of Mexico to the Arctic Ocean. The Great Lakes are the most prominent natural feature of the region (Fig. 1). They have a combined surface area of about 245,000 square kilometers and are among the largest, deepest lakes in the world. They are the largest single aggregation of fresh water on the planet (excluding the polar ice caps) and are the only glacial feature on Earth visible from the surface of the moon (The Nature Conservancy 1994a). The Great Lakes moderate the region’s climate, which presently ranges from subarctic in the north to humid continental warm in the south (Fig. 2), reflecting the movement of major weather masses from the north and south (U.S. Department of the Interior 1970; Eichenlaub 1979). The lakes act as heat sinks in summer and heat sources in winter and are major reservoirs that help humidify much of the region. They also create local precipitation belts in areas where air masses are pushed across the lakes by prevailing winds, pick up moisture from the lake surface, and then drop that moisture over land on the other side of the lake. The mean annual frost-free period—a general measure of the growing-season length for plants and some cold-blooded animals—varies from 60 days at higher elevations in the north to 160 days in lakeshore areas in the south. The climate influences the general distribution of wild plants and animals in the region and also influences the activities and distribution of the human population. The wild plants and animals and the natural systems that support them in the Great Lakes region are valuable resources of considerable local, regional, and national interest. They are also, in part, transboundary resources that we share with our Canadian neighbors to the north. The way these resources are changing over time is inadequately known and is a cause for concern for resource users and for those charged with managing and protecting these unique and valuable resources. This chapter describes the wild plants and animals and the systems that support them in the Great Lakes region; addresses their condition; and points out the gaps in our knowledge about them that, if filled, would aid in their conservation and appropriate use.
The mottled duck ( Anas fulgivula ) is a non-migratory duck dependent on coastal habitats to meet all of its life cycle requirements in the Western Gulf Coast (WGC) of Texas and Louisiana, USA. This population of mottled ducks has experienced a moderate decline during the past 2 decades. Adult survival has been identified as an important factor influencing population demography. Previous work based on band-recovery data has provided only annual estimates of survival. We assessed seasonal patterns of female mottled duck survival from 2009 to 2012 using individuals marked with satellite platform transmitter terminals (PTTs). We used temperature and movement sensors within each PTT to indicate potential mortality events. We estimated cumulative weekly survival and ranked factors influential in patterns of mortality using known-fate modeling in Program MARK. Models included 4 predictors: week; hunting and non-hunting periods; biological periods defined as breeding, brooding, molt, and pairing; and mass at time of capture. Models containing hunt periods, during and outside the mottled duck season, comprised essentially 100% of model weights where both legal and illegal harvest had a negative influence on mottled duck survival. Survival rates were low during 2009–2011 (12–38% annual rate of survival), when compared with the long-term banding average of 53% annual survival. During 2011, survival of female mottled ducks was the lowest annual rate (12%) ever documented and coincided with extreme drought. Management actions maximizing the availability of wetlands and associated upland habitats during hunting seasons and drought conditions may increase adult female mottled duck survival.
The question of adapting to radar images the existing hardware that form topographic maps through stereo-photogrammetric models, is examined in principle. Such hardware utilizes a human/ computer hybrid. Although the problem of brightness differentials between corresponding landmarks can be dealt with pseudo-photoclinometrically, the main problem is whether the perspective in a radar image can be conceived to mimic that of a photographic image obtained by a suitably positioned camera. This conception is found to be possible, providing the characteristic relief subtends to a very small angle at the radar and at the fictitious camera. The photogrammetric model parameters must be determined a priori. ?? 1986 D. Reidel Publishing Company.
Because radarclinometry is fundamentally describable in terms of a nonlinear, first-order, partial differential equation, one expects that it can, in principle, be carried out by direct deterministic integration beginning at a given threshold profile along the azimuthal coordinate. Such a boundary condition could be provided by the altimetry profile obtained on a preceding or succeeding orbital revolution of the radar-bearing spacecraft. Notwithstanding the mismatched resolutions of the radar altimeter and the radar imaging system as planned for the Megallan mission to Venus, there are fundamental considerations, not involving system noise, that influence the possibility of success of this approach. From the topographic map of the Lake Champlain West quadrangle in the Adirondack Mountains of the U.S., a radar image is synthesized. Radarclinometry, in surface integral form, recaptures the topographic map when the applicable radar reflectance function is weakly variable over the range of application, but it diverges beyond a certain point for nominally variable reflectance functions. The effect can be understood by using results from the "shape-from-shading" literature. (This literature is produced by a group within the artificial intelligence community who have been independently attacking, for all practical purposes, photoclinometry, except that they have not given primacy to images of terrain.) The ubiquity of the instability suggests that the value of the surface integral approach is much in doubt. ?? 1988 Kluwer Academic Publishers.
The project to develop a line-integral approach to 2-dimensional radarclinometry and to bring it to the status of producing topographic maps from real radar images has been concluded. The final developments of the theory itself have involved a trial-and-error resolution of the curvature decision process at each integration step over range as follows: (1) Locally Indeterminate Azimuth-Azimuth Curvature is invoked if the range-directed path of integration is within 1 ??? in angle of the tangent to a local characteristic curve of the partial differential equation of radarclinometry (equivalent to a lapse in the necessity for an auxiliary curvature assumption); (2) Local Cylindricity is invoked if the local image isophote has a radius-of-curvature greater than 50 pixels; (3) Least-Squared Local Sphericity is invoked if the characteristic curve trends at greater than 70 ??? to the range direction (the auxiliary curvature assumption is becoming a sufficiently strong influence as to warrant the overconstraint), and (4) the default hypothesis, which is invoked most often, is the localization through the Euler/Lagrange equation from the calculus of variations of the global principle of minimization of the surface area of the terrain. The development of the set of line integrals into a 2-dimensional topographic surface is not practically achieved by branching the line integral at the range threshold, because the radarclinometry equations are too frequently coupled but weakly to the slope component in the direction of radar-azimuth, and under circumstances for which the powerfully influential auxiliary curvature assumption is too unrealistic. In other words, a line integration in radar-azimuth is far more frequently directed orthogonally to the local characteristic curve than is one carried out over range. Such orthogonality results in stepping the strike under the exclusive control of the curvature assumption. Instead, a quasi-surface-integration step is taken by modeling the dependence on initial strike of the gravitational potential energy of the vertical slab of terrain under the range-profile. The adopted starting strike for the range integral is the one which minimizes the gravitational potential energy. This radarclinometric method, in combination with my recently published method for determining an effective radar back-scattering function from one-dimensional slope statistics and image pixel-signal statistics, was applied to three images. First, to separate theoretical difficulties from experimental impediments, an artificial radar image was generated from a topographic map of the Lake Champlain West quadrangle in the Adirondack Mountains. Except for the regional trend in elevation, to which radarclinometry is insensitive by design, the agreement between the original and derived topography appears good. The morphologies agree and the range of relief is the same to within 4%. As an example of data of the highest quality available from space-borne radar at the present time, a SIR-B image of very rugged terrain in the coastal mountains of Oregon was similarly processed. The result, after filtering to redistribute photoclinometric errors about the two-dimensional spatial spectrum, agrees with ground truth almost as well. As an example of the worst possible data, in terms of signal-to-noise ratio and radar incidence angle (no detraction from the praise due the first high resolution space-borne radar-imaging of Venus intended), a Venera-15 image segment in Sedna Planitia just north-east of Sapho was processed, using Venera altimetry and Pioneer roughness data for slope statistics, in spite of the resolution mis-match. Considerably more trial-and-error filtering was required. The result appears plausible, but an error check is, of course, impossible. ?? 1990 Kluwer Academic Publishers.
A method is derived for determining the dependence of radar backscatter on incidence angle that is applicable to the region corresponding to a particular radar image. The method is based on enforcing mathematical consistency between the frequency distribution of the image's pixel signals (histogram of DN values with suitable normalizations) and a one-dimensional frequency distribution of slope component, as might be obtained from a radar or laser altimetry profile in or near the area imaged. In order to achieve a unique solution, the auxiliary assumption is made that the two-dimensional frequency distribution of slope is isotropic. The backscatter is not derived in absolute units. The method is developed in such a way as to separate the reflectance function from the pixel-signal transfer characteristic. However, these two sources of variation are distinguishable only on the basis of a weak dependence on the azimuthal component of slope; therefore such an approach can be expected to be ill-conditioned unless the revision of the transfer characteristic is limited to the determination of an additive instrumental background level. The altimetry profile does not have to be registered in the image, and the statistical nature of the approach minimizes pixel noise effects and the effects of a disparity between the resolutions of the image and the altimetry profile, except in the wings of the distribution where low-number statistics preclude accuracy anyway. The problem of dealing with unknown slope components perpendicular to the profiling traverse, which besets the one-to-one comparison between individual slope components and pixel-signal values, disappears in the present approach. In order to test the resulting algorithm, an artificial radar image was generated from the digitized topographic map of the Lake Champlain West quadrangle in the Adirondack Mountains, U.S.A., using an arbitrarily selected reflectance function. From the same map, a one-dimensional frequency distribution of slope component was extracted. The algorithm recaptured the original reflectance function to the degree that, for the central 90% of the data, the discrepancy translates to a RMS slope error of 0.1 ???. For the central 99% of the data, the maximum error translates to 1 ???; at the absolute extremes of the data the error grows to 6 ???. ?? 1988 Kluwer Academic Publishers.
Radarclinometry, the invention of which has been previously reported, is a technique for deriving a topographic map from a single radar image by using the dependence upon terrain-surface orientation of the integrated signal of an individual image pixel. The radiometric calibration required for precise operation and testing does not yet exist, but the imminence of important applications justifies parallel, rather than serial, development of radarclinometry and radiometrically calibrated radar. The present investigation reports three developmental advances: (1) The solid angle of integration of back-scattered specific intensity constituting a pixel signal is more accurately accounted for in its dependence on surface orientation than in previous work. (2) The local curvature hypothesis, which removes the requirement of a ground-truth profile as a boundary condition and enables the formulation of the theory in terms of a line integral, has been expanded to include the three possibilities of Local Cylindricity, Local Biaxial Ellipsoidal Hyperbolicity, and Least-Squares Local Sphericity. (3) The theory is integrated in the cross-ground-range direction, which is ill-conditioned compared to the ground-range direction, whereas the original formulation was based on enforced isotropy in the two-dimensional power spectrum of the topography. It was found necessary to prohibit the hypothesis of Local Biaxial Ellipsoidal Hyperbolicity in the cross-range stepping, for reasons not completely clear. Variation in the proportioning between curvature assumptions had produced topographic maps that are in good mutual agreement but not realistic in appearance. They are severely banded parallel to the ground-range direction, most especially at small radar zenith angles. Numerical experimentation with the falsification of topography through incorrect decalibration as performed on a Gaussian hill suggests that the banding and its exaggeration at high radar incidence angles could easily be due to our lack of radiometric calibration. ?? 1987 D. Reidel Publishing Company.