The volumetric evolution of Surtsey has been estimated on the basis of digital elevation models derived from NASA scanning airborne laser altimeter surveys (20 July 1998), as well as digitized 1:5,000-scale topographic maps produced by the National Land Survey of Iceland and by Norrman.Subaerial volumes have been computed from co-registered digital elevation models (DEM's) from 6 July 1968, 11 July 1975, 16 July 1993, and 20 July 1998 (scanning airborne laser altimetry), as well as true surface area (above mean sea level).Our analysis suggests that the subaerial volume of Surtsey has been reduced from nearly 0.100 kmJ on G July 1968 to 0.075 km' on 20 July 1998.Linear regression analysis of the temporal evolution of Surtsey's subaerial volume indicates that most of its subaerial surface will be at or below mean sea-level by approximately 2100.This assumes a conservahve estimate of continuation of the current pace of marine erosion and mass-wasting on the island, including the indurated core of the conduits of the Surtur I and Surtur I1 eruptive vents.If the conduits are relatively resistant to marine erosion they will become sea stacks after the rest of the island has become a submarine shoal, and some portions of the island could survive for centuries.The 20 July 1998 scanning laser altimeter surveys f ~~r t h e r indicate rapid enlargement of erosional canyons in the northeastern portion of the partial tephra ring associated with Surtur I. Continued airborne and eventually spaceborne topographic surveys of Surtsey are planned to refine the inter-annual change of its subaerial volume.
We report preliminary observations obtained from the NEAR Laser Rangefinder (NLR) and NEAR Multispectral Imager (MSI) for approx. 300 craters seen on 433 Eros to address Eros crater formation and degradation processes. Additional information is contained in the original extended abstract.
Impact cratering of the earth's surface is discussed and compared with lunar craters. The basic types found on earth are either simple craters or complex impact structures and basins. Meteorite fragments and shock metamorphism provide evidence of a crater's formation by meteorite impact. Known craters on earth are ordered by location and a few principal facts are given for each crater and the general terrain in which it is located. A satellite picture of each crater and maps identifying crater locations are provided.
Samples of the lunar regolith returned by Apollo astronauts show large variations (0 to >10 wt%) in TiO 2 abundance indicating complex compositional zonation within the lunar mantle. A long held goal of the lunar science community is the accurate determination of TiO 2 abundances on the lunar surface through remote sensing methods. To date only limited progress has been made in this area using spacecraft spectral measurements acquired in visible through near‐infrared wavelengths. Here we show that variations in the ratios of ultraviolet (UV) to visible (VIS) reflectances in images taken by the Hubble Space Telescope indicate a strong correlation with TiO 2 abundances determined from returned samples at the Apollo 17 landing site, and little correlation with the “maturity” of lunar soils. These new findings imply that UV‐VIS observations may lead to an alternate and improved method of remotely mapping TiO 2 ‐bearing materials (probably as ilmenite) across the lunar surface and enable more refined studies of lunar crustal composition, surface volcanism, and subsurface magma evolution processes. Additionally, accurate identification and quantification of TiO 2 rich deposits serves to guide future human exploration of the Moon.
Surface lidar techniques are now being demonstrated in low Earth orbit with a single beam of pulsed laser radiation at 1064 nm that profiles the vertical structure of Earth surface landforms along the nadir track of a spacecraft. In addition, a profiling laser altimeter, called MOLA, is operating in elliptical Martian orbit and returning surface topography data. These instruments form the basis for suggesting an improved lidar instrument that employs multiple beams for extension of sensor capabilities toward the goal of true, 3-dimensional mapping of the Moon or other similar planetary surfaces. In general the lidar waveform acquired with digitization of a laser echo can be used for laser distance measurement (i.e. range-to-the-surface) by time-of-flight measurement and for surface slope and shape measurements by examining the detailed lidar waveform. This is particularly effective when the intended target is the lunar surface or another planetary body free of any atmosphere. The width of the distorted return pulse is a first order measure of the surface incidence angle, a combination of surface slope and laser beam pointing. Assuming an independent and absolute (with respect to inertial space) measurement of laser beam pointing on the spacecraft, it is possible to derive a surface slope with-respect-to the mean planetary surface or its equipotential gravity surface. Higher-order laser pulse distortions can be interpreted in terms of the vertical relief of the surface or reflectivity variations within the area of the laser beam footprint on the surface.
