Application of coupled-wave Wentzel-Kramers-Brillouin approximation to ground penetrating radar

This paper deals with bistatic subsurface probing of a horizontally layered dielectric half-space by means of ultra-wideband electromagnetic waves. In particular, the main objective of this work is to present a new method for the solution of the two-dimensional back-scattering problem arising when a pulsed electromagnetic signal impinges on a non-uniform dielectric half-space; this scenario is of interest for ground penetrating radar (GPR) applications. For the analytical description of the signal generated by the interaction of the emitted pulse with the environment, we developed and implemented a novel time-domain version of the coupled-wave Wentzel-Kramers-Brillouin approximation. We compared our solution with finite-difference time-domain (FDTD) results, achieving a very good agreement. We then applied the proposed technique to two case studies: in particular, our method was employed for the post-processing of experimental radargrams collected on Lake Chebarkul, in Russia, and for the simulation of GPR probing of the Moon surface, to detect smooth gradients of the dielectric permittivity in lunar regolith. The main conclusions resulting from our study are that our semi-analytical method is accurate, radically accelerates calculations compared to simpler mathematical formulations with a mostly numerical nature (such as the FDTD technique), and can be effectively used to aid the interpretation of GPR data. The method is capable to correctly predict the protracted return signals originated by smooth transition layers of the subsurface dielectric medium. The accuracy and numerical efficiency of our computational approach make promising its further development

Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars

The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1 × 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-μm reflectivity with an accuracy of 5% have also been obtained

Understanding our celestial neighbors: an indian perspective in planetary sciences and exploration

The planetary exploration program of the Indian Space Research Organization is described. The important results obtained from the two successful missions, Mars orbiter Mission (2014) and the earlier Chandrayaan-1 mission (2008-9) to moon are summarized. High-resolution maps of Valles Marineris enabled several surface, aqueous and atmospheric features to be delineated and the highly elliptical orbit of MOM enabled imaging of the surface of the farther side of Deimos as well as study of Mars exospheric constituents. The results from Chandrayaan-1 mission changed many lunar concepts e.g. from dry, passive and inactive to moon to wet, tectonically and volcanically active moon. Some recent results based on the space borne and laboratory based study of Titan, Pluto, Comets and meteorites coming from Mars and Vesta are summarized. The future planetary exploration plans, such as Chandrayaan-2 and second Mars mission are briefly mentioned

Design and Construction of an Optical Polarimeter for the Study of Ice-like Analogs using Near Zero Phase Angle Measurements

Previous studies for analog samples measuring polarized backscatter near zero phase angles have suggested strong presence of multiple scattering effects. Radar data for Mercury, Moon and other Icy Galilean satellites exhibit high circular polarization ratios with decreasing phase angle that indicates the possible presence of icy deposits in the polar craters. An examination of powder samples with known composition and grain sizes was undertaken to try and further understand the interaction of polarized light with closely packed particulate medium. The goal of this research was to construct and test a long arm Goniometric optical instrument capable of measuring polarization ratios in the range from 0-5 degree phase angle for understanding and differentiating the scattering effects that occur near zero phase angle. Measuring signal intensity and circular polarization ratios with the Goniometric polarimeter for various analog samples will provide an understanding for the characteristics of embedded scatterers within the icy regoliths

6-meter wavelength polarimetric inverse synthetic aperture radar mapping of the Moon

Remote sensing of planetary surfaces is an effective method for gaining knowledge of the processes that shape the planetary bodies in our solar system. This is useful for uncovering the environment of the primordial solar system and to study the current state of the upper crusts of the other planets in our neighborhood. A recent 6-meter wavelength polarimetric radar map of the Moon showed unexpectedly low depolarized radar returns in two regions on the lunar nearside. These two areas were a highland region between Mare Imbrium and Mare Frigoris, and the highland area surrounding the Schiller-Zucchius impact basin. These two regions showed characteristics unlike those of typical highland regions of the lunar surface. So far, there has been no readily available explanation for this observation. In this study, it is shown that the likely cause is an increased loss tangent due to chemical differences in the first few hundred meters of the lunar soil. We also show the absence of any coherent subsurface, which could be the preserved remains of an ancient basaltic plain. We do this by comparing the 6-meter polarimetric radar map to other relevant data sets: 1) surface TiO_2 and FeO abundance, 2) surface rock population, 3) radar maps of the Moon with other wavelengths, and 4) visual spectrum images of the Moon. The area near the Schiller-Zucchius basin was shown to be consistent with other areas with similar surface chemical compositions, but the region between Mare Imbrium and Mare Frigoris showed significantly lower mean power in comparison to otherwise similar regions. While we can not conclusively determine the cause, we hypothesize that the low radar return is explained by an increased concentration of iron and titanium oxides in the volume beneath the surface, potentially due to remnants of primordial lunar volcanism. The results show that long wavelength polarimetric radar measurements of the Moon are very powerful tools for studying the earliest stages of the evolution of the Moon

Design and Demonstration of a Miniature Lidar System for Rover Applications

Public awareness of harmful human environmental effects such as global warming has increased greatly in recent years and researchers have increased their efforts in gaining more knowledge about the Earth's atmosphere. Natural and man-made processes pose threats to the environment and human life, so knowledge of all atmospheric processes is necessary. Ozone and aerosols are important factors in many atmospheric processes and active remote sensing techniques provide a way to analyze their quantity and distribution. A compact ground-based lidar system for a robotic platform meant for atmospheric aerosol measurements was designed, tested, and evaluated. The system will eventually be deployed for ozone and aerosol measurements in Mars and lunar missions to improve our knowledge and understanding of atmospheres on Mars and the Moon. Atmospheric testing was performed to test the operability of the receiver system to acquire the lidar return signal from clouds and aerosols

Laboratory for Oceans

A review is made of the activities of the Laboratory for Oceans. The staff and the research activities are nearly evenly divided between engineering and scientific endeavors. The Laboratory contributes engineering design skills to aircraft and ground based experiments in terrestrial and atmospheric sciences in cooperation with scientists from labs in Earth sciences

A Multispectral Assessment of Complex Impact Craters on the Lunar Farside

Hypervelocity collisions of asteroids onto planetary bodies have catastrophic effects on the target rocks through the process of shock metamorphism. The resulting features, impact craters, are circular depressions with a sharp rim surrounded by an ejecta blanket of variably shocked rocks. With increasing impact energy, the inner crater cavity can preserve complex morphologies including terraced walls, central uplifts, and melted rocks. The lack of erosion due to the absence of water or an atmosphere makes the Moon the perfect target to study impact crater processes, in particular the distribution of highly shocked materials within impact craters of different sizes. This study focuses on the characterization and distribution of highly shocked impact melt deposits using multispectral satellite datasets around three complex craters on the farside of the Moon. The study sites have varying morphologies of central uplifts on the crater floor: 1) the 81 km Olcott crater has a cluster of peak hills; 2) Kovalevskaya crater is a 113 km diameter complex crater with a central peak; and 3) Schrodinger basin has a central peak ring. Models propose that the collapse of crater walls and central uplifts during the final stages of crater formation determine where much of the melt rich rocks are eventually emplaced. The results of this study indicate that for increasing crater sizes, the volume of melt-rich rocks generated also increases – at rates greater than model estimates. Impact melt deposits are emplaced beyond the crater rims at each of the sites and preserve a range of morphologies, including melt veneers, melt sheet, and ponded deposits. The regional and local topography, together with crater modification processes greatly affect where the impact melts are finally emplaced. The compositional analyses of the farside crust, using multispectral reflectance spectroscopy in the UV-VIS-NIR range, indicates that there is increasing evidence of highly mafic compositions (i.e., rocks rich in high-Ca pyroxene, olivine, spinel) intercalated within the original crustal highlands (rocks rich in plagioclase feldspar, and low-Ca pyroxenes) on the lunar farside, proving that the lunar farside is a far more geologically complicated terrain than originally assumed

Future exploration of Venus (post-Pioneer Venus 1978)

A comprehensive study was performed to determine the major scientific unknowns about the planet Venus to be expected in the post-Pioneer Venus 1978 time frame. Based on those results the desirability of future orbiters, atmospheric entry probes, balloons, and landers as vehicles to address the remaining scientific questions were studied. The recommended mission scenario includes a high resolution surface mapping radar orbiter mission for the 1981 launch opportunity, a multiple-lander mission for 1985 and either an atmospheric entry probe or balloon mission in 1988. All the proposed missions can be performed using proposed space shuttle upper stage boosters. Significant amounts of long-lead time supporting research and technology developments are required to be initiated in the near future to permit the recommended launch dates

Determining Amplitude Corrections for the Assessment of Surface Roughness Within A Lidar Footprint

The research presented in this thesis is under the context of the OSIRIS-REx mission, a NASA led asteroid sample return mission being launched in 2016 towards the asteroid 101955 Bennu. Aboard the spacecraft is the OSIRIS-REx Laser Altimeter (OLA), which is using the backscattered intensity for instrument calibration. By applying the novel solution of amplitude correction, it is possible to gain additional functionality out of this instrument. This thesis presents a simulation written by the author that accurately models laser altimeter performance. The simulation is used successfully to study OLA’s receiver to reduce error in the range measurements and to remove the effects of large-scale topographic features on the amplitude. The remaining amplitude variations will be interpreted as mineralogical or morphological variations that may impact the viability or the desirability of the site for sample collection