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Lisa R. Gaddis

Publications and source records attributed to Lisa R. Gaddis.

50 records · Page 3Linked to original sources
USGS2001

The roughness of natural terrain: A planetary and remote sensing perspective

We examine the various methods and parameters in common use for quantifying and reporting surface topographic "roughness." It is shown that scale-dependent roughness parameters are almost always required, though not widely used. We suggest a method of standardizing the parameters that are computed and reported so that topographic data gathered by different workers using different field techniques can be directly and easily intercompared. We illustrate the proposed method by analyzing topographic data from 60 different surfaces gathered by five different groups and examine the information for common features. We briefly discuss the implications of our analysis for studies of planetary surface roughness, lander safety, and radar remote sensing modeling and analysis.

Journal of Geophysical Research E: Planets↗
USGS2001

Lunar orbiter digitization and cartographic processing

Digitization and cartographic processing of 5 Lunar Orbiter (LO) IV frames (109H, 110H, 114H, 115H, and 114M) are now complete, and these data are available online at http://wwwflag.wr.usgs.gov/USGSFlag/Space/LunarOrbiter/lunorbWebtop.html. Coverage ofthese data extends from Eratosthenes crater on the west to Mare Serenitatis in the east, and from Aristoteles crater in the north to Rima Hyginus in the south. Geologic features in this area encompass a wide variety of lunar units, processes, and ages, and they include parts of the Apennine Mountains, the KREEP-rich Apennine Bench Formation, Rima Bode pyroclastics (Figure 1), Mare Vaporum, Sulpicius Gallus, and the Imbrium basin ejecta southeast of the basin rim. These data products demonstrate our capability for digitizing and cartographically processing the LO data.

Conference Paper↗
USGS2000

Compositional analyses of small lunar pyroclastic deposits using Clementine multispectral data

Clementine ultraviolet-visible (UVVIS) data are used to examine the compositions of 18 pyroclastic deposits (15 small, three large) at 13 sites on the Moon. Compositional variations among pyroclastic deposits largely result from differing amounts of new basaltic (or juvenile) material and reworked local material entrained in their ejecta upon eruption. Characterization of pyroclastic deposit compositions allows us to understand the mechanisms of lunar explosive volcanism. Evidence for compositional differences between small pyroclastic deposits at a single site is observed at Atlas crater. At all sites, compositional variation among the small pyroclastic deposits is consistent with earlier classification based on Earth-based spectra: three compositional groups can be observed, and the trend of increasing mafic absorption band strength from Group 1 to Group 2 to Group 3 is noted. As redefined here, Group 1 deposits include those of Alphonsus West, Alphonsus Southeast, Alphonsus Northeast 2, Atlas South, Crüger, Franklin, Grimaldi, Lavoisier, Oppenheimer, Orientale, and Riccioli. Group 1 deposits resemble lunar highlands, with weak mafic bands and relatively high UV/VIS ratios. Group 2 deposits include those of Alphonsus Northeast 1, Atlas North, Eastern Frigoris East and West, and Aristarchus Plateau; Group 2 deposits are similar to mature lunar maria, with moderate mafic band depths and intermediate UV/VIS ratios. The single Group 3 deposit, J. Herschel, has a relatively strong mafic band and a low UV/VIS ratio, and olivine is a likely juvenile component. Two of the deposits in these groups, Orientale and Aristarchus, are large pyroclastic deposits. The third large pyroclastic deposit, Apollo 17/Taurus Littrow, has a very weak mafic band and a high UV/VIS ratio and it does not belong to any of the compositional groups for small pyroclastic deposits. The observed compositional variations indicate that highland and mare materials are also present in many large and small pyroclastic deposits, and they suggest that volcanic glasses or spheres may not be dominant juvenile components in all large pyroclastic deposits.

Journal of Geophysical Research E: Planets↗
USGS1999

Digital mapping of the Mars Pathfinder landing site: Design, acquisition, and derivation of cartographic products for science applications

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.

Journal of Geophysical Research E: Planets↗
USGS1999

Preliminary results on photometric properties of materials at the Sagan Memorial Station, Mars

Reflectance measurements of selected rocks and soils over a wide range of illumination geometries obtained by the Imager for Mars Pathfinder (IMP) camera provide constraints on interpretations of the physical and mineralogical nature of geologic materials at the landing site. The data sets consist of (1) three small “photometric spot” subframed scenes, covering phase angles from 20° to 150°; (2) two image strips composed of three subframed images each, located along the antisunrise and antisunset lines (photometric equator), covering phase angles from ∼0° to 155°; and (3) full‐image scenes of the rock “Yogi,” covering phase angles from 48° to 100°. Phase functions extracted from calibrated data exhibit a dominantly backscattering photometric function, consistent with the results from the Viking lander cameras. However, forward scattering behavior does appear at phase angles >140°, particularly for the darker gray rock surfaces. Preliminary efforts using a Hapke scattering model are useful in comparing surface properties of different rock and soil types but are not well constrained, possibly due to the incomplete phase angle availability, uncertainties related to the photometric function of the calibration targets, and/or the competing effects of diffuse and direct lighting. Preliminary interpretations of the derived Hapke parameters suggest that (1) red rocks can be modeled as a mixture of gray rocks with a coating of bright and dark soil or dust, and (2) gray rocks have macroscopically smoother surfaces composed of microscopically homogeneous, clear materials with little internal scattering, which may imply a glass‐like or varnished surface.

Journal of Geophysical Research E: Planets↗
USGS1997

Results from the Mars Pathfinder camera

Images of the martian surface returned by the Imager for Mars Pathfinder (IMP) show a complex surface of ridges and troughs covered by rocks that have been transported and modified by fluvial, aeolian, and impact processes. Analysis of the spectral signatures in the scene (at 440- to 1000-nanometer wavelength) reveal three types of rock and four classes of soil. Upward-looking IMP images of the predawn sky show thin, bluish clouds that probably represent water ice forming on local atmospheric haze (opacity ∼0.5). Haze particles are about 1 micrometer in radius and the water vapor column abundance is about 10 precipitable micrometers.

Science↗
USGS1996

Modeling of fluidized ejecta emplacement over digital topography on Venus

The FLOW computer model of McEwen and Malin (1989) modified for application to the study of Venus fluidized ejecta blankets (FEBs) demonstrates that relatively low viscosities, yield strengths, and initial velocities are required to duplicate the observed flow paths of the outflow materials. The model calculates the velocities and simulated flow paths of gravity flows over Magellan topography. The model is formulated to determine flow movements from initial conditions, gravitational acceleration, and resistance to motion as described by Coulomb, viscous, and turbulent resistance forces. Successful duplication of observed FEB flow paths has been achieved for the FEB craters Addams, Isabella, and Cochran. When used as a simple energy‐line model, the model requires low coefficients of friction to extend FEBs to near their observed termini in the synthetic aperture radar (SAR) imagery, although the resulting straight flow lines do not follow the observed flow paths well. For Bingham flow, the model requires low values of viscosity and yield strength which are more similar to pyroclastic or debris flows than basaltic lavas. Flows of 100‐m depth require 1 to 2 orders of magnitude higher values of both viscosity and yield strength than 10‐m‐deep flows. The complicated nature of the flow lines for the low velocity model suggests that FEBs were probably emplaced under variably laminar and turbulent flow conditions, where underlying topography influenced both the direction and energy of flow materials.

Journal of Geophysical Research E: Planets↗
USGS1996

Decomposition of AVIRIS spectra: Extraction of spectral reflectance, atmospheric, and instrumental components

Presents techniques that use only information contained within a raw, high-spectral-resolution, hyperspectral Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) scene to estimate and remove additive components (atmospheric scattering and instrument dark current). These techniques allow normalization of multiplicative components (instrument gain, topography, atmospheric transmission) and enhancement, extraction, and identification of relative-reflectance information related to surface composition and mineralogy. The authors' derivation of additive components from raw AVIRIS data is based on an adaptation of Crippen's "regression intersection method (RIM)." As does RIM, the authors use pairs of surface units that are spectrally homogeneous, spatially extensive, and located in rugged terrain. However, their technique utilizes the long-wavelength spectral data of AVIRIS to derive and remove atmospheric scattering components for each unit. AVIRIS data from the Kelso Dunes and Granite Mountain areas of southern California served as spectrally contrasting, topographically modulated surfaces for illustration of this technique. For a given site and wavelength pair, subtraction of the wavelength-dependent additive component from individual bands will remove topographic shading in both sites in band-to-band ratio images. Normalization of all spectra in the scene to the average scene spectrum results in cancellation of multiplicative components and produces a relative-reflectance scene. Absorption features due to mineral absorptions that depart from the average spectrum can be identified in the relative-reflectance AVIRIS product. The validity of these techniques is demonstrated by comparisons between relative-reflectance AVIRIS spectra derived from application of this technique and those derived by using the standard calibration techniques of JPL. Calibrated spectra were extracted from an AVIRIS scene of the Upheaval Dome area of Canyonlands National Park, UT. Results show that surface-reflectance information can be extracted and interpreted in terms of surface mineralogy after application of these techniques to AVIRIS data.

IEEE Transactions on Geoscience and Remote Sensing↗
USGS1992

Lava-flow characterization at Pisgah Volcanic Field, California, with multiparameter imaging radar

Multi-incidence-angle (in the 25° to 55° range) radar data acquired by the NASA/JPL Airborne Synthetic Aperture Radar (AIRSAR) at three wavelengths simultaneously and displayed at three polarizations are examined for their utility in characterizing lava flows at Pisgah volcanic field, California. Pisgah lava flows were erupted in three phases; flow textures consist of hummocky pahoehoe, smooth pahoehoe, and aa (with and without thin sedimentary cover). Of the eight AIRSAR images used here, four were calibrated to within an accuracy of ±2 dB with trihedral corner reflectors, and data from these calibrations were used to process the additional images to a conservatively estimated ±5 dB level of accuracy. Calibrated radar backscatter data (σ°, in dB) were plotted as a function of incidence angle at three wavelengths (P-band, 68 cm; L-band, 24 cm; and C-band, 5.6 cm) and three polarizations (HH, horizontal transmit/horizontal receive; HV, horizontal transmit/vertical receive; and VV, vertical transmit/vertical receive) for eight major units at Pisgah for which multi-incidence-angle AIRSAR data were available. The eight units consist of near-vent and distal aa flows; near-vent and distal, hummocky pahoehoe flows; a mantled, hummocky pahoehoe flow; a platform pahoehoe flow; an alluvial fan; and a playa. Analyses of these backscatter data show that major unmodified volcanic units at Pisgah are readily distinguishable from each other and that they exhibit diffuse (HH, VV) and/or multiple (HV) scattering behavior typical of rough surfaces at these wavelengths. These analyses show that discrimination of smooth lavas (platform pahoehoe) from mantled units with greater primary roughness (hummocky pahoehoe) is difficult and must rely on supporting observations (such as evidence of localized weathering and/or sediment deposition, contrast with surrounding units, and superposition of flow units). L-band backscatter and image data at HV polarization show the best discrimination of Pisgah lava flows, with optimal unit separation observed between ∼40° and 50° incidence angles. Backscatter data shown as a function of relative age of Pisgah flows indicate that dating of lava flows on the basis of average radar backscatter may yield ambiguous results if primary flow textures and modification processes are not well understood.

California↗
USGS1990

Volcanism in Northwest Ishtar Terra, Venus

Soviet Venera 15/16 radar images and topographic data for an area in NW Ishtar Terra, Venus (74°N, 313°E) contain evidence for the existence of a complex volcanic center. Located at the intersection of Akna and Freyja Montes (both elevated ∼4 to 7 km above the planetary reference radius of 6051 km), this volcanic center has a complex caldera system, possibly more than one major eruptive vent, and associated lava flows at lower elevations. Evidence for a volcanic center at NW Ishtar Terra includes: a smooth-surfaced unit with moderate radar brightness; adjacent (possibly associated) bright flows extending northwestward more than 300 km; an irregularly shaped depression 200 by 250 km in size and ∼2.0 km deep; arcuate slopes that appear to mark the rims of several semicircular depressions within the larger depression; and 5.5-km-elevation ridge separating volcanic deposits of northern Lakshmi Planum from those of NW Ishtar Terra. The lack of a notable shield construct at NW Ishtar and the similarity between smooth terrain and undivided plains of Lakshmi Planum suggest that volcanic units at NW Ishtar Terra may represent an earlier (perhaps younger) stage of volcanism than that attributed to Colette and Sacajawea Paterae of Lakshmi Planum. A westward migration in volcanic activity from Sacajewea to Colette NW Ishtar is supported by relative youth of Colette as compared to Sacajawea, the relatively young stage of volcanism at NW Ishtar Terra, and the superposition of this volcano on the banded terrain of Akna and Freyja Montes.

Icarus↗
USGS1990

Lava flow surface textures: SIR-B radar image texture, field observations, and terrain measurements

Space Shuttle Imaging Radar (SIR-8) images, field observations, and small-scale (cm) terrain measurements are used to study lava flow surface textures related to emplacement processes of a single hawaiian lava flow. Although smooth pahoehoe textures are poorly characterized on the SIR-B data, rougher pahoehoe types and the a'a flow portion show image textures attributed to spatial variations in surface roughness. Field observations of six distinct lava flow textural units are described and used to interpret modes of emplacement. Terrain measurements of these units show that surface roughness differs across and along the flow, apparently due to shear during flow emplacement. The radar smooth/rough boundary between pahoehoe and a'a occurs at a vertical relief of -10 cm on this lava flow. While direct observation and measurement most readily yield information related to lava eruption and emplacement processes, analyses of remote sensing data such as those acquired by imaging radars and altimeters can provide a means of quantifying surface texture, identifying the size and distribution of flow components, and delineating textural unit boundaries.

Hawaii↗
USGS1989

Geologic analyses of Shuttle Imaging Radar (SIR-B) data of Kilauea Volcano, Hawaii

Analyses of imaging radar data of volcanic terranes on Earth and Venus have emphasized the need for a clearer understanding of how these data can be most effectively used to accomplish important volcanological goals, including the interpretation of eruptive styles and the characterization of the geologic history of volcanic centers. The second Shuttle Imaging Radar experiment (SIR-B) obtained two digital images over the summit caldera and the Southwest Rift Zone of Kilauea Volcano in 1984. Our geologic analyses of these images indicate that SIR-B data are particularly useful for delineating the distribution and surface textural variations of a'a lava flows, for mapping large-scale topographic features with radar-facing slopes, and for identifying an areally extensive pyroclastic deposit. Analyses of the SIR-B data of Kilauea, however, do not permit unambiguous identification of landforms such as pahoehoe lava flows, cinder cones, and fissures. Although separation of low-return units such as pahoehoe lava flows and adjacent pyroclastic ash is not greatly improved using standard image-enhancement techniques, the texture-analysis technique applied here did facilitate discrimination of such smooth-surfaced volcanic deposits. Although analyses of the SIR-B data permit a generally accurate interpretation of the eruptive history of Kilauea, the inability to distinguish low-return pahoehoe flows results in misinterpretation of several aspects of Kilauea volcanism, suggesting that caution should be exercised in the interpretation of SAR data of volcanic terranes.

Hawaii↗
USGS1985

Remote sensing of lunar pyroclastic mantling deposits

Mantling deposits on the Moon are considered to be pyroclastic units emplaced on the lunar surface as a result of explosive fire fountaining. These pyroclastic units are characterized as having low albedos, having smooth fine-textured surfaces, and consisting in part of homogeneous, Febearing volcanic glass and partially crystallized spheres. Mantling units exhibit low returns on depolarized 3.8-cm radar maps, indicating an absence of surface scatterers in the 1- to 50-cm-size range. A number of reflectance spectra from several regional pyroclastic deposits are presented for the first time; these data support a previous interpretation that mantling units have a unique spectral signature which is indicative of the presence of a significant Fe-bearing volcanic glass component. The Rima Bode region is discussed as an example of an area in which several types of remote sensing data (including 3.8-cm radar, spectral reflectance, and multispectral vidicon data) were used to reconstruct the geologic events surrounding the emplacement of a regional pyroclastic mantling deposit. The recognition of numerous varieties of volcanic glass samples, especially relatively high-albedo (e.g., green, yellow) glasses, suggests the existence of additional, unrecognized mantling deposits with albedos higher than those studied to date. On the basis of the remote sensing data summarized and presented, five new areas have been identified which may represent higher-albedo regional pyroclastic deposits.

Icarus↗