[Show abstract][Hide abstract] ABSTRACT: PRE-PRINT - 12 May 2015 - (c) 2015 The Authors --- MAHLI (Mars Hand Lens Imager) is a 2-megapixel, Bayer pattern color CCD camera with a macro lens mounted on a rotatable turret at the end of the 2-meters-long robotic arm aboard the Mars Science Laboratory rover, Curiosity. The camera includes white and longwave ultraviolet LEDs to illuminate targets at night. Onboard data processing services include focus stack merging and data compression. Here we report on the results and status of MAHLI characterization and calibration, covering the pre-launch period from August 2008 through the early months of the extended surface mission through February 2015. Since landing in Gale crater in August 2012, MAHLI has been used for a wide range of science and engineering applications, including distinction among a variety of mafic, siliciclastic sedimentary rocks; investigation of grain-scale rock, regolith, and eolian sediment textures and structures; imaging of the landscape; inspection and monitoring of rover and science instrument hardware concerns; and supporting geologic sample selection, extraction, analysis, delivery, and documentation. The camera has a dust cover and focus mechanism actuated by a single stepper motor. The transparent cover was coated with a thin film of dust during landing, thus MAHLI is usually operated with the cover open. The camera focuses over a range from a working distance of 2.04 cm to infinity; the highest resolution images are at 13.9 µm per pixel; images acquired from 6.9 cm show features at the same scale as the Mars Exploration Rover Microscopic Imagers at 31 µm/pixel; and 100 µm/pixel is achieved at a working distance of ~26.5 cm. The very highest resolution images returned from Mars permit distinction of high contrast silt grains in the 30–40 µm size range. MAHLI has performed well; for most science and engineering purposes, its images need not be calibrated. The positioning and repeatability of robotic arm placement of the MAHLI camera head have been excellent on Mars, often with the hardware arriving within millimeters of expectation. Stability while imaging is usually such that the images are sharply focused; some exceptions—thought to result from motion induced by wind—have occurred during longer exposure LED-illuminated night imaging. Image calibration includes relative radiometric correction by removal of dark current and application of a flat field. Dark current is negligible to minor for typical daytime exposure durations and temperatures at the Gale field site. A pre-launch flat field product is usually applied to the data but new products created from images acquired by MAHLI of the Martian sky are superior and can provide a relative radiometric accuracy of ~6%. The camera lens imparts negligible distortion to its images; camera models derived from pre-launch data, with CAHV and CAHVOR parameters captured in their archived labels, can be applied to the images for analysis. MAHLI data and derived products, including pre-launch images, are archived with the NASA Planetary Data System (PDS). This report includes supplementary calibration and characterization data that are not available in the PDS archive.
[Show abstract][Hide abstract] ABSTRACT: We examined the spectral properties of a selection of Titan's impact craters that represent a range of degradation states. The most degraded craters have rims and ejecta blankets with spectral characteristics that suggest that they are more enriched in water ice than the rims and ejecta blankets of the freshest craters on Titan. The progression is consistent with the chemical weathering of Titan's surface. We propose an evolutionary sequence such that Titan's craters expose an intimate mixture of water ice and organic materials, and chemical weathering by methane rainfall removes the soluble organic materials, leaving the insoluble organics and water ice behind. These observations support the idea that fluvial processes are active in Titan's equatorial regions.
Geophysical Research Letters 04/2015; 42(10):n/a-n/a. DOI:10.1002/2015GL063824 · 4.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: ABSTRACT: DOI: 10.1002/2014JE004678 The small crater Airy-0 was selected from Mariner 9 images to be the reference for the Mars prime meridian. Initial analyses in the year 2000 tied Viking Orbiter and Mars Orbiter Camera images of Airy-0 to the evolving Mars Orbiter Laser Altimeter global digital terrain model to update the location of Airy-0. Based upon this tie and radiometric tracking of landers / rovers from earth, new expressions for the Mars spin axis direction, spin rate and prime meridian epoch value were produced to define the orientation of the Martian surface in inertial space over time. Since the Mars Global Surveyor mission and Mars Orbiter Laser Altimeter global digital terrain model were completed some time ago, a more exhaustive study has been performed to determine the accuracy of the Airy-0 location and orientation of Mars at the standard epoch. THEMIS IR image cubes of the Airy and Gale crater regions were tied to the global terrain grid using precision stereo photogrammetric image proce ssing techniques. The Airy-0 location was determined to be about 0.001∘ east of its predicted location using the currently defined IAU prime meridian location. Information on this new location and how it was derived will be provided to the NASA Mars Exploration Program Geodesy and Cartography Working Group for their assessment. This NASA group will make a recommendation to the IAU Working Group on Cartographic Coordinates and Rotational Elements to update the expression for the Mars spin axis direction, spin rate and prime meridian location.
The Journal of Geophysical Research Planets 12/2014; · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The small crater Airy-0 was selected from Mariner 9 images to be the reference for the Mars prime meridian. Initial analyses in the year 2000 tied Viking Orbiter and Mars Orbiter Camera images of Airy-0 to the evolving Mars Orbiter Laser Altimeter global digital terrain model to update the location of Airy-0. Based upon this tie and radiometric tracking of landers / rovers from earth, new expressions for the Mars spin axis direction, spin rate and prime meridian epoch value were produced to define the orientation of the Martian surface in inertial space over time. Since the Mars Global Surveyor mission and Mars Orbiter Laser Altimeter global digital terrain model were completed some time ago, a more exhaustive study has been performed to determine the accuracy of the Airy-0 location and orientation of Mars at the standard epoch. THEMIS IR image cubes of the Airy and Gale crater regions were tied to the global terrain grid using precision stereo photogrammetric image proce ssing techniques. The Airy-0 location was determined to be about 0.001∘ east of its predicted location using the currently defined IAU prime meridian location. Information on this new location and how it was derived will be provided to the NASA Mars Exploration Program Geodesy and Cartography Working Group for their assessment. This NASA group will make a recommendation to the IAU Working Group on Cartographic Coordinates and Rotational Elements to update the expression for the Mars spin axis direction, spin rate and prime meridian location.
The Journal of Geophysical Research Planets 11/2014; 119(12). DOI:10.1002/2014JE004678 · 3.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Cassini Synthetic Aperture Radar has been acquiring images of Titan's surface since October 2004. To date, 59% of Titan's surface has been imaged by radar, with significant regions imaged more than once. Radar data suffer from speckle noise hindering interpretation of small-scale features and comparison of re-imaged regions for change detection. We present here a new image analysis technique that combines a denoising algorithm with mapping and quantitative measurements that greatly enhances the utility of the data and offers previously unattainable insights. After validating the technique, we demonstrate the potential improvement in understanding of surface processes on Titan and defining global mapping units, focusing on specific landforms including lakes, dunes, mountains and fluvial features. Lake shorelines are delineated with greater accuracy. Previously unrecognized dissection by fluvial channels emerges beneath shallow methane cover. Dune wavelengths and inter-dune extents are more precisely measured. A significant refinement in producing digital elevation models is shown. Interactions of fluvial and aeolian processes with topographic relief is more precisely observed and understood than previously.
Benches in bathymetry are observed in northern sea Ligeia Mare. Submerged valleys show similar depth suggesting that they are equilibrated with marine benches. These new observations suggest a liquid level increase in the northern sea, which may be due to changes on seasonal or longer timescales.
[Show abstract][Hide abstract] ABSTRACT: Cartography is fundamental to planetary science and as such, a lack of appropriate consideration of this foundation can have and has had serious and expensive consequences to both the scientific return from planetary missions and the safety of future lander missions. In this abstract we highlight the need for, and recommend cooperative planning of, such cartographic work at the national and international level. In an effort to support the planetary exploration initiatives of the various spacefaring nations, we detail specific negative consequences of not properly accounting for cartographic constraints during mission planning and execution. We will also pose several unanswered questions that must be addressed before new exploration efforts should commence. To assure the best possible return on space exploration investments, we recommend that the following planetary cartographic issues be considered:
1. Adequate resources for mapping at all stages from mission design through calibration, operations, development of processing algorithms and software, and processing to archiving;
2. Easy access to data sets and metadata from all nations; consistent (or at least well-documented) data formats; consistent cartographic standards;
3. Cooperation and support leading to the joint analysis of data sets from many nations, in turn leading to integration in a single cartographic coordinate framework at known accuracy levels, and the ability to leverage the powerful synergistic value of multiple data sets. Possible actions that could be taken to achieve these goals will also be presented.
[Show abstract][Hide abstract] ABSTRACT: We present an electromagnetic model that relates the microwave backscatter and thermal emission from linear dune fields to their compositional, physical (roughness, subsurface porosity/heterogeneity) and geometrical (slope, orientation) properties. This model shows the value of exploring these highly directional and geometrical features in light of both their backscattering cross-section and emissivity. Compared to Cassini concurrent radar and radiometry data acquired from October 2004 to June 2011 over Titan’s dune fields, it provides clues to understand variations among dune regions on the largest Saturn’s moon. In particular, it brings a formal support to the idea first advanced in Le Gall et al. (Le Gall, A., Janssen, M.A., Wye, L.C., Hayes, A.G., Radebaugh, J., Savage, C., Zebker, H., Lorenz, R.D., Lunine, J.I., Kirk, R.L., Lopes, R.M.C., Wall, S., Callahan, P., Stofan, E.R., Farr, T. and the Cassini Radar Team . Icarus 213, 608–624) that the size of the interdune valleys (relative to that of the dunes) varies across Titan as well as the diffuse scattering properties of these interdune areas due to different thickness of sand cover (i.e. bedrock contribution) or degree of compaction/heterogeneity of the sand cover. The Fensal and Belet dune fields, in particular, are quite different in terms of these properties. The comparison between the model and Cassini data also reveals the potential presence of structures, possibly small-superposed dunes, oriented perpendicular to the dune crests in the Aztlan region.
[Show abstract][Hide abstract] ABSTRACT: The undifferentiated plains first mapped by Lopes et. al. (2010, Icarus 205) are vast expanses of terrains that appear bland in Cassini RADAR Synthetic Aperture Radar images, hence the designation 'blandlands'. While the interpretation of several other geologic units on Titan, such as dunes and well-preserved impact craters, has been relatively straightforward, the origin of the 'blandlands' has remained mysterious. SAR images show that the 'blandlands' are mostly found at mid-latitudes and appear relatively featureless at radar wavelengths, with no significant topography. Their gradational boundaries and paucity of features in SAR data make geologic interpretation particularly challenging. We have mapped the distribution of these terrains using SAR swaths up to T92, which cover > 50% of Titan's surface. We compared SAR images with their de-noised counterparts (Lucas et. al.,2001, AGU Fall Meeting), the topography using SARTopo method (Stiles et. al., 2009, Icarus 202) and, where possible, the response from radiometry. We examined and evaluated different formation mechanisms. Previous work (Lopes et. al., AGU, 2012) proposed that plains were either (i) sedimentary in origin, resulting from fluvial or lacustrine deposition or accumulation of photolysis products created in the upper atmosphere or (ii) cryovolcanic in origin, consisting of overlapping flows of low relief, obscured by accumulation of sediments. The results from our analysis suggest that the sedimentary origin is the most likely, and that plains materials are similar or the same as dune materials. Plains occur mostly at mid-latitudes, while dunes occur mostly at low latitudes. This may be a result of wind patterns, decrease in sand supply, or changes in properties of sand, perhaps moisture content, all of which would inhibit the formation of large dunes.
[Show abstract][Hide abstract] ABSTRACT: The longevity of the Cassini mission, which has been orbiting the Saturn
system since 2004, has started to permit the generation of novel data
products that utilize overlapping radar observations of Titan. Repeat
observations allow investigations of temporal change, surface properties
via microwave backscatter modelling at SAR resolution, and the
generation of digital terrain models (DTMs). We will utilize these
capabilities to discuss constraints on the evolution of Titan's North
Polar Landscape. Discussion will include (1) implications of the absence
of observed temporal change in Northern lakes, (2) morphologic evidence
for dynamic base level changes separated by intermittent periods of
quiescence, (3) topographically closed depressions that imply karstic
collapse and/or dissolution processes, and (4) the identification of a
regionally common elevation amongst the floors of paleolake basins and
shorelines of Kraken, Ligeia, and Punga Mare.
[Show abstract][Hide abstract] ABSTRACT: We present evidence to support the cryovolcanic origin of some features,
which includes the deepest pit known on Titan (Sotra Patera) and some of
the highest mountains (Doom and Erebor Montes). We interpret this region
to be a cryovolcanic complex of multiple cones, craters, and flows.
Elsewhere, a circular feature, approximately 100 km across, is
morphologically similar to a laccolith, showing a cross pattern
interpreted to be extensional fractures. However, we find that some
other previously supposed cryovolcanic features were likely formed by
other processes. We discuss implications for eruption style and
composition of cryovolcanism on Titan. Our analysis shows the great
value of combining data sets when interpreting Titan's geology and in
particular stresses the value of topographic data.
[Show abstract][Hide abstract] ABSTRACT: Introduction: This abstract is one in a series of reports on our efforts to map the topography of Saturn's satellite Titan at resolutions as high as a few kilometres [1–4], based on radargrammetric analysis of stereo image pairs from the Cassini RADAR . This instrument uses microwaves with 2.2-cm λ to form synthetic aperture (SAR) images with 350-1400 m resolution, as well as obtaining radiometric, scat-terometric, and altimetric data. To date, the instrument has obtained full resolution SAR swaths useful for stereomap-ping on 33 Titan flybys between Ta and T77. These images form 110 possible stereopairs, covering a combined area greater than 2% of Titan. In this abstract, we report on substantial recent progress in controlling the majority of the available SAR images and provide a first look at the most recent digital topographic models (DTMs), which are being produced rapidly now that the control is complete. Technical approach: To perform stereo analysis of Cas-sini SAR data, we use the software package SOCET SET (® BAE Systems)  for controlling sets of images so topo-graphic results are consistent with one another and with pri-ori data such as SAR topography elevations; creation of DTMs with powerful, highly adjustable image matching algorithms; and manual editing or even creation of DTMs. To apply these functions to Cassini data, we used the SOCET Developer's Toolkit to implement "sensor model" software that computes the transformations between pixel coordinates and ground coordinates by rigorous modeling of the physical process of SAR image formation . The USGS in-house cartographic software package ISIS  is used to prepare the images and metadata for ingestion into SOCET SET. Figure 1. Cassini RADAR SAR image coverage of Titan through flyby T77, showing the clusters of overlapping images forming the northern (blue) and southern (red) control networks. A few images (gray) have yet to be connected to either network. Simple Cylindrical projection with north at top, centered on 180°W, with 30° grid.
44th Lunar and Planetary Science Conference; 03/2013