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Improved Method for Estimating Lunar Volcanic Dome Volumes

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Improved Method for Estimating Lunar Volcanic Dome Volumes Improved Method for Estimating Lunar Volcanic Dome Volumes Using GIS Tools 1Washington University in St Louis and the McDonnell Center for the 2University of Western Ontario and the Centre for Planetary Space Sciences, 1 Brookings Drive, St Louis, MO 63130 1 2 1 Science and Exploration, 1151 Richmond St., London, Canada ([email protected]) Francis Baum , Michael Zanetti , Brad Jolliff N6A5B7 ([email protected]) Introduction: Volume estimates of lunar volcanic domes usually approximate their topography Gruithuisen Gamma LRO-NAC DTM on Shaded Relief Methodology Steps Gruithuisen Gamma LRO-NAC Image with basic three dimensional shapes, such as paraboloids or cones, so that a simple volume with azimuth lines & bounding rectangle equation can be used. For example, volume estimates of the Gruithuisen and Mairan domes Create contour lines: calculated in 2003 [1] treated each dome as a simple paraboloid. More recent volume estimates [2] To find the approximate base height and outline of a used a circular truncated cone approximation. However, more robust volume estimates and other volcanic dome, first contour lines were generated dimensional measurements can be calculated using Digital Terrain Models (DTMs) and various using LROC NAC/WAC DTM rasters [7] that covered Geographical Information System (GIS) tools. Here we discuss the tools and methods for the dome and surrounding area. Image and determining volumes of volcanic constructs on the Moon using DTMs, common ArcGIS [3] tools, topography interpretation at the discretion of the and the GeoEVE (Geologic Event Volume Estimator) tool [4]. We present the results from case geologist were also used. studies of these tools with respect to putative lunar silicic volcanic constructs [5]. Adjust dome outline: Methodology Overview: We use Lunar Reconnaissance Orbiter Camera (LROC) Wide and For some dome outlines, a buffer was created from Narrow Angle Camera (WAC, NAC) imagery and their DTMs [6][7] with various GIS tools strung its base contour to uniformly extend the dome’s together using ArcGIS ModelBuilder and ArcPy scripting software to help improve defining and Mairan North LRO-NAC DTM on Shaded Relief outline. Dome outlines were also modified manually Mairan North LRO-NAC Image verifying the outlines of lunar volcanic domes and to measure their lengths, widths, heights, to account for geologic features (e.g., impact volumes and 3D surface areas. All GIS tools mentioned in this poster are ArcGIS built-in tools or craters). custom tools/scripts, developed by the authors, for use with ArcMap 10.2.2 or later (the GeoEVE tool is available on request from the authors). Verify base outline with topographic profiles: Case studies of lunar volcanic domes: Using the methods and tools described in this poster, To help verify and refine each dome’s outline, an we measured the dimensions and volume estimates of various lunar volcanic domes (Table 1), ArcPy script was written that executed the following including: steps: • Gruithuisen (Gh) Gamma, Delta and Northwest (NW) • Located the highest elevation DTM pixel within a • Mairan Northwest (M-NW) dome’s outline and created a point there. • Compton-Belkovich (CB) volcanic complex’s Beta • Created azimuth cross-section lines radiating • Cauchy Omega ( ), aka Donna from this summit point out to the edge of a buffer • Diana and Grace, south of Mons Esam surrounding the dome’s outline. • Arago Alpha and Beta Cauchy Omega LRO-NAC DTM on Shaded Relief Cauchy Omega LRO-NAC Image • Generated topographic profile tables and graphs, For comparison, Table 1 lists in parentheses the dimensions and volume estimates for the using the Stack Profile tool [8], along each azimuth Gruithuisen domes from [2], which also used WAC/NAC images and DTMs. The Gruithuisen domes’ cross-section line. volume estimates in [1] were not used for comparison because their dimensions were derived from • Determined the horizontal distance from the lower resolution Lunar Orbiter IV imagery and their paraboloid volume calculations used a dome’s summit to each topographic profile’s minimum estimated maximum radial extent. Also, the Gh-Delta and Gh-NW domes’ volume estimates in [1] elevation. were each partitioned into multiple dome components (e.g., lower and upper domes), making • Created feature points, in the NAC DTM’s comparisons even less consistent. Volume estimates based on the paraboloid and truncated cone, coordinate system, at these horizontal distances by using our dimension estimates, were also calculated and included in Table 1. using ArcGIS’ Linear Referencing [9] capability. Results: The first three volume estimates listed in the bottom part of Table 1 use a flat, horizontal To help verify and manually adjust each dome’s plane for the dome’s base. Of these, given a roughly circular dome, the paraboloid seems to outline, 72 azimuth cross-section lines were used, overestimate the volume and the truncated cone underestimates it. For a dome that is more spaced 5 degrees apart. rectangular (e.g., Gh-Delta, CB-Beta), its mean base radius misrepresents the dome’s basic shape South of Mons Esam LRO-NAC DTM on Shaded Relief South of Mons Esam LRO-NAC Image and causes these two 3D-shape volume equations to give high volume estimates. Also, for domes that have a volcanic vent or caldera (e.g., Cauchy , Diana, Grace) or significant impact craters (e.g., Measure dome’s horizontal dimensions: Gh-Gamma), these two volume equations don’t account for the missing volume. Since the Surface Volume and GeoEVE tools use DTMs that model a dome’s actual surface, their volume estimates To measure the length, width, and orientation (i.e., are closer to the true volume. Also, because the GeoEVE tool models a dome’s base from the azimuth of the longer side) of a dome’s outline, the surrounding topography (see Figures below) using multiple Monte-Carlo-like runs, we suggest that Minimum Bounding Geometry (MBG) tool [10] was its volume estimates are more robust. used to create a rectangle of the smallest width enclosing the input feature. The MBG tool was also used to create a circle to measure a dome’s mean ArcGIS ModelBuilder models of GeoEVE tool processing base radius. Estimate dome’s 3D surface area and volume Model pre-event surface and estimate dome’s volume using a flat, horizontal reference plane as its base: using the GeoEVE tool: These two dome measurements were calculated using the Surface Volume To calculate more robust volume estimates of each dome, our custom- (SV) tool [11] with NAC/WAC DTMs clipped to the dome’s outline and a built GeoEVE tool [4] was used to (a) model the dome’s base (i.e., pre- base height value derived from the contour line that most closely followed event surface) as a flat, sloped plane interpolated from the surrounding the dome’s outline. topography and then (b) calculate a volume estimate of the clipped DTM located above this plane. Table 1: Summary of dimension and volume estimates Acknowledgements: We thank the LRO project for support (BJ) and the LROC team for production of DTMs, which we acquired from the PDS Geosciences Node Lunar Orbital Data Explorer (products of NASA/GSFC/ASU). a paraboloid volume Vp = [(π/2)Rb2H]; b truncated cone volume Vtc = [(πH/3)(Rb2+ RbRs+ Rs2)] References: [1] Wilson, L. and Head, J. W. (2003) JGR, 108(E2), 5012, 6-1-6-7 [2] Ivanov, M. A., et. al. (2016) Icarus 273, 262-283 [3] ArcGIS® 10.x software by Esri, (http://esri.com) [4] Baum, F. and Zanetti, M. (2017) LPSC XLVIII, 2779 [5] Glotch, et. al. (2010) Science, 329(5998), 1510-1513 [6] Scholten, F., et. al. (2012) JGR 117, E00H17 [7] Henriksen, M. R., et. al., (2017) Icarus 283, 122-137 [8-11] ArcGIS Help: [8] Stack Profile [9] What is linear referencing? [10] Minimum Bounding Geometry [11] Surface Volume .
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