We derived near‐global lunar topography from stereo image data acquired by the Wide‐angle Camera (WAC) of the Lunar Reconnaissance Orbiter Camera (LROC) system. From polar orbit tracks, the LROC WAC ...provides image data with a mean ground resolution at nadir of 75 m/pixel with substantial cross‐track stereo overlap. WAC stereo images from the one‐year nominal mission and the first months of the science mission phase are combined to produce a near‐global digital terrain model (DTM) with a pixel spacing of 100 m, the Global Lunar DTM 100 m, or “GLD100.” It covers 79°S to 79°N latitudes, 98.2% of the entire lunar surface. We compare the GLD100 with results from previous stereo and altimetry‐based products, particularly with the Lunar Orbiter Laser Altimeter (LOLA) altimetry, which is the current topographic reference for the Moon. We describe typical characteristics of the GLD100 and, based upon the comparison to the LOLA data set, assess its vertical and lateral resolution and accuracy. We conclude that the introduced first version of the stereo‐based GLD100 is a valuable topographic representation of the lunar surface, complementary to the LOLA altimetry data set. Further improvements can be expected from continuative investigations.
Key Points
New lunar topography model
The 100 meter lunar raster DTM
Stereo‐photogrammetry using LROC WAC
Cometary nuclei consist mostly of dust and water ice. Previous observations have found nuclei to be low-density and highly porous bodies, but have only moderately constrained the range of allowed ...densities because of the measurement uncertainties. Here we report the precise mass, bulk density, porosity and internal structure of the nucleus of comet 67P/Churyumov-Gerasimenko on the basis of its gravity field. The mass and gravity field are derived from measured spacecraft velocity perturbations at fly-by distances between 10 and 100 kilometres. The gravitational point mass is GM = 666.2 ± 0.2 cubic metres per second squared, giving a mass M = (9,982 ± 3) × 10(9) kilograms. Together with the current estimate of the volume of the nucleus, the average bulk density of the nucleus is 533 ± 6 kilograms per cubic metre. The nucleus appears to be a low-density, highly porous (72-74 per cent) dusty body, similar to that of comet 9P/Tempel 1. The most likely composition mix has approximately four times more dust than ice by mass and two times more dust than ice by volume. We conclude that the interior of the nucleus is homogeneous and constant in density on a global scale without large voids. The high porosity seems to be an inherent property of the nucleus material.
The structure of the upper layer of a comet is a product of its surface activity. The Rosetta Lander Imaging System (ROLIS) on board Philae acquired close-range images of the Agilkia site during its ...descent onto comet 67P/Churyumov-Gerasimenko. These images reveal a photometrically uniform surface covered by regolith composed of debris and blocks ranging in size from centimeters to 5 meters. At the highest resolution of 1 centimeter per pixel, the surface appears granular, with no apparent deposits of unresolved sand-sized particles. The thickness of the regolith varies across the imaged field from 0 to 1 to 2 meters. The presence of aeolian-like features resembling wind tails hints at regolith mobilization and erosion processes. Modeling suggests that abrasion driven by airfall-induced particle "splashing" is responsible for the observed formations.
The near-Earth asteroid (162173) Ryugu, the target of Hayabusa2 space mission, was observed via both orbiter and the lander instruments. The infrared radiometer on the MASCOT lander (MARA) is the ...only instrument providing spectrally resolved mid-infrared (MIR) data, which is crucial for establishing a link between the asteroid material and meteorites found on Earth. Earlier studies revealed that the single boulder investigated by the lander belongs to the most common type found on Ryugu. Here we show the spectral variation of Ryugu's emissivity using the complete set of in-situ MIR data and compare it to those of various carbonaceous chondritic meteorites, revealing similarities to the most aqueously altered ones, as well as to asteroid (101955) Bennu. The results show that Ryugu experienced strong aqueous alteration prior to any dehydration.
The Dawn spacecraft Framing Camera (FC) acquired over 2400 clear filter images of Ceres with a resolution of about 140m/pixel during the six cycles in the High Altitude Mapping Orbit (HAMO) phase ...between August 18 and October 21, 2015. We ortho-rectified the images from the first cycle and produced a global, high-resolution, controlled photomosaic of Ceres. This global mosaic is the basis for a high-resolution Ceres atlas that consists of 15 tiles mapped at a scale of 1:750,000. The nomenclature used in this atlas was proposed by the Dawn team and was approved by the International Astronomical Union (IAU). The full atlas is available to the public through the Dawn Geographical Information System (GIS) web page http://dawngis.dlr.de/atlas and will become available through the NASA Planetary Data System (PDS) (http://pdssbn.astro.umd.edu/).
•The mosaic of Ceres was created using camera data from HAMO orbit phase.•An atlas of Ceres consisting of fifteen tiles was created.•The nomenclature for surface features was approved by the IAU and applied to the atlas.
We report on the results of the Mars Express High-Resolution Stereo Camera (HRSC) experiment pertaining to one of its major aims, mapping the surface of Mars by high-resolution digital terrain models ...(DTM, up to 50
m grid spacing) and orthoimages (up to 12.5
m resolution). We introduce the specifications and characteristics of these data products and give an overview of the procedures that have been developed and are applied for their derivation. We also address the performance characteristics of the mapping project related to different aspects of internal accuracy, accuracy with respect to the global reference system, and regional aspects. Using adaptive processing techniques for terrain reconstruction and a revised approach to the improvement of orientation data, a mean precision of the resulting 3D points of about 12
m is obtained, exceeding the mean ground resolution of the stereo images. Using Mars Orbiter Laser Altimeter (MOLA) data, the HRSC models are firmly tied to the global reference system at the scale of the HRSC DTM grid spacing in the lateral dimension, and to within few meters vertically. HRSC high-resolution DTMs are typically generated using a grid size of about 2 times the mean ground resolution, but usually not larger than 3 times the mean ground resolution, and not smaller than 3 times the precision of the integrated 3D points derived from stereo image analysis. Statistically, every grid cell is based on at least one measured 3D point. Thus, horizontal DTM resolution is well established with regard to the precision and density of the derived 3D points, while the concurrent aim of a detailed terrain representation at maximum possible resolution is pursued. Comparison with the DTM derived from MOLA data allows us to identify specific advancements related to this updated view of Martian topography. We also address the mapping performance of HRSC in comparison to MOLA with respect to latitude and to different surface types and morphologies. Finally, comparison with MOLA highlights typical complementarities of the two different approaches for mapping planetary surfaces.
Images from the Optical Navigation Camera system (ONC) onboard the Hayabusa2 spacecraft show the MASCOT lander during its descent to the surface of asteroid (162173) Ryugu. We used results from a ...previous stereo-photogrammetric analysis that provided precise ONC image orientation data (camera position and pointing), ONC orthoimages, and an ONC-based 3D surface model to combine them with the visibilities of MASCOT itself and its shadow on-ground within the ONC images. We integrated additional information from instruments onboard MASCOT (MASMag, MARA, MASCam) and derived MASCOT’s release position and modeled its free-fall descent path and its velocity over 350 s from its release at ∼41 m altitude above ground until its first contact with the surface of Ryugu. After first contact, MASCOT bounced over the surface of Ryugu for 663 s and came to rest at its first settlement point after four intermediate surface contacts. We again used ONC images that show MASCOT and partly its shadow and reconstructed the bouncing path and the respective velocities of MASCOT. The achieved accuracy for the entire descent and bouncing path is ∼0.1 m (1σ).
After its release and a descent and bouncing phase, the Hayabusa2 lander MASCOT came to a final rest and MASCOT’s camera MASCam acquired a set of images of the surface of Ryugu. With MASCam’s ...instantaneous field of view of about 1 mrad, the images provide pixel scales from 0.2 to 0.5 mm pixel−1 in the foreground and up to 1 cm pixel−1 for surface parts in the background. Using a stereo-photogrammetric analysis of the MASCam images taken from slightly different positions due to commanded and unintentional movements of the MASCOT lander, we were able to determine the orientation for the different measurement positions. Furthermore, we derived a 3D surface model of MASCOT’s vicinity. Although the conditions for 3D stereo processing were poor due to very small stereo angles, the derived 3D model has about 0.5 cm accuracy in the foreground at 20 cm distance and about 1.5 cm at a distance of 40–50 cm.
•We investigate illumination conditions of potential landing sites near the lunar south pole.•We discuss the influence of data resolution on the results.•We show how to refine LOLA DTMs to be used ...for further studies such as illumination.•We find a location 10m above ground, which is illuminated for 95.65% of the considered time period.
The illumination conditions of the lunar south pole are investigated using a geometrically adjusted, 20m/pixel Digital Terrain Model (DTM) from laser tracks of the Lunar Orbiter Laser Altimeter (LOLA). Several comparisons with Narrow Angle Camera (NAC) images have been made to cross-validate the results. Illumination conditions were first evaluated over a region of 20×20km over a one-year period (October 22, 2018 – October 22, 2019) at surface level and 2m above ground. Three potential landing sites are investigated in more detail. A 19-year study covering the lunar precessional cycle was carried out at surface level, 2 and 10m above ground for a site found at “Connecting Ridge”, the ridge connecting the Shackleton and de Gerlache crater. This area was found to be an ideal site for future landing missions with respect to illumination conditions. We identified locations receiving sunlight for 92.27% of the time at 2m above ground and 95.65% of the time at 10m above ground. At these locations the longest continuous periods in darkness are typically only 3–5days.
A high-resolution 3D surface model, map-projected to a digital terrain model (DTM), and precisely ortho-rectified context images (orthoimages) of MASCOT landing site area are important data sets for ...the scientific analysis of relevant data that have been acquired with MASCOT’s image camera system MASCam and other instruments (e.g., the radiometer MARA and the magnetometer MASMag). We performed a stereo-photogrammetric (SPG) analysis of 1050 images acquired from the Hayabusa2 Optical Navigation Camera system (ONC) during the asteroid characterization phase and the MASCOT release phase in early October 2018 to construct a photogrammetric control point network of asteroid (162173) Ryugu. We validated existing rotational parameters for Ryugu and improved the camera orientation (position and pointing) of the ONC images to decimeter accuracy using SPG bundle block adjustment. We produced a high-resolution DTM of the entire MASCOT landing site area. Finally, based on this DTM, a set of orthoimages from the highest-resolution ONC images around MASCOT’s final rest position complements the results of this analysis.
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