Geology topics

Jurgen Oberst

Publications and source records attributed to Jurgen Oberst.

5 recordsLinked to original sources

USGS2010

Report of the IAU Working Group on cartographic coordinates and rotational elements: 2009

Every three years the IAU Working Group on Cartographic Coordinates and Rotational Elements revises tables giving the directions of the poles of rotation and the prime meridians of the planets, satellites, minor planets, and comets. This report takes into account the IAU Working Group for Planetary System Nomenclature (WGPSN) and the IAU Committee on Small Body Nomenclature (CSBN) definition of dwarf planets, introduces improved values for the pole and rotation rate of Mercury, returns the rotation rate of Jupiter to a previous value, introduces improved values for the rotation of five satellites of Saturn, and adds the equatorial radius of the Sun for comparison. It also adds or updates size and shape information for the Earth, Mars’ satellites Deimos and Phobos, the four Galilean satellites of Jupiter, and 22 satellites of Saturn. Pole, rotation, and size information has been added for the asteroids (21) Lutetia, (511) Davida, and (2867) Šteins. Pole and rotation information has been added for (2) Pallas and (21) Lutetia. Pole and rotation and mean radius information has been added for (1) Ceres. Pole information has been updated for (4) Vesta. The high precision realization for the pole and rotation rate of the Moon is updated. Alternative orientation models for Mars, Jupiter, and Saturn are noted. The Working Group also reaffirms that once an observable feature at a defined longitude is chosen, a longitude definition origin should not change except under unusual circumstances. It is also noted that alternative coordinate systems may exist for various (e.g. dynamical) purposes, but specific cartographic coordinate system information continues to be recommended for each body. The Working Group elaborates on its purpose, and also announces its plans to occasionally provide limited updates to its recommendations via its website, in order to address community needs for some updates more often than every 3 years. Brief recommendations are also made to the general planetary community regarding the need for controlled products, and improved or consensus rotation models for Mars, Jupiter, and Saturn.

Celestial Mechanics and Dynamical Astronomy↗

USGS2007

The HRSC DTM test

The High Resolution Stereo Camera (HRSC, [1]) is part of the orbiter payload on the Mars Express (MEX) mission of the European Space Agency (ESA), orbiting the Red Planet in a highly elliptical orbit since January 2004. For the first time in planetary exploration, a camera system has especially been designed to meet the requirements of photogrammetry and cartography for mapping the complete surface of a planet [2]. For this purpose HRSC operates as a push broom scanning instrument with 9 CCD line detectors mounted in parallel in the focal plane of the camera. Data acquisition is achieved by five panchromatic channels under different observation angles and four colour channels. At periapsis the ground resolution of the nadir channel amounts to 12.5 m, the stereo channels are typically operated at a 2x coarser resolution with the two photometry and the four colour channels at 4x or 8x coarser resolution. The data provided by HRSC are well suited for the automatic generation of Digital Terrain Models (DTMs) and other 3D data products. Such products are of vital interest to planetary sciences. As the Mars Express mission has recently been extended the prospects for a complete topographic mapping of Mars by HRSC at very high resolution are very good, indeed. Image matching is well researched and has been documented in the literature. In general, it is agreed that in simple terrain and with adequate image acquisition geometry very good results can be achieved by totally automated approaches. Things start to be much more complicated if more complex situations are faced, such as steep terrain, height discontinuities, occlusions, poor texture, shadows, atmospheric dust, clouds, increased image noise, compression artefacts etc., some of which are commonplace in HRSC images. Nevertheless, automatic DTM generation from HRSC images by means of image matching has reached a very high level over the years. The systematic processing chain at DLR for producing preliminary DTMs with 200 m resolution [3] runs well and stable. In addition, several groups are able to produce DTMs using different approaches, or have developed alternative modules for parts of the DTM generation process [2]. Also, a few groups have been developing shape-from-shading techniques which have reached pre-operational efficiency. It is against this background that the desire was expressed to compare the individual approaches for deriving DTMs from HRSC images in order to assess their advantages and disadvantages. Based on carefully chosen test sites the test participants have produced DTMs which have been subsequently analysed in a quantitative and a qualitative manner. This paper reports on the results obtained in this test, more details can be found in [4].

Conference Paper↗

USGS2006

The HRSC DTM test

The High Resolution Stereo Camera (HRSC) has been orbiting the planet Mars since January 2004 onboard the ESA Mars Express mission and delivers imagery which is being used for topographic mapping of the planet. The HRSC team is currently conducting a systematic inter-comparison of different alternatives for the production of high resolution Digital Terrain Models (DTMs) from the multilook HRSC push broom imagery. Based on carefully chosen test sites the test participants have produced DTMs which have been subsequently analysed in a quantitative and a qualitative manner. This paper reports on the results obtained in this test.

Conference Paper↗

USGS2004

Comparison of USGS and DLR topographic models of Comet Borrelly and photometric applications

Stereo analysis of images obtained during the 2001 flyby of Comet Borrelly by NASA's Deep Space 1 (DS1) probe allows us to quantify the shape and photometric behavior of the nucleus. The shape is complex, with planar facets corresponding to the dark, mottled regions of the surface whereas the bright, smooth regions are convexly curved. The photometric as well as textural differences between these regions can be explained in terms of topography (roughness) at and below the image resolution, without invoking significant variations in single-particle properties; the material on Borrelly's surface could be quite uniform. A statistical comparison of the digital elevation models (DEMs) produced from the three highest-resolution images independently at the USGS and DLR shows that their difference standard deviation is 120 m, consistent with a matching error of 0.20 pixel (similar to reported matching accuracies for many other stereo datasets). The DEMs also show some systematic differences attributable to manual versus automatic matching. Disk-resolved photometric modeling of the nucleus using the DEM shows that bright, smooth terrains on Borrelly are similar in roughness (Hapke roughness θ =20°) to C-type asteroid Mathilde but slightly brighter and more backscattering (single-scattering albedo w =0.056, Henyey–Greenstein phase parameter g =−0.32). The dark, mottled terrain is photometrically consistent with the same particles but with roughnesses as large as 60°. Intrinsically darker material is inconsistent with the phase behavior of these regions. Many local radiance variations are clearly related to topography, and others are consistent with a topographic explanation; one need not invoke albedo variations greater than a few tens of percent to explain the appearance of Borrelly.

Icarus↗

USGS2002

USGS and DLR topographic mapping of Comet Borrelly

In the fall of 2001, NASA's Deep Space 1 (DS1) probe imaged Comet Borrelly during a flyby encounter. Three of the Borrelly images have geometry suitable to photogrammetrically map the nucleus, which form two stereopairs with an expected precision (EP) of ~410 m and ~670 m each. DS1 team members at the USGS and DLR have independently produced digital elevation models (DEMs) of Borrelly. Automatic stereo-matching algorithms were used by both USGS and DLR, but the USGS DEM was additionally manually edited in stereo. We accomplished a quantitative statistical comparison of the DEMs and found they have a standard deviation of 120 m, which is small compared to the EP above. There are systematic differences, we estimate the stereomatching error to only 0.20 pixel RMS, which is similar to the level of subpixel matching accuracy obtained in a wide variety of other mapping situations. The resulting DEMs enable a variety of applications such as perspective views, photometric modeling and studies of the energy balance of the nucleus. We hope to use the USGS DEM as a starting point to extrapolate the shape of the hidden side of the nucleus. This would not only let us determine the volume and moments of inertia of the nucleus, but would lead to a calculation of the insolation onto the nucleus averaged over an entire orbit, and thence to a model of the evolution of nuclear shape.

Conference Paper↗