As­ter­oids in 3D – da­ta pro­cess­ing at DLR

Global photo mosaic of Vesta
Glob­al pho­to mo­sa­ic of Ves­ta
Image 1/3, Credit: DLR (CC-BY 3.0)

Global photo mosaic of Vesta

The first glob­al map of the as­ter­oid Ves­ta gen­er­at­ed from im­ages ac­quired with the Fram­ing Cam­era. In Ju­ly and Au­gust 2011, Dawn or­bit­ed the third largest ob­ject in the as­ter­oid belt ini­tial­ly in a 'map­ping or­bit' at an al­ti­tude of about 2400 kilo­me­tres above its sur­face. In do­ing so, the cam­era ac­quired hun­dreds of im­ages with a spa­tial res­o­lu­tion of about 250 me­tres per pix­el. What is re­ferred to as ‘sim­ple cylin­dri­cal pro­jec­tion’ was se­lect­ed for the rep­re­sen­ta­tion of this glob­al map. In this map pro­jec­tion the south pole is not a point but is ex­tend­ed as a line the length of the equa­tor. Thus, the south pole cov­ers the en­tire low­er edge of the im­age and all char­ac­ter­is­tics of this re­gion are rep­re­sent­ed in dis­tor­tion. The spa­tial res­o­lu­tion of the pho­to is 750 me­tres per pix­el.
'Snowman' crater
'Snow­man' crater
Image 2/3, Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA.

'Snowman' crater

Three con­nect­ed craters are found in Ves­ta's north­ern hemi­sphere; for this rea­son, sci­en­tists have named them 'snow­man'. NASA's Dawn space­craft ob­tained this im­age with its Fram­ing Cam­era on 6 Au­gust 2011. The im­age res­o­lu­tion is about 260 me­tres per pix­el.
Perspective view of a part of the edge of the south pole basin on Vesta
Per­spec­tive view of a part of the edge of the south pole basin on Ves­ta
Image 3/3, Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Perspective view of a part of the edge of the south pole basin on Vesta

A vis­i­tor from Earth would en­counter a dra­mat­ic land­scape at Ves­ta's south pole: cliffs sev­er­al kilo­me­tres high, deep trench­es and craters which have formed the south­ern tip of this fas­ci­nat­ing pro­to­plan­et in the as­ter­oid belt, and a moun­tain mas­sif up to 15 kilo­me­tres high. For the sci­en­tists work­ing on the Dawn mis­sion, it is not yet clear how this wild land­scape was formed – col­li­sions with oth­er as­ter­oids con­tribut­ed, but al­so the in­ter­nal pro­cess­es that played a role dur­ing the as­ter­oid’s ear­ly for­ma­tion phas­es. This di­ag­o­nal view was de­rived from a glob­al dig­i­tal el­e­va­tion mod­el of the as­ter­oid cre­at­ed from stereo im­age da­ta ob­tained with the Ger­man Fram­ing Cam­era on board NASA's Dawn space probe at an al­ti­tude of 2420 kilo­me­tres above Ves­ta's sur­face. The im­ages, which were ac­quired dur­ing Dawn's ob­ser­va­tion or­bit, have a res­o­lu­tion of about 250 me­tres per pix­el.

The Framing Camera on board the Dawn spacecraft will acquire images of the surface of Vesta and Ceres from various perspectives and under changing light conditions. These images will then provide the basis for creating 3D models of the asteroids.

Three-dimensional images allow the scientists to analyse geological formations in detail. The exact three-dimensional survey of numerous craters of an asteroid is also exciting. On the basis of the shape and height of their edges, the scientists can work out the force of the impact, the mass of the projectile and the composition of the impacted area.

Main task of the DLR scientists: assigning precise coordinates to the Dawn image data and preparing high precision maps of Vesta and Ceres

The Max Planck Institute for Solar System Research provides the systematically corrected raw image data from the Framing Camera needed for further processing. From this, the DLR Institute of Planetary Research then creates the three-dimensional image products for the mapping and scientific study of Vesta and Ceres. The stereo software used for this purpose is thoroughly tested. It has been used for years in the three-dimensional mapping of the Moon, Mars and Mercury. All image data from the two 'Dawn asteroids' will be collected and stored at DLR and will subsequently be transferred to NASA's Planetary Data System (PDS).

For the three-dimensional image data processing, the DLR researchers use what is known as stereo photogrammetric methods. Photogrammetry uses information from at least two images of the same region of the asteroid, but taken from different perspectives. This stereo data is processed in such a way that elevation information can be derived for each pixel, which then allows the generation of a highly detailed three-dimensional terrain model. The information produced from these perspectives of the surface, which change with each orbit of the spacecraft, is taken into account and continuously improved during stereo processing. Here, the accuracy of the 3D model being created also depends on the high-precision calibration of the Framing Camera, which was carried out before the launch with great care. In the finished model, details with elevation differences of less then 10 metres can be shown.

The stereo software was subjected to a thorough test before its real-life application on Vesta. This was based on simulations of photos of the asteroid prepared by the NASA Jet Propulsion Laboratory from earlier blurry images of Vesta acquired by the Hubble Space Telescope. From these, DLR researchers were able to develop a corresponding virtual 3D model of the asteroid before Dawn's arrival at Vesta.

  • Elke Heinemann
    Ger­man Aerospace Cen­ter (DLR)

    Com­mu­ni­ca­tions and Me­dia Re­la­tions
    Telephone: +49 2203 601-2867
    Linder Höhe
    51147 Cologne
  • Prof.Dr. Ralf Jaumann
    Freie Uni­ver­sität Berlin
    In­sti­tute of Ge­o­log­i­cal Sci­ences
    Plan­e­tary Sci­ences and Re­mote Sens­ing
    Telephone: +49-172-2355864
    Malteserstr. 74-100
    12249 Berlin
  • Ulrich Köhler
    Ger­man Aerospace Cen­ter (DLR)
    In­sti­tute of Plan­e­tary Re­search
    Rutherfordstraße 2
    12489 Berlin

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