Jörg Albertz

HRSC on Mars Express - Photogrammetric and Cartographic Research

The High Resolution Stereo Camera (HRSC) on the European spacecraft Mars Express is the first camera on a planetary mission especially designed for photogrammetric and cartographic purposes. Since January 2004 the camera has been taking image data from the Martian surface, characterized by high-resolution, stereo capability and color. These data provide an enormous potential for the generation of 3D surface models, color orthoimages, topographic and thematic maps, and additional products. The image data acquired undergo calibration and systematic processing to orthoimages and 3D data products. Within the international HRSC Science Team the members of the Photogrammetric/Cartographic Working Group are concerned with further refinements in order to achieve highest quality data products. These activities comprise improvements of the exterior orientation of the camera, various approaches to enhance DTM quality, and the generation of maps in the standard scale of 1:200 000 and larger scales as well. The paper reports on these activities and the results achieved so far.

NEW DATA ON THE DIMENSIONS OF BRACHIOSAURUS BRANCAI AND THEIR PHYSIOLOGICAL IMPLICATIONS

There are highly divergent data on the body m a s s (mb) of Brachiosaurus (B.). The range of the body-mass estimations lies between 14900 and 102000 kg for this giant dinosaur [1-6] . This is mainly due to the fact that different specimens and varying techniques are used for the volume (V) estimations, such as equations from the circumferences of femur and humerus [4] or from the volume of models [5]. The precise determination of Vis important for calculating the body surface area (SA) as well as for allometric equations, which are often based on Mb. Herewith, we present a photogrammetric method to determine the metrical dimensions of giant sauropods such as B. The data presented here are based on the skeleton of B. brancai from the Upper Jurassic of Tendaguru (East Africa, Tanzania), mounted and exhibited at the Museum of Natural History in Berlin (Germany). The major part of the skeleton belongs to one single specimen of B. brancai recovered from the Middle Saurian Bed at Tendaguru. The tail originates from another individual of the same species of similar size found in the Upper Saurian Bed. In addition, skeletal remains of B. brancai excavated in different sites in the surroundings of the Tendaguru hill were used for the mounting, partly original and partly modeled. The presacral vertebral column (cervicals, dorsals) and the skull have been replaced by plaster copies modeled from originals of the main skeleton due to their extreme fragility and weight. The right shoulder blade, four dorsal ribs, and some bones of the left forefoot have been modeled in plaster according to counterparts of the other body side. Some missing elements are substituted by bones belonging to individuals of the same size such as the right ilium, the right ischium, and the left lower leg. Other missing items have been replaced by originals (e.g., left femur) or copies of bones from different-sized animals (e.g., sacrum, most hindfoot bones). At the very end of the tail four small pieces were added. Like the missing first caudal vertebra, most of the hemapophyses (chevrons) are plaster imitations [6]. As can be seen in Fig. 1, we divided the presumable shape of B. brancai into XI parts. Each part was separately calculated and the Vi-xi are given in Table 1. From the V found, the Mb was calculated assuming a density of 1000 kg per m 3 tissue [5, 7]. On the basis of the above findings, we investigated further whether the presumable organ volumes derived by allometric equations could be fitted into the anatomical dimensions given by the skeleton. The advantage of the photogrammetrical approach is that when the values are taken from a specimen, the complete shape of the animal is stored in the computer. This allows later derivation of other forms and dimensions, which is almost impossible from a model. In the case of a small model being built from the data and later becoming enlarged, the smallest deviation is multiplied by a factor of 10-50 depending on the size of the model. Therefore, regardless of the size of a model, it is defined by these exact basal metric values. The anatomical data of B. brancai derived by stereophotogrammetry and the presumable physiological data calculated after equations given for endotherms are summarized in Table1, Table2, and Fig. 2. According to these, the Mb of B. braneai is ca. 74420 kg (skeleton 11480 kg). Accordingly, the M b estimations in [1] are similar to our findings, whereas those in [2, 4 6 ] are far too low. It is not clear whether the estimation in [3] for B. refers to the Berlin specimen. If so, it is far too high. The S A (Table 2) was found to be at least (without any skin-

Photogrammetric analysis of clementine multi-look angle images obtained near mare orientale

Abstract A local point network and a DTM (Digital Terrain Model) are derived from Clementine UVVIS multi-look angle images that were obtained on April 30, 1994, covering a small region of the Lunar Orientale Basin (19.5°S to 15°S and 84.5°W to 86.0°W). The nominal camera pointing and spacecraft trajectory data were photogrammetrically adjusted, a procedure which was found to improve estimates of the coordinates of 41 control points significantly to an internally consistent accuracy of 30 m in the horizontal and 50 m in the height direction. The terrain model correlates well with features identified in the image data, two craters, volcanic constructs, and the dark lavafilled Lacus Veris, located in a topographic depression. The terrain model indicates a steep 2000 m drop in elevation within a range of only 6–8 km towards the center of Orientale Further studies of the lunar topography in this particular region using Clementine stereo data seem well warranted and feasible.

Enhancement of satellite image data by data cumulation

Abstract The visibility of targets in satellite image data is clearly limited by the spatial resolution of the sensor. This is why many attempts have been made and will be continued to improve the performance of earth-observation sensor systems by reducing the size of the instantaneous field of view (IFOV). However, this is not the only way to achieve higher geometrical resolution in satellite imagery as long as additional information, which is available in multiple scene coverage, remains unutilized. Therefore, an approach has been developed which makes use of this type of information by merging the data from several images of the same area. This enhancement technique is called Data Cumulation. The paper starts with the theory of sampling image data over a scene, discusses the theoretical background of the approach and describes it implementation. Simulated Data Cumulation has been carried out using both artificial targets and satellite image data as well. The method was proven to be effective if certain requirements are met. The usefulness of the approach as well as its limitations are discussed in the paper.

The Mapping Performance of the HRSC/SRC in Mars Orbit

The images obtained by the HRSC (High Resolution Stereo Camera) on Mars Express show excellent potential for topographic mapping of the planet. The derived stereo models agree with topographic data obtained earlier by MOLA (Mars Orbiter Laser Altimeter) on the Mars Global Surveyor: For the image scenes from the Mars Express commissioning phase that were studies, we find absolute difference in heights as small as 50 m and laterial positional differences along MOLA tracks of about 100 m. We show that HRSC effectively fills the gap between the MOLA tracks. SRC (Super Resolution Channel) images as well placed at their nominal geometric positions and reveal further detail within the HRSC context images. However, many of the images, fall short of the expected image quality for reasons to be examined.