Systematische Bündelausgleichung großer photogrammetrischer Blöcke einer Zeilenkamera am Beispiel der HRSC-Daten

In der vorliegenden Arbeit wird ein Verfahren zur photogrammetrischen Auswertung der Aufnahmen einer Zeilenkamera beschrieben. Es wurde zur systematischen Bündelausgleichung großer Blöcke, bestehend aus den Bildstreifen der High Resolution Stereo Camera (HRSC), entwickelt. Die HRSC umkreist bereits seit Ende 2003 den Planeten Mars. Sie ist an Bord der europäischen Weltraummission Mars Express. Die Kamera wurde unter Berücksichtigung von photogrammetrischen Aspekten entwickelt und liefert stereoskopische Aufnahmen, aus denen sich dreidimensionale Daten ableiten lassen. Die spektralen Kanäle dieser Zeilenkamera zeichnen zusätzlich Farbinformation auf. Da sich benachbarte Streifen überlappen, ist es möglich, photogrammetrische Blöcke zu bilden und großflächige Mosaike zu erstellen. Diese bilden eine einzigartige Grundlage für die Kartierung der Marsoberfläche mit hoher geometrischer Auflösung und Konsistenz. Für eine präzise Passgenauigkeit der Streifen ist es notwendig, die Orientierungsdaten, welche Position und Ausrichtung der Kamera zum Zeitpunkt der Aufnahme beschreiben, in einer Bündelausgleichung zu rekonstruieren. Die dafür notwendigen Methoden werden in dieser Arbeit in vier Abschnitten beschrieben und entsprechend in der Umsetzung in vier Module eingeteilt. Es handelt sich dabei um: 1) die Vorverarbeitung der Bilddaten, 2) die Bestimmung von Verknüpfungspunkten durch Bildzuordnung, 3) die Bündelausgleichung mit einem Geländemodell als Passinformation sowie 4) die Evaluierung der Orientierungsdaten. Um auch große Blöcke automatisch und systematisch verarbeiten zu können, wird das vorgestellte Verfahren in zwei Stufen unterteilt: In der ersten Stufe wird die äußere Orientierung jedes Streifens zunächst einzeln bestimmt. Um dabei auch hochfrequente Schwingungen, denen die Kamera zum Zeitpunkt der Aufnahmen mitunter ausgesetzt ist, modellieren zu können, wird für die Bündelausgleichung das Konzept der Orientierungspunkte erweitert: Indem sich die Distanz zwischen den Orientierungspunkten an die örtliche, von der vorliegenden Bildinformation abhängige Verknüpfungspunktanzahl anpasst, lässt sich die äußere Orientierung für eine deutlich größere Anzahl von Streifen rekonstruieren, als es bislang möglich war. In der zweiten Stufe werden die Orientierungsdaten aller Streifen eines Blocks in einer gemeinsamen Bündelausgleichung optimiert. Um die dafür notwendigen Verknüpfungspunkte zu bestimmen, wird der Block in Teilblöcke unterteilt. Dazu werden zwei neue Varianten vorgestellt und untersucht. Aufgrund der Heterogenität der Streifen und deren Anordnung sind die resultierenden Verknüpfungspunkte ungleichmäßig im Block verteilt und werden durch einen neu entwickelten Verknüpfungspunktfilter optimiert. Der gesamte Ablauf der Bündelausgleichung ist in beiden Stufen so konzipiert, dass sich große Datenmengen automatisch verarbeiten lassen. Einige dafür notwendige Stellgrößen werden im experimentellen Teil dieser Arbeit empirisch bestimmt. Dabei werden auch rechentechnische Aspekte berücksichtigt. Für die Experimente stehen 4418 HRSC-Streifen zu Verfügung. Die Orientierungsdaten nach der Bündelausgleichung werden jeweils mit den nominellen Daten verglichen. So wird zunächst der Einfluss des neuen Ansatzes mit variabler Orientierungspunktdistanz systematisch untersucht. Anschließend wird gezeigt, dass sich die Genauigkeit der Daten bei 96,2 % der Streifen durch die Bündelausgleichung steigert. Zur Validierung der zweiten Stufe des Verfahrens werden zunächst einzelne Blöcke unterschiedlicher Größe exemplarisch betrachtet. Daraufhin wird die Übertragbarkeit des Verfahrens auf andere Daten anhand von insgesamt 32 regionalen Blöcken bestätigt. Die jeweils resultierenden Orientierungsdaten werden ebenfalls systematisch evaluiert. Es wird dabei aufgezeigt, dass sich die Passgenauigkeit der Streifen für alle Blöcke deutlich steigert: Abweichungen, gemessen als Raumstrecke zwischen Objektpunkten in benachbarten Streifen, reduzieren sich im Durchschnitt von 142,9 m auf 55,3 m

Optimizing the distribution of tie points for the bundle adjustment of hrsc image mosaics

For a systematic mapping of the Martian surface, the Mars Express orbiter is equipped with a multi-line scanner: Since the beginning of 2004 the High Resolution Stereo Camera (HRSC) regularly acquires long image strips. By now more than 4, 000 strips covering nearly the whole planet are available. Due to the nine channels, each with different viewing direction, and partly with different optical filters, each strip provides 3D and color information and allows the generation of digital terrain models (DTMs) and orthophotos. To map larger regions, neighboring HRSC strips can be combined to build DTM and orthophoto mosaics. The global mapping scheme Mars Chart 30 is used to define the extent of these mosaics. In order to avoid unreasonably large data volumes, each MC-30 tile is divided into two parts, combining about 90 strips each. To ensure a seamless fit of these strips, several radiometric and geometric corrections are applied in the photogrammetric process. A simultaneous bundle adjustment of all strips as a block is carried out to estimate their precise exterior orientation. Because size, position, resolution and image quality of the strips in these blocks are heterogeneous, also the quality and distribution of the tie points vary. In absence of ground control points, heights of a global terrain model are used as reference information, and for this task a regular distribution of these tie points is preferable. Besides, their total number should be limited because of computational reasons. In this paper, we present an algorithm, which optimizes the distribution of tie points under these constraints. A large number of tie points used as input is reduced without affecting the geometric stability of the block by preserving connections between strips. This stability is achieved by using a regular grid in object space and discarding, for each grid cell, points which are redundant for the block adjustment. The set of tie points, filtered by the algorithm, shows a more homogenous distribution and is considerably smaller. Used for the block adjustment, it yields results of equal quality, with significantly shorter computation time. In this work, we present experiments with MC-30 half-tile blocks, which confirm our idea for reaching a stable and faster bundle adjustment. The described method is used for the systematic processing of HRSC data.DLR/50 QM 1601BMWi/50 QM 160

Modeling spacecraft oscillations in hrsc images of mars express

Since January 2004 the High Resolution Stereo Camera (HRSC) is mapping planet Mars. The multi-line sensor on board the ESA Mission Mars Express images the Martian surface with a resolution of up to 1 2 m per pixel in three dimensions and in color. As part of the Photogrammetric/Cartographic Working Group of the HRSC Science Team the Institute of Photogrammetry and GeoInformation (IPI) of the Leibniz Universitat Hannover is involved in photogrammetrically processing the HRSC image data. To derive high quality 3D surface models, color orthoimages or other products, the accuracy of the observed position and attitude information in many cases should be improved. This is carried out via a bundle adjustment. In a considerable number of orbits the results of the bundle adjustment are disturbed by high frequency oscillations. This paper describes the impact of the high frequency angular spacecraft movement to the processing results of the last seven years of image acquisition and how the quality of the HRSC data products is significantly improved by modeling these oscillations.DLR/50 QM 090

Topographic mapping of the Mars MC quadrangles using HRSC data

The High Resolution Stereo Camera (HRSC) of ESA’s Mars Express mission [1, 2] is still running nominally and delivering new image strips to fill remaining gaps that lead to a contiguous coverage of the Martian surface at high resolution stereo. As a push broom scanning instrument with nine CCD line detectors mounted in parallel, its unique feature is the ability to obtain along-track stereo images and four colors during a single orbital pass. Thus, panchromatic stereo and color images from single orbits of the HRSC have been used to produce digital terrain models (DTMs) and orthoimages of the Martian surface since 2004 [3]. Since 2010 new HRSC multi-orbit data products have been generated, which have been developed into a global mapping program organized into MC-30 half-tiles, since 2014 [4,5]. Based on continuous coverage of an area, regional DTMs and orthomosaics can be produced by combining image data from multiple orbits using specifically adapted techniques for block-adjustment, DTM interpolation and image equalization [6]. The resulting DTMs and color orthomosaics are the baseline for a controlled topographic map series of Mars. The extents of the regional products follow the MC-30 (Mars Chart) global mapping scheme of Greeley and Batson [7]. For the generation of the DTMs and color mosaics, the MC- 30 quadrangles are further divided into East (E) and West (W). In parallel to the completion of the first half-tile DTM and color mosaic (MC-11-E) we developed a concept for a topographic map series of Mars [8,9]. To limit data volumes and map sizes, each quadrangle is subdivided into eight tiles (i.e. each half-tile into four tiles). The map scale of 1:700,000 is a compromise between the high DTM and orthomosaic resolution of 50 m/pxl and an acceptable hardcopy format of about 1 m in width to 2 m in height (≜14 pxl/mm). MC-11 was selected to be produced first because it contains the finally selected landing site, Oxia Planum, of ESA’s ExoMars mission with the Rosalind Franklin rover. After MC-11, the Global Topography and Mosaics Task Group (GTMTG) of the HRSC Science Team focussed on MC-13, which hosts the landing site of the Perseverance rover from NASA’s Mars 2020 mission, Jezero crater. The next HRSC MC quadrangles will also be equatorial ones (i.e. 19 and 20). All maps are available for the public at the HRSC team website (http://hrscteam.dlr.de/HMC30/index.html). [1] Neukum, G., et al., ESA Special Publication, 1240, pp. 17-36, 2004. [2] Jaumann, R., et al., Planetary and Space Science 55, pp. 928-952, 2007. [3] Gwinner, K., et al., Earth and Planetary Science Letters, 294, pp. 506-519, 2010. [4] Gwinner, K, et al., 41st Lunar and Planetary Science Conference, #2727, 2010. [5] Dumke, A., et al., Lunar and Planetary Science Conference, #1533, 2010. [6] Gwinner, K. et al., Planetary and Space Science, 126, pp. 93-138, 2016. [7] Greeley, R. and Batson, G., Planetary Mapping, Cambridge University Press, Cambridge, 1990. [8] Schulz, K., Bachelor Thesis, Beuth Hochschule für Technik Berlin, 2017. [9] Kersten, E., et al., EPSC Abstracts Vol. 12, EPSC2018-352, 2018

Global bundle adjustment with variable orientation point distance for precise mars express orbit reconstruction

The photogrammetric bundle adjustment of line scanner image data requires a precise description of the time-dependent image orientation. For this task exterior orientation parameters of discrete points are used to model position and viewing direction of a camera trajectory via polynomials. This paper investigates the influence of the distance between these orientation points on the quality of trajectory modeling. A new method adapts the distance along the trajectory to the available image information. Compared to a constant distance as used previously, a better reconstruction of the exterior orientation is possible, especially when image quality changes within a strip. In our research we use image strips of the High Resolution Stereo Camera (HRSC), taken to map the Martian surface. Several experiments on the global image data set have been carried out to investigate how the bundle adjustment improves the image orientation, if the new method is employed. For evaluation the forward intersection errors of 3D points derived from HRSC images, as well as their remaining height differences to the MOLA DTM are used. In 13.5 % (515 of 3,828) of the image strips, taken during this ongoing mission over the last 12 years, high frequency image distortions were found. Bundle adjustment with a constant orientation point distance was able to reconstruct the orbit in 239 (46.4 %) cases. A variable orientation point distance increased this number to 507 (98.6 %).German Federal Ministry for Economic Affairs and Energy (BMWi)German Aerospace Center (DLR)/50 QM 130

Building footprints Oldenburg derived from aerial imagery

<p>This data set contains about 78000 georeferenced polygons representing all building footprints within the administrative boundaries of the city of Oldenburg, Lower Saxony, Germany. These geometries were created by a deep learning-based image segmentation. The model for this was trained at the State Office of Lower Saxony for Geoinformation and Surveying (LGLN).</p> <p>We publish this data under the CC0 license. <br>You can do whatever you want with it. There are no restrictions.<br><br>If you do something great with the data set, we'd love to hear about it: <a href="mailto:[email protected]">[email protected]</a><br>If you use this dataset, you are welcome to reference it - but you don't have to.<br>Would you like builiding footprints for another area? We'd love to hear about it.</p><p>v1.1: Information on the height of the buildings has now been added to the field 'meta'.</p&gt

Analyzing a block of HRSC image strips for a simultaneous bundle adjustment

10 years ago the first European interplanetary mission Mars Express was launched and sent into orbit around Mars. One of the scientific instruments on board the orbiter is the High Resolution Stereo Camera (HRSC). This multi-line sensor with five panchromatic and four multispectral CCD lines was developed by the German Aerospace Center (DLR) for photogrammetric mapping purposes. It images the Martian surface with a resolution of up to 12 m per pixel, depending on the altitude. The along-track stereo capability of the camera delivers image strips with three-dimensional information, which cover nearly the whole planet. For a derivation of more accurate digital terrain models and orthoimages the orientation data of the camera is improved via bundle adjustment. To map larger regions overlapping image strips can be used to form photogrammetric blocks, thus allowing a simultaneous adjustment of the different strips. Compared to the adjustment of individual strips, an adjustment of the entire block reduces not only local, but also regional inconsistencies in the data. With the growing number of HRSC image strips in this ongoing mission, number, size and complexity of potential blocks increases. To cope with these data a method for a semi-automated analysis, selection and combination of suitable strips for the design of more accurate and reliable blocks has been developed. The method takes the inhomogeneity of the HRSC data into account by adapting the processing parameters, if necessary for each strip

LANDSAFE: LANDING SITE RISK ANALYSIS SOFTWARE FRAMEWORK

The European Space Agency (ESA) is planning a Lunar Lander mission in the 2018 timeframe that will demonstrate precise soft landing at the polar regions of the Moon. To ensure a safe and successful landing a careful risk analysis has to be carried out. This is comprised of identifying favorable target areas and evaluating the surface conditions in these areas. Features like craters, boulders, steep slopes, rough surfaces and shadow areas have to be identified in order to assess the risk associated to a landing site in terms of a successful touchdown and subsequent surface operation of the lander. In addition, global illumination conditions at the landing site have to be simulated and analyzed. The Landing Site Risk Analysis software framework (LandSAfe) is a system for the analysis, selection and certification of safe landing sites on the lunar surface. LandSAfe generates several data products including high resolution digital terrain models (DTMs), hazard maps, illumination maps, temperature maps and surface reflectance maps which assist the user in evaluating potential landing site candidates. This paper presents the LandSAfe system and describes the methods and products of the different modules. For one candidate landing site on the rim of Shackleton crater at the south pole of the Moon a high resolution DTM is showcased. * CorrespondingLandSAf