PHOTOGRAMMETRIC PROCESSING OF PLANETARY LINEAR PUSHBROOM IMAGES BASED ON APPROXIMATE ORTHOPHOTOS

The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLII-3, 2018 ISPRS TC III Mid-term Symposium “Developments, Technologies and Applications in Remote Sensing”, 7–10 May, Beijing, China PHOTOGRAMMETRIC PROCESSING OF PLANETARY LINEAR PUSHBROOM IMAGES BASED ON APPROXIMATE ORTHOPHOTOS X. Geng 1, 2, *, Q. Xu 1, S. Xing 1, Y.F. Hou 1, C.Z. Lan 1, J.J. Zhang 2 1 Zhengzhou Institute of Surveying and Mapping, Zhengzhou, China - 2 Xi’an Information Technique Institute of Surveying and Mapping, Xi’an, China Commission III, WG III/II KEY WORDS: Planetary Photogrammetry, Planetary Images, Linear Pushbroom Images, Approximate Orthophotos, Image Matching, Digital Terrain Model ABSTRACT: It is still a great challenging task to efficiently produce planetary mapping products from orbital remote sensing images. There are many disadvantages in photogrammetric processing of planetary stereo images, such as lacking ground control information and informative features. Among which, image matching is the most difficult job in planetary photogrammetry. This paper designs a photogrammetric processing framework for planetary remote sensing images based on approximate orthophotos. Both tie points extraction for bundle adjustment and dense image matching for generating digital terrain model (DTM) are performed on approximate orthophotos. Since most of planetary remote sensing images are acquired by linear scanner cameras, we mainly deal with linear pushbroom images. In order to improve the computational efficiency of orthophotos generation and coordinates transformation, a fast back-projection algorithm of linear pushbroom images is introduced. Moreover, an iteratively refined DTM and orthophotos scheme was adopted in the DTM generation process, which is helpful to reduce search space of image matching and improve matching accuracy of conjugate points. With the advantages of approximate orthophotos, the matching results of planetary remote sensing images can be greatly improved. We tested the proposed approach with Mars Express (MEX) High Resolution Stereo Camera (HRSC) and Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) images. The preliminary experimental results demonstrate the feasibility of the proposed approach. 1. INTRODUCTION Planetary photogrammetry is the main method to produce digital orthophoto map (DOM) and digital terrain model (DTM) of celestial bodies. Planetary mapping products are foundation of landing sites selection and mission path planning (Di et al., 2008; Kirk et al., 2008; Naß et al., 2017), which are also essential to planetary scientific research such as geology and geomorphology (Wang et al., 2017; Wardlaw et al., 2018). Currently, there are millions of planetary remote sensing images acquired by orbital imaging instruments. However, only a small portion of these images are fully processed, due to lacking professional people and powerful software tools. The well-known open source software in planetary mapping community, namely Integrated Software for Imagers and Spectrometers (ISIS) developed by United States Geological Survey (USGS), supports many planetary missions (Edmundson et al., 2013). As a matter of fact, ISIS is the de facto standard for preprocessing of planetary images. The Ames Research Centre of National Aeronautics and Space Administration (NASA) also developed a suite of open source 3D surface reconstruction software to facilitate planetary mapping (Shean et al., 2016). On the other hand, commercial digital photogrammetric workstation (DPW) such as SoftCopy Exploitation Tool SET (SOCET SET) provided by BAE Systems is also used to process planetary images with necessary format conversion (Scholten et al., 2005; Kirk et al., 2008; Gwinner et al., 2009). Though commercial DPWs are more robust and efficient than open source software, they are mainly developed for earth observation remote sensing images and only support limited planetary images such as High Resolution Imaging Science Experiment (HiRISE) aboard Mars Reconnaissance Orbiter (MRO) and Narrow Angle Cameras (NACs) aboard Lunar Reconnaissance Orbiter (LRO). Orbital imaging instruments used for planetary mapping always adopt linear pushbroom cameras, for example NACs on LRO, HiRISE on MRO, Mars Orbiter Camera (MOC) on Mars Global Surveyor (MGS) and High Resolution Stereo Camera (HRSC) on Mars Express (MEX). It is widely acknowledged that the photogrammetric processing of linear pushbroom images is more complicated than conventional frame images. Moreover, the imaging instruments used for planetary mapping differ greatly, which makes the processing of planetary images more complex. Hence, the developed processing method for specific imaging instrument maybe not suitable for other imaging instruments. In a word, photogrammetric processing of planetary remote sensing images is still a very challenging task. Though there are available open source and commercial software tools, it is still meaningful to develop processing techniques of planetary images. In this paper, we propose a general photogrammetric processing framework for planetary linear pushbroom images. The proposed approach is characterized by image matching based on approximate orthophotos. Here, "approximate orthophotos" means that orbital photographs are rectified with a rough DTM such as Mars Orbiter Laser Altimeter (MOLA) DTM or a preliminary auto-generated DTM rather than final high resolution DTM products. It is noted that the HRSC team also adopted the concept of approximate orthophotos to derive Mars mapping products (Albertz et al., 2005; Scholten et al., 2005). The different points of our method are: (1) a fast back-projection algorithm of linear pushbroom images is introduced to improve * Corresponding author This contribution has been peer-reviewed. https://doi.org/10.5194/isprs-archives-XLII-3-391-2018 | © Authors 2018. CC BY 4.0 License. 391 The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Volume XLII-3, 2018 ISPRS TC III Mid-term Symposium “Developments, Technologies and Applications in Remote Sensing”, 7–10 May, Beijing, China the computational efficiency of orthophotos generation and coordinates transformation of conjugate points; (2) an iteratively refined DTM and DOM strategy is developed to accurately determine the approximate values of conjugate points. 2. METHODS 2.1 Basic Principle Since planetary remote sensing images have little texture features, image matching is the most difficult task in planetary photogrammetry. Conventional image matching methods including both area-based matching (ABM) and feature-based matching (FBM) usually deliver unsatisfactory results for planetary images. Thus, many researchers proposed optimized image matching algorithms for planetary remote sensing images. Semi-global matching (SGM) algorithm won great success in earth observation fields (Hirschmüller, 2008), (...truncated)