Using Digitized Spacecraft Film and a Revised Lunar Control Network for Photogrammetric Mapping

USING DIGITIZED SPACECRAFT FILM AND A REVISED LUNAR CONTROL NETWORK FOR PHOTOGRAMMETRIC MAPPING Mark R. Rosiek R.L. Kirk B.A. Archinal T.L. Becker L. Weller B. Redding E. Howington-Kraus D. Galuszka U.S. Geological Survey 2255 N. Gemini Dr Flagstaff AZ 86001 [email protected] ABSTRACT This paper reports on the results of photogrammetric mapping with Lunar Orbiter, Apollo panoramic and Apollo metric camera digitized photographs using modern softcopy digital mapping techniques and a revised lunar control network to establish control. We will report on the differences between Digital Elevation Models (DEMs) collected from Lunar Orbiter, Apollo panoramic and metric camera digitized photographs. Our test area is the Rima Hadley region, which includes the Apollo 15 landing site. This area is covered by multiple sources of data that can be used for comparison and evaluation of accuracy. The original Lunar Orbiter photographs reconstructed in the 1960s had limited utility for mapping due to a stair-step offset in the reconstructed photographs. These images have been re- cently digitized and digitally reconstructed to fit the reseaux and the fiducials to the camera calibration data. The Apollo imagery was previously used to produce topographic maps using different control networks. These previous networks have kilometer-size offsets between them and were also limited in size and accuracy. A revised lunar control network, the Unified Lunar Control Network 2005, improves the accuracy and the density of control points and includes solved-for for elevations of the control points. We find that all the image sets studied provide useful DEMs with minimal requirement for interactive editing but varying tradeoffs between area covered and resolution. The Apollo metric camera data are the cleanest and would support topomapping of nearly 20% of the Moon at 50 m post spacing. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorse- ment by the U.S. Government. INTRODUCTION We are evaluating the utility of using modern softcopy digital mapping techniques for extracting digital elevation models (DEMs) from Lunar Orbiter (LO) and Apollo digitized photographs. These photographs were used in the 1960s-70s for mapping, mission planning, and control purposes. Previous work with LO imagery was difficult due to image artifacts, and the mapping was not controlled to any horizontal or vertical datum (Hansen, 1970). Mapping with Apollo imagery used 2 different control networks. The hardcopy maps that resulted are the Lunar Topographic Orthophotomap (LTO) and Lunar Orthophotomap (LO) map series (Wu and Doyle, 1990). Since these maps were produced, the lunar control network has been improved (Archinal et al., 2006a, b) and the LO images are now available as digitized photographs with the artifacts greatly reduced (Gaddis et al., 2003, Weller et al., 2006). The tools available for softcopy mapping permit the generation of DEMs, from which contour maps can be made if desired, but the digital DEMs contain more detailed topographic information that can also be used for image rectification, photometric correction, slope analyses, etc. Use of the current control and datum en- sures that the topographic data can be used in conjunction with data from current and future missions. Thus the products enabled by this study supersede earlier maps and will be useful for upcoming lunar missions including SELENE – Japan, Chang'e 1 – China, Chandrayaan-1 – India, and Lunar Reconnaissance Orbiter – USA. ASPRS 2006 Annual Conference Reno, Nevada May 1-5, 2006 SOURCE DATA Lunar Orbiter Imagery LO photographs were collected by five missions, LO-I through -V, during 1966–1967. Stereo models are provided both by the overlap of photographs for global mapping and by deliberate targeting of specific sites of interest. LO IV coverage of the nearside includes 6°-wide bands of stereo at 0° and ±30° latitude, and from about ±60° latitude to the poles (>25% of the nearside in all). The resolution of the imagery is between 30 and 100 m. The other LO missions returned stereo imagery of spot areas with higher resolution (10 - 40 m) (Hansen, 1970). These images were used for Apollo landing site selection, but the full topographic information was not extracted because errors in reconstructing the photographs from sections scanned on the spacecraft produced artifacts in the form of linear "cliffs" in the stereomodels. Apollo Imagery Apollo 15, 16, and 17 photographed ~20% of the Moon immediately under their orbital tracks using both a frame mapping camera and a panoramic camera. The frame camera was a Fairchild metric camera with a 4.5 x 4.5 in film format. Stereo models are obtained by overlapping photographs along the flight line and between flight lines. When digitized at 10 µm, a metric camera photograph provides a useful resolution of about 15 m/pixel. The panoramic camera was an Itek panoramic camera with 45.24 x 4.5 in film format. Stereo models are obtained by using forward and aft looking photographs acquired along the same flight line. When digitized at 10 µm, a panoramic photograph has a resolution at image center of about 2 m/pixel and at the edge of the image the resolution is about 4 m/pixel. Additional information on the digitization process is provided below. Clementine In 1994, the Clementine spacecraft acquired digital images of the Moon at visible and near infrared wave- lengths, as well as laser altimeter data (Nozette et al., 1994). The Clementine laser altimeter (Lidar) data have a vertical accuracy of approximately 100 m, horizontal accuracy 3,000m, a surface spot size of 200m, and a spatial resolution of 2.5 . Altimetry data were collected between 79 S - 81 N (Smith et al., 1997, Neumann, 2001). The altimeter data and polar Clementine stereo data (Rosiek et al., 2002) was used to initialize the radii values in the ULCN 2005 control network described in the next paragraph. We will also use the altimeter points to analyze the DEMs that are collected from Apollo and LO images. Control We used control from two sources. First, Table 1. Lunar Horizontal Control Net Comparison. for horizontal and vertical control we used Name # points # images Horz. Acc. Vert. Acc. points from an interim solution of the Uni- ULCN 1,478 Unknown 100 m to 3 km Few km? fied Lunar control Network 2005 (ULCN Few km to CLCN 271,634 43,871 Sphere 2005). This network combines the Unified some>15 km Lunar Control Network (ULCN) and the ULCN 2005 272,931 43,871 Few km ~ 1 km or less Clementine Lunar Control Network (CLCN). Second, we also used points near the Apollo 15 landing site that were described in Davies and Colvin (2000). The ULCN was described in the last major publication about a lunar control network (Davies et al., 1994). See Table 1 for statistics on this and the other networks discussed here. Images for this network are from the Apollo, Mariner 10, and Galileo missions, and Earth-based photographs. The importance of this network is that its accuracy is relatively well quantified and published information on the network is available. The CLCN includes measurements on 43,871 Clementine 750-nm images. The purpose of this network was to determine the geometry for the Clementine Basemap Mosaic (CBM) (USGS, 1997). After the completion of the CBM, horizontal errors of 15 km or more were noticed and therefore these same errors are present in the CLCN (Malin and Ravine, 1998; Cook et al., 2000; Cook at al, 2002). The errors seem to have arisen for several reasons, including that only a few (22) near side points were fixed to ULCN positions, the camera angles were uncon- strained, and the tie points were all constrained to lie on a mass-centered sphere of radius 1736.7 km. We have merged the ULCN and CLCN and have addressed the horizontal accuracy problems of the CLCN, with the intent to create a new ULCN. Our new solution(s) include 3 changes. 1) The camera angles are constrained to within 0.03° of their a priori Navigation and Ancillary Information Facility (NAIF) values (Acton, 1999). 2) The coordinates of all identifiable ULCN points are constrained to their reported accuracy (Davies et al., ASPRS 2006 Annual Conference Reno, Nevada May 1-5, 2006 1994). 3) Radii of all tie points are solved for. Our current results show horizontal position changes from the CLCN on average of ~7 km with some changes of dozens of km. The final results are in preparation (Archinal et al., 2006b). Site Map The site mapped in this project is the Rima Hadley region, including the Apollo 15 landing site. This area has ex- cellent coverage by LO and Apollo images, and previous mapping products exist to compare with our results. We se- lected images 4102_H3 and 4103_H1 from LO IV, images 5105_MED, 5106_MED, 5107_MED, 5106_H1, 5106_H2, and 5106_H3 from LO V, images 0583, 0585, and 0587 from the Apollo 15 metric camera, and images 9809, 9811, 9814, and 9816 from the Apollo 15 panoramic camera. Figure 1 shows the image footprints. PROCEDURES We are using a commercial photogrammetric work- station with SOCET SET (® BAE Systems) software to view the images in stereo, select control and tie points, and collect Figure 1. Footprints of images used in this our DEMs. The LO and Apollo images, obtained by digitiza- study, shown on a Clementine image mosaic tion of film as described below, are imported into the work- with north at top. Blue: LO IV frames 4102_H3 station in TIFF file format. Support data were obtained from and 4103_H1; Green: LO V frames 5105_MED, the National Space Science Data Center and entered by hand.

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