Data Set Overview : This data set presents digital elevation maps (DEM) of the portions of the surface of the nucleus of comet 19P/Borrelly that were illuminated and visible during the Deep Space 1 encounter. During the approach to the nucleus, the spacecraft executed a turn to keep the body-mounted camera oriented on the target. In combination with this turn, the changing viewing geometry allows subsequent images to be associated into stereo pairs, from which valuable information can be extracted about the three-dimensional structure of the nucleus.  The maps were separately created by members of the US Geological Survey (USGS) and by the German Aerospace Center (Deutschen Zentrum fur Luft- und Raumfahrt - DLR) using a series of three of the best available images taken by the Miniature Integrated Camera and Spectrometer (MICAS) aboard the Deep Space 1 spacecraft as it flew by the comet nucleus. The elevations were derived by using parallax measurements between two pairs of images to determine elevation above a reference plane. The unit surface normal vector was also calculated for the USGS model. Descriptions of the stereo analysis procedure are provided in Soderblom, et al. (2002) [SODERBLOMETAL2002], Kirk, et al. (2004) [KIRKETAL2004] for the USGS model and Oberst et al. (2004) [OBERSTETAL2004] for the DLR model.  Kirk, et al. (2004), note that: Elevations relative to an arbitrary zero (approximately the lowest point on the limb) range to approximately 4600 m, with only a small area above 4000 m. There is a trend from low areas at the 'top' end of the nucleus ... to areas higher than 3000 m at the 'bottom' end. Hence, the bottom of the nucleus appears to be tilted toward the camera.  'Top' and 'bottom', as referenced above, are with respect to the images as published in Kirk, et al. (2004). In these images the elongated nucleus is presented with the narrower end in the lower left corner.  A comparison of the two models, which are derived from the same data, but use different techniques to derive the elevations, provide an estimate of the uncertainties in the elevation. Although the differences vary with position on the nucleus, the mean error is about 85 m.   Parameters : The DEM data are presented in individual ASCII files (one each for the USGS and DLR models) listing X, Y and Z coordinates for the grid points. The USGS model also provides the corresponding Nx, Ny, and Nz elements of the unit surface normal vector at each point.  Processing : The three highest-resolution images, identified in the PDS data set DS1-C-MICAS-3-EDR-VISCCD-BORRELLY-V1.0 as CCD_MID_5_3, CCD_MID_5_4, and CCD_NEAR_01, were used to generate the elevation map. (Copies of these three images are included in the data/images directory for this data set). A description of the image processing and calibration can be found in Soderblom et al. (2002) [SODERBLOMETAL2002] and Oberst et al. (2000) [OBERSTETAL2000].  The CCD_MID_5_3 / CCD_NEAR_01 stereo pair was used for the standard topographic models, while the CCD_MID_5_4 / CCD_NEAR_01 pair was used to derive separate models in order to check for consistency. The details of converting the stereoscopic data into an elevation model are described in Kirk, et al. (2004) [KIRKETAL2004] for the USGS model and Oberst et al. (2004) [OBERSTETAL2004] for the DLR model.  The USGS data were received at the SBN as a series of six two-dimensional arrays of numbers (in ASCII text). Each of these source files contained the value for a single coordinate or vector element (X, Y, Z, Nx, Ny, Nz). SBN personnel combined the corresponding coordinates and elements from these files into the single table presented here, discarding null values and sorting on increasing X and Y.  Coordinate System : Because only one side of the comet nucleus was observed, the X-Y coordinate system used for these data was a local space rectangular system defined by the investigators. The elevation (Z) is defined with respect to a reference plane that is roughly in the plane of the sky. Details regarding the coordinates used in the two models are given in the COORDS.TXT file in the documents directory.  The solar phase angle relating to the image was 51.624 degrees, so the Sun was 39.376 degrees out of the plane of the image, with a clock angle of 265.116 degrees.  SBN personnel noted that there are some negative Z values, located mainly near the image limb.   Media/Format : This data set is available for electronic download.  Author : Unless otherwise noted, the text in this file was prepared by Tony Farnham and Ed Grayzeck, Small Bodies Node.

Confidence Level Overview : No smoothing has been applied to these models, and depending on the use, it is recommended that users employ some form of smoothing to suppress the noise in the data set.  Review : The USGS data set were reviewed in October 2003, and the DLR data were reviewed in May 2004.