M. Caplinger Malin Space Science Systems, Inc. · Malin Space Science Systems, Inc. San Diego,...
4
PLANETARY CARTOGRAPHY AT MSSS M. Caplinger Malin Space Science Systems, Inc. San Diego, California Introduction: Though the primary focus at Malin Space Science Systems (MSSS) is on building and operating instruments through the archiving of raw data, we have also pursued research interests in planetary cartography. This abstract describes three of these efforts using data from the Mars Orbiter Camera on MGS. Outreach: In 2000 MSSS was approached by National Geographic Maps (NG Maps) to produce a map of Mars for an insert to accompany an arti- cle about the MGS mission. A rendering based on MGS data and showing both topography and sur- face shading was desired. After consultation with the MOLA team, they graciously provided a pre- release version of the global MOLA Digital Ter- rain Model at 16 pixels per degree (ppd) resolution. For surface albedo, we assembled a mosaic of MOC red Wide Angle (WA) images taken during the "geodesy campaign" in May-June 1999 (map- ping cycle M01, [1]) and "Science Campaign C" in December 1999 (mapping cycle M10). Brightness matching between images was controlled by using lower-resolution daily global map images, built by hand, as base maps. This global image mosaic was also processed to a resolution of 16 ppd. Extensive filtering and edge matching was performed at this stage, by hand, to remove visible flaws caused by transmission errors and remaining brightness mismatches. The MOLA DTM was converted into two shaded relief maps: one using a physical shading model, and another using the normalized gradient mode of the Generic Mapping Tools (GMT) software. The latter helped to emphasize the subtle topography visible in the MOLA data. The physical and non- physical shaded relief and the image mosaic were combined by a linear function; the Winkel-Tripel and polar stereographic projections requested by NG Maps were generated using GMT. Although the MOC WA did acquire two-color (red and blue) images of the entire planet, clouds obscured many areas in the blue images. To create a color image without clouds, only the red part of the MOC images was used. Color images of the planet, previously assembled from Viking data by the United States Geological Survey, were used to create a function that mapped red brightness to color, and this function was then applied to the MOC images. Figure 1 shows the resulting image. NG Maps applied labeling and a latitude-longitude grid to the image and it was integrated into the sheet titled "Mars Revealed", which appeared in the February 2001 issue of NATIONAL GEO- GRAPHIC magazine. In October 2001, NG Maps received the John Bartholomew Award for excel- lence in small-scale thematic cartography from the British Cartographic Society for this product. Global WA Orthophoto Mosaic: The map described above was produced by projection to a spheroid. At its low resolution, no further correc- tion was needed for adequate seam matching, but at the intrinsic resolution of the geodesy campaign images (about 240 m/pxl), topography can cause as much as 20 pixels of disparity shift, which becomes objectionable. Starting in mid-2001, we modified our map-projection software to apply the topographic correction, using the MOLA 16 ppd dataset. Use of the MOC geometric model derived at USGS [2] (with the red camera’s C05 term corrected; C05 = -0.1539636) leads in principle to subpixel edge matching. In most cases this is borne out, though we have noted some periods of poor or missing spacecraft ephemeris and/or orien- tation data. While the spacecraft position and orientation information and the camera geometry model appear to be sufficient for the production of good uncontrolled mosaics, the wide range of pho- tometric and atmospheric conditions makes shad- ing correction problematic. We are addressing this in our current products by again using a hand- corrected base map to normalize brightness. While not preserving of absolute photometry, this approach provides qualitative albedo information and does not enhance detector pixel-to-pixel varia- tion as high-pass filtering might. Derivation of a photometric model capable of truly removing edges remains work for the future. Figure 2 shows an area of a mosaic constructed at 64 ppd with and without topographic color overlay. Narrow Angle Stereo Processing: starting in Febru- ary 2001 the MGS spacecraft has been executing Roll-Only Targeted Observations (ROTOs) based 1
Transcript of M. Caplinger Malin Space Science Systems, Inc. · Malin Space Science Systems, Inc. San Diego,...
PLANETARY CARTOGRAPHY AT MSSS
M. CaplingerMalin Space Science Systems, Inc.
San Diego, California
Introduction: Though the primary focus at MalinSpace Science Systems (MSSS) is on building andoperating instruments through the archiving of rawdata, we have also pursued research interests inplanetary cartography. This abstract describesthree of these efforts using data from the MarsOrbiter Camera on MGS.
Outreach: In 2000 MSSS was approached byNational Geographic Maps (NG Maps) to producea map of Mars for an insert to accompany an arti-cle about the MGS mission. A rendering based onMGS data and showing both topography and sur-face shading was desired. After consultation withthe MOLA team, they graciously provided a pre-release version of the global MOLA Digital Ter-rain Model at 16 pixels per degree (ppd) resolution.For surface albedo, we assembled a mosaic ofMOC red Wide Angle (WA) images taken duringthe "geodesy campaign" in May-June 1999 (map-ping cycle M01, [1]) and "Science Campaign C" inDecember 1999 (mapping cycle M10). Brightnessmatching between images was controlled by usinglower-resolution daily global map images, built byhand, as base maps. This global image mosaic wasalso processed to a resolution of 16 ppd. Extensivefiltering and edge matching was performed at thisstage, by hand, to remove visible flaws caused bytransmission errors and remaining brightnessmismatches.
The MOLA DTM was converted into two shadedrelief maps: one using a physical shading model,and another using the normalized gradient mode ofthe Generic Mapping Tools (GMT) software. Thelatter helped to emphasize the subtle topographyvisible in the MOLA data. The physical and non-physical shaded relief and the image mosaic werecombined by a linear function; the Winkel-Tripeland polar stereographic projections requested byNG Maps were generated using GMT.
Although the MOC WA did acquire two-color (redand blue) images of the entire planet, cloudsobscured many areas in the blue images. To createa color image without clouds, only the red part ofthe MOC images was used. Color images of theplanet, previously assembled from Viking data bythe United States Geological Survey, were used to
create a function that mapped red brightness tocolor, and this function was then applied to theMOC images. Figure 1 shows the resulting image.
NG Maps applied labeling and a latitude-longitudegrid to the image and it was integrated into thesheet titled "Mars Revealed", which appeared inthe February 2001 issue of NATIONAL GEO-GRAPHIC magazine. In October 2001, NG Mapsreceived the John Bartholomew Award for excel-lence in small-scale thematic cartography from theBritish Cartographic Society for this product.
Global WA Orthophoto Mosaic: The mapdescribed above was produced by projection to aspheroid. At its low resolution, no further correc-tion was needed for adequate seam matching, butat the intrinsic resolution of the geodesy campaignimages (about 240 m/pxl), topography can cause asmuch as 20 pixels of disparity shift, whichbecomes objectionable. Starting in mid-2001, wemodified our map-projection software to apply thetopographic correction, using the MOLA 16 ppddataset. Use of the MOC geometric model derivedat USGS [2] (with the red camera’s C05 termcorrected; C05 = -0.1539636) leads in principle tosubpixel edge matching. In most cases this isborne out, though we have noted some periods ofpoor or missing spacecraft ephemeris and/or orien-tation data. While the spacecraft position andorientation information and the camera geometrymodel appear to be sufficient for the production ofgood uncontrolled mosaics, the wide range of pho-tometric and atmospheric conditions makes shad-ing correction problematic. We are addressing thisin our current products by again using a hand-corrected base map to normalize brightness. Whilenot preserving of absolute photometry, thisapproach provides qualitative albedo informationand does not enhance detector pixel-to-pixel varia-tion as high-pass filtering might. Derivation of aphotometric model capable of truly removingedges remains work for the future. Figure 2 showsan area of a mosaic constructed at 64 ppd with andwithout topographic color overlay.
Narrow Angle Stereo Processing: starting in Febru-ary 2001 the MGS spacecraft has been executingRoll-Only Targeted Observations (ROTOs) based
1
on planning done by MSSS. ROTOs have beenused both to image high-priority targets (such aslanding sites) more quickly than the orbit track ofMGS would otherwise allow, and to acquire stereocoverage of selected targets. The stereo attributesof these images are well-described by others [3].MSSS has recently contracted with HarrisCorporation’s Government Communications Sys-tems Division to process 150 such stereo pairsusing Harris’ automated photogrammetry tools andmanual editing. DTM post spacing will be 3 NApixels, and MOLA altimetry will be used to vali-date the product. Figure 3 shows a shaded reliefversion of an early processing test, prior to manualediting. Initial data products are expected by mid-2002.
References: [1] Caplinger, M. and M. Malin, TheMars Orbiter Camera Geodesy Campaign, JGR, inpress. [2] Kirk, R.L., T.L. Becker, E.M. Eliason,J. Anderson, and L.A. Soderblom, GeometricCalibration of the Mars Orbiter Cameras andCoalignment with Mars Orbiter Laser Altimeter(abstract), LPSC XXXII, 2001. [3] Kirk, R.L., E.Howington-Kraus, and B.A. Archinal, High Reso-lution Digital Elevation Models of Mars fromMOC Narrow Angle Stereoimages, ISPRS Extra-terrestrial Mapping Workshop (this workshop),2001.
Figure 1: MOC/MOLA NGS global mosaic
2
Figure 2A: MOC WA global mosaic, eastern Valles Marineris
Figure 2B: MOC WA global mosaic with MOLA topography color overlay
3
Figure 3A: MOC NA image M03-01521 (Gale Crater)
Figure 3B: shaded relief of topography extracted from M03-01521 and E01-01026
4
