Three Years of Mars Cartography




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Three Years of Mars Cartography
Using HRSC Data


J. Albertz1, S. Gehrke1, H. Lehmann1, M. Wählisch2,
G. Neukum
3, and the HRSC Co-Investigator Team


1 Technische Universität Berlin, Geodesy and Geoinformation Science, Secretariat H12,
Straße des 17.Juni 135, D-10623 Berlin, {albertz|stephan|h.lehmann}@igg.tu-berlin.de


2 German Aerospace Center (DLR), Institute of Planetary Research, Berlin-Adlershof, Rutherfordstraße 2,
D-12489 Berlin, marita.waehlisch@dlr.de


3 Freie Universität Berlin, Institute of Geological Sciences, Malteserstr. 74-100, D-12249 Berlin, gneukum@zedat.fu-berlin.de

Abstract


Since January 2004, the High Resolution Stereo Camera (HSRC) on board of Mars Express is imaging the Mar­tian surface. The data acquired provide both full color and systematic stereo; it is well suited to derive Digital Terrain Models, color orthoimages, and, based on that, topographic and thematic maps. The standard map series of the Mars Express mission is the Topographic Ima­ge Map Mars 1:200,000. Map production is carried out using the cartographic software package Planetary Image Mapper (PIMap), which has been developed at Tech­nische Universität Berlin. An overview of HRSC maps of the past three years is given. This comprises the sheets of the standard se­ries as well as related topo­gra­phic and also thematic map products.

Introduction


The High Resolution Stereo Camera (HRSC) on the European Mars Express mission began operation in January 2004. The camera is returning both full color and mul­tiple stereo – a unique data set for systematic de­rivation of Digital Terrain Models (DTM), color orthoimages, and, based on that, high quality cartographic products, which are mainly based on the cartographic concepts of the Topo­graphic Image Map Mars 1:200,000 series (Albertz et al., 2004; Kirk, 2005; Lehmann et al., 1997). The series’ layout scheme is flexible to the generation of spe­cial target maps, thematic maps, and related products.

In order to au­tomate the map generation process, the carto­graphic software package Planetary Image Map­per (PIMap) has been developed at Technische Uni­versität Berlin (TUB) by Gehrke et al. (2006b). Using this soft­ware, map pro­duction is carried out at TUB in co­operation with the German Aerospace Cen­ter (DLR), which is res­­pon­sible for pho­togram­me­tric pro­cessing of HRSC data (Gwinner et al., 2005; Scholten et al., 2005). Other HRSC team members are involved, especially with regard to thematic mapping.

An average sheet of the Topographic Ima­ge Map Mars 1:200,000 displays approximately 120x120 km; conside­ring an HRSC image width of 60 km in highest resolution of 12 m/pixel, it is evident that mosaics of adjacent orbits are necessary to cover the mapped area. Therefore, especially in the early stage, map sheets needed to be adapted to individual orbits by location and/or scale. The first maps within the regular sheet lines could be generated in summer 2004. Until the present day, a variety of topographic and also thematic maps of different Martian regions has been produced. Furthermore, it has been shown that HRSC data of highest reso­lu­tion is suitable for mapping even in scales up to 1:50 000.

The Topographic Image Map Mars 1:200,000 SeRies


The large-scale Topographic Image Map Mars 1:200,000 map series was developed to allow for op­timum carto­graphic representation of HRSC data (Lehmann et al., 1997). It is based on HRSC orthoimages and features contour lines, topographic names as well as map titles, desig­nations, and several legend entries (Albertz et al., 2004; Albertz et al., 2005b; Gehrke et al., 2006b). The Mar­tian surface is covered in 10,372 individual sheets in equal-area projections: Sinusoidal projection for lati­tudes between 85° north and south and Lambert Azi­muthal Equal-Area projection around the poles. While all map sheets feature 2° in latitude, the lon­gitude ex­tent in­crea­ses from 2° in the equatorial zone towards 360° at the poles. Therefore, the mapped area is similar for all sheets (about 120x120 km2). The series’ car­to­graphic concept forms the basis for spe­cial tar­get maps in different scales and also for thematic mapping (Albertz et al., 2004).

Table 1: Regions of Mars and related HRSC map products. (Map type designators following Greyley & Bat­son, 1990: OM = orthoimage mosaic; C = contour lines; N = nomenclature; T = topography, i.e. both contours and nomenclature; G = geo­logy; K = color)




Region

HRSC Orbit(s)

Covered Area: Lat/Lon

Scale(s)

Map Type(s)

Alba Patera

68

39.1N - 41.0N

255.0E - 257.5E

200k

OMKT

Albor Tholus

32

18.0N - 20.0N

149.5E - 151.1E

200k

OMKT, OMKN

Candor Chasma

1235

7.9S - 5.9S

282.3E - 284.3E

200k

OMC

Centauri/Hellas

2510

41.0S - 37.0S

95.0E - 97.5E

200k, 300k

OMKT

Chasma Boreale

1154

83.0N - 87.0N

306.0E - 336.0E

200k

OMKT, OMKN

Dokka

1177

77.0N - 79.0N

210.0E - 220.0E

200k

OMKN

Hydraotes Chaos

18

0.7N - 1.7N

322.7E - 324.6E

100k

OMKT

Iani Chaos

912, 923, 934

3.0S - 1.0N

342.0E - 344.0E

200k, 100k, 50k

OMKT

Mangala Valles

286, 299

9.0S - 3.0S

208.0E - 210.0E

200k

OMKT, OMKN

Nanedi Valles

894, 905, 927

3.8N - 5.8N

311.3E - 313.3E

200k

OMC

North Pole

1154, 1167

89.0N - 90.0N

0.0E - 360.0E

200k

OMKN

Sabrina Valles

894, 905, 927

9.8N - 13.3N

310.0E - 314.0E

400k

OMKT

Tithonium Chasma

442

7.0S - 5.0S

268.0E - 270.0E

200k

OMKT

Centauri/Hellas

2510

39.8S - 36.8S

95.0E - 97.5E

300k

G (OMKG)

Gusev

24, 27, 285, 335

18.0S - 10.0S

172.0E - 179.0E

600k

G

Hale/Bond

511, 533

30.5S - 38.0S

320.5E - 327.0E

600k, 750k

G (OMKG)




Figure 1: Location of mapped regions on Mars, based on Viking color data (USGS, 2007). Due to the small scale, individual map sheets cannot be shown.

The common Martian reference body for planimetry is a rotatio­nal ellipsoid with an equatorial axis of 3396.19 ± 0.10 km and a polar axis of 3376.20 ± 0.10 km. This para­meter set is defined by the International Astronomical Union (IAU) as the Mars IAU 2000 ellipsoid (Seidelmann et al., 2002). According to IAU conventions two different types of ellip­soidal coordinate systems are in use. One consists of positive western longitudes in combi­nation with planeto­gra­phic latitudes (west/planetographic), the other one of positive eastern longitudes and planeto­centric latitudes (east/pla­neto­centric). The latter is recommended by the Mars Geodesy/Carto­graphy Wor­king Group (MGCWG) to be emplo­yed in future map products (Dux­bury et al., 2002). Therefore, the east/ planetocentric sys­tem is defined also as the standard for Mars Express mapping (Albertz et al., 2005b).

An Areoid (Martian Geoid) is the topographic refe­rence surface for heights (Seidelmann et al., 2004). It has been de­rived from Mars Global Surveyor data and is defined by the mean equatorial radius of 3396.0 km (Smith et al., 2001).

Map Products


Altogether 69 map sheets in 14 dif­ferent regions have been derived from HRSC data be­tween 2004 and early 2007 – compare Figure 1 and Table 1.

Topographic Standard Sheets


In general, conside­ring HRSC image widths (> 60 km), adja­cent orbits have to be mosaicked to cover a sheet of the Topo­gra­phic Image Map Mars 1:200,000 series. How­ever, maps within the regular sheet lines have already been accom­plished in summer 2004 showing the Mangala Valles complex. Since then, several sheets of different regions of Mars have been produced (Albertz et al., 2005a, 2005b; Gehrke et al., 2006a; Gehrke et al., 2007a). Figure 2 shows two adjacent standard sheets in the north-polar region on either side of the 85° parallel, which is the transition of the two map pro­jec­tions. These topogra­phic maps combine high-reso­lution HRSC ortho­images with contour lines from Mars Orbi­ter Laser Alti­meter (MOLA). The sheets “M 200k 84.00N/ 315.00E OMKT” (Sinusoidal projection) and “M 200k 86.00N/326.00E OMKT” (Lambert Azimu­thal project­tion) of the Topo­graphic Image Map Mars 1:200,000 cover 2° by 18° and 2° by 24°, res­pec­tively. The depicted Chasma Boreale al­most divides the ice cap and reveals (in Martian summer) layered struc­tures of water ice and dust. Con­tour lines nicely fit with these layers and, moreover, give a good impres­sion of the topography of the almost textureless ice cap (Gehrke et al., 2007a). The standard map sheet of the north pole itself has also been produced.

Sys­tematic mapping in larger scales, i.e. 1:100,000 and 1:50,000, can be achieved by divi­ding stan­dard sheets into quarters and sixteenth, res­pec­tively. The suitability of high quality HRSC data, which are both acquired under optimum conditions and adeptly processed, for mapping in those scales has been de­monstrated in Iani Chaos: A triplet of topographic image maps, a standard product within the regular sheet lines of the series,


“M 200k 2.00S/343.00E OMKT”, and two de­rived maps, “M 100k 2.50S/343.50E OMKT” and “M 50k 2.25S/ 343.25E OMKT”, have been generated (Gehrke et al., 2006a).

Special Target Maps


Especially in the early stage of the Mars Express mission map sheets needed to be adapted to individual orbits by location and/or scale. The very first HRSC map, e.g., was a special target map of Hydraotes Chaos in 1:100,000 (Albertz et al., 2004). The “Topographic Image Map Mars 1:400,000, M 400k 11.50N/312.00E OMKT, Sa­bri­na Vallis Region” with additional in­for­ma­tion from the Catalog of Large Mar­tian Impact Cra­ters has been recently presented by Gehrke et al. (2007b).

Thematic Maps


Several thematic map products have been generated in cooperation with other HRSC team members. Exemplary products are a geologic map of Gusev (Albertz et al., 2005b) and a new approach of a combined topo­gra­phic-thematic map illustrating the geomor­pho­lo­gy of Centauri and Hellas Montes (Lehmann et al., 2006). The most recent thematic product is a special target map of the Hale-Bond region by Hiesinger et al. (2007). In this area, the putative outflow channel Uzboi Vallis is heavily modified by the two impact craters. The valley floor is characterized by relatively smooth terrain between morphologically sharp blocks of eroded ejecta material (Fi­gure 3).

HRSC DTM Test Maps


It is evident that DTMs in highest quality are indis­pen­sable for the derivation of accurate contour lines. Besides systematic pro­ces­sing of all HRSC data (Scholten et al., 2005) exist several en­han­cing and alternative approa­ches (Albertz et al., 2005b; Gwinner et al., 2005), which have been com­pared in the HRSC DTM Test (Heipke et al., 2007). Part of the eva­lua­tion process – particularly regarding the contour line quality – was the generation of topographic map sheets from all de­li­vered DTMs in two different test areas, Nanedi Valles and Candor Chas­ma. These sheets follow the layout and scale of the standard map series.

Figure 2: Map sheets “M 200k 84.00N/315.00E OMKT” in Sinusoidal projection and “M 200k 86.00N/326.00E OMKT” in Lambert Azi­muthal projection. The index map (lower right image) was combined from both sheets and illustrates their rela­tive location, with map surfa­ces marked in yellow, and neighboring sheets of the Topographic Image Map Mars 1:200,000 series in their pro­jec­tions. The subsection of the northern sheet (upper left image) is shown in scale 1:400,000, which is half of the original size.


Figure 3: Geomorphologic map “M 600k 34.50S/323.75E OMKG” of the Hale and Bond crater region.

Conclusion


A variety of high quality HRSC maps in scales up to 1:50,000 is available from Technische Uni­ver­sität Ber­lin. The Topographic Image Map Mars 1:200,000 series has proven to be a useful and guide-lining standard. From the experience gained during three years HRSC cartography and operational appli­cation of PIMap it is clear that we are well pre­pared for systematic map generation from HRSC data.

References


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Albertz, J., Attwenger, M., Barrett, J., et al., 2005a. HRSC on Mars Express – Photogrammetric and Cartographic Research. Photo­grammetric Engineering & Remote Sensing, Vol. 71, No. 10, pp. 1153-1166.

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