English: Prepared on behalf of the Planetary Geology and Geophysics Program, Solar
System Exploration Division, Office of Space Science, National Aeronautics and
Space Administration
NOTES ON BASE
This sheet is one in a series of maps of the Galilean satellites of Jupiter at a
nominal scale of 1:15,000,000. This series is based on data from the Galileo
Orbiter Solid-State Imaging (SSI) camera and the Voyager 1 and 2 space-
craft.
PROJECTION
Mercator and Polar Stereographic projections used for this map of Europa
are based on a sphere having a radius of 1,562.09 km. The scale is
1:8,388,000 at ±56° latitude for both projections. Longitude increases to the
west in accordance with the International Astronomical Union (1971;
Davies and others, 1996). Latitude is planetographic.
CONTROL
The process of creating a geometric control network began with selecting
control points on the individual images, making pixel measurements of
their locations, using reseau locations to correct for geometric distortions,
and converting the measurements to millimeters in the focal plane. These
data are combined with the camera focal lengths and navigation solutions
as input to a photogrammetric triangulation solution (Davies and others,
1998; Davies and Katayama, 1981). The solution used here was computed
at the RAND Corporation in June 2000. Solved parameters include the
radius (given above) of the best-fitting sphere, the coordinates of the con-
trol points, the three orientation angles of the camera at each exposure
(right ascension, declination, and twist), and an angle (W0) that defines the
orientation of Europa in space. W0—in this solution 36.022°—is the angle
along the equator to the east, between the 0° meridian and the equator’s
intersection with the celestial equator at the standard epoch J2000.0. This
solution places the crater Cilix at its defined longitude of 182° west (Davies
and others, 1996).
MAPPING TECHNIQUE
This global map base uses the best image quality and moderate resolution
coverage supplied by Galileo SSI and Voyager 1 and 2 (Batson, 1987;
Becker and others, 1998; 1999; 2001). The digital map was produced using
Integrated Software for Imagers and Spectrometers (ISIS) (Eliason, 1997;
Gaddis and others, 1997; Torson and Becker, 1997). The individual images
were radiometrically calibrated and photometrically normalized using a
Lunar-Lambert function with empirically derived values (McEwen, 1991;
Kirk and others, 2000). A linear correction based on the statistics of all
overlapping areas was then applied to minimize image brightness varia-
tions. The image data were selected on the basis of overall image quality,
reasonable original input resolution (from 20 km/pixel for gap fill to as
much as 40 m/pixel), and availability of moderate emission/incidence
angles for topography and albedo. Although consistency was achieved
where possible, different filters were included for global image coverage as
necessary: clear/blue for Voyager 1 and 2; clear, near-IR (757 nm), and
green (559 nm) for Galileo SSI. Individual images were projected to a
Sinusoidal Equal-Area projection at an image resolution of 500 m/pixel.
The final constructed Sinusoidal projection mosaic was then reprojected to
the Mercator and Polar Stereographic projections included on this sheet.
NOMENCLATURE
Names on this sheet are approved by the International Astronomical Union
(IAU, 1980, 1986, 1999, and 2001). Names have been applied for features
clearly visible at the scale of this map; for a complete list of nomenclature
of Europa, please see http://planetarynames.wr.usgs.gov. Font color was
chosen only for readability.