lunar and planetary science xxx 1933.pdf digital ... · common coverage. month one orbital data...

DIGITAL PROCESSING FOR A GLOBAL MULTISPECTRAL MAP OF THE MOON FROM THECLEMENTINE UVVIS IMAGING INSTRUMENT. E. M. Eliason1, A. S. McEwen2 , M. S. Robinson3, E.M. Lee1, T. Becker1, L. Gaddis1, L. A. Weller1, C. E. Isbell1, J. R. Shinaman1, , T. Duxbury4, E. Malaret5,1United States Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ, 2Lunar and Planetary Laboratory,University of Arizona, Tucson, AZ, 3Northwestern University, Evanston, IL, 4Jet Propulsion Laboratory,Pasadena, CA, 5Applied Coherent Technology, Herndon, VA.

Introduction: The primary scientific objective ofthe Clementine Mission during its two month orbitabout the Moon was to acquire global multispectralimaging of the lunar surface using the UVVIS andNIR camera imaging systems [1,2]. A multi-spectralglobal Digital Image Model (DIM) of the Mooncontaining controlled image mosaics has beencompiled by the U.S. Geological Survey, in acollaborative effort with the many authors listedabove, for distribution to the science community [3].The recently released DIM consists of the five spectralbands (415, 750, 900, 950, and 1000 nm) from theUVVIS imaging instrument. The imaging has beenradiometrically corrected, geometrically controlled toa lunar geodetic control network, and photometricallynormalized to form uniformly illuminated mosaics ofthe lunar surface. Figure 1, a color ratio compositeideally suited for enhancing subtle color differencesamong lunar terrain types, illustrates the results of theglobal mapping effort. The global mosaics portrayedare projected in a sinusoidal equal-area projectionwith a resolution of 1.0 km/pixel.

Radiometric Calibration: Radiometric calibrationsteps for the UVVIS imaging have been well tested,validated, and documented [4]. The calibrationprocess provides corrections for camera gain andoffset operating modes, variable sensitivity acrossCCD camera array, sensitivity and dark-currentdependence on temperature, non-linearity of theanalog-to-digital converters, and conversion toradiometric units. We do not attempt any correctionfor scattered/stray light, although such correctionsmay be important for examining small high-contrastfeatures, especially dark areas [5]. In assembling theglobal DIM, we discovered small difference (<5%)between the first and second month orbital data that inpart can be attributed to calibration drift of the UVVIScamera. A correction for reconciling calibrationdifferences between the first and second month wasdeveloped and applied. This procedure comparedmonth one and month two orbital data in areas ofcommon coverage. Month one orbital data werematched to adjacent coverage of month two data usinga latitude-dependent least-squares fit procedure.

Geometry: A global base map created from theUVVIS 750 nm imaging, completed in 1996, provides

the geometric control for the multispectral DIM. Thebase map underwent rigorous cartographic processingto tie the imaging to a lunar geodetic networkresulting in an absolute positional accuracy of betterthan 0.5 km/pixel for 95% of the surface.

The registration of the bands is critically importantto mapping compositional variations from the subtledifferences in reflectivity with wavelength.Misregistration of less than one pixel can cause colordiscrepancies along spectral boundaries. We used aprocedure to register spectral bands to a precision of0.2 pixel.

Phase Function Normalization: The Clementineimagery was acquired under a broad range of viewingconditions with phase, emission, and incidence anglesvarying from 0 to 90° resulting in large scenebrightness variations among the image collection. Inorder to form mosaics with uniform scene brightness aphotometric normalization procedure [6] was appliedto the individual images before compiling the globalmosaic. Differences in phase behavior, especially nearzero phase, as a function of terrain type was observedin the resulting mosaics. A second-order correction tothe phase function for near zero phase observationswas developed and applied to the data. This procedurecompared areas of overlap among low and high-phaseimaging for determining a multiplicative correction tothe low-phase imaging which forced overlapping areasto spectrally match. The resulting multiplicativecorrections were then applied to the low-phaseimaging in non-overlap areas.

References: [1] Nozette, S., et. al., (1994), TheClementine Mission to the Moon: Scientific Overview.Science, 266, 1835-1838. [2] McEwen, A., andRobinson, M., (1997), Mapping of the Moon byClementine, Adv. Space Res., 19, 1523-1527. [3]Isbell, C., et. al., Clementine: A Multi-spectral Digitalimage Model Archive of the Moon, LPS XXX, thisvolume. [4] McEwen, A., et. al., (1998), Summary ofRadiometric Calibration and PhotometricNormalizations Steps for the Clementine UVVISimages, LPS XXIX, on CD-ROM media. [5] RobinsonM., et. al., Clementine UVVIS Global Mosaic: a newtool for understanding the Lunar Crust, LPS XXX, thisvolume, [6] McEwen, A., (1996), A Precise LunarPhotometric Function, LPSC XXVII, 841-842.

Lunar and Planetary Science XXX 1933.pdf

A GLOBAL MUTISPECTRAL MAP OF THE MOON, E. M. Eliason, et. al.

Figure 1 - False color composite of ratioed image showing the eastern hemisphere (top figure) centered at 90° Eastlongitude and the western hemisphere (bottom figure) centered at 90° West longitude. The latitude range extends70° North and South. The color composite is created using 415/750 nm (blue), 750/950 nm (green), and 750/415(red). Ratio composites cancel the albedo component and enhance the color signature differences. Blue to red colortones show overall color differences in the ultraviolet to near-infrared. Yellow and orange colors indicate a greaterabundance of iron and magnesium-rich materials. The full resolution global image has approximately 110,000pixels in longitude and 55,000 pixels in latitude.

Lunar and Planetary Science XXX 1933.pdf