THE CLEMENTINE UVVIS GLOBAL LUNAR MOSAIC
Eric Eliason, Chris Isbell, Ella Lee, Tammy Becker, Lisa Gaddis
United States Geological Survey
2255 North Gemini Drive
Flagstaff, AZ 86001
Lunar and Planetary Laboratory
University of Arizona
Tucson, AZ 85721
Department of Geological Sciences
Evanston, IL 60208
July 1, 1999
CONTENTSReturn to CD Home Page.
1 - INTRODUCTION
The Clementine Ultraviolet/Visible (UVVIS) mosaic [Eliason et al., 1999; Isbell et al., 1999; Robinson et al., 1999] of Earth's Moon is a radiometrically and geometrically controlled, photometrically modeled global Mosaicked Digital Image Model (DIM) [Batson, 1987; Batson, 1990] compiled using more than 400,000 images from multiple spectral observations of the Ultraviolet/Visible camera onboard the Clementine Spacecraft. The UVVIS mosaic is mapped in the Sinusoidal Equal-Area Projection [Snyder, J.P, 1987] at a resolution of 100 meters per pixel and requires approximately 68 gigabytes of digital storage This database is partitioned into quadrangles (quads) or "tiles" equivalent to those of the previously released Clementine 750 nanometer Basemap Mosaic (PDS volumes CL_3001 through CL_3015). This 100 m/pixel portion of the DIM is presented on 78 CD volumes. Tiles are stored as image files of approximately 2100 pixels on a side. Pixels are 16-bit signed integers. A phase angle image database, at equivalent resolution, accompanies the UVVIS DIM. Additional CD volumes will contain reduced-resolution planetwide coverage at 0.5, 2.5, and 12.5 km/pixels. A final ancillary volume will include additional information in support of the UVVIS DIM. This final volume will include an 'image source' index file and a 'browse' interface for the entire UVVIS DIM CD collection.
Although the tiling scheme is equivalent to the original basemap, each 30-degree gore of the basemap is now divided into six sets of quadrangles such that each set completes a 650 megabyte CD volume. The full-resolution tiling and CD archive scheme is available in graphical form in the 'scheme.pdf' (Portable Document Format [PDF]) file found in the 'document' directory of each CD.
PDS standards require inclusion of "catalog" files that describe aspects of the mission, spacecraft, instrument, and dataset. These files are located in the 'catalog' directory of each CD volume. In order to minimize the amount of redundant information that exists in the documentation collection, we reference these files throughout this document. The catalog files, ending with the '.cat' extension, are organized as ASCII text files and contain PDS labels for automatically ingesting the documents into a catalog system.
The CD volume set contains ancillary data files that support the UVVIS mosaic. These files include browse images stored in a 'JPEG' format, 'HTML' documents that support a web browser interface to the CDs, image index files that tabulate the contents of the CD volume set, and documentation files that describe the archive collection. For more information on the contents and organization of the CD volume set refer to the "Files, Directories, and Disk Contents" section of this document.
Using a web browser application (e.g. Netscape or MS Internet Explorer) open the 'index.htm' file located in the 'root' directory of each CD. The html document will direct you to other informational documents and the image browser for rapidly viewing the image collection.
The browse image consists of large, medium, and small browse images of enhanced color and comparative ratio images for each Clementine UVVIS DIM product. Three browse image renditions are available to the user: enhanced color, color ratio, and black/white 750 nm images. The enhanced color images use the 415 nm (blue), 750 nm (green), and 950 nm (red) spectral bands to portray the Moon in near-natural color. The color ratio browse images use the 415/750 (blue), 750/950 (green), and 750/415 (red) [e.g., Belton et al., 1992]. The ratio rendition serves to cancel out the dominant brightness variations of the scene (controlled by albedo variations and topographic shading) and enhances color differences related to soil mineralogy and maturity. The lunar highlands, mostly old (~4 b.y.) gabbroic anorthosite rocks, are depicted in shades of red (old) and blue (younger). The lunar maria (~3.8 b.y. to ~2 b.y.), mostly iron-rich basaltic materials of variable titanium content, are portrayed in shades of yellow/orange (iron-rich, low titanium) and blue (iron-rich, higher titanium). Superimposed on and intermingled with these basic units are materials from basins and craters of various ages, ranging from the ancient Serenitatis basin (~3.8 b.y.; red and blue highland rim, filled with younger, yellow-colored low-titanium maria) to the young, fresh crater, Tycho (~100 m.y.; bright blue rays on older, red highland surface).
Software tools for viewing and accessing of the image collection are available through the Planetary Data System's (PDS) Internet services. Refer to the 'aareadme.txt' located in the 'root' for more information on these tools. The program NASAView can be used to display the full resolution image products. NASAView is a PDS product display tool that runs on multiple platforms with a common graphical user interface. The current version (version 2.5.2) does not support the Clementine multispectral products. A new version will support multispectral data and is planned for release in late summer 1999. See the PDS Home Page for information on NASAView and it's availability (http://pds.jpl.nasa.gov/). The PDS Home Page will lead you to the site for direct access to NASAView (currently located at the URL: http://pds.jpl.nasa.gov/license.html). Once the proper version of NASAView is installed on your system, it can also be incorporated with your web browser as a helper application. Refer to your particular web browser document for information on helper applications. The MapMaker system enables users to generate seamless image maps for any latitude-longitude region at a variety of scales and map projections. For more information on the MapMaker system, contact the PDS Imaging Node (http://www-pdsimage.jpl.nasa.gov/PDS/, or e-mail firstname.lastname@example.org).
Additionally, each image file is associated with an Integrated Software for Imagers and Spectrometers (ISIS) [Eliason, 1997; Torson and Becker, 1997] detached label. The detached ISIS label allows for images to be accessed and processed within the ISIS system (available through the USGS, Flagstaff, AZ at http://wwwflag.wr.usgs.gov/).
2 - CLEMENTINE MISSION
The Clementine Mission [Nozette et al., 1994; McEwen and Robinson, 1997], officially designated as the Deep Space Program Science Experiment (DSPSE), was the first in a planned series of technology demonstrations jointly sponsored by the Ballistic Missile Defense Organization (BMDO) of the Department of Defense and the National Aeronautics and Space Administration (NASA). Clementine was launched on 1994-01-25 aboard a Titan IIG rocket from Vandenburg Air Force Base in California. The mission included two months of systematic lunar mapping (1994-02-26 through 1994-04-21), which was to have been followed by a flyby of the near-Earth asteroid Geographos (1994-08-31). An onboard software error, combined with improbable hardware conditions, on 1994-05-07 led to accidental spin-up of the spacecraft and loss of attitude control gas. This precluded the flyby of Geographos. The spacecraft itself was affectionately known as Clementine since, as in the song of the same name, it would be 'lost and gone forever' after completing its short mission.
Clementine's primary objective was qualification of lightweight imaging sensors and component technologies (including a star tracker, inertial measurement unit, reaction wheel, nickel hydrogen battery, and solar panel) for the next generation of Department of Defense spacecraft. DSPSE represented a new class of small, low cost, and highly capable spacecraft that fully embraced emerging lightweight technologies to enable a series of long-duration deep space missions. A second objective was the return of data about the Moon and Geographos to the international civilian scientific community.
The UVVIS mosaic was created using the Clementine EDR Image Archive [Eliason et al., 1995] produced by the Clementine mission. The EDR (Engineering Data Record) data are raw images and they contain the inherent properties of unprocessed and uncorrected data. The Clementine EDR Image Archive contains more than 1.9 million images acquired during active mission operations. For information on how to obtain this archive contact the PDS Imaging Node or visit their world wide web site.
3 - ULTRAVIOLET/VISIBLE CAMERA (UVVIS)
The Ultraviolet/Visible (UVVIS) camera [Kordas et al., 1995; Jolliff, 1999; Gaddis et al., 1999a; Gaddis et al., 1999b] has a catadioptic telescope using fused silica lenses focused onto a metachrome-coated charge-coupled device (CCD) imager. Active wavelength response is limited on the short wavelength end by the transmission of fused silica and the optical blur of the lens. Wavelength response on the long end is limited by the response of the CCD. Six spectral bands can be selected from a filter wheel assembly allowing observations in the 415, 750, 900, 950, 1000 nm wavelengths. An additional broad band filter was available on the filter wheel. For more information on the UVVIS camera refer to the 'uvviscat.cat' file in the 'catalog' directory.
4 - LUNAR ORBIT SUMMARY
The Clementine spacecraft maintained a polar orbit during the systematic mapping of the surface of the Moon [McEwen and Robinson, 1997]. Mapping of virtually 100% of the lunar surface was done in two lunar days (two Earth months). In order to obtain full coverage during these two months, the required image overlap for the UVVIS and Near-infrared (NIR) cameras was ~15% in the down-track and ~10% in the cross-track directions. This required an inclination of the orbit of 90 degrees plus-or-minus 1.0 degree with reference to the lunar equator with the periselene of the lunar orbit maintained at an altitude of 425 plus-or-minus 25 km. To provide the necessary cross-track separation for the alternating imaging strips to cover the entire surface of the Moon, the orbital period was approximately 5 hours, during which the Moon rotated approximately 2.7 degrees beneath the spacecraft. Images were taken and recorded only in the region of periselene, leaving sufficient time to replay the data to Earth.
The best data for lunar mineral mapping is obtained if the solar phase angle is less than 30 degrees. The solar phase angle is defined as the angle between the vector to the Sun and the vector to the spacecraft from a point on the Moon's surface. To maximize the time in which the solar phase angle is less than 30 degrees, the plane of the lunar orbit should contain the Moon-Sun line halfway through the two-month lunar mapping period. Therefore, insertion into the lunar orbit was selected so that, as the Moon-Sun line changes with Earth's motion about the Sun, the Moon-Sun line will initially close on the orbital plane, and then lie in the orbital plane halfway through the mapping mission. The angle between the Moon-Sun line and the orbital plane was close (less than 5 degrees) for approximately five weeks before becoming zero. The table shown below contains a list of Clementine's orbital parameters. For more information on the Lunar orbit refer to the 'mission.cat' file located in the 'catalog' directory.Clementine Orbital Parameters
=========================================================================== Orbital Period: 4.970 hr < P < 5.003 hr Altitude of Periselene: 401 km < radius < 451 km Eccentricity: 0.35821 < e < 0.37567 Right Ascension: -3 deg < Omega < +3deg(referred J2000) Inclination: 89 deg < i < 91 deg Argument of Periselene: -28.4 deg < w < -27.9 deg (1st month) 29.2 deg < w < 29.6 deg (2nd month)
5 - GEOMETRIC ACCURACY
The Clementine UVVIS mosaic was geometrically controlled to the previously published Clementine Basemap Mosaic by tying individual UVVIS images that make up a color set to the corresponding image in the color set that was used to produce the basemap mosaic. A description of the method for controlling the basemap mosaic follows:
The basemap mosaic significantly improves the geometric control of the Moon from previous maps and ground control points. On the basis of best-effort measurements of the spacecraft orbit and pointing, UVVIS geometric distortions, and time tags for each observation, the Clementine SPICE [Acton, 1996] data alone provide positional accuracy better than 1 kilometer over most of the Moon. With residual, primarily small, random pointing errors, then the accuracy approaching the UVVIS scale becomes achievable.
The goal of the basemap is for 95% of the Moon (excluding the oblique observation gap fills) to be better than 0.5 km/pixel absolute positional accuracy and to adjust the camera angles so that all frames match neighboring frames to within an accuracy of 2 pixels. To achieve these goals we required camera alignment and pointing data accurate to a few hundredths of a degree. We determined the absolute alignment of the UVVIS with respect to spacecraft-fixed axes (A and B Star Tracker Camera quaternions) by analyzing a major subset of the over 17,000 images of Vega, over 6,000 images of the Southern Cross, and a few hundred images of the Pleiades, taken during the approach to the Moon and throughout the lunar mapping mission phase. Multiple star images within a single picture were used to determine the UVVIS focal length and optical distortion parameter values.
Approximately 265,000 match points were collected at the USGS from ~43,000 UVVIS 750 nm images providing global coverage. About 80% of these points were collected via autonomous procedures, whereas the remaining 20% required the more time-consuming but highly accurate pattern-recognition capability of the human eye-brain. We also developed streamlined procedures for the supervised collection of match points. The new procedures saved several person-years of effort and represent new capabilities useful with other planetary datasets. The automated success rate exceeded 90% along each spacecraft orbit track, where the overlap regions of successive images are highly correlated, but failed when the overlap region is narrow and/or nearly featureless. ('Failure' is defined as less than 3 points per image with correlation coefficients greater than 0.85; thus, many good match points were rejected because we could not be certain that the matches were valid without verification.) Across-track matching was more difficult due to changes in scale and illumination angle, but a fair success rate (~60%) was nevertheless achieved via the use of 'window-shaping' (local geometric reprojections). The oblique gap-fill images were the most difficult to match and required substantial human intervention. Matching the polar regions was time-consuming because each frame overlaps many other frames. Most match points were found to a precision of 0.2 pixel.
The USGS match points were provided to the RAND Corporation for analytical triangulations. Using these match points, control points from the Apollo region, and the latest NAIF/SPICE (Navigation and Ancillary Information Facility/ Spacecraft, Planet Instrument, C-matrix, and Event kernels) [Acton,1996] information, RAND determined improved camera orientation angles for the global set of UVVIS images. A constant lunar radius of 1737.4 kilometers was assumed, a significant source of error near the oblique gap fills. The analytical triangulation is a least-squares formulation designed to adjust the latitude and longitude of the control points and the camera orientation angles to best fit the match points. The triangulation was first computed on 'packets' of match points (each covering about one-eighth of the Moon), then checked and rechecked at the USGS via plots and test mosaics to fix and add match points as needed. The final (global) analytical triangulation required solving ~660,000 normal equations. The mean error is less than 1 pixel. This effort is by far the largest analytical triangulation ever applied to a planetary body other than Earth. The results fully define the planimetric geometry of the basemap, to which future systematic products will be tied.
This concludes the discussion regarding the description of the method for controlling the previously released basemap mosaic.
6 - DATA PROCESSING
The Integrated Software for Imagers and Spectrometers (ISIS) processing system [Eliason, 1997; Torson and Becker, 1997], developed by the U.S. Geological Survey, was used to generate the UVVIS mosaic. Processing within ISIS includes radiometric and geometric correction, spectral registration, photometric normalization, and image mosaicking. Radiometric correction applies 'flat fielding,' dark current subtraction, non-linearity correction, and conversion to radiometric units. Geometric transformations tie each raw image with a ground control network and convert from raw image coordinates to the Sinusoidal Equal-Area projection. Photometric normalization is applied to balance brightness variations due to illumination differences among the images in a mosaic. Images are then mosaicked together to form a global map of continuous image coverage for the entire planetary body.
The UVVIS mosaic was processed in five stages or "levels." All corrections made during these stages have some degree of uncertainty; the processing sequence was designed to process from corrections with highest probability of accuracy to those with the lowest. The first level of processing, level 0, prepares the data for processing by ISIS. The raw images are converted to ISIS format and ancillary data such as viewing geometry are added to the labels of the image file. Level 1 processing applies radiometric corrections and removes artifacts from the image. Level 2 performs geometric processing to remove optical distortions and to convert the image geometry to a standard map projection. Level 3 performs photometric processing for normalizing the sun-viewing geometry of an image scene. Level 4 performs mosaicking of individual images to create global or regional views for the planetary surface.Level 0
The Level 0 processing step prepares the raw image data and associated metadata for processing by the ISIS system. Level 0 processing consists of two program steps. The first step reads the format of the raw image and converts it to an ISIS file. Additionally this step will extract the metadata from the input image labels for inclusion into the ISIS label. The metadata may contain information such as the instrument operating modes, temperature of the camera focal plane, UTC time of observation, and other information necessary to rectify an image. The second step extracts navigation and pointing data ("SPICE" kernel data) for inclusion into the ISIS file.
The next level of processing, Level 1, performs radiometric correction and data clean-up on an image. Level 1 consists of a series of programs to correct or remove image artifacts such as 1) camera shading inherent in imaging systems, 2) brightness anomalies caused by minute dust specks located in the optical path, 3) microphonic noise introduced by operation of other instruments on the spacecraft during image observations, and 4) data drop-outs and spikes due to missing or bad data from malfunctioning detectors or missing telemetry data. Level 1 processing results in an "ideal" image that would have been recorded by a camera system with perfect radiometric properties (although in practice residual artifacts and camera shading remain). The density number (DN) values of a radiometrically corrected image are proportional to the brightness of the scene. The details for radiometric correction are described in section 7.
Producing the Clementine UVVIS mosaic required geometric processing to be performed on the individual images that make up the database. The individual images are geometrically transformed from spacecraft camera orientation to a common map coordinate system of a specific resolution. Before geometric transformation, images must first be geometrically matched to each other to establish relative geometric control among the images and then the image set must be tied to a ground control net to establish absolute ground truth. The process of matching images and tying the image set to ground truth minimizes the spatial misregistration along image boundaries.
Level 2 performs geometric processing which includes correcting camera distortions as well as transformation from image coordinates to map coordinates. The image transformation is based on the original viewing geometry of the observation (including the optical distortion model of the camera), relative position of the target, and the mathematical definition of the map projection. An additional resampling method is employed to perform sub-pixel registration of the 5 bands in the color set.
Using the ISIS system the Sinusoidal Equal-Area projection data can be transformed to other map projections.
Photometric normalization is applied to images that make up the UVVIS DIM in order to balance the brightness levels among the images that were acquired under different lighting conditions. To illustrate, consider two images of the same area on the Moon where one image was acquired with the Sun directly overhead and the second with the Sun lower to the horizon. The image with the higher sun angle would be significantly brighter than the image with the low sun angle. Photometric normalization of the two images would cause them to be adjusted to the same brightness level.
Radiometrically calibrated spacecraft images measure the brightness of a scene under specific angles of illumination, emission, and phase. For an object without an optically significant atmosphere, this brightness is controlled by two basic classes of information: 1) the intrinsic properties of the surface materials, including composition, grain size, roughness, and porosity; and 2) variations in brightness due to the local topography of the surface. Photometric normalization is effective only to the extent that all geometric parameters can be modeled. The local topography is not included in the model (i.e. the planetary surface is thought of as a smooth sphere). However, illumination geometry at each pixel certainly depends on local topography; unless the topographic slope within a pixel is accurately known and compensated, the photometric correction cannot be perfect. Section 8 describes the photometric normalization.
Compilation of an accurate digital mosaic of the individual images is the final stage in the construction of the UVVIS DIM. The DIM is created by first generating a blank (or null) image that represents the regional or global image map of the Moon. The individual images are then mosaicked into the initially blank image map. The order in which individual images are placed into the mosaic is an important consideration. Because images are mosaicked one on top of the other, images that get laid down first are overwritten in the area of overlap by subsequent images that are added to the mosaic. Images that have the lowest data quality or resolution should be laid down first, followed by images with highest quality. With this method the areas of image overlap contain the highest quality images.
7 - RADIOMETRIC CALIBRATION
The radiometric calibration process converts raw density-number (pixel brightness) values to reflectance. The radiometric calibration algorithm, previously described [McEwen et al., 1998], is summarized below. For all equations provided in the document the asterisk character (*) is used to denote a multiplication and the double asterisk (**) is used to denote exponentiation.
STEP 1. Global offset corrections
Step_1_DN(j,i) = raw_DN(j,i) - C4*OFFSET_MODE_ID - C5 where: raw_DN(j,i) = data values from PDS Clementine EDR image archive for a UVVIS image. j = row or line number from 1 (top) to 288 (bottom) i = column or sample number from 1 (left) to 384 (right). C4 = -8.177 OFFSET_MODE_ID = offset mode of camera, this value obtained from PDS labels (values may be 0,1,2,3,4,5,6, or 14) C5 = 15.56STEP 2. Divide by gain
Step_2_DN(j,i) = Step_1_DN(j,i)/g(GAIN_MODE_ID) where: GAIN_MODE_ID = offset mode of camera, this value obtained from PDS labels (values may be 1, 2, or 4) g(GAIN_MODE_ID) = gain value Mode 1 = 1.0 (by definition) Mode 2 = 2.907 Mode 4 = 6.906STEP 3. Subtract pixel-dependent dark current
Step_3_DN(j,i) = Step_2_DN(j,i) - [DC(j,i) + C3] where: DC(j,i) = dark current correction file, line and sample number dependent normalized to a mean of 0.0. C3 = 7.13STEP 4. Non-linearity Correction
Step_4_DN(j,i) = Step_3_DN(j,i) * XMUL where: XMUL = A + B*Step_3_DN(j,i) + C*step_3_DN(j,i)**2 + D*Step_3_DN(j,i)**3 A = 1.062 B = -0.1153E-02 C = 0.6245E-05 D = -0.1216E-07STEP 5. Temperature-Dependent Offset Correction
Step_5_DN(j,i) = Step_4_DN(j,i) - C2(T)*u where: C2(T) = 0.003737 * exp(0.0908*(T-273.15)) (exp = exponent function) T = FOCAL_PLANE_TEMPERATURE from PDS label u = t + readout time t = corrected exposure time = EXPOSURE_DURATION + 0.0494 (EXPOUSRE_DURATION obtained from PDS values) readout time = 60.05 + 0.1*(j-1)STEP 6. Frame Transfer Correction
Step_6_DN(j,i) = Step_5_DN(j,i) - ro(i,t) where: ro(i,t) = column_sum(i)*dt/(t + 288*dt) column_sum(i) = sum of all 288 Step_4_DN values in column i. dt = frame transfer time per row = 0.00068 Note: Frame transfer effect is under-corrected if there are saturated pixels in a column. It is best to use raw_DN = 255 to estimate column sum (rather than exclude saturated pixels).STEP 7. Flat-Field and Exposure Time Normalization
Step_7_DN(j,i) = Step_6_DN(j,i)/[U(j,i,l)*t] where: U(j,i,l) = the filter (l) dependent flat-field correction normalized to 1.0 at the Vega position (row 141, column 188). t = corrected exposure time = EXPOSURE_DURATION + 0.0494 The units of Step_7_DN(j,i) are now counts/ms.STEP 8. Normalize to Sun-Moon Distance of 1 AU
Step_8_DN(j,i) = Step_7_DN(j,i) * [(SOLAR_DISTANCE/AU)**2] where: AU = 149,597,870 km SOLAR_DISTANCE = sun-to-target distance(extracted from PDS labels)Step 9. Conversion to Reflectance
R(j,i) = Step_8_DN(j,i)*Cr(l) where: Cr(l) = values derived based on Carle Pieters' spectral calibration to Apollo 16 soils (see description below for derivations)
CENTER_FILTER_WAVELENGTH Cr(l) --------------------------------- 415 nm 0.020101 750 nm 0.011662 900 nm 0.010118 950 nm 0.010300 1000 nm 0.023063 --------------------------
Radiometric normalization coefficients (Cr(l) in Step 9) for Clementine imaging were developed by Carle Pieters based on laboratory spectra from Apollo 16 landing site soils returned to Earth [Pieters et al., 1991]. The Clementine EDR frame 'lub1845i.295' was used to define the radiometric normalization coefficients for the UVVIS imaging. The image sub-area: 52-62 (sample) x 87-118 (line) relative to the upper left pixel addressed at 1,1 was selected as the control area assuming the soils were representative of the returned Apollo 16 landing site soils. For the spectral range of the 750 nm filter, laboratory observations gave 0.1868 fractional reflectance (18.68% reflectance at 30 degrees illumination, 0 degrees emission). To convert from counts/millisecond (Rraw column in table below) normalized to 30 degrees incidence and 0 degrees emission (Rclem) to reflectance (Relab) the coefficient AvgCr(l) is applied. The table shown below lists the normalization coefficients AvgCr(l) of each UVVIS filter. The AvgCr(l) coefficients convert counts/millisecond camera output to fractional reflectance. Note: Cr(l) values above were rederived following non-linearity correction; they differ slightly from those originally reported at Brown University because they skipped the non-linearity correction and used different offset coefficients (C3 and C5).
Photometric Angles Filter Frame EM IN PH Rraw Cphot Rclem Relab Cr AvgCr ------------------------------------------------------------------- A lua1850i.295 2.3 26.8 28.7 5.6 0.960 5.37 .1077 .020026 A lua1851i.295 2.4 26.8 28.7 5.5 0.960 5.33 .1077 .020176 .020101 B lub1845i.295 2.3 26.8 28.7 15.8 0.961 15.23 .1776 .011661 B lub1846i.295 2.3 26.8 28.7 15.8 0.961 15.22 .1776 .011662 .011662 C luc1842i.295 2.2 26.8 28.7 19.4 0.962 18.68 .1893 .010131 C luc1843i.295 2.3 26.8 28.7 19.5 0.962 18.73 .1893 .010105 .010118 D lud1838i.295 2.2 26.8 28.8 19.6 0.963 18.83 .1941 .010308 D lud1839i.295 2.2 26.8 28.8 19.6 0.963 18.85 .1941 .010292 .010300 E lue1835i.295 2.2 26.8 28.8 9.0 0.964 8.69 .2004 .023040 E lue1836i.295 2.2 26.8 28.8 9.0 0.964 8.68 .2004 .023085 .023063
The Apollo 16 control area used for the analysis of the normalization coefficients corresponds to the area located in quadrangle "ui10s015" sub-area samples 940-956 and lines 540-587.
Possible sources of error in the Clementine data include residual calibration errors (~1% filter-to-filter) [Pieters et al., 1997], photometric variations within a scene, and scattered light [Gaddis et al., 1999b]. Residual photometric variations include the effects of wavelength-dependent variations at levels of about 0.2% across a Clementine frame and ~0.5% between frames. Scatter light is possible anomalous brightness in which high-albedo units influence the measured values of low-albedo units (and vice versa) to varying degrees at different wavelengths. In the Clementine data scattered light has estimated magnitudes of 10% to 13% at all wavelengths [Li et al., 1999; Robinson et al 1999].
8 - PHOTOMETRIC FUNCTION NORMALIZATION
The photometric function normalization used in the compilation of the UVVIS multispectral mosaic has been previously described in [McEwen, 1996; McEwen et al., 1998]. The data are normalized to R30, the reflectance expected at an incidence angle (i) and phase angle (p) of 30.0 degrees and an emission angle (e) of 0.0 degrees matching the photometric geometry of lunar samples measured at the reflectance laboratory at Brown University [Pieters et al., 1991]. The focus is on the precision of the normalization, not the putative physical significance of the photometric function parameters. The modified Lunar-Lambert function used in the processing is as follows:
XL(i,e,p) = 2*L(p)*u0/(u+u0) + (1-L(p))*u0 where: i = incidence angle e = emission angle p = phase angle u = cos(e) u0 = cos(i) L = variation of the limb-darkening parameter expressed as a third-order polynomial: L(p) = 1.0 + A*p + B*(p**2) + C*(p**3) A = -0.019 B = 0.242E-3 C = -1.46E-6The phase function correction based on work from Helfenstein [McEwen, 1996] is defined as follows:
F(p) = B(p,h,b0)*[(1-f)*P(p,g1) + f*P(p,g2)]
B(p,h,b0) = 1 + b0/(1+tan(p/2)/h) (Backscatter function) P(p,g) = (1-g**2)/(1+g**2+2*g*cos(p)**1.5) b0 = wave length dependent constant (see table below) The g1 parameter is expected to vary with albedo modeled as: g1 = d*R30 + e (however, d=0 for Clementine processing, thus eliminating any correction for albedo). R30 = normalized albedo
To describe the backscatter function at less than 2 degrees phase angle, the following linear functions are used based on results from Burratii [McEwen, 1996]:
F(p) = 1.0 + xb xb = xb0 + xb1 * wave_length where: xb0 = -0.0817 xb1 = 0.0081 Final normalization to the RELAB geometry is given by: R30 = R(i,e,p)*[XL(30,0,30)/XL(i,e,p)]*[F(30)/F(p)] where: f,g2,b0,h = parameters determined by fits to a dataset. These values are provided for each spectral filter. Note that d=0 means that we do not attempt to vary the photometric correction as a function of albedo. Filter b0 h d e f g2
----------------------------------------------- A (415 nm) 2.31 0.062 0 -0.222 0.5 0.39 B (750 nm) 1.60 0.054 0 -0.218 0.5 0.40 C (900 nm) 1.35 0.052 0 -0.226 0.5 0.36 D (950 nm) 1.35 0.052 0 -0.226 0.5 0.36 E (1000 nm) 1.35 0.052 0 -0.226 0.5 0.36
After completion of the processing for the UVVIS quadrangles, a minor program bug was discovered in the photometric normalization program. The bug incorrectly calculated the value for XL(30,0,30). Instead of using 30 degrees phase angle, the program incorrectly used the phase angle of the image XL(30,0,p). The result was an up to 3% error in brightness at the poles. The ratio of the bands however were not effected by this bug. Because the phase angle was available as a backplane a correction was applied to the final published data available on the CD-ROM set.
A correction was applied to the mosaic to correct for the photometric bug. In our fix, we assumed a phase angle of 15 degrees at the equator and 90 degrees at the poles as per the equation shown below:
corr = radiance value is corrected by dividing by corr. pbase = average phase angle at equator during mission (15 deg). subsol = sub-solar latitude. lat = latitude of pixel to be corrected. p = Phase angle developed as a function of latitude. pbase = 15 subsol = 0.0 p = acos( sin(90-subsol) * sin(90-lat) * cos(pbase) + cos(90-subsol)*cos(90-lat) )/rad A = -0.019 B = 0.000242 C = -0.00000146 XL30 = 1.0 + A*30 + B*30*30 + C*30*30*30 R30 = (2.0*XL30*COS(30*RAD))/(1.0+COS(30*RAD))+ (1.0-XL30)*COS(30*RAD) XL = 1.0 + A*PHASE + B*PHASE*PHASE + C*PHASE*PHASE*PHASE R = (2.0*XL*COS(30*RAD))/(1.0+COS(30*RAD))+ (1.0-XL)*COS(30*RAD) corr = R/R30
9 - SECOND-ORDER RADIOMETRIC/PHOTOMETRIC CORRECTIONS
During compilation of the UVVIS mosaic, differences in phase function behavior near zero phase were observed for different albedo materials. The phase function model applied to the data did not include an albedo dependent term (d was set to zero, see above) and thus one would expect to observe these differences.
Additionally, we discovered small differences (<3%) between the first and second month orbital data that in part can be attributed to calibration drift of the UVVIS camera over the two month observation period as well as improper modeling of the instrument sensitivity dependence on instrument temperature. The effect was especially apparent in the visual display of the ratio of two spectral bands.
A correction for reconciling near-zero phase function and calibration differences between the first and second month was developed. The procedure compared month-one and month-two orbital data in areas of common areal coverage. Month-one orbital data, containing little or no data coverage near zero phase, was used to control and adjust the month-two data. (The areal coverage of month-one and month-two data are interleaved.)
A least squares procedure was developed for matching month-two data to month-one data. For each UVVIS spectral band of each month-two orbit, a ratio of the month-one/month-two reflectance values for areas of common coverage was plotted as a function of latitude and phase angle. A third-order polynomial was used to model the ratio differences between month-one and month-two:
B12(orbit,w,p,lat) = A(orbit,w)*lat**3 + B(orbit,w)*lat**2 + C(orbit,w)*lat + D(orbit,w)/p**3 + E(orbit,w)/p**2 + F(orbit,w)/p + G(orbit,w) where: B12(orbit,w,p,lat) = the ratio of month-one reflectance to month-two reflectance in areas of common coverage. A,B,C,D,E,F,G = coefficients derived from the least squares fit. A set of coefficients exists for each UVVIS spectral band and each month-two orbit. orbit = orbit number of month-two orbit to be corrected. w = UVVIS spectral wavelength. lat = latitude p = phase angle. A 1/p**n function was used because the correction is greatest near zero phase and asymptotically approaches 1.0 at large phase angles.The final correction to the month-two orbit data is given as:
R_Cor(w,i,j) = R(w,i,j)*B12(orbit,w,p,lat) where: R_Cor(w,i,j) = corrected reflectance value at pixel i,j for month-two orbit.
R(w,i,j) = original reflectance value at pixel i,j for month-two orbit.
A set of coefficients A-G was developed and applied for each month-two orbit. For future reference, these coefficients can be found in the 'coef.tab' file located in the index directory on the final volume of the CD-ROM volume set.
10 - CONVERSION OF 16-BIT PIXEL VALUES TO FLOATING NUMBERS
To convert the 16-bit integer values found in the image arrays of the UVVIS multispectral mosaic to fractional reflectance an offset and scaling factor need to be applied as shown:
FRACTIONAL_REFLECTANCE = (SCALING_FACTOR * DN) + OFFSET where: DN = 16-bit pixel value of UVVIS DIM image array. SCALING_FACTOR = 1.3500E-04 OFFSET = 0.00
The ISIS system automatically converts the 16-bit integer values to floating point values by applying the scaling factor and offset values.
11 - FILES, DIRECTORIES, AND DISK CONTENTS
The files on this CD volume set are organized starting at the root or 'parent' directory. Below the parent directory is a directory tree containing data, documentation, and index files. In the table below directory names are indicated by brackets (<...>), upper-case letters indicate an actual directory or file name, and lower-case letters indicate the general form of a set of directory or file names.DIRECTORY/FILE CONTENTS
<root> | |-AAREADME.TXT Introduction to the CD volume (ASCII Text) | |-INDEX.HTM Hypertext Markup Language(HTML) file for use | as a user interface to files on this CD. | |-ERRATA.TXT Description of known anomalies and errors | present on the volume set (optional file). | |-VOLDESC.CAT A description of the contents of this | CD volume in a format readable by | both humans and computers. | |-<CATALOG> Catalog Directory | | | |-CATINFO.TXT Describes Contents of the Catalog directory | | | |-DATASET.CAT Clementine UVVIS DIM Mosaic description | | | |-DSMAP.CAT Map Projection description | | | |-INSTHOST.CAT Clementine Spacecraft description | | | |-MISSION.CAT Clementine Mission description | | | |-PERSON.CAT Contributors to Clementine UVVIS Mosaic | | | |-REF.CAT References for Clementine UVVIS Mosaic | | | |-UVISINST.CAT UVVIS Camera description | |-<DOCUMENT> Documentation Directory. The files in this | | directory provide detailed information | | regarding the Clementine UVVIS Mosaic. | | | |-DOCINFO.TXT Description of files in the DOCUMENT | | directory. | | | |-VOLINFO.TXT Documentation regarding the | | contents of this CD Volume Set. | | | |-VOLINFO.HTM HTML document for VOLINFO.TXT | | | |-VOLINFO.LBL PDS Label file describing the VOLINFO | | documents. | | | |-SCHEME.PDF Adobe Acrobat Portable Document Format file | showing UVVIS tiling and CD volume scheme. | |-<INDEX> Directory for the image index files. | | | |-INDXINFO.TXT Description of files in <INDEX> directory. | | | |-INDEX.TAB Image Index table specific to each volume. | | | |-INDEX.LBL PDS label for INDEX.TAB | | | |-CUMINDEX.TAB Image Index table for entire CD collection. | | | |-CUMINDEX.LBL PDS label for CUMINDEX.TAB. | |-<DATA> Data directory containing UVVIS DIM tiles. | | | |-<tsppymmm.xxx> Data filenames where; | (For this UVVIS CD Volume Set) | t = U (Clementine UVVIS Mosaic) | = P (Phase angle image (for <PHASE> dir) | | (For past or future CD Volumes) | = B (Clementine Basemap Mosaic) | = U (UVVIS Cube) | = N (NIR Cube) | = L (LWIR Image Data) | = H (Hi-res Image Data) | | s = (Resolution - km/pixel) | = A (0.004 km/pixel - future mapping) | = B-D (For future mapping as needed) | = E (0.02 km/pixel - future mapping) | = F-H (For future mapping as needed) | = I (0.1 km/pixel) | = J (0.15 km/pixel) | = K-L (For future mapping as needed) | = M (0.5 km/pixel) | = N-P (For future mapping as needed) | = Q (2.5 km/pixel) | = R-T (For future mapping as needed) | = U (12.5 km/pixel) | = V-Z (For future mapping as needed) | | pp = (00-90) Center latitude of Image File. | (Two digit truncated integer) | | y = N (Positive latitude) | = S (Negative latitude) | = <none> (Not used for full latitude | coverage. i.e. -90 to 90) | | mmm = (000-360) Center longitude of Image. | (Three digit truncated integer) | xxx = IMG (PDS Labeled Image File) | = LAB (ISIS Detached Label File) | = JPG (JPEG small, medium, and | large Browse Images) <BROWSE> | Directory Tree only | = HTM (<BROWSE> Directory Tree only) | |-<PHASE> Directory containing phase angle images. | | | |-<tsppymmm.xxx> Phase angle filenames as defined | in <DATA> above. | |-<BROWSE> Directory tree containing enhanced color and | ratio Browse (reduced resolution) JPEG | images for each image data product on the CD. | |-BROWINFO.TXT Description of <BROWSE> content. | |-BRCOLOR.HTM Graphics (map)-based HTML interface to | enhanced color browse data | (Accessed by INDEX.HTM file). | |-BRRATIO.HTM Graphics (map)-based HTML interface to | color ratio browse data | (Accessed by INDEX.HTM file). | |-BRBW.HTM Graphics (map)-based HTML interface to | b/w (750nm) browse data | (Accessed by INDEX.HTM file). | |-LOCATOR.HTM CD Volume/Quad Locator Map. | |-CLEMLOGO.GIF Various icons, logos, and images |-USGSLOGO.GIF used by HTML documents on the CD. |-CLEMGRID.GIF |-GR17.GIF |-GR38.GIF | | |-<COLOR> | |-<SMALL> | |-<MEDIUM> Directory tree containing small, medium, | |-<LARGE> and large sized JPEG images (enhanced color, | color ratio, and b/w (750nm)) for each |-<RATIO> DIM product. These JPEG images are primarily | |-<SMALL> used by the HTML documents on the CD. | |-<MEDIUM> small images are ~60x60 pixels | |-<LARGE> medium images are ~400x400 pixels | large images are ~1000x1000 pixels |-<750nm> |-<SMALL> |-<MEDIUM> |-<LARGE>
12 - IMAGE FILE ORGANIZATION
The image files are stored in a PDS compliant format. An image file contains a label area (header) at the beginning of the file followed by the image data. The number of bytes of the label area is a multiple of the number of bytes that make up an image line (number of samples * 2 bytes/pixel). The image label area contains ASCII text data that describing the image file (see Image Labels section below). The label area can be viewed with a simple ASCII editor on most computer systems.
ISIS access to UVVIS DIM
Each UVVIS image file (*.img filename extension) is associated with an Integrated Software for Imagers and Spectrometers (ISIS) 'qube object' detached label (.lab filename extension). This detached label allows for images to be accessed and processed within the ISIS system (available through the USGS, Flagstaff, AZ). Within ISIS, users should reference the detached label file when accessing image files on the CD set. The ISIS detached label contains a pointer to the actual image file so both files (.img and .lab) should remain in the same directory if transferring data from CD to other media.
Pixel Storage Order
The Clementine UVVIS mosaic is stored as image files with 16-bit signed integer pixels. The storage order of the pixels is "most significant byte order first." This is the storage order for Unix/Sun and Macintosh systems. For other systems such as IBM-compatible PC, Dec/Alpha, and VAX systems, the high and low order bytes of the pixels will need to be swapped before the data can be used. The ISIS program "convert" will automatically convert the data to the proper storage order.
Special Pixel Values
Pixels in an image array can contain special values to denote a special condition about a pixel. The following values designate a special pixel:
-32768 - NULL - The pixel is "empty" and no data were acquired for this pixel location in the image array. This condition typically occurs when a gap exists in the image map such as when an image was not acquired for an area of the Moon.
-32767 - Low Processing Saturation - Processing on the pixel caused its value to go outside the low-end dynamic range of the 16-bit signed integer.
-32766 - Low Instrument Saturation - The pixel of the raw image was "bit clipped" and did not contain a valid value. For example, if the bias of the camera was set so that the low DN values could not be stored in the dynamic range of the raw image.
-32765 - High Instrument Saturation - The pixel of the raw image was high-end saturated and could not be stored in the dynamic range of the raw image. For example, if part of an image scene was too bright to be recorded by the imaging instrument.
-32764 - High Processing Saturation - Processing on the pixel caused its value to go outside the high-end dynamic range of the 16-bit signed integer.
The label area of an image file contains descriptive information about the image. The label consists of keyword statements that conform to version 3 of the Object Description Language (ODL) developed by NASA's PDS project. There are three types of ODL statements within a label: structural statements, keyword assignment statements, and pointer statements.
Structural statements provide a shell around keyword assignment statements to delineate which data object the assignment statements are describing. The structural statements are:1) OBJECT = object_name
The OBJECT statement begins the description of a particular data object and the END_OBJECT statement signals the end of the object's description. All keyword assignment statements between an OBJECT and its corresponding END_OBJECT statement describe the particular object named in the OBJECT statement. The END statement terminates a label. A keyword assignment statement contains the name of an attribute and the value of that attribute. Keyword assignment statements are described in more detail in Appendix A of this document. These statements have the following format:
name = value
Values of keyword assignment statements can be numeric values, literals, and text strings.
Pointer statements are a special class of keyword assignment statements. These pointers are expressed in the ODL using the following notation:
^object_name = location
If the object is in the same file as the label, the location of the object is given as an integer representing the starting record number of the object, measured from the beginning of the file. The first label record in a file is record 1. Pointers are useful for describing the location of individual components of a data object. Pointer statements are also used for pointing to data or label information stored in separate files. An example of a detached label (i.e., label information stored in a separate file) is shown below: By convention, detached labels are found in the LABEL directory.
^STRUCTURE = 'logical_file_name'
The value of 'logical_file_name' is the name of the detached label file containing the description.
The keyword statements in the label are packed into the fixed-length records that make up the keyword label area. Each keyword statement is terminated by a carriage-return and line-feed character sequence. An example of a Clementine UVVIS DIM image label is shown below. Descriptions of the keywords used in the UVVIS label are found in Appendix A.Example PDS Label for Clementine UVVIS DIM Image files
PDS_VERSION_ID = PDS3 /* FILE FORMAT AND LENGTH */ RECORD_TYPE = FIXED_LENGTH RECORD_BYTES = 3688 FILE_RECORDS = 10637 LABEL_RECORDS = 2 INTERCHANGE_FORMAT = BINARY /* POINTERS TO START RECORDS OF OBJECTS IN FILE */ ^IMAGE = 3 /* IMAGE DESCRIPTION */ DATA_SET_ID = "CLEM1-L-U-5-DIM-UVVIS-V1.0" PRODUCT_ID = "UI03N003" PRODUCER_INSTITUTION_NAME = "UNITED STATES GEOLOGICAL SURVEY" PRODUCT_TYPE = MDIM MISSION_NAME = "DEEP SPACE PROGRAM SCIENCE EXPERIMENT" SPACECRAFT_NAME = "CLEMENTINE 1" INSTRUMENT_NAME = "ULTRAVIOLET/VISIBLE CAMERA" INSTRUMENT_ID = "UVVIS" TARGET_NAME = "MOON" FILTER_NAME = ("A","B","C","D","E") CENTER_FILTER_WAVELENGTH = (415.000,750.000,900.000, 950.000,1000.000) BANDWIDTH = (40.000,10.000,20.000, 30.000,30.000) START_TIME = "N/A" STOP_TIME = "N/A" SPACECRAFT_CLOCK_START_COUNT = "N/A" SPACECRAFT_CLOCK_STOP_COUNT = "N/A" PRODUCT_CREATION_TIME = 1999-01-27T16:10:29 NOTE = "UVVIS 5-BAND MOSAIC" /* DESCRIPTION OF OBJECTS CONTAINED IN FILE */ OBJECT = IMAGE BANDS = 5 BAND_STORAGE_TYPE = BAND_SEQUENTIAL BAND_NAME = "N/A" LINES = 2127 LINE_SAMPLES = 1844 SAMPLE_TYPE = MSB_INTEGER SAMPLE_BITS = 16 SAMPLE_BIT_MASK = 2#1111111111111111# OFFSET = 0.0 SCALING_FACTOR = 1.350000E-04 VALID_MINIMUM = -32752 NULL = -32768 LOW_REPR_SATURATION = -32767 LOW_INSTR_SATURATION = -32766 HIGH_INSTR_SATURATION = -32765 HIGH_REPR_SATURATION = -32764 MINIMUM = 521 MAXIMUM = 2465 CHECKSUM = 2621856957 END_OBJECT = IMAGE OBJECT = IMAGE_MAP_PROJECTION ^DATA_SET_MAP_PROJECTION = "DSMAP.CAT" COORDINATE_SYSTEM_TYPE = "BODY-FIXED ROTATING" COORDINATE_SYSTEM_NAME = "PLANETOGRAPHIC" MAP_PROJECTION_TYPE = "SINUSOIDAL" MAP_RESOLUTION = 303.2334900 MAP_SCALE = 0.1000000 MAXIMUM_LATITUDE = 7.0000000 MINIMUM_LATITUDE = -0.0132000 EASTERNMOST_LONGITUDE = 6.0131998 WESTERNMOST_LONGITUDE = 0.0000000 LINE_PROJECTION_OFFSET = 2123.6345297 SAMPLE_PROJECTION_OFFSET = 4549.5024429 A_AXIS_RADIUS = 1737.4000000 B_AXIS_RADIUS = 1737.4000000 C_AXIS_RADIUS = 1737.4000000 FIRST_STANDARD_PARALLEL = "N/A" SECOND_STANDARD_PARALLEL = "N/A" POSITIVE_LONGITUDE_DIRECTION = EAST CENTER_LATITUDE = 0.0 CENTER_LONGITUDE = 15.0000000 REFERENCE_LATITUDE = "N/A" REFERENCE_LONGITUDE = "N/A" LINE_FIRST_PIXEL = 1 SAMPLE_FIRST_PIXEL = 1 LINE_LAST_PIXEL = 2127 SAMPLE_LAST_PIXEL = 1844 MAP_PROJECTION_ROTATION = 0.0000000 VERTICAL_FRAMELET_OFFSET = "N/A" HORIZONTAL_FRAMELET_OFFSET = "N/A" END_OBJECT = IMAGE_MAP_PROJECTION END
13 - INDEX FILES
Each CD volume in the Clementine UVVIS mosaic contains an image index file ('index.tab') with catalog information specific to each volume. A cumulative index file ('cumindex.tab') is also provided. It contains entries for the entire UVVIS CD collection. The image index files and their associated PDS label files ('index.lbl' and 'cumindex.lbl') are located in the 'index' directory. The catalog information in the index table includes the file names, CD volumes, and mapping parameter information. Final volume(s) of this UVVIS CD set contain an additional source file index table ('srcindx.tab' and corresponding PDS label 'srcindx.lbl'). It contains information about the EDR image collection used to assemble the UVVIS DIM and the images that make up 5-band color sets. This file contains an entry for each EDR image that was used in this database. Information in this file includes the improved camera pointing data (c-matrix) derived from tying to the geometric control network established by the RAND Corporation. For more information on the contents of the index files refer to the label files. Additionally, the final volume contains a file of coefficients ('coef.tab' and corresponding PDS label 'coef.lbl') used for the second order corrections described in section 9.
14 - ACKNOWLEDGMENTS
The National Aeronautics and Space Administration is charged with the responsibility for coordination of a program of systematic exploration of the planets by U.S. spacecraft. To this end, it finances spaceflight missions and data analysis and research programs administered and performed by numerous institutions. The Geological Survey of the U.S. Department of Interior performs digital cartographic mapping in support of NASA's program of planetary exploration and scientific research.
The Clementine UVVIS DIM Mosaic was compiled for the National Aeronautics and Space Administration (NASA) by the United States Geological Survey (USGS) under the direction of Eric M. Eliason (USGS) and Alfred McEwen (University of Arizona). Mark Robinson (Northwestern University) provided tremendous support and expertise in the compilation of the UVVIS mosaic. Ella Lee and Tammy Becker headed the USGS technical group responsible for its compilation. Cartographic and archive design, data conversion for PDS compliance, and production of CDs was performed by Chris Isbell. The Lunar Geometric Control network was derived by Mert Davies and Tim Colvin (both from the RAND Corporation).
Generation of the UVVIS DIM is a very complex process that involves and depends on an extended number of people. In addition to those already mentioned, completion of this product is the result of contributions by the following individuals and groups:
Kevin Adams, Janet Barrett, Kris Becker, Annie Bennett, Sandy Castro, Pete Coffin, Patty Garcia, Ana Grecu, JoAnn Isbrecht, James Mathews, Janet Richie, Tony Rosanova, Jana Ruhlman, Jac Shinaman, Robert Sucharski, Rob Waltz, Lynn Weller
Developers and programmers within the ISIS programming group of USGS-Flagstaff, AZ
15 - REFERENCES
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Batson, R.M., Digital Cartography of the Planets: New Methods, Its Status, and Its Future: Photogrammetric Engineering and Remote Sensing, Vol. 53, No. 9, p.1211-1281, 1987.
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Eliason, E.M., McEwen, A.S., Robinson, M.S., Lee, E.M., Becker, T.L., Gaddis, L., Weller, L.A., Isbell, C.E., Shinaman, J.R., Duxbury, T., Malaret, E., Clementine: A Global Multi-Spectral Map of the Moon from the Clementine UVVIS Imaging Instrument: Lunar and Planetary Science Conference 30th, pp. 1933-1934, 1999.
Eliason, E.M., Production of Digital Image Models Using the ISIS System: Lunar and Planetary Science Conference 28th, pp. 331-332, 1997.
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Gaddis, L.R., B.R. Hawke, M.S. Robinson, and C.R. Coombs, Juvenile Materials in Lunar Pyroclastic Deposits: Lunar and Planetary Science Conference 30th, pp. 1732-1733, 1999a.
Gaddis, L.R., and B.R. Hawke, M.S. Robinson, and C. Coombs, Compositional Analyses of Small Lunar Pyroclastic Deposits Using Clementine Multispectral Data, J. Geophys. Res., in press, 1999b.
Isbell, C.E., E.M. Eliason, Adams, K.C., Becker, T.L., Bennett, A.L., Lee, E.M., McEwen, A.S., Robinson, M.S., Shinaman, J.R., and Weller, L.A., Clementine: A Multi-Spectral Digital Image Model Archive of the Moon: Lunar and Planetary Science Conference 30th, pp. 1812-1813, 1999.
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Jolliff, B.L., Clementine UVVIS Multispectral Data and the Apollo 17 landing site: What can we tell and how well?: J. Geophys. Res., Vol. 104, No. E6, pp. 14,123-14,148, 1999.
Kordas, J.R., I.T. Lewis, R.E. Priest, W.T. White, D.P. Nielsen, H. Park, B.A. Wilson, M.J. Shannon, A.G. Ledebuhr, and L.D. Pleasance, UV/visible Camera for the Clementine Mission: Society of Photo-optical Instrumentation Engineers (SPIE), 2478, pp. 175-186, 1995.
Li, Lin, J.F. Mustard, and C.M. Pieters, The Effects of Scattered Light in the Clementine UVVIS Camera on Mixture Analysis, Lunar and Planetary Science Conference 30th, pp. 1356-1357, 1999.
McEwen, A.S., E. Eliason, P. Lucey, E. Malaret, C. Pieters, M. Robinson, T. Sucharski, Summary of Radiometric Calibration and Photometric Normalization Steps for the Clementine UVVIS Images: Lunar and Planetary Science Conference 29th, pp. 1466-1467, 1998.
McEwen, A.S., M. Robinson, Mapping of the Moon by Clementine: Adv. Space Research, Vol. 19, No. 10, pp. 1523-1533, 1997.
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APPENDIX A - KEYWORD ASSIGNMENTS
This section defines the keywords used in the image label area of the Clementine UVVIS mosaic.
PDS_VERSION_ID = PDS3 This dataset conforms to version 3 of the PDS standards. RECORD_TYPE = FIXED_LENGTH This keyword defines the record structure of the file as fixed-length record files. RECORD_BYTES = xxxx Record length in bytes for fixed-length records (number of samples *2). FILE_RECORDS = xxxx Total number of fixed-length records contained in the file. LABEL_RECORDS = x Number of fixed-length label records in the file. INTERCHANGE_FORMAT = BINARY Data are organized as BINARY values. ^IMAGE = x Pointer to the first record that contains image data. (The first record in the file is designated as record 1.). DATA_SET_ID = "CLEM1-L-U-5-DIM-UVVIS-V1.0" The PDS defined dataset identifier for the Clementine UVVIS mosaic. PRODUCT_ID = "UI03N003" Unique product identifier for this image file. This value is the same as the file name. (Format described in the "FILES, DIRECTORIES, AND DISK CONTENTS" section above.) PRODUCER_INSTITUTION_NAME = "UNITED STATES GEOLOGICAL SURVEY" Identifies the producer organization of this data product. PRODUCT_TYPE = MDIM This keyword identifies the image product as a Mosaicked Digital Image Model (MDIM). MISSION_NAME = "DEEP SPACE PROGRAM SCIENCE EXPERIMENT" The keyword identifies the product name of the mission. (This is the official name of the Clementine Mission.) SPACECRAFT_NAME = "CLEMENTINE 1" Name of the spacecraft that acquired the data. INSTRUMENT_NAME = "ULTRAVIOLET/VISIBLE CAMERA" Name of the instrument that acquired the image data. INSTRUMENT_ID = "UVVIS" Abbreviated name of the instrument that acquired the image data. TARGET_NAME = "MOON" Target of the data product. FILTER_NAME = ("A","B","C","D","E") Images acquired from each filter of the UVVIS camera were used to complete the Clementine UVVIS DIM mosaic. CENTER_FILTER_WAVELENGTH = (415.000,750.000,900.000, 950.000,1000.000) The center filter wavelength (nanometers) of each UVVIS filter. BANDWIDTH = ((40.000,10.000,20.000, 30.000,30.000) The bandwidth (nanometers) of each UVVIS filter. START_TIME = "N/A" STOP_TIME = "N/A" SPACECRAFT_CLOCK_START_COUNT = "N/A" SPACECRAFT_CLOCK_STOP_COUNT = "N/A" Start_Time, Stop_Time, and clock counts are not applicable (N/A) for this data product but are required keywords. PRODUCT_CREATION_TIME = 1999-01-27T12:56:11 Time at which the image product was produced. NOTE = "UVVIS 5-BAND MOSAIC" Note field always says UVVIS 5-BAND MOSAIC. OBJECT = IMAGE BANDS = 5 There are five spectral bands in the UVVIS DIM mosaic. BAND_STORAGE_TYPE = BAND_SEQUENTIAL Storage order is band sequential. BAND_NAME = "N/A" Band name keyword is not applicable. LINES = xxxx Number of lines (rows) in image array. LINE_SAMPLES = xxxx Number of samples (columns) in image array. SAMPLE_TYPE = MSB_INTEGER Data are stored in "Most Significant Byte" order first format. This is the storage order of Sun workstations and Macintosh computers. Other systems, such as IBM/PC compatible computers and DEC/VAX systems will need to reverse the byte order of the 16-bit pixels before the data can be used. SAMPLE_BITS = 16 There are 16 bits per sample (2 bytes). SAMPLE_BIT_MASK = 2#1111111111111111# This keyword indicates all bits within a 16-bit word are used in the expression of the value. OFFSET = 0.0 SCALING_FACTOR = 1.350000E-04 The OFFSET and SCALING_FACTOR keywords contain values used to convert the 16-bit integer pixel value to radiometric units. FRACTIONAL_REFLECTANCE = (PIXEL* SCALING_FACTOR) + OFFSET VALID_MINIMUM = -32752 Lowest valid value that can be stored in pixel (always -32752). NULL = -32768 Value of empty pixels or missing data (always -32768). LOW_REPR_SATURATION = -32767 Value of pixel if processing caused a low-end value pixel to go outside dynamic range of a 16-bit signed integer (always -32767). LOW_INSTR_SATURATION = -32766 Value if pixel was low-end saturated (always -32766). For example, if the bias of the camera was set so that low DN values could not be stored in the pixel. HIGH_INSTR_SATURATION = -32765 Value of pixel if processing caused a high-end value pixel to go outside dynamic range of a 16-bit signed integer (always -32765). HIGH_REPR_SATURATION = -32764 Value if pixel was high-end saturated (always -32764). For example, if the scene was too bright for the image to record at the pixel value became saturated. MINIMUM = xxxx Minimum value in image array. MAXIMUM = xxxx Maximum value in image array. CHECKSUM = xxxxxxxx Sum of all bytes in the image object. Used to validate that an image file was properly stored on the media. END_OBJECT = IMAGE OBJECT = IMAGE_MAP_PROJECTION ^DATA_SET_MAP_PROJECTION = "DSMAP.CAT" Name of file containing additional information about the map projection. DSMAP.CAT is located in the 'catalog' directory. COORDINATE_SYSTEM_TYPE = "BODY-FIXED ROTATING" COORDINATE_SYSTEM_NAME = "PLANETOGRAPHIC" Coordinate system used in the map projection. MAP_PROJECTION_TYPE = "SINUSOIDAL" Name of map projection. MAP_RESOLUTION = xxx.xxxxx Map resolution (pixels per degree) at the reference point of the projection. MAP_SCALE = x.xxxxxx Map scale (kilometers per pixel) at the reference point of the rojection. MAXIMUM_LATITUDE = xx.xxxxxxx Maximum latitude of the image file MINIMUM_LATITUDE = xx.xxxxxxx Minimum latitude of the image file. EASTERNMOST_LONGITUDE = xxx.xxxxxxx Easternmost longitude of the image file. WESTERNMOST_LONGITUDE = xxx.xxxxxxx Westernmost longitude of the image file LINE_PROJECTION_OFFSET = xxxxx.xxxxxxx SAMPLE_PROJECTION_OFFSET = xxxxx.xxxxxxx Projection offsets are used to define the relationship between line and sample of the image array and the latitude and longitude coordinate on the surface of the planet. See 'dsmap.cat' file located in the 'catalog' directory for information on these keywords. A_AXIS_RADIUS = 1737.4000000 B_AXIS_RADIUS = 1737.4000000 C_AXIS_RADIUS = 1737.4000000 Three-axis radius of the Moon used in the derivation of the map products that make up the UVVIS 5-band mosaic. FIRST_STANDARD_PARALLEL = "N/A" SECOND_STANDARD_PARALLEL = "N/A" Standard parallels of map, not used in this Sinusoidal Equal-Area projection. POSITIVE_LONGITUDE_DIRECTION = EAST The Moon coordinate system uses a positive longitude direction of east. Longitude values increase in the eastern direction. CENTER_LATITUDE = 0.0 Center latitude of the map projection. CENTER_LONGITUDE = xxxx.xxxx Center longitude of the map projection. REFERENCE_LATITUDE = "N/A" REFERENCE_LONGITUDE = "N/A" Reference latitude and longitudes are not used in the Sinusoidal Equal-Area projection. LINE_FIRST_PIXEL = 1 SAMPLE_FIRST_PIXEL = 1 The first pixel (upper left) in the image array is defined as line 1, sample 1. LINE_LAST_PIXEL = xxxx SAMPLE_LAST_PIXEL = xxxx The last pixel (lower right) in the image arrays is defined by these keywords. MAP_PROJECTION_ROTATION = 0.0000000 Map projection rotation always 0 for the Clementine UVVIS DIM. VERTICAL_FRAMELET_OFFSET = "N/A" HORIZONTAL_FRAMELET_OFFSET = "N/A" These keywords are not applicable for the Sinusoidal Equal-Area projection. END_OBJECT = IMAGE_MAP_PROJECTION END
APPENDIX B - GEOMETRIC DEFINITION OF A PIXEL
The purpose here is to describe the spatial or geometric definition of a pixel used in the generation and utilization of the digital image products. A broad range of factors enters into this question. For example, is a pixel to be conceived of as a point or as an area? The point definition would be most convenient, for instance, when dealing with coordinate grid overlays. This results in an odd number of pixels across a map that has an even number of spatial increments. For changing scales (for instance by even powers of 2) this definition becomes a problem. In this case it makes more sense to treat a pixel as a finite area. Then an even number of pixels covers an even number of spatial increments and decreasing/increasing scales by a power of 2 becomes trivial. However, grids now fall between pixels, at least in a mathematical sense. Their treatment in the generation of hardcopy therefore becomes an issue.
It was decided that the area concept of a pixel was the better choice; we would have to live with the asymmetries introduced in things like cartographic grids. There are various solutions: (1) use two pixels for the width of a grid line, (2) stagger grid pixels back-and-forth across the mathematical position, (3) use a convention whereby grid lines are systematically drawn offset from their mathematical position.
The next issue is the conversion between integer coordinates and real coordinates of the pixel mesh. We adopt the convention that pixels are numbered (or named if you like) beginning in the upper left corner with line 1, sample 1 (pixel 1,1); lines increase downward; samples increase to the right. (Even this is not a universal standard; some astronomical systems begin, perhaps more logically, in the lower left corner.) There are three reasonable possibilities for aligning a real, or floating point, coordinate system with the pixel mesh: the coordinate 1.0, 1.0 could be the upper left, the center, or the lower right of pixel 1,1. The convention historically used for geometric calibration files (Reseau positions) and also used in the Multimission Image Processing Laboratory at the Jet Propulsion Laboratory, is that the center of the pixel is defined as its location in real coordinates. In other words, the real coordinates of the center of pixel 1,1 are 1.0, 1.0. The top left corner of the pixel is 0.5, 0.5 and the bottom right corner is 1.49999...,1.499999. The bottom and right edge of a pixel is the mathematically open boundary. This is the standard adopted in the image products.
Cartographic conventions must also be defined. The map projection representation of a pixel is mathematically open at the increasing (right and lower) boundaries, and mathematically closed at its left and upper boundaries. An exception occurs at the physical limits of the projection; the lower boundary of the lowest pixel is closed to include the limit of the projection (e. g. the south pole). The figure below shows the coordinates of Pixel 1,1.
Coordinates of Pixel 1,1
longitude 180.0 179.00001 | | latitude | | line 90.0 -- ----------------- -- 0.5 | | | | | | | | | + | | (1.0,1.0) | | | | | | | 89.00001 -- ----------------- -- 1.49999 | | | | sample 0.5 1.49999
Finally, we must select a convention for drawing grid lines for various cartographic coordinates on planetary images and maps. The convention used for the image products is that a grid line is drawn in the pixels that contain its floating point value until the open boundary is reached and then an exception is made so that the outer range of latitude and longitude will always appear on the image. This means, in the example given above, a 10 degree grid would start on pixel 1 and be drawn on every tenth pixel (11,21,31,...) until the open boundary is reached. Then the line would be drawn on the pixel previous to the open boundary (line 180 instead of line 181, or sample 360 instead of 361).To summarize, the conventions are: