PDS: Data Set Information

Data Set Information
DATA_SET_NAME	VL1/VL2 MARS LANDING SITE ROCK POPULATIONS V1.0
DATA_SET_ID	VL1/VL2-M-LCS-5-ROCKS-V1.0
NSSDC_DATA_SET_ID
DATA_SET_TERSE_DESCRIPTION
DATA_SET_DESCRIPTION	Dataset Overview : The imaging system on each Viking Lander consisted of two identical cameras. These cameras operated throughout the mission, returning nearly 6600 images. Rocks were identified in the images, and their locations and dimensions were determined. Statistical distributions for the rocks were derived. This data set includes a table giving locations and dimensions of 425 rocks (plus 2 possible outcrops) located near VL1 (file VL1ROCKS.TAB) and a second table of 499 rocks near VL2 (file VL2ROCKS.TAB). It also includes derivative tables showing number density and areal coverage as a function of rock diameter (VL1NORML.TAB and VL2NORML.TAB, respectively). The VL1 population, with the two 'outcrops' omitted, has also been included as a 'VL0' set of files. These rock size-frequency and size-area distributions are updated versions of earlier work [MOORE&KELLER1990] and [MOORE&KELLER1991]. Intermediate products -- tables of axial ratios and areas for rocks and of rock distributions according to surface type -- have also been included. These may be of interest to users seeking more details of the statistical analysis or alternative descriptors of the rock population. Tables of axial ratios have file names of the form VLAXRAT.TAB; tables of rock distribution by surface type have names of the form VLSURFS.TAB. Parameters : The basic tables cover 425 rocks and 2 possible outcrops at the Lander 1 site and 499 rocks at Lander 2. They include three types of information: (1) the xyz-coordinates; (2) the lengths, widths, and heights; and (3) a descriptor of the apparent burial state of each rock. Length L is the longest visible (horizontal) dimension, width W is the orthogonal horizontal dimension, and height H is the vertical exposure of the rock above the surrounding surface. The burial descriptors are subjective and include three categories: 'perched,' 'partly buried,' and 'deeply buried.' For construction of rock size- frequency and area-size distributions, the average rock diameter D is taken to be the geometric mean of the length and width; the corresponding rock area is approximated as (PI/4)(D2). Derivative tables include parameters such as the average axial ratio for rocks computed from each pair of rock dimensions and the number density and areal coverage of rocks as a function of diameter. Processing : The rock size-frequency and size-area distributions were obtained from images and maps of surface materials by estimating the areas occupied by materials within the camera fields of view. The process involved several steps. Measurements on the smallest, closest rocks were combined with measurements of large rocks over great distances to obtain a composite distribution function for about 80 square meters at each site. First, maps of surface material were divided into two regions. The 'near field' extended to about 3 meters in front of each Lander and was approximately within reach of the surface sampler arm. The 'far field' extended to about 9 meters. Data on rock dimensions and locations for the near field came from three sources: (1) 1/10-scale base maps that showed the sizes and locations of rocks [MOOREETAL1987]; (2) unpublished working maps and data; and (3) Lander camera images. Rocks and clods with dimensions larger than about 0.01 meter could be measured and located in the near field. Data on dimensions and locations for the far field also came from three sources: (1) 1/20-scale contour maps [LIEBES1982]; (2) Lander camera mosaics with overlaid contours [LIEBES1982]; and (3) Lander camera images. Large rocks were located directly on the contour maps and the mosaics; then they were measured directly from the maps. Smaller rocks that were not intersected by contours were located using stereometric procedures; their sizes were calculated from their ranges and from the angles they subtended. Second, different types of surface materials were identified. Three types of materials were mapped at both Lander sites: (1) fine materials, (2) soil-like materials, and (3) rocks. For the far fields of both landers, fine material included uniform-appearing materials that were free of small rocks and clods except along contacts with other soil-like materials. The thickness of deposits of fine material in the far field, which were superposed on soil-like materials and rocks at both sites, were estimated to range from 0.01 or 0.02 meters to more than 0.25 meters at Lander 1 and from 0.01 meters to about 0.3 meters at Lander 2. Known locations of large rocks permitted delineation of areas covered by fine materials and rock outcrops by visual inspection. These areas were obtained graphically from the maps; allowances for areas occupied by rocks within the areas of fine and soil-like materials were computed. The area of fines near footpad 2 of Lander 1 were included with fines of the far field because they were thick and free of small rocks. The soil-like areas in the near fields of Landers 1 and 2 contained rocks as small as, or perhaps even smaller than, 0.022 meters. Two areas at the Lander 1 site were mapped as outcrops [BINDERETAL1977], but it is possible that they could be large rocks [SHARP&MALIN1984] or a single rock about 3 meters long. Third, cumulative rock distribution functions at each Lander site were obtained by combining the measured distributions in the near field, far field, and fine areas. All rocks with average diameters greater than 0.25 meters in the near and far fields were included in the cumulative distribution. Rocks smaller than 0.25 meters in the near field were considered to be representative of that size range in both the near and far fields -- except where fine materials were mapped. That is, since small rocks are not resolved in the far field, areas between moderate and large rocks in the far field were assumed to have the same distribution as in the near field. All rocks within the deposits of fines were assumed to be large enough to have been measured accurately and were included in the cumulative distribution. The cumulative rock distribution function was then the distribution of rocks larger than 0.25 meters everywhere, plus the total rock distribution from fines areas, plus the distribution of rocks smaller than 0.25 meters in the near field scaled to 'fill in' the spaces among rocks larger than 0.25 m in the far field; this total was then normalized by the total area (about 80 m2 at both sites). The results are presented in the tables VLNORML.TAB; the contributions from the different surface types are tabulated in VLSURFS.TAB. Data : Two tables contain basic rock population data derived from images, maps derived from images, and other data. Tables VL1ROCKS.TAB and VL2ROCKS.TAB contain the data for Landers 1 and 2, respectively. Each row in the table contains an ID keyed to hand-drawn overlays for the atlas of lander images [LIEBES1982], an indicator of the environment in which the rock was located (near field, far field, outcrop, drift material, or excluded from statistical tabulations because of anomalous settings), the XYZ coordinates of the rock based on the Local Gravity-Normal (LGN) map grid in [LIEBES1982] in meters, estimates of the dimensions of the rock (meters) and its orientation in the LGN frame, a subjective evaluation of its burial state (perched, partly buried, buried, or unknown), and miscellaneous notes such as names associated with certain well-known rocks. The data fields are in 11 columns totaling 82 bytes each; each row is terminated with an ASCII carriage-return line-feed pair. Each table is accompanied by a detached PDS label which fully describes its format and content. VL0ROCKS.TAB is identical to VL1ROCKS.TAB except that the two 'outcrops' have been omitted. It is accompanied by detached PDS label VL0ROCKS.LBL. VL1AXRAT.TAB is a table of binned results of calculations based on VL1ROCKS.TAB. The area of each rock and three axial ratios were computed and binned as follows: AREA : LWPI/4 binned according to DLW : SQRT(LW) ARLW : MIN(L,W)/MAX(L,W) binned according to DLW : SQRT(LW) ARWH : MIN(W,H)/MAX(W,H) binned according to DWH : SQRT(WH) ARLH : MIN(L,H)/MAX(L,H) binned according to DLH : SQRT(LH) where ARxy denotes axial ratio of dimensions x and y Dxy denotes average diameter using dimensions x and y L : estimated longest dimension of the rock W : estimated width of the rock (orthogonal to length) H : estimated vertical exposure of a perched rock, or twice the exposure of a partly buried rock (see below for discussion of buried rocks) and MIN(X,Y) is the smaller of X and Y MAX(X,Y) is the larger of X and Y The lowest bin boundary was set at 1/128th meter; boundaries then increased by powers of SQRT(2) (0.008, 0.011, ... , 1.000, 1.414 m). The area reported in VL1AXRAT.TAB is the sum of the areas of all the rocks assigned to that bin. For axial ratios the quantity reported for each bin is the average and standard deviation of the axial ratios of the rocks in that bin. The results are tabulated separately according to surface type (drift area, far field, near field, and excluded) and burial state (perched, partially buried, buried, and unknown). Cumulative results for all bins were then computed for each surface type and burial state combination; these are shown in summary lines in the table. Since there are three dimensions for each rock, axial ratios were calculated using each of the three possible pairings. Because the height of buried rocks is very uncertain, axial ratios based on heights of buried rocks were excluded from the averages and standard deviations; instead, those rocks were assigned to a special 'undefined' bin (bin number 1). VL1AXRAT.TAB is composed of 16 sub-tables, one for each combination of surface type and burial state. Each sub-table has 19 rows; the first is for rocks which could not be binned (e.g., the computation required H for a buried rock), the next 17 are for bins in increasing average diameter, and the last is a summary for all diameters. VL1AXRAT.TAB is accompanied by a detached PDS label which fully describes both its content and format (VL1AXRAT.LBL). VL1SURFS.TAB is a table of VL1 rock numbers and areal coverage (both incremental and cumulative) in decreasing order of rock diameter for each of the three surface types -- drift material, far field, and near field. For each surface type (drift material, far field, and near field) rocks were sorted into bins according to diameter (square root of length times width), the area covered was estimated (diameter squared times pi divided by 4), and a running sum was accumulated. Total area and area covered by rocks for each surface type at VL1 were: Surface Type Total Area Area Covered Area Covered by Rocks by Rocks >0.25m -------------- ---------- ------------ --------------- Drift Material 15.27 m2 0.4102 m2 0.0534 m2 Far Field 57.85 m2 6.7229 m2 5.4397 m2 Near Field 10.48 m2 1.3153 m2 0.0560 m2 The inter-rock area in the far field was 52.4103 m2, where inter-rock was taken to mean area not covered by a rock of diameter 0.25 meters or larger. Inter-rock area in the near field was 10.4240 m2. Ratio of the total inter-rock area (far field plus near field) to the near field inter-rock area was 6.0278; this was the scale factor used to multiply the near field distribution for diameters less than 0.25 m in constructing the VL1NORML.TAB table below. VL1SURFS.TAB is accompanied by a detached PDS label which fully describes both its content and format (VL1SURFS.LBL). VL1NORML.TAB is a table of rock number and area density for the entire VL1 site. A distribution function is first formed by summing the following: (1) the near field distribution of rocks larger than 0.25 m (2) the far field distribution of rocks larger than 0.25 m (3) 6.0278 times the near field distribution of rocks smaller than 0.25 m (4) the total distribution of rocks in the drift material Then the density is derived by dividing the distribution by the total area (83.60 m*2). The table has columns for the rock number and rock area distribution per bin, the cumulative rock number and rock area as a function of bin, the rock number and rock area density per bin, and the cumulative rock number and rock area density per bin. VL1NORML.TAB replicates the results reported earlier by [MOORE&KELLER1990] and [MOORE&KELLER1991], with minor corrections. VL1NORML.TAB is accompanied by a detached PDS label which fully describes both its content and format (VL1NORML.TAB). VL2AXRAT.TAB, VL2SURFS.TAB, and VL2NORML.TAB are the respective files for the Viking Lander 2 site. Each is accompanied by a detached PDS label. VL0AXRAT.TAB, VL0SURFS.TAB, and VL0NORML.TAB are the respective files for the Viking Lander 1 site but with the two 'outcrops' omitted. Each is accompanied by a detached PDS label. Ancillary Data : None. Coordinate Systems : The photogrammetric reference points of the two cameras on each Lander were separated by 0.822 m [LIEBES&SCHWARTZ1977]. If the Lander were resting on a perfectly flat surface, the origin of the Lander Aligned Coordinate System (LACS) would be 1.583 m below the midpoint of this line and 0.470 m to the rear (toward Footpad 1, or in the LACS -Z direction). The line from Camera 2 to Camera 1 would point in the +Y direction. LACS +X was down, making a right-handed orthogonal system. The LACS was fixed with respect to the body of the Lander. The LGN origin coincided with the LACS origin, but its Z axis pointed toward zenith. Its +Y axis pointed in the direction of the LACS +Z projection onto the horizontal plane. The LGN +X axis completed the right-handed orthogonal frame. Loosely quoting [LIEBES1982]: 'To the extent that lander tilt may be considered small, the LGN may be visualized as having its x-axis approximately anti-parallel to the LACS y-axis (and thus pointing roughly parallel to the direction from Camera 1 to Camera 2). The LGN y-axis points roughly parallel to the LACS z-axis, or in the horizontal direction outward and approximately forward from the lander, and roughly perpendicular to the intercamera baseline.' For Lander 1, north was 141.91 degrees counter-clockwise about the LGN Z-axis, from the LGN Y-axis. The Lander 1 deck was tilted 2.99 degrees at azimuth 285.17 degrees (clockwise) from north. For Lander 2, north was 29.14 degrees counter-clockwise about the LGN Z-axis, from the LGN Y axis. The Lander 2 deck was tilted down 8.21 degrees at azimuth 277.70 degrees (clockwise) from north [LIEBES1982]. Rock positions are given with respect to the Local Gravity- Normal (LGN) map grid defined in [LIEBES1982]. Rock orientations indicate the direction of the long axis of the rock and are measured clockwise from the LGN Y-axis. Software : The SOFTWARE directory includes FORTRAN 77 source code for a single program which will carry out a statistical analysis of the basic rock data (e.g., VL1ROCKS.TAB) and generate the corresponding derivative files (e.g., VL1AXRAT.TAB, VL1SURFS.TAB, and VL1NORML.TAB). Note that the table formats produced by the program will be in somewhat different than formats for the tables in the data set. During assembly of the data set, the software was compiled under SunSoft FORTRAN 77 4.0 and executed under Solaris 2.5.1. During PDS peer review the software was compiled (but not run) using Fortran PowerStation 4.0 under Windows95 and on a workstation running SunOS 4.1.4. Bin boundaries start at 1/128 m and increase by factors of sqrt(2)[MOORE&KELLER1990][MOORE&KELLER1991]; results can be conveniently displayed on log-log plots. The software included with this archive (see below) can easily be modified for other bin definitions.
DATA_SET_RELEASE_DATE	1998-12-31T00:00:00.000Z
START_TIME	1976-07-20T12:00:00.000Z
STOP_TIME	1982-11-13T12:00:00.000Z
MISSION_NAME	VIKING
MISSION_START_DATE	1975-08-20T12:00:00.000Z
MISSION_STOP_DATE	1983-02-01T12:00:00.000Z
TARGET_NAME	MARS
TARGET_TYPE	PLANET
INSTRUMENT_HOST_ID	VL1 VL2
INSTRUMENT_NAME	CAMERA 1 CAMERA 2
INSTRUMENT_ID	CAM1 CAM2
INSTRUMENT_TYPE	CAMERA
NODE_NAME	Geosciences
ARCHIVE_STATUS	ARCHIVED
CONFIDENCE_LEVEL_NOTE	Confidence Level Overview : Compilation of maps of surface materials based on images from stationary cameras on landed spacecraft is limited primarily by obscuration of the surface. First, sides of large rocks may be hidden from the field of view of cameras. Second, areas that contain small rocks may be hidden by large rocks, by surfaces that slope away from the cameras, and by spacecraft parts. Third, many small rocks in the far field simply cannot be mapped because of the decrease in camera resolution with increasing distance and the overwhelming number of rocks. These problems become more severe with increasing distance. Hence, only rocks larger than about 0.03 to 0.05 m could be mapped in the far field, and the maps were confined to areas roughly 9 m by 15 m. Areas behind very large rocks were excluded from analyses except where interpretation of the images suggested that uniform deposits of fine materials could be confidently inferred. Data Coverage and Quality : As mentioned above, the burial status of each rock at a landing site was defined to be either perched, partially buried, or deeply buried. Roughly 60 percent of rocks at VL-1 are partially buried, with the remaining 40 percent evenly split between perched and deeply buried. For each burial depth and sample region, the mean and standard deviation of the axial ratios W/L and H/L were calculated. The H/L ratio was not calculated for deeply buried rocks, since only the topmost surfaces of these rocks were exposed. While the horizontal dimensions of the buried rocks are probably under-estimates, the average width-to-length ratio is about 0.7, regardless of depth. The vertical rock dimension is the most uncertain measurement; even perched rocks likely have settled into the regolith somewhat. On average, the height-to-length ratio is about 0.48 for perched rocks and 0.42 for partially buried rocks at VL1, with a relatively high variance in each case. From these values, one can calculate that the vertical exposure of partially buried rocks is about 85 percent, assuming that partially buried rocks have the same average axial ratios and relative orientations as perched rocks. However, since a partially buried rock may be exposed on one side (allowing estimation of the vertical dimension) and buried on the other side, the average burial depth is difficult to estimate. Both W/L and H/L remain approximately constant as a function of rock size. A sophisticated analysis of measurement errors was beyond the scope of the original research [MOORE&KELLER1990] [MOORE&KELLER1991] and of this archiving effort. It would also have exceeded the needs of most investigators interested in Mars rock distributions. To carry out such an analysis a photogrammetrist would measure each of 500 or so 'points' three to five times, arriving at a distribution of errors which is related to base-height ratio (or range). From that point, one must consider errors in differences in ranges and then elevations and differences in elevation. The interested reader is referred to Figure 10 in [LIEBES&SCHWARTZ1977] for estimates of errors as a function of range and azimuth in the Viking Lander image data set. Mapping and analyses also improve understanding of the types and amounts of materials at the Lander sites. Of particular importance is the fraction of area covered by uniform-appearing bright fine materials. Casual inspection of images and mosaics suggests that such deposits are small and scarce, but the fraction of area covered by these fine materials at VL2 is 0.298. The fraction of area covered by rocks at VL2 is 0.159 -- not significantly different from the 0.14 obtained by [MOOREETAL1979][MOOREETAL1987] or the 0.188 obtained by [MOORE&JAKOSKY1989]. All values are in agreement with the rock abundance 0.20+/-0.10 obtained from IRTM data [CHRISTENSEN1986].
CITATION_DESCRIPTION	Simpson, R. A., VL1/VL2 MARS LANDING SITE ROCK POPULATIONS V1.0, VL1/VL2-M-LCS-5-ROCKS-V1.0, NASA Planetary Data System, 1998
ABSTRACT_TEXT	The imaging system on each Viking Lander consisted of two identical cameras. These cameras operated throughout the mission, returning nearly 6600 images. Rocks were identified in the images, and their locations and dimensions were determined. Statistical distributions for the rocks were derived.
PRODUCER_FULL_NAME	RICHARD A. SIMPSON
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