 
 
Viking Orbiter 1 Image Times DBK File
===========================================================================
 
     Created by Boris Semenov, NAIF/JPL, March-July, 1996; comments were
     augmented/reformatted in April 2000.
 
 
File Contents
--------------------------------------------------------
 
     This SPICE Data Base Kernel (DBK) file contains all variants of Viking
     Orbiter 1 (VO1) camera image time tags that have been collected by
     NAIF from different science groups involved in VO image cartographic
     application.
 
 
Applicability
--------------------------------------------------------
 
     This file can be used to obtain one or more variants of time tag of an
     individual VO1 camera image by searching for some and/or all non-NULL
     time tags that correspond to the image FSC.
 
     This file can also be used to get a list images used in a particular
     data set (see list of data sets in the "Data Table Structure" section
     below) by searching the data set's TIME column for all non-NULL values
     and returning FSCs corresponding to them.
 
 
Data Table Structure
--------------------------------------------------------
 
     This file contains a single table called ``VO1_TIMES'' which has the
     following columns:
 
           IMAGE_NUMBER             INT    FSC count (or "image number")
                                           corresponding to a VO1 camera
                                           image;
 
           BATSON_TIME              TIME   time of the image used by R.M.
                                           Batson of the USGS Astrogeology
                                           Branch (BATSON set);
 
           DAVIES_TIME              TIME   time of the image used by M.
                                           Davies of the Rand Corporation
                                           (DAVIES set);
 
           GEM_TIME                 TIME   time of the image stored in GEM
                                           (Viking Image Geometry) files
                                           produced by K.Edwards of the
                                           USGS (GEM set);
 
           MOSAIC_TIME              TIME   time of the image used in the
                                           USGS Mars Digital Image Mosaic
                                           (MOSAIC set);
 
           MSSS_AUTO_TIME           TIME   time of the image used by Malin
                                           Space Science Systems (MSSS)
                                           company (M. Malin, M. Caplinger)
                                           for automatic image registration
                                           (MSSS_AUTO set);
 
           MSSS_MANUAL_TIME         TIME   time of the image used by MSSS
                                           for manual image registration
                                           (MSSS_MANUAL set);
 
           SEDR_TIME                TIME   time of the image stored in the
                                           original VO SEDR data set
                                           generated by the Viking Project
                                           (SEDR set);
 
           WASHU_TIME               TIME   time of the image contained in
                                           the PDS Viking image catalog at
                                           Washington University, Saint
                                           Louis (WASHU set);
 
           WU_TIME                  TIME   time of the image used by S. Wu
                                           of the USGS (Wu set);
 
           SEDR_BATSON_DIFFERENCE   DP     difference between SEDR and
                                           Batson's times;
 
           SEDR_DAVIES_DIFFERENCE   DP     difference between SEDR and
                                           Davies' times;
 
           SEDR_GEM_DIFFERENCE      DP     difference between SEDR and GEM
                                           times;
 
           SEDR_MOSAIC_DIFFERENCE   DP     difference between SEDR and
                                           Mosaic times;
 
           SEDR_MSSS_DIFFERENCE     DP     difference between SEDR and MSSS
                                           times;
 
           SEDR_WASHU_DIFFERENCE    DP     difference between SEDR and
                                           WashU catalog times;
 
           SEDR_WU_DIFFERENCE       DP     difference between SEDR and Wu's
                                           times;
 
     All *TIME columns are of ``TIME'' type, i.e. store the time as
     Ephemeris Time in seconds past J2000. All *DIFFERENCE columns contains
     DP number of seconds which is the difference between corresponding
     TIMEs.
 
 
Pedigree
--------------------------------------------------------
 
     The data stored in this file were extracted from the data sets
     provided by USGS, Flagstaff (SEDR, GEM, Batson, Davies and Wu sets),
     MSSS, San Diego (MSSS_AUTO and MSSS_MANUAL sets) and Washington
     University, Saint Louis (WashU set).
 
     The times in a few of these sets (BATSON, WU, MOSAIC, both MSSS sets
     and part of DAVIES set) are mostly the same as those in the GEM set.
     But since during data processing some errors were introduced
     (especially in the BATSON set) all of these data sets are included in
     this DBK file. Moreover, since not all VO images were used in the
     cartographic application of each group, all "derived" sets contain
     significantly smaller numbers of time tags.
 
     Perhaps only the three most complete sets will be of an interest for a
     future VO image analysis; these are SEDR, GEM and WASHU time tag sets.
 
     Since the only "complete" set produced during the mission was the SEDR
     set, it is assumed that the GEM and WASHU time tags were "derived"
     from it later during VO data processing.
 
     To create this DBK file, the UTC image time tags were extracted from
     the original data sets and were converted to Ephemeris Time.
 
 
Known and Possible Origins of Time Tag Differences
--------------------------------------------------------
 
     Unfortunately the time tags in SEDR, GEM and WASHU sets are different.
     It's very difficult to decide now, many years after the mission, what
     are the origins of these differences.
 
     One of the main differences stems from the way time tags were stored
     in each of these sets. In the GEM files tags were stores in are
     "middle-of-exposure" times in JED date format (ex. 2443365.317484 for
     FSC 33919977). All these tags are truncated to 6 decimals. This causes
     a loss of precision since .000001 of day corresponds to 0.0864
     seconds.
 
     The time tags stored in SEDR files are middle-of-exposure times in UTC
     day-of-year format (ex. 1977-221 // 19:36:22.570 for FSC 33919977).
     Here the tags are given to a millisecond.
 
     The tags in WASHU set (PDS catalog) are beginning-of-exposure time (in
     accordance to Ed Guiness) in UTC Calendar date format (ex.
     1977-08-09T19:36:22.596Z for FSC 33919977). These are given to a
     millisecond too.
 
     For the period of time starting at Jan. 1, 1978 and ending about three
     months later differences between SEDR and GEM and SEDR and WASHU time
     tags are greater that 1 second. This can be explained with the
     assumption made above that GEM and WASHU tags were derived from SEDR
     tags. Then possibly during this process strange looking SEDR UTC
     DOY-format tags like "1977-375//..." (instead of "1978-10/...") were
     converted to ET incorrectly. i.e. the leap second of Jan 1, 1978 was
     not taken into account when derived time tags were calculated.
 
     To make comparisons of tags in these sets easier the differences
     between the SEDR tags and the corresponding tags from each of other
     sets are provided in separate columns in this EK file.
 
 
Data Set Comparisons
--------------------------------------------------------
 
     This subsection contains statistics and points out some specific
     problems resulting from a comparison of these data sets.
 
 
TABLE 1. NUMBER OF RECORDS IN VO1 TIME TAG DATA SETS
 
                           in source  included
                             files     in DBK
                          ----------  ---------
        BATSON                9337       9328 (-7 dupl, -2 bad FSCs)
        DAVIES                1315       1315
        GEM                  35569      35569
        MOSAIC                3521       3521
        MSSS_AUTO             3086       3086
        MSSS_MAN              8175       8175
        SEDR                 33517      33517
        WASHU                34918      34918
        SWU                    587        587
 
     Some FSCs were duplicated in VO1 BATSON data set; i.e. the same FSC
     value was included twice with different corresponding JED times. For
     each pair of duplicate FSCs the FSC whose corresponding JED time seems
     to be incorrect was not included in this DBK file. These "not
     included" FSC-JED pair are below:
 
        26923395  2443156.5513080000
        34700402  2443405.7840340000
        39256001  2443642.0002380000
        39294549  2443643.9991270000
        39294552  2443643.9991790000
        52513428  2443038.6449790000
        54395405  2444427.0070470000
 
     A few FSC tags found in the BATSON data set couldn't be found in any
     of the most complete data sets -- SEDR, GEM or WASHU. These FSCs were
     also not included in this DBK file but are listed below:
 
        43485635  2443861.3157300000
        54423249  2443334.3385800000
 
 
Recommendations
--------------------------------------------------------
 
     What recommendations can be given to a person who will process VO
     SPICE data in the future? There is not an obvious answer, but a good
     bet will be to use original SEDR time tags.
 
 
Usage Note
--------------------------------------------------------
 
     The Data in this file may accessed via SPICE Toolkit EK subroutines or
     examined using SPICE utility program INSPEKT.
 
 
Related Kernels
--------------------------------------------------------
 
     An LSK file is required by INSPEKT in order to access the data in this
     file.
 
     The DBK file ``VO1_TREC.BDB'' containing results of VO image time tags
     accuracy and reliability analysis, including an attempt to correct
     some of these tags, can be used obtain time tags corrected by NAIF.
 
 
Contacts
--------------------------------------------------------
 
     If you have any question regarding this data contact NAIF at JPL:
 
        Charles H. Acton, Jr
        (818)-354-3869
        chuck.acton@jpl.nasa.gov
 
        Boris V. Semenov
        (818)-354-8136
        boris.semenov@jpl.nasa.gov
 
 
