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UNAVCO 1996 Annual Report
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3.0 Data Management and Archive Support
GPS data management encompasses the range of activities necessary to
ensure that high-quality GPS data and its accompanying meta-data (descriptive
data) are collected, transported, organized and safely stored in designated
GPS archives, and then made readily available from these archives to the
rest of the GPS community. The UNAVCO GPS Community Archive at the UNAVCO
Boulder Facility (henceforth referred to as the "UNAVCO Archive"
or the "Archive") and NASA's Crustal Dynamics Data Information
System (CDDIS) at the Goddard Space Flight Center represent two such designated
archives.
At UNAVCO, the Data Management and Archiving Group (DMAG) has long
recognized that there is considerable overlap between the acquisition,
transport, archival, and retrieval phases of GPS data management. The long-term
goals of a GPS data archive should ensure the safe long-term storage of,
and ready access to, accurate and correct data and all necessary meta-data.
GPS data archiving is greatly simplified and improved when all phases of
data handling match these long-term archival goals. UNAVCO is dedicated
to the task of making this a reality for the GPS community and central
to this task is the UNAVCO Archive.
The purpose of the Archive is three-fold. First, it serves as physical
storage for the PI who is primarily responsible for the GPS data collection.
Second, it serves as an on-line repository of GPS data for the present
GPS community. Third, it serves as a long-term archive for future researchers
who may want to search, identify, and recover validated GPS data and meta-data
at earlier precise positions, in a specific spatial or temporal frame of
interest. Not coincidentally, these three functions translate into the
three primary components of the UNAVCO Archive (see Figure
3-1):
- Physical Repository: Physical media (e.g. floppy disks, tapes, etc.),
field log sheets, maps, photographs, and other physical records turned
in to UNAVCO by the PI are organized, checked-in and stored in a dedicated
room. Data are duplicated and stored on backup media. Data in the Physical
Repository can be requested from the DMAG staff by telephone or email and
sent using an agreed-upon physical format.
- On-line Repository: Data and associated meta-data copied from the Physical
Repository, or obtained electronically over the Internet, are first catalogued
and stored on a 15-Gbyte RAID disk system and later migrated to a 500-Gbyte
digital linear tapedrive jukebox. These data and meta-data are only minimally
verified but are readily available to the GPS Community via the Internet.
- Archive Database: Data and meta-data in the On-line Repository are
completely validated using log sheets, shipping invoices, PI notes, and
other sources of information using an interactive data-entry interface
to an Oracle relational database system. This validated meta-data and links
to the data in the Physical and On-line Repositories are stored in a relational
database especially designed for GPS data and meta-data; this is the Archive
Database. Once data and its meta-data have been validated (and possibly
corrected) and this information entered into the Archive Database, the
GPS Community may search and retrieve selected data using a search-and-retrieve
user-interface on the World Wide Web to the same relational database system.
Data are sent electronically over the Internet to the person making the
request.
Figure 3-1. UNAVCO Archive Operations
To facilitate the GPS community's ability to collect, transfer and
retrieve correct GPS data and meta-data, the DMAG also engages in other
data management tasks peripherally related to the central task of maintaining
the Archive, but which directly compliment and simplify archival goals.
These related tasks include:
- design and standardization of log sheets, both physical and electronic,
for recording of necessary meta-data (see "Log Sheets" below)
- development of software for the extraction and validation of data and
meta-data from raw native binary data formats from various GPS receivers
(see "TEQC" below)
- co-development of safe GPS data transfer protocols (see "LDM/IDD"
below)
- co-design and -development of the "Seamless Archive", allowing
for the GPS Community to access data and meta-data at any of the designated
GPS archives without the need for knowing details about a specific archival
site or where or how the data are stored
- accomplishment of all these goals, as well as the primary task of maintaining
the Archive, in a fashion consistent with the wide heterogeneity of the
GPS Community which:
- is involved in both episodic (campaign) and permanent station projects
- uses a multiplicity of receiver types (e.g. Trimble, Ashtech, Rogue/TurboRogue/TurboStar,
Leica, TI-4100, etc.)
- accesses these receivers using a wide variety of communications, downloading
or data-logging methods
- uses a wide variety of computer hardware and operating systems
- has a wide variety of data-release constraints (e.g. non-restricted
availability, restricted availability, availability after time lapse from
data collection, etc.)
The sections below discuss both the primary archiving tasks and these
associated activities.
- 3.1 - Archival Process
- 3.2 - Current Archive
Status
- 3.3 - Data Management
and Archive Tasks in FY97
- 3.4 - Data Management
and Archiving Group (DMAG) Staff and Budget
1996 Annual Report - 23 SEP 1997
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