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Archived from NCAR: https://github.com/NCAR/lrose-cedric/blob/master/sprint/source/wsr88d.tape-documentation
509 lines
23 KiB
Text
509 lines
23 KiB
Text
[Image] NEXRAD DOCUMENTATION
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----------------------------------------------------------------------------
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LEVEL II TAPE DOCUMENTATION
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WSR-88D BASE DATA
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INTRODUCTION:
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Weather Surveillance Radar - 1988 Doppler (WSR-88D), or NEXt Generation
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RADar (NEXRAD), Level II data are the base digital data produced by the
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signal processor (mean radial velocity, reflectivity, and spectrum width) at
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the full spatial and temporal resolution of the radar. Level II data also
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contain status messages, performance/maintenance data, volume scan strategy,
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clutter filter bypass map, and wideband communication console messages.
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These are the same data transmitted over high-speed, wideband communications
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to the WSR-88D Radar Product Generator (RPG) for processing by the
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meteorological analysis algorithms.
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Initially it was thought that Level II recorders would be used at selected
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sites, and only when significant weather events were taking place. As system
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development progressed, it became evident that the Level II data would be of
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vital importance to ensure proper calibration of the radars and for use by
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researchers to investigate events in more detail than would be possible by
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using the Level III products. The Level II data can also be used to test
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revised algorithms that may later be applied to operational use.
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The NEXRAD agencies (Departments of Commerce, Defense, and Transportation)
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recognized the value of Level II data. In June 1994, the agencies agreed to
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record Level II data throughout the WSR-88D network. The Level II recording
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is not essential to the operational use of the WSR-88D system. The NEXRAD
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agencies agreed to certain procedures to minimize the impact of Level II
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data collection on the operations of base weather stations, forecast offices
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and FAA control locations. The priority of Level II recorder maintenance,
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reloading of tapes and continuous recording of data will be assigned by the
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local site management.
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RECORDING:
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The vast amounts of data collected at the Radar Data Acquisition (RDA) site
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made it mandatory that the most economical recording devices and media
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available at that time be used. It was determined that EXABYTE tape drives
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and 8mm tapes provided the most viable system. Depending on operation of the
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radar, the recorder model used, and station requirements, one tape may be
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filled every 1.8 days for each site. Data grade tapes are used for recording
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and archiving. Initially, sites were equipped with EXABYTE 8200 recorders.
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These tapes can contain up to 2.3 gigabytes per tape. Later, EXABYTE 8500
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recorders were installed which record at higher density with up to 4.7
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gigabytes per tape. Also available are 8500c (capable of recording in a
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standard compressed mode), and 8505 which is a half height drive fully
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downward compatible. The 8505 records up 4.7 gigabytes in an uncompressed
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mode.
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PROCESSING AND ARCHIVING:
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The Level II recorder system consists of an 8mm reorder, 10-tape jukebox
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(automated sequential loading of new tapes), an uninterruptable power supply
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ans a controller board seated in the RDA computer. Under jukebox operation
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the 10-tape supply will last 11 to 27 days depending on the radar scanning
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strategies used. Tapes are received at the National Climatic Data Center
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(NCDC) from the individual sites in 10-tape cases. Incoming tapes are
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processed on a series of 8505 EXABYTE drives, reblocked, cataloged,
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inventoried, and archived. The original tapes are sent to an off-site
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storage facility for security back-up to the NCDC NEXRAD files.
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SPECIAL NOTE:
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The WSR-88D is a very complex system. Program modifications and engineering
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changes are rather constant features during the phase-in process. Some early
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pre-production models experienced considerable difficulties in the recording
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of Level II data. Even today, tapes are received that contain spurious,
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erroneous, or illegal configurations. We have attempted to recover as much
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data as possible from these problem tapes. The user is cautioned that these
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anomalies may be encountered while reading the archive tapes. Special care
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must be taken to ensure that illegal configurations do not contaminate any
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summaries or statistical studies.
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NCDC will be glad to assist in solving problems encountered in reading the
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tapes, but technical questions about the data themselves must be addressed
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to the:
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NWS/Operational Support Facility
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Operations Branch
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1200 Westheimer Dr.
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Norman, OK 73069
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Telephone: (405) 366-6530
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FAX: (405) 366-6550
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Definitive information about all aspects of the Doppler radar is contained
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in Federal Meteorological Handbook No. 11 (FMH-11), Volumes A through D.
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These may be ordered from the National Climatic Data Center.
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DATA AVAILABILITY:
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As stated previously, all NCDC archives are being generated on EXABYTE 8505
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drives. Users must specify whether they require 8200 or 8500 mode tapes. If
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copies are requested in the 8200 mode, two or more output tapes may be
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required. A header record will appear on each output tape.
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Each 8mm tape records approximately 10 hours of Volume Coverage Pattern 11
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(VCP 11), 18 hours of VCP 21, or 40 hours of VCP 31 or 32 using the EXABYTE
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8200 mode. Using the EXABYTE 8500 mode doubles both the storage capacity and
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number of hours of data possible per 8mm tape.
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FORMAT:
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HEADER FILE: The first file on tape contains only one 31616 byte record.
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This record is called the header record.
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HEADER RECORD: This 31616 byte "physical record" is divided into 494
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"logical records" of 64 bytes each with position 1 as the first byte.
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POSITIONS FORMAT DESCRIPTION
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1 - 8 C*8 Always ARCHIVE2
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9 - 12 C*4 4-letter site ID. e.g. KLMB
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13 - 18 C*6 NCDC tape number. e.g. N00001
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19 Blank
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20 - 28 C*9 Date tape written. dd-MMM-yy e.g. 19-FEB-93
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29 Blank
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30 - 37 C*8 Time tape written. hh:mm:ss. e.g. 10:22:59
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(local time)
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38 Blank
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39 - 43 C*5 Data Center writing tape: RDASC or NCDC
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(Left justified, blank filled)
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44 - 48 C*5 WBAN Number of this NEXRAD site. (This is a unique
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5-digit number assigned at NCDC. Numbers are
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contained in the NCDC NEXRAD Station History file
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(WSR-88D RDA LOCATIONS). The file also contains the
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four letter site ID, Latitude, Longitude, Elevation,
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and Standard location name.)
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49 - 53 C*5 Tape output mode. Current values are 8200, 8500,
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8500C
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54 - 58 C*5 A volume number to be used for copies and extractions
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of data from tapes. The form would be VOL01, VOL02,
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VOL03 ....VOLnn.
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59 - 64 Blank (Available for future use.)
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65 - 31616 May be used for internal controls or other
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information at each archive center. Information of
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value to users will be documented at the time of tape
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shipment.
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During the process of copying archive tapes, positions 1-18 and 44-48 will
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be duplicated. New values will be written in positions 19-43 and 49-58.
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DATA FILES:
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A new data file is created upon completion of a volume scan. A data file
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contains a title, a complete radar volume scan (360 degree revolutions at
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each specified elevation cut) of base data, digital radar data message, and
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any control/response messages from the RDA to the RPG. The title is the
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first record located in each data file and contains a file name, creation
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date, and creation time. After the title record through the remainder of the
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data file, variable length records containing base data intermixed with
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control/response messages are recorded. Messages and base data are
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distinguishable by a message header coded for either digital radar base data
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or one of the thirteen types of messages. The message header uses a format
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common to both data and messages and is included in each 2432 byte packet.
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Depending on the predefined volume scan strategy (selected elevations, sweep
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rate, pulse rate etc.) used during the collection period, each data file
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could contain either five, six, or ten minutes of base data.
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Control/response messages are used during actual operations and are of
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limited use for post analyses.
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DATA TYPES SUPPORTED WITHIN DATA FILES:
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A Concurrent minicomputer serves as the host computer for generation of all
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Archive Level II data. Depending on the computer used for reading the tapes,
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the data types may be different from those used in the Concurrent system.
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The Concurrent computer byte (8 bits) structure places bit 0 as the left
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most bit and designates bit 0 as the Most Significant Bit (MSB). Bit 7 for a
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byte, bit 15 for a halfword (2 bytes), bit 31 for a fullword (4 bytes) and
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bit 63 for a double word (8 bytes) are all the Least Significant Bit (LSB)
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for their respective data formats.
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Level II is recorded using the following data types:
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Unsigned byte (byte) - number ranging from 0-255
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Character (C) - Standard ASCII characters
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Signed Short Integer (I*2) - Most Significant Bit (MSB) is the sign bit
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(bit 0). (1-Negative, 0-Positive).
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Signed Long Integer (I*4) - MSB (bit 0) is the sign bit.
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Single Precision Real (R*4) - MSB (bit 0) is the sign bit (positive),
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bit 1-7 is the exponent in excess-64 notation format, and bit 8-31 is
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the fraction field. An example may be helpful:
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Starting with 4180 69E8 (hex), the sign bit = 0 (positive), the
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exponent = +1 [e.g. 41 (hex) converted to 65 (dec) - 64 (excess 64
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notation) = +1], and the fraction 8069E8 (hex) shifted by exponent of
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+1 gives 8.069E8 (hex). To convert 8.069E8 (hex) to decimal, start with
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the whole number 8 (hex) which in this case equals 8 (dec). Next, the
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precision of the fraction .069E8 must be noted. This fraction has 5
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digits of precision. Next, the fraction portion in hex (069E8) is
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converted to decimal (27112) and divided by 16 raised to the power of
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the precision of the fraction (5). In other words 27112/(16**5) =
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.02585 plus the whole number 8, gives 8.02585 in decimal.
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DATA RECORDS:
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Within the data file, base data and control/response messages are stored
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using a variable record-length structure. The convention here is to begin
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with byte 0 as the first byte. Included as the first record of each data
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file is a volume scan title containing the following information:
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Bytes Format Description
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0-8 C*9 Filename (root) - "ARCHIVE2."
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9-11 C*3 Filename (extension) - "1", "2", etc.
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12-15 I*4 Modified Julian Date referenced from 1/1/70
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16-19 I*4 Time - Milliseconds from midnight (UTC) of the day
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when the file was created.
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20-23 Unused
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All remaining records in the data file are composed of data and
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command/response messages which are initially stored in separate 2432 byte
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packets within an RDA memory buffer. During the archive process the packets
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are copied from memory and grouped together to form a record. Record lengths
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are variable and are always sized in multiples of the 2432 byte packets.
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During the reblocking process, physical records are set to 31616 bytes (2432
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x 13).
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The following example shows a portion of one packet which includes
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Concurrent computer Channel Terminal Manager (CTM) information, a message
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header, and a digital radar data message containing reflectivity only.
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0000 0000 0980 0000 0002 0000 04B8 0001
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0060 1E9E 04B0 1841 0001 0001 0480 14A2
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1E9E 1234 6530 0059 0001 0058 0001 0000
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FE89 03E8 00FA 01CC 0000 0001 4180 69E8
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0064 0000 0000 0000 0015 0000 0000 0000
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0000 0064 0000 0000 0000 FFF4 0064 0000
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0000 0000 0000 0000 0000 0000 0000 0000
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0000 0000 0000 0000 0000 0000 0000 0000
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005A 5A00 0070 6D51 6455 6060 4F54 0040
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5C3F 4049 4900 4D42 4349 434E 4B3D 4430
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4340 3F3D 4644 4443 3A3D 473F 3A3A 3D3D
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3C45 3A43 433C 3E43 413C 393F 3F40 4038
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(etc.)
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Using the above example, each portion of the packet is described in detail.
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Remember, this packet may be one of several contained in one record within
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the data file.
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Bytes 0-11 (halfwords 1-6) Channel Terminal Manager (CTM)
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information:
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0000 0000 0980 0000 0002 0000 04B8 0001
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0060 1E9E 04B0 1841 0001 0001 0480 14A2 Archive II (the data tape) is a
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1E9E 1234 6530 0059 0001 0058 0001 0000 copy of messages or data packets
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FE89 03E8 00FA 01CC 0000 0001 4180 69E8 prepared for transmission from the
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0064 0000 0000 0000 0015 0000 0000 0000 RDA to the RPG. CTM information is
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0000 0064 0000 0000 0000 FFF4 0064 0000 attached to a message or data
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0000 0000 0000 0000 0000 0000 0000 0000 packet for checking data integrity
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0000 0000 0000 0000 0000 0000 0000 0000 during the transmission process
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005A 5A00 0070 6D51 6455 6060 4F54 0040 and is of no importance to the base
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5C3F 4049 4900 4D42 4349 434E 4B3D 4430 data (omit or read past these
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4340 3F3D 4644 4443 3A3D 473F 3A3A 3D3D bytes).
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3C45 3A43 433C 3E43 413C 393F 3F40 4038
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(etc.)
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Bytes 12-27 (halfwords 7-14) Message Header:
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0000 0000 0980 0000 0002 0000 04B8 0001 This information is
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0060 1E9E 04B0 1841 0001 0001 0480 14A2 used to identify
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1E9E 1234 6530 0059 0001 0058 0001 0000 either base data or one of thirteen
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FE89 03E8 00FA 01CC 0000 0001 4180 69E8 types of messages that may follow
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0064 0000 0000 0000 0015 0000 0000 0000 in bytes 28 - 2431. This header
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0000 0064 0000 0000 0000 FFF4 0064 0000 includes the information indicated
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0000 0000 0000 0000 0000 0000 0000 0000 below:
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0000 0000 0000 0000 0000 0000 0000 0000
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005A 5A00 0070 6D51 6455 6060 4F54 0040
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5C3F 4049 4900 4D42 4349 434E 4B3D 4430
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4340 3F3D 4644 4443 3A3D 473F 3A3A 3D3D
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3C45 3A43 433C 3E43 413C 393F 3F40 4038
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(etc.)
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Halfword Format Description
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7 I*2 Message size in halfwords measured from this
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halfword to the end of the record.
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8 I*1 (Left Byte) Channel ID:
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0 = Non-Redundant Site
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1 = Redundant Site Channel 1
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2 = Redundant Site Channel 2
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8 I*1 (Right Byte) Message type, where:
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1 = DIGITAL RADAR DATA (This message
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may contain a combination of either
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reflectivity, aliased velocity, or
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spectrum width)
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2 = RDA STATUS DATA.
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3 = PERFORMANCE/MAINTENANCE DATA.
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4 = CONSOLE MESSAGE - RDA TO RPG.
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5 = MAINTENANCE LOG DATA.
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6 = RDA CONTROL COMMANDS.
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7 = VOLUME COVERAGE PATTERN.
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8 = CLUTTER CENSOR ZONES.
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9 = REQUEST FOR DATA.
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10 = CONSOLE MESSAGE - RPG TO RDA.
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11 = LOOP BACK TEST - RDA TO RPG.
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12 = LOOP BACK TEST - RPG TO RDA.
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13 = CLUTTER FILTER BYPASS MAP - RDA to RPG.
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14 = EDITED CLUTTER FILTER BYPASS MAP - RPG to RDA.
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9 I*2 I.D. Sequence = 0 to 7FFF, then roll over back to 0.
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10 I*2 Modified Julian date starting from 1/1/70.
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11-12 I*4 Generation time of messages in milliseconds of day past
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midnight (UTC). This time may be different than time
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listed in halfwords 15-16 defined below.
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13 I*2 Number of message segments. Messages larger than message
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size (halfword 7 defined above) are segmented and
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recorded in separate data packets.
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14 I*2 Message segment number.
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Bytes 28-127 (halfwords 15-64) Digital Radar Data Header:
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0000 0000 0980 0000 0002 0000 04B8 0001 This information describes the
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0060 1E9E 04B0 1841 0001 0001 0480 14A2 date, time, azimuth,
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1E9E 1234 6530 0059 0001 0058 0001 0000 elevation, and type
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FE89 03E8 00FA 01CC 0000 0001 4180 69E8 of base data included
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0064 0000 0000 0000 0015 0000 0000 0000 in the radial. This
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0000 0064 0000 0000 0000 FFF4 0064 0000 header includes the
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0000 0000 0000 0000 0000 0000 0000 0000 following
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0000 0000 0000 0000 0000 0000 0000 0000 information:
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005A 5A00 0070 6D51 6455 6060 4F54 0040
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5C3F 4049 4900 4D42 4349 434E 4B3D 4430
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4340 3F3D 4644 4443 3A3D 473F 3A3A 3D3D
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3C45 3A43 433C 3E43 413C 393F 3F40 4038
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(etc.)
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Halfword Format Description
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15-16 I*4 Collection time for this radial in
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milliseconds of the day from midnight (UTC).
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17 I*2 Modified Julian date referenced from 1/1/70.
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18 I*2 Unambiguous range (scaled: Value/10. = KM).
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19 I*2 Azimuth angle (coded: [Value/8.]*[180./4096.] = DEG).
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An azimuth of "0 degrees" points to true north while "90
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degrees" points east. Rotation is always clockwise as
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viewed from above the radar.
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20 I*2 Radial number within the elevation scan.
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21 I*2 Radial status where:
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0 = START OF NEW ELEVATION.
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1 = INTERMEDIATE RADIAL.
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2 = END OF ELEVATION.
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3 = BEGINNING OF VOLUME SCAN.
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4 = END OF VOLUME SCAN.
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22 I*2 Elevation angle (coded:[Value/8.]*[180./4096.] = DEG).
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An elevation of "0 degree" is parallel to the pedestal
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base while "90 degrees" is perpendicular to the pedestal
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base.
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23 I*2 RDA elevation number within the volume scan.
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24 I*2 Range to first gate of reflectivity data (METERS).
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Range may be negative to account for system delays
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in transmitter and/or receiver components.
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25 I*2 Range to first gate of Doppler data.
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Doppler data - velocity and spectrum width (METERS).
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Range may be negative to account for system delays in
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transmitter and/or receiver components.
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26 I*2 Reflectivity data gate size (METERS).
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27 I*2 Doppler data gate size (METERS).
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28 I*2 Number of reflectivity gates.
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29 I*2 Number of velocity and/or spectrum width data gates.
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30 I*2 Sector number within cut.
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31-32 R*4 System gain calibration constant (dB biased).
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33 I*2 Reflectivity data pointer (byte # from the start of
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digital radar data message header). This pointer
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locates the beginning of reflectivity data.
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34 I*2 Velocity data pointer (byte # from the start of digital
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radar data message header). This pointer locates
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beginning of velocity data.
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35 I*2 Spectrum-width pointer (byte # from the start of
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digital radar data message header). This pointer
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locates beginning of spectrum-width data.
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36 I*2 Doppler velocity resolution.
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Value of: 2 = 0.5 m/s
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4 = 1.0
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37 I*2 Volume coverage pattern.
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Value of: 11 = 16 elev. scans/ 5 mins.
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21 = 11 elev. scans/ 6 mins.
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31 = 8 elev. scans/ 10 mins.
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32 = 7 elev. scans/ 10 mins.
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38-41 Unused. Reserved for V&V Simulator.
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42 I*2 Reflectivity data pointer for Archive II playback.
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Archive II playback pointer used exclusively by RDA.
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43 I*2 Velocity data pointer for Archive II playback.
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Archive II playback pointer used exclusively by RDA.
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44 I*2 Spectrum-width data pointer for Archive II playback.
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Archive II playback pointer used exclusively by RDA.
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45 I*2 Nyquist velocity (scaled: Value/100. = M/S).
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46 I*2 Atmospheric attenuation factor (scaled:
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[Value/1000. = dB/KM]).
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47 I*2 Threshold parameter for minimum difference in echo
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power between two resolution volumes for them not
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to be labeled range ambiguous (i.e.,overlaid)
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[Value/10. = Watts].
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48-64 Unused.
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Bytes 128-2431 (halfwords 65-1216) Base Data:
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0000 0000 0980 0000 0002 0000 04B8 0001 This information includes the three
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0060 1E9E 04B0 1841 0001 0001 0480 14A2 base data moments; reflectivity,
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1E9E 1234 6530 0059 0001 0058 0001 0000 velocity and spectrum width.
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FE89 03E8 00FA 01CC 0000 0001 4180 69E8 Depending on the collection method,
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0064 0000 0000 0000 0015 0000 0000 0000 up to three base data moments may
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0000 0064 0000 0000 0000 FFF4 0064 0000 exist in this section of the
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0000 0000 0000 0000 0000 0000 0000 0000 packet. (For this example, only
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0000 0000 0000 0000 0000 0000 0000 0000 reflectivity is present.) Base data
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005A 5A00 0070 6D51 6455 6060 4F54 0040 is coded and placed
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5C3F 4049 4900 4D42 4349 434E 4B3D 4430 in a single byte and
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4340 3F3D 4644 4443 3A3D 473F 3A3A 3D3D is archived in the
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3C45 3A43 433C 3E43 413C 393F 3F40 4038 following format:
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(etc.)
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Halfword Format Description
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65-294 BYTE Reflectivity data (0 - 460 gates) (coded:
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[((Value-2)/2.)-32. = dBZ], for Value of 0 or
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1 see note below).
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65-754 BYTE Doppler velocity data (coded: for doppler velocity
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resolution of 0.5 M/S, [((Value-2)/2.)-63.5 = M/S];
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for doppler resolution of 1.0 M/S, [(Value-2)-127.]
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= M/S], for Value of 0 or 1 see note below), (0 - 92
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gates). Starting data location depends on length of
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the reflectivity field, stop location depends on length
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of the velocity field. Velocity data is range unambiguous
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out to 230 KM.
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65-1214 BYTE Doppler spectrum width (coded: [((Value - 2)/2.)-63.5
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= M/S], for Value of 0 or 1 see note below), (0 - 920
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gates). Starting data location depends on length of
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the reflectivity and velocity fields, stop location
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depends on length of the spectrum width field. Spectrum
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width is range unambiguous out to 230 KM.
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Four bytes of trailer characters referred to the Frame
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Check Sequence (FCS) follow the data. In cases where
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the three moments are not all present or the number of
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gates for each moment have been reduced, the record is
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padded out to a constant size of 1216 halfwords (2432
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bytes) following the trailer characters.
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Note:
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Any base data value of 0 is data below Signal to Noise Ratio(SNR) thresholds
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set for that specific base data. Any base data value of 1 is data considered
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range ambiguous (i.e., overlaid).
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----------------------------------------------------------------------------
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[Image] NEXRAD DOCUMENTATION
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----------------------------------------------------------------------------
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http://www.ncdc.noaa.gov/pub/data/nexrad/tapeii.html
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Created by Dick Cram (dcram@ncdc.noaa.gov)
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Last updated 18 April 96
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