CCSD1Z00000100000052CCSD1R00000300000032 DELIMITER=EOF; TYPE=CCSD1F000001; CCSD1C00000400000026 ADI=NURSWI03; SUD=NURSUC03; CCSD1R00000300000032 DELIMITER=EOF; TYPE=CCSD1D000002; Tracking Information - Revision: 1 Rel. Date: 3/13/95 S/W vers: 9 Data vers: 9 Whole Data Set ============== Keyword Value Description ------- ----------------- DataSetName: WINDII data files ------------ DataSource: Upper Atmospheric Research Satellite (UARS), WIND ----------- Imaging Interferometer (WINDII) ScientificContact: Scientific aspects of the data: ------------------ Dr. Gordon Shepherd Department of Earth and Atmospheric Sciences York University 4700 Keele Street North York, Ontario Canada M3J 1P3 email: gordon@windic.yorku.ca Data Generation: Dr. Brian Solheim Centre for Research in Earth and Space Science York University 4700 Keele Street North York, Ontario Canada M3J 1P3 email: brian@windic.yorku.ca SourceCharacteristics: ---------------------- These data were derived from the WINDII instrument which was flown on the UARS spacecraft. The data were processed using the Science Data Production Processing Software (SDPPS) which was run on the Central Data Handling Facility (CDHF) at Goddard Space Flight Center. UARS has catalogued all levels of data product at the CDHF including an instrument log file and an observatory log file. This document describes the level 3 data product. The UARS spacecraft has a nearly circular orbit with an average altitude of 585 kilometers and with an inclination of 57 degrees. The orbit precesses about 5 degrees per day relative to the sun, thus over a period of about 72 days the entire diurnal cycle is sampled. For each day of data, the local solar time is nearly constant for a given latitude. The satellite is yawed through 180 degrees every 36 days, in order to keep the sun on the same side of the spacecraft and protect the cold side instruments. WINDII is located on the cold side of the spacecraft. WINDII makes its measurements along the limb of the atmosphere with two fields of view (FOV) centered at 45 degrees and 135 degrees from the spacecraft velocity vector. Each FOV is 4 degrees (horizontal) by 6 degrees (vertical). The UARS yaw maneuvers dictate the latitudes seen by WINDII. When the spacecraft is flying forward WINDII is looking southward and sees latitudes between 72 degrees south and 45 degrees north. When UARS is flying backwards WINDII is looking northward and sees latitudes between 45 degrees south and 72 degrees north. Thus only the region between 45 degrees south and 45 degrees north is sampled continuously while the high latitudes are sampled on alternating months. InvestigationObjectives: ------------------------ The WINDII instrument measures winds and temperatures in the upper mesosphere and lower thermosphere from observations of the Earth's airglow. Measurements are made both day and night providing global coverage in this region of the atmosphere. These geophysical products may thus be used for further studies of the dynamics of the upper atmosphere and of coupling between the upper and middle atmosphere. InstrumentAttributes: --------------------- WINDII is a field widened Michelson interferometer with an eight position filter wheel to select target emissions. It has a large forward baffle which together with limb pointing mirrors and telescopes define two fixed fields of view. The two FOVs are combined in a field combining prism and are then imaged, side by side, through the Michelson and camera optics onto a charge coupled detector (CCD). One FOV looks forwards at 45 degrees from the satellite velocity vector and one FOV looks backwards at 135 degrees from the velocity vector. Both FOV boresights are inclined 22.1 degrees below the spacecraft nominal horizontal plane. Each FOV is 4 degrees horizontal by 6 degrees vertical. This gives an altitude coverage of 70 to 300 km for each field of view. The horizontal range is 160 km at the limb in each field of view. Due to oblateness of the earth the vertical coverage varies by about 20 km over one orbit. The attitude of the UARS satellite is controlled and the final attitude is known so that the look direction is well known. The CCD has 320 pixels in the horizontal, 160 pixels in each FOV, and 256 pixels in the vertical. This gives a maximum altitude resolution of 1 km. WINDII is allocated a low bit rate of 2000 bits per second, hence the CCD image area must be divided into bins and these bins arranged in windows within each field of view. The airglow emissions measured by WINDII are weak and binning the pixels also improves signal to noise. The binning is done on the CCD and the signal from each bin is converted to a digital value by a 12 bit analog to digital converter. Camera parameters, windowing, exposure time, filter, phase step, are transmitted along with the image data for each image. Engineering data is also sent on a separate 1 Kbit/second channel. Onboard calibration sources are used to monitor the phase of the instrument as part of the normal measurement cycle. These frequent calibrations are taken, along with dark current measurements, every 10 to 15 minutes. A dark current image is taken with the baffle doors closed, all calibration sources turned off and with the same windowing and exposure time as the corresponding atmospheric measurement. Thus the dark current is measured directly in order to track changes in the temperature of the CCD detector. Approximately once a week a full calibration is performed. The data from these infrequent calibrations are analyzed offline in order to look for any changes in the instrument over the course of the UARS mission. When changes are found the Characterization Data Base (CDB) is updated. This CDB is used as input to the SDPPS and is stored as a set of catalogued files at the CDHF. The data files created by the SDPPS contain a reference to the CDB file used. The calibration data is not required to use the level 3 data product but is used primarily in the level 0 to level 1 processing. The normal operating mode of the instrument is to make a measurement of the background followed by an atmospheric emission line measurement. The various measurements are selected by moving a filter wheel which contains 7 interference filters and a blank filter. The sequence of measurements is defined by sequences of filter groups. The filter group is a table which is stored in memory in the instrument which defines the bin size (number of pixels in the vertical and horizontal), the number of bins in a window (number of rows in the vertical and number of columns in the horizontal). The measurement window can be located anywhere in the field of view. The window location is the same in each of the two fields of view and is defined in the filter group by the number of rows of bins from the bottom of the CCD and the number of pixels in the horizontal from the outer edge of the CCD. The calibration source used for this filter is also defined as is dark current calibration. MeasuredParameters: ------------------- Wind, Temperature and Emission rate with global coverage at 2 to 4 km altitude resolution. Altitude range = 70 to 300 km. DataSetQuality: --------------- The data quality is given by the standard deviation of the quantity. Each data element in each file is stored along with a standard deviation which has been calculated by the analysis software. The nominal error is 10 m/s for the wind and 25 K for temperature. DataProcessingOverview: ----------------------- Raw telemetry for 24 hours is processed within 24 hours wall-clock time at the Central Data Handling Facility (CDHF) in production mode. Vector wind and temperature on a standard UARS time/altitude grid or latitude/altitude grid are output. The time grid, L3AT data, corresponds to fixed intervals along the spacecraft track with increments of 65.536 seconds. The latitude grid, L3AL data, goes from -88.0 degrees to +88.0 degrees in 4.0 degree increments. The altitude grid, common to both L3AT and L3AL data for WINDII, is defined as: z(i) = 5*i for 1 <= i <= 12, z(i) = 60 + (i-12)*3 for 13 <= i <= 32, z(i) = 120 + (i-32)*5 for 33 <= i <= 88. Characterization data contained in a data base is used to provide instrument calibration parameters to the production software for level 1 processing. All the algorithms used to process the data are defined in detail in various software design documents, however, these are not needed to understand the WINDII data. The algorithms are set up to operate on measurements in sequence. One atmospheric measurement is composed of a background image and 4 (90 degree phase steps), 8 (45 degree phase steps) or 2*4 (90 degree phase steps for each group of 4 images) phase images. A 2*4 phase image measurement is called a "repeated measurement". Frequent calibration measurements are also processed and used with the corresponding atmospheric measurements. A frequent calibration measurement comprises a dark current image and 4 phase images of one of the onboard calibration lamps. The data processing is divided into three main jobs. The first job reads the raw telemetry files or level 0 data and interprets the data packet headers. The measurements are separated according to the atmospheric line observed and saved in intermediate files. Next the instrument calibration data is used to subtract dark current and to convert the count rate per bin to a line of sight intensity given in rayleighs. Once the known instrument corrections are made effects due to the UARS spacecraft are determined. The orbit attitude data are used to compute the location of the tangent point for each line of sight for each measurement bin. The frequent phase measurements are also processed in the first job step. The level 1 data, catalogued at the end of job step 1, contain the calibrated data and the geo-referencing data. These data are input to job step 2. WINDII views the limb of the airglow and so the intensity measured in each bin is the line of sight integral of the volume emission rate modified by the Michelson interferogram. In the second job step the level 1 bin intensities for each of the 4 or 8 phase steps are used to compute what are termed "apparent quantities". These contain the atmospheric information. The apparent phase is the intensity weighted line integral giving the atmospheric wind. The apparent visibility is the intensity weighted line integral giving the atmospheric temperature. The apparent intensity is the line integral of the volume emission rate. Each measurement is composed of vertical columns of bins. A column gives a vertical scan through the airglow layer. A typical image has 6 columns, each about 25 km wide. In order to reduce the effects of gravity waves on the final wind and temperature these 6 columns are averaged together to form a single vertical profile for each field of view. The apparent intensity is inverted using constrained Twomey inversion to give the volume emission rate profile (see "Introduction to the Mathematics of Inversion in Remote Sensing and Indirect Measurements" by S. Twomey, Development in Geomathematics series, Elsevier, New York, 1977). This is then used to deconvolve the apparent phase and visibility. Finally the wind and temperature profiles are computed from the inverted phase and visibility for each field of view. The last step in the level 2 processing is to combine the line of sight winds from each FOV to form the desired vector winds. This is done by selecting data from the forward FOV which overlaps data from the backward FOV. The zonal and meridional components of the wind are computed only if the two FOVs see the same volume and the volume emission rates and temperatures (both scalar quantities) agree within specified limits. The level 2 data are saved for each measurement with no interpolation. The final job step reads the level 2 data and interpolates from the natural measurement locations to the standard UARS grid. Only the wind and the temperature are gridded and saved in the level 3 data product. A parameter file at level 3 gives the source of the data used to derive the wind and temperature. DataUseage: ----------- The data may be used to provide global synoptic maps of wind and temperature in the upper mesosphere and lower thermosphere. DataOrganization: ----------------- There are 5 file classes : L2-AQ : Contains apparent quantities of wind, temperature and emission rate for both fields of view. L2-FD : Contains deconvoluted quantities of wind, temperature and emission rate. One file for each field of view. L2-CD : Contains wind and temperature derived from combining the 2 fields of view at their common volume of intersection. The vector wind is stored as zonal and meridional components. L2-DS : Contains the Gaussian Fit Parameters and parameters which describe the inversion constraint matrices used in the deconvolution. L3 : Gridded data on time/altitude or latitude/altitude grid. FileClasseRelationShips: ------------------------ L2-CD is derived from the 2 L2-FD files which are derived from L2-AQ. The L2-CD or combined data are used as input to the level 3 gridding. LitReferences: -------------- "UARS CDHF Software System (UCSS) Programmer's Guide to Production Software Support Services", NASA, Goddard Space Flight Center, contract NAS 5-31000, February 1993. "WINDII, the Wind Imaging Interferometer on the Upper Atmosphere Research Satellite", G.G. Shepherd et al., J. Geophys. Res., 98, 10725, (1993) "Validation of O(1S) Wind Measurements by WINDII: the WIND Imaging Interferometer on UARS", W.A. Gault et al., J. Geophys Res., submitted, (1995) File Class ========== Keyword Value ------- ----- FileClassName: L3AT -------------- RecordTypeNames: Label, data. ---------------- Algorithms: ----------- The level 2 combined data, L2CD, provide the input to the level 3 gridding routines. Profiles are linearly interpolated to the time grid points. The altitudes have already been interpolated to the UARS altitude grid in the combine routine which creates L2CD files. Standard UARS fill data is used for missing or invalid data. The fill value of X'00008000' is used since it is a reserved value and not a valid floating point number. FileClassSyntax: ---------------- The file starts with one or more label records. The label is produced automatically by the UCSS routines used to open (OPENL3AT), and write (WRITEL3AT) the file. The label is followed by one or more data records. FileClassFieldRelationships: ---------------------------- Level 2 combined data records are read by the Level 3 processing software and used to produce the Level 3 data records. The results are written out, each measurement type to its own file, using the standard UCSS routine (WRITEL3AT). FileClassMisc: -------------- A Level 3AT data file consists of a collection of profiles of atmospheric data that are indexed by the time values associated with the profiles. The standard values at which 3AT records may be written are from 0 UT to 24 UT every "UARS minute" (65.536 seconds). The following files are created by the WINDII Level 3 data processing in the 3AT format: L3AT_TEMP L3AT_MERID L3AT_ZONAL The naming convention for the subtype is as follows: the first four characters of the subtype represent the data level (3AL or 3AT), this is followed by an underscore, then a four character representation of measurement type (TEMP stands for temperature, MERID for meridional wind and ZONAL for zonal wind). See the UCSS Programmer's Guide to Production Software Support Services for further details about the standard data array. Record ------------------------------------------------------------------------------- RecordName: Label ----------- RecordStructure: ---------------- The record structure is as created by the standard UCSS calls to open and write to this file. See the UCSS Programmer's Guide to Production Software Support Services for details about this record. The structure of the label is the same as for the Generic_Level_3AT_data_format described in the NURSUC03 SFDU metadata file. RecordLength: ------------- See the UCSS Programmer's Guide to Production Software Support Services for details about this record and NURSUC03. RecordFieldNames: ----------------- See the UCSS Programmer's Guide to Production Software Support Services for details about this record and NURSUC03. RecordSyntax: ------------- See the UCSS Programmer's Guide to Production Software Support Services for details about this record and NURSUC03. Record ------------------------------------------------------------------------------- RecordName: Data ----------- RecordStructure: ---------------- Each data record of a Level 3AT file contains a single array of data values for one parameter or species type for a specific time and latitude. The record structure is as created by the standard UCSS calls to open (OPENL3AT) and write (WRITEL3AT) to this file. Records are variable length, but all data records in a single file should be of the same length. The data array is organized according to the rules of the UARS standard data array. (See the UCSS Programmer's Guide to Production Software Support Services for further details.) RecordLength: ------------- Determined by the number of data points in the data structure. Each data record in a file should be of the same length. RecordFieldNames: ----------------- Satellite identifier, record type, instrument identifier, physical record count, spare , total number of points in the record, number of actual points, starting index of the first actual point, record time in UDTF, latitude, longitude, local solar time, solar zenith angle, data values, quality values. RecordSyntax: ------------- Each data record is made up of one of each of the fields above, in the order listed above. Fields ------------------------------------------------------------------------------- --------------------- Field # 01 --------------------- 1.01) FieldName: Satellite identifier 1.02) FieldMnemonic: N/A 1.03) FieldSyntax: ASCII Character*4 string 1.04) FieldUnits: N/A 1.05) FieldResolution: N/A 1.06) FieldRange: Should always hold 'UARS' 1.07) FieldDescription: Holds the identifier for the satellite which produced the data. 1.08) FieldRepresentation: 4A 1.09) FieldDisplayFormat: A4 1.10) FieldFillCode: N/A 1.11) FieldMasks: N/A --------------------- Field # 02 --------------------- 2.01) FieldName: Record type 2.02) FieldMnemonic: N/A 2.03) FieldSyntax: ASCII Character*2 string 2.04) FieldUnits: N/A 2.05) FieldResolution: N/A 2.06) FieldRange: Should always hold ' 3' 2.07) FieldDescription: Identifies the data as type Level 3AL 2.08) FieldRepresentation: 2A 2.09) FieldDisplayFormat: A2 2.10) FieldFillCode: N/A 2.11) FieldMasks: N/A --------------------- Field # 03 --------------------- 3.01) FieldName: Instrument identifier 3.02) FieldMnemonic: N/A 3.03) FieldSyntax: ASCII Character*12 string 3.04) FieldUnits: N/A 3.05) FieldResolution: N/A 3.06) FieldRange: Should always hold 'WINDII ', left justified and blank filled. 3.07) FieldDescription: Holds the identifier for the current instrument 3.08) FieldRepresentation: 12A 3.09) FieldDisplayFormat: A12 3.10) FieldFillCode: N/A 3.11) FieldMasks: N/A --------------------- Field # 04 --------------------- 4.01) FieldName: Physical Record Count 4.02) FieldMnemonic: N/A 4.03) FieldSyntax: ASCII Character*8 string 4.04) FieldUnits: N/A 4.05) FieldResolution: N/A 4.06) FieldRange: Integer >= 2 4.07) FieldDescription: Constant value of ' 1' indicates the label record is the logical first record in the file. Value is right justified and blank filled. Count does not include SFDU label. 4.08) FieldRepresentation: 8A 4.09) FieldDisplayFormat: A8 4.10) FieldFillCode: N/A 4.11) FieldMasks: N/A --------------------- Field # 05 --------------------- 5.01) FieldName: Spare (#1) 5.02) FieldMnemonic: N/A 5.03) FieldSyntax: ASCII Character*2 string 5.04) FieldUnits: N/A 5.05) FieldResolution: N/A 5.06) FieldRange: N/A 5.07) FieldDescription: Spare, constant value X'0000' 5.08) FieldRepresentation: VI2 5.09) FieldDisplayFormat: I2 5.10) FieldFillCode: N/A 5.11) FieldMasks: N/A --------------------- Field # 06 --------------------- 6.01) FieldName: Total number of points in the record 6.02) FieldMnemonic: Max_Points 6.03) FieldSyntax: Scalar 6.04) FieldUnits: N/A 6.05) FieldResolution: N/A 6.06) FieldRange: 1 to 88 where 88 is the maximum number of altitude levels in the standard data array for the altitude grid. 6.07) FieldDescription: Maximum number of altitude levels stored in data and quality arrays for this record. 6.08) FieldRepresentation: VI4 6.09) FieldDisplayFormat: I4 6.10) FieldFillCode: N/A 6.11) FieldMasks: N/A --------------------- Field # 07 --------------------- 7.01) FieldName: Number of actual points in the record 7.02) FieldMnemonic: Num_Points 7.03) FieldSyntax: Scalar 7.04) FieldUnits: N/A 7.05) FieldResolution: N/A 7.06) FieldRange: Integer >= 1, <= 88 7.07) FieldDescription: For WINDII data this is the same as Max_Points 7.08) FieldRepresentation: VI4 7.09) FieldDisplayFormat: I4 7.10) FieldFillCode: N/A 7.11) FieldMasks: N/A --------------------- Field # 08 --------------------- 8.01) FieldName: Starting index of the first actual point 8.02) FieldMnemonic: Start_index 8.03) FieldSyntax: Scalar 8.04) FieldUnits: N/A 8.05) FieldResolution: N/A 8.06) FieldRange: Integer >= 1, <= 88 8.07) FieldDescription: Index in standard data array of starting altitude level. 8.08) FieldRepresentation: VI4 8.09) FieldDisplayFormat: I4 8.10) FieldFillCode: N/A 8.11) FieldMasks: N/A --------------------- Field # 9 --------------------- 9.01) FieldName: Record time in UDTF 9.02) FieldMnemonic: N/A 9.03) FieldSyntax: One dimensional array of length 2 9.04) FieldUnits: First value - years and days, Second value - milliseconds. 9.05) FieldResolution: 1 millisecond 9.06) FieldRange: First value - Years since 1900 (~90 to 100) times 1000 plus 1 to 365, Second value - 0 to 86,400,000 9.07) FieldDescription: Holds the center (average) time for the current data record. The first value is the encoded year and day of the year (92003 being the 3rd day of January, 1992). The second value is the number of milliseconds since the start of the day (midnight). See the UCSS Programmer's Guide to Production Software Support Services for details about this field. 9.08) FieldRepresentation: 2 * VI4 9.09) FieldDisplayFormat: I5, I8 9.10) FieldFillCode: 0, 0 9.11) FieldMasks: N/A --------------------- Field # 10 --------------------- 10.01) FieldName: Latitude 10.02) FieldMnemonic: N/A 10.03) FieldSyntax: Scalar 10.04) FieldUnits: Degrees 10.05) FieldResolution: N/A 10.06) FieldRange: -88 to 88 (values must be multiples of 4) 10.07) FieldDescription: Holds the geodetic latitude for the current data. 10.08) FieldRepresentation: VR4 10.09) FieldDisplayFormat: F6.2 10.10) FieldFillCode: N/A 10.11) FieldMasks: N/A --------------------- Field # 11 --------------------- 11.01) FieldName: Longitude 11.02) FieldMnemonic: N/A 11.03) FieldSyntax: Scalar 11.04) FieldUnits: Degrees 11.05) FieldResolution: N/A 11.06) FieldRange: 0.0 to 360.0 11.07) FieldDescription: Geodetic longitude for the current data. 11.08) FieldRepresentation: VR4 11.09) FieldDisplayFormat: F7.2 11.10) FieldFillCode: N/A 11.11) FieldMasks: N/A --------------------- Field # 12 --------------------- 12.01) FieldName: Local Solar Time 12.02) FieldMnemonic: LST 12.03) FieldSyntax: Scalar 12.04) FieldUnits: hours 12.05) FieldResolution: N/A 12.06) FieldRange: 0.0 to 24.0 12.07) FieldDescription: This field is created by the UCSS WRITEL3AL 12.08) FieldRepresentation: VR4 12.09) FieldDisplayFormat: F6.2 12.10) FieldFillCode: N/A 12.11) FieldMasks: N/A --------------------- Field # 13 --------------------- 13.01) FieldName: Solar Zenith Angle 13.02) FieldMnemonic: SZA 13.03) FieldSyntax: Scalar 13.04) FieldUnits: degrees 13.05) FieldResolution: N/A 13.06) FieldRange: 0.0 to 180.0 13.07) FieldDescription: This field is created by the UCSS WRITEL3AL 13.08) FieldRepresentation: VR4 13.09) FieldDisplayFormat: F6.2 13.10) FieldFillCode: N/A 13.11) FieldMasks: N/A --------------------- Field # 14 --------------------- 14.01) FieldName: Data values 14.02) FieldMnemonic: Data3A 14.03) FieldSyntax: One dimensional array of length Max_points 14.04) FieldUnits: Depends on the type of data being written to the current file. The following lists the file subtypes, the data types stored in those subtypes, and the respective units for this field: L3AT_TEMP Temperature Degrees Kelvin L3AT_MERID Meridional wind Meters per second L3AT_ZONAL Zonal wind Meters per second 14.05) FieldResolution: Approx. 1e-7 times its value (it has the resolution afforded by its VAX FORTRAN storage/representation as a four byte real value). 14.06) FieldRange: Depends on the type of data being written to the current file. The following lists the file subtypes and the respective ranges for this field: L3AT_TEMP nominal 0 to 2000 K L3AT_MERID nominal -200 to +200 m/s L3AT_ZONAL nominal -200 to +200 m/s These are just nominal values and real values could be larger. 14.07) FieldDescription: Holds the Num_points data values for consecutive elements in the UARS standard data array starting at the element index, Start_index. An individual Level 3 file has only one subtype, and holds only one type of data (measurement type or species). See the units description above for the file subtypes and the corresponding measurement types which occur for this field. See the UCSS Programmer's Guide to Production Software Support Services for details about the standard data array and this field. 14.08) FieldRepresentation: Num_points * VR4 14.09) FieldDisplayFormat: E10.2 14.10) FieldFillCode: Invalid Real Number, X'00008000' 14.11) FieldMasks: N/A --------------------- Field # 15 --------------------- 15.01) FieldName: Quality values 15.02) FieldMnemonic: Qual3A 15.03) FieldSyntax: One dimensional array of length Max_points 15.04) FieldUnits: Depends on the type of data being written to the current file. The following lists the file types and the respective units for this field: L3AT_TEMP Temperature (degrees Kelvin) L3AT_MERID Meridional wind (meters per second) L3AT_ZONAL Zonal wind (meters per second) 15.05) FieldResolution: Approx. 1e-7 times its value (it has the resolution afforded by its VAX FORTRAN storage/representation as a four byte real value). 15.06) FieldRange: Depends on the type of data being written to the current file. The following lists the file types and the respective ranges for this field: L3AT_TEMP nominal 0 to 100 K L3AT_MERID nominal 0 to 10 m/s L3AT_ZONAL nominal 0 to 10 m/s These are just nominal values, the real values could be larger. 15.07) FieldDescription: Holds the Num_points quality values for consecutive elements in the UARS standard data array starting at the element index, Start_index. All WINDII Level 3 files use the standard deviation of a measurement as its quality value. See the UCSS Programmer's Guide to Production Software Support Services for details about the standard data array and this field. 15.08) FieldRepresentation: Num_points * VR4 15.09) FieldDisplayFormat: E10.2 15.10) FieldFillCode: Invalid Real Number, X'00008000' 15.11) FieldMasks: N/A FieldName: Specifies the full descriptive name of the field. FieldMnemonic: Specifies the abreviated name of the field used by software supplied to access the file by the orginator of the data. FieldSyntax: Describes the organization and length of the field, e.g. scalar, one-dimensional array, .... FieldUnits: Specifies the units of the data contained in the field. FieldResolution: Specifies the measurement resolution in the above units. Other representations may be used and documented here. FieldRange: The range of reasonable values. Both upper and lower limits should be specified. The limits should pertain to instrumental restrictions, not theoretical expectations. (opt) FieldDescription: Describes the field, including any significant attributes not specifically addressed by any other keyword. FieldRepresentation: Specifies the physical representation of the field within a file. The description must include the length in bits or bytes, the organization of the bits and the allowable operations. An acceptable method of description is to specify the data type, e.g. INTEGER*4, REAL*8. The table at the end of this section defines abreviations which may be used. FieldDisplayFormat: Describes a display format which may be used to view the data, with sufficient significant digits. Descriptions shall be FORTRAN format descriptors. (opt) FieldFillCode: Specifies the data value to be used for missing or invalid data (opt). FieldMasks: Specifies masks used to isolate specific data items with length of less than one byte. (opt) FieldRepresentation Abbreviations Abreviation Meaning VIn VAX two's complement binary integer of n bytes length. UVIn VAX binary integer of n bytes length, to be interpreted as an unsigned quantity. IIn IBM two's complement binary integer of n bytes length. UIn IBM binary integer of n bytes length, to be interpreted as an unsigned quantity. VRn VAX floating point value, n bytes in length. IRn IBM floating point value, n bytes in length. Fn IEEE Standard floating point value, n bytes in length nA string of n ASCII characters. nE string of n EBCDIC characters.