Since VDA format is ascii, its parsing incurs certain overheads. It is not recommended for adoption as am internal format for data analysis software packages. The main use case of VDA format is a distribution of Level-2 data and results of data analysis of a specific VLBI experiment for geodesy and absolute astrometry between various data analysis software packages. Software analysis packages are supposed to be able to transform from the VDA format to their internal format and vice versus without loss of information.
Level 2 VLBI data in the context of this document means results of fringe fitting program in a form of total group delay, total phase delay rate, and the total phase. The datafile in VDA format contains also other variables that describes the VLBI experiment and results of its analysis. In the context of this document as set of data that corresponds that was schduled indepndently is called experiment. Experiment duration varies from 30 minutes to 15 days, althoug durations less than 1 hour and longer than 24 hours are unusual. During an experiment N stations observe M sources. Duration of time when an array or its part observe a given source before slewing to another source is called scan. Data collectated by a pair or stations during scan is called observation.
A valid AVGF file consists of the format label and one or more chunks. Each chunk consists of 5 mandatory sections in the following order:
Sections FILE, PREA, and TOCS describe the data, Section DATA presents the data. The data are considered as a set of four-dimensional arrays of one of the types: CHARACTER*1, INTEGER*2,INTEGER*4, INTEGER*8, REAL*4, REAL*8 and of one of the classes: SES, SCA, STA, BAS. Fortran notation is used for describing arrays: a) dimensions starts from 1; b) the index over first dimension runs first, i.e. elements order is a(i,j), a(i+1,j), a(i+2,j) etc. The dimensions 3 and 4 depend on the class of the data.
Throughout this document the strings that should be present in the VDA file are highlighted. Examples that are not a part of definitions are also highlighted.
For historical reasons an individual array of data is called LCODE. An LCODE defines a 8-character long name, a string or arbitrary length with its description, class, type, and four dimensions. A class determines the scope of the LCODE and dimensions of the high level. Supported classes:
An LCODE can be defined only once. There are five mandatory LCODEs that should be defined at the beginning of the first chunk. The VDA format does not regulate which other LCODEs should be present, in which order, and in which chunk. The order of codes and their allocation in the chunk is selected by the generating software.
VGOSDA Format of 2019.09.09
PREA.1 @section_length: 15 keywords
A preamble section of chunks others than the first has only one mandatory keyword: @section_length. An empty preamble section must have value 0 of this keyword.
The first record of the text section defines the number of chapters. This is a mandatory record. Format: Prefix Keyword Value Unit.
TEXT.1 @section_length: 1 chaptersThe first record of a chapter has 8 mandatory fields followed by the chapter title. Chapter title can be empty. Format: Prefix Keyword1 Value1 Value2 Unit1 Keyword2 Value3 Unit2 [Title]
@@chapter 1 1 records, max_len: 16The following n records have format: TEXT and chunk index separated by dot, one blank and the character string.
TOCS.1 @section_length: 53 lcodesThe following records have format: Prefix LCODE Class Type Dim1 Dim2 Description
TOCS.1 SITNAMES SES C1 8 10 IVS site namesIn this example LCODE SITNAMES is of session type (i.e. with the scope of entire experiment). It has character type and has dimensions 8, 10, 1, 1. The first dimension 8 defines the length of a string. The second dimension 10 defines the number of strings.
There are 5 mandatory keywords that must be defined at the beginning of the first chunk. They all have session class and integer*4 type.
DATA.5 @section_length: 650859 recordsThe following records have format: Prefix LCODE Dim3 Dim4 Dim1 Dim2 Value
DATA.1 GR_DELAY 4466 0 1 1 7.267257847095946D-03 DATA.1 GR_DELAY 4466 0 2 1 7.267232471203255D-03In this example group delay for observation with index 4466 is shown. The group delay was defined as array with dimensions 2,1,4538,1 in the table of contents. The first dimension runs over bands. The first value group delay corresponds to the 1st band and the second to 2nd band. The frequency of bands are determined in another LCODE (REF_FREQ in this case). The VDA itself does not specity the unit of LCODE. Units are supposed to be defined in the LCODE description or in an external document.
CHUN.4 @chunk_size: 72856 records
Splitting an VDA file into chunks is for facilitating an interface with other formats for Level-2 geodetic VLBI results. A valid AVGF file is supposed to have at least one chunk. Splitting data in chunks is determined by the generator process.
Some data are station dependent, for instance cable calibration, some are observation-dependent, for instance group delays. They are stored differently. Array OBS_TAB stored at the LCODE with the same name determines relationship between observation index and the indices of station-dependent parameters. For an observation with index k station-dependent LCODEs will have indices OBS_TAB(2,k) for the 1st (i.e. reference) station of a baseline and OBS_TAB(3,k) for the 2nd (i.e. remote) station of a baseline.
History of LCODE naming is traced in 70s. Renaming LCODEs is discouraged because of a risk of breaking compatibility. Addition of new LCODEs carries a low risk.
TOCS.1 NUMB_OBS SES I4 1 1 Number of observations in the session TOCS.1 NUMB_SCA SES I4 1 1 Number of scans in the session TOCS.1 NUMB_STA SES I4 1 1 Number of sites TOCS.1 NOBS_STA SES I4 10 1 Number of observations per site TOCS.1 OBS_TAB SES I4 3 4538 Observation tables: scan index, indices of the first and the second station TOCS.1 SITNAMES SES C1 8 10 IVS site names TOCS.1 BAND_NAM SES C1 2 1 Band names TOCS.1 CORPLACE SES C1 32 1 Correlator place name TOCS.1 COR_TYPE SES C1 8 1 Correlator type: MK3 MK4 K4 S2 VLBA MITAKA-1 TOCS.1 COR_VERS SES C1 8 1 Correlator software and/or hardware version TOCS.1 DEL_RATE BAS R8 2 1 Phase delay rates per band (d/l) TOCS.1 EXP_CODE SES C1 32 1 Experiment code TOCS.1 EXP_DESC SES C1 80 1 Experiment description TOCS.1 EXP_NAME SES C1 80 1 Experiment program name TOCS.1 GDAMBSP BAS R8 2 1 Group delay ambiguity spacings per band (sec) TOCS.1 GRDELERR BAS R8 2 1 Group delay errors per band (sec) TOCS.1 GRRATERR BAS R8 2 1 Group delay rate errors per band (d/l) TOCS.1 GR_DELAY BAS R8 2 1 Group delays per band (sec) TOCS.1 GR_RATE BAS R8 2 1 Group delays rate per band (d/l) TOCS.1 ION_GDEL BAS R8 1 1 Ionospheric contribution to group delay at the first band (sec) TOCS.1 ION_GERR BAS R8 1 1 Uncertainty of ionospheric contribution to group delay at the first band (sec) TOCS.1 ION_PRAT BAS R8 1 1 Ionospheric contribution to phase delay rate at the first band (sec) TOCS.1 ION_RERR BAS R8 1 1 Uncertainty of ionospheric contribution to phase delay rate at the 1st band (d/l TOCS.1 MJD_OBS SCA I4 1 1 MJD of fringe reference time at pseudo-UTC timecale for the scan (days) TOCS.1 NUMB_SOU SES I4 1 1 Number of observed sources TOCS.1 NUM_BAND SES I4 1 1 Number of frequency bands observed in the experiment TOCS.1 NUM_CHAN SES I4 1 1 Number of frequency channels at all bands TOCS.1 NUM_CHBN SES I4 1 2 Number of frequency channels per band TOCS.1 N_AVBAND SES I4 1 1 Number of frequency bands for which information is availble TOCS.1 PHDELERR BAS R8 2 1 Phase delay error (rad) TOCS.1 PHRATERR BAS R8 2 1 Phase delay rate delay errors per band (d/l) TOCS.1 PI_NAME SES C1 80 1 Name of the principal investigator TOCS.1 QUALCODE BAS C1 2 2 Quality code as char*2 value: 5-9 is good, 0 -- non-detection, letter -- failure TOCS.1 REC_MODE SES C1 80 1 Recording mode TOCS.1 REF_FREQ BAS R8 2 1 Reference frequency for phase delay per band (Hz) TOCS.1 SBDELERR BAS R8 2 1 Single-band delay errors per band (sec) TOCS.1 SB_DELAY BAS R8 2 1 Single-band delays per band (sec) TOCS.1 SCANNAME SCA C1 16 1 Scan name TOCS.1 SCANPIMA SCA C1 10 1 Pima internal scan name TOCS.1 SIT_COOR SES R8 3 10 Site coordinates in a crust-fixed terrestrial reference system: X, Y, Z (meters) TOCS.1 SKYFRQCH SES R8 16 1 Sky frequency of channels in Hz TOCS.1 SNRATIO BAS R8 2 1 Fringe amplitude signal to noise ratio (d/l) TOCS.1 SOU_COOR SES R8 2 68 Source coordinates in a baricenteric reference system: right asc. decl. (rad) TOCS.1 SOU_IND SCA I4 1 1 Source name index TOCS.1 SRCNAMES SES C1 8 68 Source names TOCS.1 STA_IND BAS I4 2 1 Station names indexes TOCS.1 TOTPHASE BAS R8 2 1 Total fringe phases at time of arrival singal at station 1 per band (rad) TOCS.1 UTC_MTAI SES R8 1 1 Difference UTC minus TAI at first time tag of the database (sec) TOCS.1 UTC_OBS SCA R8 1 1 Pseudo-UTC time tag of fringe reference time for the scan (sec) TOCS.2 ANT_GAIN STA R4 2 1 Antenna gain per band K/Jy TOCS.2 APRCLOOF STA R8 1 1 Apriori clock offset used for correlation TOCS.2 APRCLORT STA R8 1 1 Apriori clock rate used for correlation TOCS.2 APR_DEL BAS R8 2 1 Apriori delay (sec) TOCS.2 APR_PHAS BAS R8 2 1 Apriori fringe phase (rad) TOCS.2 APR_PHGC BAS R8 2 2 Apriori fringe phase per station at the geocenter (rad) TOCS.2 APR_RATE BAS R8 2 1 Apriori delay rate (d/l) TOCS.2 BITSAMPL SES I2 1 1 Number of bits per sample TOCS.2 CHAN_SDB SES I2 16 1 Index of lower (-1) or upper (1) sideband per channel TOCS.2 CHAN_WDT SES R8 16 1 Frequency channel width in Hz per channel TOCS.2 DELW_CEN BAS R8 2 1 Delay window center used for fringe search (sec) TOCS.2 DELW_WDT BAS R8 2 1 Delay window width used for fringe search (sec) TOCS.2 FRN_AMPL BAS R8 2 1 Normalzied fringe amplitude in range [0, 1] TOCS.2 FRT_OFFS SCA R8 2 1 Fringe refrenence time offset relative to the scan start (sec) TOCS.2 GCRESPHS BAS R8 2 1 Residual fringe phase at time of arrival singal at geocenter (rad) TOCS.2 GC_PHASE BAS R8 2 1 Fringe phase at time of arrival singal at the conventionalgeocenter (rad) TOCS.2 IND_CHN1 BAS I2 10 1 Indexes of channels used in bandwidth synthesis in band 1 TOCS.2 IND_CHN2 BAS I2 6 1 Indexes of channels used in bandwidth synthesis in band 2 TOCS.2 NOISERMS BAS R4 2 1 RMS of the fringe amplitude noise (d/l) TOCS.2 NUM_AP1 BAS I2 10 2 Number of accumulation periods used in band 1 per channel per sideband TOCS.2 NUM_AP2 BAS I2 6 2 Number of accumulation periods used in band 2 per channel per sideband TOCS.2 NUM_SAM1 BAS R8 10 1 Number of samples used in bandwidth synth. in band 1 per freq. chan and sideband TOCS.2 NUM_SAM2 BAS R8 6 2 Number of samples used in bandwidth synth. in band 2 per freq. chan and sideband TOCS.2 NUSEDCHN BAS I2 2 1 Number of channels used in bandwidth synthesis per band TOCS.2 PCAL_CM1 STA R4 2 10 Complex phase cal (real/image) per channel at the 1st band TOCS.2 PCAL_CM2 STA R4 2 6 Complex phase cal (real/image) per channel at the 2nd band TOCS.2 PCAL_FR1 STA R8 1 10 Phase cal frequency per channel at the 1st band TOCS.2 PCAL_FR2 STA R8 1 6 Phase cal frequency per channel at the 2nd band TOCS.2 POLARIZ BAS C1 2 2 Polarization label: RR, RL, LR, or LL TOCS.2 RATE_CEN BAS R8 2 1 Rate window center used for fringe search (d/l) TOCS.2 RATE_WDT BAS R8 2 1 Rate window width used for fringe search (d/l) TOCS.2 RESGRRAT BAS R8 2 1 Residual group delay rate (d/l) TOCS.2 RESMBDEL BAS R8 2 1 Residual multiband group delay (sec) TOCS.2 RESPHAS BAS R8 2 1 Residual fringe phase TOCS.2 RESPHRAT BAS R8 2 1 Residual phase delay rate (d/l) TOCS.2 RESSBDEL BAS R8 2 1 Residual singleband group delay (sec) TOCS.2 RES_GRDL BAS R8 2 1 Residual group delay reported by the post-correlator software (sec) TOCS.2 RES_PHGC BAS R8 2 1 Resodual fringe phase per station at the geocenter (rad) TOCS.2 RES_RATE BAS R8 2 1 Apriori phase delay rate reported by the post-correlator software (d/l) TOCS.2 SAMPLRAT SES R8 1 1 Sample rate in Hz TOCS.2 SCAN_DUR BAS R8 2 1 Scan duration per band (sec) TOCS.2 SPCH_WDT SES R8 16 1 Spectral channel width in Hz per channel TOCS.2 TSYS1 STA R4 1 10 System temperature per channel at the 1st band (K) TOCS.2 TSYS2 STA R4 1 6 System temperature per channel at the 2nd band (K) TOCS.2 UVSTAORD BAS I2 1 1 Original station order in the baseline: 1 (ascending) or -1 (descending) TOCS.2 UV_CHN1 BAS R4 2 10 UV data: real and image part per channel at the 1st band (d/l) TOCS.2 UV_CHN2 BAS R4 2 6 UV data: real and image part per channel at the 2nd band (d/l) TOCS.3 AIR_TEMP STA R8 1 1 Air temperature at the station (K) TOCS.3 ATM_PRES STA R8 1 1 Atmospheric pressure at the station (Pa) TOCS.3 CABL_DEL STA R8 1 1 Cable delay (sec) TOCS.3 CABL_SGN SES I2 10 1 Cable sign: +1 or -1 TOCS.3 CAL_INFO SES I4 4 1 Information about class and type of available calibrations TOCS.3 CAL_NAME SES C1 8 1 Name of available calibrations TOCS.3 MEANCABL SES R8 10 1 Mean cable delay (sec) TOCS.3 N_CALIB SES I2 1 1 Number of available calibrations TOCS.3 REL_HUMD STA R8 1 1 Relative humidity at the station (0-1)
TOCS.1 EXPSERNO SES I2 1 1 Experiment serial number at correlator TOCS.1 MK3_DBNM SES C1 10 1 Mark-3 DBH database name TOCS.1 PIMA_CNT SES C1 128 1 Full path name of pima control file TOCS.1 PIMA_VER SES C1 24 1 Version of PIMA software TOCS.2 PIND_OBS BAS I4 1 1 Internal index of observation used by PIMA TOCS.2 SRT_OFFS SCA R8 1 1 Scan refrenence time offset relative to the scan start (sec) TOCS.4 ATM_CNS SES R8 10 32 Reciprocal weights of constraints on atm. path delay rate per station, soltype TOCS.4 ATM_INTR SES R8 32 1 Lenght of time span between spline nodes for atm. path delay per soltyp (sec) TOCS.4 AUTO_SUP BAS I4 1 1 Bit field of automatic suppression status for combination of observables TOCS.4 BAND_2ND BAS I2 1 1 Bit field with status of information about the second band observations TOCS.4 BAS_USE SES I4 45 1 Bit field of baseline selection status TOCS.4 BSCL_CNS SES R8 45 32 Reciprocal weights of constraints on basdep. clock, per baseline, per soltype TOCS.4 BSCL_EST SES I4 45 1 Estimation status for baseline depedent clock, per baseline TOCS.4 CAL_STS SES I4 10 1 Bit field of using available calibrations per station, per calibration TOCS.4 CLO_CNS SES R8 10 32 Reciprocal weights of constraints on clock rate per station, per solution type TOCS.4 CLO_INTR SES R8 32 1 Lenght of time span between spline nodes for clock function per soltyp (sec) TOCS.4 DATYP SES I2 1 1 Type of the observable or a combination of observables used in the solution TOCS.4 DGCL_EST SES I2 10 32 Degree of global clock function polynomial per station, per solution type TOCS.4 EDIT_STS SES I4 1 1 Bit field of database editing status for different types of solutions TOCS.4 EFF_FREQ BAS R8 3 2 Effective ionospheric frequencies for gr.del, ph.del, ph.rate per band (Hz) TOCS.4 EOP_CNS SES R8 11 32 Reciprocal weights of constraints on EOP related parameters TOCS.4 EOP_EST SES I4 11 1 Estimation status for EOP-related parameters TOCS.4 NUM_CLBR SES I4 1 1 Number of clock breaks in the experiment TOCS.4 NUM_CLRF SES I4 1 1 Number of clock reference stations TOCS.4 N_GRAMB BAS I4 2 1 Number of group delay ambiguities to be added to measured group delays per band TOCS.4 N_PHAMB BAS I4 2 1 Number of phase delay ambiguities to be added to measured phase delays per band TOCS.4 RWBASNAM SES C1 16 45 Baseline names for additive baseline-dependent reweighting parameters TOCS.4 RWDELVAL SES R8 32 45 Additive baseline-dependent reweighting parameters for delays (sec) TOCS.4 RWRATVAL SES R8 32 45 Additive baseline-dependent reweighting parameters for delay rates (d/l) TOCS.4 SOCO_CNS SES R8 68 32 Reciprocal weights of constraints on source coordinates per object, per soltype TOCS.4 SOCO_EST SES I4 2 68 Estimation status for source coordinats per component, per object TOCS.4 SOU_USE SES I4 68 1 Bit field of source selection status TOCS.4 STA_CLRF SES C1 8 1 Names of clock reference stations TOCS.4 STA_USE SES I4 10 1 Bit field of station selection status TOCS.4 STPS_CNS SES R8 10 32 Reciprocal weights of constraints on site positions per site, per solution type TOCS.4 STPS_EST SES I4 3 10 Estimation status for station positions per component, per station TOCS.4 SUPMET SES I2 1 1 Code of the suppression method used in the solution TOCS.4 TEC_STS SES I4 10 1 Flag of availability/usage of the external ionosphere calibration TOCS.4 TIL_INTR SES R8 32 1 Lenght of time span between spline nodes for atmospphere tilt per soltyp (sec) TOCS.4 TLOF_CNS SES R8 10 32 Reciprocal weights of constraints on atm. tilt offset per station, per soltype TOCS.4 TLRT_CNS SES R8 10 32 Reciprocal weights of constraints on atm. tilt rate per station, per soltype TOCS.4 USER_REC BAS I4 1 1 Bit field of analyst defined recovery status for combination of observables TOCS.4 USER_SUP BAS I4 1 1 Bit field of analyst defined suppression status for combination of observables TOCS.5 APR_EOP BAS R8 3 2 Aprori EOP array as Euler angles and its derivatives (rad) TOCS.5 AZIMUTH STA R8 1 1 Apparent source azimuth at both stations of the baseline (rad) TOCS.5 DER_DEL BAS R8 64 1 Array of partial derivatives of theoretical path delay wrt parameters of the mod TOCS.5 DER_RAT BAS R8 64 1 Array of partial derivatives of theoretical delay rate wrt parameters of the mod TOCS.5 ELEV STA R8 1 1 Apparent source elevation at both stations of the baseline (rad) TOCS.5 EOP_TAB SES R8 15 3 Table of aprori EOP as Euler angles with frequencies > 2 cpd filtered out TOCS.5 MJD_EOP SES I4 1 1 Modified Julian date of the first epoch for the table of apriori EOP TOCS.5 NUT_DER BAS R8 2 1 Partial derivatives wth nutation deaily offset parameters (sec) TOCS.5 N_APREOP SES I4 1 1 Number of nodes with apriori EOP TOCS.5 STEP_EOP SES I4 1 1 Step of the EOP table of apriori EOP (sec) TOCS.5 TAI_EOP SES I4 1 1 TAI time tag of first epoch of the table of apriori EOP (sec) TOCS.5 THGR_DEL BAS R8 1 1 Theoretical group delay (sec) TOCS.5 THPH_DEL BAS R8 1 1 Theoretical phase delay (sec) TOCS.5 THPH_RAT BAS R8 1 1 Theoretical phase delay date (d/l) TOCS.5 TH_PROG SES C1 64 1 Name and version of the program which computed theoretical path delays TOCS.5 TH_RUDAT SES C1 24 1 Date and time of theoretical delay compuation TOCS.5 UV_COOR BAS R8 2 1 UV coordinates of the baseline vector projectioncalibration