MeasurementSet definition version 3.0β

MS v3.0 working group:
Dijkema T.J., Golap K., Hiriart R., Nakazato T., Pokorny M., Pouzols F., Raba,R., van Diepen G.

July, 2019

A pdf version of this note is available.

Contents

1 Introduction
2 Summary of changes
 2.1 MAIN table
 2.2 ARRAY table
 2.3 FIELD table
  2.3.1 Direction information
 2.4 FLAG_CMD
 2.5 OBSERVATION table
 2.6 SOURCE table
 2.7 SPECTRAL_WINDOW table
3 New sub-tables
  3.0.1 BEAM subtable
  3.0.2 EPHEMERIDES
 3.1 INTERFEROMETER_MODEL
  3.1.1 Multi element station based antenna (PHASED_ARRAY subtable)
  3.1.2 SCAN subtable
  3.1.3 Associated tables (CAL_TABLES)
4 MS v3.0 layout
 4.1 MAIN table: Data, coordinates and flags
 4.2 MAIN table: continued
 4.3 ANTENNA: Antenna characteristics
 4.4 BEAM: Beam information
 4.5 CORRELATOR_TYPE: Doppler tracking information
 4.6 DOPPLER: Doppler tracking information
 4.7 EPHEMERIDES: Ephemerides information
 4.8 FEED: Feed characteristics
 4.9 FIELD: Field positions for each source
 4.10 FLAG_CMD: Flag commands
 4.11 FREQ_OFFSET: Frequency offset information
 4.12 HISTORY: History information
 4.13 INTERFEROMETER_MODEL: VLBI Interferometer information
 4.14 OBSERVATION: Observation information
 4.15 PHASED_ARRAY: phased array station information
 4.16 POINTING: Antenna pointing information
 4.17 POLARIZATION: Polarization setup information
 4.18 PROCESSOR: Processor information
 4.19 SCAN: Scan information
 4.20 SOURCE: Source information
 4.21 SPECTRAL_WINDOW: Spectral window description
 4.22 STATE: State information
 4.23 SYSCAL: System calibration
 4.24 WEATHER: weather station information
5 Units and Measures
 5.1 Units and Measures
6 References

1 Introduction

The MeasurementSet (MS) defines a format in which interferometer visibilities and single-dish data are stored. It is implemented in software packages using casa/casacore code. Version 2.0 (Note 229; Kemball and Wieringa 2000) of the MeasurementSet has been in use since 2000 in different packages and at different telescopes. This revision is to correct or help in common usages by adding missing data that was felt needed for data reduction. In V2.0 we feel that sometimes schema structure was defined to help with efficiency issues that was forseen (e.g definition of a FLOAT_DATA column for single dish). In this revision we try to not do that. We realize that a given data structure can be implemented in different ways in software to achieve maximum efficiency or speed. This is the reason why we have tried to keep the information redundancy to a minimum and focussed on completeness(although we may attach an addendum in the future, to this document, to describe implementation choices especially with regards to IO rates and large data issues) .

The changes are not backward compatible; so converters will be needed between v2.0 and v3.0 and vice versa. Some of the changes are to help common needs and complaints like column versioning (removing the need of CORRECTED_DATA or FLAG_VERSION) others are expansion for VLBI and non-dish arrays (e.g LOFAR).

Here are some of the major changes from MS V2.0 to MS V3.0:

Some features and reasons for some changes made and not made:

2 Summary of changes

This section contains a description of the changes proposed for each table in the MS definition. A full definition of the v3.0 MS format is given in Section 5.

All the subtables not mentioned here will have an explicit ID column; in v3.0 implicit row number being an ID is no longer valid. For example ANTENNA subtable will have a ANTENNA_ID column added as a key.

2.1 MAIN table

2.2 ARRAY table

2.3 FIELD table

Changes applicable to the FIELD table are discussed in this section.

An explicit FIELD_ID

2.3.1 Direction information

The PHASE_DIR information is to be derived from the ephemeris subtable if the EPHEMERIS_ID is not -1.

A new column optional DURATION column is added; when present in combination with TIME (time origin) it defines the time range for when the information for direction for a given FIELD_ID. In this fashion step function phasecentering that happens in some correlators

2.4 FLAG_CMD

FLAG_CMD table is made an optional subtable.

2.5 OBSERVATION table

Apart from the explicit OBSERVATION_ID column version 3.0 adds the ARRAY_CENTER: A new column which will give the full Measures position of where the array center is assumed for each ARRAY_ID

2.6 SOURCE table

The SOURCE table already had a SOURCE_ID column. In this version it it proposed to generalize the SOURCE_MODEL. Apart from a TableRecord it can take a URL which will point to catalogue style source list or even images representing the model associated with a SOURCE_ID and SPECTRAL_WINDOW_ID.

2.7 SPECTRAL_WINDOW table

Apart from the explicit SPECTRAL_WINDOW_ID column; an optional column LO_FREQUENCY which (can be vector of frequencies) gives the Local Oscillator frequencies in the chain of frequency conversion.

3 New sub-tables

New sub-tables added to MS v3.0 are included in this Section.

3.0.1 BEAM subtable

This table was proposed in v2.0 but we explicitly define it here. It is referenced from the FEED table or from the newly proposed PHASED_ARRAY table here.

3.0.2 EPHEMERIDES

This optional table is explicitly defined and is referred to from the FIELD table via the EPHEMERIS_ID column.

3.1 INTERFEROMETER_MODEL

This optional subtable contains information necessary for VLBI arrays

3.1.1 Multi element station based antenna (PHASED_ARRAY subtable)

Information about elements that makes a station antenna, combination scheme etc

3.1.2 SCAN subtable

This will carry the information about the scan intent and information necessary to tie back information from the online system

3.1.3 Associated tables (CAL_TABLES)

A lot of data processing or online correction information are carried as non standard subtables. The formal existance of calibration tables associated with a given MS will satisfy the needs of many of the non-standard subtables.

4 MS v3.0 layout

There is a MAIN table containing a number of data columns and keys into various subtables. There is at most one of each subtable. The subtables are stored as keywords of the MS, and all defined sub-tables are tabulated below. Optional sub-tables are shown in italics.




Subtables



Table
Contents
Keys



ANTENNA

Antenna characteristics

ANTENNA_ID

BEAM

Beam information

BEAM_ID

(DOPPLER)

Doppler tracking

DOPPLER_ID, SOURCE_ID

(EPHEMERIDES)

Ephemeris information for near field objects

EPHEMERIS_ID, TIME

FEED

Feed characteristics

FEED_ID, ANTENNA_ID, TIME, SPECTRAL_WINDOW_ID

FIELD

Field position

FIELD_ID

(FLAG_CMD)

Flag commands

TIME

(FREQ_OFFSET)

Frequency offset information

FEED_ID, ANTENNAn, FEED_ID, TIME, SPECTRAL_WINDOW_ID

HISTORY

History information

OBSERVATION_ID, TIME

(INTERFEROMETER_MODEL)

Information for VLBI observations

ANTENNA_ID, FIELD_ID, SPECTRAL_WINDOW_ID, TIME

OBSERVATION

Observer, Schedule, etc

OBSERVATION_ID

(PHASED_ARRAY)

phased array stations information

PHASED_ARRAY_ID, ANTENNA_ID

POINTING

Pointing information

ANTENNA_ID, TIME

POLARIZATION

Polarization setup

POLARIZATION_ID

PROCESSOR

Processor information

PROCESSOR_ID

(QUALITY_FREQUENCY_STATISTIC)

Frequency related statistics

Frequency

(QUALITY_BASELINE_STATISTIC)

Baseline related statistics

ANTENNA1, ANTENNA2, Frequency

(QUALITY_TIME_STATISTIC)

Time related statistics

TIME, Frequency

SCAN

scan information

SCAN_NUMBER

(SOURCE)

Source information

SOURCE_ID, SPECTRAL_WINDOW_ID, TIME

SPECTRAL_WINDOW

Spectral window setups

SPECTRAL_WINDOW_ID

STATE

State information

STATE_ID

(SYSCAL)

System calibration characteristics

FEED_ID, ANTENNA_ID, TIME, SPECTRAL_WINDOW_ID

(WEATHER)

Weather info for each antenna

ANTENNA_ID, TIME




Note that all optional columns are indicated in italics and in parentheses.

4.1 MAIN table: Data, coordinates and flags






MAIN table: Data, coordinates and flags





Name
Format
Units
Measure
Comments










Columns










Keywords





MS_VERSION

Float

MS format version






Key





TIME

Double

s

EPOCH

Integration midpoint

(TIME_EXTRA_PREC)

Double

s

extraTIME precision

ANTENNA1

Int

First antenna

ANTENNA2

Int

Second antenna

(ANTENNA3)

Int

Third antenna

FEED1

Int

Feed on ANTENNA1

FEED2

Int

Feed on ANTENNA2

(FEED3)

Int

Feed on ANTENNA3

SPECTRAL_WINDOW_ID

Int

Spectral window id.

POLARIZATION_ID

Int

polarization id.

PROCESSOR_ID

Int

Processor id.

(PHASE_ID)

Int

Phase id.

FIELD_ID

Int

Field id.






Non-key attributes





INTERVAL

Double

s

Sampling interval

EXPOSURE

Double

s

The effective integration time

TIME_CENTROID

Double

s

EPOCH

Time centroid

(PULSAR_BIN)

Int

Pulsar bin number

(PULSAR_GATE_ID)

Int

Pulsar gate id.

SCAN_NUMBER

Int

Scan number

ARRAY_ID

Int

Subarray number

OBSERVATION_ID

Int

Observation id.

STATE_ID

Int

State id.

(BASELINE_REF)

Bool

Reference antenna

UVW

Double(3)

m

UVW

UVW coordinates

(UVW2)

Double(3)

m

UVW

UVW (baseline 2)






4.2 MAIN table: continued






MAIN table: continued





Name
Format
Units
Measure
Comments










Data





(DATA)

Complex(Nc, Nf)

Complex visibility matrix (synthesis arrays)

(VIDEO_POINT)

Complex(Nc)

Video point

(LAG_DATA)

Complex(Nc, Nl)

Correlation function

WEIGHT

Float(Nc, N f )

Weight for each channel






Flag information





FLAG

Bool(Nc, N f )

Cumulative data flags






Notes:
Note that Nl= number of lags, Nc= number of correlators, Nf= number of frequency channels, and Ncat= number of flag categories.
MS_VERSION
The MeasurementSet format revision number, expressed as major_revision.minor_revision. This version is 2.0.
SORT_ORDER
Sort order as either ”ASCENDING” or ”DESCENDING”.
TIME
Mid-point (not centroid) of data interval.
TIME_EXTRA_PREC
Extra time precision.
ANTENNAn
Antenna number ( 0), and a direct key index into the ANTENNA sub-table. For n > 2, triple-product data are implied.
FEEDn
Feed number ( 0). For n > 2, triple-product data are implied.
SPECTRAL_WINDOW_ID
Spectral window identifier ( 0), and a direct key index into the SPECTRAL_WINDOW sub-table.
POLARIZATION_ID
Polarization identifier ( 0), and a direct key index into the POLARIZATION sub-table.
PROCESSOR_ID
Processor indentifier ( 0), and a direct key index into the PROCESSOR sub-table.
PHASE_ID
Switching phase identifier ( 0)
FIELD_ID
Field identifier ( 0) a direct key index into the FIELD sub-table.
INTERVAL
Data sampling interval. This is the nominal data interval and does not include the effects of bad data or partial integration.
EXPOSURE
Effective data interval, including bad data and partial averaging.
PULSAR_BIN
Pulsar bin number for the data record. Pulsar data may be measured for a limited number of pulse phase bins. The pulse phase bins are described in the PULSAR sub-table and indexed by this bin number.
PULSAR_GATE_ID
Pulsar gate identifier ( 0), and a direct index into the PULSAR_GATE sub-table rownr.
SCAN_NUMBER
Arbitrary scan number to identify data taken in the same logical scan. Not required to be unique; ( 0) a direct key index into the SCAN sub-table.
ARRAY_ID
Subarray identifier ( 0), which identifies data in separate subarrays, as defined in Section 3.3.
OBSERVATION_ID
Observation identifier ( 0), which identifies data from separate observations, as defined in Section 3.3.
STATE_ID
State identifier ( 0), as defined in Section 3.1.5.
BASELINE_REF
Flag to indicate the original correlator reference antenna for baseline-based correlators (True for ANTENNA1; False for ANTENNA2).
UVW
uvw coordinates for the baseline from ANTENNE2 to ANTENNA1, i.e. the baseline is equal to the difference POSITION2 - POSITION1. The UVW given are for the TIME_CENTROID, and correspond in general to the reference type for the PHASE_DIR of the relevant field. I.e. J2000 if the phase reference direction is given in J2000 coordinates. However, any known reference is valid. Note that the choice of baseline direction and UVW definition (W towards source direction; V in plane through source and system’s pole; U in direction of increasing longitude coordinate) also determines the sign of the phase of the recorded data.
UVW2
uvw coordinates for the baseline from ANTENNE3 to ANTENNA1 (triple-product data only), i.e. the baseline is equal to the difference POSITION3 - POSITION1. The UVW given are for the TIME_CENTROID, and correspond in general to the reference type for the PHASE_DIR of the relevant field. I.e. J2000 if the phase reference direction is given in J2000 coordinates. However, any known reference is valid. Note that the choice of baseline direction and UVW definition (W towards source direction; V in plane through source and system’s pole; U in direction of increasing longitude coordinate) also determines the sign of the phase of the recorded data.
DATA, LAG_DATA
At least one of these columns should be present in a given MeasurementSet. In special cases one or more could be present (e.g., single dish data used in synthesis imaging or a mix of auto and crosscorrelations on a multi-feed single dish). If only correlation functions are stored in the MS, then N f  is the maximum number of lags (Nl) specified in the LAG table for this LAG_ID. If both correlation functions and frequency spectra are stored in the same MS, then N f  is the number of frequency channels, and the weight information refers to the frequency spectra only. The units for these columns (eg. ’Jy’) specify whether the data are in flux density units or correlation coefficients.
VIDEO_POINT
The video point for the spectrum, to allow the full reverse transform.
WEIGHT
The weight for each channel, with the same shape as DATA, as assigned by the correlator or processor.
FLAG
An array of Boolean values with the same shape as DATA (see the DATA item above) representing the cumulative flags applying to this data matrix. Data are flagged bad if the FLAG array element is True.

4.3 ANTENNA: Antenna characteristics






ANTENNA: Antenna characteristics





Name
Format
Units
Measure
Comments










Columns










Keys





ANTENNA_ID

Int

unique antenna id






Data





NAME

String

Antenna name

STATION

String

Station name

TYPE

String

Antenna type

MOUNT

String

Mount type:alt-az, equatorial, X-Y, nasmyth, coude, orbiting, bizarre

POSITION

Double(3)

m

POSITION

Antenna X,Y,Z phase reference positions

OFFSET

Double(3)

m

POSITION

Axes offset of mount to FEED REFERENCE point

DISH_DIAMETER

Double

m

Diameter of dish

(ORBIT_ID)

Int

Orbit id.

(MEAN_ORBIT)

Double(6)

Mean Keplerian elements

(PHASED_ARRAY_ID)

Int

Phased array id.






Notes:
This sub-table contains the global antenna properties for each antenna in the MS. It is indexed directly from MAIN via ANTENNAn.
ANTENNA_ID
ID of the antenna.
NAME
Antenna name (e.g. ”NRAO_140”)
STATION
Station name (e.g. ”GREENBANK”)
TYPE
Antenna type. Reserved keywords include: (”GROUND-BASED” - conventional antennas; ”SPACE-BASED” - orbiting antennas; ”TRACKING-STN” - tracking stations).
MOUNT
Mount type of the antenna. Reserved keywords include: (”EQUATORIAL” - equatorial mount; ”ALT-AZ” - azimuth-elevation mount; ”X-Y” - x-y mount; ”SPACE-HALCA” - specific orientation model.)
POSITION
In a right-handed frame, X towards the intersection of the equator and the Greenwich meridian, Z towards the pole. The exact frame should be specified in the MEASURE_REFERENCE keyword (ITRF or WGS84). The reference point is the point on the az or ha axis closest to the el or dec axis.
OFFSET
Axes offset of mount to feed reference point.
DISH_DIAMETER
Nominal diameter of dish, as opposed to the effective diameter.
ORBIT_ID
Orbit identifier. Index used in ORBIT sub-table if ANTENNA_TYPE is ”SPACE_BASED”.
MEAN_ORBIT
Mean Keplerian orbital elements, using the standard convention (Flatters 1998):
PHASED_ARRAY_ID
Phased array identifier. Points to a PHASED_ARRAY sub-table which points back to multiple entries in the ANTENNA sub-table and contains information on how they are combined.

4.4 BEAM: Beam information






BEAM: Beam information





Name
Format
Units
Measure
Comments










Columns










Key





BEAM_ID

Int

Beam id.






Data





TYPE

String

definition type from a fixed set of strings. E.g POLYNOMIAL, AIRY, NUMERIC, IMAGE

COEFFICIENTS

Double(NUM_COEFFICIENTS)

Depending on TYPE would be polynomial coefficients or numeric values rescaled at 1GHz

BEAM_ROTATION

Int

sign of rotation w.r.t parallactic angle

(ALTERNATE_URL)

String url

for types that cannot be expressed as coefficients e.g IMAGE






Notes:
This sub-table contains Beam information. Referred to from the FEED and PHASED_ARRAY subtables.
BEAM_ID
Beam identifier
TYPE
The way the beam information is expressed. Fixed set of strings possible (POLYNOMIAL, AIRY, NUMERIC, IMAGE, GAUSSIAN,INVERSEPOLYNOMIAL, COSPOLYNOMIAL, ZERNIKE)
COEFFICIENTS
The coefficients for the expressed type. All the beams are defined at 1GHz; exceptio for IMAGE: it can have the spectral coordinates expressed in the image
BEAM_ROTATION
sign of beam rotation angle with respect to parallatic angle.
ALTERNATE_URL
Information on how to access beams that are expressed as images (from some telescope archive for e.g).

4.5 CORRELATOR_TYPE: Doppler tracking information






CORRELATOR_TYPE: Doppler tracking information





Name
Format
Units
Measure
Comments










Notes:
This optional sub-table contains correlator information referred to from the PROCESSOR subtable.

4.6 DOPPLER: Doppler tracking information






DOPPLER: Doppler tracking information





Name
Format
Units
Measure
Comments










Columns










Key





DOPPLER_ID

Int

Doppler tracking id.

SOURCE_ID

Int

Source id.






Data





TRANSITION_INDEX

Int

Transition index. Indexes into transitions list in SOURCE

VELDEF

Double

m/s

Doppler

Velocity definition of Doppler shift.






Notes:
This sub-table contains frame information for different Doppler tracking modes. It is indexed from the SPECTRAL_WINDOW_ID sub-table (with SOURCE_ID as a secondary index) and thus allows the specification of a source-dependent Doppler tracking reference for each SPECTRAL_WINDOW. This model allows multiple possible transitions per source per spectral window, but only one reference at any given time.
DOPPLER_ID
Doppler identifier, as used in the SPECTRAL_WINDOW sub-table.
SOURCE_ID
Source identifier (as used in the SOURCE sub-table).
TRANSITION_INDEX
This index selects the appropriate line from the list of transitions stored for each SOURCE_ID in the SOURCE table.
VELDEF
Velocity definition of the Doppler shift, e.g., RADIO or OPTICAL velocity in m/s.

4.7 EPHEMERIDES: Ephemerides information






EPHEMERIDES: Ephemerides information





Name
Format
Units
Measure
Comments










Keywords





OBSLOC

String

observer’s location for ephemerides






Columns










Key





EPHEMERIS_ID

Int

ephemeris id.






Data





TIME

Double

s

EPOCH

Time of direction measurement

DIRECTION

Double(2)

rad

DIRECTION

Direction of object from obsloc position.

DISTANCE

Double

km

Distance from observer at time

RADIAL_VELOCITY

Double

m/s

Radial velocity of source

(SHAPE)

Double(3)

rad

Apparent elliptical shape in angular units (Major, minor, pos. angle)

(ALTERNATE_URL)

String

Location of Ephemerides table for this ephemeris_id






Notes:
This sub-table contains ephemeris information as referred to from FIELD table.

Either multiple rows of information for a given EPHEMERIS_ID is given in this table with time or a URL is provided to get an ephemeris table of known format (e.g the one used by Measures in casacore)

EPHEMERIS_ID
identifier referenced in FIELD table
TIME
Epoch of observation of object
DIRECTION
Measures direction of object at given time and seen from OBSLOC position.
RADIAL_VELOCITY
Velocity of object
SHAPE
Apparent Elliptical shape of object
ALTERNATE_URL
Location of a ephemeris table in documented format.

4.8 FEED: Feed characteristics






FEED: Feed characteristics





Name
Format
Units
Measure
Comments










Columns










Key





ANTENNA_ID

Int

Antenna id

FEED_ID

Int

Feed id

SPECTRAL_WINDOW_ID

Int

Spectral window id.

TIME

Double

s

EPOCH

Interval midpoint

INTERVAL

Double

s

Time interval






Data description





NUM_RECEPTORS

Int

# receptors on this feed






Data





BEAM_ID

Int

Beam model

BEAM_OFFSET

Double(2, NUM_RECEPTORS)

rad

DIRECTION

Beam position offset (on sky but in antenna reference frame).

(FOCUS_LENGTH)

Double

m

Focus length

(PHASED_FEED_ID)

Int

Phased feed

POLARIZATION_TYPE

String (NUM_RECEPTORS)

Type of polarization to which a given RECEPTOR responds.

POL_RESPONSE

Complex (NUM_RECEPTORS, NUM_RECEPTORS)

Feed polzn. response

POSITION

Double(3)

m

POSITION

Position of feed relative to feed reference position for this antenna

RECEPTOR_ANGLE

Double (NUM_RECEPTORS)

rad

The reference angle for polarization.






Notes:
A feed is a collecting element on an antenna, such as a single horn, that shares joint physical properties and makes sense to calibrate as a single entity. It is an abstraction of a generic antenna feed and is considered to have one or more RECEPTORs that respond to different polarization states. A FEED may have a time-variable beam and polarization response. Feeds are numbered from 0 on each separate antenna for each SPECTRAL_WINDOW_ID. Consequently, FEED_ID should be non-zero only in the case of feed arrays, i.e. multiple, simultaneous beams on the sky at the same frequency and polarization.
ANTENNA_ID
Antenna number, as indexed from ANTENNAn in MAIN.
FEED_ID
Feed identifier, as indexed from FEEDn in MAIN.
SPECTRAL_WINDOW_ID
Spectral window identifier. A value of -1 indicates the row is valid for all spectral windows.
TIME
Mid-point of time interval for which the feed parameters in this row are valid. The same Measure reference used for the TIME column in MAIN must be used.
INTERVAL
Time interval.
NUM_RECEPTORS
Number of receptors on this feed. See POLARIZATION_TYPE for further information.
BEAM_ID
Beam identifier. Points to an optional BEAM sub-table defining the primary beam and polarization response for this FEED. A value of -1 indicates that no associated beam response is defined.
BEAM_OFFSET
Beam position offset, as defined on the sky but in the antenna reference frame.
FOCUS_LENGTH
Focus length. As defined along the optical axis of the antenna.
PHASED_FEED_ID
Phased feed identifier. Points to a PHASED_FEED sub-table which in turn points back to multiple entries in the FEED table, and specifies the manner in which they are combined.
POLARIZATION_TYPE
Polarization type to which each receptor responds (e.g. ”R”,”L”,”X” or ”Y”). This is the receptor polarization type as recorded in the final correlated data (e.g. ”RR”); i.e. as measured after all polarization combiners.
POL_RESPONSE
Polarization response at the center of the beam for this feed. Expressed in a linearly polarized basis (ex,ey) using the IEEE convention.
POSITION
Offset of feed relative to the feed reference position for this antenna (see ANTENNA sub-table).
RECEPTOR_ANGLE
Polarization reference angle. Converts into parallactic angle in the sky domain.

4.9 FIELD: Field positions for each source






FIELD: Field positions for each source





Name
Format
Units
Measure
Comments










Columns










Key





FIELD_ID

Int

Field id.






Data





NAME

String

Name of field

CODE

String

Special characteristics of field

TIME

Double

s

EPOCH

Time origin for the directions and rates

NUM_POLY

Int

Series order

DELAY_DIR

Double(2, NUM_POLY+1)

rad

DIRECTION

Direction of delay center.

PHASE_DIR

Double(2, NUM_POLY+1)

rad

DIRECTION

Phase center.

REFERENCE_DIR

Double(2, NUM_POLY+1)

rad

DIRECTION

Reference center

SOURCE_ID

Int

Index in Source table

(EPHEMERIS_ID)

Int

Ephemeris id.






Notes:
The FIELD table defines a field position on the sky. For interferometers, this is the correlated field position. For single dishes, this is the nominal pointing direction.
FIELD_ID
Field id.
NAME
Field name; user specified.
CODE
Field code indicating special characteristics of the field; user specified.
TIME
Time reference for the directions and rates. Required to use the same TIME Measure reference as in MAIN.
NUM_POLY
Series order for the *_DIR columns.
DELAY_DIR
Direction of delay center; can be expressed as a polynomial in time. Final result converted to the defined Direction Measure type.
PHASE_DIR
Direction of phase center; can be expressed as a polynomial in time. Final result converted to the defined Direction Measure type.
REFERENCE_DIR
Reference center; can be expressed as a polynomial in time. Final result converted to the defined Direction Measure type. Used in single-dish to record the associated reference direction if position-switching has already been applied. For interferometric data, this is the original correlated field center, and may equal DELAY_DIR or PHASE_DIR.
SOURCE_ID
Points to an entry in the optional SOURCE subtable, a value of 1 indicates there is no corresponding source defined.
EPHEMERIS_ID
Points to an entry in the EPHEMERIS sub-table, which defines the ephemeris used to compute the field position. Useful for moving, near-field objects, where the ephemeris may be revised over time.

4.10 FLAG_CMD: Flag commands






FLAG_CMD: Flag commands





Name
Format
Units
Measure
Comments










Columns










Key





TIME

Double

s

EPOCH

Mid-point of interval

INTERVAL

Double

s

Time interval






Data





TYPE

String

FLAG or UNFLAG

REASON

String

Flag reason

LEVEL

Int

Flag level

SEVERITY

Int

Severity code

APPLIED

Bool

True if applied in MAIN

COMMAND

String

Flag command






Notes:
The FLAG_CMD sub-table defines global flagging commands which apply to the data in MAIN, as described in Section 3.1.8.
TIME
Mid-point of the time interval to which this flagging command applies. Required to use the same TIME Measure reference as used in MAIN.
INTERVAL
Time interval.
TYPE
Type of flag command, representing either a flagging (”FLAG”) or un-flagging (”UNFLAG”) operation.
REASON
Flag reason; user specified.
LEVEL
Flag level ( 0); reflects different revisions of flags which have the same REASON.
SEVERITY
Severity code for the flag, on a scale of 0-10 in order of increasing severity; user specified.
APPLIED
True if this flag has been applied to MAIN, and update in FLAG_CATEGORY and FLAG. False if this flag has not been applied to MAIN.
COMMAND
Global flag command, expressed in the standard syntax for data selection, as adopted within the project as a whole.

4.11 FREQ_OFFSET: Frequency offset information






FREQ_OFFSET: Frequency offset information





Name
Format
Units
Measure
Comments










Columns










Key





ANTENNA1

Int

Antenna 1.

ANTENNA2

Int

Antenna 2.

FEED_ID

Int

Feed id.

SPECTRAL_WINDOW_ID

Int

Spectral window id.

TIME

Double

s

EPOCH

Interval midpoint

INTERVAL

Double

s

Time interval






Data





OFFSET

Double

Hz

Frequency offset






Notes:
The table contains frequency offset information, to be added directly to the defined frequency labeling in the SPECTRAL_WINDOW sub-table as a Measure offset. This allows bands with small, time-variable, ad hoc frequency offsets to be labeled as the same SPECTRAL_WINDOW_ID, and calibrated together if required.
ANTENNAn
Antenna identifier, as indexed from ANTENNAn in MAIN.
FEED_ID
Antenna identifier, as indexed from FEEDn in MAIN.
SPECTRAL_WINDOW_ID
Spectral window identifier.
TIME
Mid-point of the time interval for which this offset is valid. Required to use the same TIME Measure reference as used in MAIN.
INTERVAL
Time interval.
OFFSET
Frequency offset to be added to the frequency axis for this spectral window, as defined in the SPECTRAL_WINDOW sub-table. Required to have the same Frequency Measure reference as CHAN_FREQ in that table.

4.12 HISTORY: History information






HISTORY: History information





Name
Format
Units
Measure
Comments










Columns










Key





TIME

Double

s

EPOCH

Time-stamp for message

OBSERVATION_ID

Int

Points to OBSERVATION table






Data





MESSAGE

String

Log message

PRIORITY

String

Message priority

ORIGIN

String

Code origin

OBJECT_ID

String

Originating ObjectID

APPLICATION

String

Application name

CLI_COMMAND

String(*)

CLI command sequence

APP_PARAMS

String(*)

Application paramters






Notes:
This sub-table contains associated history information for the MS.
TIME
Time-stamp for the history record. Required to have the same TIME Measure reference as used in MAIN.
OBSERVATION_ID
Observation identifier (see the OBSERVATION table)
MESSAGE
Log message.
PRIORITY
Message priority, with allowed types: (”DEBUGGING”, ”WARN”, ”NORMAL”, or ”SEVERE”).
ORIGIN
Source code origin from which message originated.
OBJECT_ID
Originating ObjectID, if available, else blank.
APPLICATION
Application name.
CLI_COMMAND
CLI command sequence invoking the application.
APP_PARAMS
Application parameter values, in the adopted project-wide format.

4.13 INTERFEROMETER_MODEL: VLBI Interferometer information






INTERFEROMETER_MODEL: VLBI Interferometer information





Name
Format
Units
Measure
Comments










Columns










Key





TIME

Double

s

EPOCH

Time-stamp for message

ANTENNA_ID

Int

Antenna id.

FIELD_ID

Int

field id.

SPECTRAL_WINDOW_ID

Int

Spectral window id.






Data





PHASE_DELAY

Double(Nr, num_poly)

s

Phase delay polynomial for each receptor

GROUP_DELAY

Double(Nr, num_poly)

s

Group delay polynomial for each receptor

PHASE_RATE

Double(Nr, num_poly)

Rate of change of phase delay

GROUP_RATE

Double(Nr, num_poly)

Rate of change of group delay

DISP_DELAY

Double(Nr, nunm_poly)

s

Dispersive delay

DISP_DELAY_RATE

Double(Nr, num_poly)

Dispersive delay rate

CLOCK_ERROR

Double(Nr, num_poly)

Clock error as delay polynomial

CLOCK_ERROR_RATE

Double(Nr, num_poly)

Rate of clock error modelled as a delay rate polynomial






Notes:
This sub-table contains information associated for VLBI
TIME
Time-stamp as origin for all time based polynomials model.
FIELD_ID
Field id, FIELD subtable
ANTENNA_ID
antenna id, antenna subtable
SPECTRAL_WINDOW_ID
Spectral window id.
PHASE_DELAY
phase delay modelled as a time polynomial for each receptor.
PHASE_RATE
rate of change for phase delay .
GROUP_DELAY
Group delay.
GROUP_RATE
Group delay rate.
DISP_DELAY
Dispersive delay
DISP_DELAY_RATE
Dispersive delay rate
CLOCK_ERROR
CLOCK_ERROR_RATE

4.14 OBSERVATION: Observation information






OBSERVATION: Observation information





Name
Format
Units
Measure
Comments










Columns










Key





OBSERVATION_ID

Int

Observation id.






Data





TELESCOPE_NAME

String

Telescope name

ARRAY_CENTER

Double(3)

m

POSITION

Reference position for array

TIME_RANGE

Double(2)

s

EPOCH

Start, end times

OBSERVER

String

Name of observer(s)

LOG

String(*)

Observing log

SCHEDULE_TYPE

String

Schedule type

SCHEDULE

String(*)

Project schedule

PROJECT

String

Project identification string.

RELEASE_DATE

Double

s

EPOCH

Target release date






Notes:
This table contains information specifying the observing instrument or epoch. See the discussion in Section 3.3 for details. It is indexed directly from MAIN via OBSERVATION_ID.
OBSERVATION_ID
Observation id. key
TELESCOPE_NAME
Telescope name (e.g. ”WSRT” or ”VLBA”).
ARRAY_CENTER
Reference position used by the correlator for e.g.
TIME_RANGE
The start and end times of the overall observing period spanned by the actual recorded data in MAIN. Required to use the same TIME Measure reference as in MAIN.
OBSERVER
The name(s) of the observer(s).
LOG
The observing log, as supplied by the telescope or instrument.
SCHEDULE_TYPE
The schedule type, with current reserved types (”VLBA-CRD”, ”VEX”, ”WSRT”, ”ATNF”).
SCHEDULE
Unmodified schedule file, of the type specified, and as used by the instrument.
PROJECT
Project code (e.g. ”BD46”)
RELEASE_DATE
Project release date. This is the date on which the data may become public.

4.15 PHASED_ARRAY: phased array station information






PHASED_ARRAY: phased array station information





Name
Format
Units
Measure
Comments










Columns










Key





ANTENNA_ID

Int

Antenna ID.

PHASED_ARRAY_ID

Int

phased array id.






Data





POSITION

Double(3)

m

POSITION

Position of antenna field

COORDINATE_SYSTEM

Double(3,3)

m

DIRECTION

Local coordinate system

ELEMENT_OFFSET

Double(3, Nant)

m

POSITION

Offset per element

(BEAM_ID)

Int

Beam id.

ELEMENT_FLAG

Bool(Nant)

Flag of elements in array






Notes:
The table contains information about phased array information. It refers to antenna ids in ANTENNA table, FEED_ID for feed used in forming this phased array.
ANTENNA_ID
Index into the ANTENNA table to show to which ANTENNA this phased array belongs. Note that this is an n-to-1 mapping: one ANTENNA can consist of multiple PHASED_ARRAYs.
POSITION
Position of the antenna field in absolute ITRF coordinates
COORDINATE_SYSTEM
(cartesian) direction vectors in ITRF (or measure defined) describing the local field coordinate system. This defines the antenna field plane, and the ’up’ direction, the normal direction to the antenna field plane. Note that in general this is not the zenith direction. The coordinate system is necessary to evaluate the beam pattern directions. The coordinate system can also be used for describing polarization alignment.
ELEMENT_OFFSET
Relative offsets of each element from POSITION
ELEMENT_FLAG
flag for invalid antennas in array not used.
BEAM_ID
Beam id as defined in BEAM table.

4.16 POINTING: Antenna pointing information






POINTING: Antenna pointing information





Name
Format
Units
Measure
Comments










Columns










Key





ANTENNA_ID

Int

Antenna id.

TIME

Double

s

EPOCH

Interval midpoint

INTERVAL

Double

s

Time interval






Data





NAME

String

Pointing position desc.

NUM_POLY

Int

Series order

TIME_ORIGIN

Double

s

EPOCH

Origin for the polynomial

DIRECTION

Double(2, NUM_POLY+1)

rad

DIRECTION

Antenna pointing direction

TARGET

Double(2, NUM_POLY+1)

rad

DIRECTION

Target direction

(POINTING_OFFSET)

Double(2, NUM_POLY+1)

rad

DIRECTION

A priori pointing correction

(SOURCE_OFFSET)

Double(2, NUM_POLY+1)

rad

DIRECTION

Offset from source

(ENCODER)

Double(2)

rad

DIRECTION

Encoder values

(POINTING_MODEL_ID)

Int

Pointing model id.

TRACKING

Bool

True if on-position

(ON_SOURCE)

Bool

True if on-source

(OVER_THE_TOP)

Bool

True if over the top






Notes:
This table contains information concerning the primary pointing direction of each antenna as a function of time. Note that the pointing offsets for inidividual feeds on a given antenna are specified in the FEED sub-table with respect to this pointing direction.
ANTENNA_ID
Antenna identifier, as specified by ANTENNAn in MAIN.
TIME
Mid-point of the time interval for which the information in this row is valid. Required to use the same TIME Measure reference as in MAIN.
INTERVAL
Time interval.
NAME
Pointing direction name; user specified.
NUM_POLY
Series order for the polynomial expressions in DIRECTION and POINTING_OFFSET.
TIME_ORIGIN
Time origin for the polynomial expansions.
DIRECTION
Antenna pointing direction, optionally expressed as polynomial coefficients. The final result is interpreted as a Direction Measure using the specified Measure reference.
TARGET
Target pointing direction, optionally expressed as polynomial coefficients. The final result is interpreted as a Direction Measure using the specified Measure reference. This is the true expected position of the source, including all coordinate corrections such as precession, nutation etc.
POINTING_OFFSET
The a priori pointing corrections applied by the telescope in pointing to the DIRECTION position, optionally expressed as polynomial coefficients. The final result is interpreted as a Direction Measure using the specified Measure reference.
SOURCE_OFFSET
The commanded offset from the source position, if offset pointing is being used.
ENCODER
The current encoder values on the primary axes of the mount type for the antenna, expressed as a Direction Measure.
TRACKING
True if tracking the nominal pointing position.
ON-SOURCE
True if the nominal pointing direction coincides with the source, i.e. offset-pointing is not being used.
OVER-THE-TOP
True if the antenna was driven to this position ”over the top” (az-el mount).

4.17 POLARIZATION: Polarization setup information






POLARIZATION: Polarization setup information





Name
Format
Units
Measure
Comments










Columns










Data description columns





NUM_CORR

Int

# correlations






Data





CORR_TYPE

Int(NUM_CORR)

Polarization of correlation

CORR_PRODUCT

Int(2, NUM_CORR)

Receptor cross-products






Notes:
This table defines the polarization labeling of the DATA array in MAIN, and is directly indexed by POLARIZATION_ID.
NUM_CORR
The number of correlation polarization products. For example, for (RR) this value would be 1, for (RR, LL) it would be 2, and for (XX,YY,XY,YX) it would be 4, etc.
CORR_TYPE
An integer for each correlation product indicating the Stokes type as defined in the Stokes class enumeration.
CORR_PRODUCT
Pair of integers for each correlation product, specifying the receptors from which the signal originated. The receptor polarization is defined in the POLARIZATION_TYPE column in the FEED table. An example would be (0,0), (0,1), (1,0), (1,1) to specify all correlations between two receptors.

4.18 PROCESSOR: Processor information






PROCESSOR: Processor information





Name
Format
Units
Measure
Comments










Columns










Data





TYPE

String

Processor type

SUB_TYPE

String

Processor sub-type

TYPE_ID

Int

Processor type id.

MODE_ID

Int

Processor mode id.

(PASS_ID)

Int

Processor pass number






Notes:
This table holds summary information for the back-end processing device used to generate the basic data in the MAIN table. Such devices include correlators, radiometers, spectrometers, pulsar-timers, amongst others. See Section 4.0.4 for further details.
TYPE
Processor type; reserved keywords include (”CORRELATOR” - interferometric correlator; ”SPECTROMETER” - single-dish correlator; ”RADIOMETER” - generic detector/integrator; ”PULSAR-TIMER” - pulsar timing device).
SUB_TYPE
Processor sub-type, e.g. ”GBT” or ”JIVE”.
TYPE_ID
Index used in a specialized sub-table named as subtype_type, which contains time-independent processor information applicable to the current data record (e.g. a JIVE_CORRELATOR sub-table). Time-dependent information for each device family is contained in other tables, dependent on the device type.
MODE_ID
Index used in a specialized sub-table named as subtype_type_mode, containing information on the processor mode applicable to the current data record. (e.g. a GBT_SPECTROMETER_MODE sub-table).
PASS_ID
Pass identifier; this is used to distinguish data records produced by multiple passes through the same device, where this is possible (e.g. VLBI correlators). Used as an index into the associated table containing pass information.

4.19 SCAN: Scan information






SCAN: Scan information





Name
Format
Units
Measure
Comments










Columns










Key





SCAN_NUMBER

Int

Scan number id; referred from the Main table






Data





SCAN_INTENT

String

Fixed set of string defining the intent of the scan

(EXECBLOCK_ID)

Int

Execution block id

(TIME)

Double

s

EPOCH

start time of scan

(INTERVAL)

Double

s

time from begining from which scan is valid






Notes:
This sub-table contains associated scan information for the MS.
SCAN_NUMBER
Scan number as referred from main table
SCAN_INTENT
Intent for the scan (an scan number may have multiple intents). Fixed set of string for a telescope e.g CAL_POINTING or TARGET
EXECBLOCK_ID
A number that is unique to the observation execution block. Used to get more info from the online system of some telescopes.
TIME
Time of start for that scan
TIME_INTERVAL
interval for which this scan is observed from TIME

4.20 SOURCE: Source information






SOURCE: Source information





Name
Format
Units
Measure
Comments










Columns










Key





SOURCE_ID

Int

Source id

TIME

Double

s

EPOCH

Midpoint of time for which this set of parameters is accurate

INTERVAL

Double

s

Interval

SPECTRAL_WINDOW_ID

Int

Spectral Window id






Data description





NUM_LINES

Int

Number of spectral lines






Data





NAME

String

Name of source as given during observations

CALIBRATION_GROUP

Int

# grouping for calibration purpose

CODE

String

Special characteristics of source, e.g. Bandpass calibrator

DIRECTION

Double(2)

rad

DIRECTION

Direction (e.g. RA, DEC)

(POSITION)

Double(3)

m

POSITION

Position (e.g. for solar system objects)

PROPER_MOTION

Double(2)

rad/s

Proper motion

(TRANSITION)

String(NUM_LINES)

Transition name

(REST_FREQUENCY)

Double(NUM_LINES)

Hz

FREQUENCY

Line rest frequency

(SYSVEL)

Double(NUM_LINES)

m/s

RADIAL VELOCITY

Systemic velocity at reference

(SOURCE_MODEL)

TableRecord or String

Default csm

(PULSAR_ID)

Int

Pulsar id.






Notes:
This table contains time-variable source information, optionally associated with a given FIELD_ID.
SOURCE_ID
Source identifier ( 0), as specified in the FIELD sub-table.
TIME
Mid-point of the time interval for which the data in this row is valid. Required to use the same TIME Measure reference as in MAIN.
INTERVAL
Time interval.
SPECTRAL_WINDOW_ID
Spectral window identifier. A -1 indicates that the row is valid for all spectral windows.
NUM_LINES
Number of spectral line transitions associated with this source and spectral window id. combination.
NAME
Source name; user specified.
CALIBRATION_GROUP
Calibration group number to which this source belongs; user specified.
CODE
Source code, used to describe any special characteristics f the source, such as the nature of a calibrator. Reserved keyword, including (”BANDPASS CAL”).
DIRECTION
Source direction at this TIME.
POSITION
Source position (x,y,z) at this TIME (for near-field objects).
PROPER_MOTION
Source proper motion at this TIME.
TRANSITION
Transition names applicable for this spectral window (e.g. ”v=1, J=1-0, SiO”).
REST_FREQUENCY
Rest frequencies for the transitions.
SYSVEL
Systemic velocity for each transition.
SOURCE_MODEL
Reference to an assigned component source model table or a URL to access source model
PULSAR_ID
An index used in the PULSAR sub-table to define further pulsar-specific properties if the source is a pulsar.

4.21 SPECTRAL_WINDOW: Spectral window description






SPECTRAL_WINDOW: Spectral window description





Name
Format
Units
Measure
Comments










Columns










Key





SPECTRAL_WINDOW_ID

Int

Spectral window id






Data description columns





NUM_CHAN

Int

# spectral channels






Data





NAME

String

Spectral window name

REF_FREQUENCY

Double

Hz

FREQUENCY

The reference frequency.

CHAN_FREQ

Double(NUM_CHAN)

Hz

FREQUENCY

Center frequencies for each channel in the data matrix.

CHAN_WIDTH

Double(NUM_CHAN)

Hz

Channel width for each channel in the data matrix.

MEAS_FREQ_REF

Int

FREQUENCY Measure ref.

EFFECTIVE_BW

Double(NUM_CHAN)

Hz

The effective noise bandwidth of each spectral channel

RESOLUTION

Double(NUM_CHAN)

Hz

The effective spectral resolution of each channel

TOTAL_BANDWIDTH

Double

Hz

total bandwidth for this window

NET_SIDEBAND

Int

Net sideband

(BBC_NO)

Int

Baseband converter no.

(BBC_SIDEBAND)

Int

BBC sideband

IF_CONV_CHAIN

Int

The IF conversion chain

(RECEIVER_ID)

Int

Receiver id.

(LO_FREQUENCY)

Double

LO frequency

FREQ_GROUP

Int

Frequency group

FREQ_GROUP_NAME

String

Freq. group name

(DOPPLER_ID)

Int

Doppler id.

(ASSOC_SPW_ID)

Int(*)

Associated spw_id.

(ASSOC_NATURE)

String(*)

Nature of association






Notes:
This table describes properties for each defined spectral window. A spectral window is both a frequency label for the associated DATA array in MAIN, but also represents a generic frequency conversion chain that shares joint physical properties and makes sense to calibrate as a single entity.
SPECTRAL_WINDOW_ID
spectral window id key.
NUM_CHAN
Number of spectral channels.
NAME
Spectral window name; user specified.
REF_FREQUENCY
The reference frequency. A frequency representative of this spectral window, usually the sky frequency corresponding to the DC edge of the baseband. Used by the calibration system if a fixed scaling frequency is required or in algorithms to identify the observing band.
CHAN_FREQ
Center frequencies for each channel in the data matrix. These can be frequency-dependent, to accommodate instruments such as acousto-optical spectrometers. Note that the channel frequencies may be in ascending or descending frequency order.
CHAN_WIDTH
Nomical channel width of each spectral channel. Although these can be derived from CHAN_FREQ by differencing, it is more efficient to keep a separate reference to this information.
MEAS_FREQ_REF
Frequency Measure reference for CHAN_FREQ. This allows a row-based reference for this column in order to optimize the choice of Measure reference when Doppler tracking is used. Modified only by the MS access code.
EFFECTIVE_BW
The effective noise bandwidth of each spectral channel.
RESOLUTION
The effective spectral resolution of each channel.
TOTAL_BANDWIDTH
The total bandwidth for this spectral window.
NET_SIDEBAND
The net sideband for this spectral window.
BBC_NO
The baseband converter number, if applicable.
BBC_SIDEBAND
The baseband converter sideband, is applicable.
IF_CONV_CHAIN
Identification of the electronic signal path for the case of multiple (simultaneous) IFs. (e.g. VLA: AC=0, BD=1, ATCA: Freq1=0, Freq2=1)
RECEIVER_ID
Index used to identify the receiver associated with the spectral window. Further state information is planned to be stored in a RECEIVER sub-table.
LO_FREQUENCY
LO frequency used for this spectral window
FREQ_GROUP
The frequency group to which the spectral window belongs. This is used to associate spectral windows for joint calibration purposes.
FREQ_GROUP_NAME
The frequency group name; user specified.
DOPPLER_ID
The Doppler identifier defining frame information for this spectral window.
ASSOC_SPW_ID
Associated spectral windows, which are related in some fashion (e.g. ”channel-zero”).
ASSOC_NATURE
Nature of the association for ASSOC_SPW_ID; reserved keywords are (”CHANNEL-ZERO” - channel zero; ”EQUAL-FREQUENCY” - same frequency labels; ”SUBSET” - narrow-band subset).

4.22 STATE: State information






STATE: State information





Name
Format
Units
Measure
Comments










Columns










Key





STATE_ID

Int

State id key






Data





SIG

Bool

Signal

REF

Bool

Reference

CAL

Double

K

Noise calibration

LOAD

Double

K

Load temperature

SUB_SCAN

Int

Sub-scan number

OBS_MODE

String

Observing mode






Notes:
This table defines the state parameters for a particular data record as they refer to external loads, calibration sources or references, and also characterizes the observing mode of the data record, as an aid to defining the scheduling heuristics. It is indexed directly via STATE_ID in MAIN.
SIG
True if the source signal is being observed.
REF
True for a reference phase.
CAL
Noise calibration temperature (zero if not added).
LOAD
Load temperature (zero if no load).
SUB_SCAN
Sub-scan number ( 0), relative to the SCAN_NUMBER in MAIN. Used to identify observing sequences.
OBS_MODE
Observing mode; defined by a set of reserved keywords characterizing the current observing mode (e.g. ”OFF-SPECTRUM”). Used to define the schedule strategy.

4.23 SYSCAL: System calibration






SYSCAL: System calibration





Name
Format
Units
Measure
Comments










Columns










Key





ANTENNA_ID

Int

Antenna id

FEED_ID

Int

Feed id

SPECTRAL_WINDOW_ID

Int

Spectral window id

TIME

Double

s

EPOCH

Midpoint of time for which this set of parameters is accurate

INTERVAL

Double

s

Interval






Data





(PHASE_DIFF)

Float

rad

Phase difference between receptor 0 and receptor 1

(TCAL)

Float (Nr)

K

Calibration temp

(TRX)

Float (Nr)

K

Receiver temperature

(TSKY)

Float (Nr)

K

Sky temperature

(TSYS)

Float (Nr)

K

System temp

(TANT)

Float (Nr)

K

Antenna temperature

(TANT_TSYS)

Float(Nr)

Tant Tsys

(TCAL_SPECTRUM)

Float (Nr, Nf)

K

Calibration temp

(TRX_SPECTRUM)

Float (Nr, Nf)

K

Receiver temperature

(TSKY_SPECTRUM)

Float (Nr, Nf)

K

Sky temperature spectrum

(TSYS_SPECTRUM)

Float (Nr, Nf)

K

System temp

(TANT_SPECTRUM)

Float (Nr, Nf)

K

Antenna temperature spectrum

(TANT_TSYS_SPECTRUM)

Float (Nr,Nf)

Tant Tsys spectrum






Flags





(PHASE_DIFF_FLAG)

Bool

Flag for PHASE_DIFF

(TCAL_FLAG)

Bool

Flag for TCAL

(TRX_FLAG)

Bool

Flag for TRX

(TSKY_FLAG)

Bool

Flag for TSKY

(TSYS_FLAG)

Bool

Flag for TSYS

(TANT_FLAG)

Bool

Flag for TANT

(TANT_TSYS_FLAG)

Bool

Flag for Tant Tsys






Notes:
This table contains time-variable calibration measurements for each antenna, as indexed on feed and spectral window. Note that Nr= number of receptors, and Nf= number of frequency channels.
ANTENNA_ID
Antenna identifier, as indexed by ANTENNAn in MAIN.
FEED_ID
Feed identifier, as indexed by FEEDn in MAIN.
SPECTRAL_WINDOW_ID
Spectral window identifier.
TIME
Mid-point of the time interval for which the data in this row are valid. Required to use the same TIME Measure reference as that in MAIN.
INTERVAL
Time interval.
PHASE_DIFF
Phase difference between receptor 0 and receptor 1.
TCAL
Calibration temperature.
TRX
Receiver temperature.
TSKY
Sky temperature.
TSYS
System temperature.
TANT
Antenna temperature.
TANT_TSYS
Antenna temperature over system temperature.
TCAL_SPECTRUM
Calibration temperature spectrum.
TRX_SPECTRUM
Receiver temperature spectrum.
TSKY_SPECTRUM
Sky temperature spectrum.
TSYS_SPECTRUM
System temperature spectrum.
TANT_SPECTRUM
Antenna temperature spectrum.
TANT_TSYS_SPECTRUM
Antenna temperature over system temperature spectrum.
PHASE_DIFF_FLAG
True if PHASE_DIFF flagged.
TCAL_FLAG
True if TCAL flagged.
TRX_FLAG
True if TRX flagged.
TSKY_FLAG
True if TSKY flagged.
TSYS_FLAG
True if TSYS flagged.
TANT_FLAG
True if TANT flagged.
TANT_TSYS_FLAG
True if TANT_TSYS flagged.

4.24 WEATHER: weather station information






WEATHER: weather station information





Name
Format
Units
Measure
Comments










Columns










Key





ANTENNA_ID

Int

Antenna number

TIME

Double

s

EPOCH

Mid-point of interval

INTERVAL

Double

s

Interval over which data is relevant






Data





(H2O)

Float

m2

Average column density of water

(IONOS_ELECTRON)

Float

m2

Average column density of electrons

(PRESSURE)

Float

hPa

Ambient atmospheric pressure

(REL_HUMIDITY)

Float

Ambient relative humidity

(TEMPERATURE)

Float

K

Ambient air temperature for an antenna

(DEW_POINT)

Float

K

Dew point

(WIND_DIRECTION)

Float

rad

Average wind direction

(WIND_SPEED)

Float

m/s

Average wind speed






Notes:
This table contains mean external atmosphere and weather information.
ANTENNA_ID
Antenna identifier, as indexed by ANTENNAn from MAIN.
TIME
Mid-point of the time interval over which the data in the row are valid. Required to use the same TIME Measure reference as in MAIN.
INTERVAL
Time interval.
H2O
Average column density of water.
IONOS_ELECTRON
Average column density of electrons.
PRESSURE
Ambient atmospheric pressure.
REL_HUMIDITY
Ambient relative humidity.
TEMPERATURE
Ambient air temperature.
DEW_POINT
Dew point temperature.
WIND_DIRECTION
Average wind direction.
WIND_SPEED
Average wind speed.

5 Units and Measures

5.1 Units and Measures






Units and Measures





Name
Format
Units
Measure
Comments










Column keywords





QuantumUnits

String Vector

Units of the data in the column

MEASINFO

Record

subfields defining the unit






Subfields of MEASINFO





type

String

lowercase name of the Measure type (e.g., frequency)

Ref

String

Uppercase name of the frame (e.g., LSRK)

VarRefCol

String

Name of the column containing the frames

VarRefTypes

String Vector

All frame names for this type

VarRefCodes

Int Vector

All frame codes for this type






QuantumUnits
Its value is a vector of strings, usually containing a single value (e.g., rad) applying to all values in the column. If the column cells contain array values, QuantumUnits can define multiple units. For example, the telescope position could be stored as longitude, latitude, height with units rad,rad,m.
type
Its value is one of the Measures types which are epoch, position, direction, frequency, doppler, radialvelocity and earthmagnetic.
Ref
This field is used if the entire column has the same frame. Its value is one the the frame names for the given Measures type. For instance: J2000, B1950, ECLIPTIC, etc. for the direction measure.
VarRefCol
This field is used if each row in the column can have its own reference frame. Its value is the name of the column containing the frame. The column can contain strings giving the frame name or can contain integers giving the frame codes. If integers are used, the following two fields (VarRefTypes and VarRefCodes) can be defined to make the stored frame codes resilient to possible future changes.
VarRefTypes and VarRefCodes
These fields can be used if VarRefCol is defined. They contain a vector of strings and integers giving the the frame names and codes for this Measures type. They map a frame code to its name. It makes it possible that the Measures classes can renumber the frame codes without affecting the stored frame codes (the frame names are not changed).
These fields are optional. If VarRefTypes is not defined, it is assumed that the frame codes in the table are the same as in the Measures classes.
Notes:
The possible units can be found in the Casacore Unit classes. They can be listed using the TaQL command ’show units’.
The possible measure types and frames can be found in the Casacore Measures classes (such as MDirection). They can be listed using the TaQL command ’show meastypes’.

6 References

Kemball, A.J., Wieringa, M.H., 2000, casacore Note 229.