## MeasurementSet deﬁnition version 3.0$\beta$

July, 2019

### 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:

• Explicit keys One of the major complaints of ms v2.0 is the use of row ids in subtables as implicit keys. In v3.0 we are moving to explicit keys; e.g ANTENNA subtable will have a column ANTENNA_ID so that when making a subset MS re-indexing is not needed in the main table. This makes it easier to make a subset of an MS without the need to reindex the data in the main table or any subtables.
• Single-dish processing: FLOAT_DATA is replaced by DATA unifying it with interferometer. It is left to the software column implementation to store ﬂoats eﬃciently rather than have multiple columns deﬁned for diﬀerent data types. We do not need to deﬁne in the schematic how the data is to be stored and accessed for eﬃciency purposes. The implementation can decide to compress data or keep as ﬂoat or integers but on request a given DATA column cell, for e.g, single precision complex numbers are served.
• Synthesis calibration: The need for calibrations table as part the MeasurementSet has been felt by several telescopes and those using v2.0 (e.g ALMA and EVLA) have been using non standard tables to carry calibration type information.
• Data,weight, ﬂag versioning Non standard columns (e.g CORRECTED_DATA) or kludges have been used by casa (for e.g) to deal with having version of data, ﬂag or weight. These three columns have the same shapes in every row of an MS V3.0. Whenever changes are made, e.g. in ﬂagging or calibration, and a new version is needed a new triplet of columns will be made. It is left to software implementation to do the smart thing (not making unnecessary copies). E.g if ﬂagging only is done and need to be saved in a new version of FLAG column, the new version of DATA an WEIGHT are just virtual columns pointing back to the previous version.
• Data DescriptionThe concept of data description is being deprecated. It saved a column of integers but users found it confusing. SPECTRAL_WINDOW_ID and POLARIZATION_ID are explicit columns in the main table.
• VLBI data reduction: From v2.0 added an optional subtable INTERFEROMETER_MODEL
• Phased Array interferometers: A new optional subtable, PHASED_ARRAY, which will be deﬁning which antennas form a phased array station.
• BEAM, EPHEMERIDES and SCAN subtables: In MS V2.0 the BEAM (BEAM_ID), EPHEMERIDES (EPHEMERIS_ID) and SCAN (SCAN_NUMBER) subtables are referred to but were not deﬁned. Here we explicitly deﬁne these optional subtables.

• Changes: The changes proposed here are designed to be as incremental as possible and taking into account what usage at diﬀerent telescopes and software packages has found lacking.
• Compatibility: Some of the changes proposed here are not backwards compatible but converters can be written to move data between version 2.0 and 3.0. As there is more information in version 3.0 going to version 2.0 may be lossy.
• Calibration information: Many of the direct and peripheral information stored at data collection can be stored as calibration terms (Jones or Mueller matrices). Therefore MS v3.0 will carry in its deﬁnition optional calibration tables which may carry monitoring information that can be used to modify the data, weights and ﬂags. The calibration tables deﬁnition will be added to this document once it is ﬁnalized
• Storage: A future document will provide results and suggestion for data storage structures for some commonly used access patterns and storage system in use.
• Multi measurement sets: The reason for Multi Measurement Sets (MMS) was to bypass an issue in the impementation in parallel access subsection of an ms could not be locked separately. We therefore postpone the need to deﬁne the MMS format if no implementation of multi-lockable Measurementsets is do-able.

### 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

• removal of FLAG_CATEGORY

This column has not been used eﬀectively. With the versioning of FLAG below it is redundant.

• Removal of SIGMA WEIGHT being always considered to be $\frac{1}{{\sigma }^{2}}$ this a redundant column.
• Removal of FLAG_ROW The purpose of this column was to avoid having to renumber rows when e.g. removing an antenna. This is not necessary with explicit row numbers anymore.
• Redeﬁnition of WEIGHT to be WEIGHT_SPECTRUM With most of contemporary inteferometers being spectral machines with possibility of distinctive weights per channel, usage of MSv2.0 WEIGHT is low w.r.t WEIGHT_SPECTRUM. In this version WEIGHT column will have the same shape as the data.
• Versioning of (DATA, WEIGHT, FLAG) triplet These three columns will have the same shapes. There may be many versions them in an MS. But the active version will be refered to as DATA, WEIGHT and FLAG. The versions need not be copies. For e.g if only DATA is corrected and a new version is made. The active DATA will refer to DATA1 column while the active WEIGHT, FLAG (thus WEIGHT1 and FLAG1) will refer to the to WEIGHT0 and FLAG0 respectively. We leave it to the software to implement these in the most optimal fashion without making duplicate copies. This removes the need for non-standard column like CORRECTED_DATA or FLAG_VERSION etc.
• Merging of DATA and FLOAT_DATA It is unnecessary to have explicit DATA and FLOAT_DATA. The software implementation can do the optimal storage in the presence of ﬂoat data only and serve it as complex.
• Replacement of DATA_DESC_ID This unique ID has caused more confusion than the extra column of integers is worth. In this version we are reverting to having explicit POLARIZATION_ID and SPECTRAL_WINDOW_ID which refers to keys in the POLARIZATION and SPECTRAL_WINDOW subtables directly. DATA_DESC_ID column is removed.

#### 2.2 ARRAY table

• ARRAY_ID An explicit ID column is newly deﬁned.
• ARRAY_CENTER A new column which will give the full Measures position of where the array center is assumed for each ARRAY_ID

#### 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, ANTENNA$n$, 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($Nc$, $N\ast f$) Weight for each channel Flag information FLAG Bool($Nc$, $N\ast f$) 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 $major\text{_}revision.minor\text{_}revision$. 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.
ANTENNA$n$
Antenna number ($\ge 0$), and a direct key index into the ANTENNA sub-table. For $n>2$, triple-product data are implied.
FEED$n$
Feed number ($\ge 0$). For $n>2$, triple-product data are implied.
SPECTRAL_WINDOW_ID
Spectral window identiﬁer ($\ge 0$), and a direct key index into the SPECTRAL_WINDOW sub-table.
POLARIZATION_ID
Polarization identiﬁer ($\ge 0$), and a direct key index into the POLARIZATION sub-table.
PROCESSOR_ID
Processor indentiﬁer ($\ge 0$), and a direct key index into the PROCESSOR sub-table.
PHASE_ID
Switching phase identiﬁer ($\ge 0$)
FIELD_ID
Field identiﬁer ($\ge 0$) 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 ($\ge 0\right)$, 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; ($\ge 0$) a direct key index into the SCAN sub-table.
ARRAY_ID
Subarray identiﬁer $\left(\ge 0\right)$, which identiﬁes data in separate subarrays, as deﬁned in Section 3.3.
OBSERVATION_ID
Observation identiﬁer $\left(\ge 0\right)$, which identiﬁes data from separate observations, as deﬁned in Section 3.3.
STATE_ID
State identiﬁer $\left(\ge 0\right)$, 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 $N\ast f$ 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 $N\ast f$ 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 ANTENNA$n$.
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):
• 0: Semi-major axis of orbit ($a$) in $m$.
• 1: Ellipticity of orbit ($e$).
• 2: Inclination of orbit to the celestial equator ($i$) in $deg.$
• 3: Right ascension of the ascending node ($\Omega$) in $deg.$
• 4: Argument of perigee ($\omega$) in $deg.$
• 5: Mean anomaly ($M$) in $deg.$
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.
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 ANTENNA$n$ in MAIN.
FEED_ID
Feed identiﬁer, as indexed from FEED$n$ 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 $\left({\stackrel{\to }{e}}_{x},{\stackrel{\to }{e}}_{y}\right)$ 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 $\left(\ge 0\right)$; 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.
ANTENNA$n$
Antenna identiﬁer, as indexed from ANTENNA$n$ in MAIN.
FEED_ID
Antenna identiﬁer, as indexed from FEED$n$ 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 ANTENNA$n$ 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 $subtype\text{_}type$, 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 $subtype\text{_}type\text{_}mode$, 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 ($\ge 0\right)$, 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 $\left(x,y,z\right)$ 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)
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).
SUB_SCAN
Sub-scan number $\left(\ge 0\right)$, 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($Nr$) $\frac{{T}_{ant}}{{T}_{sys}}$ (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 ($Nr$,$Nf$) $\frac{{T}_{ant}}{{T}_{sys}}$ 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 $\frac{{T}_{ant}}{{T}_{sys}}$
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 ANTENNA$n$ in MAIN.
FEED_ID
Feed identiﬁer, as indexed by FEED$n$ 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
TSKY
Sky temperature.
TSYS
System temperature.
TANT
Antenna temperature.
TANT_TSYS
Antenna temperature over system temperature.
TCAL_SPECTRUM
Calibration temperature spectrum.
TRX_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 ${m}^{-2}$ Average column density of water (IONOS_ELECTRON) Float ${m}^{-2}$ 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 ANTENNA$n$ 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.