Subject: Single Dish FITS Format

From: [email-masked]
Date: Tue, 5 Sep 89 13:44:27 EDT

National Radio Astronomy Observatory 
September 5, 1989

Dear participant,

  In 1986, Betty Stobie and Lorrie Morgan collaborated with representatives
from IRAM and the JCMT to develop a FITS format for transporting data taken at
single-dish telescopes.  The format was to be sufficiently general that the
needs of all observatories could be accomodated within it.  Unfortunately,
both Betty and Lorrie left NRAO before this effort could be carried to 
completion.

  In its present state, their memo describing the FITS format suffers
from many ambiguous statements and definitions and is seriously incomplete in
several respects.  In attempting to be general, that memo allowed so much
leeway that ostensibly "standard" FITS tapes, those written according to the
guidelines set down by the memo, are significantly different in Tucson and
Green Bank.

  This is not to imply that the approach taken by Stobie and Morgan and
their collaborators is unsuitable or inappropriate.  In fact, we believe
that their philosophy and approach are sound.  However, the inadequacies of
the memo need to be corrected and the ambiquities resolved.  A short list of
additions or changes to the memo is, we believe, all that is needed to make
it a starting point for designing a universal format.

  To initiate discussion into a reformulation of the single-dish data
exchange format, we have reproduced the text of the 1986 memo in the next
twenty or so pages.  That is followed by some comments and suggestions for
necessary corrections and improvements, and by an example of the output
which would be obtained from a FITS-writer adhering to the modified spec-
ification.

  Please note that many important and very general issues are dealt
with in a cursory fashion in the comments following the 1986 memo, and it
remains for the larger group of participants to discuss them more fully.
These issues include: possible binary representations of the data; how best
to employ a table format to contain the data--whether to use a higher dimen-
sional table format such as the 3-D extension now used for interferometer
uv-data; handling of data arising from multi-channel/multi-feed receivers;
definition of scans and scan_numbers; definition of header keywords which
are arrays;  how to treat matters which remain particular and internal to
individual telescopes; whether to include specifics of mapping modes and
descriptive coordinate origins; and many others.

       Comments, please?


Original Stobie and Morgan memo:

                          National Radio Astronomy Observatory
                                Charlottesville, Virginia

                                     October 21, 1986

To:  Single Dish Users
From: Betty Stobie, Lorrie Morgan
Subject: Single Dish FITS tape

Since the last User's Meeting the NRAO's Single Dish Programmers have been
working very hard to develop a complete and descriptive format for a single
dish FITS tape.  The advantages of using the FITS format are many:  Most users
are already familiar with the basic concept of a FITS tape, it is completely
self-documenting, and the ASCII representation can be digested by any computer
that the astronomer has at his home institution.

The first thing that had to be accomplished was to build a vocabulary of
keywords that would describe various parameters that applied to single dish
data.  Once that was done, it was important to decide exactly how the data
were going to be represented on tape.  Should it be in binary or ASCII?  If
the data would be in ASCII, how could they be incorporated into the FITS
format without violating fundamental rules of the structure of a FITS tape?
The final decision was that the FITS Tables extention would be perfect.
Single Dish header parameters would be represented in the table's header, and
the data would comprise the actual table in ASCII.  Various FITS Tables
keywords would describe in great detail the format of the table and how a
computer program could read it.

The next problem to overcome was that it was highly unlikely that our new
keywords would be approved by the FITS International Standards Committee.
So we came up with the SINGLDSH card.  The only difference between a standard
FITS card and the SINGLDSH card is in which column the keyword begins.  In the
standard FITS card, the keyword begins in column 1.  However, in the SINGLDSH
card, the word SINGLDSH begins in column 1, and the keyword begins in
column 19.  Columns 10 -- 16 will contain a qualifier that is more for
documentation purposes than anything else.  This qualifier will describe
whether the data parameter is a GENERAL single dish parameter, or whether it
really only applies to one telescope. The qualifier for the 12 -- Meter
telescope is NRAO--12M, and for the Green Bank telescopes is NRAO--GB.
(Please see the attached example of how this is implemented.)

Attached to this memo are the following:  First you will find a summary of the
keywords that appear on SINGLDSH cards.  For each parameter there is a short
definition of that single dish data parameter, followed by its FITS keyword,
followed by the units of that parameter, followed by a small note. This
summary does not include standard AIPS keywords, as those are already defined
in previous FITS documents.  Following the summary is a glossary which
describes in more detail the SINGLDSH card parameters.  An example of a single
dish FITS tape is the last section of this package.


                                - 1 -

                     Summary of SINGLDSH Card Keywords

_______________________________________________________________________________

Basic Information
_______________________________________________________________________________

Length of Header                              | HEADLEN  | Bytes   |
Length of Data                                | DATALEN  | Bytes   |
Scan Number                                   | SCAN     |         |
Observer Initials                             | OBSID    |         | C*8
Observer Name                                 | OBSERVER |         | C*16
Telescope Descriptor                          | TELESCOP |         | C*8
Project Identification                        | PROJID   |         | C*8
Source Name                                   | OBJECT   |         | C*16
Type of Data and Observing Mode               | OBSMODE  |         | C*8
Frontend Descriptor                           | FRONTEND |         | C*8
Backend Descriptor                            | BACKEND  |         | C*8
Data Precision of Spectrum                    | PRECIS   |         | C*8

_______________________________________________________________________________

Pointing Parameters
_______________________________________________________________________________

Total Az/RA Pointing Correction               | XPOINT   | Arcsec  |
Total El/Dec Pointing Correction              | YPOINT   | Arcsec  |
User Az/RA Pointing Correction                | UXPNT    | Arcsec  |
User El/Dec Pointing Correction               | UYPNT    | Arcsec  |
Pointing Constants (4)                        | PTCON    |         |12M only
Receiver Box or Secondary Orientation         | ORIENT   | Deg     |
Radial Focus                                  | RFOCUS   | M       |
North-South Focus                             | VFOCUS   | M       |
East-West Focus                               | HFOCUS   | M       |
R.A. Pointing Coefficients (3)                | RAPT     |         |GB only
Dec Pointing Coefficients (4)                 | DECPT    |         |GB only
Level Pointing Coefficients (4)               | LEVPT    |         |GB only
Extra Pointing Coefficients (10)              | EXPT     |         |GB only

_______________________________________________________________________________

Observing Parameters
_______________________________________________________________________________

Universal Time Date                           | UTDATE   |         | YYYY.MMDD
Universal Time                                | HOURUT   | Hours   |
LST                                           | HOURLST  | Hours   |
Number of Receivers                           | NORCVR   |         |
Number of Switching Variables                 | NOSWVAR  |         |
Number of Phases per Cycle                    | NOPHASE  |         |
Length of Cycle                               | CYCLLEN  | Sec     |
Sample Period                                 | SAMPRAT  | Sec     |



                                   - 2 -

_______________________________________________________________________________

Positions
_______________________________________________________________________________

Epoch                                         | EPOCH    | Years   |
Commanded Source X                            | XSOURCE  | Deg     |
Commanded Source Y                            | YSOURCE  | Deg     |
Commanded Reference X                         | XREF     | Deg     |
Commanded Reference Y                         | YREF     | Deg     |
Commanded Epoch Right Ascension               | EPOCRA   | Deg     |
Commanded Epoch Declination                   | EPOCDEC  | Deg     |
Commanded Galactic Longitiude                 | GALLONG  | Deg     |
Commanded Galactic Latitude                   | GALLAT   | Deg     |
Commanded Azimuth                             | AZ       | Deg     |
Commanded Elevation                           | EL       | Deg     |
Indicated X Position                          | INDX     | Deg     |
Indicated Y Position                          | INDY     | Deg     |
Descriptive Origin(3)                         | DESORG   | Deg     |
Coordinate System Code                        | COORDCD  |         | C*8

_______________________________________________________________________________

Environment
_______________________________________________________________________________

Ambient Temperature                           | TAMB     | Deg C   |
Pressure                                      | PRESURE  | mm Hg   |
Relative Humidity                             | HUMIDTY  | %       |
Index of Refraction                           | REFRAC   |         |
Dew Point                                     | DEWPT    | Deg C   |
MM H2O                                        | MMH2O    | mm      |

_______________________________________________________________________________

Map Parameters
_______________________________________________________________________________

Map Scanning Angle                            | SCANANG  | Deg     |
X Position at Map Reference Position Zero     | XZERO    | Deg     |
Y Position at Map Reference Position Zero     | YZERO    | Deg     |
Delta X or X Rate                             | DELTAXR  | Arcsec or Arcsec/sec
Delta Y or Y Rate                             | DELTAYR  | Arcsec or Arcsec/sec
Number of Grid Points                         | NOPTS    |         |
Number of X Grid Points                       | NOXPTS   |         |
Number of Y Grid Points                       | NOYPTS   |         |
Starting X Grid Cell Number                   | XCELL0   |         |
Starting Y Grid Cell Number                   | YCELL0   |         |
XY Reference Frame Code                       | FRAME    |         |



                                   - 3 -

_______________________________________________________________________________

Data Parameters
_______________________________________________________________________________

Beam Fullwidth at Half Maximum                | BFWHM    | Arcsec  |
Off Scan Number                               | OFFSCAN  |         |
Bad Channel Value                             | BADCHV   |         |
Velocity Correction                           | RVSYS    | M/Sec   |
Velocity with respect to Reference            | VELOCTY  | M/Sec   |
Velocity Definition and Reference             | VELDEF   |         | C*8
Type of Calibration                           | TYPECAL  |         | C*8

_______________________________________________________________________________

Engineering Parameters
_______________________________________________________________________________

Antenna Aperture  Efficiency                  | APPEFF   |         |
Antenna Beam Efficiency [ETA(MB)]             | BEAMEFF  |         |
Antenna Gain                                  | ANTGAIN  |         |
ETAL Rear Spillover & Scattering Efficiency   | ETAL     |         |
ETAFSS Forward Spillover & Scattering Eff     | ETAFSS   |         |

_______________________________________________________________________________

Telescope Dependent Parameters  -- Green Bank (Qualifier will be NRAO-GB)
_______________________________________________________________________________

L1                                            | L1       | Hz      |
L1F1                                          | L1F1     | Hz      |
L1F2                                          | L1F2     | Hz      |
L2                                            | L2       | Hz      |
L2F1                                          | L2F1     | Hz      |
L2F2                                          | L2F2     | Hz      |
LA                                            | LA       | Hz      |
LB                                            | LB       | Hz      |
LC                                            | LC       | Hz      |
LD                                            | LD       | Hz      |
Level Correction                              | LEVCORR  |         |
Pointing Fudge(2)                             | PTFUDGE  |         |
Center Frequency Formula (4)                  | CFFORM   |         | C*32

_______________________________________________________________________________

Phase Block:  Repeated for the Number of Switching Variables (NOSWVAR)
_______________________________________________________________________________

Switching Variable                            | SWVAR    |         |
Variable Value                                | VARVAL   |         |
Variable Descriptor                           | VARDES   |         | C*8
Phase Table                                   | PHASTB   |         | C*8


                                   - 4 -

_______________________________________________________________________________

Telescope Dependent Parameters  -- 12M (Qualifier will be NRAO-12M)
_______________________________________________________________________________

Synthesizer Frequency                         | SYNFREQ  | Hz      |
LO Factor                                     | LOFACT   | Hz      |
Harmonic                                      | HARMONC  | Hz      |
LO IF                                         | LO IF    | Hz      |
First IF                                      | FIRSTIF  | Hz      |
Reference Azimuth Offset                      | RAZOFF   | Arcsec  |
Reference Elevation Offset                    | RELOFF   | Arcsec  |
Beam Throw                                    | BMTHROW  | Arcsec  |
Beam Orientation                              | BMORENT  | Deg     |
Baseline Offset                               | BASEOFF  | Deg     |
Observing Tolerance                           | OBSTOL   | Arcsec  |
Sideband                                      | SIDEBAND |         |

_______________________________________________________________________________

Receiver Descriptor Block : Repeated for Number of Receivers (NORCVR) times.
_______________________________________________________________________________

Receiver Number                               | RCVR     |         |
Observed Frequency                            | OBSFREQ  | Hz      |
Rest Frequency or Total Power Calibration     | RSTFREQ  | Hz      |
Frequency Resolution or SP Calibration        | FREQRES  | Hz      |
Bandwidth                                     | BW       | Hz      |
Receiver Temperature                          | TRX      | K       |
Calibration Temperature                       | TCAL     | K       |
Source System Temperature                     | STSYS    | K       |
Reference System Temperature                  | RTSYS    | K       |
Source Temperature                            | TSOURCE  | K       |
RMS of Mean                                   | TRMS     |         |
Reference Point Number                        | REFPT    |         |
X Value at the Reference Point                | X0       |         |
Delta X                                       | DELTAX   |         |
Total Integration Time                        | INTTIME  | Sec     |
Number of Integrations or channels            | NOINT    |         |
Starting Point Number                         | SPN      |         |
H2O Opacity                                   | TAUH2O   |         |
H2O Temperature                               | TH2O     | K       |
O2 Opacity                                    | TAUO2    |         |
O2 Temperature                                | TO2      | K       |
Polarization                                  | POLARIZ  |         | C*8
RHO                                           | RHO      | Deg     |
THETA                                         | THETA    | Deg     |
Calibration value                             | CALVOLTS | Volts   |

                                - 5 -

                      Single Dish FITS Format Glossary

Basic Information

     These parameters are used to identify the block of data with a
particular Observer/Project/Telescope.

     Scan Number - SCAN
            A number assigned at the telescope to be associated with
            this scan.
            If this scan is not averaged but is exported as individual
            records, then the record number is appended after the
            decimal point.  A maximum of 9999 records are allowed.
            For example, record number one of scan 500 would be 500.0001  .

     Observer Initials - OBSID
            A data ID used to segregate each observer's data.

     Observer Name - OBSERVER
            Name of the primary Observer.

     Telescope Descriptor - TELESCOP
            A field of eight characters to describe where the data are taken.
            NRAO12M               NRAO42M               NRAO93M
            MPI100M               IRAM30M               NRO45M
            PMO14M                OSO20M                MASS14M
            UTX5M                 UK-D15M               IRAM15M

     Project Identification - PROJID
            The program ID associated with the proposal as it appears on
            the telescope schedule.

     Source Name - OBJECT
            As provided by the observer.

     Type of Data and Observing Mode - OBSMODE
            Field of 8 characters where four describe the type of data
            and four describe the observing mode.
            Type of Data                           Observing Mode
            LINE                                   PSSW      PLSW
            CONT                                   FQSW      SHSW
            FSAM                                   BMSW      LDSW
            PULS                                   TLPW

    Frontend Descriptor - FRNTEND
            A field of 8 characters to describe the receiver used.
            Typical NRAO frontends are:
            2C3MMSIS             140CASS             2.7-1.2M
            2C3MMSHM             21CM 4CH            1.2-0.6M
            2MM                  11CM3CH             100-30CM
            .8MM                 6/25 6CM            25-20 CM
            BOLOMETR             23-17CM             6/2525CM
                                 15-0.6CM


                                   - 6 -

    Backend Descriptor - BACKEND
            A field of 8 characters to describe the backend used.
            Typical NRAO backends are:
            DIGITAL              STD A/D            FABRITEK
            384ACIII             1024ACIV           1536HYSP
            .03MHZFB             .1MHZ FB           .25MHZFB
            .5MHZ FB             1.MHZ FB           2.MHZ FB

    Data Precision of the Spectrum - PRECIS
            The specification of the nuber of bits and data type used
            to represent the data.  It may be one of the following:
            L*1   I*2   I*4  R*4   R*8   R*16   C*8   C*16

Pointing Parameters

     This group of parameters refers to the telescope pointing, both
those offsets and terms provided by the observer and those computed by
the online program.

     Total Az/RA Pointing Correction - XPOINT
            The total pointing correction applied in the X (horizontal)
            direction.

     Total El/Dec Pointing Correction - YPOINT
            The total pointing correction applied in the Y (vertical)
            direction.

     User Az/RA Pointing Correction - UXPNT
            Additional X pointing correction supplied by the observer.

     User El/Dec Pointing Correction - UYPNT
            Additional Y pointing correction supplied by the observer.

     Pointing Constants and Coefficients - PTCON, RAPT, DECPT, LEVPT, EXPT
            Constants to describe a secondary pointing correction.
            At the 12M these are A0, C, B0 and EL0 in the expressions below:
            Delta Az = A0 * COS(EL) + C
            Delta El = B0 * COS(EL) + EL0
            At the 42M these constants refer to the PVAL's.

     Receiver or Secondary Orientation - ORIENT
            Rotation or polarization angle orientation of the receiver
            or reflector at the prime focus.

     Radial Focus - RFOCUS
            Radial focus position.

     North-South Focus - VFOCUS
            Vertical focus offset.

     East-West Focus - HFOCUS
            Horizontal focus offset.


                                   - 7 -

Observing Parameters

     A group of parameters that characterize the when and how of the
observations.

    Universal Time Date - UTDATE
    Universal Time  - HOURUT
    LST - HOURLST
            Date and time at the start of the observation.

    Number of Receivers - NORCVR
            The number of independent polarizations or channels of this
            frontend.  When receiver channels refer to different positions
            in the sky, they are expressed as separate scans.

     The following parameters are defined as a very general description
of observations made with one or more of the observing variables being
switched.  For example, in beam-switched observations one variable, sky
position, is switched (via subreflector motion or a comparision of two
feed horns).  One could also imagine beam switching at the same time that
polarization was switched -- in this case 2 variables are switched.   IF
"phase" of a switched variable is used to describe one state of the switch,
then a 2-position subreflector nutation, for example, would be a switch with
"2 phases" per cycle.  Similarly, if one switches between a center frequency
and 2 offset frequencies, then this switch has "3 phases" per cycle and
so forth.

     Number of Switching Variables - NOSWVAR
            A simple count of the number of variables being switched.

     Number of Phases per Cycle - CYCLLEN
            A count of the number of different states of the
            switched variables.

     Sample Period - SAMPRAT
            The time required to complete a single sample.  A sample
            may be composed of multiple cycles.  Also known as the
            SAMPLE RATE.

Positions

     For each scan the telescope is given, or computes following the
observer's instructions, a position at a particular epoch.  The right
ascension of that position is "Epoch Right Ascension" and the declination
is "Epoch Declination".  At the time of the observation, however, the
telescope is directed to a position corresponding to horizontal coordinate
"xcoord", which may be either RA(date) or AZ(date), and corresponding
to vertical coordinated "ycoord", which may be DEC(date) or EL(date).
The actual position that the telescope points to differs from "xcoord"
and "ycoord" by whatever are the current pointing offsets.  This position,
i.e., the position at which the telescope actually points, is the "indicated"
position described by horizontal coordinate "indicated x telescope
position" and vertical telescope coordinate "indicated y telescope
position".  Finally, using RA(epoch) one calculates the Galactic
coordinates "longitude and latitude".  For all observations the above


                                   - 8 -

parameters have meaning and  are computed.  If the observer wishes to
define his own coordinate system relative to one of the standard
coordinate systems defined above, he does so with the descriptive
coordinate array.

     Epoch - EPOCH
            As specified by the observer.

     Commanded Source Xcoord - XSOURCE
            Horizontal coordinate of source or position in the coordinate
            system specified by the observer.

     Commanded Source Ycoord - YSOURCE
            Vertical coordinate of source or position in the coordinate
            system specified by the observer.

    Commanded Reference Xcoord - XREF
            Horizontal coordinate of the reference position in the
            coordinate system specified by the observer.

    Commanded Reference Ycoord - YREF
            Vertical coordinate of the reference position in the
            coordinate system specified by the observer.

     Epoch Right Ascension - EPOCRA
            RA at "Epoch" of the source or position specfied.

     Epoch Declination - EPOCDEC
            Dec at "Epoch" of the source or position specified.

     Commanded Galactic Longitude - GALLONG
            Longitude of the source or position specified.

     Commanded Galactic Latitude - GALLAT
            Latitude of source or position specified.

     Commanded Azimuth - AZ
            Azimuth of the source or position specified.

     Commanded Elevation - EL
            Elevation of the source or position specified.

    Indicated Xcoord - INDX
            Horizontal telescope coordinate of the position actually
            observed, i.e. position measured by horizontal encoder.

    Indicated Ycoord - INDY
            Vertical telescope coordinate of the position actually
            observed, i.e., position measured by vertical encoder.



                                   - 9 -

    Descriptive Origin(3) - DESORG
            An orthogonal 2-dimensional coordinate system defined by
            the observer by means of
               a. - horizontal position
               b. - vertical position
               c. - position angle describing the orientation on the
                    sky, of the "horizontal axis".

    Coordinate System Code - COORDCD
            An 8 character string indicating in which coordinate system
            the observations are commanded:
                Galactic - GALACTIC
                1950 RA, Dec - 1950RADC
                Epoch RA, Dec - EPOCRADC
                Mean RA, Dec at start of scan - MEANRADC
                Apparent RA, Dec - APPRADC
                Apparent HA, Dec - APPHADC
                1950 Ecliptic - 1950ECL
                Epoch Ecliptic - EPOCECL
                Mean Ecliptic at start of scan - MEANECL
                Apparent Ecliptic - APPECL
                Azimuth, Elevation - AZEL
                User defined coordinate system - USERDEF
                2000 RA, Dec - 2000RADC
                Indicated RA, Dec - INDRADC

Environment

     The environment parameters define the external physical conditions
affecting the telescope.

     Ambient Temperature - TAMB
     Pressure - PRESURE
     Relative Humidity - HUMIDTY
     Index of Refraction - REFRAC
     Dew Point DEWPT
     MM H2O - MMH2O

Map Parameters

     The purpose here is to store an entire map as a single entity.
The map is understood to be rectangular with dimensions "xpoints" by
"ypoints" where these parameters simply count the number of map cells
along the two orthogonal axes of the rectangular map.  The orientation
on the sky of the rectangle is defined by "map scanning angle", with
this angle referring to the orientation of the horizontal, x, axis.
A reference point for the map on the sky is specified by means of the
horizontal and vertical telescope coordinates "xposition at zero" and
"yposition at zero", respectively.  The reference point need not be
the center of the rectangle and, in fact, need not even be within the
region mapped.  The rectangle to be mapped is fully described by the
parameters "starting xcell" and "starting ycell", together with the
total number of points to be sampled in each coordinate "xpoint" and
"ypoint", respectively.

                                   - 10 -

     For example, suppose we wish to construct a square map with 41
points on a side centered on the reference position.  In this case,

         Starting xcell    :  XCELL0 = -20
         Starting ycell    :  YCELL0 = -20
         Number of xpoints :  NOXPTS = 41
         Number of ypoints :  NOYPTS = 41

On the other hand, suppose we wish to make the same map near, but not
including, that same reference position.  Then, perhaps

         Starting xcell    :  XCELL0 = 20
         Starting ycell    :  YCELL0 = -61
         Number of xpoints :  NOXPTS = 41
         Number of ypoints :  NOYPTS = 41

and the region from (x,y) = (20,-61) to (x,y) = (61,-20) will be mapped.

     Map Scanning Angle - SCANANG
            Orientation on the sky in the reference frame specified by
            "XY Reference Frame Code" of the rectangle to be mapped.
            It is not the angle through the rectangle that the telescope
            is driven.  This provides an alternate capability to that
            of using descriptive coordinates.

     X position at Zero - XZERO
            Horizontal telescope coordinate at the map reference position.
            Together with "Y position at Zero", this defines the cell
            (X,Y) = (0,0) at the map reference position.

     Y position at Zero - YZERO
            Vertical telescope coordinate at the map reference position.

     Delta X or X Rate - DELTAXR
            The cell size or distance (in minutes of arc/minutes of time)
            between cells on the x axis.

     Delta Y or Y Rate - DELTAYR
            The cell size or distance between cells on the y axis.

     Number of X points - NOXPTS
            Map sample points along the "x-edge" of the rectangle.

     Number of Y points - NOYPTS
            Map sample points along the "y-edge" of the rectangle.

     Number of Points - NOPTS
            Total number of cells in the map.  This should be (x*y).

     Starting X cell - XCELL0
            Cell number.  May be positive, negative or zero.  It is
            used to define the position of the rectangle to be mapped
            with respect to the reference position which, by definition
            is (x,y) = (0,0).


                                   - 11 -

    Starting Y cell - YCELL0
            Cell number as above.

    XY Reference Frame Code - FRAME
            An eight character code which states whether the grid is
            polar (POLR) or cartesian (CART) and whether items 3 and
            4 refer to STEP sizes or SCANning rates.

Observing Parameters

     Beam Full Width at Half Maximum - BFWHM
            Telescope main beamwidth at the observing frequency.

     Off Scan Number - OFFSCAN
            Scan number of the last designated total power off scan.

     Bad Channel Value - BADCHV
            The antenna temperature to be assigned to those filterbank
            channels that are noted as defective.

     Velocity with respect to the Reference - VELOCTY
            The source velocity specified by the observer relative to
            the velocity reference frame.

     Velocity Definition and Reference - VELDEF
          An eight character field to describe the velocity system.
          The velocity definition may be:
          RADI                 OPTL                RELV
          The velocity reference may be:
          LSR         HELO     EART       BARI     OBS

Engineering Parameters

     This is an area for describing the physical aspects of the
telescope.

     Antenna Aperture Efficiency - APPEFF
            The ratio of total power observed to the total power
            incident on the telescope.

     Antenna Beam Efficiency - BEAMEFF
            The fraction of the beam lying in a diffraction limited
            main beam.

     Antenna Gain - ANTGAIN

     ETAL -
            Rear Spillover and Scattering Efficiency

     ETAFSS -
            Forward Spillover and Scattering Efficiency



                                   - 12 -

Telescope Dependent Parameters

     This is an area words reserved for those parameters that are unique
to a given telescope.
     For the Green Bank telescopes they are:
the LO values - L1, L1F1, L1F2, L2, L2F1, L2F2, LA, LB, LC, LD ,
the level correction, the pointing fudge(2), and the center frequency
formula(4).
     For the 12M telescope they are:
synthesizer frequency, LO Factor, Harmonic LOIF, first IF, reference
azimuth offset, reference elevation offset, beam throw, beam orientation,
baseline offset, sideband and observing tolerance.

Phase Block

     This block describes what variables are switched in the scan.
For instance, a scan may be position switched, beam switched, frequency
switched, load switched, focus switched, polarization switched, or
any combination of the above or simply a measure of total power.
The variable value is the value of one switch state.  For example, to
switch high and low about a center frequency requires three variable
values.  A total power observation requires one value.
     Associated with each variable value is a variable descriptor of
eight characters and a 32 bit phase table which reflects when that
particular state is on with a one and when it is off with a 0.  These
three parameters are repeated for as many times as there are switching
states.  Also note that the phases appear in the description of the
spectrum in the same order as they appear here.

     This Switching Variable - SWVAR

     Variable Value - VARVAL
            The value of a single switch state.

     Variable Descriptor - VARDES
            An 8 character descriptor of the switching variable.

     Phase Table - PHASTB
            A bit-map description of when each switch state is on and
            off.  An integration can have a maximum of 32 states.

     An example of a phase block is shown below:
An observation is made by switching the telescope position and the
focus.  There are five switching states.  The table would look like
Variable Values - 0, +30, -30, +54, -54
Variable Descriptors - POSN ON, POSN HI, POSN LO, FOCUS HI, FOCUS LO
Phase Table - 0 0 1 1 1 1 0 0
              1 1 0 0 0 0 0 0
              0 0 0 0 0 0 1 1
              1 0 1 0 1 0 1 0
              0 1 0 1 0 1 0 1



                                   - 13 -

Descriptor Block for each Receiver Channel

     Certain parameters vary with an individual receiver channel.  When
multiple polarizations are used, this block must be repeated for each
channel.

     This receiver number - RCVR

     Observed Frequency - OBSFREQ
            The center frequency of the observation.

     Rest Frequency/Total Power Calibration - RSTFREQ
            In the spectral line observation the rest frequency of the
            observation or in the continuum observation the total power
            calibration.

     Frequency Resolution/Switched Power Calibration - FREQRES
            In the spectral line observation the frequency spacing of the
            spectral line backend or in the continuum observation the
            switched power calibration.

     Bandwidth - BW
            The total bandwidth in MHz of this receiver channel.

     Receiver Temperature - TRX
            The receiver temperature measured for a given channel.

     Calibration Temperature - TCAL
            The value of the noise tube diode or other calibration
            temperature used to calibrate the data.

     Source System Temperature - STSYS
            The system temperature measured on source.

     Reference System Temperature - RTSYS
            The system temperature measured on reference.

     Source Temperature - TSOURCE
            Source temperature computed for a series of on-off samples.

     RMS -
            RMS value about the mean source temperature.

     Reference Point Number - REFPT
            The position in the spectral line device for which the
            observer enters a freqency and/or velocity.  It is usually
            the first or center channel.

     X value at the Reference Point - X0
            Value of the x-axis at the reference point.

     Delta X - DELTAX
         The step size along the x-axis.



                                   - 14 -

     Total Integration Time - INTTIME
            The total integration time for this receiver channel.

     Number of Integrations or Channels - NOINT
            The number of data points for this receiver channel.

     Starting Point Number - SPN
            The starting point location of this receiver channel in
            the data area.

     H2O Opacity - TAUH2O
            The opacity of water as computed by a model.

     H2O Temperature - TH2O
            The temperature of water.

     O2 Opacity - TAUO2
            The opacity of oxygen as computed by a model.

     O2 Temperature - TO2
            The temperature of oxygen.

     Polarization Description - POLARIZ
            An eight character field to describe the type of polarization
            and the angle.  The type may be RC, LC or LIN.  The angle
            can be expressed to the nearest tenth of a degree.


                                - 15 -

Original Example from Stobie and Morgan Memo:

      0........1.........2.........3.........4.........5.........6.........7...
      1234567890123456789012345678901234567890123456789012345678901234567890123

1: 1  SIMPLE  =                    T                / Standard FITS format
1: 2  BITPIX  =                    8                / Character information
1: 3  NAXIS   =                    0                / No image data array prese
1: 4  EXTEND  =                    T                / There may be standard ext
1: 5
1: 6  DATE    = '09/18/86'                          / Date tape written
1: 7  ORIGIN  = 'TUCVAX  '                          / Site which wrote this tape
1: 8
1: 9  COMMENT  This is a FITS tape of Tucson
1:10  COMMENT  Spectral Line data.  It is written
1:11  COMMENT  using the FITS Tables Extension
1:12  COMMENT  format.  The first 2880-byte record
1:13  COMMENT  is the main FITS header.  Following
1:14  COMMENT  the main header is a table for each
1:15  COMMENT  scan.  Each table contains one or more
1:16  COMMENT  header records followed by one or more
1:17  COMMENT  data records.
1:18
1:19
1:20  COMMENT  General Single Dish parameters have
1:21  COMMENT  the GENERAL qualifier.  Telescope
1:22  COMMENT  dependent parameters have a qualifier
1:23  COMMENT  which indicates the telescope.
1:24  COMMENT  In a SINGLDSH card, the qualifier
1:25  COMMENT  starts in column 10, the keyword in
1:26  COMMENT  column 19, and the "=" in column 27.
1:27  END
1:28
1:29
1:30
1:31
1:32
1:33
1:34
1:35
1:36

                                - 16 -

      0........1.........2.........3.........4.........5.........6.........7...
      1234567890123456789012345678901234567890123456789012345678901234567890123

2: 1  XTENSION= 'TABLE   '                          / Standard table
2: 2  BITPIX  =                   16                / 16-bits per "pixel"
2: 3  NAXIS   =                    2                / Simple 2-D matrix
2: 4  NAXIS1  =                    8                / # chars in field
2: 5  NAXIS2  =                    8                / # fields in data table
2: 6  PCOUNT  =                    0                / No "random" parameters
2: 7  GCOUNT  =                    1                / Only one group
2: 8  TFIELDS =                    1                / # columns in data table
2: 9  TBCOL1  =                    1                / Starting column
2:10  TFORM1  = 'I8      '                          / Format of data entry
2:11  TTYPE1  = 'CH-TEMP '                          / Heading for column 1
2:12  TUNIT1  = 'K       '                          / Units of data for column 1
2:13  TSCAL1  =                 0.15                / Real=(Data/TSCAL1)+TZERO1
2:14  TZERO1  =                 -.25                / Zero offset
2:15  SINGLDSH GENERAL  HEADLEN =  1024.0000        / Length of header in bytes
2:16  SINGLDSH GENERAL  DATALEN =  32.000000        / Length of data in bytes
2:17  SINGLDSH GENERAL  SCAN    =  8702.0000        / Scan number
2:18  SINGLDSH GENERAL  OBSID   = 'DEH WS  '        / Observer & Operator Initi
2:19  SINGLDSH GENERAL  OBSERVER= 'HOGG            '/ Observer Name
2:20  SINGLDSH GENERAL  TELESCOP= 'NRAO 12M'        / Telescope
2:21  SINGLDSH GENERAL  PROJID  = 'TEST    '        / Project ID
2:22  SINGLDSH GENERAL  OBJECT  = 'VENUS           '/ Source Name
2:23  SINGLDSH GENERAL  OBSMODE = 'CONTBMSW'        / Type of data & observing
2:24  SINGLDSH GENERAL  FRNTEND = '2C3MMSHM'        / Front End
2:25  SINGLDSH GENERAL  BACKEND = 'STD A/D '        / Back End
2:26  SINGLDSH GENERAL  PRECIS  = 'R*4     '        / Data precision
2:27  SINGLDSH GENERAL  XPOINT  = 0.00000000E+00    / Az/RA Pointing Corr (Arcs
2:28  SINGLDSH GENERAL  YPOINT  = 0.00000000E+00    / El/Dec Pointing Corr (Arc
2:29  SINGLDSH GENERAL  UXPNT   =  6.7977800        / User Az/RA Correction (Ar
2:30  SINGLDSH GENERAL  UYPNT   = -32.752941        / User El/Dec Correction(Ar
2:31  SINGLDSH GENERAL  PTCON1  = 0.00000000E+00    / Pointing constant - PVLS
2:32  SINGLDSH GENERAL  PTCON2  = 0.00000000E+00    / Pointing constant - PVLS
2:33  SINGLDSH GENERAL  PTCON3  =  41500000.        / Pointing constant - PVLS
2:34  SINGLDSH GENERAL  PTCON4  = 0.00000000E+00    / Pointing constant - PVLS
2:35  SINGLDSH GENERAL  ORIENT  = 0.00000000E+00    / Rcvr Box or Sec Orient (D
2:36  SINGLDSH GENERAL  UTDATE  =  1986.0914        / Universal Time Date(YYYY.

                                - 17 -

      0........1.........2.........3.........4.........5.........6.........7...
      1234567890123456789012345678901234567890123456789012345678901234567890123

3: 1  SINGLDSH GENERAL  HOURUT  =  1.6625977        / Universal Time (hours)
3: 2  SINGLDSH GENERAL  HOURLST =  17.738038        / LST (hours)
3: 3  SINGLDSH GENERAL  NORCVR  =  1.2000000        / Number of Receivers
3: 4  SINGLDSH GENERAL  NOSWVAR = 0.00000000E+00    / Number of Switching Varia
3: 5  SINGLDSH GENERAL  NOPHASE = 0.00000000E+00    / Number of Phases per Cycle
3: 6  SINGLDSH GENERAL  CYCLLEN = 0.00000000E+00    / Length of cycle (Sec)
3: 7  SINGLDSH GENERAL  SAMPRAT =  5.0000000        / Sample Period (Sec)
3: 8  SINGLDSH GENERAL  EPOCH   =  1950.0000        / Epoch of observation (Yea
3: 9  SINGLDSH GENERAL  XSOURCE =  211.82739        / Comm. Source RA (Deg)
3:10  SINGLDSH GENERAL  YSOURCE = -17.182789        / Comm. Source Dec (Deg)
3:11  SINGLDSH GENERAL  XREF    = 0.00000000E+00    / Comm. Reference RA (Deg)
3:12  SINGLDSH GENERAL  YREF    = 0.00000000E+00    / Comm. Reference Dec (Deg)
3:13  SINGLDSH GENERAL  EPOCRA  =  211.82739        / Comm. Epoch RA (Deg)
3:14  SINGLDSH GENERAL  EPOCDEC = -17.182789        / Comm. Epoch Dec (Deg)
3:15  SINGLDSH GENERAL  GALLONG = 0.00000000E+00    / Comm. Galactic Longitude
3:16  SINGLDSH GENERAL  GALLAT  = 0.00000000E+00    / Comm. Galactic Latitude (
3:17  SINGLDSH GENERAL  AZ      =  234.86573        / Comm. Azimuth (Deg)
3:18  SINGLDSH GENERAL  EL      =  18.501036        / Comm. Elevation (Deg)
3:19  SINGLDSH GENERAL  INDX    = 0.00000000E+00    / Indicated X Position (Deg)
3:20  SINGLDSH GENERAL  INDY    = 0.00000000E+00    / Indicated Y Position (Deg)
3:21  SINGLDSH GENERAL  DESORG  = 0.00000000E+00    / Descriptive origin
3:22  SINGLDSH GENERAL  DESORG  = 0.00000000E+00    / Descriptive origin
3:23  SINGLDSH GENERAL  DESORG  = 0.00000000E+00    / Descriptive origin
3:24  SINGLDSH GENERAL  COORDCD = '1950RADC'        / Coordinate system code
3:25  SINGLDSH GENERAL  TAMB    =  19.209999        / Ambient Temp (Deg C)
3:26  SINGLDSH GENERAL  SCANANG = 0.00000000E+00    / Map scanning angle (Deg)
3:27  SINGLDSH GENERAL  XZERO   = 0.00000000E+00    / X Pos at Map Ref Pos Zero
3:28  SINGLDSH GENERAL  YZERO   = 0.00000000E+00    / Y Pos at Map Ref Pos Zero
3:29  SINGLDSH GENERAL  DELTAXR = 0.00000000E+00    / Delta X or X Rate (Arcsec)
3:30  SINGLDSH GENERAL  DELTAYR = 0.00000000E+00    / Delta Y or Y Rate (Arcsec)
3:31  SINGLDSH GENERAL  NOPTS   = 0.00000000E+00    / Number of Grid Points
3:32  SINGLDSH GENERAL  NOXPTS  = 0.00000000E+00    / Number of X Grid Points
3:33  SINGLDSH GENERAL  NOYPTS  = 0.00000000E+00    / Number of Y Grid Points
3:34  SINGLDSH GENERAL  XCELLO  = 0.00000000E+00    / Starting X Cell Grid Numb
3:35  SINGLDSH GENERAL  YCELLO  = 0.00000000E+00    / Starting Y Cell Grid Numb
3:36  SINGLDSH GENERAL  FRAME   = '        '        / XY Reference Frame Code

                                - 18 -

      0........1.........2.........3.........4.........5.........6.........7...
      1234567890123456789012345678901234567890123456789012345678901234567890123

4: 1  SINGLDSH GENERAL  BFWHM   =  35.000000        / Beam Fwdth at Half Max(Ar
4: 2  SINGLDSH GENERAL  OFFSCAN = 0.00000000E+00    / Off-Scan number
4: 3  SINGLDSH GENERAL  BADCHV  =  2.0000000        / Bad channel value
4: 4  SINGLDSH GENERAL  RVSYS   = 0.00000000E+00    / Velocity Correction (M/S)
4: 5  SINGLDSH GENERAL  VELOCTY = 0.00000000E+00    / Velocity wrt Reference (M
4: 6  SINGLDSH GENERAL  VELDEF  = '      '          / Velocity Definition
4: 7  SINGLDSH GENERAL  TYPECAL = 'NOISE TU'        / Type of Calibration
4: 8  SINGLDSH GENERAL  APPEFF  = 0.44999999        / Antenna Aperture Efficien
4: 9  SINGLDSH NRAO-12M SYNFREQ = 0.19476300E+10    / Synthesizer Frequency (Hz)
4:10  SINGLDSH NRAO-12M LOFACT  = 0.00000000E+00    / LO Factor (Hz)
4:11  SINGLDSH NRAO-12M HARMONC =  45000000.        / Harmonic (Hz)
4:12  SINGLDSH NRAO-12M LOIF    = 0.10000000E+09    / LO IF (Hz)
4:13  SINGLDSH NRAO-12M FIRSTIF = 0.15000000E+10    / First IF (Hz)
4:14  SINGLDSH NRAO-12M RAZOFF  = -232.97845        / Ref Az Offset (Arcsec)
4:15  SINGLDSH NRAO-12M RELOFF  = -32.752941        / Ref El Offset (Arcsec)
4:16  SINGLDSH NRAO-12M BMTHROW =  1.5000000        / Beam Throw (Arcsec)
4:17  SINGLDSH NRAO-12M BMORENT = 0.00000000E+00    / Beam Orientation (Deg)
4:18  SINGLDSH NRAO-12M BASEOFF =  26.080000        / Baseline Offset (Deg)
4:19  SINGLDSH NRAO-12M OBSTOL  =  5.0000000        / Observing Tolerance (Arcs
4:20  SINGLDSH NRAO-12M SIDBAND = 0.00000000E+00    / Sideband
4:21  SINGLDSH GENERAL  RCVR    =  1.0000000        / This receiver number
4:22  SINGLDSH GENERAL  OBSFREQ = 0.86243350E+11    / Observed Frequency (Hz)
4:23  SINGLDSH GENERAL  RSTFREQ = 0.92000000E+09    / Rst Freq or TP Cal (Hz)
4:24  SINGLDSH GENERAL  FREQRES = 0.70200000E+09    / Freq Res or SP Cal (Hz)
4:25  SINGLDSH GENERAL  BW      = 0.60000000E+09    / Band Width (Hz)
4:26  SINGLDSH GENERAL  TRX     = 0.00000000E+00    / Receiver Temp (K)
4:27  SINGLDSH GENERAL  TCAL    =  8.0000000        / Calibration Temp (K)
4:28  SINGLDSH GENERAL  STSYS   =  310.00000        / Signal System Temp (K)
4:29  SINGLDSH GENERAL  RTSYS   = 0.00000000E+00    / Ref System Temp (K)
4:30  SINGLDSH GENERAL  TSOURCE =  21.547501        / Source Temp (K)
4:31  SINGLDSH GENERAL  TRMS    = 0.17749977        / RMS of Mean
4:32  SINGLDSH GENERAL  REFPT   =  1.0000000        / Ref Point Number
4:33  SINGLDSH GENERAL  X0      =  1.0000000        / Velocity at Ref Point (M/
4:34  SINGLDSH GENERAL  DELTAX  =  1.0000000        / Delta X
4:35  SINGLDSH GENERAL  INTTIME =  5.0000000        / Total Integration Time (S
4:36


                                - 19 -

      0........1.........2.........3.........4.........5.........6.........7...
      1234567890123456789012345678901234567890123456789012345678901234567890123

5: 1  SINGLDSH GENERAL  NOINT   =  8.0000000        / # Integrations or channels
5: 2  SINGLDSH GENERAL  SPN     =  1.0000000        / Starting point number
5: 3  SINGLDSH GENERAL  TAUH2O  = 0.50000001E-01    / H2O Opacity
5: 4  SINGLDSH GENERAL  TH2O    = 0.00000000E+00    / H2O Temp (K)
5: 5  SINGLDSH GENERAL  TAUO2   = 0.00000000E+00    / O2 Opacity
5: 6  SINGLDSH GENERAL  TO2     = 0.00000000E+00    / O2 Temp (K)
5: 7  SINGLDSH GENERAL  POLARIZ = '        '        / Polarization
5: 8  END
5: 9
5:10
5:11
5:12
5:13
5:14
5:15
5:16
5:17
5:18
5:19
5:20
5:21
5:22
5:23
5:24
5:25
5:26
5:27
5:28
5:29
5:30
5:31
5:32
5:33
5:34
5:35
5:36
 
                                - 20 -

      0........1.........2.........3.........4.........5.........6.........7...
      1234567890123456789012345678901234567890123456789012345678901234567890123

6: 1       710   32767   32767     488       0   31700   31893     310       0
6: 2
6: 3
6: 4
6: 5
6: 6
6: 7
6: 8
6: 9
6:10
6:11
6:12
6:13
6:14
6:15
6:16
6:17
6:18
6:19
6:20
6:21
6:22
6:23
6:24
6:25
6:26
6:27
6:28
6:29
6:30
6:31
6:32
6:33
6:34
6:35
6:36


                                - 21 -

Corrections and changes to the Stobie and Morgan memo:

Cover page:  We STRONGLY suggest that data be in binary form, either in
IEEE floating point or integer.  Writing data in ASCII has proved to be too
expensive (in CPU and in tape) to support once we consider the large volumes
of data which have been and will be accumulated.

We still believe that the TABLE extension to FITS give us the versatility to
handle the complicated, multi-phase data produced by backends which
already exist and will exist in the future.

The hierarchical keyword approach is also a good one but probably was not taken
far enough in the original memo.  For example, we can see certain keywords as
being necessary for certain analysis systems but no provision was made for
these variable.  In the original memo, analysis keywords were under the
GENERAL category when they should probably be under a new category with a name
like ANALYSIS  PROGNAME  KEYWORD where PROGNAME is the name of the analysis
program which requires or produces a value for that keyword.

No where in their memo do they discuss the method whereby new GENERAL keywords
are to be added to the list.  We propose a committee approach, made up of
people from a few observatories, which will oversee the creation of new
keywords.

Apparently, the keywords under the IRAM-30M, NRAO-43M, NRAO-12M,
etc. categories should be under the control of the respective observatories.
Likewise, if the ANALYSIS category is added, the programmers in charge of the
various analysis programs should have control over the keywords under their
respective category.

In many cases, the units or definitions of the various keywords in the original
memo are wrong or don't exist.  Whether pointing corrections, for example, are
in arc seconds or degrees is a trivial point but one which all must agree
upon.  In many cases in the memo, some parameters have values which are not in
SI units.  Only SI units should be used.

The memo does not describe the layout of the tape.  We could block the output
tapes by a factor of ten from 2880 byte records to 28,800 bytes.  This would
save both time and tape.  In addition, we suggest that, whenever possible,
a single FITS file be used for one data set.  However, some observers may
want unblocked records and one scan/one file type of FITS files; do we
leave them the option?

When a keyword does not have a value, maybe because that keyword doesn't
apply to the telescope or observations, then that keyword should not appear in
the FITS header.  The assigning of zero to keywords which have no value can
lead to major problems.

In a single file, keywords should not be repeated unless the value of
the keyword has changed.  For example, if all scans in the FITS file were
taken at the same position in the sky, then the keywords which give the
position will only appear once in the file.  This will save tape since only
a handful of keywords probably will change from scan to scan.


                                - 22 -

Summary of SINGLDSH Card Keywords:

Basic Information:

HEADLEN, DATALEN are not needed and are ill defined quantities

Most readers and analysis programs will need to know the value of OBSMODE.
Probably, OBSMODE should be a telescope dependent keyword (i.e.,
as SINGLDSH IRAM-30M OBSMODE =  .....).  The same should hold for
FRONTEND and BACKEND.

PRECIS is confused with the BITPIX parameter. If the latter is to have its
usual meaning, PRECIS should be eliminated or entirely redefined.

Pointing Parameters:

The sense of the pointing corrections is not defined in the memo.  We suggest
that the correction be in the sense of (measured - catalog).  The units for
these corrections should be degrees, and not arcsec.

Items like PTCON, RAPT, DECPT, LEVPT, EXPT are different for each telescope
in the world.  Many observers don't care about these items once they leave
the telescope.  We suggest that each observatory develop and take care of its
own set of keywords for pointing coefficients and that these keywords go under
the NRAO-12M, IRAM-30M, etc subcategories.

ORIENT is ill defined in the sense of rotation.  We should pick some convention
and stick with it.  Observers with polarization experiments will thank us for
it.

Observing Parameters:

The handling of multi-feed data will become more and more important as time
goes on.  Probably the only way of storing such data is to give each feed
its own scan number.  Probably some convention should be accepted; for example
an observer's tenth observation taken through feed 4 could be given the scan
number 10.004.  Since we are not repeating keywords, we will only be wasting
a minimum amount of tape.

We also suggest that multi polarization data should be handled in the same
way and not stored as a unit, as is stated in the original memo.  NORCVR will
then always have the value of one and that keyword, since it is useless, can
be eliminated.

Positions:

In the memo, DESORG was an array of length three.  Since keyword arrays cannot
be handled in a FITS header, one option we have is to make such keywords look
look like PTCON in the preceding example:  DESORG01, DESORG02....  Other array
keywords created in the future could be handled in a similar fashion.

Every observatory has its own definition of DESORG.  We should pick some
convention for designating a user-defined coordinate system.

We suggest the introduction of APPRA and APPDEC for storing apparent RA, DEC.


                                - 23 -

Environment:

Other keywords could be added, as the Single-Dish FITS committee sees fit.

Map Parameters:

The keywords described in the memo are very specific to the way mapping is
done at the 12-meter telescope.  Few observatories and telescopes would want
to map in the same fashion.  Therefore, we suggest that these mapping
parameters be under the NRAO-12M category and that each observatory develop
its own set of mapping parameters.  (Note that many of the memo's mapping
keywords are ill defined or ambiguous.)

Data Parameters:

TYPECAL is also a telescope specific item and should be treated like FRNTEND.

Engineering Parameters:

No comment except that the definitions of these parameters must be agreed
upon at some level.

Telescope Dependent Parameters:

Here is where each observatory has full control of what is to be included.
Certain critiques should be adhered to in order that the results will be a
legitimate FITS file.  For example, only SI units please.  No redundant
keywords, unless you want only the latest value of a keyword to be used.

Phase Table:

Again, we have the same problem as DESORG in that the same keyword can be
given different values.  Numeric suffixes should be added to SWVAR, VARVAL,
VARDES, and PHASTB.  For example, you could have VARDES1, VARDES2, etc.
The keyword SWVAR would become unnecessary.

The bit-map encoding of the phase information in PHASTB might better be made
out of a series of ASCII ones and zeros.  Taking the example in the memo, we
get:

SINGLDSH  GENERAL   PHASTB1 = '00111100          ' / Phase Table 1
SINGLDSH  GENERAL   PHASTB2 = '11000000          ' / Phase Table 2
SINGLDSH  GENERAL   PHASTB3 = '00000011          ' / Phase Table 3

etc.


                                - 24 -

Receiver Descriptor Block:

As suggested by the memo, the receiver descriptor keywords could be repeated
as many times as the value of NORCVR.  However, like DESORG, there was no
thought into multiple values for the same keywords.  If we always have
NORVCR = 1, as suggested above, then this problem disappears.  Else, we
will have to add numeric suffixes to all these keywords (e.g., OBSFREQ1,
OBSFREQ2, BW1, BW2, etc.)

If NORCVR = 1 or is eliminated, then RCVR may possibly be eliminated.

Having the same keyword serve two purposes (e.g. RSTFREQ is rest frequency
or Total Power Calibration, whatever that may be), is foolhardy.  Separate
keywords should be developed so that, if you need both values you can store
them.  If you need one, then only that one is placed into the file.

Some observatories use Janskies instead of Kelvin to describe TCAL or
TSOURCE.  Maybe we should introduce a keyword (e.g., GENERAL TUNIT = 'Jansky'
or = 'K') which gives the units for these keywords.  Nowhere is the units for
the DELTAX and X0 given.  Let us introduce a new XUNIT keyword for providing
that information.

The values of TAUH20, TH20, etc. depend upon model atmosphere and measurements.
Each observatory calculates these parameters differently and no universally
accepted definition of these variables exists.  Should these parameters be
under the IRAM-30M, NRAO-43M class of category and not under GENERAL?

RHO and THETA are NRAO features which may not apply to other telescopes.
We are planning to place these keywords under the NRAO-12M or NRAO-43M
categories.

                                - 25 -

Example of corrected FITS file:

SIMPLE  =                    T                / Standard FITS format
BITPIX  =                    8                / Character information
NAXIS   =                    0                / No image data array present
EXTEND  =                    T                / There may be standard extensions
DATE    = '03/27/89'                          / Date tape was written
ORIGIN  = 'TUCVAX  '                          / Site which wrote this tape
END
                 [   Blank lines to the end of 2880 byte record ]

XTENSION= 'TABLE   '                          / Standard table
BITPIX  =                    8                / BINARY Table
NAXIS   =                    2                / Simple 2-D matrix
NAXIS1  =                    4                / # chars in row
NAXIS2  =                   52                / # rows in data table
PCOUNT  =                    0                / No "random" parameters
GCOUNT  =                    1                / Only one group
TFIELDS =                    1                / # columns in data table
TBCOL001=                    1                / Starting column
TFORM001= '1J      '                          / Format of data entry
TTYPE001= 'CH-TEMP '                          / Heading for column 1
TUNIT001= 'K       '                          / Units of data for column 1
TSCAL001=        1.23111665E-01               / degK=(Data*TSCAL001)+TZERO00
TZERO001=        8.23852969E+04               / Zero offset (K)
SINGLDSH GENERAL  SCAN    =   4.87800000E+03  / Scan number
SINGLDSH GENERAL  OBSID   = 'HSL TWF         '/ Observer Initials
SINGLDSH GENERAL  OBSERVER= 'HARVEY_LISZT    '/ Observer Name
SINGLDSH GENERAL  TELESCOP= 'NRAO 12M        '/ Telescope
SINGLDSH GENERAL  PROJID  = 'B515            '/ Project ID
SINGLDSH GENERAL  OBJECT  = 'JUPITER         '/ Source Name
SINGLDSH NRAO-12M OBSMODE = 'CONTDON         '/ Type of data & observing mode
SINGLDSH NRAO-12M FRNTEND = '3.0MMSCH        '/ Front End
SINGLDSH NRAO-12M BACKEND = 'DIGITAL         '/ Back End
SINGLDSH GENERAL  PRECIS  = 'I*4             '/ Data precision
SINGLDSH GENERAL  XPOINT  =   8.18823471E+01  / Az/RA Pointing Corr (arcsec)
SINGLDSH GENERAL  YPOINT  =   1.17416201E+01  / El/Dec Pointing Corr (arcsec)
SINGLDSH GENERAL  UXPNT   =   0.00000000E+00  / User Az/RA Correction (arcsec)
SINGLDSH GENERAL  UYPNT   =   1.17416201E+01  / User El/Dec Correction(arcsec)
SINGLDSH NRAO-12M PTCON1  =   0.00000000E+00  / Pointing constant-PVLS (arcsec)
SINGLDSH NRAO-12M PTCON2  =   0.00000000E+00  / Pointing constant-PVLS (arcsec)
SINGLDSH NRAO-12M PTCON3  =   0.00000000E+00  / Pointing constant-PVLS (arcsec)
SINGLDSH NRAO-12M PTCON4  =   0.00000000E+00  / Pointing constant-PVLS (arcsec)
SINGLDSH GENERAL  ORIENT  =   0.00000000E+00  / Rcvr Box or Sec Orient (deg)
SINGLDSH GENERAL  RFOCUS  =   4.80000000E-02  / Radial Focus (m)
SINGLDSH GENERAL  VFOCUS  =   0.00000000E+00  / North-South Focus (m)
SINGLDSH GENERAL  HFOCUS  =   0.00000000E+00  / East-West Focus (m)
SINGLDSH GENERAL  UTDATE  =   1.98902100E+03  / Universal Time Date(YYYY.MMDD)
SINGLDSH GENERAL  HOURUT  =   4.71679683E-01  / Universal Time (hours)
SINGLDSH GENERAL  HOURLST =   2.36953330E+00  / LST (hours)
SINGLDSH GENERAL  NORCVR  =   1.00000000E+00  / Number of Receivers
SINGLDSH GENERAL  NOSWVAR =   3.00000000E+00  / Number of Switching Variables
SINGLDSH GENERAL  NOPHASE =   3.00000000E+00  / Number of Phases per Cycle
SINGLDSH GENERAL  CYCLLEN =   5.00000000E+00  / Length of cycle (sec)
SINGLDSH GENERAL  SAMPRAT =   5.00000000E+00  / Sample Period (sec)
SINGLDSH GENERAL  EPOCH   =   1.95000000E+03  / Epoch of observation (year)
SINGLDSH GENERAL  XSOURCE =   5.41298921E+01  / Cmmnd Source RA (deg)           
                                - 26 -

SINGLDSH GENERAL  YSOURCE =   1.86124692E+01  / Cmmnd Source Dec (deg)
SINGLDSH GENERAL  XREF    =   5.41298921E+01  / Cmmnd Reference RA (deg)
SINGLDSH GENERAL  YREF    =   1.86124692E+01  / Cmmnd Reference Dec (deg)
SINGLDSH GENERAL  EPOCRA  =   5.41298921E+01  / Cmmnd Epoch RA (deg)
SINGLDSH GENERAL  EPOCDEC =   1.86124692E+01  / Cmmnd Epoch Dec (deg)
SINGLDSH GENERAL  GALLONG =   1.69134800E+02  / Cmmnd Galactic Longitude (deg)
SINGLDSH GENERAL  GALLAT  =  -2.86571515E+01  / Cmmnd Galactic Latitude (deg)
SINGLDSH GENERAL  AZ      =   1.22980957E+02  / Cmmnd Azimuth (deg)
SINGLDSH GENERAL  EL      =   6.82819749E+01  / Cmmnd Elevation (deg)
SINGLDSH GENERAL  INDX    =   1.22981000E+02  / Indicated X Position (deg)
SINGLDSH GENERAL  INDY    =   6.82820301E+01  / Indicated Y Position (deg)
SINGLDSH GENERAL  DESORG1 =   1.00000000E+00  / Descriptive origin (deg)
SINGLDSH GENERAL  DESORG2 =   1.00000000E+00  / Descriptive origin (deg)
SINGLDSH GENERAL  DESORG3 =   1.00000000E+00  / Descriptive origin (deg)
SINGLDSH GENERAL  COORDCD = '1950RADC'        / Coordinate system code
SINGLDSH GENERAL  TAMB    =   6.67999983E+00  / Ambient Temp (deg C)
COMMENT   No Mapping was done
SINGLDSH GENERAL  BFWHM   =   3.50000000E+01  / Beam Fwdth at Half Max(arcsec)
SINGLDSH GENERAL  OFFSCAN =   1.90000000E+01  / Off-Scan number
SINGLDSH GENERAL  BADCHV  =   1.00000000E+60  / Bad channel value
SINGLDSH GENERAL  RVSYS   =   4.00000000E+03  / Velocity Correction (m/s)
SINGLDSH GENERAL  VELOCITY=   1.23000000E+00  / Velocity wrt Reference (m/s)
SINGLDSH NRAO-12M VELDEF  = 'RADIEART   '     / Velocity Def and Ref
SINGLDSH GENERAL  TYPECAL = 'NOISE TU'        / Type of Calibration
SINGLDSH GENERAL  APPEFF  =   4.79999989E-01  / Antenna Aperture Efficiency
SINGLDSH NRAO-12M SYNFREQ =   1.87115810E+09  / Synthesizer Frequency (Hz)
SINGLDSH NRAO-12M LOFACT  =   1.00000000E+06  / LO Factor (Hz)
SINGLDSH NRAO-12M HARMONIC=   4.20000000E+01  / Harmonic
SINGLDSH NRAO-12M LOIF    =   1.00000000E+08  / LO IF (Hz)
SINGLDSH NRAO-12M FIRSTIF =   1.50000000E+09  / First IF (Hz)
SINGLDSH NRAO-12M RAZOFF  =   1.17416201E+01  / Ref Az Offset (arcsec)
SINGLDSH NRAO-12M RELOFF  =   1.88483906E+01  / Ref El Offset (arcsec)
SINGLDSH NRAO-12M BMTHROW =   2.39776245E+02  / Beam Throw (arcsec)
SINGLDSH NRAO-12M BMORENT =   0.00000000E+00  / Beam Orientation (deg)
SINGLDSH NRAO-12M BASEOFF =   0.00000000E+00  / Baseline Offset (deg)
SINGLDSH NRAO-12M OBSTOL  =   5.00000000E+00  / Observing Tolerance (arcsec)
SINGLDSH NRAO-12M SIDBAND =   'UPPER       '  / Sideband
SINGLDSH NRAO-12M WL      =   1.50000000E+00  / Wavelength (focus)
SINGLDSH NRAO-12M PBEAM   =   1.19888123E+02  / Plus beam offset
SINGLDSH NRAO-12M MBEAM   =  -1.19888123E+02  / Minus beam offset
SINGLDSH NRAO-12M SROFF   =   0.00000000E+00  / RA/Dec offsets
SINGLDSH GENERAL  SWVAR1  =   1.00000000E+00  / This switching variable
SINGLDSH GENERAL  VARVAL1 =   0.00000000E+00  / Variable Value
SINGLDSH GENERAL  VARDES1 = 'POSN ON '        / Variable Descriptor
SINGLDSH GENERAL  PHASTB1 = '100'             / Phase Table
SINGLDSH GENERAL  SWVAR1  =   2.00000000E+00  / This switching variable
SINGLDSH GENERAL  VARVAL1 =  10.00000000E+00  / Variable Value
SINGLDSH GENERAL  VARDES2 = 'POSN OFF'        / Variable Descriptor
SINGLDSH GENERAL  PHASTB2 = '011'             / Phase Table
SINGLDSH GENERAL  SWVAR3  =   3.00000000E+00  / This switching variable
SINGLDSH GENERAL  VARVAL3 =   0.00000000E+00  / Variable Value
SINGLDSH GENERAL  VARDES3 = 'NTUBE ON'        / Variable Descriptor
SINGLDSH GENERAL  PHASTB3 = '001'             / Phase Table
SINGLDSH GENERAL  RCVR    =   1.00000000E+00  / This receiver number

                                - 27 -

SINGLDSH GENERAL  OBSFREQ =   8.01870000E+10  / Observed Frequency (Hz)
SINGLDSH GENERAL  RSTFREQ =   0.00000000E+00  / Rst Freq or TP Cal (Hz)
SINGLDSH GENERAL  FREQRES =   1.00000000E+06  / Freq Res or SP Cal (Hz)
SINGLDSH GENERAL  BW      =   6.00000000E+08  / Band Width (Hz)
SINGLDSH GENERAL  TRX     =   64.5600000E+00  / Receiver Temp (K)
SINGLDSH GENERAL  TCAL    =   6.00000000E+00  / Calibration Temp (K)
SINGLDSH GENERAL  STSYS   =   100.230000E+00  / Signal System Temp (K)
SINGLDSH GENERAL  REFPT   =   1.00000000E+00  / Ref Point Number
SINGLDSH GENERAL  X0      =   1.00000000E+00  / Velocity at Ref Point (m/s)
SINGLDSH GENERAL  DELTAX  =   1.00000000E+00  / Delta X
SINGLDSH GENERAL  INTTIME =   5.00000000E+00  / Total Integration Time (sec)
SINGLDSH GENERAL  NOINT   =   5.20000000E+01  / # Integrations or channels
SINGLDSH GENERAL  SPN     =   1.00000000E+00  / Starting point number
SINGLDSH GENERAL  TAUH2O  =   0.30700000E+00  / H2O Opacity
END

                [ Blanks to end of 2880 byte record followed by
                [ 2880 byte records of data in binary ]

XTENSION= 'TABLE   '                          / Standard table
BITPIX  =                    8                / BINARY Table
NAXIS   =                    2                / Simple 2-D matrix
NAXIS1  =                    8                / # chars in row
NAXIS2  =                   52                / # rows in data table
PCOUNT  =                    0                / No "random" parameters
GCOUNT  =                    1                / Only one group
TFIELDS =                    1                / # columns in data table
TBCOL001=                    1                / Starting column
TFORM001= '1J      '                          / Format of data entry
TTYPE001= 'CH-TEMP '                          / Heading for column 1
TUNIT001= 'K       '                          / Units of data for column 1
TSCAL001=        1.00128129E-01               / degK=(Data*TSCAL001)+TZERO00
TZERO001=        9.62883984E+04               / Zero offset
SINGLDSH GENERAL  SCAN    =   4.87900000E+03  / Scan number
SINGLDSH GENERAL  TAMB    =   6.68999983E+00  / Ambient Temp (deg C)
SINGLDSH NRAO-12M SYNFREQ =   1.91234567E+00  / Synthesizer Frequency (Hz)
END

                [Blank lines to end of 2880 byte records followed by
                 2880 byte records containing data in binary]

....etc.