From dwells@fits.CX.NRAO.EDU Sat Aug 26 16:25:05 1989 X-VM-v5-Data: ([nil nil nil nil nil nil nil nil nil] ["3744" "Sat" "26" "August" "89" "16:19:17" "EDT" "Don Wells" "dwells@fits.CX.NRAO.EDU " nil "96" "DISHFITS is operational." "^From:" nil nil "8"]) Received: from NRAO.EDU by fits.cx.nrao.edu (4.0/SMI-DDN) id AA00379; Sat, 26 Aug 89 16:25:03 EDT Received: from fits.cx.nrao.edu by NRAO.EDU (1.1/DCW-2m) id AA21663; Sat, 26 Aug 89 16:25:05 EDT Received: by fits.cx.nrao.edu (4.0/SMI-DDN) id AA00361; Sat, 26 Aug 89 16:19:20 EDT Return-Path: Message-Id: <8908262019.AA00354@fits.cx.nrao.edu> Status: RO From: dwells@fits.CX.NRAO.EDU (Don Wells) Sender: dishfits-request@fits.CX.NRAO.EDU To: dishfits@fits.CX.NRAO.EDU Subject: DISHFITS is operational. Date: Sat, 26 Aug 89 16:19:17 EDT Dear Participants in the Single-Dish FITS Workshop: I have established an E-mail exploder to facilitate rapid communication among the worldwide radio single dish community, with the hope that you can arrive in Green Bank on 31-October with a fair approximation of consensus already established. DISHFITS is identical to the AIPS 'BANANAS' exploder in its operation. Any mail sent to one of the following addresses dishfits@nrao.edu 6654::dishfits ..!uunet!nrao.edu!dishfits will be broadcast to the mailing list. Within a few days the address DISHFITS@NRAO on BITNET will also be effective (it has not yet been enabled on the BITNET gateway); until then BITNET users can always transmit to the NRAO.EDU address, which is a good idea anyway, because NRAO's BITNET gateway is not as robust as the CUNYVM gateway in New York. The current mailing list is: roy@oso.chalmers.se rjc@star.jb.man.ac.uk downes@frgag51.bitnet rekers@rpepping.oz.au rnorris@rpepping.oz.au preben@dgaeso51.bitnet hanisch@stsci.edu martin@tucsmt.as.arizona.edu phillips@tacos.caltech.edu snell@fcavax.phast.umass.edu schloerb@fcavax.phast.umass.edu wbaan@naic.bitnet j.weiss%nasamail@ames.arc.nasa.gov rww@hoh-2.att.com "psi%ukth::hem"@nssdca.gsfc.nasa.gov jball@cvax.cv.nrao.edu p073twi@mpirbn.uucp nnakai@nro.japan bburns@nrao.edu rmaddale@nrao.edu hliszt@nrao.edu cbiemes@tucvax.tuc.nrao.edu wbatrla@nrao.edu pmurphy@bass.tuc.nrao.edu demerson@tucvax.tuc.nrao.edu dwells@suns.umd.edu dwells@nrao.edu rbrown@nrao.edu bvance@nrao.edu egreisen@nrao.edu gseielst@nrao.edu The address "nnakai@nro.japan" above is not valid; if any of you know an E-mail address for Nobeyama Observatory please tell me. If any of you want to be removed from the list, or want me to add one or more of your colleagues, just send mail to me (dwells@nrao.edu). Please check the list for completeness and correctness. This mailing list is not intended to be limited to people who will actually attend the 31-October meeting at Green Bank --- rather, it is appropriate for anyone who has an interest in FITS data formats for single dish radio astronomy. DISHFITS resides on a computer called FITS.CX.NRAO.EDU (a Sun-3/60G) which was purchased with funds from a grant for 'Development and Support of FITS Format Standards', for which I am Principal Investigator and for which Anthony Villasenor (Program Manager, Information Systems, Office of Space Science and Applications, NASA Headquarters-EI) is the technical officer. This grant is part of the support of progress toward FITS standardization for the Astrophysics Data System project of the NASA Astrophysics Division (which funds and oversees NASA astronomy flight missions, for example). A closely related effort of the ADS project is the new FITS Standards Office located at the National Space Science Data Center at Goddard Space Flight Center, about which you will soon hear more. I want to thank Tony Villasenor for his support of astronomy's continuing effort to reduce the entropy of astronomical data formats, and I want to applaud the ADS for funding the Standards Office. So, any of you who have anything to say are welcome to transmit! Best regards, Don Donald C. Wells, Associate Scientist | NSFnet: dwells@nrao.edu [192.33.115.2] National Radio Astronomy Observatory | SPAN: NRAO::DWELLS [6654::] Edgemont Road | BITnet: DWELLS@NRAO Charlottesville, VA 22903-2475 USA | UUCP: ...!uunet!nrao.edu!dwells +1-804-296-0277 (38:02.2N/78:31.1W) | TWX=510-587-5482, Fax=+1-804-296-0278 Cc: bgeldzahler@nhqvax.span, griegler%nasamail@ames.arc.nasa.gov, j.weiss%nasamail@ames.arc.nasa.gov, sawyer@nssdca.span, schlesinger@ncf.span, villasenor%nasamail@ames.arc.nasa.gov From dishfits-request@fits.CX.NRAO.EDU Tue Sep 5 14:21:17 1989 Received: from NRAO.EDU (cv3.cv.nrao.EDU) by fits.cx.nrao.edu (4.0/SMI-DDN) id AA10589; Tue, 5 Sep 89 14:21:09 EDT Received: from fits.cx.nrao.edu by NRAO.EDU (1.1/DCW-2m) id AA00906; Tue, 5 Sep 89 14:19:49 EDT Received: by fits.cx.nrao.edu (4.0/SMI-DDN) id AA10534; Tue, 5 Sep 89 14:00:13 EDT Return-Path: X-Vms-Mail-To: DISHFITS Message-Id: <890905134427.000074260F1@cvax.CV.NRAO.EDU> Status: RO From: HLISZT@NRAO.EDU Sender: dishfits-request@fits.CX.NRAO.EDU To: DISHFITS@fits.CX.NRAO.EDU Subject: Single Dish FITS Format 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.