A preliminary list of Radar headers for comments and suggestions

Data Acquisition Modes

There are several data acquisition modes, some of which may be hidden. For example, for short Round Trip Times, it is may be better to put the T/R times in the per-record rather than per-file header.

File Headers for Arecibo Radar Data

I include the headers from various old (NURAD-era) files, and anything else that seems reasonable. There were various hardware-specific pieces of information in the old system (frequencies of specific LOs) that will likely be different now. Capital letters generally indicate that an old NURAD or MAIN header exists

1996 December 5: I've gone through this and tried to consider how it fits into the AO header scheme, as described in Phil Perrilat's .h files. These will be marked NAO (new AO) for now. Phil has libraries to read and write some / most of these.

1996 December 13: Don insists that the format must be one continuous data stream, i.e., no separate files for transmit and receive (which was what I suggested), and with the ephemerides interspersed. Perhaps this could be a "group"? with records ETRRRRRR ETRRRRRR, or something like that. He also wants multiple copies of the xmit and ephemeris information in case of tape problems.

What to do about day boundaries, especially between transmit and receive???

Head-of-File Header Information

Magic Number
Some sort of "magic number" to identify this an AO raw data file. (NAO: HDRAO_STD.hdrMarker / HDRAO_IS_HDR(phdr))
Header ID
Version number for header so that, in principle, you can determine the format from a database. This may not be necessary if it's keyword-value. NAO: Each piece of the header (main, RI, experiment) has a version number, which means you have to be careful to start, but maintainance should be fairly easy. (HDR_XXX_VERSION, HDRAO_STD.version)
Tape ID number (The AO# if possible, like a tape label)
File ID
File sequence number. This is in the format YYDDD.NNNNN, where YY is the last two digits of the year, DDD is the DOY, and NNNNN increments from one each day. There was a motion at a RA meeting to make the first 5 digits be MJD, but it was quashed. NAO: HDRAO_STD.scanNumber
observer ID
Operator ID
The observer and operator ID could just be an 80 character field for "who was there" The "cognizant observer" and/or "cognizant operator" should be here.
program ID/Experiment Number
Time allocation ID (may be useful to document observation or lack thereof for various purposes) NAO: Is this HDRAO_STD.expNumber?
Configuration File Date
Date when setup file was generated, or possibly submitted to the system (or both, better yet). NAO: Does this go in the sec.inp? Or where?
run number
data file sequence number
UT date of experiment start NAO: HDRAO_STD.date, HDRAO_STD.time
Julian date of experiment start
Is Radar
This is an AO radar experiment (AO transmitter is used), and uses the XYZ transmitter. NAO: HDRAO_STD.expNumber?
UT Time of receive start for first pulse (used to be AST?) NAO: in decoder header
Exposure time
Length of time to exposure end
Transmit start
UT Time of transmit start for first pulse
Transmit time
length of transmit time
Transmitter Location
Which transmitter
Transmit Ephemeris
Transmit coords and Doppler
Transmit Dropouts
Times and reasons for transmit failure
Receiver Bandwidth NAO: HDRAO_DECODER
Base Transmit Frequency, either actual or (center or first?) for frequency hopping.
Base Receive Frequency
Number of channels (what does this mean in the current scheme?)
Number of polarizations. NAO: HDRAO_DECODER
Circular or linear polarization?
Acquisition time for one cycle. This is probably a code length (for ranging), or a convenient interval for FT for CW. In the old system, frequency-hopping arranged to have an integral number of these, plus some slop on each side, in each "hop".
Samples * Channels / IPP
Code Length
Code length in bauds. 0 for CW, -N for (2^N)-1 long code NAO: HDRAO_DECODER
Code ID
Some sort of identification for the code (0 for CW). NAO: HDRAO_DECODER
Code start position
Position in code when transmitter started. -1 for "unknown"?? NAO: HDRAO_DECODER
Baud Length
Baud length in ns. NAO: HDRAO_DECODER
Sample Gate Time
Sample time in ns (probably 1 or 2 times Baud Length) Old system used both this and NSPB (Number of samples per baud)
Gate Delay
Time between "tick" and sample start.
Sampler samples per baud
samples per baud, probably 1 or 2. NAO: HDRAO_DECODER
Output samples per baud
Samples ber baud output from device: the decoder can combine 2 samples per baud except at 50ns. NAO: HDRAO_DECODER
Number of different frequencies for frequency hopping. NAO: HDRAO_
Delta-frequency for hopping;
Time for each frequency
Restart flag (so the system knows to resume an in-progress experiment)
Ephemeris Delay
Time interval between start of data taking and expected arrival of first echo so that the turnon is clear.
IDL In decnew. What is it?
"Time from marker to data start" Time from tick to code-start (measured?)
The complete ephemeris, at 1 minute intervals. Was that ever too long? Save XDoppler, RDoppler, RTT, RA2000, Dec2000, Az, El
Ephemeris Setup
How to regenerate the ephemeris. If it's a two-body ephemeris for the short term, this can just be the elements. In that case, the elements ought to have a version, like MPC number, or something like that.
Interpolation Methods
The ephemeris is sub-interpolated. The current method is the 4th order polynomial generated using 5 minutes of ephemeris and Pascal's triangle (for Doppler), and linear interpolation (I assume) for RTT and AzEl.
Various things for cals??
Transmitter power at various times
Transmitter configuration
What transmitter mode? Transmitter status.
Complex/Real Data
Direct-sampled data records are written as complex / real numbers
FT Data
FT's of direct-sampled records are written
Frequency direction
Direction of increasing frequency, or, whether a high-side (inverting) or low-side (non-inverting) LO is used.
Decoded Data
Decoded data are written
Decoded Samples Retained
Which delay bins are saved from decoded data?
Sampled Bits/sample
Bits per sample
Samples per written 32 bit word??
How samples are interleaved: IQIQ or IIQQ or I*recl Q*recl; LRLR or L*recl R*recl; which samples are in which positions? Should be sample-wise, as word packing is separate

Per-Record Header Information

I assume each transmit cycle gets at least one record, thought I suppose it's conceivable that there would be occasions not to, particularly since the fastest likely data rates for asteroids are the ones with the shortest RTTs.

Record Number
Record Number in file
Record Length
Record length
Frequency Number
Which transmitter frequency for frequency-hopping. May also be relevant for multiple receiving bands.
Transmit start
Time of transmit start for this pulse
Transmit time
length of transmit time for this pulse (Could be Transmit Stop instead)
Recv start
Time of receive start for this pulse
receive time
length of receive for this pulse (could be receive stop instead)
RTT for this observation
Avg Doppler for this observation? Or is it better to just go with the ephemeris?
Attenuators, gains, levels
These need to be recorded.

Other Observatories

For comparison, look at the Green Bank Header (a FITS BINTABLE) and the VLBA Header.

Unfortunately, Also relevant is the Definition of FITS. Yes, in 1996, there are still people using two digits for the year, and they is us.

Well, in September 1997, a four-digit year format is close to being adopted: Use DATE-OBS='2097-10-31' to represent 2097 October 31. DATE-OBS='31/10/97' will always mean 1997 October 31.

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Last update: 1997 September 15

Mike Nolan