CIMA Data Taking Modes

CIMA data taking modes

All spectral line observing modes got a parameter to specify how the data taking should be done with the introduction of CIMA version 3.0 (2.3). In CIMA 3.0, the parameter is called either 'Loops per file' or 'Strips per file' depending on the observing mode. In version 3.1 the possible data taking modes were expanded and the name was therefore changed to 'Data taking' to better reflect this new functionality. The keyword used in command file scripts ('newfile') has remained the same, but the values used by 'newfile' has been changed between the two CIMA versions. Command file users should thus be aware that command files used with verison 3.0 most likely NEEDS TO BE ADJUSTED for use with version 3.1 in respect to the 'newfile' keyword!

The available data taking modes vary depending on which backend is used. CIMA is normally only presenting You with the options available for the selected backend, but if several backends are used in parallel, it is important to notice that not all of the options apply to all backends.

Scan-based versus continuous data taking

One new feature introduced with CIMA version 3.1 is the possibility to select between scan-based and continuous data taking when using the WAPPs and/or the Mock spectrometer for spectral line observing modes. Before version 3.1 all spectral line modes only offered scan-based data taking. In scan-based data taking, the backend is started before each scan and then stopped afterwards. When making a scan-based CAL ON/OFF, the sequency is: switch on CAL, start backend, take CAL-ON data, stop backend, switch off CAL, start backend, take CAL-OFF data, stop backend. With continuous data-taking, the backend is left running between the scans; the previous example would instead be executed as: start backend, switch on CAL, take CAL-ON data, switch off CAL, take CAL-OFF data, stop backend. A scan-based data file will thus only contain valid data, while a continuous data file also will contain the data taken in between the scans.

For scan-based data taking, there is also a question about whether the backend allows You to put several scans in the same data file or not. Both the WAPPs and the interim correlator do allow You to put multiple scans in the same file, while the Mock spectrometer will start a new set of files for each scan.

The following table summarizes the important characteristics of the three main backends at Arecibo Observatory:

Backend Continuous data taking Scan-based data taking Multiple scans per file
The WAPPs YES YES YES
The Mock spectrometer YES YES No
The interim correlator No YES YES

Possible data taking options

These are the possible options that CIMA uses for the 'Data taking' parameter. NOTE that the values to be used with the 'newfile' parameter for command file observing has changed between CIMA version 3.0 (2.3) and 3.1. The two values in parenthesis represents the values that should be used in CIMA version 3.0 (2.3) and 3.1, respectively.

'Use open file' ( "-1" --- "open" )

Use scan-based data taking and add the data to the data file that is already open. This mode is available for the WAPPs and the interim correlator. If the Mock spectrometer is run in parallel with the WAPPs and this mode is selected, then the Mock spectrometer will put each scan in a new set of files.

'Put all in one file' ( "0" --- "one" )

Use scan-based data taking, start a new data file before the observation starts and then write all the data from all loops to that data file. A new file will not be created if the file that is already open happens to be empty. This mode is available for the WAPPs and the interim correlator. If the Mock spectrometer is run in parallel with the WAPPs and this mode is selected, then the Mock spectrometer will put each scan in a new set of files.

'Each beam per file' ( "-2" --- "eachbeam" )

This is a special mode only available for 'ALFA cross maps'. Use scan-based data taking and start a new data file before each beam in each loop. A new file will not be created if the file that is already open happens to be empty. This mode is available for the WAPPs. If the Mock spectrometer is run in parallel with the WAPPs and this mode is selected, then the Mock spectrometer will put each scan in a new set of files.

'1 loop / file' or '1 strip / file' ( "1" --- "1" )

Use scan-based data taking and start a new data file before each loop (or each strip in a map). A new file will not be created if the file that is already open happens to be empty. This mode is available for the WAPPs and the interim correlator. If the Mock spectrometer is run in parallel with the WAPPs and this mode is selected, then the Mock spectrometer will put each scan in a new set of files.

'1 scan / file' ( N/A --- "one" )

Use scan-based data taking and start a new data file before each scan. This mode is available for the Mock spectrometer. If the Mock spectrometer is run in parallel with the WAPPs and any other scan-based data taking mode is selected, then the Mock spectrometer will default to use this mode.

'N loops / file' or 'N strips / file' ( N --- N )

Use scan-based data taking and start a new data file before each Nth loop (or each Nth strip in a map). A new file will not be created if the file that is already open happens to be empty. This mode is available for the WAPPs and the interim correlator. If the Mock spectrometer is run in parallel with the WAPPs and this mode is selected, then the Mock spectrometer will put each scan in a new set of files.

A new file will always be started before the first loop or strip to be observed, thus for a an observation of 8 loops with '3 loops / file', a new file will be opened before loop 1, 4 and 7, thus creating two files with three loops each and a third one with the last two loops. Notice that for mapping modes that allow You to start from a random start strip, that strip will be used as the start for the counting; thus, an observation of 8 strips with '3 strips / file' that is started from strip 2 will open new files before strip 2, 5 and 8.

For command file users, notice that the number 'N' can't be a random number but has to be one of the options supported in the 'Data taking' menu which typically contains the following list of allowed values for N: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 and 25.

'Continuous / beam' ( N/A --- "contbeam" )

This is a special mode only available for 'ALFA cross maps'. Use continuous data taking and start a new data file before each beam in each loop. This mode is available for the WAPPs and the Mock spectrometer.

'Continuous / loop' ( N/A --- "contloop" )

Use continuous data taking and start a new data file before each loop (or each strip in a map). This mode is available for the WAPPs and the Mock spectrometer.

'All continuous' ( N/A --- "continuous" )

Use continuous data taking, start a new data file before the observation starts and then write all the data from all loops to that data file. This mode is available for the WAPPs and the Mock spectrometer. (Note that it is not possible to adjust the power levels at the beginning of each loop or strip if this mode is used.)

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This page is administered by Prakash Atreya ( patreya (a) naic . edu ) and was last updated on 5 December 2008.