E.1 Getting your data into AIPS

Your EVLA data are stored as an “ALMA Science Data Model” (ASDM) format file in “SDMBDF” (Science Data Model Binary Data Format) in the NRAO archive. They may be read out of the archive in that format, a CASA measurement set format, or in an AIPS-friendly uvfits format. This last is produced by the CASA uvfits writing software. Go the the web page

http://archive.cv.nrao.edu/

and select the Advanced Query Tool. Fill out enough of the form to describe your data and submit the query. If the data are not yet public, you will need the Locked Project Access Key which may be obtained from the NRAO data analysts. To avoid the need for this key, you may log in to my.nrao.edu after which it will know if you are entitled to access particular locked projects. The query will return a list of the data sets which meet your specifications. (Users logged in to an NRAO Socorro computer should use a variant of these instructions; see below.) On this form, enter your e-mail address, choose AIPS Friendly names (almost certainly does not work), AIPS FITS under the EVLA-WIDAR section and choose the desired time averaging. If the delays are not accurately known, spectral averaging can be damaging to the data amplitudes. However, the data are often recorded at one-second intervals which is rather short, making the data voluminous. Judicious averaging can help with data set size and processing times without compromising the science. Choose the data set(s) you wish to receive and submit the request. You will be told an estimate of the output data set sizes and the amount of time you will need to wait for the format translation to occur. A 19 Gbyte SDMBDF file run as a test with no averaging was estimated to produce a UVFITS file of 30.26 Gbytes and to take 103 minutes to prepare for download. That time assumes that your download job is the only one being performed. If your download fails, you will probably be told erroneously by e-mail that it worked. The output file will however be missing or incomplete. Try again before contacting NRAO for help.

If you are logged into an NRAO Socorro computer — and perhaps if you are not, — you may find a better route to acquire your data with useful additional information not available via CASA. Try requesting your data in SDMBDF format instead of uvfits and also uncheck the “Create tar file” box only if you are on a Socorro computer. (Remote users will need to have the archive load the SDMBDF file into “tar” form in the public ftp area for copying to their home machine.) If you have enough disk space, direct the data to a directory on your machine, after you have made that directory world writable (chmod 777directory-name). The downloading of the SDMBDF file is quite efficient compared to having the archive computer do all the file translation. When you are told that the SDMBDF file is ready, you may run AIPS and load the data via the verbs BDFLIST and BDF2AIPS. These verbs run programs in the OBIT software package to load your data directly into AIPS including flag (FG), index (NX), calibration (CL), over-the-top (OT), SysPower (SY), and CalDevice (CD) tables which you will not get from CASA. If you use this approach, you may skip the UVLOD and INDXR steps described below. Note that these verbs require that OBIT be installed on your computer — as it is in Socorro — and that ObitTalk be in your $PATH. OBIT is relatively easy to install and may be obtained from bcotton@nrao.edu.

Unlocked files will be downloaded to the NRAO public ftp site

ftp://ftp.aoc.nrao.edu/e2earchive/

by default and you may then use ftp to copy the file to your computer. Locked files will go to a protected ftp site and you must use ftp to download those, even within NRAO. The instructions for downloading will be e-mailed to you. Be sure to specify binary for the copy. If you are located in the AOC in Socorro, you may set an environment variable to the archive location, e.g.

export E2E=/home/ftp/pub/e2earchive  C R

for bash shells

setenv E2E /home/ftp/pub/e2earchive  C R

for C shells such as tcsh

and simply read unlocked data files directly from the public download area. Note that the file will be deleted automatically after 48 hours in both public and protected data areas.

SDMBDF files may be read into AIPS using BDFLIST to learn what is in your data set and then BDF2AIPS to translate the data. Thus

> DEFAULT BDF2AIPS’; INP  C R

to initialize all relevant adverbs.

> DOWAIT 2 ; DOCRT 1  C R

to wait for the verbs to finish and to display the log file on the terminal after the OBIT task finishes. DOWAIT 1 displays the messages as they are generated but is insensitive to returned error conditions from the OBIT tasks. Be sure to set DOWAIT -1 after using BDF2AIPS.

> ASDMF(1) = ’path_to_asdm_dir  C R

to set the full path name into the adverb. Note the lack of close quote so that case is preserved. If the name is too long (> 64 characters), put part of the name in ASDMF(1) and the rest in ASDMF(2). Trailing blanks in ASDMF(1) will be ignored.

> BDFLIST  C R

to list the contents of the SDMBDF. Note particularly the “configuration” numbers.

> OUTNA myname  C R

to set the AIPS name.

> OUTCL ’ ’  C R

to take default (UVEVLA) class.

> OUTDI 3  C R

to write the data to disk 3 (one with enough space).

> DOUVCOMP FALSE  C R

to write visibilities in uncompressed format. There are no weights at present, so there is no loss of information in compressed format, but the conversion from compressed format costs more than reading the larger data files.

> FOR CONFIG = 0:100 ; BDF2AIPS; END  C R

to load all of the configurations in your data, terminating with error messages on the first configuration number not present in your data (when DOWAIT is 2).

There are other adverbs — NCHAN, NIF, BAND, and CALCODE — available if needed to limit which data are read. CONFIG is frequently all that is needed to select data, but these others may be needed if more complicated modes of observing were used.

The uvfits data file may be read from disk into AIPS using UVLOD or FITLD, using:

> DEFAULT UVLOD’ ; INP  C R

to initialize and review the inputs needed.

> DATAIN ’E2E:filename  C R

where filename is the disk file name in logical area E2E; (see 3.10.3).

> OUTNA myname  C R

to set the AIPS name.

> OUTCL ’ ’  C R

to take default (UVDATA) class.

> OUTSEQ 0  C R

to take next higher sequence #.

> OUTDI 3  C R

to write the data to disk 3 (one with enough space).

> DOUVCOMP FALSE  C R

to write visibilities in uncompressed format. There are no weights at present, so there is no loss of information in compressed format, but the conversion from compressed format costs more than reading the larger data files.

> INP  C R

to review the inputs.

> GO  C R

to run the program when you’re satisfied with inputs.

Watch the messages from UVLOD to see where your data set goes and whether the task ran properly. When it is finished, check the output header:

> INDI n; GETN m  C R

to select the data set on disk n and catalog number m.

> IMHEAD  C R

to examine the header.

Note that the header does not show the usual complement of AIPS extension files. CASA translates the on-line data into its internal format and then writes the uvfits file read by AIPS. Since CASA does not have files comparable to AIPS index and CL tables, it does not provide them. To build index and calibration tables, use;

> TASK INDXR’ ; INP  C R

to select the task and review its inputs.

> INFILE  ’ ; PRTLEV = 0  C R

to be sure not to use an input text file and to avoid excess messages.

> CPARM = 0 , 0 , 1/2  C R

to make a CL table 1 with a 30-second interval.

> BPARM τ , 0  C R

to take default EVLA gains and a zenith opacity of τ. Set τ = -1 for no opacity correction. You may set τ = 0, which is now recommended, to get new default opacities. These are based on a detailed model predicting the opacity at any frequency from that at 22 GHz. The combination of weather and seasonal model long used by FILLM and INDXR is now used solely to estimate the 22 GHz opacity.

> GO  C R

to run the task after checking the inputs.

INDXR now uses new EVLA gains information which includes some frequency dependence within the new wide bands. OBIT’s application of weather and gains appears to have errors — re-create the CL table 1 and index table with INDXR even if you got your data via OBIT.

It is a good idea to list the structure of your data set and your antenna locations on the printer and to keep those listings next to your work station for reference:

> DEFAULT LISTR ; INP  C R

to initialize the LISTR inputs and review them.

> INDI n; GETN m  C R

to select the data set on disk n and catalog number m.

> OPTYPE SCAN’ ; DOCRT -1  C R

to choose a scan listing on the printer.

> GO ; GO PRTAN  C R

to print the scan listing and the antenna file contents.

Read these with care. There have sometimes been problems with antenna identifications, with the order of the IF frequencies, and even with identification of sources by scan. Task SUFIX may be used to correct the last problem and, if desired, FLOPM may be used to reverse the frequency order. Oddly ordered IFs may require UVCOP to split them apart followed by VBGLU to paste them back together. You may have to use SETJY or TABPUT to change the CALCODE of some sources if your calibration sources have a blank calibrator code or your target sources have a non-blank calibrator code.