Correlation & Logistics

We operate the correlator 80 hours per week, from which time system testing and development must also come. Our basic unit of correlation is usually a tape pass. Our control software is best suited to continuous tape motion; reasonably short gaps in the schedule are ``waited out" in real time. Preparation for a pass, assuming the tapes are pre-positioned to approximately the correct footage, is $\sim$9 minutes (for thin tape, passes are typically either 22 or 44 minutes). This preparation time includes:

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calculations: parsing the VEX file, selecting stations/scans to include, and computing the a priori model.

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tape manipulation: going to a priori footage, positioning the heads transversely such that they read tracks with an expected time-on-tape (i.e., one within the bounds of the requested scans), positioning the tape longitudinally such that the time-on-tape corresponds to the initial scan time, and waiting until the slowest tape is ready.

When correlation of the experiment is finished we review the output, looking for any necessary recorrelations that weren't caught in the course of the original correlation. The shift to thin-tape-only operation has improved playback quality; this together with the excision of TRM byte slips has markedly reduced the amount of passes requiring recorrelation. Once all recorrelations are exhausted, we make a variety of information available to the PI (as described in §3.3), and arrange for shipment of the resulting FITS data. Unless contacted by the PI to the contrary, we aim to release an experiment's tapes four weeks after the PI is notified of the experiment's completion, in order to ensure the supply of tapes in the pool remains replenished for future observations -- which is of increased importance now that the EVN has moved to thin-tape-only operation. Besides the review products mentioned below, the PI of course may also discuss the experiment/correlation with the responsible JIVE support scientist and/or arrange for visiting JIVE for help in data reduction if desired. Specific programs exist to provide financial support for European PIs from non-EVN institutes and their collaborators to encourage visits to EVN institutes, including JIVE -- see the EVN web page under the ``Access to the EVN" menu item.