Time Resolution and Data Rates

by Stephan W. Witz last modified Apr 11, 2012

The minimum integration time that will be supported for OSRO is 1 second, for A configuration. For B, C, and D configurations the minimum integration time is 3 seconds, unless a shorter integration time is explicitly requested and justified.

The maximum recommended integration time for any EVLA observing is 60 seconds, but given current computing capabilities there is no reason to use integration times longer than 10 seconds. For high frequency observers with short scans (e.g., fast switching, as described in Rapid Phase Calibration and the Atmospheric Phase Interferometer (API)), shorter integration times may be preferable.

Observers should bear in mind the data rate of the EVLA when planning their observations. For the correlator configurations discussed in Correlator Configurations, and integration time Δt, the data rate is:

Data rate = 14.4 MB/sec × Nant × (Nant−1)/(27×26)/(Δt/1 sec)
= 51.8 GB/hour × Nant ×(Nant−1)/(27×26)/(Δt/1 sec)
...equation (4)

which corresponds to 1.2 TB/day when using the full 27-element array with 1 second integrations. While analyzing such data sets is not too difficult with current computers, data transfer will clearly be more of an issue than in the past. Most observers currently download their data via ftp directly from the archive. The Archive Access Tool (https://science.nrao.edu/facilities/evla/data-archive/evla) will allow some level of frequency averaging to decrease data set sizes before ftp, for users whose science permits; note that the full spectral resolution will be retained in the NRAO archive for all observations. Observers may also request their data on disk drives.