The EVLA Use Case Tool

This simple tool was designed and built to provide a use-case summary for possible EVLA projects. The reasoning behind such use cases are twofold:

• Required resources for the EVLA and WIDAR can be more accurately estimated by the staff, especially required data rates, data volume and widar modes (and when they are needed).
• When users, proposers, and staff take the time to fill out the use case form, they can become more familiar with WIDAR and EVLA resources and how to estimate those resources, and thus take the first steps to understanding the EVLA / WIDAR system.

This web page is intended to assist users / proposers in filling out the use-case form. Each entry is briefly described, and when useful, an example is given. One may proceed to the tool itself by clicking here . For further assistance please contact Mark Claussen.

• Legacy ID --- the proposal ID that the Proposal Selection Tool assigns which begins with an "A"; example --- AH964. When the use case form is being filled out in conjunction with a proposal, the legacy id will be assigned by the PST once the proposal is submitted.


• Title --- a brief descriptive title. This can be a shortened version of the proposal title.


• Principal Investigator Name and Email Address --- these are automatically filled in for you.


• Total Time --- the total time required for the project, including all calibration and overhead. Please make sure the units are included.


• Desired Date --- the date / configuration when the observations could be attempted.


• Goal --- A brief description of the science or technical goals of the project.


• Source name and position (optional).


• Subarrays --- This is an optional field. EVLA subarrays won't be available at the beginning of 2010 trimester 1 (March 1, 2010).


• Field of View --- An optional field. The field of view required for your experiment. Compare what is needed to the EVLA antenna primary beam; this will help you decide on the imaging needs for your project (post processing).


• Sensitivity Required --- This is the sensitivity required for the scientific goals of the project.


• On Source Time --- This follows directly from the required sensitivity. But one must also deal (perhaps) with confusion, weather, array configuration, etc.


• Polarization --- A drop down menu. Full polarization (all polarization products), just dual circular (RCP and LCP), or a single (circular) polarization. This also affects what sensitivity can be achieved.


• Frequency/Frequency Range --- The frequency band needed for the project, and in addition, the frequency range. Examples: (1) The 26 - 40 GHz band (Ka band); range 24 - 32 GHz. (2) The entire L band (1 - 2 GHz).


• Total Bandwidth per Polarization --- The total bandwidth required for the project. For continuum projects one might want the best sensitivity which would drive them to larger bandwidths (8 GHz, for example). For spectral line projects, depending on the the resolution needed, the bandwidths could be much smaller.


• Velocity/Frequency Resolution --- The velocity (frequency) resolution will set the number of spectral channels needed, given the total bandwidth. (Continuum) Example: 8 MHz spectral spectral channels: 16 spectral channels per cross-correlation. This enables full-beam deconvolution (at Ka band), if needed.


• Correlator Setup --- This should give information about how many subband pairs, the total number of spectral channels, and perhaps the time averaging. The information in this step should lead into, and help calculate, the next parameter (Data Rate and Total Data Volume).


• Data Rate and Total Data Volume --- Using information from the Correlator Setup, the data rate can be calculated. We assume that 10 bytes per visibility is nominal. Then a rough estimate for the data rate can be made by: data rate = nchan * nbase * 10 bytes/vis / dt (sec) where nchan is the total number of spectral channels, summed over all subbands and polarization products, nbase is the number of baselines (351 for the 27 antenna EVLA), and dt is the dump time in seconds. As an example, assuming 10 second time dumps, 2048 total channels, for the full EVLA, gives a rate 0.7 MBy/s, and a total data volume for 8 hours of 21 GBy.


• Observation/Calibration --- Check all that of these calibration modes that should be needed. We may not have everything here, and the Special Comments box can be used to make comments on other needs.


• Post Processing --- In this box should go specific post processing requirements - examples: wide-field imaging; polarization imaging; spectral index imaging; mosaicing; spectral line imaging; narrow band vs wide band processing... and other post processing needs that might be envisioned.


• Special Comments --- This is for other comments about the project that might not be encompassed in other parts of the use-case form.

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