- I recommend heading over to Emil Lenc's widefield calculator if you want to do any widefield imaging: see http://www.atnf.csiro.au/people/Emil.Lenc/Calculators/wfcalc.php
- Use the button below the heading "uv Coverage" ("Beam Shape") to switch between the uv coverage and the beam shape
- For changes in parameters to take effect, you must press "calculate".
- Hover the mouse over an antenna name to get tooltip text describing the antenna. Some antennas have SEFDs which are guesses at best - this text will let you know if this is the case.
- This tool gives the theoretical sensitivity achievable in the absence of
calibration errors etc. The weak source approximation is assumed in all
calculations - observing strong sources will cause a degradation of
sensitivity, compared to the values displayed.
- The uv tracks and beam shape displayed are approximate (do not take into
account calibrator observations) and should be taken as a guide only.
- Observing time is assumed to be allocated such that the source will transit the midpoint of the two most widely separated antennas halfway through the observation.
- This calculator knows nothing of the bandwidths available at each observatory, so "caveat emptor" if you start using estimates based on very wide recorded bands.
- Likewise, not all stations have dual-polarisation at all frequencies - you'll need to check this and interpolate the effect on image sensitivity between all-dual-pol and all-single-pol.
- Be careful with your allocation of Arecibo time - this calculator knows nothing of the HA limits, and only has a "guesstimate" of elevation limit (70 degrees) so don't allocate yourself more time than Arecibo can really track.
- Italicised antennas are not yet available (and some may never be, as the list includes short-listed sites for future antennas).
- Correlator efficiency is assumed to be 0.88, appropriate for the 4 level sampling and the DiFX software correlator.
- Currently the maximum bandwidth LBA-wide is 32 MHz, dual polarisation or
64 MHz single pol. Check the double data rate recording box to enable enable
double bandwidth recording at the ATNF antennas with dual DASs, Narrabri/Parkes/Mopra.
- Two density weighting options are supplied: Natural and Uniform. Natural weighting does not change the uv samples, and gives the best signal to noise ratio. Uniform weighting weights all points inversely proportional to the surrounding density of uv samples, which effectively upweights the long baselines and downweights the short baselines (since they are generally closer together).
- Two signal to noise weighting options are supplied: unweighted and 1/sigma^2. Normal does not weight the points by their signal to noise ratio. 1/sigma^2 weights points inversely proportional to the variance of their noise. This has the effect of downweighting points which have bad signal to noise and improving image sensitivity (although often at the expense of resolution as the longest baselines often have the worst signal to noise).
- For the Tid_70m antenna at 2.3 GHz, the quoted sensitivity is for single polarisation observations at a bandwidth <= 30 MHz. For dual polarisation observations or single polarisation observations with 32 MHz bandwidth or above, sensitivity on the Tid baselines will be degraded by a factor of 1.25, with a roughly similar impact on image sensitivity.