Tau, Seeing, and Sensitivities

When you are writing your proposals (and observing templates, should you be awarded telescope time or fallback time), remember that there are web-based tools to assist you with calculating RMS noise of your observations.

The SCUBA integration-time calculator is available here.

The heterodyne integration-time calculator is available here.

High quality projects that can be done in poor weather (band 4/5) are always in demand. The opacity in the A-band window is typically a factor of 4 less than at 850 microns, so one could argue that working with reciever A in tau-cso = 0.3 is similar to working with SCUBA 850 in grade 2 conditions - certainly excellent results can be achieved. The following table should give you some idea of whether your project could be done with receiver A (or B) in grade 4 or 5 weather, and just how bad the weather can be before it's pointless to continue.

If tau is 0.15 you get a certain rms in one hour.

If tau is 0.20 you'll get the same rms in 1.4 hours

If tau is 0.25 you'll get the same rms in 2.0 hours

If tau is 0.30 you'll get the same rms in 2.6 hours

If tau is 0.35 you'll get the same rms in 3.2 hours

If tau is 0.40 you'll get the same rms in 4.0 hours.

Note that tau and seeing data can now be downloaded from the archive for any date/time from 1997 onwards. Click here for more information. In addition, WVM data can also be downloaded from the web here.

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