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Sensitivity Calculator

The ALMA Sensitivity Calculator (ASC) is launched by either clickingon the button in the Toolbar or by selecting Tool $\rightarrow$ Sensitivity Calculator... . We give here only a brief description ofthis tool; a more in-depth guide to the ASC can be found in theDocuments section of the ALMA Science Portal ( http://www.almascience.org ).

Figure 5.4: The ALMA Sensitivity Calculator.
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After having defined the input parameters (Observing Frequency,Bandwidth, Water Vapour Column Density, etc.) in the common area inthe upper part of the interface, using the number of antennas andrequired sensitivity, the tool calculates the integration times forthe Main (12m Array) ALMA Array , for the ALMA CompactArray (7m Array) and for a Total PowerArray . The tool also provides the inversefacility, i.e. for estimating the sensitivities given an inputintegration time. The layout of the calculator is displayed inFigure  5.4 .

In the GUI, the user has to specify the bandwidth per polarization;multiplying this by the number of polarizations ( Single or Dual ) gives the effective bandwidth. Sensitivity can be specified as a flux density if the unit isJy or as a brightness temperature if theunit is in K. If a flux density sensitivity is entered, a brightnesstemperature equivalent is displayed in the following grey field andvice versa. Note that if the sensitivity is entered in temperatureunits, the angular resolution must also have non-zero value in orderfor the calculator to work! For Cycle 0, the angular resolutioncorresponding to one of the two configurations should be chosen (asdisplayed on the Control and Parameter page of the Science Goal).

System temperature and atmospheric parameters are displayed for thespecified frequency. There are 7 choices of water vapour(PWV) data: 0.4722 mm, 0.658 mm, 0.9134mm, 1.262 mm, 1.796 mm, 2.748 mm, and 5.184 mm; these correspond tothe octiles measured over many years at the ALMA site. If Calculator Chooses is selected, an appropriate choice will be madebased on the entered frequency i.e. Band 9 observations must be madein conditions with low water vapour.

Finally, with the Integration Time Unit Option the output unitfor the integration time field can be specified when using the Calculate Integration Time option. If Automatic is chosen ,the tool itself selects the appropriate unit. The current unit can beenforced in subsequent calculations using Keep displayed unit whilst specific units can be selected using In sec , In min , In hour and In day .


next up previous contents index
Next: Spectral Line Selection Tool Up: Tools Previous: Calibration Time Estimate Tool   Contents   Index
The ALMA OT Team, 2011 May 20