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Sensitivity Calculator

The ALMA Sensitivity Calculator (ASC) will calculate the necessary integration times for a given sensitivity (or vice versa) for your ALMA observing project. Input and output parameters are explained below. Additional information is available to users on the valid range for each parameter by hovering your mouse pointer over each field in the calculator applet (this does not currently work in Safari). The ALMA Sensitivity Calculator Guide gives a brief description of how the ASC works.

The calculator defaults to the number of antennas available during Cycle 0, but the user can select a higher number of antennas in order to compare the capability in future cycles. The resulting integration times refer only to the on-source time and do not take any kind of overheads into account. Furthermore, the ASC calculates the integration time/sensitivity for a single pointing. The case of pointed mosaics is discussed in the ALMA Technical Handbook.

A Java Plug-in must be installed in order to run the calculator. If the calculator is not displayed, then it is likely that this plug-in is not installed. Instructions for installing the plug-in may vary, depending on the browser and operating system used. A Plug-in compatible with the Java Development Kit version1.5 or 1.6 (i.e. Java 5 or 6) is required. Users should contact their local IT department for installation help if necessary.

Parameters

  • Polarization: There are two options: "Single" and "Dual". Single Polarization allows for very high spectral resolution at the cost of sensitivity. Users will usually want "Dual" for continuum and for spectral line modes not requiring the highest spectral resolution modes.
  • Bandwidth Per Polarization: 7.5 GHz should be selected for continuum observations. For spectral line observations, the width of the resolution element in which the user is interested should be entered.
  • Observing Frequency: This must be set within the boundaries of ALMA bands 1 to 10; the four bands available in Cycle 0 are highlighted below. Bands 1 and 2 may become part of ALMA as part of a future development plan.
    • Band 1: 31 GHz - 45 GHz
    • Band 2: 67 GHz - 90 GHz
    • Band 3: 84 GHz - 116 GHz (ES)
    • Band 4: 125 GHz - 163 GHz
    • Band 5: 163 GHz - 211 GHz (only 6 receivers)
    • Band 6: 211 GHz - 275 GHz (ES)
    • Band 7: 275 GHz - 373 GHz (ES)
    • Band 8: 385 GHz - 500 GHz
    • Band 9: 602 GHz - 720 GHz (ES)
    • Band 10: 787 GHz - 950 GHz
  • Water Vapour Column Density: The "Calculator Chooses" option will select an appropriate value according to the input frequency (e.g. high frequencies must be observed in good weather). The user may also choose preferred observing conditions based on years of monitoring data - seven octiles are provided. See the Weather page for further information on weather statistics and atmospheric transmission.
  • Number of Antennas: This field defaults to "16" for Cycle 0. There will be no 7-m or Total Power antennas available for Cycle 0.
  • Resolution: A value should be entered here if the user is interested in surface brightness sensitivity. For planning Cycle 0 observations, this value should be approximately equal to the maximum resolution of the two available configurations (maximum baselines of 125 and 400m).
  • Sensitivity/Integration Time: One of these quantities needs to be specified in order to calculate the other. Choosing the unit "Kelvin" will cause the ASC to use surface brightness units and will thus require that an angular resolution be entered in order to give sensible results.

Troubleshooting

Some users may experience problems with the calculator, depending on the OS, Java version/vendor and browser.used. Below is a list of known issues and solutions.

  • Reload the page - it may take multiple attempts. It might also be necessary to restart the browser.
  • Is Java enabled in your browser preferences? Javatester.org will tell you which version of Java is being used by applets. You must have Java 5 or 6 installed and recent versions of these are encouraged.
  • "IcedTea" variants of Java do not appear to work well with the ASC. The user is advised to install the Sun version instead.
  • If all else fails, try running appletviewer http://www.almascience.org/call-for-proposals/sensitivity-calculator/ on your command line. This always seems to work, but this helpful text will not be visible.

If problems are still encountered after trying all of the above, please contact the Helpdesk (requires registration). Non-registered users can access the Knowledgebase by using the same Helpdesk link.

Contact

Any questions about the ASC should be addressed to the Helpdesk (registration required). We are particularly interested to hear about any undesirable behaviour and bugs as well as any improvements that you would like to see.

Acknowledgment

This java applet was adapted from the ALMA Sensitivity Calculator in the ALMA Observing Tool by Hiroshi Yatagai. The Observing Tool is the software tool that will be used for the preparation of ALMA Observing Projects. The Tool is built by the Proposal and Observing Preparation System team within the ALMA Computing IPT.