ALMA Sensitivity Calculator

This tool 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. You can also get additional information on the valid range for each parameter by hovering your mouse pointer over each field in the calculator applet.

To run the calculator you need the Java Plug-in installed. If you do not see the calculator then it is likely that you do not have it installed. Instructions for installing the plugin will vary depending on your browser and operating system. A plugin compatible with the Java Development Kit version 1.6 (or Java6) is recommended (version 1.5 should work at the moment). Please contact your IT department for installation help if necessary.

Parameters

Common Parameters

  • Sensitivity Type: Choose between a point-like or extended source.
  • RA/Dec: Coordinates of the observation target.
  • Effective Bandwidth: The standard observing mode will be using two polarizations. Therefore, for continuum observations with 8GHz bandwidth an effective bandwidth of 16GHz needs to be selected. For line observations, use double the spectral resolution element width.
  • Frequency: Observing frequency. This must be within the boundaries of ALMA bands 1 to 10, which are as follows:
    • Band 1: 31 GHz - 45 GHz
    • Band 2: 67 GHz - 90 GHz
    • Band 3: 84 GHz - 116 GHz
    • Band 4: 125 GHz - 163 GHz
    • Band 5: 163 GHz - 211 GHz
    • Band 6: 211 GHz - 275 GHz
    • Band 7: 275 GHz - 373 GHz
    • Band 8: 385 GHz - 500 GHz
    • Band 9: 602 GHz - 720 GHz
    • Band 10: 787 GHz - 950 GHz
  • Observatory Site: For ALMA observations, leave this as Chajnantor.
  • Water Vapour Column Density: "ETC Chooses" will select an appropriate value according to the input frequency.
  • Sensitivity Unit: This will change automatically according to your choice in the "Sensitivity Type" field.

Individual Parameters

  • Number of Antennas: 50 for entire main array, but in practice the entire array need not be used and subsets of the main array may work independently.
  • Beamsize: Desired angular resolution, or FWHM of the synthesized beam. Only editable for extended source observations.
  • Sensitivity/Exposure Time: Noise level and telescope integration time. Input one to calculate the other.

Contact

Please address questions relating to the ALMA ETC to Andy Biggs (abiggs [AT] eso.org).

Acknowledgment

This java applet was adapted from the Exposure Time 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 Prepation System team within the ALMA Computing IPT.