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Infrared Exposure Time Calculator

General description

The ETC consists of two pages. The input page, presents the observation parameters the entry fields and widgets for the target information, expected atmospheric conditions, instrument configuration, observation parameters such as exposure time or signal-to-noise, and results selection. An "Apply" button submits the parameters to the model executed on the ESO Web server. The results page presents the computed results, including number of counts for the object and the sky, signal-to-noise ratios, instrument efficiencies, PSF size etc.. The optional graphs are displayed within Java applets allowing interactive manipulation. The results are also provided in ASCII and GIF formats for further analysis and printing. Finally a summary of the input parameters is appended to the result page.

Note: These tools are only provided for technical assessment of observation feasibility. Variations of the atmospheric conditions can strongly affect the required observation time. Calculated exposure time do not take into account instrument and telescope overheads. Users are advised to exert caution in the interpretation of the results and to report any result which may be suspected to be inconsistent.

The exposure time calculator models the observation chain which includes the target spectral distribution, atmosphere parameters, instrument configuration, and detector setup. The following diagram illustrates the observation chain for imaging.


Input Spectrum

From the following, choose the spectrum shape you want for your target.

Sky Conditions

Imaging ETC

Spectroscopy ETC

Detector and Observation Setup

The Exposure Time Calculator is made of 2 interactive Web forms. Fill in the input form to define the kind of object you want to observe, the atmospheric conditions, instrument and detector setups. Set a Signal to Noise Ratio (SNR) to achieve and get an Exposure Time estimation, or the opposite: given a DIT, NDIT and NINT (i.e. exposure time), estimate the SNR you would get.

The output form will give you estimates for SNR or Exposure Time, together with graphs you selected for output. These graphs are interactive Java applets which may require that you setup your browser to activate them. Help can be found from the output page about how to use the Java applets.

To set up the observation, either a SNR or an exposure time must be user-defined. The simulation computes then the associated value.

Do not confuse exposure time and total observation time, the latter being a sum of exposure time and overheads in the telescope and instrument. Please consult the user manuals for guidance on the choice of the integration parameters.

Possible Outputs in Imaging

Possible Outputs in Spectroscopy

Version Information

Send comments and questions to usd-help@eso.org