VISIR Exposure Time Calculator

Infrared Imaging Mode Version 6.0.1
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Target Flux Distribution

Uniform (constant with wavelength)
Blackbody: Temperature: K
Greybody: Temperature: K, Exponent:
Object Flux scaled to: mJy   at the central wavelength of the selected configuration
Emission line: Wavelength: nm
  Flux: 10-16 W/m2
  FWHM: nm   (the minimal width is set by the sampling)

Target Geometry

Spatial Distribution: Point Source
Extended Source   Magnitudes and line flux are given per arcsec2 for extended sources

Sky Conditions

PWV: mm Probability % of realising the PWV ≤ 2.50 mm
Seeing/Image Quality:
For point sources, the resulting Image Quality FWHM is modeled by the ETC considering the transfer functions of the atmosphere, telescope and instrument. See the helpfile for details.
Seeing: arcsec FWHM in V-band at zenith (use this value in the proposal)
              Probability ---% of realising the seeing ≤ 0.80 arcsec
IQ: arcsec (to be used for the OB constraint set)
              The corresponding seeing and probability will be indicated in the ETC output page
Image Quality is not a parameter in AO modes

Instrument Setup

Objective: mas/pixel


S/N ratio: S/N = The total integration time (without overheads) INT=NDIT*DIT. In reality, the optimal DIT depends on the atmospheric conditions at the time of observation - the actual partition of NDIT is done on-the-fly. In this model, a DIT typical for the chosen filter is assigned, and NDIT is computed according to the S/N or INT requested by the user.
Exposure Time: INT = s

In imaging, the calculations correspond to the sensitivity obtained with chopping and nodding in perpendicular direction, such that all 4 beams appear on the detector.

Plots: Toggle All / No Plots

S/N as a function of Exposure Time
System Efficiency
Input Spectrum in Physical Units
Sky Radiance Spectrum in physical units (ph/s/m2/micron/arcsec2)
Total Background Spectrum
Sky Transmission Spectrum