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VISIR Exposure Time Calculator

Infrared Imaging Mode Version 5.1.0
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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
Single 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

Altitude of Target above Horizon Alt= [19.5, 90] °       Alt and X are coupled through the
plane parallel approximation X=sec(z),
z being the zenith distance z=90°−Alt
Airmass X = [1, 3]
Seeing : arcsec   (FWHM at 500 nm)
Precipitable Water Vapor PWV Typical Season:
Explicit PWV = mm  (Paranal median ≈ 2.5mm)

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 Transmission Spectrum
Sky Radiance Spectrum in Physical Units (ph/s/m2/micron/arcsec2)
Detailed S/N info


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