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VISIR Exposure Time Calculator

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Infrared Imaging Mode Version 6.0.1
Description.
F.A.Q
 
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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

PWV: mm Probability 55% for a PWV smaller or equal to the requested value
Airmass:
Seeing: arcsec FWHM in V-band at zenith (use this value in the proposal). The seeing is irrelevant for extended sources.
Probability 60% for a seeing smaller or equal to the requested value
For point sources, the resulting Image Quality FWHM is modeled by the ETC considering the transfer functions of the atmosphere, telescope and instrument. For details see the helpfile.

Instrument Setup

Filter:
Objective: mas/pixel

Results

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
Details of Image Quality Calculations (only for pointsources)
 
Detailed S/N info

      

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