VISIR Exposure Time Calculator
Infrared Imaging Mode Version P114
Description
FAQ
 
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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

Moon FLI: Airmass:
Almanac
Time
Time step forward/back


Target
Target coordinates Name or ID:  
α      δ     
UT rise
culm.
set		 Hour Angle azimuth altitude zenith distance airmass FLI moon/sun
phase angle		 moon/target
separation
Target
Moon
Sun
An advanced almanac is available in the ESO SkyCalc sky model calculator
PWV:     mm     Probability % of realising the PWV ≤ 10.00 mm
Seeing/Image Quality:
Turbulence Category:   (FWHM of the atmospheric PSF outside the telescope at zenith at 500 nm)
IQ: arcsec FWHM at the airmass and reference wavelength
              The corresponding seeing and turbulence category will be indicated in the output page
Image Quality is not a parameter in AO modes

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