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LSST Exposure Time Calculator

Version 4.3 - new sky background model

In the four sections of this form, select the appropriate astronomical source, instrument, telescope, observing condition and observation parameters. Click on the calculate button () at the bottom of any section to submit the parameters from all the sections to the server. The results are reported in a separate web page that can be resized and printed.

General guidance on use of the Exposure Time Calculator (ETC) is available; specific help on each section of the form is available by following the more info and other (blue highlighted) links. Changes, enhancements and bugs within the ETC are listed chronologically.

Information on the standalone version of the ETC.

Astronomical source definition

Spatial profile and brightness:(more info)
Choose one of point, extended or user-defined source profile and the brightness in any filter/wavelength
Point source (nominal PSF) with spatially integrated brightness (e.g. 19.3 mag or 2e-17 W/m^2/um)
Extended source having ...
  Gaussian profile with full width half maximum of arcsec and spatially integrated brightness of (e.g. 19.3 mag or 2e-17 W/m^2/um)
  Uniform surface brightness (e.g. 21.6 mag / sq arcsec)
  disabled Exponential profile with spatially integrated brightness (e.g. 19.3 mag or 2e-17 W/m^2/um) and half-light radius of arcsec (disabled)
  disabled Elliptical r^(1/4) profile with spatially integrated brightness (e.g. 19.3 mag or 2e-17 W/m^2/um) and half-light radius of arcsec (disabled)
disabled User-defined 2D image read from file (disabled)
with the above brightness normalization applied in filter band or disabled at a wavelength micron (latter option disabled)
Spectral distribution: (more info)
Choose one SED, the redshift and extinction
Library spectrum of a non-stellar object
Library spectrum of a star with spectral type
Single emission line at wavelength micron with line flux and line width km/s on a flat (in wavelength) continuum of flux density
Model black body spectrum with temperature K
Model power-law spectrum (S_lambda = lambda ^ )
User-defined spectrum read from file (size < 1MB)
with the spectrum mapped to a redshift z = or a radial velocity v = km/s
...and subject to dust reddening by a foreground screen (see more info on the extinction law) having a visual extinction of Av = mag (disabled) disabled


Instrument (LSST) and telescope configuration

Instrument optical properties:(more info)
Color filter:  
Detector:  
Detector properties:(more info)
CCD readout noise of 5 e-
CCD dark current of .0015 e-/s
pixel size of 10 microns
No CCD binning; camera plate scale is 0.20 arcsec/pixel
Telescope configuration:(more info)
Mirror coating: aluminium  silver (not yet implemented)


Observing condition constraints

Note: you should read the explanatory notes for the meaning of the various settings and percentiles.
Seeing (fwhm):    arcsecs
Sky transparency: average, no humidity correction
Cloud cover (transmittance): photometric patchy cloudy usable
Sky background (lunar phase): 0 day 3 day 7 day 11 day 14 day
    (solar cycle): average min max
Typical air mass during observation: 1.0 1.2 1.5 2.0


Details of observation

Calculation method:(more info)
Select the calculation method
Total S/N ratio resulting from exposures each having an exposure time of secs and with a fraction of exposures that observe the source
Total integration time to achieve a S/N ratio of using an exposure time for each exposure of secs and with a fraction of exposures that observe the source
Analysis method: (more info)
Software aperture that gives 'optimum' S/N ratio and with a sky aperture times the target aperture
Software aperture of diameter (or slit length) arcsec and with a sky aperture times the target aperture
Optimal Filter: (more info)
psf-weighted filter
not weighted


Last update August 15, 2006; Perry Gee