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Exposure Time Calculator

Filter Name  
Scale   arcsec/pixel
Source Type 
Source Brightness  Jy

Please Note

Currently the TIMMI2 Exposure Calculator is under development and testing. At this stage calculations are for imaging mode in N1, N10.4, N11.9, N12.9, M and Q bands. The output signal-to-noise values are highly dependable on sky conditions and should be used as a guide only.


The TIMMI2 exposure calculator provides a plot of the signal-to-noise versus time, for a given source brightness.

The calculations are based on the assumption that the sky background is the dominant noise source. The following formula is used

sn = [source x (sqrt(time)] / [convf x Npixel x sky]

sn = signal/noise
source = source brightness (Jy)
time = exposure time (sec)
convf = conversion factor (Jy sec/ADU)
Npixel = number of pixels
sky = sky brightness (ADU/sqrt(sec)/pixel)

The conversion factor and sky brightness have been derived from the TIMMI2 monitoring program.

The number of pixels can be determined as follows:

For point source:      Npixel = [size/(2 x scale)]^2 x pi

For extended source:     Npixel = (1/scale)^2

scale = pixel scale (0.2" or 0.3")
size = diffraction limit (1.4" in Q band and 0.7" for N and M bands)

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