TIMMI2  Exposure Time Calculator

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.

Description

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]

where

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

where

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

Site comments: ls-infrared@eso.org Last modified: Fri May 18 15:54:48 SAT 2001