NSFCam Signal-To-Noise Calculator

This form can be used to estimate the S/N for objects with a given magnitude and a specified exposure time. The user should specify the source mag, the integration time (in sec) for an individual frame, the number of coadds, the total number of separate exposures (i.e., dither positions), the plate scale (arcsec/pixel), the seeing (at 2.2 microns), and the aperture size (in arcsec) used for the source photometry.

The program will calculate the S/N for the input parameters in each passband (J,H,K,K',L,L',M,M'), as well as the seeing in each band, the fraction of the total source flux contained in the aperture, the counts expected from the source (alone) in the aperture, the counts expected in the peak pixel from source plus background, and the counts in the sky background per pixel. Note that saturation will occur if the exposure time for a single image is too long, and the counts exceed the well depth. Also, the minimum allowable integration time for a full frame (256 x 256 pixels) is 0.0774 sec; shorter exposure times can be achieved only by reading out a smaller sub-array. The program assumes that the flat-fielding is perfect and that the background is determined from an aperture containing three times as many pixels as the source aperture. It uses values of the sky background and photometric zero points recently measured with NSFCam. It does not (yet) take into account differences in the zero points for the different plate scales.

Please note that the observing efficiency needs to be included separately. At thermal wavelengths the efficiency is typically ~33-50% due to the short on-chip integrations (~0.1sec) and so the exposure time calculated with the calculators needs to be increased by a factor of three to two times. For on-chip integration times longer than one second or so the observing efficiency is close to 100%.

   NSFCam 1 platescales: 0.055, 0.148, 0.30
   NSFCam 2 platescale : 0.40 
   Guidedog platescale : 0.1162 
   Kyle     platescale : 0.10

Contact John Rayner for further information or assistance.

This readme.html provide some documentation.

Inputs/Command:
    Source Mag: 12.0
     Itime_sec: 60
        Coadds: 3
     Exposures: 1
   Plate Scale: 0.148
        Seeing: 0.7
    Aperture R: 1.0 
       Command: none

Output:
none

Required Signal-to-Noise Ratio:
Integration time(sec) for individual frames:
Number of coadds:
Number of separate exposures:
Plate Scale (arcsec/pixel):
Seeing (FWHM in arcsec) at 2.2 microns:
Photometric Aperture Radius (in arcsec):