## IQ-R4 » History » Version 4

Jiangang Hao, 07/09/2012 09:37 AM

 1 2 3 1 Jiangang Hao h1. IQ-R4 1 Jiangang Hao 1 Jiangang Hao Requirements: 1 Jiangang Hao 1 Jiangang Hao * TO.2: The delivered PSF from the telescope, instrument, and other factors exclusive of the site seeing will be no greater than 0.55 arcsec FWHM (DES-doc-806-v25). 1 Jiangang Hao 1 Jiangang Hao * R-18: The PSF FWHM in each of the r, i, and z bands should, over all exposures and over the survey area, have a median of less than 0.9”. Moreover, for 95% of the survey area, there should be at least one exposure in each of these bands for which the mean PSF FWHM is 0.9” or smaller (DES-doc-20-v32). 1 Jiangang Hao 1 Jiangang Hao 1 Jiangang Hao 1 Jiangang Hao Procedures:  1 Jiangang Hao 1 Jiangang Hao * When pointing to the Zenith, the PSF FWHM from DECam are compared to the CTIO DIMM seeing measurements according to the model FWHM^2 = DIMM^2 + \sigma^2. The best fit value is \sigma <= 0.55" across the full array. Therefore, we can measure the contribution of the PSF from the DECam by subtracting the DIMM seeing from the measured PSF by quadrature.  1 Jiangang Hao 2 Jiangang Hao * Step 1: Point the telescope to zenith, take 10 exposures of 100 sec each in r, i and z band.  2 Jiangang Hao * Step 2: Measure the FWHM around bright stars after Flat-fielding and bias-subtraction 2 Jiangang Hao * Step 3: Get the DIMM FWHM from http://www.ctio.noao.edu/environ/environ.html and calculate the FWHM due to the DECam. The maximum of the sqrt(WFHM^2 - DIMM^2) should be less than 0.55". This is a check of TO.2.  2 Jiangang Hao * Step 4: Get the median of the FWHM and check whether it is less than 0.9" in r, i and z band.  3 Jiangang Hao 3 Jiangang Hao 3 Jiangang Hao Code availability: 3 Jiangang Hao 3 Jiangang Hao In terms of the Gaussian Fit, the codes are available to measure the FWHM.  3 Jiangang Hao 3 Jiangang Hao Question: 3 Jiangang Hao 4 Jiangang Hao Here, the FWHM in the requriement is in terms of the Gaussian fit/weight or not?