IQ-R4 » History » Version 7

Jiangang Hao, 07/23/2012 01:29 PM

1 1 Jiangang Hao
h1. IQ-R4
2 1 Jiangang Hao
3 1 Jiangang Hao
4 1 Jiangang Hao
5 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).
6 1 Jiangang Hao
7 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).
8 1 Jiangang Hao
9 1 Jiangang Hao
10 6 Jiangang Hao
h2. Prerequisites
11 1 Jiangang Hao
12 6 Jiangang Hao
10 standard exposures in each of the r, i, z band. The images needs to be processed (flat fielding, bias subtraction) and a list of bright stars (positions in CCD coordinates) are needed.
13 1 Jiangang Hao
14 7 Jiangang Hao
h2. Procedures 
15 6 Jiangang Hao
16 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. 
17 1 Jiangang Hao
18 2 Jiangang Hao
* Step 1: Point the telescope to zenith, take 10 exposures of 100 sec each in r, i and z band. 
19 5 Jiangang Hao
* step 2: Extract the objects on the images and get a list of bright stars (magnitude range?). Here, we need the data reduction pipeline to reduce the data.  
20 5 Jiangang Hao
* Step 3: Measure the FWHM around bright stars after Flat-fielding and bias-subtraction
21 5 Jiangang Hao
* Step 4: Get the DIMM FWHM from 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. 
22 3 Jiangang Hao
* Step 5: Get the median of the FWHM and check whether it is less than 0.9" in r, i and z band. 
23 1 Jiangang Hao
24 3 Jiangang Hao
25 7 Jiangang Hao
h2. Code availability
26 3 Jiangang Hao
27 3 Jiangang Hao
In terms of the Gaussian Fit, the codes are available to measure the FWHM. 
28 5 Jiangang Hao
29 3 Jiangang Hao
30 7 Jiangang Hao
h2. Caveats
31 3 Jiangang Hao
32 4 Jiangang Hao
Here, the FWHM in the requriement is in terms of the Gaussian fit/weight or not?