; ACTNOISE ;--------------------------------------------------------------- ;! puts estimate of actual image uncertainty and zero in header ;# Verb Analysis modeling catalog ;----------------------------------------------------------------------- ;; Copyright (C) 1995, 1999, 2009 ;; Associated Universities, Inc. Washington DC, USA. ;; ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; ;; This program is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public ;; License along with this program; if not, write to the Free ;; Software Foundation, Inc., 675 Massachusetts Ave, Cambridge, ;; MA 02139, USA. ;; ;; Correspondence concerning AIPS should be addressed as follows: ;; Internet email: aipsmail@nrao.edu. ;; Postal address: AIPS Project Office ;; National Radio Astronomy Observatory ;; 520 Edgemont Road ;; Charlottesville, VA 22903-2475 USA ;----------------------------------------------------------------------- ACTNOISE LLLLLLLLLLLLUUUUUUUUUUUU CCCCCCCCCCCCCCCCCCCCCCCCCCCCC ACTNOISE: Verb to put estimate actual noise in image header INNAME Image name (name) INCLASS Image name (class) INSEQ 0.0 9999.0 Image name (seq. #) INDISK 0.0 9.0 Disk drive # PIXSTD RMS about mean pixel value PIXAVG Estimate of zero level in image ---------------------------------------------------------------- ACTNOISE Type: Verb Use: ACTNOISE is a verb to put an estimate of the actual rms of the image into the image header. Gaussian fitting tasks (SAD, IMFIT, JMFIT) will use any positive ACTNOISE found in the image header. If there is none, then they use all image pixels to fit the width of the peak in the histogram in order to estimate this noise. Such automatic fits can have problems in the actual fitting and will use all pixels even if that is inappropriate (e.g., images blanked with zeros, images corrected for the primary beam, ...). A less obvious consideration: the fit rms is for signal-free regions, while the noise after Clean is larger on source than off. You may use this verb to estimate the on-source uncertainty. PIXSTD may be set with verbs IMSTAT and TVSTAT. Do not include any real signal while doing this, since the real signal will raise the rms , making it not represent the real noise. The task IMEAN may be used to fit the histogram for an rms in a sub-image --- or better still, it may be used to plot the histogram so that you may make a proper estimate of the actual noise. IMEAN will use and update (if DOCAT > 0) the ACTNOISE and ACTMEAN keywords. Note that SAD, IMFIT, and JMFIT use ACTNOISE only in estimating the uncertainties in the fit parameters. IMEAN will use ACTNOISE to help it fit for a better estimate of the actual noise in the sub-image it is considering. Adverbs (input): INNAME......Image name(name). Standard defaults. INCLASS.....Image name(class). Standard defaults. INSEQ.......Image name(seq. #). 0 => highest. INDISK......Disk drive # of image. 0 => any. PIXSTD......Estimate of the actual noise in the image in the same units as the image. If PIXSTD <= 0, then the Gaussian fitting tasks will fit the histogram to determine the noise level. PIXAVG......Estimate of the zero level about which the PIXSTD is distributed in the same units as the image. ----------------------------------------------------------------