MOPEX Online Manual

PRF Estimate Modules: PRF Estimate

PURPOSE

This module combines the postage stamp images generated by the module Crop Stack into the final PRF.

PARAMETER BLOCK

&PRF_ESTIMATE
  MinNumber_Replacement_Pixels = 8,
  Reject_NaNs = 0,
  Outlier_Threshold = 3,
  Min_Outlier_Overlap = 0.5,
  Max_Ratio_Outliers = 0.1,
  Max_Number_Outliers = 0,
  Flux_Column_Name = 'flux',
  PRF_ResampleX_Factor = 4,
  PRF_ResampleY_Factor = 4,
  Zero_Edge = 0,
  Fit_Seed = 0,
  Fit_X = 5,
  Fit_Y = 5,
  Center_Box_X = 7,
  Center_Box_Y = 7,
&END

INPUTS

MinNumber_Replacement_Pixels: (int) The minimum number of pixels neighboring a NAN to be used for computing the median value that will replace the NaN.

Reject_NaNs: (int) The maximum number of NaNs to be replaced before an image is rejected.

Outlier_Threshold: (int) The number of trimmed sigmas below and above the trimmed mean to determine outliers from the stack of registered, interpolated postage stamps.

Min_Outlier_Overlap: (float) The fractional overlap between an original pixel and an outlier pixel in the common, interpolated grid that will trigger rejection of that original pixel.

Max_Ratio_Outliers: (float) The maximum allowable fraction of outlier pixels in an input postage stamp before that image is rejected. This condition AND the condition for Max_Number_Outliers must be exceeded before an image is excluded.

Max Number Outliers: (float) The maximum allowable number of outlier pixels in an input postage stamp before that image is rejected. This condition AND the condition for Max_Ratio_Outliers must be exceeded before an image is excluded.

Flux_Column_Name: (string) The name of the column in the input point source list corresponding to the flux of each source. If not given, the flux will be estimated as the sum of all the pixels within each postage stamp.

PRF_ResampleX_Factor, PRF_ResampleY_Factor: (int) The ratio of the input image pixel size to the sampling distance in the X, Y directions in the final coaddition.

Zero_Edge: (int) The size in pixels of the margin to the PRF to be set to 0.

Fit_Seed: (int) The seed for random number generation to be used by simulated anneal fitting. If set to 0, the current time is used. If negative, the fitting is not performed.

Fit_X, Fit_Y: (int) Fitting area size in pixels.

Center_Box_X, Center_Box_Y: (int) The size in pixels of the region of the point source images to be considered central. If pixels within the central region have NaN values, then that postage stamp is rejected from the stack.

OUTPUTS

Generated Anneal Status File: The table containing diagnostic information about the fitting used to estimate the point source flux and position.

Generated PRF file: The output PRF file. Note that this file does not contain WCS information, so the MOPEX GUI will give a warning when the FITS file is viewed.

Generated PRF Coverage File: The corresponding coverage file.

Generated PRF Sigma file: The corresponding uncertainty file.

Generated Star file: The corresponding Star file.

Generated Status List file: Lists whether each input postage stamp image was included in the final stack and, if not, the reason it was rejected.

NOTE: If the Split By Array Position module is turned on, the output files will be replicated for each region of the PRF Map. The output file names will have have _i appended to them for the i^th region, and the GUI will label the output with PRF#i.

DISCUSSION

This module combines the postage stamps into the final PRF. The postage stamps are resampled and shifted to the common grid using bicubic interpolation. The stack is combined using a simple mean, and the standard deviation is found for each pixel position. During the processing, a variety of outlier rejection tests are applied to each point source image. Only those that pass each test are included in the final stack. The output status file describes the fate of each postage stamp.

In addition to outlier rejection, the module replaces each NaN in the input image with the median of a number of the neighboring pixels. If Reject_NaNs is greater than 0, then bad pixels are replaced only if their number is less than or equal to Reject_NaNs. Otherwise the image is excluded from the list of images to be used for PRF estimation. Another reason for rejecting an image is if a NaN pixel is found in the center of the input image. The size of the center is specified with the namelist parameters Center_Box_X, Center_Box_Y both defaulting to 7.