34.13. PSF: Detector Point Spread Function

The point spread function (PSF) file contains a series of records that define the spatial point spread function for each detector at a series of wavelengths. The file contains an OVERSAMPLE variable that define the amount that each detector will be spatially oversampled (N x N). Each function entry record includes a wavelength and the weights for each sub-pixel sample. The weights are automatically normalized when the function data is read in so that the final pixel power is not changed (or the integrated PSF value is 1.0).

DIRSIG_PSF
#
# This is an example DIRSIG "point spread function" (PSF) file.
# This file is loaded by providing its filename to the
# PSF_FILENAME variable in the BAND section of the CFG file.
# The various variables and sections are discussed below.
#

# The OVERSAMPLE variable indicates the amount that each pixel
# will be oversampled (NxN) and the size of the PSF kernels
# listed in the FUNCTION section.  The value assigned to this
# OVERSAMPLE variable overrides the value in the BAND section
#
OVERSAMPLE = 5

#
# The FUNCTION section defines PSF convolution kernels at a discrete
# set of wavelengths.  These kernels are then interpolated to provide
# the PSF at all wavelengths.  If the PSF is well behaved, the spectral
# PSF could be defined by only a couple of points.
# 
# IMPORTANT: The kernels must be listed in decreasing frequency or in
#            increasing wavelength at this time.
#
FUNCTION {

    #
    # Each function entry must have a FREQUENCY and a WAVELENGTH variable
    # and a DATA section.  The DATA section is simply a list of the
    # kernel weights.  The weights are listed in the following order:
    # [x0,y0], [x1,y0], ... [xN,y0, [x0,y1], [x1,y1], ... [xN,y1] ... [xN,yN].
    # Each kernel is normalized so that the total weight is equal to 1.0
    #
    ENTRY {
        WAVELENGTH = 0.3
        DATA = {
            0.3752 0.4607 0.5000 0.4607 0.3752
            0.4607 0.6126 0.7071 0.6126 0.4607
            0.5000 0.7071 1.0000 0.7071 0.5000
            0.4607 0.6126 0.7071 0.6126 0.4607
            0.3752 0.4607 0.5000 0.4607 0.3752
        }
    }
    ENTRY {
        WAVELENGTH = 20.0
        DATA = {
            0.3752 0.4607 0.5000 0.4607 0.3752
            0.4607 0.6126 0.7071 0.6126 0.4607
            0.5000 0.7071 1.0000 0.7071 0.5000
            0.4607 0.6126 0.7071 0.6126 0.4607
            0.3752 0.4607 0.5000 0.4607 0.3752
        }
    }
}