Earthshine blog

Earthshine blog

"Earthshine blog"

A blog about a system to determine terrestrial albedo by earthshine observations. Feasible thanks to sheer determination.

Conservation of flux

Exploring the PSFPosted by Peter Thejll Jan 22, 2012 01:37PM
During convolution of synthetic images with various PSFs we need to consider if flux is conserved. We calculate such images for a range of alfas and show here the difference in percent of the total flux of the image relative to the ideal image.

Percentage-change PSF-file
-1.6768524 % out1p4.fits
-0.060953825 % out1p6.fits
0.014277556 % out1p8.fits
0.027423956 % out1p9.fits

That is, in an image convolved by the broad PSF with alfa=1.4 1.67% of the flux is lost, while only 0.03% of the flux is changed when convolving with a PSF with alfa=1.9 (the narrowest possible).

The loss (and gain) in flux is not understood yet - but is perhaps related to clipping (in the case of the broad PSF) of halo when the images are padded 3x3 in order to perform the FFT, or roundoff (narrow PSF - many values are rounded below 1 to 0).

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