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Earthshine blog

"Earthshine blog"

A blog about a telescopic system at the Mauna Loa Observatory on Hawaii to determine terrestrial albedo by earthshine observations. Feasible thanks to sheer determination.

Flatfield errors

Error budget Posted on Nov 02, 2011 18:11

I have compared four central 30×30 pixel areas in all the available sky master flatfields. A minimum of 3 masters were available in each filter. The selected regions a (blue), b (red), c (pink) and d (green) are shown in the figure. The flatfield used in the figure is the B master for night JD2455827.

For each filter and region, I have checked the difference between the largest and smallest mean value, expressed as a percentage of the smaller value. These (worst case) changes lie in the range 0.03-0.36%. I seems we can count on the error in a master flatfield to be very low!

The best master flatfields seem to be the B and V filter with only a single case of a change above 0.1%.

The worst region of the four is the green region. This is true for all filters. Perhaps these worst case changes in the worst region can be used as an estimate for the error in a master flatfield?

BBSO code

Post-Obs scattered-light rem. Posted on Nov 02, 2011 16:31

Now have a non-interactive version of the BBSO method for removing scattered light, written in IDL.

It takes about 10 seconds to ‘clean up’ the DS of one image.

The code is in SCIENCEPROJECTS/EARTHSHINE/ and runs by using a script:

./go_linearclean.scr filename.fits

a file is produced called


The method is non-intercative because the user no longer has to specify disc rim and disc center with a cursor. The estimation is done by edge-detection methods and an algorithm to fit a circle to three points in the plane, not on a line.