Blog Image

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.

Rainbow Angle

Links to sites and software Posted on Nov 06, 2011 14:53

Table of “Rainbow angle” as seen from MLO. The angle is SEM. Times are UTC. Sun is down.


Post-Obs scattered-light rem. Posted on Nov 06, 2011 09:48

With various systems to simulate realistic observations at hand – Chris’ noise simulator and Hans’ ideal image simulator – it becomes possible to pose some questions, such as:

1) Is it better to reduce every
blessed image and then average derived results, or should images be
coadded and then reduced?

2) Knowing that the bias has a 1-count
amplitude, 20-minute period is it then a sensible
strategy to scale a low-noise ‘superbias’ to the observed but noisy bias?

3) What is the relationship between precision in alfa and scatter in
DS/BS ratio, in the presence of realistic noise?

A partial, idealized, answer to 3) is hinted at by considering the change in DS and BS intensities as a function of change in alfa:

DS change: -15.9935 %
BS change: 0.0893807 %
alfa ch: 0.995023 % [Note that PSF was normalized]

I.e. If we change alfa by 1% we get a 16% change in a typical DS point and a 0.1% change in a typical BS point. This suggest that we need to know alfa to an accuracy of 0.6% (alfa was 1.7) or 0.006. This would be the typical step-size of a grid-search, for instance, and the tolerance on any downward-descent search. Perhaps it is easy to get such accuracy with methods that ‘fit the sky’ – such as both the BBSO and our own forward methods.

How does the above change in the presence of realistic noise?