Earlier we showed the performance of the linear and logarithmic BBSO method. Now we have added the EFM method.
As before, plots are not shown well on this blog, so please download this pdf file and look at it:
You see the same 5 panels on each page – one panel per filter. On the panels you see the behaviour of the ‘ratio of ratios’ against phase – that is, the DS/BS ratio in observations relative to a set of synthetic lunar model images.
First page: RAW data – i.e. no scattered light has been removed. Full Moon is at the centre of the plot so we see the effect of scattered light – the obs/model ratio is increasingly not 1 as we near FM.
Second page: the linear BBSO method has been appllied to images. We see a reduction in scattered light – points ‘move down’ towards the 1-line.
Third page: logarithmic version of BBSO method – a slight improvement is seen.
Fourth page – the new one: the EFM method – a quite large improvement is seen over the best of the others! Many of the selected points are now lying on a flat seqeunce, except points towards New Moon, and some outliers.
The EFM data has been ‘selected’ in the sense that the parameter alfa, determined from images, has been used to select ‘good cleanups’. A histogram of the detected alfa values was made and a notable peak found and only images with alfa in a narrow range were used for the above plot. Alfa between 1.67 and 1.73 were picked. The absence of VE2 points is due to this – the peak of the VE2 alfa distribution is between 1.60 and 1.66. We must investigate whether these are ‘good’ solutions. [added later: a brief visual inspection seems to imply that the 1.7 solutions are the good ones – not the majority, which for VE2, lies in the peak at 1.63. Hmm.]
Speculatively, we note the ‘turnup’ of points towards New Moon. We ahave earlier discussed that this may be due to some feature or failure of the synethtic lunar image model to correctly portray the Moon at large phase angles. On the other hand the ‘turnups’ now look less like a gradual sequence, and more like a ‘jump’ up. The ‘jumps’ occur near 40 degrees from New Moon – …. is this the ‘rainbow angle’? The jump seems large – the rainbow angle paper spoke not of factors of 2 and 3 and 4 but of percentages. On the other hand the phenomenon has never been observed, as far as we know. It would be nice to have points ‘outside’ the rainbow angle to see the jump go down again (if this is the rainbow, that is). We note here that as we get closer to New Moon the lunar sicle is narrow and it becomes increasingly important to place the ‘patch’ in which the BS brightness is measured – here is an opportunity to experiment with DS/total ratios, instead.
Work continues …
