April 13th, 2019

2009

Simultaneous calibration and imaging

https://youtu.be/UGL_OL3OrCE?t=1173
"So we do calibration at the same time as imaging"

~~~~~~~~~~~~
https://en.wikipedia.org/wiki/Calibration
Calibration in measurement technology and metrology is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy.
~~~~~~~~~~~~

The only image of "known accuracy" that these scientists had during black hole imaging -- was a theoretical image of how that black hole should look like.
But it is invalid to use that theoretical image as a self-proof that this theoretical image is correct.

So this team of "black hole photographers":
1) Took an extremely sparse signals from their several telescopes.
2) "Calibrated" their "signal interpretation" algorithm based on the theoretical black hole image (that they wanted to see).
3) Made "calibrated" "signal interpretation" algorithm to interpret sparse signals.
4) Not surprisingly, their "signal interpretation" algorithm produced theoretical black hole image that these "photographers" wanted to see.

What these "black hole photographers" did is NOT science, but scientific scam.

That explains why these "photographers" instead of photographing Sagittarius A (that is 26 thousand light years away) chose to photograph Messier 87 (that is 53 million light years away -- 2000 times further!)

At shorter distances there is not enough room for creative "calibration" of sparse signals.

See also:
Extracting a black hole image from "sparse telescope matrix"

Originally posted at: https://dennisgorelik.dreamwidth.org/170075.html
2009

Calibration Free Imaging

It gets better:
~~~~~~~~~~~
https://youtu.be/UGL_OL3OrCE?t=1177
19:37
What you can do is to use methods where you [have] do not need any calibration whatsoever and you can still can get pretty good results.
So here on the bottom at the top is the truth image, and this is simulated data, as we are increasing the amount of amplitude error and you can see here ... it's hard to see ... but it breaks down once you add too much gain here. But if we use just closure quantities - we are invariant to that.
So that really, actually, been a really huge step for the project, because we had such bad gains.
~~~~~~~~~~~

"Вот тут мне карта и поперла".


==============
https://youtu.be/UGL_OL3OrCE?t=2242
37:22
And you can notice like at the bottom we get really terrible reconstruction, just cause if it fits the data very well, because you know it maybe wants to smooth out the flux as much as possible and we don't select things like that in the true data.
==============

I posted a comment below that video:
~~~~~~~~~
19:39 "Calibration Free Imaging"
Does it mean that you were using measurements tools (telescopes) without prior calibration?
~~~~~~~~~
but it got deleted... twice.

Originally posted at: https://dennisgorelik.dreamwidth.org/170455.html