<p>The point of the paper is not that <em>no</em> calibration has been used previously. It points out that they now use a more refined method and set of parameters to calibrate the data.</p>
<p>That in general is usual procedure: the more data you gather, and the longer a mission runs, the better you understand your instrumentation and all external factors which influence the data you gather - and especially the sensitivity towards different systematic and instrument errors. Thus with data becoming available you only have the people to work on the problems, often Bachelor, Master or PhD students. Thus prior to instrument availability and detailed data analysis you can only do a coarse calibration based on general knowledge of the problem. Five years is a reasonable and good time interval two have one to two generation of students work on it and get an good overall picture which considers all aspects you mention (and probably more) in the necessary detail and assess their contribution in a way which satisfies scientific scrutiny including the review process.</p>

CC BY-SA 4.0
2020-07-10T09:47:55.010Z
Is it possible to cite any specific supporting sources or examples to help demonstrate that this is based on facts and not just an opinion? Thanks!
uhoh
CC BY-SA 4.0
2020-07-11T21:04:41.727Z
It's hard to link with proof of what I see during my daily work. I am not aware of studies who relate published calibrations to time after mission start or end
planetmaker
CC BY-SA 4.0
2020-07-12T01:46:15.443Z
I googled "van Weeren et al  LOFAR Abell 399 and Abell 401" and found [Probabilistic direction-dependent ionospheric calibration for LOFAR-HBA](https://www.researchgate.net/publication/339015210_Probabilistic_direction-dependent_ionospheric_calibration_for_LOFAR-HBA) There seems to be a pretty good explanation starting in the second paragraph of the Introduction section.
uhoh
CC BY-SA 4.0
2020-07-12T01:50:30.810Z
also see [However, a problem
at low frequencies is that the ionospheric phase distortions are
frequency dependent, increasing towards lower frequencies. At
about 60 MHz this means that if this effect is not included only
about 1 MHz bandwidth can be used for calibration, depending
on the ionospheric conditions](https://hal.archives-ouvertes.fr/hal-00721924/document)
uhoh
CC BY-SA 4.0
2020-07-12T02:47:00.080Z
While previous calibrations of higher frequency radio observation were based on precipitable water vapor and involved modest bandwidths where the dispersion from the water vapor was small and well behaved, LOFAR must deal with the strong refraction of low frequencies by the ionosphere where strong dispersion was an additional problem. So I think the answer is that this posed a much larger challenge than the state of the art for higher frequency radio astronomy.
uhoh
CC BY-SA 4.0
2021-08-01T08:49:23.507Z
temporary and reversible -1, I think it should not be hard to support your answer with some citations or links (I've tried to help by providing you some suggestions in comments). Once that's done I'll reverse it and (hopefully) will accept your answer. *thanks!*
uhoh
CC BY-SA 4.0
2023-04-13T09:07:39.510Z
Answer needs to discuss what those improvements were.
ProfRob
CC BY-SA 4.0
2024-12-25T02:01:53.910Z
fyi I've added a bounty, and you're certainly eligible to receive it if you can add sufficient information
uhoh
CC BY-SA 4.0
2020-07-10T08:42:34.637Z
2020-07-10T08:42:34.637Z
planetmaker
<p>Quanta Magazine's <a href="https://www.quantamagazine.org/the-hidden-magnetic-universe-begins-to-come-into-view-20200702/" rel="nofollow noreferrer">The Hidden Magnetic Universe Begins to Come Into View</a> is a fascinating review of a rapidly evolving field in astronomy.</p>
<p>It contains some statements:</p>
<blockquote>
<p><strong>In their paper last year, van Weeren and 28 co-authors inferred the presence of a magnetic field in the filament between galaxy clusters Abell 399 and Abell 401</strong> from the way the field redirects high-speed electrons and other charged particles passing through it. As their paths twist in the field, these charged particles release faint “synchrotron radiation.”</p>
<p>The synchrotron signal is strongest at low radio frequencies, making it ripe for detection by LOFAR, an array of 20,000 low-frequency radio antennas spread across Europe.</p>
<p><strong>The team actually gathered data from the filament back in 2014 during a single eight-hour stretch, but the data sat waiting as the radio astronomy community spent years figuring out how to improve the calibration of LOFAR’s measurements.</strong> Earth’s atmosphere refracts radio waves that pass through it, so LOFAR views the cosmos as if from the bottom of a swimming pool. The researchers solved the problem by tracking the wobble of “beacons” in the sky — radio emitters with precisely known locations — and correcting for this wobble to deblur all the data. When they applied the deblurring algorithm to data from the filament, they saw the glow of synchrotron emissions right away.</p>
</blockquote>
<p>The filament between galaxy clusters Abell 399 and Abell 401 is also discussed in <a href="https://astronomy.stackexchange.com/q/32199/7982">How is it determined that the X-ray and radio intensity come from a magnetic field bridge between two clusters of galaxies?</a></p>
<p><strong>Question:</strong> Why exactly did it take five years for the radio astronomy community to &quot;figure out&quot; how to improve  the calibration these LOFAR measurements and apply deblurring algorithms? Answers to</p>
<ul>
<li><a href="https://astronomy.stackexchange.com/q/13930/7982">Would Adaptive Optics be Useful in Radio Astronomy?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/18791/7982">What is precipitable water vapor in millimeter-wave radioastronomy and how is it measured?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/34412/7982">What can be learned from low frequency radio astronomy available outside of Earth&#39;s ionosphere?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/36699/7982">In the 1950&#39;s how were radio-astrometric positions with portable dishes so precise they could be assigned to their dim optical counterparts (Quasars)?</a></li>
<li><a href="https://astronomy.stackexchange.com/q/34532/7982">What exactly is interplanetary scintillation; what was the Interplanetary Scintillation Array looking for? Did it successfully observe any?</a></li>
</ul>
<p>suggest that correcting for spatial variations in water vapor or other effects is a known thing in radio astronomy. However discussions at <a href="https://astronomy.stackexchange.com/q/22217/7982">How large does refraction become in radioastronomy?</a> suggest that the ionosphere becomes increasingly important at low frequency (the &quot;LOF&quot; in LOFAR) so perhaps this was part of the challenge?</p>

CC BY-SA 4.0
2020-07-10T02:10:49.783Z
companion question: [What do these statements about interstellar magnetic fields really mean?](https://astronomy.stackexchange.com/q/36861/7982)
uhoh
<observational-astronomy><radio-astronomy><radio-telescope><interstellar-medium><lofar>
Why did it take five years to "figure out" how to use astrometric calibration sources to deblur LOFAR images?
uhoh
# Why did it take five years to "figure out" how to use astrometric calibration sources to deblur LOFAR images?

(Asked by: username_0 on 2020-07-10)

Quanta Magazine's [The Hidden Magnetic Universe Begins to Come Into View](https://www.quantamagazine.org/the-hidden-magnetic-universe-begins-to-come-into-view-20200702/) is a fascinating review of a rapidly evolving field in astronomy.

It contains some statements:

> **In their paper last year, van Weeren and 28 co-authors inferred the presence of a magnetic field in the filament between galaxy clusters Abell 399 and Abell 401** from the way the field redirects high-speed electrons and other charged particles passing through it. As their paths twist in the field, these charged particles release faint “synchrotron radiation.”
>
> The synchrotron signal is strongest at low radio frequencies, making it ripe for detection by LOFAR, an array of 20,000 low-frequency radio antennas spread across Europe.
>
> **The team actually gathered data from the filament back in 2014 during a single eight-hour stretch, but the data sat waiting as the radio astronomy community spent years figuring out how to improve the calibration of LOFAR’s measurements.** Earth’s atmosphere refracts radio waves that pass through it, so LOFAR views the cosmos as if from the bottom of a swimming pool. The researchers solved the problem by tracking the wobble of “beacons” in the sky — radio emitters with precisely known locations — and correcting for this wobble to deblur all the data. When they applied the deblurring algorithm to data from the filament, they saw the glow of synchrotron emissions right away.

The filament between galaxy clusters Abell 399 and Abell 401 is also discussed in [How is it determined that the X-ray and radio intensity come from a magnetic field bridge between two clusters of galaxies?](https://astronomy.stackexchange.com/q/32199/7982)

**Question:** Why exactly did it take five years for the radio astronomy community to "figure out" how to improve the calibration these LOFAR measurements and apply deblurring algorithms? Answers to

* [Would Adaptive Optics be Useful in Radio Astronomy?](https://astronomy.stackexchange.com/q/13930/7982)
* [What is precipitable water vapor in millimeter-wave radioastronomy and how is it measured?](https://astronomy.stackexchange.com/q/18791/7982)
* [What can be learned from low frequency radio astronomy available outside of Earth's ionosphere?](https://astronomy.stackexchange.com/q/34412/7982)
* [In the 1950's how were radio-astrometric positions with portable dishes so precise they could be assigned to their dim optical counterparts (Quasars)?](https://astronomy.stackexchange.com/q/36699/7982)
* [What exactly is interplanetary scintillation; what was the Interplanetary Scintillation Array looking for? Did it successfully observe any?](https://astronomy.stackexchange.com/q/34532/7982)

suggest that correcting for spatial variations in water vapor or other effects is a known thing in radio astronomy. However discussions at [How large does refraction become in radioastronomy?](https://astronomy.stackexchange.com/q/22217/7982) suggest that the ionosphere becomes increasingly important at low frequency (the "LOF" in LOFAR) so perhaps this was part of the challenge?

**Tags:** observational-astronomy, radio-astronomy, radio-telescope, interstellar-medium, lofar

> **Comments:**
> **username_0**: companion question: [What do these statements about interstellar magnetic fields really mean?](https://astronomy.stackexchange.com/q/36861/7982)  

---

## 1 answers

### Answer by username_1 on 2020-07-10. Score: 4

The point of the paper is not that *no* calibration has been used previously. It points out that they now use a more refined method and set of parameters to calibrate the data.

That in general is usual procedure: the more data you gather, and the longer a mission runs, the better you understand your instrumentation and all external factors which influence the data you gather - and especially the sensitivity towards different systematic and instrument errors. Thus with data becoming available you only have the people to work on the problems, often Bachelor, Master or PhD students. Thus prior to instrument availability and detailed data analysis you can only do a coarse calibration based on general knowledge of the problem. Five years is a reasonable and good time interval two have one to two generation of students work on it and get an good overall picture which considers all aspects you mention (and probably more) in the necessary detail and assess their contribution in a way which satisfies scientific scrutiny including the review process.

> **Comments:**
> **username_0**: Is it possible to cite any specific supporting sources or examples to help demonstrate that this is based on facts and not just an opinion? Thanks!  
> **username_1**: It's hard to link with proof of what I see during my daily work. I am not aware of studies who relate published calibrations to time after mission start or end  
> **username_0**: I googled "van Weeren et al  LOFAR Abell 399 and Abell 401" and found [Probabilistic direction-dependent ionospheric calibration for LOFAR-HBA](https://www.researchgate.net/publication/339015210_Probabilistic_direction-dependent_ionospheric_calibration_for_LOFAR-HBA) There seems to be a pretty good explanation starting in the second paragraph of the Introduction section.  
> **username_0**: also see [However, a problem at low frequencies is that the ionospheric phase distortions are frequency dependent, increasing towards lower frequencies. At about 60 MHz this means that if this effect is not included only about 1 MHz bandwidth can be used for calibration, depending on the ionospheric conditions](https://hal.archives-ouvertes.fr/hal-00721924/document)  
> **username_0**: While previous calibrations of higher frequency radio observation were based on precipitable water vapor and involved modest bandwidths where the dispersion from the water vapor was small and well behaved, LOFAR must deal with the strong refraction of low frequencies by the ionosphere where strong dispersion was an additional problem. So I think the answer is that this posed a much larger challenge than the state of the art for higher frequency radio astronomy.  
> **username_0**: temporary and reversible -1, I think it should not be hard to support your answer with some citations or links (I've tried to help by providing you some suggestions in comments). Once that's done I'll reverse it and (hopefully) will accept your answer. *thanks!*  
> **username_2**: Answer needs to discuss what those improvements were.  
> **username_0**: fyi I've added a bounty, and you're certainly eligible to receive it if you can add sufficient information  

---

