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Operating VRI (Radio Interferometry)



 
 
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  #1  
Old March 17th 06, 12:01 AM posted to sci.astro
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Default Operating VRI (Radio Interferometry)

On another thread, we drifted off on to the topic of the Java VRI program
that's on the web at http://www.narrabri.atnf.csiro.au/astronomy/vri.html.
That thread is getting a bit long, so I thought I'd pick up on VRI here. I'm
interested in completing a single example. The other thread gave me some
clues how to proceed, but I thought I'd try this out here (* see note at
bottom). This is pretty much an arbitrary and ficticious example based on a
limited knowledge of how this works. I learned in the other post that the
sequence, Source, FFT, Apply and FFT-1 is basic to the operation. The rest
was obtained by playing with this.

There are four panels arranged as:

Image Panel (IP) | Antenna Panel (AP)
-------------------------------------------
Transform Panel (TP) | Coverage Panel (CP)

AP has a green background with a single dish icon
CP has a background with a red point. If the nearby
In (Zoom) button is pressed, it's dashed line.

I created the acronyms for convenience here.

There are various buttons around the panel. Initially, there are three
buttons to the side of each panel that are common: In (Zoom), Out and Reset.
As I proceed with the example as below, a FFT and FFT-1 (inverse) will
appear. Above the four panels are fill-in boxes for the source and antenna.
Below the panels are fill-in boxes for the source, HA interval, frequency
and bandwidth of the source, and source declination.

1. Select source as Wide Double, two point objects appear in the IP
2. Set the Lat to 45.0. Press Enter to make sure it's set.
Use the slider bars at the bottom to set
the Dec to 0.0 and the HAs to -5.1 (top slider) and +5.1. You may
not get +/- 5.1, so do what you can to be close.
3. Drag the antenna icon four times to form a square with
one icon in the center. Make each side about 1".
A A
A
A A
Press the Plot button and some red horizontal lines will appear
in the CP. The FFT button appears on the left. When this button
appears seems to vary. It may appear in an earlier step.
4. Press the FFT button and vertical grey lines appear in the FP
with a white background, and the FFT-1 button appears on the left.
5. Press the Apply button below the CP. if The Ampl choice is set
below the TP, then a group of dashed horizontal lines appear in the FP.
6. Press FFT-1. Two vertical rows appear of dots (circles?) in the IP.

So what have I got in the IP? Can someone offer a more meaningful example?


* I find VRT sometimes rather erratic (inconsistent) in its behavior.
Sometimes buttons like FFT and FFT-1 just appear at almost a whim. When I'm
forced to start again because of some missed item, I reload the page.
Proceeding again often does not get quite the same responses. The behavior
of this program is somewhat inconsistent. If one sets up the antennas as
above, but uses the sliders before setting them, then the extreme values
(5.1 vs 4.9 hrs) will be slightly different than if done afterwards. The
initial default value for lat (-30.xxx) changes in the number of decimal
points once you select Custom. I sometimes wonder about the effectiveness of
the Reset button. Sometimes it doesn't seem to help recover from a previous
bad entry.

Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet
--
"Nature invented space so that everything didn't
have to happen at Princeton." -- Martin Rees,
Britain's Royal Astronomer, in a lecture at Princeton

Web Page: home.earthlink.net/~mtnviews

  #2  
Old March 17th 06, 10:23 AM posted to sci.astro
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Posts: n/a
Default Operating VRI (Radio Interferometry)

W. Watson wrote:
On another thread, we drifted off on to the topic of the Java VRI
program that's on the web at
http://www.narrabri.atnf.csiro.au/astronomy/vri.html. That thread is
getting a bit long, so I thought I'd pick up on VRI here. I'm interested
in completing a single example. The other thread gave me some clues how
to proceed, but I thought I'd try this out here (* see note at bottom).
This is pretty much an arbitrary and ficticious example based on a
limited knowledge of how this works. I learned in the other post that
the sequence, Source, FFT, Apply and FFT-1 is basic to the operation.
The rest was obtained by playing with this.

There are four panels arranged as:

Image Panel (IP) | Antenna Panel (AP)
-------------------------------------------
Transform Panel (TP) | Coverage Panel (CP)

AP has a green background with a single dish icon
CP has a background with a red point. If the nearby
In (Zoom) button is pressed, it's dashed line.

I created the acronyms for convenience here.

There are various buttons around the panel. Initially, there are three
buttons to the side of each panel that are common: In (Zoom), Out and
Reset. As I proceed with the example as below, a FFT and FFT-1 (inverse)
will appear. Above the four panels are fill-in boxes for the source and
antenna. Below the panels are fill-in boxes for the source, HA interval,
frequency and bandwidth of the source, and source declination.

1. Select source as Wide Double, two point objects appear in the IP
2. Set the Lat to 45.0. Press Enter to make sure it's set.
Use the slider bars at the bottom to set
the Dec to 0.0 and the HAs to -5.1 (top slider) and +5.1. You may
not get +/- 5.1, so do what you can to be close.
3. Drag the antenna icon four times to form a square with
one icon in the center. Make each side about 1".
A A
A
A A


OK but this won't give particularly good u-v coverage. As a nice simple
example to get started use the classic E-W equally spaced dish
configuration. It is much easier to understand.

A A A A A

Then when the Earth rotates for 12 hours you get ellipses depending on
the the declination of the object (perfect circles for object at the pole).

Another cute configuration for small numbers of antennae is a Golumb ruler:

A A A A
1 3 2

This gives a set of unique baseline lengths 1,2,3,4,5,6

Press the Plot button and some red horizontal lines will appear
in the CP. The FFT button appears on the left. When this button
appears seems to vary. It may appear in an earlier step.
4. Press the FFT button and vertical grey lines appear in the FP
with a white background, and the FFT-1 button appears on the left.
5. Press the Apply button below the CP. if The Ampl choice is set
below the TP, then a group of dashed horizontal lines appear in the FP.
6. Press FFT-1. Two vertical rows appear of dots (circles?) in the IP.

So what have I got in the IP? Can someone offer a more meaningful example?


The transform of on instantaneous set of data. To get a meaningful image
you need to set the start and end hour angles of the observation to be
-6h to +6h (any 12 hour period will do provided the source doesn't set).

After changing this press "Reset" and you should see a nice set of red
ellipses in the U-V coverage domain.

* I find VRT sometimes rather erratic (inconsistent) in its behavior.
Sometimes buttons like FFT and FFT-1 just appear at almost a whim.


They should appear when there is something relevant for them to act
upon. I find the naming of the "Reset" button to make observations less
than intuitive. In a way it is a shame that the Image Panel is reused
for the output synthesised image since it prevents a direct comparison.

When
I'm forced to start again because of some missed item, I reload the
page. Proceeding again often does not get quite the same responses. The
behavior of this program is somewhat inconsistent. If one sets up the
antennas as above, but uses the sliders before setting them, then the
extreme values (5.1 vs 4.9 hrs) will be slightly different than if done
afterwards. The initial default value for lat (-30.xxx) changes in the
number of decimal points once you select Custom. I sometimes wonder
about the effectiveness of the Reset button. Sometimes it doesn't seem
to help recover from a previous bad entry.


It worked as I expect when I tried it before, but then I probably do
what it is expecting (quite possible that it doesn't recover gracefully
from some unexpected or inconsistent initial states I suppose).

Just checked again. Hmmm... something has gone wrong with it!

The Hour Angle settings offered here currently range from 0h to 0h for
both start and end of observations. Unless you can get it to observe for
a few hours to generate tracks in the U-V plane it will always give
unsatisfactory results in the synthesised image.

The mirror at Jodrell Bank that I use is still working OK.
Try that instead : http://www.jb.man.ac.uk/vri/

Regards,
Martin Brown
  #3  
Old March 18th 06, 06:38 AM posted to sci.astro
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Default Operating VRI (Radio Interferometry)

That link doesn't work for me. It doesn't exist. I get a msg that
www.jb.man.ac.uk could not be found. A URL like
http://www.jb.man.ac.uk/vri/vri/guide.html does exist.

The mirror at Jodrell Bank that I use is still working OK.
Try that instead : http://www.jb.man.ac.uk/vri/

Regards,
Martin Brown




Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet
--
"Nature invented space so that everything didn't
have to happen at Princeton." -- Martin Rees,
Britain's Royal Astronomer, in a lecture at Princeton

Web Page: home.earthlink.net/~mtnviews
  #4  
Old March 18th 06, 11:47 AM posted to sci.astro
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Posts: n/a
Default Operating VRI (Radio Interferometry)


"W. Watson" wrote in message
ink.net...
That link doesn't work for me. It doesn't exist. I get a msg that
www.jb.man.ac.uk could not be found. A URL like
http://www.jb.man.ac.uk/vri/vri/guide.html does exist.

The mirror at Jodrell Bank that I use is still working OK.
Try that instead : http://www.jb.man.ac.uk/vri/


Works for me today, I just clicked that link.

George

p.s. I'm using Sun Java 2 latest version:

www.java.com


  #5  
Old March 18th 06, 06:13 PM posted to sci.astro
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Posts: n/a
Default Operating VRI (Radio Interferometry)

George Dishman wrote:

"W. Watson" wrote in message
ink.net...

That link doesn't work for me. It doesn't exist. I get a msg that
www.jb.man.ac.uk could not be found. A URL like
http://www.jb.man.ac.uk/vri/vri/guide.html does exist.


The mirror at Jodrell Bank that I use is still working OK.
Try that instead : http://www.jb.man.ac.uk/vri/



Works for me today, I just clicked that link.

George

p.s. I'm using Sun Java 2 latest version:

www.java.com


Thanks. Working today. One of those web mysteries.

Hmmm, still is gimpy. It was set for Merlin, and I changed it to Custom,
then specified Wide double. The AP continues to show the Merlin
configuration. The AP Reset does nothing. Maybe I need Java 2. How do I
tell what my Mozilla browser is using for Java?

Interesting, If I move the Merlin antenna icons, they move individually but
leave a network of lines behind.


Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet
--
"Nature invented space so that everything didn't
have to happen at Princeton." -- Martin Rees,
Britain's Royal Astronomer, in a lecture at Princeton

Web Page: home.earthlink.net/~mtnviews
  #6  
Old March 18th 06, 07:20 PM posted to sci.astro
external usenet poster
 
Posts: n/a
Default Operating VRI (Radio Interferometry)


"W. Watson" wrote in message
ink.net...
George Dishman wrote:

p.s. I'm using Sun Java 2 latest version:

www.java.com


Thanks. Working today. One of those web mysteries.

... Maybe I need Java 2. How do I tell what my Mozilla browser is using
for Java?


The link above has a bright orange "Download Now"
button. To the right of that, not very obvious,
there is a "verify Installation" link.

George


  #7  
Old March 19th 06, 10:07 PM posted to sci.astro
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Default Operating VRI (Radio Interferometry)

George Dishman wrote:

"W. Watson" wrote in message
ink.net...

George Dishman wrote:


p.s. I'm using Sun Java 2 latest version:

www.java.com



Thanks. Working today. One of those web mysteries.

... Maybe I need Java 2. How do I tell what my Mozilla browser is using
for Java?



The link above has a bright orange "Download Now"
button. To the right of that, not very obvious,
there is a "verify Installation" link.

George



I updated my Java by going to
http://www.java.com/en/download/installed.jsp, and then started into Dan's
suggestions using the site http://www.jb.man.ac.uk/vri/. Again, I couldn't
get rid of the Merlin antennas by using Custom. Even selecting Double Wide
gave nothing. I think that site is generally inoperable.

Finally, I went to the Austrlian site. I put five antennas in a row
separated by about 1000km. I couldn't get the sliders anywhere near +/- 12
hrs of HA. The range must be dependent upon some factor I'm not aware of.

I'm going to contact Mark at the Aus. site and see if he's got any
suggestions. My other msg to him is still unanswered.

Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet
--
"Nature invented space so that everything didn't
have to happen at Princeton." -- Martin Rees,
Britain's Royal Astronomer, in a lecture at Princeton

Web Page: home.earthlink.net/~mtnviews
  #8  
Old March 20th 06, 04:18 PM posted to sci.astro
external usenet poster
 
Posts: n/a
Default Operating VRI (Radio Interferometry)

"WW" == W Watson writes:

WW On another thread, we drifted off on to the topic of the Java VRI
WW program that's on the web at
WW http://www.narrabri.atnf.csiro.au/astronomy/vri.html. That
WW thread is getting a bit long, so I thought I'd pick up on VRI
WW here. I'm interested in completing a single example. The other
WW thread gave me some clues how to proceed, but I thought I'd try
WW this out here (...). This is pretty much an arbitrary and
WW ficticious example based on a limited knowledge of how this
WW works. I learned in the other post that the sequence, Source, FFT,
WW Apply and FFT-1 is basic to the operation. The rest was obtained
WW by playing with this.

WW There are four panels arranged as:
[...]

WW 1. Select source as Wide Double, two point objects appear in the
WW IP

First, what do you expect from selecting a wide double? Hint: What's
the Fourier transform of two delta functions located at (-x, 0) and
(x, 0).

WW 2. Set the Lat to 45.0. Press Enter to make sure it's set. Use
WW the slider bars at the bottom to set the Dec to 0.0 and the HAs to
WW -5.1 (top slider) and +5.1. You may not get +/- 5.1, so do what
WW you can to be close.

Note that the default telescope is the ATCA, a southern hemisphere
telescope. Setting the latitude to +45 deg. means that you are trying
to observe a source below the horizon. I suggest leaving it set at
ATCA or choosing WSRT, another east-west array.

Also note that the default configuration specified is the 6A, which
means that you have to zoom in quite a lot in the antenna display
before the scale is such that you see the individual antennas.

WW 3. Drag the antenna icon four times to form a square with one icon
WW in the center. [...]

As others have indicated, stick with an east-west array for the time
being.

Note that you'll also probably have to zoom in to see the u-v plane.
I don't see much until I've zoomed in to a scale of 100 klambda.


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  #9  
Old March 20th 06, 06:36 PM posted to sci.astro
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Posts: n/a
Default Operating VRI (Radio Interferometry)

Joseph Lazio wrote:

"WW" == W Watson writes:


....

WW 1. Select source as Wide Double, two point objects appear in the
WW IP

First, what do you expect from selecting a wide double? Hint: What's
the Fourier transform of two delta functions located at (-x, 0) and
(x, 0).

One for a single dirac. Dunno for two off hand*. It's been a long time
since I needed to know. Nevertheless, what is used in unimportant to
understanding the operation. Getting a decent working example is what I'm
after. That's what I'm after.

(*See entry 21 in
http://ipml.ee.duth.gr/~papamark/circuits/Table%20of%20Fourier%20Transforms.htm)

The program documentation is very sparse, and the behavior of the program is
erratic. See my recent post above on the resulting updating Java to use VRI.
The last time the doc was updated was 2002 I believe. The results at two
different web sites differ.

WW 2. Set the Lat to 45.0. Press Enter to make sure it's set. Use
WW the slider bars at the bottom to set the Dec to 0.0 and the HAs to
WW -5.1 (top slider) and +5.1. You may not get +/- 5.1, so do what
WW you can to be close.

Note that the default telescope is the ATCA, a southern hemisphere
telescope. Setting the latitude to +45 deg. means that you are trying
to observe a source below the horizon. I suggest leaving it set at
ATCA or choosing WSRT, another east-west array.

Well, yes, but I specified Custom. Presumably, when I say 45 degrees I'm
specifying the location of the antenna, a Custom antenna. I specified the
source at a + declination. I would thin it would be visible.

Also note that the default configuration specified is the 6A, which
means that you have to zoom in quite a lot in the antenna display
before the scale is such that you see the individual antennas.

It's not clear to me that the # of antennas apply in the Custom situation. I
would like to think that when I populated the AP that the program is smart
enough to know that I've given five antennas. Maybe not.

WW 3. Drag the antenna icon four times to form a square with one icon
WW in the center. [...]

As others have indicated, stick with an east-west array for the time
being.

Yes, seems fine, but it was also suggested that I should use an HA from +/-
12 hours. I posted a response to that. It doesn't seem possible (the sliders
won't allow it) with the setup I used in the example. It would be good to
understand why I cannot get +/- 12. Object position? Antenna E-W spread?

Note that you'll also probably have to zoom in to see the u-v plane.
I don't see much until I've zoomed in to a scale of 100 klambda.


My recent post shows that I specified a 1000km between antennas. The sliders
gave me no more than =/- 6 hours.


Wayne T. Watson (Watson Adventures, Prop., Nevada City, CA)
(121.015 Deg. W, 39.262 Deg. N) GMT-8 hr std. time)
Obz Site: 39° 15' 7" N, 121° 2' 32" W, 2700 feet
--
"Nature invented space so that everything didn't
have to happen at Princeton." -- Martin Rees,
Britain's Royal Astronomer, in a lecture at Princeton

Web Page: home.earthlink.net/~mtnviews
  #10  
Old March 21st 06, 12:49 PM posted to sci.astro
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Posts: n/a
Default Operating VRI (Radio Interferometry)

"WW" == W Watson writes:

WW Joseph Lazio wrote:

WW ... 1. Select source as Wide Double, two point objects appear in
WW the IP

First, what do you expect from selecting a wide double? Hint:
What's the Fourier transform of two delta functions located at (-x,
0) and (x, 0).


WW One for a single dirac. Dunno for two off hand*. It's been a long
WW time since I needed to know. Nevertheless, what is used in
WW unimportant to understanding the operation. Getting a decent
WW working example is what I'm after. That's what I'm after.

GIGO. I'm trying to ask you to understand what the possible answers
might be. If you understand what the possible answers might be,
you'll have a better sense of what's being displayed and when the
answer might be correct.

WW 2. Set the Lat to 45.0. Press Enter to make sure it's set. Use
WW the slider bars at the bottom to set the Dec to 0.0 and the HAs to
WW -5.1 (top slider) and +5.1. You may not get +/- 5.1, so do what
WW you can to be close.

Note that the default telescope is the ATCA, a southern hemisphere
telescope. Setting the latitude to +45 deg. means that you are
trying to observe a source below the horizon. I suggest leaving it
set at ATCA or choosing WSRT, another east-west array.


WW Well, yes, but I specified Custom. Presumably, when I say 45
WW degrees I'm specifying the location of the antenna, a Custom
WW antenna. I specified the source at a + declination. I would thin
WW it would be visible.

Yes. I still think sticking to an east-west array (ATCA or WSRT)
would be a good idea until you understand what's being shown.

WW Yes, seems fine, but it was also suggested that I should use an HA
WW from +/- 12 hours. I posted a response to that. It doesn't seem
WW possible (...) with the setup I used in the example. It would be
WW good to understand why I cannot get +/- 12. Object position?
WW Antenna E-W spread?

I suspect that you misread what somebody else suggested. Without
checking, my recollection is that the suggestion was to look for a
full track, so a total hour angle duration of 12 hour or +/- 6h.

Stop and think about it for a minute: A duration of +/- 12h doesn't
make much sense. An hour angle of -12h occurs when the source is on
the other side of the Earth. Not until the source reaches an hour
angle of roughly -6h does it even begin to rise. Same for positive
hour angles: At roughly +6h, the source begins to set.

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