Test LBA system at Pittiövaara

The original plan was to build 96 LBA aerials at KAIRA. That plan was altered because of ground stability considerations, limited signal processing and some other interesting ideas. So, although we've installed 48 aerials at KAIRA, the remainder will be used for other tests and experiments.

At the moment, we've installed four of these aerials at Pittiövaara, a small field station not far from the main institute at Sodankylä. These are being used to test a new digital signal processing concept being developed by SGO.

One of the test aerials at the Pittiövaara site. (Photo: D. McKay-Bukowski)

Of course, at KAIRA, being much further into the Arctic you would never get trees like this!

LOFAR observations of Virgo A

Today, ASTRON announced some stunning new results of the radio galaxy Virgo A (also referred to as Vir A, M87, etc.) along with a great image taken by the International LOFAR Telescope:

This false colour image shows the galaxy M87. Optical light is shown in white/blue (Credits: SDSS), the radio emission in yellow/orange (LOFAR). At the centre, the radio emission has a very high surface brightness, showing where the jet powered by the supermassive black hole is located. Credits: Francesco de Gasperin, on behalf of the LOFAR collaboration.

From their press release...

Using a brand-new radio telescope, astronomers have produced one of the best images ever made at the lowest frequencies of giant bubbles produced by a super-massive black hole. The observations were performed at frequencies ranging from 20 to 160 MHz which are normally used for communications by {aeroplane} pilots. The picture shows what looks like a giant balloon filled with radio emitting plasma, which exceeds the size of an entire galaxy.

Refer to the full press-release in the links section below for details.

Links

• ASTRON press release
• Article on VirA (M87)

Winter welcome

Well, in the past few weeks Winter has been arriving. In fact, things are moving faster than we can keep up with this web log (... so much to do!). In any case, here are some of the first Winter scenes from Sodankylä Geophysical Observatory for the season.

View from the EISCAT building. (Photo: D. McKay-Bukowski)

A wintry scene along the road through Tähtelä. (Photo: D. McKay-Bukowski)

Observing tips #3 — Starting/stopping KBT experiments

KBT (KAIRA Background Task) as an observing system for scheduling and running pre-designed scripts. The following is the instruction set for getting KBT observations started.

Starting KBT observations

1.  Be organised and log in to KAIRA01 at least 30 mins in advance, thus checking that you have a password, etc.
2. When you have been allocated the telescope, you will receive an e-mail from someone (usually the previous observer). 
3. When you get the "it's all yours now" e-mail, log in to the LCU.
4. Double check the system is reset and ready to use. To do this, type:
   
   %  swlevel
   
   You should see "Currently set level is 0" and all processes are down. If not, get help.
5. Check the current experiment with kbt.
   
   %  kbt --status
   
   It should be STOPPED. If not, get help.
6. Change the experiment to yours.
   
   % kbt --list
   % kbt --experiment=rio3_v45z
   
7. Start the experiment
   
   % kbt --start
   
   Your experiment is now starting. Note that it takes 2 minutes to fully start. Eventually, you will get your prompt back.
8. Your experiment is now running. You should check that it is recording data files. First, use kbt to find where the data is going:
   
   % kbt --variables
   
   Look for "datapath".
9. Use "ls" to inspect the datapath and check that the data is being recorded.If all is going well, there is no need to give the system further attention until the observations are over.

Stopping KBT observations

1. Stop your observations with KBT.
   
   %  kbt --stop
   
   Note that this might take a little while.
2. Double check that the system is reset and ready to use for the next observer. To do this, type:
   
   %  swlevel
   
   You should see "Currently set level is 0" and all processes are down. If not, get help.
3. Then, and this is VERY IMPORTANT, send an e-mail to the next observer with a CC to lofar-obs to inform the observing team that you are finished.

That's it! You should now consider exporting your data.

Arctic skies

Just a nice image to finish the week. Enjoy...

The Arctic sky, looking southwest past the KAIRA HBA array. Photo: D. McKay-Bukowski.

Freezing over

We took these photographs are the Sodankylä Geophysical Observatory recently. With theonset of the Autumn, the temperatures are dropping rapidly and winter will soon be upon us. And, of course, the water in the area is starting to freeze over.

First crystals forming in the puddles. (Image: D. McKay-Bukowski)

The Kitinen River starting to freeze over. (Image: D. McKay-Bukowski)

VHF upgrade at SGO — Part 3

And finally, the new receiver is installed on the 32 m antenna.

The new prime-focus, VHF feed. (Photo: D. McKay-Bukowski)

VHF upgrade at SGO — Part 2

Today work started on replacing the sub-reflector with a VHF prime-focus feed.

The crane (right) prepares to suspend the old sub-reflector, while the mobile platform allows the workers to get in close. (Image: D. McKay-Bukowski)

VHF upgrade for the EISCAT antenna at SGO

Due to the encroachment of radio-frequency interference (RFI) it was decided to convert the two EISCAT remote stations to operate at VHF frequencies. This is great news for KAIRA as it gives us some long baselines at the common frequency. Of course we've mentioned Sodankylä before; this is where the host institute is located.

At SGO, there is a 32m antenna (which used to have a UHF receiver). This is now being converted to a VHF system. The new receiver and feed can be seen in the lower left of the photograph.

The final image shows a close-up shot of the new system. It will replace the sub-reflector addionally converting the dish to a primary feed. Here, it is still on the trailer as it was brought over from Kiruna, Sweden.

The conversion is due to take place on 23rd October 2012. (Images: D. McKay-Bukowski)

Reindeer near KAIRA

Even though it is late in the year, we are still getting reindeer near the site. These ones visited the other day (but did not manage to get in!)

Reindeer on the entrance road to KAIRA. (Photo: D. McKay-Bukowski)

LBA mausoleum sealed

With winter approaching, and the LBA cabling problem sorted out, we've sealed up the mausoleum ready for winter.

The LBA cable mausoluem, with a bit of frost on the roof. (Photo: D. McKay-Bukowski)

Snow's getting closer

Actually taken a couple of weeks back, but even back then the snowline was descending down the mountain slopes. In the foreground is the RF-container, which houses the KAIRA digital signal processing electronics.

The RF-container at KAIRA, with the HBA mausoleum attached to the front of it. (Photo: D. McKay-Bukowski)

LBA silhouette

A dramatic image to end the week. This photograph was taken looking up past the Low-Band antennas towards the the western skyline near Iso-Malla. With a stunningly clear sky it is perfect conditions for seeing the aurora. We've had a successful week, this week, so it seems fitting to finish it with a shot of the aerials where the radio waves from the depths of space first make contact.

LBA aerials at KAIRA. (Photo: D. McKay-Bukowski)

Have a nice weekend!

First all-sky image with KAIRA

Yesterday we managed to take our first all-sky image with KAIRA. The observing frequency is 59.6 MHz and we used the entire LBA array.

First all-sky image with KAIRA. A 1-second integration at 59.6 MHz.

The image is not calibrated (in fact, we still have a long way to go). However, there are still a number of features visible: The three red areas on the left are (from bottom to top) the galactic plane, Cyg A and Cas A. The amber-coloured patch just to the right of Cas A is probably a calibration effect.

The next step is to acquire calibration data and determined better solutions for the amplitude, phase and delay errors.

Getting this far has been a lot of work, so thanks to everyone who has helped achieve this.

Polarisation testing on the LBA

Now that the cables are all connected, we need to test that they are all correct and working. We've already done the tests on the band-pass spectra, now we need to check that all polarisations are correctly connected. To do this, we modify the field pattern of each dipole using a large metal object (we had a loop antenna handy, so we used that).

Applying the loop antenna to the antenna. Is it just me, or does this look like Grindelwald's Sign?

We then go from X- to Y-polarisation on each antenna, applying the antenna to each, and look at the drop-out pattern, when plotting RCU (= channel number) versus time (= sequence number).

Progression of signal drops, going from dipole to dipole. Onwards and upwards, and not a single step back!

As you can see, there is a monotonically increasing progression, which means that the polarisation are correct. The slight wave in the line reflects the addition walking time between antennas at various parts of the process.

Yet another quality-assurance check complete!

Ionospheric Scintillation with KAIRA Mode "357"

Last Friday, 28th September, we described how we had managed to combine use of the Low-Band Antenna (LBA) and High-Band Antenna (HBA) parts of the KAIRA array simultaneously during observations, a mode we labelled "357".  

We have been experimenting with this mode for two weeks now, and have even extended it a little further by dividing the HBA tiles used so that they can "point" in two different directions at once:  Each HBA tile consists of 16 dipole antennas which are usually combined using an analogue beam-former.  This analogue beam is quite wide (~20 degrees) and can be directed anywhere in the sky.  However, if we wish to use the HBA array with multiple beams, these beams will have little, if any, sensitivity if they point outside of this analogue beam.  Only one analogue beam can be formed; it is not possible to form any others... unless they use different tiles of course!  

Now each sub-division of the complete array will reduce the sensitivity accordingly.  So principally we have been using the new mode to observe two very powerful radio sources in the sky, Cassiopeia-A and Cygnus-A.   Although these are quite broad radio sources, the widths of the beams we are using make these appear to be "point" radio sources to KAIRA.  This means that the sources appear to scintillate ("twinkle") in radio light.  

Plots from a simultaneous observation of the radio sources Cassiopeia-A (upper plot) and Cygnus-A (lower plot).  The x-axis is time, in seconds, over approximately a one-hour period; each point on the y-axis corresponds to an observing frequency, with the zero point being equivalent to 30MHz and the 121 point being equivalent to 250MHz.  The plots have been normalised by subtracting a running average to bring out the structures.

The scintillation is exactly the same effect that we see in visible stars in the night sky:  In this case, the stars appear to twinkle because of density variations moving around in our atmosphere.  The effect is very much like watching a stone in a slightly rough pool of water: The stone appears to shift and shimmer with the ripples on the water.  In the case of radio stars, they may appear to twinkle because of density variations moving around in our ionosphere, or the solar wind, or even the interstellar medium.

The structures that we can see in these plots of data from KAIRA are most likely to be due to ionospheric scintillation.  The radio waves are scattered and refracted by density structures of different sizes moving around in the ionosphere.  Where the structures in these plots appear vertical at the highest frequencies, the scintillation is said to be "weak":  In other words, the radio waves are scattered by the density variations but these scattered waves do not subsequently interfere between themselves.  At the lowest frequencies, we can see the scattered waves interfering amongst themselves, in some cases forming a classic 'hash' pattern as the waves are alternately enhanced and cancelled as they interfere.

The real dragon?

Still on the line of flying dragons, we then had one evening with a most peculiar cloud formation. As the sun set, the light caught a most incredible cloud formation. It was shaped like a huge bird... an albatross was what immediately sprang to mind when I saw it. The shape was amazingly clear and the rest of the sky was totally clear. I have no idea what caused it, but it was certainly very beautiful.

 

A peculiar cloud as seen from KAIRA on 25th September 2012. (Photo: D. McKay-Bukowski)

A slightly closer view. Sadly the tiny little camera that I have fails to do justice to this amazing sight. (Photo: D. McKay-Bukowski)

I can certainly understand how people long ago would be amazed by such apparitions in the sky. It is certainly fascinating to consider what our ancestors might have made of this.

A great bird; a portent of winter?

Or maybe a great white dragon?

The dragon!

After yesterday's post about Durin's Day, we couldn't resist but put this one up as well. Actually, to be fair, this photograph was taken a couple of weeks back, but we'll ignore that minor detail.

Aircraft are rare in this part of the world. But there are a few around. This one is one of the float-planes that is based on Kilpisjärvi. It flies the routes between the lakes during the warmer months. On this particular day, it flew in around Saana, arced over the LBA and then eased down over the trees between the customs station and Pikku Malla... not doubt to land on the main lake.

A float plane over KAIRA's LBA. (Photo: D. McKay-Bukowski)