Variations in scintillation

Ionospheric scintillation is the variation in the amplitude and phase of radio signals as they pass through the ionosphere. What is happening is small-scale variations in the electron density result in differences in the ionosphere's refractive index at radio-frequencies. It is sort of the radio equivalent of the "twinkle of stars". The localised variations in refractive index cause momentary focusing, defocusing or shifting of the incoming radio waves. For broad, diffuse structures in the sky (like the synchrotron emission from the Galaxy) all of these effects average out for different directions. But for a point-source (such as bright "radio stars") the singular line -of-sight can result in dramatic differences.

One of KAIRA's regular experiments has a number of "beams" on the sky. These are sort of like pixels in an image and they monitor the variation in power levels coming from that direction. Most of these have been set up for specific geodetic directions. But we also have some that track astronomical sources.

The following plot shows the radio power coming from the bright radio object Cassiopeia A (or "Cas A" for short).

As can be seen, there are some huge variations. There is a natural variation as Cas A rises higher and lower in the sky (it never sets completely as it is circumpolar at these latitudes). However, this is only a variation between approx. 96.5 and 97.5 on the arbitrary scale used above. The point where the strong scintillation occurs shows huge variations.

Compare the difference between, say, samples around 25000 and around 35000. Not only can the effect be very great, but it can change very quickly too.

The remains

Following the great Kilpisjärvi Storm of 2014, the telescope rescue crew scoured the surrounding landscape trying to find and recover debris. Part of this was recovering as much scattered electronics as possible... some of which may be able to be cleaned up and re-used as spares.

This sad crate of fragments are some of the parts salvaged during that operation. (Click on the photograph to enlarge.)

Salvaged parts from the destroyed LOFAR HBA tile at KAIRA. (Photo: L. Roininen)

Film editing

This week two of the SGO staff were in the United Kingdom to sit in on part of the final edit of the KAIRA film. As we have mentioned before, we're producing a film about KAIRA, its construction and its science. The main production team is from a company called Site-Eye. They specialise in construction site filming, time-lapse and other specialist filming work. They have been excellent and we've been really happy with the work they've done for us.

During our visit to their film-production offices we went through the KAIRA film and tweaked some sequences and cut/extended some scenes to get the balance just right. Site-Eye are now working on the sound engineering and sub-titles, and we hope to have it ready for public release very soon now.

Alex from Site-Eye working on the KAIRA film. (Photo: D. McKay-Bukowski)

Have a nice weekend, everyone!

JIVE ASTRON Daily Image -- Storm Report

For those who didn't see it, KAIRA was featured yesterday on the JIVE/ASTRON Daily Image. This long-running web-log features images and news from these two organisations. As KAIRA is built of LOFAR technology, which is from ASTRON, and yours truly used to work for JIVE, we have always been keen to support their long-running outreach efforts. And yes, it is always fun to get an article posted there!

Yesterday's article was about the recent storm damage. For those who follow the KAIRA web log, this will be nothing new, as we've covered the topic in detail here. However, we did put together a nice montage and we have that here today.

However, the JIVE/ASTRON Daily Image article does provide a great summary of the recent problems (and solutions!), so go check it out if you haven't already done so.

Direct link: http://www.astron.nl/dailyimage/main.php?date=20140326

Radio bright sun -- Part 2

Yesterday we showed some KAIRA data of a very active sun. It was so bright that it easily outshone Cas A and Cyg A. Given this, we surmised it should be possible to see the solar signal with a single dipole.

Sure enough, that was the case.

The following plot shows the subband statistics for a single antenna (LBA aerial #45, Y-polarisation).

The vertical axis is frequency, shown as both the subband number (left-hand side) and frequency in MHz (right-hand side). The broad band of noise between 8 and 25 MHz (approx.) are the sum of countless shortwave radio transmissions. Below 8 MHz and about 80 MHz, there is little signal due to the LOFAR RFI suppression filters and the weaker amplifier and aerial responses.

Radio bright sun

On 20 March 2014, the Sun was particularly active. As it passed over the southern horizon, KAIRA detected strong radio emission. We had the station correlator running at the time and managed to capture this all-sky image sequence.

The video covers the period from approx. 10:05 until 10:15 UTC. Each frame is a 1-second integration, however it has been sped up to reduce the duration. The date/time (UTC) is shown in the filename at the top-left of the image sequence. The observing frequency is subband 300 (= approx. 58.6 MHz, with 195 kHz bandwidth).

The object near the centre of the image is Cas A and to its right is Cyg A. These are normally very bright radio sources. However, the sun (on the lower edge) easily outshines them... especially around 10:09 UTC (about 0:24 in the video). For the purposes of making this sequence, we really had to turn down the contrast to prevent complete saturation.

When the sun is radio-bright, strange artefacts can be seen in other parts of the image. These are the "sidelobe" responses of the telescope and are not real sources.

It says something about the strength of the solar radio bursts, when the sidelobe response can outshine even Cas A!

Astronomical Association URSA meeting in Inari

The Finnish astronomical association, URSA, held the event called "Tähtipäivät" - "The Star Days" in the Sámi cultural centre Sajos in Inari, 20-23 March 2014. Esa Turunen, the director of the Sodankylä Geophysical Observatory, gave a public lecture in the event. The talk was titled "Avaruusalus planeetta Maa" - "Spaceship Planet Earth". The audience consisted of Finnish professional and amateur astronomers as well as on a number of other interested persons (including myself). Of course, Esa talked about KAIRA as it is, in a sense, the biggest radio telescope on Finnish soil. Hence, today we feature two photos from Esa's talk!

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