Friday, 25 July 2014

Meet the press

We had a visit from a report this week, to interview some of the staff about KAIRA, the Centre of Excellence for Inverse Problems, EISCAT and the general operations of Sodankylä Geophysical Observatory. So, reporting on the reporting, today we have a photograph of just that!

Lassi and Esa being photographed in front of the 32m dish.

Have a nice weekend everyone!

Thursday, 24 July 2014

Ionospheric "Scintillation Arcs"

Compact radio sources twinkle (“scintillate”) because of variations in density moving around in the interstellar medium, the solar wind and the Earth's ionosphere, in exactly the same way as the visible stars scintillate due to the Earth's atmosphere. This scintillation has been studied for many years and is used as a way of probing these density variations and gleaning information about, for example, the density and velocity of the solar wind.  With KAIRA we have been observing ionospheric scintillation since operations started in 2012.

When viewed as a time series, the scintillation manifests itself as rapid variations in received intensity. If the received signal is also split up into a number of frequency channels across the available bandwidth, the time series' for each channel can be stacked and plotted in a dynamic spectrum which shows how the pattern of scintillation varies with both observing frequency and time.

In modelling the scintillation, we often assume that the signal is scattered by a “thin screen” of density variations (imagine an irregular grid through which light might be diffracted), moving at a certain velocity relative to the radio source. The scattered waves then interfere as they travel further from the screen and the resulting interference pattern is what we receive as scintillation. Multiple thin screens along the line sight can be used to model scattering due to a thicker medium.

Now imagine pairs of waves being scattered by the thin screen: Each pair of scattered waves has a Doppler shift due to the movement of the screen and a time delay between them due to the different path length that each wave has likely followed. A “map” of these Doppler shifts and time delays between every pair of scattered waves can be formed by taking the so-called “secondary spectrum” - effectively the 2-dimensional power spectrum (squared amplitude of the 2-dimensional FFT) of the dynamic spectrum. When this analysis is applied to pulsar observations to study scintillation in the interstellar medium, a clear arc structure termed a “scintillation arc” (first discovered by Dan Stinebring in 2001), is often seen. Over the years this has proved an invaluable tool for probing the interstellar medium.

Now, for we believe the first time, scintillation arcs have been found in the secondary spectra of ionospheric scintillation seen in observations of Cygnus A taken using the KAIRA. It is believed that these also represent the first such broadband (relative to the observing frequency) observations of arcs due to any scattering medium and also the first found using LOFAR hardware. These results have now been written up in a paper recently submitted.

The image shows an example segment of dynamic spectrum and an example secondary spectrum, with the x-axis being Doppler shift and the y-axis being a parameter equivalent to time delay.

Wednesday, 23 July 2014

Weather radar

Yesterday we described our walk up the ski slopes of Luosto on that hot summer's evening. But what was at the top?

Well, it turns out there is a large weather radar (= säätutka) there. This is operated by our colleagues at the Finnish Meteorological Institute (FMI).

The "blue stone". (Photo: D. McKay-Bukowski)

The FMI weather radar site. (Photo: D. McKay-Bukowski)

Lassi ignores the warning signs. (Photo: D. McKay-Bukowski)

It's a really lovely place. A bit like a lighthouse. A pity it is remotely operated, as I'd so love to work in a place like that.

Tuesday, 22 July 2014

A bit of a walk

Along similar lines to the recent post on swimming, we have another little adventure. This was the decision on Monday evening to go for a walk... this time to Luosto. Lassi organised this, similar to our excursion last year to Viiankijärvi, which was a chance to get outdoors away from the work and see some Lappish scenery.

Anyway, there are some ski slopes there not far from the Amethyst Mine, and we climbed up the hill there. Today, we have a couple of photographs from that trip... in stark comparison to the conditions of last January. Remember our scene from last time?

Intrepid adventurers from SGO. (Photo: D. McKay-Bukowski)

The ski-slopes... looking forlorn in the summer. (Photo: D. McKay-Bukowski)

Still a great walk, with lovely weather conditions. (Photo: D. McKay-Bukowski)

After the discovery of the giant river pike after our bit of a swim, we might have been quite nervous about what we might have found at the top of the mountain. And indeed there was something quite unusual at the top.

But you will have to wait until tomorrow to find out what it was!

Monday, 21 July 2014

A bit of a swim... the other side of the story

You could barely make this up.

In a bizarre twist to Sunday's "a bit of a swim" story, there was another river story going on just downstream.

At what would have been more-or-less the same time, SGO director Esa Turunen was fishing in the Kitinen river and caught a very large hauki (a type of aggressive river fish common in the waters up here).

Hauki and Esa (Photo: E. Turunen)

But what is "hauki" in English? Well, I guess we could go and ask the fish...

So, fish... what is your English name?

Don't tell him, pike! 

Sorry, couldn't resist that one.

Sunday, 20 July 2014

A bit of a swim

Sodankylä Geophysical Observatory is situated along the banks of the Kitinen River. A quick search on the Internet (or looking at all Kitinen-tagged posts on the weblog here), will turn up plenty of photographs of a frozen expanse of ice sheets and sub-zero temperatures. However it does melt in the spring and in the summer it is really quite and idyllic spot.


On the evening of the 15th, I decided to see if I could swim across the river. In fact, I first swam across the river, then up to the island and then back again.

The total distance was just over 600 metres, although in reality, I doubt I swam it as absolutely straight lines. There is a current running north to south, so that would have swept me off course a bit. At this time of year, the water is pretty murky, due to the the meltwater seeping through the tundra to get to the river. And the opposite banks are really quite muddy and swampy... so SGO is definitely on the best side of the river here.

Of course the next morning my shoulders were killing me. Even clicking the computer mouse button was a struggle at first. Still, it was all good fun!

Friday, 18 July 2014

Operaatio kakku -- part 2

Yesterday we described the great cake exercise, which was an attempt to have an excuse to engage in conversation with our colleagues from FMI.

Well, the cakes were all completed successfully. They were:

  1. Date cake with caramel sauce
  2. Sea buckthorn roullade
  3. Raisin, lavender and honey roullade
  4. Lemon drizzle cake

Cakes #2 (back left), #3 (front) and #4 (back right)

Cleaning up didn't take too long and the cakes were carefully transported to Polaria on the morning of 15 July 2014 (an historical occasion!). The timing was pretty good. FMI had a visiting campaign team there, so we had ample cake for everyone and to spare! So, we've had cake for the next couple of breaks as well.

The remnants of Cakes #1 and #4.

Was it a success? Most definitely. We've now established some sort of rapport to the point where (occasionally) eye-contact is made and even a murmured "hei" (*gasp*). Of course, the first comments from our own staff on returning to SGO were "Ooo... cake... great!... what's the occasion?" and, after the explanation, this was promptly followed by "What! Who authorised that?". Probably in jest, but who knows... in any case, I regard the operation as successful and will continue to extend the welcome to all our colleagues from FMI (not just to come and talk to us at morning coffee at Polaria, but also afternoon coffee at Polaria, and afternoon tea and high-tea at the EISCAT building).

What I want to know, though, is what FMI thought of all this!