Friday, 12 September 2014

KAIRA & Kiitos!

The KAIRA project has been running for some time now and, like most major scientific instruments, there has been a peer-reviewed reference paper produced which describes the facility, its technical capabilities, its scientific goals and the initial results. We have written this paper and it has been accepted by the journal IEEE Transactions on Geoscience and Remote Sensing.

TITLE:     KAIRA: the Kilpisjärvi Atmospheric Imaging Receiver Array -- system overview and first results
ABSTRACT:  The Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) is a dual array of omnidirectional VHF radio antennas located near Kilpisjärvi, Finland. It is operated by the Sodankylä Geophysical Observatory. It makes extensive use of the proven LOFAR antenna and digital signal-processing hardware, and can act as a stand-alone passive receiver, as a receiver for the European Incoherent Scatter (EISCAT) very high frequency (VHF) incoherent scatter radar in Tromsø, or for use in conjunction with other Fenno-Scandinavian VHF experiments. In addition to being a powerful observing instrument in its own right, KAIRA will act as a pathfinder for technologies to be used in the planned EISCAT_3D phased-array incoherent scatter radar system and participate in very long baseline interferometry experiments. This paper gives an overview of KAIRA, its principal hardware and software components, and its main science objectives. We demonstrate the applicability of the radio astronomy technology to our geoscience application. Furthermore, we present a selection of results from the commissioning phase of this new radio observatory.
DOI: 10.1109/TGRS.2014.2342252

With the publication of this paper, we regard the build and commissioning phase of the KAIRA facility as being complete. As a result, the time has come to close the KAIRA web log, which was written for the purposes of reporting on the build of the instrument. The first post was written on Wednesday 30-Jun-2010 and, today Friday 12-Sep-12104, we have the last.

To all our readers over the years, thank you so much for your support, comments and attention. It has been great fun writing for you and, as our web counters indicate, it has been very popular. We have covered so many topics, ranging from the technical, to the tragic, to the humerous, and the downright bizarre. And, it has been a tough project, with real blood, sweat and tears. Yet, it has all been worth it.

Even though this web log will now halt, it will remain in place for future reference. For those who still want to read about KAIRA, Sodankylä Geophysical Observatory, and Arctic Finland, the story continues on the SGO web log.

However, we will now close here with thanks. In Finnish, of course...


Thursday, 11 September 2014

EISCAT_3D Preparatory Phase

This week, we have the last general meeting of the preparatory phase for EISCAT_3D. This project is the next-generation incoherent scatter radar, which will be built in northern Fenno-Scandinavia and, perhaps, beyond. It is an ambitious project, which involved many participants from multiple countries. And, as this particular phase of the project is completed, we are meeting at the Space Physics Institute in Kiruna, Sweden, to discuss the work done, report on the progress made and make plans for the future of this important scientific instrument.

KAIRA has been heavily involved in the project. Although a large multi-purpose facility, capable of carrying out multiple receive-type experiments, it has been used specifically to test certain aspects of the EISCAT_3D proposal. Its deployment garnered useful experience in practical matters regarding the development of a new site and the utilisation and integration of commercially available components within the context of Arctic location and cross-disciplinary application. We have also used KAIRA for new signal processing techniques, such as allowing the lag-profile inversion, and thus accomplishing multibeam, remote-location reception of the EISCAT VHF transmitter signal. This is a critically important step in the construction and operation of \EISCAT for multi-beam, multi-static incoherent scatter radar, and thus true 3D volumetric ionospheric measurement. The KAIRA facility remains operational for on-going EISCAT development and prototyping endeavours.

Undoubtedly, KAIRA will continue to be involved in EISCAT work, and specifically the EISCAT_3D developments. But as this particular part of the project is accomplished, we want to note our involvement and wish the EISCAT Scientific Association all the best for their future goals.

Wednesday, 10 September 2014

Replacement parts

We've just had some parts arrive from ASTRON. The timing distribution boards are being replaced and so we had three arrive in a box from Dwingeloo. The "Fragile Glass" label on the box got us excited for a moment, but even without any bottles therein, the arrival of new electronics is cool! These will be installed on our next trip to the site and the recovered old boards will be sent back to ASTRON.

New electronics boards from ASTRON (Photo: D. McKay-Bukowski)

Tuesday, 9 September 2014

University visit

Last week a couple of us from SGO visited the main university campus in Oulu. As most of our readers will know, KAIRA is operated by Sodankylä Geophysical Observatory, which in turn is part of the University of Oulu. it is quite a long way from Kilpisjärvi to Oulu, but that's where we were last week and have a photograph of the towers of learning to share.

University of Oulu (Photo: D. McKay-Bukowski)

Monday, 8 September 2014

Sodankylä Geophysical Observatory blog

There is a new web log. At the end of August, Sodankylä Geophysical Observatory general web log was started. It is being led by established KAIRA author Lassi Roininen and will feature others from the observatory, much more generally than what we have done here. The new site continues along the same path as our KAIRA web log, but the idea is to cover more widely the Observatory activities, including published papers, conference and workshop announcements, reporting on campaigns and extensive research visits, installation of new instruments etc.. Posts will be mostly in English, but with occasional content in Finnish and other languages too. We will also use this new web log for reporting sudden onset events. Naturally, there will also have been some more casual matters from time to time, including anecdotes about life at Sodankylä Geophysical Observatory, the University of Oulu and various other things that form the Lapland experience in Arctic Finland.

So, for all regular readers here, do go an check the new SGO we blog at:

Friday, 5 September 2014

IRIS - Imaging Riometer for Ionospheric Studies

IRIS is an imaging riometer, located at Kilpisjärvi, not too far from KAIRA. It is a single-frequency riometer and images the ionospheric absorption using fixed multibeams (unlike KAIRA which uses both fixed and tracking beams, as well as interferometry). The IRIS beams are formed using Butler matrices.IRIS is operated by the University of Lancaster, UK, with assistance from SGO. It is quite an old instrument and has been operating since September 1994. Its receiver frequency is 38.2 MHz. KAIRA often runs experiments at similar frequencies (for us, subband 195) in order to carry out comparative experiments.

IRIS (Photo: D. McKay-Bukowski)

Thursday, 4 September 2014

Applied Inverse Problems 2015

A major inverse problems conference, Applied Inverse Problems, will be organised in Helsinki, Finland, May 25-29, 2015. The event website is at Important dates are:

  • Mini-symposium Proposal Deadline: September 30, 2014
  • Poster, Contributed Talk, and Minisymposium Talk Abstract Deadline: November 30, 2014
  • Calderon Prize Nomination Deadline: January 31, 2015
  • Early Bird Registration Deadline: February 11, 2015

Wednesday, 3 September 2014

LBA repairs

Well, as reported, the jänis had struck twice and that meant lots of repair work for us. Actually in total there were 14 x LBA aerials to fix.

Status on 27-Aig-2014

The storm damaged ones were the most work. There required fitting new connectors (the old ones had been ripped clean off during the impacts). The jänis-attacked LBAs were more numerous, but less time consuming.

Repaired LBA line (Photo: D. McKay-Bukowski)

The fix was adding a new length of nylon guy line. A double-fisherman's bend is used to join the new section of line to the old and a bowline is used to make the loop to hook over the peg.

To discourage the jänis from simply biting through these again, we smeared the lines with a combination of spray lubricant and grease. This is waterproof and should give a bad smell and texture, thus deterring further jänis attacks.

However, in the long-term, we'll still need to work out a better way of protecting the LBA aerial lines.

Tuesday, 2 September 2014

Jänis attacks!

Last week we made a service visit to KAIRA. There were four LBA aerials still down from the blizzard of 2014 and these needed fixing. However, on arrival at the site, we noted that there were some other LBA aerials down.


We hadn't noticed this in the data, so it must have been recent. And inspection of the field indicated that the nylon lines had been cut on multiple LBA aerials, which is what had caused them to fall.

A cut LBA line. (Photo: D. McKay-Bukowski)

Field of woe. (Photo: D. McKay-Bukowski)

We believe that the cause of this is a jänis (Wikipedia). These creatures like to gnaw on things and it looks like the LBA array was the target. Knowing our luck, it was probably the cute jänis we saw a while back.

What's worse, on the second day, we found yet more LBA aerials down. The jänis had struck again! (This led to much silliness on twitter.)

In total, some 10 LBAs were downed over two days (26-27 Aug 2014). More repair work for us then.

Monday, 1 September 2014

KAIRA spectral riometry paper out!

I'm happy to announce that our proof-of-concept study on the electron density profile estimation based on the KAIRA spectral riometry measurement has been finally published in the Geophysical Research Letters, please have a look:

Kero, A., J. Vierinen, D. McKay-Bukowski, C.-F. Enell, M. Sinor, L. Roininen, and Y. Ogawa (2014), Ionospheric electron density profiles inverted from a spectral riometer measurement, Geophys. Res. Lett., 41,  doi:10.1002/2014GL060986

By comparing our spectral riometry results to a simultaneous EISCAT VHF measurement, we were able to show that the methodology works, at least under conditions of relatively strong ionisation. This builds confidence towards continuous monitoring of height-dependent D-region ionisation by spectral riometry.

Friday, 29 August 2014

Typical KAIRA

Today's photo has a bit of everything. The LOFAR HBA tiles, the LBA array in the background, Saana dominating the horizon, the storage containers and site area, and our trusty observatory vehicle.

The KAIRA site (Photo: D. McKay-Bukowski)

Thursday, 28 August 2014


Always curious to try local produce, I tried this herb liqueur by Koskenkorva. It comes in a matt black bottle, rates at 35% and is ominously titled:  "Valhalla".

Herb ingredients are: Angelica achangelica, Artemisia absinthium, Achillea millefoium, and Glycyrrhiza glabra. 

Wednesday, 27 August 2014


Driving back late one night from KAIRA to SGO there was (yet another) hold up. This time roadworks. In fact there is a bridge under repair on the route from Kittila to Sodankylä and this is where we got stuck.

We were the only car.

And yet the delay was... well...

Plasma lines at Arecibo

25 MHz wide plasma line profile at Arecibo, 2.5 seconds of integration. 
A while ago, Thomas covered the Arecibo radar school (you can see our black rack receiver on the table in one his pictures). During the school, a little bit of data taking took place. Between his lectures, Phil Erickson ran data collection with our 25 MHz digital receiver, in anticipation for a longer campaign that will occur later this year. As I wasn't in Puerto Rico, and I've been traveling elsewhere, I'm only now starting to analyze the results. But they are quite nice.  The system can pretty much do what the existing 5 MHz wide Pentek system can do, but at 25 MHz bandwidth, allowing us to measure plasma line profiles such as this. You'll probably need to zoom in the picture to pick out the narrow plasma line. There is also a higher resolution version on line here.

Anyway, this is quite a successful first try. The IF will need to be at a different frequency than 260 (e.g., 264 would be nice), as plasma line below 10 MHz folds, and can also be seen "sliding" down from +12.5 MHz too. Another option is to bring a tuner to shift the band to a lower IF. Also, the wide band IF doesn't seem to be wide enough. The upshifted line isn't that visible due to filter roll-off. 

Monday, 25 August 2014

Data extraction

There are numerous computers in the RF-container, which handle data processing, control and storage. One of these has now been taken out and has been moved back to SGO for use there in some of our interferometric riometry development work. During the extraction of this data system, we had the side cover of the RF-container signal processing racks off, thus once can see the other computers, network gear, etc.

KAIRA data systems (Photo: D. McKay-Bukowski)

Sunday, 24 August 2014

Missing in action

Today's photograph shows the frameset of HBA tile #75. Or, we should say... the former HBA tile #75. It is missing due to a severe blizzard that swept through the site at the beginning of the year. We are still waiting for a quote from ASTRON to get this replaced.

Frameset for HBA tile #75 (D. McKay-Bukowski)

Saturday, 23 August 2014

A big blade

heading back from KAIRA to SGO the other morning, I was held up for a considerable period of time at the turn to Meltaus. The reason for this was that a convoy was moving three huge blades of a wind turbine and the first of these was starting to make the turn just as I arrived at that point.

It was quite a long wait as the turn was very difficult given the huge length of the blades. I tried to estimate the length and I suspect they are 40-50 metres long each.

Turning wind turbine blades. (Photo: D. McKay-Bukowski)

Information about the project can be found here:

Friday, 22 August 2014

Arctic green

At this time of year, the Kilpisjärvi region is pretty green. Most of the snow has melted and the trees are not quite yet changing to brown for the autumnal drop. Today's photograph was taken looking south along the western bank of the mound on which the antennas are located. The mountain on the left edge is Saana and on the right is Pikku Malla.

Looking south from KAIRA (Photo: D. McKay-Bukowski)

Thursday, 21 August 2014

LBA aerials

KAIRA has 48 low-band antenna (LBA) aerials. These were designed by ASTRON (the Netherlands Foundation for Radio Astronomy). The arrangement of the aerials looks pretty random, but in actual fact it has been carefully chosen to give a good beam-pattern for the radio telescope. Each aerial comprises a steel grid which acts as a ground plane for the aerial. The post is PVC (starting to fade in places due to UV-light exposure) and the black cap at the top contains the low-noise amplifiers (LNAs) - one for each polarisation.

The wires that extend from the cap to the corners of the ground planes are the antenna wires. The form crossed inverted-V dipoles, giving good all-sky sensitivity. Actually the wire part only goes about halfway down. The lower part is either nylon line or elastic, which is used to hold the aerial in place.

Low-Band Antenna (LBA) at KAIRA. (Photo: D. McKay-Bukowski)

Wednesday, 20 August 2014

Ounas River

Today's photograph is dawn, seen over the Ounas River, not far from Kittila.

Ounas River, Lapland, Finland.

Tuesday, 19 August 2014

Mushroom harvest

Some of our readers may recall the great mushroom picking expedition of 2013. Well, this year, our Supreme Mushroom Leader (Lassi Roininen) set forth again on another epic journey (this time without lackeys to make a mess of things) and, once more, came back with a lovely mushroom harvest.

Mushrooms from the forest.

Of course, our regular readers will know the fate of any food produce brought to the EISCAT building at Tähtelä on a Sunday afternoon... home-made pizza!

Pizza done!

Not surprisingly, everyone was happy to have a piece or two. And, you must admit, mushrooms are rarely cooked fresher than this!

Nom. nom. nom.

Monday, 18 August 2014

KAIRA site buildings

I took this photograph during a recent trip to KAIRA. The structure on the left if the RF-container. note the large grey panel on the near-side... that is the cowling to protect the airconditioner from snow and ice. The timber structure on the right is the HBA cable mausoleum. This is where additional cable delay line length is placed. Normally on LOFAR systems, this is underground. However at KAIRA both the LBA and HBA arrays have above-ground housing for the extra delay lengths. The other raised building is the site office (known locally as the "barracks").

RF-container and HBA mausoleum, and then the site office. (Photo: D. McKay-Bukowski)

Sunday, 17 August 2014

An unexpected guest

The other day there was something banging and clattering outside my room. I couldn't figure out what was going on and I didn't spy anything directly outside the window. Then, there was a strange snorting noise. Really weird.

Anyway, curiosity got the better of me and I got up to go and have a look.

Easily startled... but hopefully not back in greater numbers. (Photo: D. McKay-Bukowski)

Don't stare at me like that! (Photo: D. McKay-Bukowski)

Friday, 15 August 2014

LOFAR Aerial Photos – Nançay

Another of the LOFAR sites has become visible in aerial imagery. The French site at Nançay can now be seen in Apple's, which is supplied with iPhones and iPads. If you want to find it yourself, here are the co-ordinates: 47°22.54'N, 2°11.56'E, or go to Nançay and look for the large T-shaped antenna array north of the town. Under the left "arm" of the T, you'll find the LOFAR site.

Photo: Apple

Thursday, 14 August 2014

Sunlight on the EISCAT dish

Arriving back late at the observatory one evening I caught the late evening sun striking the 32m EISCAT dish. The photo doesn't really do it justice, but the colours and lighting were sublime.

The Sodankylä 32m EISCAT dish (Photo: D. McKay-Bukowski)

Wednesday, 13 August 2014


Currently, there's talk in the media again about the so-called "Supermoon." What is it? The Moon's orbit around the Earth is not circular, it is elliptic, and the orbit's closest point, the perigee, to Earth is about 50.000 km closer than the farthest point, the apogee. Every so often, full moon on Earth coincides with the time the Moon is at its perigee, and therefore it appears to be unusually large. When this happens, it is called "Supermoon."

The full moon of 10th August 2014 was a Supermoon, and so was 13th July 2014 /(photo above). Also the next full moon will be a Supermoon on 8th September 2014. After that it happens again in August, September, and October 2015.

See also: on, there's a side-by-side comparison of the size of the moon as seen from Earth in March and August 2014.

Photo: Thomas Ulich.

Tuesday, 12 August 2014

Reindeer antler

In the KAIRA site office we have a strange "trophy" on the wall.  This is a reindeer antler. Reindeer lose their antlers naturally and if you wander through the Finnish wilderness, you will occasionally find one. We found this one near the KAIRA site and now it is mounted on the wall.

The KAIRA reindeer antler (Photo: D. McKay-Bukowski)

Monday, 11 August 2014


Arrived at KAIRA pretty late last night. It was a moody scene. Low cloud lurking over Pikku Malla and everywhere damp and foggy.

Low cloud over KAIRA (Photo: D. McKay-Bukowski)

Friday, 8 August 2014

KAIRA Lemmings

Lemmings are very common in the Kilpisjärvi area, and they have featured on this blog before. But when we went for a service trip to KAIRA in late June, we took a simple panorama with an iPhone, and then transformed it into a circular, so-called "little planet" panorama – and we were quite surprised by what we found!

Click on the image for higher resolution; you can just make out the KAIRA site in the 4 o'clock and 8 o'clock sectors!

With this image we wish all of you a very good weekend!

Photo and processing: Thomas Ulich (on MiVyoo you'll find the original panorama and details on how it was done).

Wednesday, 6 August 2014

Little KAIRA Planet

Recently, we wrote about how to generate a panorama from 360 images of one degree field of view. However, we can play this game some more. These panoramas are 360°, which means that their outer (left and right) edges match exactly. Therefore, one can use an image manipulation program such as Gimp to create what is knows as "little planet" images. The name stems from the fact that these landscape panoramas are fully encircled by sky and thus look a bit like a planet, alas in the wrong scale.

Here's the little-planet version of the sunny KAIRA panorama, which in addition was rotated in order to have Saana at the top like in the image above. The star-shaped shades are due to the automatic exposure of the GoPro time-lapse camera.

The key ingredient to making these kind of images is Gimp's distortion filter "polar co-ordinates."

Photos and editing: Thomas Ulich.

A related and more explicit description is available on the MiVyoo blog.

Monday, 4 August 2014

KAIRA Egg-Timer Panoramas

Previously, we wrote about a 360° panoramic time-lapse film we made using an egg timer. For the photo above, we wanted to combine all 360 images (one per degree of roation) into one large panorama. This meant to cut from every photo a tiny narrow centre slice and to combine these into one large image. If you look carefully, you can make out the stripes.

On the next day, the weather was much nicer, and we repeated the egg-timer photography. However, due to the GoPro fully automatic exposure settings, and the variable lighting due to fast moving clouds and the bright Sun, it was not possible to make a nice pan-lapse out of these photos, and as you can see, the stripiness is much more pronounced in this image, even though the blue sky is very nice of course.

You can click on the above images to get larger versions.

Original photos and panoramas: Thomas Ulich.

A related article was published on the MiVyoo blog.

Friday, 1 August 2014

KAIRA Pan-Lapse Film

In late June, we visited the KAIRA site in Kilpisjärvi on a maintenance trip. One of many tasks was to repair an HBA cell, which got damaged in a severe storm in spring. Another task was to take lots of high-quality photos of KAIRA and its surroundings for various documentation and illustration purposes.

Right on the first evening, we put a tripod bridging the gap between tiles H57 and H47 on which we mounted a wide-angle GoPro camera, which was glued onto a very cheap and simple egg timer. The egg timer rotates 360° in one hour, and the camera was set to take a photo every 10 seconds, thus taking 360 images, one per degree of rotation.

The full 360° panorama can be assembled by sticking together twelve images, which are five minutes apart. The only problem is to find out how many pixel the image rotates in five minutes, which is 30° of rotation.

The photo above shows such a montage (click to enlarge), featuring the famous mountain of Saana in the sixth pane from the left. Since we have a full rotation, one photo per degree, we can assemble such a panoramic view in 360 different directions, each one showing the a full 360° panorama. Then, we combined them into a short film, giving the impression of full-panorama rotation.

The above explains how we did it, but one can understand what's going on also this way. We generate a time-lapse film from all the images, showing a slow rotation. Then we cut out the centre vertical section equivalent of 30° rotation from this film. Thereafter we glue twelve copies of the very same film side-by-side, but advance the film for each step just the right amount, so that it fits to the previous copy of the film.

We hope you enjoy the result.

We got the idea for these pan-lapse films from Ken Murphy of Murphlab, please visit his site for this and other exciting time-lapse projects.

Photos & pan-lapse: Thomas Ulich.

PS1: You might wonder why we didn't choose a nicer day with more blue sky for this experiment. In fact we did, but due to the GoPro's automatic exposure settings, the large contrasts between looking into the Sun and away from the Sun, paired with shadows of clouds moving across the sky, make the different panes/frames look very different and the result is much less pleasing. So grey skies are good for something!

PS2: Another somewhat more explicit blog post about this went out today on the MiVyoo blog.

Thursday, 31 July 2014

Trends 2014 - completed

Trends 2014 meeting was successfully completed. A number of topics were covered. For me personally, the most interesting new information was that the trends affect the space debris population. Hence, we need to follow the foF2 and hmF2 trends... and of course EISCAT and EISCAT_3D space debris measurements are important in this business! Also, bit of Ethiopia news: American colleagues will install two Fabry-Perot interferometers to Ethiopia during the coming autumn!

I presented my own stuff today and talked about dynamic linear models and estimation of time-varying hmF2 trend of the Sodankylä ionosonde data (see Figure below).

Hence, time to travel up to Sodankylä, ETA Friday evening 23 LT! (stopping at London for Th-Fr night)
hmF2 dynamic trend for Sodankylä 1957-2014.

... and presenting my stuff! (photo: Erkki Kyrölä, FMI)

Monday, 28 July 2014

Trends 2014, Cambridge UK, July 28-31

This week, in Cambridge UK, takes place 8th Workshop on Long-Term Changes and Trends in the Atmosphere 2014. The meeting started on Monday morning and will run until Thursday afternoon. I will have my talk on Thursday! As this meeting is not 'inverse problems', i.e. I am out of my comfort zone, so today we will simply feature photos from the conference venue Clare College. (It is absolutely stunning and beautiful college.) I will come back to the science covered later this week (hopefully) !!

Sunday, 27 July 2014


Last week we went for a bit of a walk to the FMI radar at Luosto. On the way, we passed some little hut... probably an electric power distribution box.

On the door was a sign... "Hengenvaara"

Now, if I understand this correctly:  "vaara" is "hill"... as in Pittiövaara or Lampivaara.

Of course this is not to be confused with "väärä", which would be "incorrect" (and also incorrect).

And "hengen" (as in "henki") is "spirits" or "souls"... or something.

So, does that mean that this hill is haunted? And, if so, by whom?

Well... probably the person who mistranslated the sign and was subsequently electrocuted!

Friday, 25 July 2014

Meet the press

We had a visit from a reporter 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.