SKA — Square Kilometer Array (Part 1)

We've just been to the Square Kilometre Array (SKA) Concept Design Review, held in Manchester in the United Kingdom. Attendance has been as an observer, but it has certainly been very useful to meet with the SKA community. There is a degree of overlap in technologies between the SKA, LOFAR, EISCAT and KAIRA projects and there are many opportunities for fruitful collaboration.

SKA will probably be mentioned a lot in the web log as the months go by. It is a big project, and sits firmly in the scientific vision of most groups undertaking radio astronomy. But what is it?

SKA, as the name suggests, is an array of antennas with a total collecting area of 1 square-kilometre. 1 square kilometre is 1 million square metres, so this is big compared to the 4800 m2 of KAIRA, and it will even outstrip LOFAR and EISCAT.

The antennas will be grouped into stations, with a large number of these stations clustered together into a 'core' (in the same way that LOFAR has a 'core' of stations that are close together).

Artist's impression of how clusters of tile-antennas in the central region
of the SKA might look. (Image: SPDO/Swinburne Astronomy Productions)

These core stations will cover an area some 5 km or so. The furthest stations will be scattered out to distances of several thousand kilometres from the core.

Layout of the central region of the SKA. (Image:
SPDO/Swinburne Astronomy Productions)

This requirement for a large area, as well as a desire to build it in the southern hemisphere (for astronomical reasons) and a need to keep away from interfering radio signals has limited the possible locations where the SKA can be built. Currently there are two candidate sites: one is Australia and one in South Africa. The decision on this will be made in the next few years.

Tomorrow we'll have a closer look at the SKA antenna systems themselves.

The EISCAT VHF transmitter

As we have seen, the site at Tromsø run by the EISCAT Scientific Association has several instruments. The most significant of these to KAIRA is the VHF transmitter, because its frequency (224 MHz) is within the high-band of the KAIRA system. This frequency is also very close to the proposed frequency of the EISCAT_3D project.

The Tromsø VHF system is a scientific radar. Using the incoherent scatter principle, it transmits radio power into the upper atmosphere and detects the faint radio echoes. From these, it can readily determine the electron density, ratio of the electron temperature to ion temperature, ratio of the ion temperature to ion mass, and the line-of-sight ion velocity.

The Tromsø VHF antenna is huge: 120×40 metres in size. It comprises 4 panels, each 30×40 metres, which can be steered in elevation independently of each other. The system cannot turn in azimuth, but it is possible to reconfigure the phase of the transmitter array to provide a small amount of horizontal directional control.

The transmission power is provided by a klystron. The transmission frequency is 224 MHz (well inside the range of a LOFAR HBA antenna) and the peak transmission power is 1.6 MW. The feed system is a line of 128 crossed dipoles at the focal line of the parabolic-cylindrical antenna panels. This line can be seen to the right of the panels in the first photograph. To get an idea of the scale, that line is actually a corridor and engineers can walk along the inside of it. The second photograph shows a close-up of one of the individual crossed dipoles.

EISACT Tromsø

Two of the EISCAT radar transmitters are located in Ramfjordmoen, close to the city of Tromsø in Norway. The people working here are employed by The University of Tromsø.

The EISCAT UHF (Ultra High Frequency) radar operates at 931 MHz and is driven by two klystrons with a peak transmission power of 2 MW. The antenna is a 32-metre diameter dish, which weighs about 100 tonnes. It is fully steerable, and can scan at speeds of 80 degrees per minute in both the azimuth and elevation axes. It can accelerate to full speed within 2 seconds.

The other radar is the VHF system, shown in the second photograph. This is a 120×40 metre antenna with a 224 MHz transmitter. This radar is of particular significance to the KAIRA project, so we'll write about it in full tomorrow.

In addition to the radars, there is a Heating Facility, which is used for modification experiments. It applies high-power transmissions of high-frequency electro-magnetic waves to the ionosphere to study its plasma parameters. The name Heating stems from the fact that these high power electromagnetic waves, which are transmitted into the ionosphere with high-gain antennas, heat the electrons and thus modify the plasma state. To create plasma turbulence, the transmitted frequencies have to be close to the plasma resonances, which are 4 to 8 MHz.

There is also a Dynasonde (a digital HF sounder) covering a frequency range of approximately 1-20 MHz. Six dipoles are used as spaced receiving antennas. Each half of each dipole is made from an aluminium tube, 11 metres long and 15 centimetres in diameter. These tubes are suspended about 2 metres above the ground. Even so, they do break sometimes through weight of snow and metal fatigue as they vibrate in the wind.

More information about these systems can be found at the EISCAT website: http://www.eiscat.se/about

But there will be more about the VHF system tomorrow!

Simple antennas, but lots of them!

Let's resume the story from Monday, when we were discussing the EISCAT Kiruna Demonstrator Array in Sweden. As we saw in that article, the array is a 12 ×4 grid of 48 Yagi aerials. If you look at an individual one of these aerials, you will see it is really very simple. Just a few rods, some bolts and a cable or two. If you look at one before it is assembled, it looks something like this:
Apart from the tools in the lower right of the photograph... that's it!

When built, the aerial looks like this (shown here at the back of the control building at Kiruna in 2006, before the construction of the actual test array). It was simply attached to a post hammered into the ground at roughly the right angle, to look towards a section of the atmosphere being 'illuminated' by the radio signals of the VHF transmitter from Tromsø.


It looks simple.

But that's the whole idea!

In order for EISCAT (or for that matter, KAIRA, LOFAR or SKA) to work, they rely on a multitude of simple antennas. Each one must be capable of receiving the correct radio frequencies with high fidelity, but as cheaply as absolutely possible.

Then, sheer numbers (plus some clever electronics and computing!) will do the rest.

Mid-February status

Another update from the test tiles at Kilpisjärvi. Conditions remain pretty much the same in terms of snow cover, although the temperatures have dropped considerably. These photographs were taken on 18^th February 2011 and can be compared to the ones taken on 31^st January 2011.

Superficially, the raised tile looks in good condition. From what we can see, all the anchors are holding well, and there has been minimal shifting of the tile. What might be a concern, however, is the condition of anchor lines and the build up of ice, as opposed to light snow. Temperatures are continuing to descend, with recent depths of –30 degrees C.


The ground tile remains an unknown. The snow cover remains just as deep as before, which in reality will mean a greater mass, as the snow will slowly become more densely packed with time.

It will be very interesting to see what emerges in the summer!

Photo credits: Markku Postila

EISCAT-Kiruna Demonstrator Array

KAIRA is not the only project working on the issue of antenna and receiver technology for EISCAT_3D. In addition, there is the so-called 'demonstrator-array', which is located at the EISCAT receiver station at Kiruna, Sweden. I contacted Lars-Göran Vanhainen from the Kiruna site and he explained what this project is all about.

The demonstrator array is a phased array of 48 Yagi antennas, arranged in a 4×12 grid. It operates at VHF frequencies and is capable of detecting signals from the VHF transmitter in Tromsø. The photograph from Lars-Göran shows these Yagi antennas in the foreground. The large dish behind the control building is the 32-metre receiver antenna of the existing EISCAT system.

The demonstrator array was mainly built to be an experimental test bed for the digital receivers and digital beam steering that was proposed in the EISCAT_3D design study. Although the design study has now been concluded, the prototype work is being continued.

The array has now been equipped with fixed delay co-axial beam steering. As it is set up, the array points towards Tromsø at an elevation of 55 degrees, which corresponds to an altitude of 300 km above the Tromsø VHF transmitter. Successful tests have been conducted and bi-static VHF data has been recorded.

Work is now in progress to tilt down the beam to 100 km above Tromsø. The 'beam' is the direction in which a radio receiver array is sensitive. It is a concept like the beam of a search-light, but in reverse; receiving, rather than transmitting.

The objective is to modify the array to be able to do E-region measurements and VHF bi-static studies of meteors and PMSE. These phenomena are both coherent and much stronger than the incoherent scattering from the ambient ionosphere, so even a decrease of the total gain due to the change in the array geometry from optimal should not have an great impact on the measurements in mind.

We'll be talking a lot more about these crucial experiments in future web-log posts!

How long are LOFAR baselines

There has been a bit of misinformation floating about the Internet recently about just how long the LOFAR baselines are. A 'baseline', in this sense, is a short-hand term for the inter-receiving-element distance. In other words, how far apart are the antennas. In the case of LOFAR, the elements are the stations, so the baselines are the distances between the LOFAR stations.

The reason why this is significant is that, ignoring calibration issues, the resolution of the radio telescope is governed by the baselines and the observing frequency. This means that for any given frequency, the longer the baselines, the better the resolution (which is the fineness of detail that the radio telescope can make out). Of course, you can't just have one long baseline... you need the shorter ones too, so that you can resolve all levels of structure in the astronomical object you are observing. (This is what the so-called uv-diagrams show: just how good the coverage of a sparse radio telescope is over all the baselines.)

But it is these 'long baselines' that get quoted in press releases, as they represent the limit of the radio telescope's resolving power.

For LOFAR, although the collecting area and intermediate baselines are dominated by the Dutch stations, it is the so-called International Stations that dominate the long baselines. These stations are:

• LOFAR DE601 — Effelsberg, Germany
• LOFAR DE602 — Unterweilenbach, Germany
• LOFAR DE603 — Tautenburg, Germany
• LOFAR DE604 — Potsdam, Germany
• LOFAR DE605 — Jülich, Germany
• LOFAR FR606 — Nançay, France
• LOFAR SE607 — Onsala, Sweden
• LOFAR UK608 — Chilbolton, United Kingdom

Additional stations, such as the proposed station at Birr Castle, Ireland, are not listed here. At the time of writing this, DE605 and SE607 are still under construction or being commissioned. And, to date, DE602 and DE604 has not yet been used in long baseline observations to the western stations.

This means that the longest baselines used so far by LOFAR is the DE603 to UK608 distance, which is 920 km. This was the longest baseline used in the image that recently made the mainstream news.

DE603 (Tautenburg, Germany)... one end of
the longest LOFAR baseline so far. (Photo:
ASTRON & Landessternwarte Tautenburg)

And at the other end, UK608 (Chilbolton, UK). Together these
two stations have a baseline of 920 km. (Photo: STFC Images)

Once all the stations under construction have been completed, the longest baseline will be FR606 to SE607, which would be 1301 km.

If KAIRA is connected to the LOFAR network, the it will add several long baselines, exceeding all of these. The shortest would be the KAIRA to SE607 baselines, at 1350 km, while the longest would be KAIRA to FR606 at 2594 km. As can be seen, ignoring position angles, these KAIRA baselines would extend the LOFAR International Telescope very well.

However, even with KAIRA, LOFAR will still fall well short of the 10,000 km that is currently being claimed by some web sites. If only the funding agencies would make those sorts of errors, then, yes, we'd definitely have 10,000 km baselines! ;-)

Tied-array Superterp

Large multi-element radio telescopes are frequently used in a special way. This mode of operation is known as 'tied-array' and the way that it works is that signals from separated antennas (or arrays of antennas) are added coherently. The sensitivity of coherently combined stations should increase by the square-root of the number of stations compared with the incoherent station sum. Instead of working as multiple stations, they work as if they are just a single station. The output sum signal can be used in experiments such as very long baseline interferometry, pulsar and transients observations, extra-terrestrial intelligence signal detection.

Within each LOFAR station, the signals from the antennas are phased to create a single output. However, on the 7th February, LOFAR announced that they had successfully combined the first data coherently from not just the antennas of a single station, but the antennas of multiple stations. The stations used were the 12 HBA fields of the so-called 'superterp' — a large collection of small LOFAR stations, grouped together in the north of the Netherlands.

The Superterp: 6 LBA fields and 12 HBA fields,
clustered together on a moated circle of land.
(Photo: ASTRON, TopFoto Assen)

This new development has greatly improved the sensitivity of the LOFAR system. The EISCAT_3D system will also make use of this technique to improve sensitivity.

LOFAR Press Release: http://www.lofar.org/first-lofar-tied-array-beam-achieved

EISCAT_3D

Mentioned on several occasions is the EISCAT_3D project.

The EISCAT Scientific Association operates three incoherent scatter radars in Tromsø (Norway) and on Svalbard. The UHF radar, which operates at 930 MHz, is the only tristatic incoherent scatter radar in the world. The transmitter is located in Tromsø and additional receiver sites are in Kiruna (Sweden) and Sodankylä (Finland).

However, there are ambitious plans afoot to build the next generation incoherent scatter radar, which will provide comprehensive 3D monitoring of the atmosphere and ionosphere above Northern Fenno-Scandinavia. This new radar system — called EISCAT_3D — will consist of multiple phased arrays, using the latest digital signal processing to achieve ten times higher temporal and spatial resolution than the present scientific radars. It will have pplications in a wide range of European research areas including Earth environment monitoring and technology solutions supporting sustainable development, well beyond atmospheric and space sciences.

EISCAT_3D will be a volumetric radar capable of imaging an extended spatial area with simultaneous full-vector drift velocities, having continuous operation modes, short baseline interferometry capability for imaging sub-beamwidth scales, real-time data access for applications and extensive data archiving facilities.

The design of the antenna arrays will be modular at different scales allowing for mass-production of the components. Some arrays will be very large, in the scale of 32,000 individual antenna elements. The receiver arrays will be located at 50-150 km distance from the transmitters, with some smaller arrays close by to support continuous interferometric observations. The total system will comprise approximately 100,000 elements. Construction is due to start in 2015.

KAIRA is an integral part of the EISCAT_3D development process. It will test whether or not LOFAR production items are suitable to the EISCAT_3D project, possibly leading to a mass deployment of LOFAR hardware in the far north. However, it is not the only possibility, and other array designs are being considered. One of these prototypes under evaluation is the Kiruna Demonstrator Array; there will be a web log post about this soon!

EISCAT_3D website: http://www.eiscat3d.se/

LOFAR Single-Station Meeting

On the 14^th and 15^th of February 2011, the latest LOFAR Single-Station meeting was held in Oxford in the United Kingdom, attended by over 20 LOFAR experts. The Single-Station meetings are an important part of the LOFAR programme. Instead of using the entire LOFAR telescope for observations, these meetings discuss what science can be achieved if the LOFAR stations work independently of the main array. They also discuss the technical issues and challenges of such experiments.

Although this mode of operation is not the standard long-baseline one, it is nevertheless an important part of the LOFAR programme, as it allows individual stations the opportunity to explore new ideas and to perform their own experiments. It also serves as a vital part of the undergraduate training, as students get an opportunity to use these huge telescope arrays for their learning.

KAIRA is a fantastic example of LOFAR hardware being used for local experiments. We gave a exposition of the work we are doing and helped promote our Finnish project. But other presentations were also of great interest to us. Issues such as pack-ice and snow drifts (Tautenburg), humidity in cold climates (Effelsberg) and new LOFAR stations (Hamburg, Aberystwyth and Birr Castle) have kept discussions active and lively. It was also great to see the best of the results from single-station facilities and the new data acquisition systems being developed by the group at Oxford University.

Our thanks go to the Oxford organising committee for hosting such an engaging and inspiring meeting and to Dell Computers for their support of the event.

HBA layout — Part 2 (KAIRA)

As we described in yesterday's article, there are three standard configurations for High-Band Arrays (HBAs) in conventional LOFAR stations. KAIRA will also use LOFAR hardware for its antennas, thus making use of the proven design and also retaining compatibility with the LOFAR system. In total, there will be 48 HBA tiles in KAIRA. But although you might first think that the KAIRA layout might look similar to a 'remote station' or perhaps even a two-part 'core station', this is not the case.

There are some constraints on the KAIRA layout. These are:

• It has to maintain a elongation in the direction of the Tromsø VHF transmitter. This is to maintain the optimal beam pattern when looking at target regions of the ionosphere.
• There needs to be good access to the site, in order to deploy the tiles, maintain them, and protect them from the Arctic conditions.
• The volume of levelling of the ground needs to be minimised. This is to save costs, but it also saves valuable time during the extremely short summer when the array will be installed.
• There needs to be the option to upgrade KAIRA from 48 tiles to a full 96 tiles, thus converting it into a full-size international station.
• And, that upgrade needs to be done in a way to achieve the standard international layout, with minimum disruption to the existing array.

This means that the most optimal layout is a 4×12 grid. From there, only one row of tiles needs to be removed, and then additional tiles added to the sides, to complete the upgrade to the full international station layout.



The 4×12 layout is then rotated so that it points at an azimuth of 313 degrees with respect to North. This puts it on the alignment axis between Kilpisjärvi and the VHF transmitter in Tromsø (we'll write more on this transmitter soon). Curiously, it is also the same layout as the Kiruna phased array, which is part of the EISCAT_3D prototype work (yes... there be an article on that soon, too!).

Working out how the array (and the possible upgrade) will be placed on the mound, has been a time-consuming process. Because the placement is so critical, a great deal of attention has been paid to the survey and analysis to make sure we get this right

This is what the configuration looks like:



The dark-blue squares are the HBA tiles of KAIRA. The red outlines are the additional tiles that would need to be added to convert KAIRA to a full international LOFAR station configuration. In addition, the four end tiles (in the lower-right) of KAIRA would need to be removed to restore the symmetry. The white dot marks the centre of the international station layout. This would also be the dummy tile in that configuration, although it is a fully active tile in the KAIRA layout.

There will be lots more about the KAIRA configuration and deployment over the coming months.

HBA layout — Part 1 (LOFAR)

As described in our previous article, LOFAR is a pan-European telescope, split into stations and in each station there is typically two arrays of antennas: the High-Band Array (HBA) and the Low-Band Array (LBA). KAIRA, which is based on LOFAR antenna hardware, will also have an HBA and LBA. But the question is what sort of LOFAR station will it be?

You see, even though LOFAR is split into many stations, not all LOFAR stations are the same. In the Netherlands — the centre of the LOFAR network — where the stations are close together, there are more of them, but they are smaller.

One of the LOFAR stations near the core of the network. Note that
there are two small patches of HBA tiles. The 'shotgun pattern' of
antennas in between them is the LBA. (Photo: LOFAR Gallery)

As you move out from the centre of the network, the stations get bigger and their configurations change. This is for a number of reasons to do with performance, cost and ease of deployment. In this article, we'll only consider the HBA in the station, as this is where the changes are the most striking and where the most pronounced difference between LOFAR and KAIRA will be realised.

Essentially, there are three types of standard LOFAR station:

• Core stations = 2 × 24 HBA tiles
• Remote stations = 48 HBA tiles
• International stations = 96 HBA tiles

This is what these configurations look like (note you can click on any of the weblog images to see larger versions):

As you can see, in reality there is one additional tile right in the centre of the international station layout. This is not an active antenna... just an empty tile. This keeps the RF-load balanced across the array and prevents wind-turbulence cells being generated at the 'hole in the middle'. There is a more detailed explanation of this on the LOFAR-UK weblog article 'Going the extra tile'.

The completed HBA at the Chilbolton LOFAR
station in Hampshire, UK. (Photo: STFC Images)

So that's the description of the LOFAR station HBA layouts. But what of KAIRA?

Despite having the same hardware, KAIRA is quite different and with some distinctive features, dictated by its multi-purpose applications, challenging build site and some interesting future plans.

But we'll discuss that in tomorrow's web log post!

LOFAR Ireland

We extend a welcome to the LOFAR community to our colleagues in Ireland.

There is a new website for 'i-LOFAR' — a LOFAR station in Ireland. This is a new proposal for another international LOFAR station, to be located at Birr Castle. At station placed here will extend the longest baseline of the LOFAR International Telescope even further.

Birr Castle itself is a historic astronomy site. It is the place where the Rosse Telescope was built; the largest telescope of its day. This 183cm optical telescope was completed in 1845 and remained the largest telescope in the world for many decades.

Once again, this historic site will be associated with the largest telescope in the world... the LOFAR International Telescope. (And, this will be the first LOFAR station with a castle!)

Visit the LOFAR Ireland website at: http://www.lofar.ie/

LOFAR status update

There are now 32 LOFAR stations operational:

• 20 core stations in the Netherlands
• 7 remote stations, also in the Netherlands
• 3 international stations in Germany (Effelsberg, Unterweilenbach, Tautenburg)
• 1 international station in France (Nançay)
• 1 international station in the United Kingdom (Chilbolton)

And more are on the way!

Where is Kilpisjärvi?

As we've mentioned before, KAIRA will be built at Kilpisjärvi (after all, it's in the name!). However, the Sodankylä Geophysical Observatory is — yes, you guessed it — located in Sodankylä. So, in response to the call for a more enlarged map (compared to our EISCAT/LOFAR/KAIRA overview map), today's web log entry does just that. Zooming in on the Lapland area, both Kilpisjärvi and Sodankylä are clearly marked and show that KAIRA is right there in the corner of Finland, quite a way from SGO.

Kilpisjärvi (Northern Sami: Gilbbesjávri) itself is actually a small settlement in the north-western part of Enontekiö municipality. That small patch of Finnish territory wedged in between Norway and Sweden is known as the Finnish arm of Lapland and Kilpisjärvi is at the end of it. The settlement is quite small, with less than 100 inhabitants. It is an isolated part of the world, with the next nearest settlement over 40 km away.

Still, it is recognisable place, perhaps because of its famous landmark: Saana (Northern Sami: Sána). This fell towers some 556 metres above the nearby Kilpis lake and its summit is a total of 1029 metres above sea-level. It is clearly visible from the KAIRA site as this photograph shows, taken at the end of the 2010 summer, when we did the site survey. It is absolutely clear that many of the best photographs of the KAIRA project that will be posted this year will feature Saana in the background!

At this time of the year however, it breaks through winter’s silent grip on the landscape and stands there as an imposing Arctic sentinel; a natural fortress for trolls, giants and other creatures of Nordic mythology.

I wonder if there are any Sami legends about this beautiful fell?

EISCAT

EISCAT can sometimes be a confusing term. Sometimes it refers to the organisation, sometimes the instruments that it operates and at other times to an upcoming project, which is closely connected with our KAIRA work.

The EISCAT Scientific Association is an international research organisation operating three powerful scientific radars in Northern Scandinavia. It is funded and operated by research councils in various member countries. EISCAT itself, stands for European Incoherent SCATter, which is a reference to the radar technique that is used (more on this later!). These radars, along with an Ionospheric Heater and Dynasonde facility are used to study the ionosphere and the interaction between the Sun and the Earth (a field broadly referred to as Solar-Terrestrial Physics).

EISCAT operate several sites. The transmitters are located near Longyearbyen (Svalbard) and Tromsø (Norway). In addition, there are receiver stations located near Kiruna (Sweden) and Sodankylä (Finland) at the SGO site. The headquarters for the EISCAT Scientific Association is located in Kiruna and there are support groups in various of the institutes and universities of the member countries. The transmitter and receiver sites are all marked on the map that was recently posted.

In addition to the existing facilities, EISCAT is now undertaking a new ambitious project - EISCAT_3D. This is a new-generation radar that will provide a huge increase in capabilities of any existing scientific radars. KAIRA, in addition to its own scientific goals and close ties to the LOFAR project, is intricately connected with this EISCAT_3D development work, and there will be a lot more posted about this during the coming months.

Finnish Meteorological Institute

Co-located with SGO is Ilmatieteen laitos — the Finnish Meteorological Institute (FMI). Today we are delighted to be able to give a small presentation of the work done by them.

Space weather research at FMI includes both modelling and monitoring activities. The Institute owns and operates the only global Magneto-Hydro-Dynamic (MHD) simulation code in Europe and has conducted pioneering work in the theoretical modelling of Geomagnetically Induced Currents (GIC). On the observational side the main asset is the MIRACLE network of auroral cameras and magnetometers which is operated in the Northern Fennoscandia as international collaboration project where FMI serves as the PI-institute. Ionospheric researchers of the Institute have developed several methods for extracting value added data products from the network observations (e.g. latitude-longitude maps of equivalent ionospheric currents and auroral precipitation flux). These tools have been used in several research projects which typically utilise also EISCAT Incoherent Scatter data and various satellite observations in the research of meso-scale magnetosphere-ionosphere coupling processes.

During recent years the trend in MIRACLE research has been to move from the two-dimensional picture to three dimensional imaging of ionospheric conditions. For this reason, FMI has started closer collaboration with SGO in a project (TOMOSCAND) which will develop tomographic analysis methods for ionospheric electron density reconstructions. The aim is to use data from both GPS and Beacon receivers in the analysis and in a later stage perhaps also the standard MIRACLE observations can be integrated to the system. The future vision is to use TOMOSCAND measurements together with EISCAT_3D for monitoring radiowave propagation conditions in the Northern Europe. FMI participates as an associate member to the EISCAT_3D Preparatory Phase activities. The KAIRA project is of particular interest to FMI because the technical development of the system has synergy with the TOMOSCAND work and the array in Kilpisjärvi is located in the core area of the current MIRACLE and forthcoming TOMOSCAND field-of-views.

Links:

• http://www.space.fmi.fi/MIRACLE
  
• http://aurora.fmi.fi

With thanks to Kirsti Kauristie and FMI.

Forests of Lapland

In the still Arctic silence, as the pale twilight of the midday touches the landscape, the trees of the forest stand peacefully under their thick blankets of snow.


There, they reach skywards, as if straining to be the first to see the sun this year. Their branches still heavy with the cold grasp of Winter. And yet, there is a feeling of serene confidence that they will pull through to greet the Spring.


And in the gloomy shadows, tiny saplings are also pushing through the banks and drifts of white on the forest floor. Not yet a hand-span tall. So fragile. Down here, there is less light and more snow.


I wonder if the little ones shiver?

Sodankylä Geophysical Observatory

Although KAIRA will be built at Kilpisjärvi, the project is administered by the Sodankylä Geophysical Observatory (SGO). This world-class facility was established in 1913 by the Finnish Academy of Science and Letters to perform geophysical measurements and research. Now an independent research department of the University of Oulu, SGO maintains its continuous measurements of the Earth's magnetic field, cosmic radio noise, seismic activities, and cosmic rays.

Since the first measurements began on 1st January 1914, SGO has spread its range and location of sensors over multiple sites stretching from the south of Finland to Svalbard. KAIRA will be the latest in this proud tradition. However, the institute remains based near Sodankylä itself on the banks of the river Kitinen and this is where most of the KAIRA team are based.

The photograph (taken a few weeks ago) shows the main institute building in the dead of the Arctic night. It is one of many buildings scattered around the site. In actual fact, this building is shared with the Finnish Meteorological Institute. More on that later!

End-of-January status

We've now received the latest images from the winter testing! These photographs were taken on 31st January 2011. In the first picture, we see that the raised tile is managing quite well on its frame. There is some snow on the cover, of course, but it is not too thick


The ground tile, on the other hand, is completely covered with snow.



Both tiles remain vulnerable. The raised tile is subject to wind damage in its elevated position. The ground tile, while safe against wind, could suffer from the accumulation of the snow and the movement of the drift.

Photo credits: Th. Ulich

Mound Mesh Model

As reported in our piece on the site survey, we need to accurately model the region where we intend to put the KAIRA antennas. Unlike most LOFAR stations, KAIRA is located in pretty rugged terrain. This means that finding a suitable space is not as easy as it first appears. Especially when we are trying to avoid cutting down trees and keeping our impact on the Arctic wilderness to the barest minimum.

The site we have selected fits these requirements pretty well. The ground is mostly material from civil works, allowing us to re-use an existing development. However, the space is not easy to work in, especially when the main antenna array has an area of over 1200 m²., which needs to be levelled to an accuracy of ±3 cm. As a result, we need to consider well the exact location of the array and the amount of levelling required.

The plot shown here is from part of that analysis work. From the survey results, a topographic mesh is fitted to the data. That is then interpolated to derive a working model of the surface. From this, the detailed planning and layout can be completed.


The map is oriented with North at the top and the direction to the EISCAT VHF transmitter marked.

Amazing new images from LOFAR

There's been some major developments on the LOFAR project. As announced in a flurry of press-releases yesterday, LOFAR has managed to combine many of its international stations which, along with the core stations in the Netherlands, have resulted in some stunning images of the radio sky. These images demonstrate the enormous capabilities of this new generation of radio receiver technology and it provides a great encouragement for all of us here working on KAIRA and the EISCAT_3D projects.

A small portion of a wide field radio image (30-34 MHz), taken by the ASTRON/LOFAR commissioning teams led by Olaf Wucknitz (Bonn) and Reinout van Weeren (Leiden Observatory).

Not only do these images reveal the wide-field capabilities of the LOFAR system, but they are also at extremely high-resolution — especially at the higher frequencies — as fine as 0.2 arcseconds (close to 1/10000 of the diameter of the moon)!

As this resolution is a factor of the baseline (distance) between stations, the possibilities of linking KAIRA and LOFAR are even more exciting.

Press-releases:

• English
  
• French
• Dutch
  
• Swedish
  

LOFAR

LOFAR (LOw Frequency ARray) is a pan-European radio telescope designed to observe the radio universe at VHF frequencies. It is designed, built and operated by ASTRON, the Netherlands Foundation for Radio Astronomy. The LOFAR system is split across multiple sites — known as stations — each of which typically has two arrays of antennas.

The antennas in each of these two arrays are different in design. One design is a vertical 'aerial' which stands about 1.8 m tall, optimised for radio frequencies in the range 30 to 80 MHz. The other design is a large 'tile', with a square area of 5 × 5 m. It is for the higher frequency range of 120 to 240 MHz.

Did you note the gap from 80 to 120 MHz? LOFAR deliberately avoids these frequencies, as this is where commercial and public FM-radio stations broadcast. There is no point trying to listen for faint cosmic radio signals at the same frequency as a high-powered neighbouring radio station.

In addition to a large cluster of LOFAR stations in the Netherlands, there are additional participants in the main LOFAR project: Germany, France, Sweden and the United Kingdom. This map is a closer view than the one posted earlier, and shows the locations of the LOFAR stations (green = complete, yellow = under construction).


KAIRA makes use of the same antenna technology that is used in LOFAR, making it compatible with the LOFAR system. This opens up some exciting prospects of linking the two projects. We'll be looking at these antenna systems soon.

In addition, there have just been some important achievements by the LOFAR project. More on that in the next post!

Putting LOFAR, EISCAT and KAIRA on the map

As one might guess from the name, the Kilpisjärvi Atmospheric Imaging Receiver Array is located in Kilpisjärvi. For those of you who didn't already know, Kilpisjärvi is a small border town located in the top-left-hand corner of Finland. It is usually very easy to find on a map, as it is quite close to the corner of the three countries: Norway, Sweden and Finland.

But possibly less familiar are the related LOFAR and EISCAT projects associated with KAIRA.

This map marks the sites of these project with EISCAT in pale blue and LOFAR in magenta. KAIRA itself is marked in red. At a latitude of +69 degrees north, KAIRA is located well above the Arctic Circle (marked in white), making its association with LOFAR a most northerly one indeed.

There'll be more about LOFAR and EISCAT over the coming weeks, so be sure to visit this weblog again soon.