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.

Inside installation

Here are some more photographs from the deployment work of the digital beamforming system which was installed on the Kiruna Demonstrator Array.

Putting the final installation into the antenna field. (Photo: D. McKay-Bukowski)

Clock, switch, USRP, receiver... the new approach! (Photo: D. McKay-Bukowski)

Setting up the network and computing. (Photo: D. McKay-Bukowski)

Installing the field equipment

This past week, a team from KAIRA/SGO, LTU and EISCAT have been installing a digital beamforming system on the Kiruna Demonstrator Array. Today, we feature some of the photographs from the installation of the field equipment.

Tomi brings out more USRP subracks. (Photo: D. McKay-Bukowski)

Johan installing the LTU receiver system. (Photo: D. McKay-Bukowski)

Lars-Göran runs the cables back into the main building. (Photo: D. McKay-Bukowski)

Receiver/USRP installation on the Kiruna Demonstrator Array

This week a team from KAIRA/SGO and LTU, together with our colleagues from EISCAT, are working to install a digital beamforming system on the Kiruna Demonstrator Array. During the next week, we'll be featuring a few photographs from this busy time.

The Kiruna Demonstrator Array (Photo: D. McKay-Bukowski)

Current configuration, 6x4 dual-polarisation directional antennas. (Photo: D. McKay-Bukowski)

Lars-Göran digging out the duct entry points. Our previous experience from KAIRA
was absolutely invaluable for this part of the work. (Photo: D. McKay-Bukowski)

Laying the new (bright yellow!) ducting for the network cables. (Photo: D. McKay-Bukowski)

The Kiruna Demonstrator Array

As we wrote earlier, we went to Kiruna last week as part of the planning for the demonstrator array work. The Kiruna EISCAT Demonstrator Array is a phased array of 48 Yagi antennas, arranged in either a 4×12 grid or 4×6 grid... depending on he configuration. It operates at VHF frequencies and is capable of detecting signals from the VHF transmitter in Tromsø.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. Part of the work that the KAIRA team is carrying out is related to this work.

Curious engineers inspect one of the equipment
cabinets. (Photo: D. McKay-Bukowski)

The view along the array. Note the signal cables run
along the frame. (Photo: D. McKay-Bukowski)

Another view (in the sunshine!). But there is still a bit
of snow on the ground. (Photo: D. McKay-Bukowski)

Kiruna EISCAT site

Today we just have a photograph from the EISCAT radar receiver site at Kiruna, Sweden. (I used to live here once.)

EISCAT Mottagarstasjon, Kiruna. (Photo: D. McKay-Bukowski)

Aurora over the E3D meeting

During the EISCAT_3D "all-hands" meeting, we were treated to some mostly-clear skies and a bit of auroral activity too.

Some of the delegates at the E3D "all-hands" meeting. Photo: Esa Turunen

First international experiment

This week, KAIRA is participating for the first time in a large international experiment with baselines of several thousands of kilometres. Apart from hoping to discover some new science, this is a perfect opportunity to link EISCAT, LOFAR and, of course, KAIRA itself. As the week goes on, we will be incorporating more and more stations into this experiment network. However, on this first night of observing the following stations are involved (from North to South): 

• ESR (EISCAT Svalbard Radar, Norway)
• KAIRA (Kilpisjärvi Atmospheric Imaging Receiver Array, Finland)
• Kiruna (EISCAT receiver station, Sweden)
• SE607 (LOFAR station at Onsala, Sweden)
• DE604 (LOFAR station at Potsdam, Germany)
• UK608 (LOFAR station at Chilbolton, UK)
• FR606 (LOFAR station at Nançay, France)

 Putting them on the map, the layout is as follows:

The observations are being carried out at approximately 224 MHz (thus allowing us to use the Kiruna receiver station). The ESR is at a different frequency, but is providing concurrent observing. And both KAIRA and UK608 are using special observing modes. Kiruna and the ESR are conventional, mechanically-steered, parabolic dishes. The others are all LOFAR-design phased arrays.

People often ask if KAIRA is part of the LOFAR network. The answer to this is: "not directly". Although there are plans to one day link KAIRA directly to LOFAR via a high speed link, we are currently running as an independent station. While this gives us the flexibility to pursue our own science programme, it certainly does not preclude us from participating in large, important, observing experiment — like this one.

Oh... and we should also point out that although this particular experiment is being run by ASTRON, this work is being done by ASTRON staff at the KAIRA site!

Stay tuned as the week goes on as, no doubt, we will have some very interesting things to report!

Tetrastatic VHF

The EISCAT facility has a number of facilities scattered across Fenno-Scandinavia. These include two so-called "remote stations", located at Kiruna (Sweden) and Sodankylä (Finland), where there are 32m antennas which currently operate in the UHF band. However, due to encroaching radio-frequency interference the decision (announced this morning on the EISCAT weblog) has been made to convert these two dishes to VHF to be able to receive scattered signals from the Tromsø VHF transmitter. To quote from their post:

The EISCAT Council, on recommendation from the EISCAT Science Oversight Committee (SOC), decided that the remote UHF receivers located at Kiruna, Sweden, and Sodankylä, Finland, should be converted to the current VHF frequency of 224 MHz. The background to this is that the UHF frequency of 930 MHz lies within the radio band, which is nowadays used for GSM mobile communication, and the frequency protection, which was in place at the remote sites, has ended a while ago. In Sodankylä, e.g., we have noticed in autumn 2011, that new transmitters had come on-line, which makes incoherent scatter observations impossible due to interference. Thus the EISCAT Scientific Association has lost its unique capability of tristatic ISR measurements.

In order to preserve this ability, a plan has been made to convert the UHF 32-m parabolic dishes to 224 MHz in order to receive echoes of the Tromsø VHF radar signal when the radar points to zenith. Unfortunately, the VHF is not allowed to point further south than zenith, but it is estimated, that even at zenith, the remote sites will see the VHF signal. Astonishingly, even though the remote antennae are designed for the higher frequency, when considering all advantages and disadvantages of the conversion, they should perform at the VHF frequency just as well as at the UHF frequency.

What is not mentioned in the announcement is that KAIRA also operates in these frequencies. This means that not only is there the ability to carry out tri-static measurement with EISCAT at VHF freqencies, but with KAIRA there is a fourth station providing the ability for tetrastatic measurements. This is a fantastic oppotunity for us and makes some of the science possibilities even more interesting.

Arctic skies

When I lived in Kiruna, I took a lot of photographs of the open sky. Here's another one I'd like to share. It is a panorama, taken from the 32m dish, looking roughly north. I hope you enjoy it.


Have a nice weekend!

How do KAIRA and LOFAR work? — Part 6 : Squinted vision

But what if the radio signal is not coming in from directly overhead? Well, as that signal goes away from the vertical position, the result will decrease. Not only will the reflected signals miss the receiver, but they will be adding out of phase as well.

At some angles, the radio waves from different parts of the system interfere. This can result in zero signal at certain angles where the radio waves from the different parts arrive out of phase, and enhanced signal at other angles where the radio waves arrive in phase.

So if you have a set of reflectors that are carefully adjusted to give good signal addition in a particular incoming direction, and then your radio signal moves, you have to tilt the entire set of reflectors and the receiver to follow it. That is, you change the direction in which your system is most sensitive. This is the reason why radio dishes are usually made so that they can be steered.

But this presents problems: as the size of the system gets bigger, you need more and more steel for the backing structure, bigger and bigger motors and better and better controllers to cope with structural deformations at different angles, wind loading and so on.

The elevation motors on the Kiruna 32m antenna.

An azimuth motor drive and gearbox
(grey+red) on the Kiruna 32m antenna.

As a result there is a limit as to how far you can go. Thus the largest fully-steerable dishes are typically 100 metres in diameter, such as the Effelsberg Radio Telescope in Germany.

The Effelsberg 100m radio telescope, Germany

This sort of size is about the limit at which structural and cost considerations make further enlargement prohibitive. Let’s face it, a large moving steel structure is complicated, difficult to maintain and very expensive to build. But there is an alternative...

(For those of you who are patient enough to have followed this so far, we’ve now covered all the pre-amble and can get on with the interesting phased array topic later this week!)

Photographs: Derek McKay-Bukowski

Arctic twilight

Last Friday, I finished the week's web-logging with just a nice photograph. Since then, I've received loads of e-mails (where 'loads' = 2) saying that it was a great idea. So, let's try the experiment again!

This week's 'end-of-week' image is also from the EISCAT receiver station at Kiruna. Like the other photograph, I took this while I was living there in 2006. Although cloud often masks out the beautiful aurorae, sometimes having some clouds is not such a bad thing. And radio-dishes always make for wonderful silhouettes.

Have a nice weekend!

Kiruna 32m at dusk. (Photo: D. McKay-Bukowski)

Kiruna dusk

'I once lived in a place ...'

While going through the photographs for the previous weblog entry, I stumbled across this one. It was taken during the late summer at the Kiruna receiver station, which is part of the EISCAT radar er receiver network. At the time, this was also where I was living (I have a tendency to live at observatories). At this time of the day and year, the lights and colours of the sky can be breathtaking. So, as a nice way to finish the week, let's just end with a photograph.

Enjoy.

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.

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!

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.