LOFAR station FI609

KAIRA has been given an official LOFAR station designation: FI609.

All LOFAR stations have 5-character designations, which are used in the computer software as a shorthand to identify the station. For the Dutch stations, the first two characters are either: CS or RS for Core Station and Remote Station, respectively. For the international stations, the first two letters are a designation of the country in which the station is located.

The number that follows is the ID number. All international stations are in the 600s-range.

• 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

And now we can proudly add:

• LOFAR FI609 — Kilpisjärvi, Finland

All we have to do now, is get it built! (More on that next week)

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 11 : Ambiguities

As we’ve seen over the past few instalments of this series, as the direction in which the radio waves approach the telescope changes, the received signals will go out of phase. This effect reduces the sensitivity of the telescope in that particular direction. Additionally, by adding a delay to the electrical signals (whether the analogue electrical signals or the digitised version) the direction in which the telescope is sensitive can be moved.

But there is a problem.

As the incoming direction changes, the signals go out of phase, and thus cancel. However, if the direction continues to change, the signals can actually start to come back in phase again. The peak of one wavefront signal comes through one receiver and adds together with the peak of a different wavefront signal that has come through the other receiver. Click on the following image to get a full-sized version and you'll see what we mean.


At first appearance this might seem like a good thing, as the telescope seems to be sensitive to several directions at once. But it is not. Instead, this leads to an ambiguity. If a signal is received, it is impossible to tell whether that source of that signal is at the ‘on axis’ direction of the telescope, or is in a region off to one side.

These directions of sensitivity that are not in the intended pointing direction of the array are referred to as ‘sidelobes’.

However, there is a way to alleviate this. This is done by adding more receivers to the array. In our example, let’s consider adding a 3rd receiver between the original two. Now, even though there may be ambiguity on the signals received by the first two receivers, the middle receiver is out of phase with the others.

The addition of additional receiving elements helps reduce the sensitivity of some of the unintended directions. This effect is sometimes referred to as ‘suppressing the sidelobes’. If we were to sketch a graph showing an approximation of the sensitivity of the system to a particular direction as we look at angles to the left and right of the primary pointing direction, it would look something like this:
Adding more and more receivers improves this even further. As more receivers are added, it will have the effect of suppressing more of the sidelobes and thus reduce the ambiguity of the telescope.

First LOFAR sites on Google Maps

There's always been some speculation as to which LOFAR stations would appear on the Satellite-view on Google-maps first. Well, it seems that two have made the claim for first place.

DE601 Effelsberg

The Effelsberg LOFAR station is located in North Rhine-Westphalia. The facility is also home to the 100m radio telescope. In the view shown by Google-Maps, the 100m dish is in the north. Below it is the LBA of the LOFAR station (with a zig-zag path running through it). And then, there is the HBA to the south. In the Effelsberg system, the HBA is not in the regular configuration as a conventional international station.



Größere Kartenansicht




DE603 Tautenburg

Tautenburg is a municipality in Thuringia, Germany. It is home to the Karl Schwarzschild Observatory, which is home to the largest optical telescope in Germany (2m mirror). The observatory is set in beautiful forest land. In the satellite image, the LOFAR fields dominate the clearing; the HBA is on the left and the LBA is on the right. The small round building just north of the LOFAR field houses the 2m optical telescope.


Größere Kartenansicht / Enlargement


Although seeing these images on Google-Maps is just a bit of fun, it is useful to see the size of the fields in the context of surrounding structures and the general landscape. A full map showing the location of all the LOFAR stations (excl. KAIRA) is provided on the LOFAR website. Take a look over the next few months and see if you can see any other stations 'appearing' in the satellite images!


Websites

Effelsberg: http://www.mpifr.de/english/radiotelescope/
Tautenburg: http://www.tls-tautenburg.de/research/lofar/index.html
LOFAR map: http://www.astron.nl/~heald/lofarStatusMap.html

How do KAIRA and LOFAR work? — Part 10 : Multi-beam operations

As we saw in the last web log entry in this series, digitising the signals gives some distinct benefits when it comes to adding a delay. Apart from being able to do it very precisely, you can change it quickly. However, digital data has another massive advantage.

It can be easily copied.

So, if you make a copy of your digital data, you can process each copy however you want. If you want to filter it differently (for example, to ‘listen’ at a different frequency) you can. However, you can also make a copy and apply different sets of delays to it. This means that if one copy of the data has one set of delays and another copy has a different set for the different antennas involved, then these two copies will be sensitive to different directions.

In other words the telescope will be looking in two different directions at once!

This technique of introducing delays and combining the signals to change the direction in which the telescope is sensitive is known as ‘beamforming’. And making digital copies and delaying them differently to sensitive in several directions is called ‘multiple beamforming’ (or sometimes ‘forming multiple beams’).


In the above diagram (which you can click to see a larger version), each received signal is digitised and split into two copies. The copies are fed into the different digital delay units (D1, D2, D3 & D4). Let’s say that D1 and D3 have no delay at all. The added signal from these will be sensitive to something from directly overhead. In this case, the original radio signal was coming in obliquely; it adds out-of-phase and no output is seen. On the other hand, by adding a delay to D2 (but not D4), the added signal from these will be sensitive to the oblique radio wave. It adds in phase and a strong output is seen.

Because the data is digital, you can copy and delay it as much as you want and there is no degradation of the signal. If you want to be sensitive in more directions, simply add more copies, delay units and adders. The limits are not related to the signal, but rather to issues of equipment, memory, power, space (... and ultimately the project budget).

In practice, systems like KAIRA and LOFAR are also limited by the amount of digital signal processing equipment. At the time of writing this, LOFAR is routinely operating with up to 30 or so different beams. However, some experimental observations have been carried out with over 250 beams.

Sticks in the snow

Just a nice image to finish the week. This photograph was taken from the Sodankylä Geophysical Observatory (SGO), looking across the Kitinen River. Enjoy!


Photo: D. McKay-Bukowski

Mid-April snow assessment — Part 3

In the last photograph from the Mid-April snow assessment (also from 15^th May 2011), we show the 'raised tile'.

Although there is still some drift snow on the sides, the general level of the snow has fallen away considerable. The cover the tile is moderately clear, although some icy patch remains in the middle.

Mid-April snow assessment — Part 2

Following on from yesterday, here are some photographs of the 'ground tile'. These were also taken on the 15^th April 2011. As you can see, the snow is starting to clear from the cover. In the first photograph, South is roughly at the left. However, at this time of the year, the direct sunlight is starting to come in from a wide range of angles.


Here's another view of the same tile, but taken from the side (90 degrees to the first photograph).


If you remember that the height of a LOFAR tile is 50cm, you can see that the snow is still that deep in places, mostly due to wind-sweeping. On the downwind side, the snow depth drops away.

Mid-April snow assessment — Part 1

The middle of April has been and gone and the time of the build draws ever nearer. Plans are already in place for the snow-clearing and testing. Here's a photograph (taken on 15^th April 2011) of one of the 'snow-marker' posts on the line-fence around the site.

Atmospheric research at Kilpisjärvi — Part 3

Also at Kilpisjärvi, SGO operates an AARDDVARK VLF-receiver next to IRIS antenna field that we described yesterday. The VLF-receiver detects changes in ionisation levels from 30 to 85km altitude in the 11 different propagation paths of VLF-transmitter signals at the frequency band 16.4-37.5 kHz. The Kilpisjärvi receiver is part of the wider receiver network. SGO has another AARDDVARK receiver in Sodankylä.

The AARDDVARK antennas. (Photo: Tero Raita)

One of the ionospheric tomography receivers of SGO is also in Kilpisjärvi. Transmitted beacon signals of the Russian low-earth-orbit satellites are used to calculate tomographic electron density maps of the F-region ionosphere. Currently 250-300 electron density reconstructions per month are processed from the data of five receiver stations across Finland and Sweden.

The tomography antenna (having just been cleared of snow).

It is a little difficult to see, but you should be able to make it
out in the foreground of the image. In the background you
can see the mighty Saana mountain. (Photo: Tero Raita)

Today most of the instruments are located near the Kilpisjärvi biological station, which is administered by the University of Helsinki. The radio instruments running in continuous-operation mode offer valuable long-term scientific datasets. The optical instruments, which only operate at night time are somewhat limited and are generally only being used from October to April due to the nightless summer time in the Arctic.

* * *

That concludes our mini-series on Atmospheric research at Kilpisjärvi. Thanks go to Tero Raita for the articles and photographs.

Atmospheric research at Kilpisjärvi — Part 2

Today we continue our guest article series by Tero Raita.

Monitoring of cosmic radio noise absorption in the D-region ionosphere (50-90km) by riometers (relative ionospheric opacity meter) started in 1980. Since 1997 SGO has operated Imaging Riometer for Ionospheric Studies (IRIS) together with University of Lancaster (for more details see: http://spears.lancs.ac.uk/iris/ ). 64 antenna elements forms 49 beams, which are sampled once per second. Beams of IRIS Kilpisjärvi overlap with present EISCAT radar range and EISCAT heater beam. And, of course, they will also overlap with the KAIRA project.

Antennas of the IRIS array. In the background are
the observatory buildings. (Photo: Tero Raita)

Geomagnetic field variations in Kilpisjärvi have been measured with variometer and three component search coil magnetometer. In 1983 Kilpisjärvi received an EISCAT cross magnetometer station. Today the variometer is part of the wider IMAGE magnetometer network. Search coil magnetometer, which are able to see higher frequencies of the field variations like Pc1 magnetic pulsations, was deployed for the support of Swedish satellite projects (FREJA and POLAR) and the instrument was operated by Department of Physics (University of Oulu). Today the whole Finnish pulsation network is operated by SGO.

Atmospheric research at Kilpisjärvi — Part 1

Despite what one might think, KAIRA is definitely not the first atmospheric or astronomical project to be established in the Kilpisjärvi area. For the next few days, we'll be featuring a multi-part series on the other instrumentation located in the region. Thanks go to Tero Raita for providing the text and photographs.

Kilpisjärvi has long history of over 30 years of scientific observation, mostly related to the Northern Lights and ionospheric processes. The Finnish Meteorological Institute has operated an all-sky camera in Kilpisjärvi since 1978. Combined with other all-sky cameras in the region, it has given good statistical information about the occurrence of the Aurorae Borealis throughout Northern Finland.

Measurements of absolute luminous intensity of the aurora emissions by photometers over winter periods started in 1979 in co-operation with the Swedish and the Canadian scientific communities. Meridian scanning and zenith photometers, developed by Department of Physics, University of Oulu, have been used in Kilpisjärvi since 1986. Also aurora TV-cameras and recently developed digital spectrograms are used today to monitor aurora processes.

The scientific observatory at Kilpisjärvi. In the background,
you can see the Saana mountain. (Photo: Tero Raita)

We'll continue with a more detailed description of some of the instruments tomorrow.

Radio bands

Throughout this web log, there are lots of references to the radio bands: UHF, VHF, VLF, etc. For example, KAIRA will receive VHF frequencies, whereas some of the EISCAT radars operate at VHF, where others work at UHF frequencies. This chart is to put them all in perspective with respect to each other.

Abbreviation	Frequency Range	Wavelength Range	Name
ELF	3 to 30 Hz	10,000 to 100,000 km	Extremely low frequency
SLF	30 to 300 Hz	1000 to 10,000 km	Super low frequency
ULF	300 to 3000 Hz	100 to 1000 km	Ultra low frequency
VLF	3 to 30 kHz	10 to 100 km	Very low frequency
LF	30 to 300 kHz	1 to 10 km	Low frequency
MF	300 to 3000 kHz	100 to 1000 m	Medium frequency
HF	3 to 30 MHz	10 to 100 m	High frequency
VHF	30 to 300 MHz	1 to 10 m	Very high frequency
UHF	300 to 3000 MHz	10 to 100 cm	Ultra high frequency
SHF	3 to 30 GHz	1 to 10 cm	Super high frequency
EHF	30 to 300 GHz	1 to 10 mm	Extremely high frequency

The two arrays of KAIRA will operate in the high and low ends of the VHF band. The KAIRA HBA will work from 120-240MHz and the KAIRA LBA will operate from 30-80 MHz. As explained earlier, there is a gap between the two, as this is where FM-radio broadcasts occur, and it is impossible to conduct delicate scientific experiments in this region of the spectrum due to such broadcasts.

Ref: http://en.wikipedia.org/wiki/ITU_Radio_Bands

Little house in the snow-drifts

This photograph was taken at the Sodankylä Geophysical Observatory (SGO) last month. Apart from showing plenty of snow, it also shows how easily it can be blown about by the wind.

Snow like this (drift snow), is picked up where the wind is stronger and tends to drop back out of the air where it slows down. This is often where there is a change in the direction of the air-flow, such as a stationary object or where there is a drop or rise in the landscape.

For KAIRA, we hope to mitigate the accumulation of snow drifts by raising our HBA tiles up to a height of approximately 2 metres. Because the air moves slower closer to the ground, one can typically expect a increase in the air speed as you go further up. This is partly what the winter testing has been demonstrating. As increased levels of snow blown by the wind can easily exceed that of directly-fallen snow, this is a serious issue that we need to consider carefully as part of the HBA evaluation.

Photo: D. McKay-Bukowski

Little pinecone

:

little pinecone,
waiting for the spring,
hoping to bask in the sunshine,
and not lie buried in another snowfall.

::

little pinecone,
watch the world above,
see the faint northern lights,
play through the branches of the forest.

::

little pinecone,
but only for a while,
next year you'll be a sapling,
and one day the tallest tree in the land.

:::
:::

Photo&text: Derek McKay-Bukowski; SGO, March 2011.

High-power large aperture radars

High-power large aperture radars were first envisioned by Bill Gordon (1958) as instruments that can measure the incoherent scatter from free electrons in the Earth's ionosphere. He also proposed that such a radar could be used to observe the Sun and various planetary targets. The first experimental measurements of ionospheric incoherent scatter was soon thereafter reported by Bowles (1958), and many of the other goals were also soon realized when the Jicamarca Radio Observatory and the Arecibo Ionospheric Observatory were built. Both of these radars are still the largest in the world, and have contributed much to our knowledge of Earth's atmosphere and space. The Jicamarca radar located in Peru has a square shaped phased array antenna field with dimensions of 300*300 m. The Arecibo Ionospheric Observatory in Puerto Rico has a spherical dish with a diameter of 305 meters.


Since the early days, many more high-power large aperture radars have been built in various places around the world: These include the Millstone Hill, Svalbard, Tromsø UHF, Tromsø VHF, Kharkiv, Irkutsk, MU, Sondrestrom, PROUST, Poker Flat, and Resolute Bay radars. There are also various large radars of comparable size around the world used for space surveillance purposes. The most recently built Poker Flat and Resolute Bay radars are digital phased array radars, which allow fast beam steering and allow 3D imaging of the ionosphere. The KAIRA receiver array will also be a phased array system, which will function as a bistatic receiver for the Tromsø VHF radar. Some of these radars are shown in the following figure

High-power large aperture radar systems of the world. Photograph credits: Arecibo (NAIC), Jicamarca (JRO), Tromsø (EISCAT Scientific Association), Svalbard (Tony van Eyken), Millstone Hill (MIT Haystack), Kharkiv (Institute of Ionosphere, Kharkiv), Poker Flat and Resolute Bay (Craig Heinsleman).

As the name already suggests, high-power large aperture radars are radars with large antenna aperture and transmission power. As the beam width of an antenna is typically inversely related with the collecting area, these radars also have fairly narrow beams (typically 1 degree). They also typically transmit fairly long coded pulses in order to increase the average transmitted power. In some bi-static planetary radar applications the transmission can be continuous.

While the primary purpose of most high-power large aperture radars is the study of ionospheric plasma, they can also be used for a large variety of other uses, including meteor, space debris, planetary , and lower atmospheric studies.

Snowmobiles

In the Arctic, one form of winter transport is the snowmobile. These vehicles — half-tracked, half-skis — are used to traverse terrain that is completely covered in ice and snow and that is generally inaccessible to other vehicles.

One of the KAIRA team during a snowmobile
expedition in late march. (Photo: Th. Ulich)

Although they can go just about anywhere, there are certain paths that are marked across the landscape that are for 'regular' snowmobile traffic. These paths are marked with crossed red bars on posts to indicate the way.

A snowmobile trail post. (Photo: D. McKay-Bukowski)

When looking at photographs of the KAIRA site, you may see some of these markers in the background, as there is a marked snowmobile trail in the vicinity of the proposed KAIRA low-band array.

Aerial photographs of LOFAR-UK Chilbolton

Some dramatic photographs have just been posted on the Press and Media Image Library of the UK's Science and Technology Facilities Council (STFC). These show the LOFAR station at Chilbolton, Hampshire, UK, as seen from the air. Although there are plenty of photographs of various LOFAR stations from the ground, and plenty of diagrams showing the layout of the sites, this is a good opportunity to get a bird's-eye view of what a station looks like.

The credit for all these images goes to Guy Gratton, who took the photographs during the afternoon of Friday 8th April 2011, and who graciously gave permission for their use by the STFC/LOFAR community. The images were taken from an aeroplane flying at an altitude of approximately 300 metres (1000 ft) over the site, through an open door on the aircraft to avoid any window reflections.

The LOFAR-UK site, as seen from the air.
(Photo: Guy Gratton (c) 2011, hosted by STFC.)

The above photograph is a great way to appreciate the scale of an international LOFAR station. The dish near the top of the photograph is the 25m parabola of the Chilbolton Observatory.

Looking specifically at the LOFAR-UK station (LOFAR-ID = UK608). The HBA
is on the left and the LBA is on the right. If you look carefully, you can just
make out the RF-container in the space between where the two fields meet
and the access road. (Photo: Guy Gratton (c) 2011, hosted by STFC.)

Banking away from the LOFAR field, you
can see the Chilbolton 25m dish (Photo:
Guy Gratton (c) 2011, hosted by STFC.)

When you start to move further back, more the surrounding facilities become apparent. Apart from the main 25m dish, there is a small 4.5m dish on the right-hand side, just below the LOFAR compound. (Don't forget you can click on images for a slightly enlarged view.)

Looking at the site from even further away, the

scale of the Chilbolton Observatory becomes clear.
(Photo: Guy Gratton (c) 2011, hosted by STFC.)

Check the STFC's Press and Media Image Library for all high-quality photographs of the LOFAR-UK station. You can also find full-resolution versions of some of the above photographs, suitable for use in printed media. Thanks goes to the Chilbolton Observatory and UK608 project teams, the RAL-Space outreach team and, of course, Guy Gratton for the great photographs.

Ground tile begins to emerge

Another set of photographs have come back from the site at Kilpisjärvi. What was most notable from them was the image that shows the ground test tile starting to emerge from the snow. In the image below, taken on 7^th April 2011, you can see the outline of the corners where the HBA tile is beginning to melt its way through the cover.


Because the tiles themselves are black, they will warm considerably when in direct sunlight, thus accelerating the melting in the exposed areas. It will be interesting to watch this tile emerge during the Spring.

Arctic photographers

There have been a number of people involved in the photographic documentation of the project. Apart from the author of this post, other members of the KAIRA team have contributed a number of photographs of the project... mostly from the installation of the test tiles. Also, as we saw recently, there was a special site inspection by Tero Raita (who was responsible for the stunning photographs in the glorious late-March sunshine). Obviously, we are indebted to him and all the others from SGO & FMI who have helped us with this.

However, throughout the winter we have been receiving weekly updates, photographs and reports. Although these have been processed and published by the KAIRA team at SGO, we must admit that the usual person who braves the not-so-pleasant Arctic weather to take those photographs and check the site is Oula Kalttopää from the Kilpisjärvi Biological Station, which is run by the University of Helsinki. A quick search on Oula's name reveals that the KAIRA project are not the only ones he has assisted over the years. And we want to add our name to those who appreciate his assistance in our project.

Kiitos!

Buried vehicles

No caption necessary. (Most people will
know how to react to a scene like this!)

Photo: Derek McKay-Bukowski, March 2011, SGO

EGU name badge

Pack up your schedule
and your old name badge
and smile, smile, smile...

Well, that's it. The EGU GA 2011 is over. It's time to pack up and head home. It has been a busy week — really hectic — but it's been great. A fantastic opportunity to meet with other scientists and share results and ideas.

EGU posters

One of the poster sessions at the EGU GA 2011.

Photo: Derek McKay-Bukowski

EGU flags

Out the front of the Austria Centre, there are the bright yellow flags of the European Geosciences Union General Assembly 2011. Just the first a some light photographs to finish off the Friday afternoon.

Photo: Derek McKay-Bukowski

Sharing technology

With the rapid deployment of new radio experiments exploiting the latest in antenna design, receiver systems and digital signal processing, it is easy to forget the common ground as projects forge ahead in their particular research directions. Yet, this is precisely where cross-discipline collaboration is ideally placed to identify and capitalise on hard-won experience and valuable lessons. The KAIRA (Kilpisjärvi Atmospheric Imaging Receiver Array) project intends to do just that. Drawing heavily on the advances in the astrophysics community, our system makes use of not only research technology, but also on the experience of deployment and commissioning.

It is only through the use of existing system design and established knowledge that KAIRA can aim to complete the ambitious build programme set out for this summer, overcoming climate and site considerations to achieve success. Furthermore, by tactical use of previous project experience, major cost savings can be made, thus making the project even more scientifically attractive.

Our feature today at the EGU GA 2011 conference highlights the links between the KAIRA and LOFAR projects and shows the areas where common technology and staff-learning can be deployed to the strategic advantage of both projects. It also looks ahead to future possible collaborations and identifies candidates such as SKA and EISCAT.


Poster presentation:
Hall Z / Author in attendance Fri, 08 Apr, 15:30–17:00
Z119 EGU2011-13106
Lateral Thinking - Sharing Technology Across Disciplines
Derek McKay-Bukowski and The KAIRA Project Team

Name in the snow

One can never tire of playing with freshly fallen snow.

Photo: Derek McKay-Bukowski, March 2011, SGO

World Wide Lightning Location Network

Just how many storms are there in the world at any given time? In a presentation just given at the EGU GA 2011, recent results show that previous estimates are probably too high. Dating from the 1920s, assessments assumed approximately 1800 storms were active at any given time. This figure was revised in the 1950s to 2200-3600, although it sank back in the 2000s with satellite date.

Now, however, the World Wide Lightning Location Network, operated by the University of Washington in Seattle, has revised this figure and the initial results show that it could be much lower... perhaps even as low as 750. However, there is great seasonal and daily variability and these results are preliminary at this stage. However, if their suggestion is validated, it will give us a new view on these atmospheric effects.

World-wide lightning detection is often done by detecting VLF radio bursts. Networks of receiving stations are located all over the world (including at the SGO in Sodankylä). By itself, the SGO station is not very useful, since you need at least three stations to locate a lightning.
Also, lightnings closer than 500 km are filtered out (saturation), so we are mostly monitoring lightnings outside Finland. In theory SGO could see any lightnings at any given location, but in reality it cannot see the weak ones and not from the other side of the globe. However, SGO can certainly directly monitor tropical evening activity in Africa, which is pretty remarkable when you think how far away it is.

Although KAIRA will not participate directly in this large-scale monitoring programme, its ability to receive VHF radio bursts from lightning will provide an opportunity to supplement atmospheric electrical research.

Website: http://wwlln.net/

How do KAIRA and LOFAR work? — Part 9 : Digital beam steering

As we saw in the last web log post on how it all works, we can adjust the cable length and thus the delay in the electrical signal to determine which directions will add in-phase (and thus be stronger) and which will add out-of-phase (and hence cancel each other out).

Although this is sometimes done by adding more cable, it doesn’t have to be. The only thing that is important is that there is the correct delay.

So, instead of using cable, we can digitise the signal and then save the data, wait a little while, and only then load them back again to feed into the adding electronics.If you are constantly taking digital data and storing them, then it is exactly the same as writing numbers into sequential memory. And if you are reading them back out at a fixed delay, then it is the effectively same thing: reading numbers from sequential memory.

As long as those data are always being written into the memory at a nice fixed rate, and are being read back out again at the same rate, all you need to do is adjust the offset between the write position and the read position and you are controlling the delay.

The limitations are that the accuracy at which you represent the incoming wave is a function of the speed at which it is being sampled. Fast memory and fast sampling requires some sophisticated electronics. There is also a limitation that the total amount of delay you can add is a function of the speed at which you are writing/reading and the total amount of memory you have.

However, with modern digital electronics, this sort of memory is relatively cheap. Additionally, changing that write-read offset (and thus the delay) can be done very quickly. As a result, you can change the signal delays, and hence the pointing direction of the entire array very quickly. To go from one side of the sky to the other takes something in the order of a millisecond.

Try doing that with a 100m radio dish!

Alternatively, you can gradually adjust the delay and move the sensitivity of the array quite slowly. This is ideal for tracking celestial sources as they appear to move slowly across the sky due to the Earth’s rotation.

However, despite the power of digital signal processing on changing the directional sensitivity of the phased array, there is another benefit as well. Stay tuned!

EISCAT_3D in the GeoCinema

The EISCAT_3D information film about EISCAT_3D is part of the programme at GeoCinema during the General Assembly 2011 of the European Geosciences Union in Vienna, Austria.

The film, produced by FFAB:UK together with EISCAT Scientific Association, explains the background, the concept, and some of the new science that will be possible when the EISCAT_3D facilities are completed.

The showing is scheduled at 11:30 on Wednesday 6th April. Do not miss this chance to see the film in the GeoCinema if you are in Vienna!

Planet Under Pressure 2012

A series of three powerful presentations on the past, present and future of climate and change, and humanities reaction to it, have been presented at the EGU General Assembly 2011. Examining factors such as ice melting rates in Greenland and Antarctica, as well as looking at the pre-historic records for large scale atmospheric change millions of years ago, the data presented showed large fluctuations in climatic conditions, but not on the rapidity of change that currently exists. Although individual measurements show the expected statistical variations associated with such a complex system, what is clear is the systematic trend and the stress that it will put on human systems: social and economic, as well as aspects of resource management.

As the subject develops, the scientific community is diversifying from just measuring and understanding the changes, but also to the strategy for coping with it. A major conference will be held on this next year. Details can be found at their website: http://www.planetunderpressure2012.net/

See also: http://egutoday.wordpress.com/2010/05/06/science-under-fire-5/

EGU 2011 GA welcome!

The EGU General Assembly 2011 in Vienna has begun!

How do KAIRA and LOFAR work? — Part 8 : Steering a phased array

Last time, we saw that a couple of detectors can be used to collect signals and that because they will add in phase from some directions and not others, there is a certain directionality to the system.

In principle, you can ‘steer’ this system to look in different directions by tipping it, but that’s not particularly efficient. The real advantage is that without moving the antennas you can change the directionality of the overall system by changing the lengths of the cables.

Let’s consider the off-zenith case from the last part.

If we now add a bit of extra cable, these off-zenith signals now add in-phase again.

In fact, the zenith signals are the ones now out of phase when they are combined electrically. So, by adding some cable length, you can control the direction in which the array is sensitive. That is, you can steer its ‘looking direction’ around the sky without actually moving the antennas themselves.

Some phased arrays indeed use cables to adjust their pointing direction. The VHF radar in Tromsø is one such system. It is mechanically steered in the vertical direction and horizontally pointed with a phased array. By manually changing the cables, the horizontal pointing direction of the array can be altered by 15 degrees.

A view inside the feeder bridge of the VHF system
at Tromsø. (Photo courtesy Mike Rietveld)

Because this needs to be done by hand, it is not patch the cables that quickly, so these sorts of directional changes are not done too often.

Although still useful (rotating a 120×40m antenna in azimuth is tricky!) there is another technique which has recently become affordable and which makes arrays like KAIRA, LOFAR and the SKA practical.

EGU 2011 reception

The reception for the EGU 2011 General Assembly has now been held at the Austria Centre Vienna. As you might imagine, there are a lot of delegates and the place is buzzing with colleagues re-united, interesting discussions and the latest news. It is going to be a busy and exciting week!

Photo: D. McKay-Bukowski.

Ready for EGU GA 2011

The EGU General Assembly 2011 is beginning now. Today delegates from around the world are arriving for this prestigious conference. It is being held held at the Austria Centre Vienna (ACV).

EGU has a strong web presence and there will be a lot of opportunities for those not able to attend the event to see what is happening and stay in touch with the latest announcements, discoveries and results as they are announced.

• EGU2011 web log: http://egu2011.wordpress.com/
• EGU2011 Twitter Feed: @egu2011
• EGU Today mobile: http://www.egutoday.eu/
• EGU Today web log: http://egutoday.wordpress.com/

KAIRA will be represented at the meeting with a presentation at Session ST3.4 and a poster paper on display at board number Z119 in hall Z.

Photographs, announcements and lots of updates will follow during the week!

Kitinen iced over

This is the Kitinen River. It flows past the Sodankylä Geophysical Observatory (SGO). When we last wrote about the SGO, we mentioned that it was on the banks of the river. Of course, back then in the dead of the polar night it was impossible to get a photograph. Well... we're putting that to rights today.


Here it is, as seen from the shore. The tracks that go out and then to the right are from a reindeer. Of course, the river is completely iced over at this time of year. But the image does give one a nice sense of the beautiful landscape at the observatory. In summer, we'll try to take another photograph of the Kitinen from the same location to compare the seasons. (Click of the image for a larger version.)

Photo: Derek McKay-Bukowski

Deciduous Trees

The area around the Sodankylä Geophysical Observatory is heavily forested. There is a good mix of trees from the conifers featured in previous posts, to the ghostly deciduous trees (as featured in this post). The photograph provides a quiet way to end end week, as next week will be very busy with the EGU 2011 conference.

But, for now, have a peaceful weekend.


Photo: D. McKay-Bukowski