Meteoroid strikes Saturn's rings

Recently, scientists have been investigating something strange with the rings of Saturn. These are strange lines that appear... quite brightly too. It is now believed that these are debris clouds, formed when meteoroids impact with the material in the rings themselves. An news item has just be posted up on the U. Oulu website about this exciting finding and announces the article that has been published on 26th April, with contributions from J. Schmidt from the University of Oulu. Quoting from it...

Meteoroids, for instance visible as bright meteors in earths atmosphere, exist all over the Solar System and it has long been anticipated that they constantly erode Saturn's rings. The rings are made of water ice particles that are partly pulverized when struck by an impact of several tens of km/s. The erosion rate of the rings, and also their pollution with external material provided by the meteoroids, is of ultimate importance for the ongoing controversial scientific debate on the age of Saturn's ring system and how it has been created.These debris clouds, providing direct evidence for the meteoritic ring erosion, were observed now for the first time. This was possible in images taken at a very special geometry, when in 2009 the sun was illuminating the Saturn system edge on, which happens only every 15 years. In this geometry the rings remain relatively dark, while the debris still stands out in full sunshine above the ring plane, making the detection possible.

 Full details:

http://www.oulu.fi/english/news/2013/04/meteoroid-impacts-shatter-saturns-rings

Dismantling the winter-test aerials

During the past year, we've had three aerials out in the swamp to the north-northwest of the arrays. The original plan was to put the LBA array there, but the ground turned out to be too unstable and too difficult to work. That led to our current arrangement... which is working very well!

However, there were still the three test aerials there, and they were left for the dead of winter.

However, we have now dismantled them and have recovered the components.

Brining in the aerials. (Photo: T. Iinatti)

To fetch them, this meant going out there with the snow-mobile and snow-trailer and then digging them out. Although this sounds pretty arduous, it is better than dealing with the swamp and the clouds of mosquitoes in the summer!

The swamp field is now completely clear of all equipment.

LBA condition

Of course, the past few weblog posts have focused on the HBA array. but what of the LBA aerials? How are they faring?

Actually... they are doing extremely well!

There is a uniform coverage of snow over the field (which is ideal) and there is no evidence of lateral shift. Also pleasing, is the fact there is no build up of ice on the wires.

The LBA array field.

 The cable mausoleum remains mostly buried though. This is okay... thankfully we have no need to access the inside of it at the moment!

The LBA-cable mausoleum.

Photos by T. Iinatti.

EU students learn about radar

Hello all KAIRA readers,

Juha Vierinen suggested that I contribute to the KAIRA blog, and I'm happy to do so.  By way of introduction, I'm Phil Erickson, a radio science and space plasma physicist from MIT Haystack Observatory on the east coast of the US in Westford, MA.  My activities include leading the team which operates the Millstone Hill large power-aperture ionospheric radar system, one of several large programs at Haystack.  I'll describe more fully our various activities and science in a future post.

This week, though, I've been away from home doing some guest lecturing to an up and coming set of students.  For several years now, a number of European universities have pooled their resources to offer a 2 year masters' degree program in space science and technology.  The Erasmus Mundus Space Masters course covers a wide range of topics, with both engineering and science tracks as choices in the second year.  As a frequent collaborator with the EISCAT ionospheric radar systems, the Space Masters program invited me to come and give several guest radar lectures as part of their first year core Radar and Optics unit.

I had the pleasure this year to work with nearly 50 interested students who asked great questions and managed to stay awake for all the material!  To make it interesting, we spent an afternoon using a MIT IAP small radar system, a marvelous teaching tool and useful radar in its own right developed by Dr. Greg Charvat and Dr. Alan Fenn at MIT Lincoln Laboratory.  This system is also known as the 'Cantenna' radar, for the distinct transmit and receive antennas on the front made from tin cans.  Running on 8 AA batteries and using a combination of laptop sound cards and MATLAB for simple signal processing, the radar fits on a kitchen cutting board and is fully capable of both Doppler and range measurements out to a considerable distance.  We however stuck to the first floor of the IRF classroom wing.  Since the students see a lot of material describing large systems, it is always nice to demonstrate that the same principles apply whether the radar is small or big.

I ship the radar ahead of time to avoid packing it in my bags, but always build the antennas anew before each run.  Normally, the antennas are containers holding the local ground coffee blend, but this year's students got an extra treat.  A trip to the local Coop supermarket yielded two tins holding biscotti - "Cantuccini Skorpor" (appropriate first word; the second is simply "biscuit" in Swedish) - and so the class got to munch on them while we ran the system.  You can see the transmitting antenna on the right and the receiving antenna on the left doing their work in our "Cantuccini" system in the photo below.

[Credit goes to Dr. Craig Heinselman, the EISCAT director, for suggesting the biscotti cans.]

(photo by Simon Delchambre)

The course is held at IRF, the Swedish Institute for Space Physics, up in northern Sweden.  IRF is a very pleasant place to visit for both collaborations and for the beauty of the arctic landscape.  Although spring is arriving and the temperatures are getting warmer, there is still a lot of snow on the ground in April for this New Englander!  I do recognize the grey skies, though.

It was great fun as usual, and it was very nice to do my part in transmitting (sorry for the bad pun) radar fundamentals to a new generation of science and technical learners.  Good luck to all in the future!

HBA repairs

The covers on the HBA are a thick UV-resistant plastic. They are secured using elastic going to screws into the timber of the framesets. Due to snow loading, wind stretching and other factors causing shift, these covers need tightening.

As the winter snow starts to recede, we are seeing instances of this stretching and the occasional loose elastic. Especially on tiles H65 and H75.

Loose HBA covers.

This particular elastic has come off completely!

As part of the servicing, we will be tightening all the connections. One advantage of the connection to timber framesets, is that this is relatively strightforward to do.

We hope that with time we can build up a better understanding of the effect, so that we can apply the knowledge to the EISCAT_3D project.

Photos by T. Iinatti.

Under the tiles

In addition to the site perimeter, we have also check underneath the HBA tiles. Of course that required a bit of digging to get to the hatch...

Digging down to get to the antenna hatch.

And, as expected, the conditions underneath the antennas are good. There is relatively little snow blown under and the original framesets are holding up well.

Conditions under the north-western section of the HBA array.

Photos by T. Iinatti.

Checking the fences

Today we have come more photographs from the recent site visit. One thing that is important to check is the condition of the fences. not just that they remain intact, but also that they are not dangerous to others... be it wildlife or people.

At this time of year, the work is done by snowmobile and snow-trailer.

Here the snow is quite deep!

Patrolling along the boundary.

Photos by: T Iinatti.

First observations from Birr's new test array

As we reported a few day ago, the Irish LOFAR (I-LOFAR) team have installed four refurbished LBA aerials at the Birr Castle site. The aerials themselves were installed on the 18th and 19th April 2013 and the system was connected up to two low-cost Callisto receivers and switched on.

Then, on 22nd April, there was an M-class solar flare, which the Birr LOFAR test station picked up without any trouble at all.

First result from the I-LOFAR test array. (Image: www.lofar.ie)

As you might imagine, the scientists there are thrilled with the result, and the KAIRA team are also delighted to see our colleagues make such rapid progress. Well done I-LOFAR!

Let's hope now that, inspired by this result, Ireland can continue to invest in this productive and successful scientific endeavour.

Read the full-story on their website:  http://www.lofar.ie/

Snow levels at KAIRA

Last week, a small expedition was sent out to the KAIRA station to carry out some maintenance work and to do the first post-winter check. We'll be posting up some of the photographs over the next couple of days.

First up, there is the general site conditions. Over the winter there was relatively little snow. The maximum depth only reached 80 cm, which is considerably down on the typical average (95cm).

Looking along the side access towards the cabins.

The snow corridor between the HBA tiles.

Along the edge of the HBA.

Snow depth in the HBA `snow corridors' is considerably deeper than the general average due to the fact that blown snow from the top of the array accumulates there. In these places, depths ranged from 120 to 190 cm.

All photographs were taken on 17-Apr-2013 by T. Iinatti.

Not much skiing left...

Although others may beg to disagree, in my opinion Winter is the best time of year: long nights, short days, decent temperature and plenty of snow. Having inherited a pair of metsäsukset (Finnish forest skis, 2.6m long) I've been making the most of the season. Although used to downhill skiing from my days in Bayern, it is still great fun and lots of good exercise to glide through the trees on the way to/from work.

But spring is now upon us and even in the few days since the above photograph was taken the snow has started to melt and the roads are now (mostly) clear. The blanket of snow in the forest will remain for a while yet, but logs and bracken are starting to poke their way through the white and the river is certainly not safe to traverse now.

Thus, for this season, the Ski Patrol will have to soon call it quits.


:-(


PS: Of course, with my skiing skills, I am instantly reminded of one of my previous skiing trips and a most memorable skiing quote that followed (bonus points if you know the reference!): 
                            "AIIIEEEE!"
                                             -- Ib Halfheart

New 4-LBA system installed at Birr, Ireland

On 3rd and 5th January 2012, severe gale­force winds battered LOFAR station UK608 at Chilbolton in the United Kingdom. By far the most destructive incident was the ripping of one of the HBA (High­Band Antenna) tile covers. This resulted in polystyrene components coming loose, breaking and fracturing. The cause was not a design flaw. Instead, it was due to loosening of the soil, due to the array being built on re­constituted ground. This caused the covers to come loose. A differential wind pressure then causes billowing until the strain
causes the cover to rip. Once exposed the internal components are vulnerable and can easily blow out from their structure.

Billowing HBA covers at LOFAR station UK608. (Photo: D. McKay-Bukowski)

There was also damage on the Low­Band Antenna (LBA) array . For the most part, this was collateral damage caused by HBA components being blown into the area. However a number of the aerials also failed in their own right. Again, this was due to ground anchors coming loose. Even in cases where the anchors held, bent steel grids still results due to unsecured sides lifting up in the 25+m/s gusts. The small, round discs at the top of the LBA antennas are the critical part. They contain the low-noise amplifier (LNA) for each of the two polarisation channels and this is where the antenna dipole wires themselves are attached.

Fallen LBAs at LOFAR station UK608. The damage is in the detail...
ripped out wires and cracked casings. (Photo: D.McKay-Bukowski)

Within weeks the UK station, which was where I was working at the time, had been repaired and was operational again. The damaged tile had been fixed and the destroyed LBAs had been replaced. The mauled LBA LNAs were kept, but it was highly unlike that they could ever be repaired.

Not so!

A few months later, I had been invited to Ireland to give a lecture and attend some meetings about LOFAR. There is a consortium in Ireland (I-LOFAR) which are planning to purchase a full LOFAR station to be located near Birr Castle. At the time, I recall discussing the storm damage from the UK station, and we talked about whether it would be possible to do anything with the damaged parts. We felt that we should give it a try, and four LBA LNA units were sent from the UK to our I-LOFAR colleagues.

Well, that was about a year ago and this week, we were delighted to learn that the I-LOFAR team have managed to get them repaired and have built a small 4-element array. For those who follow our weblog regularly, you may recall that we ourselves have built a 4-element array at Pittiövaara. So now, Ireland have one too. There are several of these "micro-LOFAR-stations" either built or under development and it will be interesting to watch progress over the coming years, not just in terms of technical achievement, but also in terms of scientific observations.

Here are some photographs of the recent work at Birr, Ireland, showing the completed 4-LBA micro-LOFAR-station that they have constructed with the recovered parts.

The completed antennas at the Birr-Castle
radio-observatory site. (Photo: P. Gallagher)

Part of the I-LOFAR team. (Photo: P. Gallagher)

The next step for them now is to get the electronics installed and operational. Once that is done, and the data acquisition system is ready, then they can commence their first observations.

But of course, I-LOFAR have ambitious plans for their project. In addition to this development described here, they are currently trying to raise funds for a full LOFAR station. This will not only bring their researchers to the forefront of astrophysics and technology research, but will provide educational outreach in mathematics, physics, and technology to students of all ages. It will also re-establish Ireland as a major contributor to modern scientific endeavour.

So, we congratulate them on their achievements so far, wish them well for the next stage of their exciting project, and shall look forward to their first results!

Links:

http://www.lofar.ie/ -- The main homepage for the Irish LOFAR consortium
http://kaira.sgo.fi/search/label/I-LOFAR -- Other I-LOFAR news on our weblog

Testing out new receivers at Haystack

The ion line channel.

We installed some new digital wide band receivers at MIT Haystack and are now testing them. To our surprise, we can get nice plasma line measurements, even in the horrible RFI environment. We can actually trace the plasma line profile all the way up to about 600 km. Hopefully we'll soon be able to incorporate these measurements to our routine observations.

At the F-region peak, plasma lines show up nicely already after a few seconds of intergration, which offers a way to accurately calibrate received power with very high time resolution.

The only problematic thing that we noticed is that the antenna or feed gain seems to be somewhat lower on the top end of the band, which causes the up-shifted lines to be attenuated.

Plasma line channel. 

Plasma lines from 480 us pulse length.

Converting between subband and frequency

UPDATED : 28-Oct-2013

As KAIRA uses LOFAR hardware, it makes use of the LOFAR signal processing and nomenclature. When dealing with the signal from each polarisation of each antenna, the radio spectrum is split into 512 channels called "subbands".
Typically, the sampler clock runs at 200 MHz, this gives a Nyquist zone of 100 MHz bandwidth. This is what is split into the 512 channels.

So, to convert from subband number to frequency, you need to multiply by the sampler clock, and divide by 2 and the number of subbands. This gives the center of the subband. To get the top end of the subband, you need to use (subband + 0.5) and, for the lower frequency of the subband, you need to use (subband - 0.5). It is this middle frequency that is usually required. Thus:

     Freq_mid = subband * 200.0 MHz  /  2  /  512

The following is a python programme that prints the lower, centre and upper frequencies of each subband.

#!/usr/bin/python
# Make a table of subband number and equivalent 

# low / centre / high frequency for the RCU mode 3.

num_subbands = 512   # Number of subbands (fixed at 512)
clock_freq = 200.0   # Sample clock freq. MHz (typically 200)

print "Units = MHz"
print "Clock frequency =",clock_freq
print "Subband  LowFreq    MidFreq   HighFreq"
for subband in xrange(0,num_subbands,1):
    freq_low = (subband-0.5) * clock_freq / 2.0 / num_subbands
    freq_mid = subband * clock_freq / 2.0 / num_subbands
    freq_high = (subband+0.5) * clock_freq / 2.0 / num_subbands
    print "  %3d   %8.4f   %8.4f   %8.4f" % \
          (subband, freq_low, freq_mid, freq_high)
print "Done"
# End of file

So, for example, for RCU-mode 3, the centre of subband 256 is exactly 50 MHz

For subbands 0 and 511, this doesn't quite hold due to the way the sampling is done. However, these two subbands are completely outside the  filter ranges, so they would never be used for operational observing anyway.

Sunshine through the forest

At this time of year, we're getting more and more sunshine. And because of the high latitude, the sunsets and long and slow and the sun gently grazes into the horizon.The lighting and ambiance are always wonderful.

Sunshine through the trees. (Photo: D. McKay-Bukowski)

The above photograph was taken at the main SGO institute at Tähtelä. The one below was taken from a place not far away from the first.

Looking down towards the Kitinen. (Photo: D. McKay-Bukowski)

One of the other dishes...

Just near the EISCAT building at the Sodankylä Geophysical Observatory is the 32m parabolic antenna.

The Sodankylä 32m dish. One of four! (Photo: D. McKay-Bukowski)

It is one of two remote dishes that are used for the EISCAT system. We've featured it on numerous web log posts in the past. But today, we'll finish the week with a bizarre story I have about these dishes that actually goes back quite some time.

In 1998, I used to work for the Joint Institute for VLBI in Europe. This was a Dutch organisation which operated VLBI (Very Long Baseline Interferometry) experiments in Europe. It made use of existing radio astronomy observatories, of which there are many dotted amongst the various European countries. Once a year, the support scientists from the various institutes would meet face-to-face to discuss technical issues, operations and other such matters. And, each year, these meetings would be held in a different location.

In 1998, the meeting was held at the Noto Observatory which is in Sicily, Italy. That observatory has a 32m dish. At the time, when we were shown around the telescope, the local scientists explained to us that this was one of several 32m dishes built to the same design and the same specification. There was a second one in Medicina, on the Italian mainland. And then, the guide explained in semi-hushed tones, there were two more 32m dishes built.... somewhere in the far north. Probably top secret? Possibly military? Interesting, but I quickly forgot about those mysterious other dishes and life moved on.

Fast forward to 2007.

I had since moved on to new places and new projects. During 2007, I worked at the Kiruna EISCAT station where there is alsoa 32m dish. We had been having some gearbox problems with it and I remember discussing the design and construction of the antenna with the engineers there. They explained that it was one of several 32m dishes built to the same design and the same specification. There was a second one at Sodankylä, in Finland. And then, it was explained in semi-hushed tones, there were two more 32m dishes built.... somewhere in the far south of Europe. Probably top secret? Possibly military?

Ding!

The penny dropped and I realised that the other two dishes must be the two Italian radio telescopes and their mysterious counterparts were, in fact, only the scientific radar receivers up here that we know and love. Nothing secret; nothing unusual.

Mystery solved.



Links to photographs of the four 32m dishes:

Medicina, Italy
Noto, Italy
Kiruna, Sweden
Sodankylä, Finland

Aurora Borealis in HD

Stian Grande, who is working for EISCAT in Tromso, has made a nice high dynamic range high resolution time-lapse video of aurora in the last few years. You can also see the EISCAT radars and the Japanese NIPR LIDAR in the video.

KAIRA command centre

We have re-organised the KAIRA team and facilities at Sodankylä Geophysical Observatory to improve the way we operate the system. We now have office-space in the EISCAT building at Tähtelä, near the 32m dish, where some of the staff can work. This also serves at the store for some of the components, spares, and computing equipment for the project.

The EISCAT building at Tähtelä. This is where the new "KAIRA
command centre" is now located. (Photo: D. McKay-Bukowski)

This is a great place to work, with good facilities and a quiet working environment with lovely surroundings. It is also close to the other parts of the institutes within Tähtelä.

Tähteläntie

Just a nice photograph to finish the weekend. This is the "main road" that runs through Tähtelä. At this time of year, there is still snow around and plenty of sunshine. The forest always is so beautiful at this time of year.

Tähteläntie (Photo: D. McKay-Bukowski)

We hope you had a nice weekend!

Polaria

Just a nice photograph to finish the week. This one is of the sign at the entrance to the main building, called "Polaria". It is located near the southern end of Tähtelä and is shared by Sodankylä Geophysical Observatory and the Finnish Meteorological Institute.

Polaria... home to SGO and FMI. (Photo: D. McKay-Bukwoski)

Have a nice weekend!

Tähtelä

Occasionally you will see this place mentioned — Tähtelä.

Tähtelä is where the main Sodankylä Geophysical Observatory is located. It is also the location of a Finnish Meteorological Institute station. Tähtelä is small place with a handful of buildings belonging to the two institutes, a main shared centre (called "Polaria") and various houses, other small buildings and research equipment. It is not really a campus, but it is not really a village either. It is just a special place.

The visitor information sign for Tähtelä. (Photo: D. McKay-Bukowski)

Tähtelä is located about 6 km south of the town of Sodankylä itself on the eastern shore of the Kitinen River.

The name Tähtelä itself means "Place of the stars". Although it is true that the institutes here are not primarily astronomical facilities, we do in fact occasionally observe astronomical objects (such as radio stars, pulsars or our own sun). And certainly some of the staff are trained astronomers who sometimes carry out astronomical research.


Note that there is another Tähtelä. It is a small railway stop, just north of Ingå in the south of Finland (LINK).

Sping at last

We're now well into spring! The equinox has passed and the days seem "normal" length at the moment and are brightening rapidly. There is still lots of snow on the ground, which makes the place look lovely and very, very bright!

Administration buildings at the northern end of Tähtelä.

However, there is still reasonable nights which makes aurora-spotting still feasible.

EWASS 2013

The European Week of Astronomy and Space Science (EWASS) will be held on 8 - 13 July 2013 in Logomo Centre in Turku, Finland. Turku is the oldest university town and the former capital of Finland.

Turku is also well-known for its location in the beautiful archipelago. The time of the meeting, early July, is usually a pleasant season in Southwest Finland with plenty of sunshine and about 20 hours of daylight. Turku, with its seven hills and the river Aurajoki, has a lively cultural life with several museums and art galleries, and it was elected one of the cultural capital cities of Europe for the year 2011. We look forward to seeing you in Turku in July 2013!

The deadline for abstract submission is 30th April 2013.

The website is: http://www.astro.utu.fi/EWASS2013/