Early access: Ionospheric tomography paper

The early-access version of the paper:

J. Norberg, L. Roininen, J. Vierinen, O. Amm, D. McKay-Bukowski and M. Lehtinen, Ionospheric tomography in Bayesian framework with Gaussian Markov random field priors, Radio Science (2015) DOI: 10.1002/2014RS005431

is available here: http://onlinelibrary.wiley.com/enhanced/doi/10.1002/2014RS005431/.


Here is the abstract:

We present a novel ionospheric tomography reconstruction method. The method is based on Bayesian inference with the use of Gaussian Markov random field priors. We construct the priors as a system of stochastic partial differential equations. Numerical approximations of these equations can be represented with linear systems with sparse matrices, therefore providing computational efficiency. The method enables an interpretable scheme to build the prior distribution based on physical and empirical information on the structure of the ionosphere. We show through synthetic test cases in a two-dimensional setup of latitude-altitude slices how this method can be applied to satellite-based ionospheric tomography and how information about the structure of the ionosphere can be implemented in the prior. The technique is capable of being easily extended to multi-frequency tomographic analysis, or used for the inclusion of other data sets of ionospheric electron density, such as ground-based observations by radars or ionosondes.

Scintillation time series from all-sky images

The standard KAIRA experiment, which is always left running if the station is not being used for campaign experiments, includes a beam which continually observes the strong natural radio source Cassiopeia A at several frequencies spread over the KAIRA low-band.  Simultaneously, all-sky images are taken at a single observing frequency with a one second cadence, such as the example below, in which Cassiopeia A is easily identified (it's the strongest source, the other easily identifiable source is Cygnus A).

On Chirstmas Day 2013 a period of very strong ionospheric scintillation (the "twinkling" of radio sources due to density variations in the ionosphere) was observed, for which a movie of all-sky images was created in which the dominant sources can be seen flickering and sometimes changing position and shape (see the KAIRA blog post).  I am now in the process of analysing these data to investigate the phase-shifting of the radio signal from Cassiopeia A caused by the density variations moving through the ionosphere.  As a first stage of this, I've been looking at the intensity of Cassiopeia A as measured from the images and comparing it to the intensity measured by the beam-formed data looking directly at this source.  A first comparison is below.

As can be seen, the two time series' match almost exactly.  Whilst this is hardly surprising, it is a relief to know that the code used to identify Cassiopeia A in the imagery is working as expected.

Ionospheric tomography in Bayesian framework with Gaussian Markov random field priors

We are pleased to report that our latest study on ionospheric tomography with a GMRF-type prior information has been accepted for publication in Radio Science. The current reference is:

J. Norberg, L. Roininen, J. Vierinen, O. Amm, D. McKay-Bukowski and M. Lehtinen, Ionospheric tomography in Bayesian framework with Gaussian Markov random field priors, Radio Science, Accepted January 2015.

We will post a link to the early-access version as soon as it is available. This is a companion paper of the so-called "tomography receiver paper" reported in Radio Science earlier. It is available here.

Current tomography project titled 'TomoScand' is a collaboration project between Finnish Meteorological Institute, Sodankylä Geophysical Observatory and MIT Haystack Observatory.

Here is a schematic plot of ionospheric tomography, where the objective
is to probe the ionosphere beacon 150/400 MHz satellite signals and to estimate
the electron density ~60-1000 km above the Earth.

Antarctica operations: SGO neutron monitors at Concordia

SGO is back in operational Antarctica measurements. Our cosmic ray research group has new neutron monitors in operation at Concordia station. Here is a photo of our two NM units in the physics shelter at Concordia. According to Ilya, data analysis is in progress. Hence, we will get back to them later on, i.e. follow-ups on the way.

Hilsen fra Longyearbyen

78°13'N. This is the geographic latitude of Longyearbyen, the main human settlement on Spitsbergen, where the University Centre on Svalbard (aka UNIS) provides first-class teaching for Bachelor, Master and PhD students in Arctic-related topics. The teaching and research carried out at UNIS are divided into four departments: Arctic Biology, Arctic Geology, Arctic Geophysics and Arctic Technology. Each year, a few hundred students from all around the world come to take part of their degree in this very peculiar environment, where unique opportunities to carry out field work in the extreme Arctic are provided.

I am presently enrolled as a student at UNIS in Arctic Geophysics to take two courses (The Upper Polar Atmosphere; Radar Diagnostics of Space Plasma). The courses include practical sessions at the Kjell Henriksen Observatory (KHO, auroral station) and in the EISCAT on Svalbard Radar (ESR) next month. 

Eventually, the sun will rise. Someday. Or so we hope.

The whole last week was dedicated to the Arctic Survival and Safety course, mandatory for all the spring semester students and aimed at providing them with the necessary knowledge and skills to carry out field work safely on Svalbard.

The extreme Arctic is full of hazards due to weather conditions and the remoteness of most of the regions of the archipelago. The students who are part of an expedition outside Longyearbyen must therefore be aware of the risks they may face and be able to act efficiently if in a difficult situation. Besides the polar bears — which although dangerous do not represent the most serious threat —, the deadly hazards awaiting for human beings are numerous: crevasses in glaciers, weak sea ice, avalanches, fragile ice caves, walruses... without mentioning the cold, the wind and the absence of resources.

The lessons included a lot of practical training, especially to rescue victims of an avalanche or fallen in a sea ice hole or in a crevasse, including first aid techniques and building of an emergency camp. Another session was dedicated to telecommunication and navigation, as in most cases the only way to call for help is to use an emergency beacon and/or a satellite phone.

On Saturday, the students were taken to Longyearbreen, a glacier very near Longyearbyen, for a full day of practice. Fortunately, it was not windy on the glacier, which helped withstanding the cold and setting up the camps. After rotating over five rescuing and survival tasks, all the students were invited to observe a demonstration of a rescue operation by a Super Puma helicopter. Pictures of that day were taken by Stefan Claes, who was one of the instructors during the week; see here.

After this very busy and intense week, the regular courses can now start. And I guess for all the students this safety course was an amazing experience and a fantastic training for both their field work expeditions and their private excursions.

XVII Northern Lapland Education Fair

It's a mid-January tradition in Sodankylä, that the local vocational school organises the annual Northern Lapland Education Fair. For the 17th time, the fair took place yesterday, 15th January 2015, and of course the University of Oulu, of which Sodankylä Geophysical Observatory is an independent department, took part as well.

The university had their trademark bright-yellow stand deployed, and Kimmo Kuortti (left) and Uula Neitola (right) were happily overwhelmed by the interest, running out of brochures all too soon. A big thank you to all the young people of Sodankylä and Northern Lapland, who showed their interest and asked a lot of questions! Next year there'll be more brochures available!

Among other examples of vocational educational programmes are the machine operators, who displayed their skills by carefully moving a long stick around using a mini digger.

Also the local Kevitsa mine was represented recruiting trainees and students looking for summer jobs.

A final example of the fair's exhibits is this computer, which is a realistic simulator of a forestry machine.

The next educational fair will take place in January 2016. If you want to know more about studying at the University of Oulu, please visit their web site at www.oulu.fi.

Welcome!

Frosty Sodankylä

It gets cold in Sodankylä in January. This is the coldest month here, and last night the thermometer bottomed out at –39.5°C! It's the coldest we've seen in many years. There used to be always some days of –40°C here in January, but not in recent years. Incidentally, –40° is the same on both the Celsius as well as the Fahrenheit scale.

Photo: Thomas Ulich.

Congratulations!

Our sincere congratulations to our friend and colleague, Prof Mike Lockwood of the University of Reading, UK, on the occasion of being awarded the Gold Medal in Geophysics of the Royal Astronomical Society for his contributions to space physics, including his work on long-term solar variability and its effect on the Earth's climate.

For the official announcement, please refer to the Royal Astronomical Societies' web site.

Congratulations from your SGO colleagues, Mike, well done!

2015

With this photo of the first sunrise of 2015 above the river Kitinen, we wish all of you a very Happy New Year 2015!

Photo: Thomas Ulich.