New version of GNU Ionospheric Tomography Receiver Out!

I finally got around to updating the ionospheric tomography receiver code than can be used to measure relative TEC using simple ground stations that listen to satellites.

Improvements are in stability, performance, phase curve fidelity, as well as in data portability. The code now uses only python and c++. The data container is now the widely supported hdf5 format. Other minor improvements include better Doppler residual estimation, as well as a new hybrid coherent and incoherent integration based phase curve estimation method that also produces error estimates for the phase curve. The performance of the new phase curve estimator is better with low signal to noise ratio.

The new algorithm is better at estimating the Doppler residuals (Doppler shift not predicted by the ephemeris), which allows me to coherently integrate longer vectors of data (use a more narrow bandwidth) and get better signal to noise ratio. This also has the effect of smearing out interference spectrally, which weakens the power spectral density overlap with the satellite. Because of this, the new algorithm produces much less jumps in the phase curve when an interfering signal intersects the satellite signal.

Recent Results on Radar Coding and Priors

Two papers by KAIRA-team have been published in the May issue of Inverse Problems and Imaging:

L. Roininen, P. Piiroinen and M. Lehtinen, Constructing Continuous Stationary Covariances as Limits of the Second-Order Stochastic Difference Equations, Inverse Problems and Imaging 7 611-647 (2013).

L. Roininen and M. S. Lehtinen, Perfect pulse-compression coding via ARMA algorithms and unimodular transfer functions, Inverse Problems and Imaging, 7 649-661  (2013).

The first paper discusses strong-weak convergence of probability measures and a certain class of discretisation-invariant Gaussian Markov random fields. These random fields can be used as a priori distributions in Bayesian statistical inversion. Developed formalism can be used whenever regularisation techniques are needed. We use these priors for ionospheric tomography and radar imaging.

The second paper focuses on a control-theoretic study on amplitude and polyphase radar coding. In collaboration with our MIT colleagues, we are working on actual implementation of these coding methods at Haystack Observatory. The methods will be used operationally in the future EISCAT_3D incoherent scatter radar!

Both papers are open-access!

Inverse Problems and Imaging: http://aimsciences.org/journals/home.jsp?journalID=11

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.

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