EISCAT Campaign in Tromsø

Time for the traditional Finnish autumn EISCAT campaign! Ilkka Virtanen and I have been running radar experiments since last Friday evening, from the control room of the Ramfjord site near Tromsø, Norway. This is the site where the EISCAT transmitters are located: the VHF – which may be used alongside the Sodankylä and Kiruna receivers for tri-static measurements –, the UHF, and the ionospheric heating system (among other instruments).

Four experiments from the Finnish EISCAT user community were scheduled for this campaign. A first experiment consisted in a continuous 48-hour run of the EISCAT Svalbard Radar (ESR) during a solar wind high-speed stream. It was run in the beginning of this month, separately from the rest of the campaign. The second experiment aimed at using the UHF radar in a 3-position scanning mode to study neutral wind acceleration during auroral activity. The third experiment was supposed to use UHF, VHF, remote VHF receivers, ESR and the Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) to cover SWARM satellite overpasses during two nights. The fourth experiment was supposed to study the lower ionosphere during pulsating aurora, using the VHF system.

Unfortunately, as this is often the case, reality reserves some surprises. In our case, these were not particularly good ones, since the KAIRA clock experiences some time drift, probably because its rubidium atomic clock needs to be replaced. Just to make sure that we have no regrets about it, the VHF is also down due to problems with a coaxial cable. As a consequence, the experiments using the VHF system could not be run as planned: the SWARM experiment only used field-aligned UHF measurements and ESR, and the pulsating aurora experiment had to be totally cancelled.

As a form of compensation, we have been granted exceptional weather here in Tromsø – while on the Finnish side of the border, thick clouds offer an uninterrupted display of medium-grey and dark-grey. And at night, the aurora gave us several nice displays during the previous nights. Some form of compensation, indeed.

The UHF radar, the aurora, and a mysterious beam of light.
Photo: M. Grandin

Plasma parameter estimation from multistatic, multibeam incoherent scatter data

We report that our latest study on multistatic, multibeam ISR, i.e. using EISCAT VHF incoherent scatter radar in conjunction with KAIRA receiver, has been accepted for publication in Journal of Geophysical Research - Space Physics. The paper is available as an early access version here. The reference is:

I. I. Virtanen, D. McKay-Bukowski, J. Vierinen, A. Aikio, R. Fallows and L. Roininen, Plasma parameter estimation from multistatic, multibeam incoherent scatter data, Journal of Geophysical Research, DOI:10.1002/2014JA020540.

Abstract:

Multistatic incoherent scatter radars are superior to monostatic facilities in the sense that multistatic systems can measure plasma parameters from multiple directions in volumes limited by beam dimensions and measurement range resolution. We propose a new incoherent scatter analysis technique that uses data from all receiver beams of a multistatic, multi-beam radar system and produces, in addition to the plasma parameters typically measured with monostatic radars, estimates of ion velocity vectors and ion temperature anisotropies. Because the total scattered energy collected with remote receivers of a modern multistatic, multibeam radar system may even exceed the energy collected with the core transmit-and-receive site, the remote data improves the accuracy of all plasma parameter estimates, including those that could be measured with the core site alone. We apply the new multistatic analysis method for data measured by the tristatic EISCAT VHF radar and the KAIRA multibeam receiver and show that a significant improvement in accuracy is obtained by adding KAIRA data in the multistatic analysis. We also demonstrate the development of a pronounced ion temperature anisotropy during high-speed ionospheric plasma flows in substorm conditions. 

Figure 1 from the Virtanen et al. paper showing some of the results obtained.

Hyperlapse: BDU antenna construction

The Boston College & Bahir Dar University radar construction is running according to the schedule. Yesterday, I took this short hyperlapse film from the 'antenna plant'. I'll post antenna field pictures before I head back to the Observatory (departure Friday evening).

Pip-pip!

EISCAT Demonstrator Array

Kiruna Demonstrator Array. Photo: Craig Heinselman.

During the FP6 EISCAT_3D Design Study, which was completed in 2009, a small radar receiver array was built at the Kiruna EISCAT site to test reception of radar signals from the Tromsø VHF transmitter using a phased-array receiver. The receiver was used later on for science applications, namely for measurements of so-called Polar Mesospheric Summer Echoes (PMSE). The photo above was taken by EISCAT Director Craig Heinselman using his quad-copter drone, which he demonstrated to his colleagues a day later.

One of three instrument cabinets of the Demonstrator Array: this is clearly an experimental setup for prototyping work. The final EISCAT_3D receiver will look much different, probably incorporating many parts into single custom-made components. Photo: Thomas Ulich.

During the FP7 EISCAT_3D Preparatory Phase, the array was modified by SGO scientists in collaboration with Technical University of Luleå and National Instruments to demonstrate reception of VHF signals using a different approach. This time the array was converted to using software-defined radio (SDR) receivers. The results of these tests are documented in the reports of the projects work packages 7 and 11 (see Deliverables and Milestones).

One of the aerials of the Demonstrator Array with the EISCAT 32-m receiver in the background. Photo: Thomas Ulich.

The aerials are derived from TV antennae, since the VHF radar operates at very similar frequencies around 224 MHz. Also EISCAT_3D is expected to operate in this part of the radio spectrum, around 233 MHz, although negotiations about frequency allocations in the Nordic countries are on-going.

With the Demonstrator Array in the background, the photo shows a small transmitter antenna, which sends a calibration signal to the array. Photo: Thomas Ulich.

Calibration of arrays is essential. The direction in which a phased array looks depends on the time delay of the signals coming in from all of its aerials. Therefore one needs to know the absolute delays introduced by the components of the array, including their manufacturing inaccuracies, before applying delays related to the viewing direction.