Fine tuning FFT LPI

Going from initial first light to calibrated and cross validated ionospheric plasma parameter measurements is not an overnight step. However, the KAIRA team is making good progress. We have now managed to get fast Fourier transform lag-profile inversion working to some extent with real world signals contaminated with space debris and meteor head echos. We can now estimate ionospheric plasma incoherent scatter autocorrelation functions and spectra with a fairly nice accuracy and computational speed.

Here is an example of a 512 second integration combined from all of the 30 beams intersecting the Tromsø VHF beam at different altitudes. With this experiment that has a 128 microsecond baud length, we can reach altitudes up to 400 km.

(Click image to enlarge)

The plots are fairly similar with monostatic VHF spectra, although there are still lots of challenges with absolute calibration of electron density. These issues can hopefully be solved by comparison with monostatic Tromsø measurements, or with future plasma line measurements with KAIRA.