The quicklook RTI (Range-Time-Intensity) plot contains the echo intensity for beam number 5 (this might change, the number is mentioned in the upper right corner) in dB units relative to background noise level as a function of range and time. The range is the distance of each radar, and is divided into 50 range gates. Range 1 corresponds to the closest point to the radar (the southernmost) and range 50 the farthest point (the northernmost). The distances are 495 and 1245 km, respectively.

The echo intensity depends in a complicated way on several factors and usually it cannot be alone used for any physical studies. But whenever the echo intensity is clearly above the noise level, the radar can measure the Doppler velocity and the power spectrum. Thus, whenever both radars measure a echo intensity which is clearly above the background (more than 5 dB, say), we can have an estimate for the electron flow velocity in the E-region and thus the ionospheric electric field.

At least the following factors affect the echo intensity:

Some references [only some, there are many more]:
  1. Kustov et al., Electric field and electron density thresholds for coherent auroral echo onset, J. Geophys. Res., 98, 7729-7736, 1993.
  2. Janhunen, Implications of flow angle stabilization on coherent E-region spectra, J. Geophys. Res., 99, 13203-13208, 1994.
  3. Uspensky et al., The amplitude of auroral backscatter-III. Effect of tilted ionospheric layer, J.Atmos.Terr.Phys., 55, 1383-1392, 1993.
  4. Williams et al., The relationship between E region electron density and the power of auroral coherent echoes at 45 MHz, Radio Sci., 34, 449-457, 1999.

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See also: Interpreting the Doppler velocity
More information: Pekka Janhunen (, tel. 358 9 1929 4635