This mode combines the alternating code and Faraday double-pulse modes into a single experiment. The Faraday double-pulse mode provides absolute estimates of the electron density profile and yields measurements of the ACF down to altitudes just above the valley region. Note that with the Alternating code mode we cannot get useful measurements below 450 km. Parameter estimation from double-pulse data is sufficiently accurate in altitudes near the F peak, where the signal-to-noise ratio is high. The double-pulse experiment may even statistically outperform the alternating code experiment since the former is not clutter limited. Error analysis for the double-pulse experiment is straightforward since the statistical errors associated with each lag of the ACF are uncorrelated.
Recently, we have successfully implemented this mode and we expect to use it in the near future to replace the conventional Faraday Double pulse mode.
The alternating code experiment is performed with the following parameters: IPP = 6000 km, PW = 240 km, BW= 15 km, bits per code = 16, number of codes=128 (Randomized AC codes). The Faraday DP mode is performed every IPP but delayed 3000 km, where the echoes from the AC mode are not expected. There is no need of ionosonde data to normalize the power measurements, since the normalization is done with the Faraday measurements at lower heights.