Fitting our simulated responses on experimental responses taken on 24 August 2016. The average absolute difference between simulated and experimental responses is 0.6 dB (top panel) and 1.5 dB (bottom panel), respectively. The vertical line is located at the plasma frequency. The response maximum does not exactly correspond to the total plasma frequency because there are two electron populations. The experimental noise level estimate is 3 dB in the top panel and 4 dB in the bottom panel, according to the fluctuations of the responses above 300 kHz.