# Design of Multifunctional Mesosphere-Ionosphere Sounding System and Preliminary Results
## 4 Typical Experimental Results
### Ionospheric Sounding  
The sounding of the ionosphere adopts the single-transmit and single-receive mode. Switching from the mesospheric sounding mode requires a two-wire dipole progressive-wave antenna to be connected to the transmitting channel as a transmitting antenna to match a larger bandwidth. In the ionosonde mode, DDS upconverter module converts the output frequency according to instructions transmitted by USB bus, and LO also changes synchronously. The frequency sweeps in a range from 2 MHz to 20 MHz with a step of 50 kHz. At each frequency point, 32 coherent accumulations were  
Figure 15: (**a**) the electron density inversion results of DAE algorithm at the local time of 11:00–12:00, 8 January 2018. (**b**) shows the signal power of X-wave mode and O-wave mode at the local time of 11:15, 8 January 2018.  
performed, and the residence time was 0.26 s. In the vertical sounding mode, the MAI system obtains the ionogram shown in Figure 16. At the local time of 17:50, 5 January, 2018, the maximum SNR is about 30 dB. The ordinary (O) and the extraordinary (X) echoes can be clearly observed. This ionogram contains the echos of the Sporadic-E (Es) layer, F1 layer, F2 layer and the 2-hop echoes of the F2 layer. In the height distribution, the virtual height of the Es layer mainly distributes near 120 km with the corresponding delay is about 0.83 ms. The virtual heights of the F1 and F2 layers are 210-305 km and 260-320 km, respectively. There is a clear turning point between them. Further, the critical frequency of F2 layer is about 60F2 = 6.15 MHz. This ionogram obtained by MAI system is typical and similar to the traditional ionograms as well. For the ionogram, we use the quasi-parabolic segments (QPS) model to invert the electron density. In QPS model, the E, F1, and F2 layers are represented by a single quasi-parabolic (QP) model [38; 39; 40; 41; 42], while the transition regions of the E-F1 and F1-F2 are represented by a reverse QP model. Therefore, the whole electron density profile can be described as in Equation (28). \[N_{F2}=a_{F2}-b_{F2}\Big{(}1-\frac{r_{F2}}{r}\Big{)}^{2}\quad\quad F2\quad \textit{layer};\quad a_{m}=N_{m},b_{m}=N_{m}(r_{m}/y_{m});a_{j\text{FF}}=a_{F1 },r_{j\text{FF}}=r_{F1}\]  
\[N_{F_{1}}=a_{F_{1}}-b_{F_{1}}\Big{(}1-\frac{r_{F_{1}}}{r}\Big{)}^{2}\quad\quad F 1\quad\textit{layer};\quad b_{j\text{FF}}=-\frac{b_{F2}r_{F2}(1-r_{F2}/r_{c \text{F2}})}{r_{F1}(1-r_{F1}/r_{c\text{F2}})}\]  
\[N_{E}=a_{E}-b_{E}\Big{(}1-\frac{r_{E}}{r}\Big{)}^{2}\quad\quad E\quad\textit{ layer};\quad r_{c\text{F2}}=-\frac{b_{F2}r_{F2}(r_{F2}/r_{F1}-1)}{a_{F2}-a_{F1 }+b_{F2}(r_{F2}/r_{F1}-1)}\]  
\[N_{j\text{FE}}=a_{j\text{FE}}+b_{j\text{FE}}\Big{(}1-\frac{r_{j\text{FE}}}{r} \Big{)}^{2}\quad\quad E-F1;\quad\quad\quad a_{j\text{FE}}=a_{E},r_{j\text{FE} }=r_{E},b_{j\text{FE}}=-\frac{b_{F1}r_{F1}(1-r_{F1}/r_{c\text{F1}})}{r_{E}(1- r_{E}/r_{c\text{F1}})}\]  
\[N_{j\text{FF}}=a_{j\text{FF}}+b_{j\text{FF}}\Big{(}1-\frac{r_{j\text{FF}}}{r} \Big{)}^{2}\quad\quad F1-F2;\quad\quad\quad r_{c\text{F1}}=-\frac{b_{F1}r_{F1 }(r_{F1}/r_{E}-1)}{a_{F1}-a_{E}+b_{F1}(r_{F1}/r_{E}-1)} \tag{28}\]  
Figure 16: An example of vertical sounding ionogram at the local time of 17:50, 5 January 2018. The calculation of the whole electron density profile is determined by nine parameters: \(N_{m}F_{2}\) is the peak of electron density in the F2 layer, \(r_{m}F_{2}\) is the peak distance from the geocentric distance, \(y_{m}F_{2}\) is half thickness of the F2 layer. \(N_{m}F_{1}\), \(r_{m}F_{1}\), \(y_{m}F_{1}\), \(N_{m}E\), \(r_{m}E\), \(y_{m}E\), are the corresponding parameters of the F1 layer and E layer, respectively. \(a_{m}=N_{m}\) is the peak electron density of the corresponding layer, \(r_{m}\) is the peak distance from the centrosphere, \(y_{m}\) is half thickness of the corresponding layer. \(b_{m}\) is the intermediate parameter of the calculation.