Ionospheric Oblique Backscattering Sounding System Research Articles

Application of Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) for the investigation of midlatitude ionospheric irregularities

An upgrade of Wuhan Ionospheric Backscattering Sounding System (WIOBSS) was developed in 2015. Based on the Universal Serial Bus (USB), and a high performance FPGA, the newly designed WIOBSS has a completely digital structure, which makes it portable and flexible. Two identical WIOBSSs, which were situated at Mile (24.31°N, 103.39°E) and Puer (22.74°N, 101.05°E) respectively, were used to investigate the ionospheric irregularities. The comparisons of group distance, Doppler shift and width between Mile-Puer and Puer-Mile VHF ionospheric propagation paths indicate that the reciprocity of the irregularities is satisfied at midlatitude region. The WIOBSS is robust in the detection of ionospheric irregularities.

Wuhan Ionospheric Oblique Backscattering Sounding System and Its Applications-A Review.

For decades, high-frequency (HF) radar has played an important role in sensing the Earth’s environment. Advances in radar technology are providing opportunities to significantly improve the performance of HF radar, and to introduce more applications. This paper presents a low-power, small-size, and multifunctional HF radar developed by the Ionospheric Laboratory of Wuhan University, referred to as the Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS). Progress in the development of this radar is described in detail, including the basic principles of operation, the system configuration, the sounding waveforms, and the signal and data processing methods. Furthermore, its various remote sensing applications are briefly reviewed to show the good performance of this radar. Finally, some suggested solutions are given for further improvement of its performance.

Design and Application of Wuhan Ionospheric Oblique Backscattering Sounding System with the Addition of an Antenna Array (WIOBSS-AA).

The Wuhan Ionospheric Oblique Backscattering Sounding System with the addition of an antenna array (WIOBSS-AA) is the newest member of the WIOBSS family. It is a multi-channel radio system using phased-array antenna technology. The transmitting part of this radio system applies an array composed of five log-periodic antennas to form five beams that span an area to the northwest of the radar site. The hardware and the antenna array of the first multi-channel ionosonde in the WIOBSS family are introduced in detail in this paper. An ionospheric detection experiment was carried out in Chongyang, Hubei province, China on 16 March 2015 to examine the performance of WIOBSS-AA. The radio system demonstrated its ability to obtain ionospheric electron density information over a wide area. The observations indicate that during the experiment, the monitored large-area ionospheric F2-layer was calm and electron density increased with decreasing latitude.

Comparison of radar waveforms combining pseudo‐random binary phase coding and chirp modulation for an high‐frequency monostatic radar

Wuhan ionospheric oblique backscattering sounding system (WIOBSS) is a low-power high-frequency monostatic radar used for ionospheric sensing and aircraft detection. In this study, a novel waveform combining the pseudo-random binary phase coding (PRBPC) and the chirp modulation is proposed for this radar. Furthermore, in terms of the radar waveform requirements, four subclasses of this waveform are theoretically compared to determine which one of them is most suitable for WIOBSS, including the inter-pulse PRBPC waveform where the width of the subpulse is equal to the chirp duration, the inter-pulse PRBPC waveform where the period of the coding sequence is equal to the chirp duration, the intra-pulse PRBPC waveform where the width of the subpulse is equal to the chirp duration, and the intra-pulse PRBPC waveform where the period of the coding sequence is equal to the chirp duration. The radar waveform requirements, the ambiguity function analysis, and the performance comparison of aforementioned waveforms are described. The analysis results show that the inter-pulse PRBPC waveform where the period of the coding sequence is equal to the chirp duration has the best performance, and can achieve higher range resolution, larger signal processing gain, and better Doppler tolerance than the conventional binary phase coded waveforms.

Application of Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) for Sea-State Detection

To combine the advantages of long detection range and small antenna array, the newly designed Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) transmits radio waves by ionospheric reflection and receives oceanic backscattered ground waves. To combine the functions of operating frequency selection and sea-state detection, WIOBSS can transmit the interpulse coding wave and frequency-modulated continuous wave waveforms in one hardware platform. The hardware and software of the radio system are introduced. A sky-wave over-the-horizon sea-state detection experiment was carried out in Chongyang and Longhai, China, on January 28, 2015. The observations of the oceanic surface echoes 130–300 km from the coastline are also presented.

Inversion of Sweep Frequency Backscatter Ionogram From Monostatic HF Sky-Wave Radar

The Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) is a monostatic high-frequency sky-wave radar used for ionospheric remote sensing. The sweep frequency backscatter ionogram (SFBI) recorded by the WIOBSS contains both backscatter echo scattered by distant terrestrial surface and vertical incidence (VI) echo reflected by local ionosphere over the sounding station. The approach for SFBI inversion introduced in this letter requires input of leading edge and peak height derived from local VI echo. The final output of this SFBI inversion approach is the 2-D electron density distribution in a vertical plane aligned in the direction of sounding. In addition, the time and geographic variation of foF2 can be obtained from a series of SFBI inversion results. Two experiments have been utilized to validate the SFBI inversion approach, and the SFBI inversion results are found to be very close to the ionosonde data. The fast-converged feature of the approach makes it possible for applications in real time. The success of the SFBI inversion approach enables us to use the WIOBSS as a vehicle-mounted system to obtain ionosphere electron density profile over a large geographic area.

A new design of low-power portable digital ionosonde

The Ionospheric Laboratory of Wuhan University is interested in upgrading its instrumentation replacing the WIOBSS (Wuhan Ionospheric Oblique Backscattering Sounding System) with a more flexible and automatic ionosonde. Then the updated ionosonde WMI (Wuhan Multifunctional Ionosonde) with automatic ionogram scaling has been developed to satisfy future research. The new system not only inherited some classic techniques from WIOBSS, such as the pulse compression and the coherent integration techniques, but also made great improvements in hardware design and software updating. This paper mainly introduces evolutions of this new ionosonde in both digital transceiver and digital signal processing domain, and also presents some observations.

Gravity waves and spreadEsobserved during the solar eclipse of 22 July 2009

[1] During the total solar eclipse of 22 July 2009, two ground-based high-frequency radio systems were applied to observe the ionospheric variations over Wuhan, China. The ionosonde recorded ionograms every 5 min; the Wuhan Ionospheric Oblique Backscattering Sounding System recorded echo range and Doppler every 1 min. Comparing the observations of the two radio systems, we found that the periodic fluctuation on the top penetration frequency of regular Es (fEs) and on the Doppler velocity of the spread Es appeared and disappeared simultaneously on the eclipse day. Moreover, wavelet analysis results show that the fEs curve and the Doppler velocity of the spread Es contain the same period of ∼35 min. The spread Es occurred owing to the off-vertical reflections from the tilted layer at the Es latitude. Atmospheric gravity waves are considered to be generated during the solar eclipse and propagate upward to deform the Es layer and produce the moving wave-like structures in the layer. The tilted plasma concentration in the moving wave-like structures induced the off-vertical HF radiowave reflections and added the Doppler modulation of also ∼35 min period on the reflected radiowave. Furthermore, the Doppler values of regular Es indicate that the layer at lower altitude was weakly disturbed and the layer at higher altitude was deeply modulated, which is in agreement with the theory that the amplitude of gravity waves increases with height.

Almost perfect sequences applied for ionospheric oblique backscattering detection

Pseudorandom sequences are often used in radio systems; however, the nonzero out‐of‐phase autocorrelation of many binary sequences induces range sidelobes which significantly reduce the echo signal‐to‐noise ratio (SNR). In this paper, the use of almost perfect sequences, exhibiting zero out‐of‐phase autocorrelation except one value in the middle is examined with reference to common m sequences and perfect sequence. The ambiguity functions demonstrate that it is possible to use the almost perfect sequences for ranging without sidelobes and that their Doppler measurement performance is similar to m sequence of the same length. This is an important result for ionospheric oblique backscattering detection where the echoes are superposed and where range sidelobes can submerge the main lobes of weak signals. The 124‐bit almost perfect sequence and the 127‐bit m sequence are applied to the Wuhan Ionospheric Oblique Backscattering Sounding System for sequence testing. The test results have proven that the almost perfect sequence exhibits a higher echo SNR for the same detection conditions.

The Wuhan Ionospheric Sounding Systems

The ionospheric laboratory of Wuhan University, Wuhan, China, has developed a new ionospheric sounding system for about seven years. The first system is used for ionospheric oblique backscattering detection and is called the Wuhan ionospheric oblique backscattering sounding system (WIOBSS). The WIOBSS is a portable monostatic backscatter ionosonde for ionospheric research and high-frequency (HF) channel management, adopting alternate transmitting and receiving patterns to transmit long coded pulse trains for high pulse-compression gain. However, it is difficult to recognize the echo path and mode only with the backscatter ionogram. Therefore, a separate remote digital receiver has been developed for auxiliary detection. The receiver is a compact radio system used to receive the transmitting signal of the WIOBSS, and it includes a Global Positioning System receiver for clock and frequency standard synchronization. Combined with the WIOBSS, the receiver has been used for ionospheric bistatic backscatter sounding and oblique incident sounding. The WIOBSS and several remote digital receivers can compose a detection network for ionospheric research and HF channel management.

A Low-Power and Small-Size HF Backscatter Radar for Ionospheric Sensing

A new high-frequency backscatter radar (Wuhan Ionospheric Oblique Backscattering Sounding System) for ionospheric sensing and study has been developed. With the new system design, oblique backscatter sounding and oblique sounding can be achieved in this radar just through simply loading appropriate software. Furthermore, due to alternate transmission and reception in equal interval, this radar can detect the ionospheric state in the range of a few thousand kilometers and achieve the largest gain of applied pseudorandom sequences. In addition, this radar usually obtains 27-dB gain from phase coded pulse compression and 21-dB gain from coherent spectral integration using pseudorandom code, pulse compression, and coherent spectral integration techniques. This radar also exploits merits of Peripheral component interconnect eXtensions for Instruments (PXI) bus technology and is designed as a modular and compact PXI-based system. Details of system design, sounding timing, and signal-processing algorithm are described. Except for the antenna systems and power amplifier, this radar's dimension is 177.8 times 431.8 times 457.2 mm. With this radar, the oblique backscatter ionogram and Dopplerionogram can be clearly obtained in the range of a few thousand kilometers with 100-W power. The oblique ionogram for propagation over a distance of several kilometers can also be clearly acquired at the time of oblique backscatter sounding. The initial observations obtained with this radar are included to demonstrate its performance.

Design and implementation of hardware architecture in ionospheric oblique backscattering sounding system

The ionospheric oblique backscattering sounding system can not only be used to detect the state of ionosphere and the condition of high frequency channel in real time, but also be used for over-the-horizon sounding. So, it has a very high military and civil value. For the characteristics of ionospheric oblique backscattering sounding, such as long sounding distance, wake echo, strong background noise, slow moving target, etc., a hardware platform of ionospheric oblique backscattering sounding system is designed. This platform adopts the technology of software radio and is designed as a new kind of general-purpose, modularized, software-based ionosonde that is based on VXI (Versa module eurocard eXtensions for Instrumentation) bus. At present, this hardware platform has been successfully used in actual ionospheric oblique backscattering sounding, and the experimental results demonstrate that this system can satisfy the demands of ionospheric oblique backscattering sounding preferably.

WIOBSS: The Chinese low-power digital ionosonde for ionospheric backscattering detection

The ionospheric laboratory of Wuhan University has developed an ionosonde over about seven years. The prototype is designed as a portable, low-power digital MF (medium frequency) and HF (high frequency) radio system with high range and Doppler resolution. The first system is used for ionospheric oblique backscattering detection and called WIOBSS (Wuhan Ionospheric Oblique Backscattering Sounding System). WIOBSS is a portable monostatic ionosonde for both ionospheric research and HF channel management, adopting alternate transmitting and receiving patterns to transmit long coded pulse trains for high pulse compression gain. The almost perfect sequences are applied to modulate the pulse train for sounding without range sidelobes and the echo phase is used to estimate the Doppler velocity and velocity fluctuation. This paper introduces the new techniques adopted by WIOBSS and presents some observations.

Preprocessing of ionospheric echo Doppler spectra

The real-time information of the distant ionosphere can be acquired by using the Wuhan ionospheric oblique backscattering sounding system (WIOBSS), which adopts a discontinuous wave mechanism. After the characteristics of the ionospheric echo Doppler spectra were analyzed, the signal preprocessing was developed in this paper, which aimed at improving the Doppler spectra. The results indicate that the preprocessing not only makes the system acquire a higher ability of target detection but also suppresses the radio frequency interference by 6–7 dB.

Ionospheric Doppler and echo phase measured by the Wuhan Ionospheric Oblique Backscattering Sounding System

Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) is a high‐frequency (HF) sky wave over‐the‐horizon radar developed for ionospheric research and HF channel management. This radar, located in Wuhan (30.35°N, 114.33°E) has been under construction by the Ionosphere Lab of Wuhan University since 2002. WIOBSS uses long coded pulses and pulse compression to achieve good sensitivity and measures the bitemporal ionospheric response, channel scattering function, and phase of echoes simultaneously and then displays the processed data as ionograms and Dopplionograms in real time. Bitemporal ionospheric response is a matrix composed of the ionospheric transmission function with delay and time variables, while the scattering function shows the spectrum of the received signals as a function of the delay and Doppler coordinates, and is obtained by the Fourier Transform of the bitemporal ionospheric response over the time variable. The application of pulse compression and coherent integration allows WIOBSS to measure ionospheric Doppler with high resolution and very low power. A method is developed to get phase data directly from the bitemporal ionospheric response. The measured phase is strung in a series and then divided into linear and nonlinear components. The angular frequency of the linear component is in direct proportion to ionospheric Doppler velocity while the fluctuation of the nonlinear component includes the information of Doppler velocity spread. The phase method based on pulse impression is able to obtain the statistic Doppler information from weak backscattered echoes in short detection time.