Communications Via Beat-Wave Excitation of ELF/VLF Waves in the Ionosphere

TECH FOCUS AREAS: Directed Energy; Network Command, Control and Communications TECHNOLOGY AREAS: Space Platform; Battlespace OBJECTIVE: The main objective of the proposed research is to predict optimal conditions for generation of extremely low frequency (ELF) and very low frequency (VLF) waves in the ionosphere F layer due to parametric beat wave interaction of two high frequency (HF) pump waves with different frequencies. The difference in the two HF transmissions should be in the ELF/VLF frequency range. The obtained results should define the necessary amplitudes of injected HF waves in the F-region ionosphere and the dimensions of the excitation region. The theoretical results will define the amplitude range of the excited ELF/VLF beat-waves and spatial localization as a function of the HF pump-wave amplitudes, frequencies, wave numbers, polarization, and incident angles. In particular: (1) Develop novel analytical models of parametric beat-wave excitation of ELF and VLF waves by HF waves propagating in inhomogeneous ionosphere plasma. (2) Create numerical code for solution of derived nonlinear equations for HF beat-wave excitation mechanism leveraging with the High-Performance Computers (HPC) capabilities. These models should allow to determine excited ELF/VLF wave amplitudes and spatial localization depending on the HF wave properties, such as frequency, wave number, polarization, amplitude, and incident angle with respect to the plasma density gradient and magnetic field orientation. (3) Collect unique experimental data on beat-wave excitation of ELF/VLF waves at the High-frequency Active Auroral Research Program (HAARP) facility and compare with theory. (4) Based on obtained data carry out comprehensive analysis of efficiency of radio frequency (RF) mixing mechanism for excitation of ELF/VLF waves in the F-layer of the ionosphere. (5) Investigate possibility of creation of frequency modulated and amplitude modulated ELF/VLF waves produced during a beat wave excitation process. (6) Develop commercialization strategy for developed new techniques and mitigation methods. DESCRIPTION: Develop a novel comprehensive effort that incorporates theory, computer simulations, and field experiments, to investigate excitation of ELF and VLF waves in the F-region ionosphere and implementation of this method for secure communication on the ground and below sea level. The proposed research aims to explore the efficiency of the beat-wave excitation mechanism for generation of ELF and VLF waves. A beat-wave frequency will be created in the ionosphere due to parametric interaction of two HF pump waves launched from the ground. The proposed theory will be validated by means of controlled experiments. We will predict optimal conditions for the ELF/VLF excitation based on the HF wave characteristics and F-region ionosphere plasma parameters. We are interested in the development of analytical models supported by field experiments to demonstrate possibility of establishing reliable secure communications via ELF/VLF waves generated in the ionosphere F layer in the process of parametric interaction of HF electromagnetic waves from the MHz diapason launched from the ground. PHASE I: D2P2 proposers should provide documentation that describes their analytic models with examples of numerical analysis for beat wave excitation of ELF/VLF waves by HF waves launched from the split array t the High-frequency Active Auroral Research Program (HAARP) facility. In addition to this, D2P2 proposers must formulate the problem correctly and derive equations that explain beat-wave excitation. PHASE II: Conduct controlled experiments and collect data on generation of ELF/VLF waves in the F layer of the ionosphere, analyze experimental data and demonstrate that beat wave generation method can efficiently create ELF/VLF waves that can be detected on the ground. Beyond the current government interest in VLF waves generation, there exists interest in the commercial sector to understand the ability of VLF waves penetrating in deep soil applications such as exploration of tunnels, mining and detection of natural resources. Present efficient commercialization strategy for newly developed techniques. PHASE III DUAL USE APPLICATIONS: Design compact mobile HF radiation sources for generation of VLF waves for different applications using beat wave technology. Validate novel low-cost beat wave approach for applications such as ionospheric modification, over the horizon radar (OTHR) applications, secure VLF communications, underground structure detection (military or commercial use). REFERENCES: M. B. Cohen, R. C. Moor, M. Golkowski and N. G. Lehtinen, ELF/VLF wave generation from the beating of two HF ionospheric heating sources, Journal of Geophysical Research, vol. 117, no. A12310, 2012; \ V. A. Puchkov, Generation of Plasma Waves in the Ionospheric Plasma by Powerful Nonmonochromatic Microwave Beams, Phys. Scr., vol. 78, no. 1, 2008; D. Main and V. Sotnikov, Parametric interaction between ELF and VLF waves, 3D LSP simulation results, Phys. Plasmas 27, 022304 (2020). KEYWORDS: Ionosphere; Very low Frequency (VLF) waves; VLF communications; Parametric Wave Interaction