Monitoring Earth Using Radio Wave Phase Imager

<p><strong>Monitoring Earth Using Radio Wave Phase Imager</strong></p> <p>Radwan Sharif, and Rodney Herring<br />MENG, CBR, CAMTEC, University of Victoria, Victoria, Canada V8W 2Y2</p> <p><strong>Abstract</strong></p> <p>The ionosphere is the highest region of Earth's atmosphere where waves exist from space and Earth disturbances and It is considered the largest sensor on Earth. Software Defined Radio (SDR) Earth Imager has been devised using a wave phase imager to obtain information about Earth disturbances. This imager creates an image of the ionosphere using an antenna array like a camera. Within the image are waves that exist on/in the surface of the ionosphere. The carrier wave is transmitted up through the atmosphere at near-vertical incidence from the Earth's surface, reflecting them off the ionosphere back down to the Earth's surface, using an antenna array to reveal a phase image. The Earth Imager was constructed at the Dominion Radio Astrophysical Observatory. From the data analysis, two types of waves obviously appeared: one with a constant frequency expecting the power losses in transmission lines, and the other with a considerable frequency spike might be Earthquakes or lightning. The experiments at the University of New Mexico's Long Wavelength Array (LWA-1 and LWA-SV) provided a high resolution. The results revealed the wavevector directions of disturbances at two sites. The intersection of wavevectors determines the source of the disturbance. The wave vector of one of the strongest sets of waves, at 0.06 cycle/m, was tracked over time at both the LWA-SV and LWA-1 stations. The most likely sources for this are losses of local power plants in Albuquerque as the highest electricity consumption.</p> <ul> <li><strong> </strong><strong>Experimental Method at DRAO</strong></li> </ul> <p>Experiments supporting this research were conducted at DRAO (Dominion Radio Astrophysical Observatory), Penticton, BC. The Earth Atmosphere Imager consisted of three main components; one radio wave transmitter, one radio wave detector comprised of a two-dimensional array of passive receivers, and a small beamformer that measured the time and phase of the transmitted and received radio waves. The phase difference in path length (L) of the radio wave traveling from the Transmitter to each receiver in the array.</p> <p><img src="" alt="" width="235" height="31" /></p> <p>Frequency (f), wavelength (λ), and speed of light (c).</p> <p><strong>Detector (antenna array)</strong></p> <p>The detector consisted of an antenna array of eight (two antenna arrays of 4) receiving antennas (20km away from the transmitter). The antennas numbered one to five, arranged in an east-west line with an approximate distance of around 15 m. The antennas numbered six to eight were branched off perpendicular from antenna 2 to form a T shape from north to south with a spacing of roughly 20 m between antennas, Figure 1.</p> <p><img src="" alt="" width="671" height="268" /></p> <p>Figure 1 Transmitted carrier and reflected radio wave</p> <p><strong>Result and Discussion (DRAO)</strong></p> <p>In summer  2018, Earth Imaging device prototypes were built and tested at the University of Victoria UVic and DRAO. Configuration two shows that the relative phase differences between the antennae were determined from antenna pairs 2/6, 2/7, and 1/8, i.e., relative to antenna 2 resulting in three relative phase measurements with constant waves (Figure 2 (a)) and large spike, Figure 2 (b).</p> <p><img src="" alt="" width="655" height="262" /></p> <p>Figure 2 (a) Waves moving in Earth's F ionization layer having a constant amplitude, frequency and direction of movement, and high amplitude, like a spike moving in Earth's F ionization (b)</p> <ul> <li><strong> </strong><strong>Experimental Method at </strong><strong>New Mexico (University Radio Observatory)</strong></li> </ul> <p><strong>LWA-SV and LWA1 Antenna Array </strong></p> <p>The LWA-SV, Figure 3, and The LWA1, Figure 4, are located in New Mexico. Each array comprises 256 pairs of dipole-type antennas.<img src="" alt="" width="644" height="429" /></p> <p>Figure 3 Position of each antenna (LWA-SV) shows as a circle in the x and y-direction</p> <p><strong>Transmitter</strong></p> <p>The Santa Fe station transmitted carrier radio waves with frequencies ranging from 3 to 7 MHz.</p> <p><strong>Experimental analysis </strong></p> <p>A waterfall displays the transmitted carrier signal strength (5.357 MHz) represented by colors over time and varies with the spectrum of frequencies. The relative unwrapped phases were calculated by taking antenna number134 and 10 as a reference, LWA-SV, and LWA-1, respectively.</p> <p><strong>Spatial Phase Image for both Stations </strong></p> <p>The imaging process of the relative unwrapped phase used a mesh made on the antenna positions and divided into several rectangular shapes.</p> <p><img src="" alt="" width="645" height="430" /></p> <p>Figure 4 Phase image of antenna locations</p> <p>A 2D Fourier transform space domain was applied to a phase image to obtain a Fourier image for each time of data collection.</p> <p><img src="" alt="" width="390" height="49" /></p> <p><strong>Result and Discussion </strong></p> <p>2D Fourier image analysis showed many spatial frequency peaks representing sets of waves on the ionosphere, Figure 5. Each pair of peaks located at different sides of the origin of the phase image is symmetric. As a result, two symmetric peaks represent one wave. One of the waves situated close to the center, having 0.06 cycles/m with a wavelength of 16.667 m, has the largest peak.</p> <p><img src="" alt="" width="653" height="261" /></p> <p>Figure 5 Fourier image of LWA-SV indicating sets of observed waves, with the strongest (yellow-red spot) having 0.06 cycles/m and a wavevector traveling North-South.</p> <p>The carrier radio wave is reflected in two spots on the ionosphere's surface between Santa Fe and LWA-SV and LWA-1. The two sets of datasets show a range of vectors in both LWA-1 and LWA-SV Fourier images. The wavevectors of 0.06 cycles/m were forwarded to Albuquerque, and their intersection occurred at Albuquerque power plants, Figure 6.</p> <p><img src="" alt="" width="666" height="444" /></p> <p>Figure 6 Mid-points, which are between Santa Fe and LWA-1 and LWA-SV, demonstrate are the wavevector intersections near Albuquerque and local power plants</p> <ul> <li><strong> </strong><strong>Conclusion</strong></li> </ul> <p>Solar, geomagnetic, mad-made, and meteorological Earth disturbing events create waves on the surface of the ionization layer. The SDR Earth Imaging technique was built and tested at DRAO, allowing for the image of two types of ionospheric waves: one with a consistent frequency and amplitude and the other with a spike. This device enables us to image a set of waves by using a radio wave phase imager. </p> <p>The Earth Imaging method was employed at both the LWA-SV and LWA-1 stations. The results show that the wavevector of one set of waves, 0.06 cycle/m, was followed over time and directed to local power generating plants and electricity use by Albuquerque.</p> <p> </p>

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