Verification and Calibration of the ICEBEAR Radar through GPU Acceleration, Noise Characterization and Calculation, and Radio Galaxy Phase Calibration

The research performed for this thesis focused on verifying, quantifying, calibrating, and improving the Ionospheric Continuous Wave (CW) E-region Bi-static Radar (ICEBEAR) data observations and quality. Graphical processing unit (GPU) acceleration was used to improve the computation speed of ICEBEAR data analysis. The ICEBEAR noise floor was studied to better understand the ICEBEAR noise environment and verify the signal to noise ratio (SNR), which affects all ICEBEAR data products. Finally, a calibration method using the radio galaxy Cygnus~A was developed to enable improved phase calibration of the ICEBEAR receiver antennas. GPUs enable high computational throughput through the use of parallel processing and specific hardware design. This part of my research used the properties of GPUs to accelerate the data analysis of ICEBEAR to be 48 times faster than the original processing capability, enabling real-time analysis of ICEBEAR data. The current noise calculation technique of taking the median power calculation of the ICEBEAR field of view is reasonable, but it is recommended that ICEBEAR switch to using an average of the furthest ranges measured by the radar. The dominant noise sources in the radar changes based on ionospheric activity, where self-clutter dominates during active periods and cosmic noise dominates during quite periods. This impacts the computation of the SNR data product and is better quantified by a far range average for all 45 baselines in the ICEBEAR radar. The detection of Cygnus~A during quiet ionospheric periods was used to calculate phase self-calibrations for the radar by comparing the measured phase difference between antennas to the expected theoretical phase difference of Cygnus~A. The technique is shown to generate similar and complementary results to the current spectrum analyzer calibration technique. Future improvements to ICEBEAR imaging analysis and future research into the improved observation of Cygnus~A will allow this new phase self-calibration method to be actively used for ICEBEAR

ICEBEAR-3D: An Advanced Low Elevation Angle Auroral E region Imaging Radar

The Ionospheric Continuous-wave E region Bistatic Experimental Auroral Radar (ICEBEAR) is an auroral E~region radar which has operated from 7 December 2017 until the September 2019. During the first two years of operation, ICEBEAR was only capable of spatially locating E~region scatter and meteor trail targets in range and azimuth. Elevation angles were not determinable due to its East-West uniform linear receiving antenna array. Measuring elevation angles of targets when viewing from low elevation angles with radar interferometers has been a long standing problem. Past high latitude radars have attempted to obtain elevation angles of E~region targets using North-South baselines, but have always resulted in erroneous elevation angles being measured in the low elevation regime (0° to ≈30° above the horizon), leaving interesting scientific questions about scatter altitudes in the auroral E~region unanswered. The work entailed in this thesis encompasses the design of the ICEBEAR-3D system for the acquisition of these important elevation angles. The receiver antenna array was redesigned using a custom phase error minimization and stochastic antenna location perturbation technique, which produces phase tolerant receiver antenna arrays. The resulting 45-baseline sparse non-uniform coplanar T-shaped array was designed for aperture synthesis radar imaging. Conventional aperture synthesis radar imaging techniques assume point-like incoherent targets and image using a Cartesian basis over a narrow field of view. These methods are incompatible with horizon pointing E~region radars such as ICEBEAR. Instead, radar targets were imaged using the Suppressed Spherical Wave Harmonic Transform (Suppressed-SWHT) technique. This imaging method uses precalculated spherical harmonic coefficient matrices to transform the visibilities to brightness maps by direct matrix multiplication. The under sampled image domain artefacts (dirty beam) were suppressed by the products of differing harmonic order brightness maps. From the images, elevation and azimuth angles of arrival were obtained. Due to the excellent phase tolerance of ICEBEAR new light was shed on the long standing low elevation angle problem. This led to the development of the proper phase reference vertical interferometry geometry, which allowed horizon pointing radar interferometers to unambiguously measure elevation angles near the horizon. Ultimately resulting in accurate elevation angles from zenith to horizon

Investigating Spatial and Temporal Structuring of E-Region Coherent Scattering Regions Over Northern Norway

Recently, it has been shown that the Spread Spectrum Interferometric Multistatic meteor radar Observing Network radar system located in northern Norway is capable of measuring ionospheric E-region coherent scatter with spatial and temporal resolutions on the order of 1.5 km and 2 s, respectively. Four different events from June and July of 2022 are examined in the present study, where the coherent scatter measurements are used as a tracer for large-scale ionospheric phenomena such as plasma density enhancements and ionospheric electric fields. By applying a two-dimensional Fourier analysis to range-time-intensity data, we perform a multi-scale spatial and temporal investigation to determine the change in range over time of large-scale ionospheric structures (>3 km) which are compared with line-of-sight velocities of the small scale structures (∼5 m) determined from the Doppler shift of the coherent scatter. The spectral characteristics of the large-scale structures are also investigated and logarithmic spectral slopes for scale sizes of 100–10 km were found to be between −3.0 and −1.5. This agrees with much of the previous work on the spatial spectra scaling for ionospheric electric fields. This analysis aids in characterizing the source of the plasma turbulence and provides crucial information about how energy is redistributed from large to small scales in the E-region ionosphere

ICEBEAR-3D: A Low Elevation Imaging Radar Using a Non-Uniform Coplanar Receiver Array for E Region Observations

The Ionospheric Continuous-wave E region Bistatic Experimental Auroral Radar (ICEBEAR) has been reconfigured using a phase error minimization and stochastic antenna location perturbation technique. The resulting 45-baseline sparse non-uniform coplanar T-shaped array, ICEBEAR-3D, is used for aperture synthesis radar imaging of low elevation targets. The reconfigured receiver antenna array now has a field of view ±45° azimuth and 0°–45° elevation at 0.1° angular resolution. Within this field of view no aliasing occurs. Radar targets are imaged using the Suppressed Spherical Wave Harmonic Transform (Suppressed-SWHT) technique. This imaging method uses precalculated constant coefficient matrices to solve the integral transform from visibility to brightness through direct matrix multiplication. The method then suppresses image artefacts (dirty beam) due to undersampling by combining brightness maps of differing harmonic order. Measuring elevation angles of targets at low elevations with radar interferometers has been a long standing problem. ICEBEAR-3D elucidates the underlying misinterpretations of the conventional geometry for vertical interferometry especially for low elevation angles. The proper phase reference vertical interferometry geometry is given which allows radar interferometers to unambiguously measure elevation angles from zenith to horizon without special calibration. The receiver antenna array reconfiguration, Suppressed-SWHT imaging technique, and proper geometry for vertical interferometry are validated by showing agreement of the meteor trail altitude distribution with numerous data sets from other radars