The Case for Combining a Large Low-Band Very High Frequency Transmitter With Multiple Receiving Arrays for Geospace Research: A Geospace Radar

We argue that combining a high‐power, large‐aperture radar transmitter with several large‐aperture receiving arrays to make a geospace radar—a radar capable of probing near‐Earth space from the upper troposphere through to the solar corona—would transform geospace research. We review the emergence of incoherent scatter radar in the 1960s as an agent that unified early, pioneering research in geospace in a common theoretical, experimental, and instrumental framework, and we suggest that a geospace radar would have a similar effect on future developments in space weather research. We then discuss recent developments in radio‐array technology that could be exploited in the development of a geospace radar with new or substantially improved capabilities compared to the radars in use presently. A number of applications for a geospace radar with the new and improved capabilities are reviewed including studies of meteor echoes, mesospheric and stratospheric turbulence, ionospheric flows, plasmaspheric and ionospheric irregularities, and reflection from the solar corona and coronal mass ejections. We conclude with a summary of technical requirements

STUDY OF THE POLAR CAP PLASMA FLOWS WITH THE CLYDE RIVER SUPERDARN RADAR

Plasma flows in the high latitude ionosphere reflect complex physical processes occurring when the Sun-originated solar wind blows around the Earth. One way of monitoring and quantifying these flows is to use Doppler velocity measurements with ground-based high-frequency (HF) radars such as the Super Dual Auroral Radar Network (SuperDARN) radars. The research presented in this thesis includes two major topics. First, we investigate quality of SuperDARN HF velocity measurements for a relatively new radar in the network, the Clyde River (CLY) radar. This has never been done in the past while the radar is critical in the network as its field of view allows one to measure plasma flow velocity roughly along magnetic parallels at extremely high latitudes. Second, after successfully validating the Clyde River radar measurements, variations in the plasma flows at radar latitudes are investigated. To accomplish the first task, measurements of the plasma velocity collected over the year 2016 at Clyde River are compared with nearly simultaneous velocity measurements from the Resolute Bay Incoherent Scatter Radar-Canada (RISR-C). Our results show that the CLY radar velocity measured in beams 4-6 is statistically comparable to the ExB component of the plasma drift along these beams (azimuthal plasma flows) measured by the RISR-C. The agreement between the two types of radars was found to be not ideal; the lines of linear fit had slopes in the range of 0.5-0.7. This is comparable with the slopes in other experiments, but slightly lower than usual. We showed that the correction of HF velocities for the index of refraction effect does not increase the slope of the line to 1 mostly because of lower HF velocities at large ExB drifts of > 700 m/s. This “underestimation” effect was found to be stronger at nighttime and its compensation by considering the index of refraction effect was less successful than at daytime. We carried out a similar comparison between Rankin Inlet (RKN) SuperDARN radar velocity measurements and that of RISR for the same period of 2016 and found reasonably good agreement as well. We showed that the strongest disagreements between HF and RISR-C velocity occurred for periods with very low CLY and RKN velocities, below 100-200 m/s in magnitude, indicating that some ionospheric echoes could be misidentified by the SuperDARN radar processing technique; this effect is more pronounced for the RKN radar. Finally, we investigated self-consistency of SuperDARN HF measurements by comparing velocities of the CLY radar and the SuperDARN radar at Inuvik (INV) in about the same direction. We found that the CLY-INV agreement is reasonable for ranges of >1000 km with pure F region echo detection by both radars. Evidence is presented that measurements at short ranges of <800 km, that are traditionally thought to be pure F region scatter as well, is sometimes contaminated with scatter from the E region with velocities below the ExB drift. On the second task, we considered multi-year CLY data set to assess seasonal variation of the plasma flow velocity in the azimuthal direction, at magnetic latitudes of ~ 81 degrees and at southward orientation of solar-related interplanetary magnetic field (IMF) Bz 0, CLY velocities remain much longer negative. In general, we found that CLY velocity data in the azimuthal direction can be interpreted in terms of a more “round” overall pattern in summer

A land-based hf transmitter for ionospheric propagation studies using superdarn radars

Thesis (MEng (Electrical Engineering))--Cape Peninsula University of Technology, 2019The goal of this project is to design, build and characterize a low power High Frequency (HF) transmitter. The transmitter will be installed and operated in Antarctica to establish a beacon at the South Pole station to be received by the Super Dual Auroral Radar Network (SuperDARN) radar installed at SANAE IV. The transmitter is specified and designed to transmit at 12.57 MHz (continuous wave) from the South Pole. It must achieve a frequency drift of 41.8_mHz or better. The transmitter must operate normally under extremely low temperature conditions down to -40°C. The transmitted wave will be refracted by the ionosphere and received by the SuperDARN radar at SANAE IV. The ground distance between the HF transmitter and the radar is approximately 2000 km. The goal of the experiment is to form a bi-static radar configuration in order to study the ionosphere, especially travelling ionospheric disturbances (TIDs), which are signatures of atmospheric gravity waves (AGWs). A 25 dBm transmitter prototype was developed using a GPS disciplined oscillator in order to achieve the frequency stability required for this project. The HF transmitter proved to conform to the power and frequency stability requirements both during propagation tests conducted between Hermanus (34.4241° S, 19.2247° E) and Pretoria (34.0558° S, 18.4589° E) in South Africa, as well as when the device was exposed to temperatures that ranged from +40°C to -45°C. Although the antenna design was beyond the scope of this project, various determinations and considerations are presented in the link budget analysis, which have been confirmed during field tests. Therefore, certain recommendations on the antenna design are given. Propagation in Antarctica is expected to differ from the field tests conducted due to the differences in density and dynamics of the polar ionosphere, compared to the mid-latitude ionosphere

Design and Implementation of a Software Defined Ionosonde. A contribution to the development of distributed arrays of small instruments

In order to make advances in studies of mesoscale ionospheric phenomena, a new type of ionosonde is needed. This ionosonde should be relatively inexpensive and small form factor. It should also be well suited for operation in a network of transmit and receiver sites that are operated cooperatively in order to measure vertical and oblique paths between multiple transmitters and receivers in the network. No such ionosonde implementation currently exists. This thesis describes the design and implementation of a coded continuous wave ionosonde, which utilizes long pseudo-random transmit waveforms. Such radar waveforms have several advantages: they can be used at low peak power, they can be used in multi-static cooperative radar networks, they can be used to measure range-Doppler overspread targets, they are relatively robust against external interference, and they produce relatively low interference to other users that share the same portion of the electromagnetic spectrum. The new ionosonde design is thus well suited for use in ionosonde networks. The technical design relies on the software defined radio paradigm and the hardware design is based on commercially available inexpensive hardware. The hardware and software implementation is shown to meet the technical and scientific requirements that were set for the instrument. The operation of the instrument is demonstrated in practice in Longyearbyen, Svalbard. With this new ionosonde design and proof of concept implementation, it has been possible to re-establish routine ionospheric soundings at Longyearbyen, Svalbard; to replace the Dynasonde instrument that was decommissioned several years ago. It is also possible to use this new design as a basis for larger networks of ionosondes. The software and hardware design is made publicly available as open source, so that anyone interested can reproduce the instrument and also contribute to the project in the future

Characterising Spatial and Temporal Ionospheric Variability with a Network of Oblique Angle-of-arrival and Doppler Ionosondes

Ionospheric variability exists on a broad range of scales, and routinely impacts skywave propagation modes of high frequency radio waves, to the detriment of radar and communication systems. In order to better understand the electron density structures associated with such variability at mid-latitudes, a network of oblique angle-of-arrival (AoA) and Doppler ionosondes were installed in central and northern Australia as part of the ELOISE campaign in 2015. This thesis analyses observations from the ELOISE AoA ionosondes, with a focus on characterising the influence of medium- to large- scale gradients and signatures of travelling ionospheric disturbances (TIDs). Following an overview of the experiment, the design and calibration of the new ionosonde system is described. With multi-channel receivers connected to each element of two twin-arm arrays, a total of eleven AoA paths of between 900 and 2700 km were collected, including nine with interleaved Doppler measurements using a special channel scattering function (CSF) capability. On-board signal processing was developed to perform real-time clear channel evaluation and CSF scheduling, and generate the AoA ionograms and delay-Doppler images with fitted electron density profiles. In further offline analysis, peak detection and mode classification was carried out, to support reflection point mapping and tilt estimation. Significant testing and validation of the new ionosonde before and after the experiment revealed AoA uncertainties on the scale of 0.2–0.5° in bearing and 0.4–0.9° in elevation. Having identified a low-elevation bias, models of tropospheric refraction and antenna mutual coupling effects were considered as possible correction strategies, but ultimately an empirical approach based on aggregated ionospheric returns was implemented. Small-scale (intra-dwell) ionospheric variability also has the potential to compromise results, through unresolved multi-mode mixing, and this has been investigated using a combination of spatial and temporal variability metrics derived from the CSF data. The analysis of large quantities of F2 peak data shows persistent diurnal patterns in the oblique AoA observables that are also well-captured by a conventional data-assimilative ionospheric model, even without the benefit of AoA and Doppler inputs. Furthermore, Doppler measurements are reproduced remarkably well using just the midpoint fitted profiles. A statistical study has quantified the level of consistency between observations and model, to provide greater confidence in the results. Many of the geophysical features can be interpreted as ionospheric gradients, as evident in the tilt estimates, and horizontally moving structures such as TIDs, using a form of Doppler-based drift analysis. While signatures of TIDs vary considerably, two simple wave-like perturbation models have been evaluated to help classify quasi-periodic behaviour in the AoA observations, as well as understand the directional filtering effect imposed by the path geometry. In some cases, a set of TID parameters can be determined by eye, but in others automatic parameter inversion techniques may be more viable. Two such techniques were implemented but results using both real and synthetic data demonstrated some significant limitations. Finally, attempts to relate TID signatures across multiple paths shows promise, but there still appears to be a strong dependence on path geometry that is difficult to eliminate.Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 202

Techniques for understanding anomalous radar spectra.

This thesis concerns the investigation of the Earth's upper atmosphere, ionosphere and magnetosphere. In particular, it involves a study of the F region, using EISCAT Svalbard Radar data. Anomalous ion line spectra have been identified in many of the radar experiments which have been conducted at that site. Such spectra are defined as deviations from the standard symmetric "double-humped" spectra derived from incoherent scatter radar echoes from the upper atmosphere. Some anomalous spectra --- where there are sharp enhancements of power over restricted height ranges --- have been attributed to satellite contamination in the beam path. Here we outline a method for detecting such contamination, and review in detail a few cases where the method enables the identification of anomalous spectra as satellite echoes, subsequently ascribed to specific orbital objects. The methods used here to identify such satellites provide, a useful way of distinguishing anomalous spectra due to satellites from those of geophysical origin. Analysis of EISCAT Svalbard Radar data reveals that an average of 8 satellites per hour are found to cross the beam. Based on a relatively small sample of the data set, it appears that at least half of the occurrences of anomalous spectra are caused by satellite contamination rather than being of geophysical origin.Those anomalous spectra which cannot be explained by satellite contamination appear to occur most frequently during or immediately before magnetic storms, as can be seen when compared with the Dst index and magnetometer data. A model of the chemical structure of the ionosphere is proposed; This gives predictions for the intensity ratios of the 6300A and 5577 A emission lines and these are compared with readings from the meridian scanning photometer at Adventdalen

Direct aeronomic measurements in the lower ionosphere -- an informal conference record / 1

Report on Conference held Oct 21, 22 and 23, 1963 Illini Union, Univ. of Illinois, Urbana, Ill."Final report, Contract DA-11-022-AMC-890 (R), Ballistics Research Laboratories, Aberdeen Proving Ground, Maryland"Includes bibliographical references and index.Contents: Measurement Techniques: Electron and ion density and electron temperature, Impedance, Conductivity, Neutral and ion composition, Magnetic field, Pressure, density and wind, Airglow, Solar radiation, Supersonic flow; Results: Results of measurements of composition, Results of measurements of electron and ion density and temperature, Results of radio propagation measurements, and Interpretation of lower ionospheric measurements