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

Estimation of Forest Biomass and Faraday Rotation using Ultra High Frequency Synthetic Aperture Radar

Synthetic Aperture Radar (SAR) data in the Ultra High Frequency (UHF; 300 MHz – 3 GHz)) band have been shown to be strongly dependent of forest biomass, which is a poorly estimated variable in the global carbon cycle. In this thesis UHF-band SAR data from the fairly flat hemiboreal test site Remningstorp in southern Sweden were analysed. The data were collected on several occasions with different moisture conditions during the spring of 2007. Regression models for biomass estimation on stand level (0.5-9 ha) were developed for each date on which SAR data were acquired. For L-band (centre frequency 1.3 GHz) the best estimation model was based on HV-polarized backscatter, giving a root mean squared error (rmse) between 31% and 46% of the mean biomass. For P-band (centre frequency 340 MHz), regression models including HH, HV or HH and HV backscatter gave an rmse between 18% and 27%. Little or no saturation effects were observed up to 290 t/ha for P-band. A model based on physical-optics has been developed and was used to predict HH-polarized SAR data with frequencies from 20 MHz to 500 MHz from a set of vertical trunks standing on an undulating ground surface. The model shows that ground topography is a critical issue in SAR imaging for these frequencies. A regression model for biomass estimation which includes a correction for ground slope was developed using multi-polarized P-band SAR data from Remningstorp as well as from the boreal test site Krycklan in northern Sweden. The latter test site has pronounced topographic variability. It was shown that the model was able to partly compensate for moisture variability, and that the model gave an rmse of 22-33% when trained using data from Krycklan and evaluated using data from Remningstorp. Regression modelling based on P-band backscatter was also used to estimate biomass change using data acquired in Remningstorp during the spring 2007 and during the fall 2010. The results show that biomass change can be measured with an rmse of about 15% or 20 tons/ha. This suggests that not only deforestation, but also forest growth and degradation (e.g. thinning) can be measured using P-band SAR data. The thesis also includes result on Faraday rotation, which is an ionospheric effect which can have a significant impact on spaceborne UHF-band SAR images. Faraday rotation angles are estimated in spaceborne L-band SAR data. Estimates based on distributed targets and calibration targets with high signal to clutter ratios are found to be in very good agreement. Moreover, a strong correlation with independent measurements of Total Electron Content is found, further validating the estimates

On the possibility of radar echo detection of ultra-high energy cosmic ray- and neutrino-induced extensive air showers

We revisit and extend the analysis supporting a 60 year-old suggestion that cosmic rays air showers resulting from primary particles with energies above 10^{18} eV should be straightforward to detect with radar ranging techniques, where the radar echoes are produced by scattering from the column of ionized air produced by the shower. The idea has remained curiously untested since it was proposed, but if our analysis is correct, such techniques could provide a significant alternative approach to air shower detection in a standalone array with high duty cycle, and might provide highly complementary measurements of air showers detected in existing and planned ground arrays such as the Fly's Eye or the Auger Project. The method should be particularly sensitive to showers that are transverse to and relatively distant from the detector, and is thus effective in characterizing penetrating horizontal showers such as those that might be induced by ultra-high energy neutrino primaries.Comment: 29 pages, 16 figures, uses aas2pp4.sty. Final version, to appear in Astroparticle Physics. Contains new figs, better estimate of angular precision possibl

Study of Coulomb collisions and magneto-ionic propagation effects on incoherent scatter radar measurements at Jicamarca

In this dissertation, Coulomb collisions and magneto-ionic propagation effects on the incoherent scatter radar measurements have been studied and analyzed in detail. The present study aims at modeling radar observations of the equatorial ionosphere carried out at the Jicamarca Radio Observatory (Lima, Peru) using antenna beams pointed perpendicular to the Earth's magnetic field B. A Monte Carlo procedure based on the simulation of charged particle trajectories in a magnetized plasma (with suppressed collective interactions) was developed to account for the effects of Coulomb collisions on the shape of the incoherent scatter spectrum. Statistics of simulated electron and ion trajectories, single-particle ACF's, and associated Gordeyev integrals are utilized in the general framework of incoherent scatter spectrum models (e.g., Kudeki and Milla, 2006) to produce theoretical spectra for different plasma configurations. Our simulation method effectively extends the procedure of Sulzer and Gonz??lez (1999) into three dimensions and is valid for all magnetic aspect angles including the direction perpendicular to B. The 3D trajectories, randomized by Coulomb collisions, are described by a generalized Langevin equation with velocity-dependent friction and diffusion coefficients taken from the standard Fokker-Planck collision model of Rosenbluth et al. (1957). A statistical analysis of the simulated trajectories shows that the ion motion is well modeled as a Brownian-motion process with Gaussian displacement distributions (and constant friction and diffusion coefficients), in which case, an analytical expression for the single-ion ACF can be obtained (e.g., Woodman, 1967). However, the simulated electron motions do not fit a Brownian model because the electron displacement distributions in the direction parallel to B are sharper than a Gaussian. To account for these effects on our incoherent scatter spectrum model, a numerical library of electron statistics in an oxygen plasma (single-electron ACF's) had to be developed. The library spans a set of densities, temperatures, and magnetic fields as needed for Jicamarca F-region applications. The antenna beams used in perpendicular-to-B radar observations at Jicamarca have angular widths of the order of a degree. Within this range of small magnetic aspect angles, different modes of magneto-ionic wave propagation are excited. These characteristic modes vary from linearly polarized in the direction perpendicular to B (Cotton-Mouton regime) to circularly polarized at aspect angles greater than 0.5 deg (Faraday rotation regime). In order to model the magneto-ionic propagation effects on incoherent scatter radar measurements, a computer algorithm based on the Appleton-Hartree equation for electromagnetic wave propagation in a magnetized plasma was developed. Simulation studies show that magneto-ionic propagation effectively modifies the shapes of the radar beams and does have an impact on the incoherent scatter radar measurements because the polarization of the incident and backscattered fields vary as they propagate through the ionosphere. A soft-target radar equation, which incorporates our collisional incoherent scatter spectrum and magneto-ionic propagation models, is formulated to model the radar measurements collected at Jicamarca. Voltages detected by the radar antenna are represented as the beam-weighted sum of ionospheric backscattered signals corresponding to the range of magnetic aspect angle directions illuminated by the antenna beam. This integration is carried out numerically using a finite-element-like integration method that takes advantage of the slow variation of physical parameters in the direction transverse to the geomagnetic field. The resultant radar model is utilized in the inversion of ionospheric parameters in a three-beam radar experiment conducted at Jicamarca. The experiment interleaves radar observations with perpendicular-to-B and off-perpendicular antenna beams. The data model matches very closely the different features of the measured data; for instance, it predicts the enhancement of the measured power in the direction perpendicular-to-B at ionospheric altitudes where the electron temperature is greater than the ion temperature. F-region electron density and temperature ratio (T_e/T_i) estimates were obtained using a least-squares inversion algorithm. The inversion results show a good agreement with ionosonde data, validating our model for incoherent scatter radar measurements

Estimating Target Heights Based on the Earth Curvature Model and Micromultipath Effect in Skywave OTH Radar

Skywave over-the-horizon (OTH) radar systems have important long-range strategic warning values. They exploit skywave propagation reflection of high frequency signals from the ionosphere, which provides the ultra-long-range surveillance capabilities to detect and track maneuvering targets. Current OTH radar systems are capable of localizing targets in range and azimuth but are unable to achieve reliable instantaneous altitude estimation. Most existing height measurement methods of skywave OTH radar systems have taken advantage of the micromultipath effect and been considered in the flat earth model. However, the flat earth model is not proper since large error is inevitable, when the detection range is over one thousand kilometers. In order to avoid the error caused by the flat earth model, in this paper, an earth curvature model is introduced into OTH radar altimetry methods. The simulation results show that application of the earth curvature model can effectively reduce the estimation error

MONITORING OF IONOSPHERIC SCINTILLATION PHENOMENA USING SYNTHETIC APERTURE RADAR (SAR)

The applications of synthetic aperture radars (SAR) have increased manifold in the past decade, which includes numerous Earth observation applications such as agriculture, forestry, disaster monitoring cryospheric- and atmospheric- studies. Among them, the potential of SAR for ionospheric studies is gaining importance. The susceptibility of SAR to space weather dynamics, and ionosphere in particular, comes at low frequencies of L- and P-bands. This paper discusses one such scintillation event that was observed by L-band Advanced Land Observation Satellite (ALOS)-2 Phased Array L-type SAR (PALSAR) over southern India on March 23, 2015. The sensors also acquired data sets on four other days on which the ionosphere was quiet. Ionospheric parameter measurements of total electron content (TEC) and amplitude scintillation (S4) index from ground-based Global Navigation Satellite System (GNSS) receiver at Tirunelveli was used to establish the ionospheric conditions on the days of SAR acquisition as well as to corroborate the S4 estimated from SAR. Multi-temporal ALOS-2 data sets were utilized to calculate S4 from two separate methods and the results have a good agreement with GNSS receiver measurements. This highlights the potential of SAR as an alternate technique of monitoring ionospheric scintillations that can be utilized as complementary to the highly accurate and dedicated measurements from the GNSS networks

Survey and simulation of space debris using EISCAT UHF

This thesis starts with a review of the evolution of space debris, what is consists of, how it is made, how it is detected and tracked, and why it is such an important topic. Some of the worst collisions have contributed to causing 49% of the total space debris. If the launch rate continues, the "Kessler Syndrome" might become a reality destroying our future outlook for space communication and exploration. Furthermore, a deeper look at the contents is done and what is the impact of these hypervelocity objects. Highly-advanced ground surveillance systems are used to track and catalog the space debris stationed around the globe, and highly sophisticated space debris models are used to estimate the density of the total space debris population in all sizes, shapes and compositions. After 60 years in space, a lot of space debris has accumulated, resulting in a large increase of density in the polar regions. However, objects below 10 cm are not easily detected, but EISCAT UHF is capable detecting the sizes below 10 cm and down to 1 cm by using beampark experiments, its location makes it suitable for detecting polar region debris. The data is then used to confirm the catalog and the models. A 24-hour beampark experiment was done on 4th of January 2018 simultaneously at Tromsø and Svalbard, specifically for this thesis. It statistically measured the range, the Doppler velocity, and the echo strength of space debris. An inversion of apogee and inclination was then done by using these parameters. A modelling of a beampark experiment was simulated, propagating objects through the EISCAT UHF beam. It extracted the data from the ESA MASTER model and the output was the number of detections per day. A comparison of the beampark experiment 2018 campaign with the simulation model indicated that the simplified model shows good correlation with the observations

Electromagnetic Wave Theory and Applications

Contains table of contents for Section 3 and reports on seven research projects.Joint Services Electronics Program Contract DAAL03-89-C-0001National Science Foundation Contract ECS 86-20029Schlumberger- Doll ResearchU.S. Army Research Office Contract DAAL03 88-K-0057National Aeronautics and Space Administration Contract NAGW-1617U.S. Navy - Office of Naval Research Contract N00014-89-J-1107National Aeronautics and Space Administration Contract NAGW-1272National Aeronautics and Space Administration Contract 958461Simulation Technologies Contract DAAH01-87-C-0679U.S. Army Corp of Engineers Contract DACA39-87-K-0022WaveTracer, Inc.U.S. Navy - Office of Naval Research Contract N00014-89-J-1019U.S. Air Force Systems - Electronic Systems Division Contract F19628-88-K-0013Digital Equipment CorporationInternational Business Machines CorporationU.S. Department of Transportation Contract DTRS-57-88-C-0007

Measuring and modelling the impact of the ionosphere on space based synthetic aperture radars

Synthetic aperture radar (SAR) is a technique widely used in applications that require all-weather imaging. The ionosphere affects the operation of these radars, with those operating at L-band (1-2 GHz) and below at risk of being seriously compromised by the ionosphere. A method of using Global Positioning System (GPS) data to synthesize the impact of the ionosphere on SAR systems has been presented. The technique was used to assess the viability of using a signal phase correction derived from a reference location in a SAR image to correct ionospheric effects across the image. A dataset of SAR images and GPS measurements collected simultaneously on Ascension Island were used to test two techniques for deriving ionospheric strength of turbulence (C$_k$L) from SAR images – one using measurements of trihedral corner reflectors (CR) and the other measurements of natural clutter. The CR C$_k$L values showed a correlation of 0.69 with GPS estimates of C$_k$L, whilst the clutter measurements showed a correlation of up to 0.91 with the CR values. Finally, a study of using the effects of intensity scintillation on SAR images to measure the S$_4$ index was performed. The study was not able to reproduce previous results, but produced significant practical conclusions

Incorporation of GNSS multipath to improve autonomous rendezvous, docking and proximity operations in space

Automated rendezvous and docking (AR&D;) operations are important for many future space missions, such as the resupply of space stations, repair and refueling of large satellites, and active removal of orbital debris. These operations depend critically on accurate, real-time knowledge of the relative position and velocity between two space vehicles. Unfortunately, Global Navigation Satellite System (GNSS) capabilities remain severely limited in close proximity to large space structures due to significant multipath effects and signal blockage. Although GNSS is used for the initial stages of approach, other instruments such as laser, radar and vision-based systems, are required to augment GNSS during AR&D; over the last few hundred meters. This dissertation evaluates the feasibility of GNSS multipath-based relative space navigation. Methods for separating and interpreting reflected signals are demonstrated using GNSS data collected during Hubble Servicing Mission 4 (HSM4), a model of the mission geometry, electromagnetic (EM) ray tracing, and a custom GNSS software receiver. EM ray tracing is used to show that a number of signals sufficient for ranging are reflected by the Hubble Space Telescope (HST) during HSM4, and the properties of these reflections are used to generate simulated GNSS data. The impact of reflected signals on code correlation shape, code tracking error, and pseudorange measurement is demonstrated using the simulated and experimental data. Relative navigation is demonstrated using simulated reflected signal measurements and the dependence of relative navigation on the reflecting object’s scattering properties is illustrated. From the tracking of data from two oppositely polarized antennas, both simulated and experimental, it is determined that multipath measurements are limited by system properties such as antenna polarization quality and front end bandwidth. Design considerations involved in optimizing a receiver to measure reflected signals are discussed