Investigation of exceptionally radar-dark regions on the lunar nearside

Presentation at the 19th International EISCAT Symposium 2019 and 46th Annual European Meeting on Atmospheric Studies by Optical Methods, Oulu, Finland, 19.08. - 23.08.19, arranged by the University of Oulu. (http://www.sgo.fi/Events/EISCAT46AM/). Remote sensing of planetary surfaces is an effective method for gaining knowledge of the processes that shape the planetary bodies in our solar system. This is useful for uncovering the environment of the primordial solar system and to study the current state of the upper crusts of the other planets in our neighborhood. A recent 6-meter wavelength polarimetric radar map of the Moon [?] showed unexpectedly low depolarized radar returns in two regions on the lunar nearside. These two areas were a highland region between Mare Imbrium and Mare Frigoris, and the highland area surrounding the Schiller-Zucchius impact basin. These two regions showed characteristics unlike those of typical highland regions of the lunar surface. So far, there has been no readily available explanation for this observation. In this study, it is shown that the likely cause is an increased loss tangent due to chemical differences in the first few hundred meters of the lunar soil. We also show the absence of any coherent subsurface, which could be the preserved remains of an ancient basaltic plain. We do this by comparing the 6-meter polarimetric radar map to other relevant data sets: 1) surface TiO2 and FeO abundance, 2) surface rock population, 3) radar maps of the Moon with other wavelengths, and 4) visual spectrum images of the Moon. The area near the Schiller-Zucchius basin was shown to be consistent with other areas with similar surface chemical compositions, but the region between Mare Imbrium and Mare Frigoris showed significantly lower mean power in comparison to otherwise similar regions. While we can not conclusively determine the cause, we hypothesize that the low radar return is explained by an increased concentration of iron and titanium oxides in the volume beneath the surface, potentially due to remnants of primordial lunar volcanism. The results show that long wavelength polarimetric radar measurements of the Moon are very powerful tools for studying the earliest stages of the evolution of the Moon. The new EISCAT 3D installation will enable new measurements in a wavelength which has not been used before. The facility can also track the Moon to obtain a long observation time, increasing resolution. The multiple receiving locations will provide excellent interferometric baselines to, among other things, resolve the range-Doppler ambiguity. Polarimetric measurements are useful for separating surface and volume scattering, as well as potential target-based decomposition modelling

GPGPU Acceleration of Incoherent Scatter Radar Plasma Line Analysis

The incoherent scatter radar (ISR) technique is a powerful remote sensing tool for ionosphere and thermosphere dynamics in the near-Earth space environment. Weak ISR scatter from naturally occurring Langmuir oscillations, or plasma lines, contain high precision information on the altitude-dependent thermal ionospheric electron density. However, analyzing this frequency-dependent scatter over a large number of radar ranges requires large computational power, especially when the goal is realtime analysis. General purpose computing on graphics processing units (GPGPU) offers immense computational speedup when compared to traditional central processing unit (CPU) calculations for highly parallelizable tasks, and it is well suited for ISR analysis applications. This paper extends a single graphics processing unit (GPU) algorithmic solution in a GPGPU framework, and discusses the algorithm developed, including GPU hardware considerations. Results indicate an order-of-magnitude improvement over CPU analysis and suggest that GPGPU can achieve realtime speed for plasma line applications.Comment: 8 pages, 1 figure, 1 table, submitting to Radio Scienc

Statistical framework for estimating GNSS bias

We present a statistical framework for estimating global navigation satellite system (GNSS) non-ionospheric differential time delay bias. The biases are estimated by examining differences of measured line integrated electron densities (TEC) that are scaled to equivalent vertical integrated densities. The spatio-temporal variability, instrumentation dependent errors, and errors due to inaccurate ionospheric altitude profile assumptions are modeled as structure functions. These structure functions determine how the TEC differences are weighted in the linear least-squares minimization procedure, which is used to produce the bias estimates. A method for automatic detection and removal of outlier measurements that do not fit into a model of receiver bias is also described. The same statistical framework can be used for a single receiver station, but it also scales to a large global network of receivers. In addition to the Global Positioning System (GPS), the method is also applicable to other dual frequency GNSS systems, such as GLONASS (Globalnaya Navigazionnaya Sputnikovaya Sistema). The use of the framework is demonstrated in practice through several examples. A specific implementation of the methods presented here are used to compute GPS receiver biases for measurements in the MIT Haystack Madrigal distributed database system. Results of the new algorithm are compared with the current MIT Haystack Observatory MAPGPS bias determination algorithm. The new method is found to produce estimates of receiver bias that have reduced day-to-day variability and more consistent coincident vertical TEC values.Comment: 18 pages, 5 figures, submitted to AM

Using radar beam-parks to characterize the Kosmos-1408 fragmentation event

We describe the use of radar beam-park experiments to characterize the space debris resulting from a recent fragmentation event, the deliberate demolition of the defunct Kosmos-1408 satellite. We identify the Kosmos-1408 fragments and present distribution of measurement parameters as well as proxy orbit parameters. We present and apply a novel technique to estimate the size of objects by matching the signal to noise ratio of the detection to the radiation pattern of the radar. With this method we estimate the size distribution of the debris cloud. We also demonstrate how a pair of beam-park observations can be used to perform a crude, yet seemingly reliable, initial orbit determination. Finally, we present followup observations 5 months after the fragmentation that show a still compact cloud of debris

A technique for volumetric incoherent scatter radar analysis

Volumetric measurements of the ionosphere are important for investigating spatial variations of ionospheric features, like auroral arcs and energy deposition in the ionosphere. In addition, such measurements make it possible to distinguish between variations in space and time. While spatial variations in scalar quantities such as electron density or temperature have been investigated with incoherent scatter radar (ISR) before, spatial variation in the ion velocity, which is a vector quantity, has been hard to measure. The upcoming EISCAT3D radar will be able to do volumetric measurements of ion velocity regularly for the first time. In this paper, we present a technique for relating volumetric measurements of ion velocity to neutral wind and electric field. To regularize the estimates, we use Maxwell's equations and fluid-dynamic constraints. The study shows that accurate volumetric estimates of electric field can be achieved. Electric fields can be resolved at altitudes above 120 km, which is the altitude range where auroral current closure occurs. Neutral wind can be resolved at altitudes below 120 km.</p

Radar observability of near-Earth objects using EISCAT 3D

Radar observations can be used to obtain accurate orbital elements for near-Earth objects (NEOs) as a result of the very accurate range and range rate measureables. These observations allow the prediction of NEO orbits further into the future and also provide more information about the properties of the NEO population. This study evaluates the observability of NEOs with the EISCAT 3D 233 MHz 5 MW high-power, large-aperture radar, which is currently under construction. Three different populations are considered, namely NEOs passing by the Earth with a size distribution extrapolated from fireball statistics, catalogued NEOs detected with ground-based optical telescopes and temporarily captured NEOs, i.e. mini-moons. Two types of observation schemes are evaluated, namely the serendipitous discovery of unknown NEOs passing the radar beam and the post-discovery tracking of NEOs using a priori orbital elements. The results indicate that 60-1200 objects per year, with diameters D > 0.01 m, can be discovered. Assuming the current NEO discovery rate, approximately 20 objects per year can be tracked post-discovery near the closest approach to Earth. Only a marginally smaller number of tracking opportunities are also possible for the existing EISCAT ultra-high frequency (UHF) system. The mini-moon study, which used a theoretical population model, orbital propagation, and a model for radar scanning, indicates that approximately seven objects per year can be discovered using 8 %-16% of the total radar time. If all mini-moons had known orbits, approximately 80-160 objects per year could be tracked using a priori orbital elements. The results of this study indicate that it is feasible to perform routine NEO post-discovery tracking observations using both the existing EISCAT UHF radar and the upcoming EISCAT 3D radar. Most detectable objects are within 1 lunar distance (LD) of the radar. Such observations would complement the capabilities of the more powerful planetary radars that typically observe objects further away from Earth. It is also plausible that EISCAT 3D could be used as a novel type of an instrument for NEO discovery, assuming that a sufficiently large amount of radar time can be used. This could be achieved, for example by time-sharing with ionospheric and space-debris-observing modes.Peer reviewe

Lightboard – a new teaching tool at the Faculty of Science and Technology at UiT

We would like to present a new tool that was built by three lecturers at UiT last semester – Lightboard. This tool was used before in other countries and other universities, but never at UiT. The COVID-19 pandemic situation motivated the lecturers to find a way to do online lectures differently. Blackboard and chalk work well for natural sciences as long as the lecture is physical and the teacher has an eye contact with the students, but this was not an option since all lectures were turned to online. The solution was found. The Lightboard gives an opportunity to face towards the students while recording the lectures and they can follow the lecturer’s hands while writing

Planetary radar science case for EISCAT 3D

Ground-based inverse synthetic aperture radar is a tool that can provide insights into the early history and formative processes of planetary bodies in the inner solar system. This information is gathered by measuring the scattering matrix of the target body, providing composite information about the physical structure and chemical makeup of its surface and subsurface down to the penetration depth of the radio wave. This work describes the technical capabilities of the upcoming 233 MHz European Incoherent Scatter Scientific Association (EISCAT) 3D radar facility for measuring planetary surfaces. Estimates of the achievable signal-to-noise ratios for terrestrial target bodies are provided. While Venus and Mars can possibly be detected, only the Moon is found to have sufficient signal-to-noise ratio to allow high-resolution mapping to be performed. The performance of the EISCAT 3D antenna layout is evaluated for interferometric range–Doppler disambiguation, and it is found to be well suited for this task, providing up to 20 dB of separation between Doppler northern and southern hemispheres in our case study. The low frequency used by EISCAT 3D is more affected by the ionosphere than higherfrequency radars. The magnitude of the Doppler broadening due to ionospheric propagation effects associated with traveling ionospheric disturbances has been estimated. The effect is found to be significant but not severe enough to prevent high-resolution imaging. A survey of lunar observing opportunities between 2022 and 2040 is evaluated by investigating the path of the sub-radar point when the Moon is above the local radar horizon. During this time, a good variety of look directions and Doppler equator directions are found, with observations opportunities available for approximately 10 d every lunar month. EISCAT 3D will be able to provide new, high-quality polarimetric scattering maps of the nearside of the Moon with the previously unused wavelength of 1.3 m, which provides a good compromise between radio wave penetration depth and Doppler resolution

USE OF EISCAT 3D FOR OBSERVATIONS OF SPACE DEBRIS

Conference paper from 7th European Conference on Space Debris ESA/ESOC, Darmstadt/Germany 18 - 21 April 2017We investigate the capabilities of the next generation ionospheric research radar EISCAT 3D (E3D) for observations of space objects. The radar is multi-static, and is therefore capable of observing instantaneous threedimensional vector velocity and position by observing round-trip delay and Doppler shift between the transmitter and three receiver sites. The radar is to be located in Northern Scandinavia, which provides a high revisitrate for high inclination objects. To model the performance of E3D for space object observations, we have included radar equation based analysis of object detectability as a function of range and size. To study the performance of the radar for orbital elements determination, we have used a linearized error covariance analysis for idealized Keplerian elements. The analysis includes range and range-rate errors due to signal-to-noise and ionospheric radio propagation. To estimate the fraction of total debris that can be observed with E3D, we have used the MASTER model [FGW+09]. E3D uses a relatively low VHF frequency (233 MHz), which experiences more radio wave propagation effects than more conventional higher frequency space surveillance radars. Our modeling shows that ionospheric ray-bending and group delay are severe enough that these effects need to be modeled in order to determine accurate orbital elements. As EISCAT 3D is an ionospheric research radar, there will be high quality ionospheric electron density measurements that can be utilized for radio propagation modeling. Our simulations indicate that the radar can be used for observations of orbital elements of objects down to 5 cm in diameter. It is therefore feasible that the radar could provide to be a useful source of accurate information of orbital elements of space debris