arXiv subjects

Juha Vierinen

Publications and source records attributed to Juha Vierinen.

10 recordsLinked to original sources

arXiv2026

The PANSY Meteor Head-echo Orbit Catalogue: Continuous Antarctic Radar Observations of Southern Meteoroid Streams

Meteor head echoes from high-power, large-aperture radars provide pulse-resolved positions and velocities for individual micrometeoroids in a submillimeter-radius range that contribute significantly to the mass influx to Earth. We present the first meteor head-echo orbit catalogue from the Antarctic Syowa Mesosphere--Stratosphere--Troposphere/Incoherent Scatter radar (PANSY). The catalogue contains two million meteors and 50 million pulse-resolved measurements. The observed radiant distribution contains the helion, antihelion, south toroidal and apex sources, and provides unprecedented head-echo coverage of southern ecliptic latitudes. The initial detection-height distribution is found to be double-banded, with both bands increasing in height with meteor speed and exhibiting distinct radiant distributions, consistent with a mixture of meteoroid-size differences and differential ablation. Estimation of dynamic mass indicates that the survey is sensitive to initial radii of approximately 100 micrometers. As part of an initial exploration of the catalogue, we investigate the nighttime alpha Capricornids (CAP) and the extended Daytime Capricornids-Sagittariids (DCS) radiant. Their similar activity durations at opposite nodes are consistent with membership in the CAP--169P/NEAT complex. The radiant distribution suggests a new meteor shower candidate, with peak flux near solar longitude 110 degrees, mean Sun-centered ecliptic radiant longitude 291.0 degrees, latitude -48.2 degrees, and geocentric speed 48.7 km s^{-1}. During catalogue production, event-level raw voltage cuts are retained temporarily to support improvements in data analysis. This first catalogue release, covering 2025 January 26 to 2026 July 26, will be useful for further studies of the southern-hemisphere Earth-crossing meteoroid population.

astro-ph.EP↗

arXiv2026

Estimating sub-frame time differences in camera image sequences

Some optical measurements require relative timing of intensity variations with accuracy much finer than the camera frame period. One motivating example is dynamic aurora, where different prompt emissions are expected to originate from different altitude regions and can therefore have millisecond-scale relative delays caused by finite energetic-electron velocities and other electron-transport effects. These delays are predicted to be a small fraction of the frame duration of typical auroral video cameras. We present a cross-spectral technique for estimating the relative delay between two time-varying optical intensity signals recorded by one or more image sensors. The method is validated with a calibration device that generates two pseudorandomly pulsed optical emissions with a known relative delay, recorded using a consumer smartphone camera. For the tested recordings, the method estimates relative delays between image-sensor regions with better than $50$~$μ$s accuracy. Although developed for high-frame-rate auroral imaging, the technique has numerous other imaging applications, including camera timing calibration and measurements of time-varying optical signals. The single-camera tests demonstrate that the method can characterize sub-frame timing differences across an image sensor, such as those produced by rolling-shutter readout. The same analysis applies to separate cameras when they observe the same time-varying signal and are synchronized to a shared clock.

physics.space-ph↗

arXiv2026

Optical and Radar Observations of the February 2025 Falcon 9 Upper-Stage Re-entry

We investigate the February 19, 2025, re-entry of a Falcon 9 upper stage using optical observations from 43 meteor cameras across central Europe together with radar detections of re-entry plasma obtained with the 32.55 MHz SIMONe Germany multistatic radar system. Optical observations of fragment emissions between 85 and 36 km altitude were used to reconstruct 30 fragment trajectories, identify two main fragment families, and fit ballistic trajectories to estimate kinetic energy loss per unit mass. The optical detection-height distribution peaks near 60 km with a standard deviation of 10 km, and both optical and radar signatures occur in the same broad altitude region as the maximum kinetic-energy loss. Radar echoes were detected at altitudes between 55 and 75 km, and the radar-derived positions are consistent with those obtained from optical observations. Two distinct radar echo types associated with the re-entry plasma were identified: (1) specular trail echoes from overdense wake plasma, with radar cross-sections (RCS) of up to 60 dBsm, and (2) short-lived non-specular trail echoes with RCS values of 20--30 dBsm, exhibiting a delay of 1--2 s compared to optical signatures. The characteristic decay time of both echo types is approximately 1 s. In the radar-echo altitude range, the estimated Knudsen numbers for meter-scale fragments are well below unity, consistent with continuum-flow conditions and shock-driven plasma production rather than ordinary meteor-like impact ionization. These serendipitous radar observations demonstrate that the atmospheric re-entry of other spacecraft, including objects smaller than the Falcon 9 upper stage such as Starlink satellites, may likewise be detectable using comparable multistatic meteor radar systems deployed globally.

physics.space-ph↗

arXiv2023

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.

physics.data-an↗

arXiv2023

A Global Radio Remote Sensing Network for Observing Space Weather Dynamics

Our current sampling of the near-Earth space environment is wholly insufficient to measure the highly variable processes therein and make predictions on par with lower atmospheric weather. We sketch out the scientific rationale for a network of radio instruments delivering dense observations of the near-Earth space environment and the broad steps necessary to implement wide-scale coverage in the next 30 years.

astro-ph.IM↗

arXiv2015

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.

astro-ph.IM↗

arXiv2014

Radiometric Measurements of Electron Temperature and Opacity of Ionospheric Perturbations

Changes in the sky noise spectrum are used to characterize perturbations in the ionosphere. Observations were made at the same sidereal time on multiple days using a calibrated broadband dipole and radio spectrometer covering 80 to 185 MHz. In this frequency range, an ionospheric opacity perturbation changes both the electron thermal emission from the ionosphere and the absorption of the sky noise background. For the first time, these changes are confirmed to have the expected spectral signature and are used to derive the opacity and electron temperature associated with the perturbations as a function of local time. The observations were acquired at the Murchison Radio-astronomy Observatory in Western Australia from 18 April 2014 to 6 May 2014. They show perturbations that increase at sunrise, continue during the day, and decline after sunset. Magnitudes corresponding to an opacity of about 1 percent at 150 MHz with a typical electron temperature of about 800 K, were measured for the strongest perturbations.

astro-ph.IM↗

arXiv2008

Transmission code optimization method for incoherent scatter radar

When statistical inversion of a lag profile is used to determine an incoherent scatter target, the posterior variance of the estimated target can be used to determine how well a certain set of transmission codes perform. In this work we present an incoherent scatter radar transmission code optimization search method suitable for different modulation types, including binary phase, polyphase and amplitude modulation. We find that the combination of amplitude and phase modulation provides better performance than traditional binary phase coding, in some cases giving better accuracy than alternating codes.

physics.data-an↗

arXiv2007

Polyphase alternating codes

This work introduces a method for constructing polyphase alternating codes in which the length of a code transmission cycle can be $p^m$ or $p-1$, where $p$ is a prime number and $m$ is a positive integer. The relevant properties leading to the construction alternating codes and the algorithm for generating alternating codes is described. Examples of all practical and some not that practical polyphase code lengths are given.

physics.data-an↗

arXiv2006

General radar transmission codes that minimize measurement error of a static target

The variances of matched and sidelobe free mismatched filter estimators are given for arbitrary coherent targets in the case of aperiodic transmission. It is shown that mismatched filtering is often better than matched filtering in terms of estimation accuracy. A search strategy for finding general transmission codes that minimize estimation error and satisfy constraints on code power and amplitude range is then introduced. Results show that nearly perfect codes, with performance close to a single pulse with the same total power can be found. Also, finding these codes is not computationally expensive and such codes can be found for all practical code lengths. The estimation accuracy of the newly found codes are compared to binary phase codes of similar length and found to be better in terms of estimator variance. Similar transmission codes might be worth investigating also for sonar and telecommunications applications.

physics.data-an↗