A5032867300- Ionosphere and magnetosphere dynamics
- Radar Systems and Signal Processing
- GNSS positioning and interference
- Earthquake Detection and Analysis
- Advanced SAR Imaging Techniques
- Geomagnetism and Paleomagnetism Studies
- Geophysics and Gravity Measurements
- Geophysical Methods and Applications
- Soil Moisture and Remote Sensing
- Microwave Imaging and Scattering Analysis
- Radio Astronomy Observations and Technology
- Synthetic Aperture Radar (SAR) Applications and Techniques
- Atomic and Subatomic Physics Research
- Statistical and numerical algorithms
- Geophysical and Geoelectrical Methods
- Meteorological Phenomena and Simulations
- Antenna Design and Optimization
- Precipitation Measurement and Analysis
- Medical Imaging Techniques and Applications
- Atmospheric and Environmental Gas Dynamics
- Advanced Wireless Communication Techniques
- Atmospheric Ozone and Climate
- Coding theory and cryptography
- Electromagnetic Scattering and Analysis
- Advanced Frequency and Time Standards
University of Oulu
2009-2019
Tallinn University of Technology
2016
Finland University
2011
University of Eastern Finland
2011
Georgia Institute of Technology
2001
Geophysical Survey
1985-1997
Finnish Meteorological Institute
1986-1996
Universität Hamburg
1993-1994
University of Helsinki
1976-1990
A new method for measuring the ionosphere plasma autocorrelation function with an incoherent scatter radar is described. This can be used in similar situations where multipulse methods have been previously. In design of transmitted signal limited by a maximum allowed modulation time and peak power to noise ratio small, this provides significantly more accurate ACF estimates than obtained frequency commutated multiple pulse measurements. simple explanation given, as well precise definition...
In a statistical inverse theory both the unknown quantity and measurement are random variables. The solution of problem is then conditional distribution variable with supposed to be known. Both variables often have their values in spaces functions or generalised while distributions has only been fully developed for Polish spaces. Also, mappings representing linear problems Gaussian priors noises usually defined on subset used. This previously correctly handled Hilbert-space-valued existence...
Summary We discuss the inversion of gas profiles (ozone, NO3, NO2, aerosols and neutral density) in upper atmosphere from spectral occultation measurements. The data are produced by ‘Global ozone monitoring stars’ instrument on board Envisat satellite that was launched March 2002. measures attenuation light spectra at various horizontal paths about 100 km down to 10–20 km. new feature is these allow concentration height profiles. A short introduction given present operational management...
The Kilpisjärvi Atmospheric Imaging Receiver Array (KAIRA) is a dual array of omnidirectional VHF radio antennas located near Kilpisjärvi, Finland. It operated by the Sodankylä Geophysical Observatory. makes extensive use proven LOFAR antenna and digital signal-processing hardware, can act as stand-alone passive receiver, receiver for European Incoherent Scatter (EISCAT) very high frequency (VHF) incoherent scatter radar in Tromsø, or conjunction with other Fenno-Scandinavian experiments. In...
In ionospheric tomography, the atmospheric electron density is reconstructed from different related measurements, most often ground-based measurements of satellite signals. Typically, tomography suffers two major complications. First, information provided by insufficient and additional required to obtain a unique solution. Second, with necessary spatial temporal resolutions, problem becomes very high dimensional, hence, computationally infeasible. With Bayesian framework, can be given prior...
Abstract. In this work we discuss inclusion of a priori information about the smoothness atmospheric profiles in inversion algorithms. The requirement can be formulated form Tikhonov-type regularization, where is considered as constraint or Bayesian optimal estimation (maximum posteriori method, MAP), included information. We develop further two recently proposed retrieval methods. One them - regularization according to target resolution develops classical Tikhonov regularization. second...
We present a novel ionospheric tomography reconstruction method. The method is based on Bayesian inference with the use of Gaussian Markov random field priors. construct priors as system stochastic partial differential equations. Numerical approximations these equations can be represented linear systems sparse matrices, therefore providing computational efficiency. enables an interpretable scheme to build prior distribution physical and empirical information structure ionosphere. show...
We introduce a new coherent dual-channel beacon satellite receiver intended for ionospheric tomography. The measurement equation includes neutral atmosphere and ionosphere propagation effects, relative errors in clocks, residual Doppler shifts caused by the ephemeris. also investigate distribution of phase curve measurements use limited angle tomography using framework statistical linear inverse problems. describe design our software present one possible hardware configuration. Finally, we...
The stochastic inversion method in ionospheric radiotomography is reviewed with a special emphasis on regularization used the process. Regularization both for preventing vigorous point‐to‐point oscillations and controlling peak altitude thickness of result. latter usually means importing priori information layer height to solver. In this paper it pointed out that due curvature Earth ionosphere, measurements contain some profile shape even case purely horizontally stratified layer. If could...
Methods are described whereby it is possible to measure directly electron temperatures by observations of the plasma line in incoherent scatter radar experiments. The method based on simultaneous lines at different spatial scales. It how can be implemented either as a combination monostatic and bistatic one frequency or dual backscatter experiment.
We propose a new class of Gaussian priors, correlation priors. In contrast to some well-known smoothness they have stationary covariances. The priors are given in parametric form with two parameters: power and length. first parameter is connected our prior information on the variance unknown. second belief how fast unknown approaches zero. Roughly speaking, length distance beyond which points may be considered independent. distribution constructed essentially independent discretization so...
Intensity scintillations of cosmic radio sources are used to study astrophysical plasmas like the ionosphere, solar wind, and interstellar medium. Normally these observations relatively narrow band. With Low Frequency Array (LOFAR) technology at Kilpisjärvi Atmospheric Imaging Receiver (KAIRA) station in northern Finland we have observed over a 3 octave bandwidth. ``Parabolic arcs'', which were discovered pulsars, can provide precise estimates distance velocity scattering plasma. Here report...
Abstract. The present standard EISCAT incoherent scatter experiments are based on alternating codes that decoded in power domain by simple summation and subtraction operations. signal is first digitised then different lagged products calculated real time. Only the saved for further analysis so both original data samples undecoded lost. A fit of plasma parameters can be later performed using recorded products. In this paper we describe a method, which makes use statistical inversion removing...
Abstract. This paper presents binary phase codes and corresponding decoding filters which are optimal in the sense that they produce no sidelobes maximise signal-to-noise ratio (SNR henceforth). The search is made by investigating all possible with a given length. After selecting code, first step to find filter produces sidelobes. for zeros frequency domain, it turns out most satisfy this requirement. An example of code cannot be decoded way single phase, i.e. long pulse. second investigate...
Abstract. In this paper we summarize the theory behind full-profile analysis of IS measurements and report first practical experiences with GUISDAP (Grand Unified Incoherent Scatter Design Analysis Package) system designed to perform any efficiently. By fitting whole plasma parameter profiles over ionosphere, instead point values parameters supposed be approximately constant small range intervals, is free underlying assumptions about slow variation as a function range. We define mathematical...
Alternating codes are nowadays a standard measurement technique in the incoherent scatter observations. In most conditions they give best accuracy for plasma autocorrelation function estimates E and F region measurements. We explain here how oversampling can be used to further increase speed of experiments. an oversampled alternating code sampling interval length postdetection filter fraction baud length, calculated both integer lag values, which multiples intermediate called fractional...
It is well known that a matched filter gives the maximum possible output signal-to-noise ratio (SNR) when input scattering signal from point like radar target in presence of white noise. However, produces unwanted sidelobes can mask vital information. Several researchers have presented various methods dealing with this problem. They employed different kinds less optimal filters terms SNR point-like than filter. In paper we present method designing codes, called perfect and almost pulse...
Abstract. We validate two-dimensional ionospheric tomography reconstructions against EISCAT incoherent scatter radar measurements. Our method is based on Bayesian statistical inversion with prior distribution given by its mean and covariance. employ ionosonde measurements for the choice of covariance parameters use Gaussian Markov random fields as a sparse matrix approximation numerical computations. This results in computationally efficient tomographic algorithm clear probabilistic...
A special incoherent scatter technique in the European Incoherent Scatter (EISCAT) Svalbard Radar (ESR) was tested November 1999. After 70‐MHz IF stage standard ESR receiver replaced by a spectrum analyzer acting as combination of down‐converter, an AD converter, and quadrature detector giving complex digital samples at rate 4 MHz. The were fed into PCI‐bus‐based programmable I/O card, which performed four‐sample summing operation to give effective sampling 1 MHz, large enough span all...
Matched filtering of quadriphase coded radar signals creates unwanted sidelobes, which may mask important information. This correspondence presents a method eliminating these sidelobes in aperiodic codes. is done by using mismatched filter. The signal-to-noise ratio (SNR) at the output filter less than SNR corresponding matched A thorough computer search has been carried out to find code-mismatched pairs with minimum possible losses considering point target presence white Gaussian noise....