A time‐frequency method for detecting VHF underdense meteor signals
Underdense meteor echoes observed using very high frequency (VHF) radar can be accurately modeled as a single complex damped sinusoid in additive white Gaussian noise. The normalized damping coefficient is expected to be between 0 and 0.3 for a VHF meteor return based on the modeled ambipolar diffusion rates near 90 km and a radar operating between 30 and 50 MHz. Current meteor echo detection routines operate either in the frequency domain, where it is difficult to detect highly damped signals, or in the time domain, where it is difficult to detect narrow band signals. An added difficulty is that typical approaches require a priori knowledge of the noise variance which can bias the performance of these estimators. In this paper, a time‐frequency waveform detector is proposed to address these problems. By normalizing the signal power and power spectral density in the time and frequency domains, respectively, a detector that is invariant to the noise variance can be implemented. The characteristics of a damped sinusoid in the time and frequency domains are exploited to construct the detector. The threshold for the proposed detector is only a function of of the time series length, and is stable with respect to a range of damping coefficients and noise levels. The time‐frequency waveform detector exhibits superior performance to the conventional energy or power detectors when the signal of interest is highly damped or the noise variance is unknown. A derivation of the time‐frequency waveform detector, comparison with the energy and power detectors and numerical results demonstrating the effectiveness of this detector are presented.
First steps toward the implementation of a cognitive radar to study plasma instabilities along the magnetic equator
Cognitive radar is envisioned to be the future of remote‐sensing systems. The idea proposed by details that a cognitive radar will have the ability to learn about the sensing environment and, over time, optimize returns from targets of interest by altering the transmitted pulse waveform. This paper focuses on the first step of the cognitive process for ionospheric radar observations in the equatorial region. In this region, three plasma irregularities are observed very regularly via radar, namely, Spread F, 150 km echoes, and electrojet. During real‐time observations, the first step of the cognitive process entails automatically recognizing the current plasma instability forming in the ionosphere. A preliminary test for the detection and classification of these events is performed off‐line using radar observations from the Jicamarca Radio Observatory, located in Lima, Peru. The chosen classification process utilizes a supervised learning algorithm (Expectation‐Maximization) to generate a probability distribution function (Gaussian Mixture Model) for each plasma instability based on certain measurable criterion. This paper outlines the training and classification process with the resulting cross validation performance subsequently reported. Results demonstrate the effectiveness of the chosen classifier because of the high cross validation and minimal misclassifications of the events.
Analysis: The Agenda 2007 Proposals: Evolution or Revolution?
On 10 February 2004 the Commission published its proposal for the financial perspective 2007-2013. A week later it adopted the third report on economic and social cohesion. These two documents form the basis of the so-called ‘Agenda 2007 reforms’. They will be the greatest challenge for the enlarged EU after the intergovernmental conference, since they will determine the financial basis for EU policy-making until the middle of the next decade. The Agenda 2007 proposals certainly hint at courageous reforms, because they place a previously unheard-of emphasis on performance and quality. Under the proposals, structural operations should generate value for money, and the funds should focus on projects which generate added value at a European level. Overall the Commission’s proposals point in the right direction, because they balance, on the one hand, solidarity for the new Member States and weak regions in the old Member States with, on the other hand, investments in future tasks. Moreover, they constitute a paradigm shift. For the first time, the Common Agricultural Policy will not be the dominant expenditure category. Now it is up to the Member States to examine the proposals politically and find a compromise between sometimes very divergent interests. It is to be hoped that, during the debate over expenditure limits and division of funds, national interests do not outweigh European interests.