Detection and Processing of bistatically reflected GPS signals from low Earth orbit for the purpose of ocean remote sensing

We will show that ocean-reflected signals from the global positioning system (GPS) navigation satellite constellation can be detected from a low-earth orbiting satellite and that these signals show rough correlation with independent measurements of the sea winds. We will present waveforms of ocean-reflected GPS signals that have been detected using the experiment onboard the United Kingdom's Disaster Monitoring Constellation satellite and describe the processing methods used to obtain their delay and Doppler power distributions. The GPS bistatic radar experiment has made several raw data collections, and reflected GPS signals have been found on all attempts. The down linked data from an experiment has undergone extensive processing, and ocean-scattered signals have been mapped across a wide range of delay and Doppler space revealing characteristics which are known to be related to geophysical parameters such as surface roughness and wind speed. Here we will discuss the effects of integration time, reflection incidence angle and examine several delay-Doppler signal maps. The signals detected have been found to be in general agreement with an existing model (based on geometric optics) and with limited independent measurements of sea winds; a brief comparison is presented here. These results demonstrate that the concept of using bistatically reflected global navigation satellite systems signals from low earth orbit is a viable means of ocean remote sensing.     

The surface Laplacian of the potential: theory and application

The use of the surface Laplacian of the potential (L_s) in bioelectricity is discussed. Different estimates of L_s, in particular the field measured by coaxial electrodes, are compared to that of the true Laplacian. A method to compute L_s on the surface of an inhomogeneous volume conductor of arbitrary shape resulting from assumed electrical sources is introduced. In two applications the sensitivity of the body surface Laplacian is compared to that of body surface potentials. This comparison is carried out for dipolar sources within the human brain as well as for distributed sources within the heart     

Prediction and measurement of the coherent and incoherent power reflected from a rough surface

A theoretical treatment based on the concept of statistical sampling shows that the signal received in the specular direction when a plane wave is incident obliquely on a rough surface can be considered as the vector sum of a constant signal and a random signal. The random signal consists of two components, which are approximately normally distributed and independent, one in phase with the constant signal and the other in phase quadrature. Except for very rough surfaces the variances of the two random components are not equal, the variance of the phase quadrature component being greater than that of the in-phase component. The theoretical results are shown to agree with those based on other theoretical approaches and are in addition confirmed by experiments using microwaves reflected from a calibrated rough-water surface.     

A new method for estimating the acoustic attenuation coefficient of tissue from reflected ultrasonic signals

The parameter characterizing the acoustic attenuation in soft tissues is an indicator of tissue state. A method which features autoregressive deconvolution and spectral smoothing is proposed for estimation of the parameter from ultrasonic signals reflected from the tissue. The results of simulation and of processing actual liver data show that the standard deviation of the estimation is approximately halved by this method, compared to the traditional spectral differences method.     

双谱估计及其在心音信号分析中的应用

应用高阶统计量技术对心音信号进行了AR模型双谱估计，分析结果表明，与传统的功率谱分析方法相比较，双谱分析方法可以提供更多更客观的信息，是分析和处理心音信号的实用而有效的工具。     

The PARIS concept: an experimental demonstration of sea surfacealtimetry using GPS reflected signals

This paper presents the passive reflectometry and interferometry system (PARIS) concept and how it originated in the European Space Agency (ESA), Noordwijk, The Netherlands, in 1993 as a novel method to perform mesoscale ocean altimetry. The PARIS concept uses signals of opportunity such as the signals from the global navigation satellite systems (GNSS), which are reflected off the ocean surface to perform mesoscale ocean altimetry. Essentially, the relative delay between the direct and the reflected signals received from a Low Earth Orbit satellite provides information about sea surface height. The paper describes an original experiment on sea surface altimetry using GPS-reflected signals. The objective of the experiment was to demonstrate the potential of the PARIS concept. This experiment is the first one ever published on performing sea surface height estimations using reflected navigation signals in a controlled environment. The key result of the experiment is the demonstration of a root mean squared (RMS) height accuracy within 5 s of 1% of the used code chip (3 m for C/A code). Direct extrapolation of this experimental result to the 10-times higher chip rate P-code signal allows us to predict a height error of 30 cm in 5 s, provided adequate models are used to take into account systematic effects. The paper ends presenting the potential of the PARIS concept for long term ocean altimetric observations in view of the current trends of the GNSS systems     

Deorientation theory of polarimetric scattering targets and application to terrain surface classification

Deorientation theory of polarimetric scattering targets is presented. Using a transformation of the target scattering vector, the target orientation is turned to a certain fixed state and polarimetric scattering of the transformed scattering vector shows the prominence of the generic characteristics of the target. A new set of parameters u, v, w, /spl psi/ is defined based on a deorientation of the target scattering vector. Numerical simulation of polarimetric scattering of nonspherical particles illustrates the meanings of the parameters u, v, w, /spl psi/ and the entropy H. An unsupervised classification scheme of the terrain surfaces is developed, which classifies the terrain surfaces using the set of u., v, H, and analyzes the orientation distribution of each class based on deorientation angle /spl psi/. As examples, a SIR-C polarimetric image over China's Guangdong Hui-Yang district is classified into eight classes and a AirSAR polarimetric image over Canada's Boreal district is orientation-analyzed using our approach of deorientation and four parameters u, v, /spl psi/, and H.     

On the deflection effect of light reflected from a moving mirror in the ether theory

The classical formula for the aberration angle of deflection angle of light reflected from moving mirror in ether is presented. The formula, confirmed in experiments and observations, differs from both classical and relativistic formulas derived by Ashworth and Davies.     

Multiscale causal connectivity analysis by canonical correlation: theory and application to epileptic brain

Multivariate Granger causality is a well-established approach for inferring information flow in complex systems, and it is being increasingly applied to map brain connectivity. Traditional Granger causality is based on vector autoregressive (AR) or mixed autoregressive moving average (ARMA) model, which are potentially affected by errors in parameter estimation and may be contaminated by zero-lag correlation, notably when modeling neuroimaging data. To overcome this issue, we present here an extended canonical correlation approach to measure multivariate Granger causal interactions among time series. The procedure includes a reduced rank step for calculating canonical correlation analysis (CCA), and extends the definition of causality including instantaneous effects, thus avoiding the potential estimation problems of AR (or ARMA) models. We tested this approach on simulated data and confirmed its practical utility by exploring local network connectivity at different scales in the epileptic brain analyzing scalp and depth-EEG data during an interictal period.     

A fast and reliable technique for muscle activity detection from surface EMG signals

The estimation of on-off timing of human skeletal muscles during movement is an important issue in surface electromyography (EMG) signal processing with relevant clinical applications. In this paper, a novel approach to address this issue is proposed. The method is based on the identification of single motor unit action potentials from the surface EMG signal with the use of the continuous wavelet transform. A manifestation variable is computed as the maximum of the outputs of a bank of matched filters at different scales. A threshold is applied to the manifestation variable to detect EMG activity. A model, based on the physical structure of the muscle, is used to test the proposed technique on synthetic signals with known features. The resultant bias of the onset estimate is lower than 40 ms and the standard deviation lower than 30 ms in case of additive colored Gaussian noise with signal-to-noise ratio as low as 2 dB. Comparison with previously developed methods was performed, and representative applications to experimental signals are presented. The method is designed for a complete real-time implementation and, thus, may be applied in clinical routine activity.     

Rate-distortion theory and application

The theoretical minimum channel capacity required to transmit a given source at a given average distortion level is discussed. The limitations and applications of the theory are reviewed with particular emphasis on the use of the results for guiding practical system design and for bounding system performance. Applications are oriented toward video sources.     

Tomographic time-frequency analysis and its application towardtime-varying filtering and adaptive kernel design for multicomponentlinear-FM signals

Since line integrals through the Wigner spectrum can be calculated by dechirping, calculation of the Wigner spectrum may be viewed as a tomographic reconstruction problem. In the paper, the authors show that all time-frequency transforms of Cohen's class may be achieved by simple changes in backprojection reconstruction filtering. The resolution/cross-term tradeoff that occurs in time-frequency kernel selection is shown to be analogous to the resolution-ringing tradeoff that occurs in computed tomography (CT). “Ideal” reconstruction using a purely differentiating backprojection filter yields the Wigner distribution, whereas low-pass differentiating filters produce cross-term suppressing distributions such as the spectrogram or the Born-Jordan distribution. It is also demonstrated how this analogy can be exploited to “tune” the reconstruction filtering (or time-frequency kernel) to improve the ringing/resolution tradeoff. Some properties of the projection domain, which is also known as the Radon-Wigner transform, are characterized, including the response to signal delays or frequency shifts and projection masking or convolution. Last, time-varying filtering by shift-varying convolution in the Radon-Wigner domain is shown to yield superior results to its analogous Cohen's class adaptive transform (shift-invariant convolution) for the multicomponent, linear-FM signals that are investigated     

An algorithm for determining the radiance reflected from the roughsea surface using MODIS-N satellite radiometer data

A new algorithm is suggested for determining the radiance B_r (&thetas;, φ) reflected from the rough sea surface. The knowledge of B_r(&thetas;, φ) is needed for excluding the reflected solar radiation from the signal at the space receiver. Information on the reflected radiance is also required when estimating the state of the sea surface from space. The information (on reflected radiance) is important for problems such as estimating the chlorophyll concentration in sea water. The suggested algorithm was constructed based on direct measurements of the radiance coefficient ρ published in V. G. Akimov ei al. (1993) and J. A Shaw et al. (1997). The experimental results show that the slope distribution of sea surface elements depends not only on the wind speed near the sea surface but also on the stability of the lower part of the marine atmospheric boundary layer. It is shown that the failure to account for this effect causes an error of ±30% when estimating B_r(&thetas;, φ)     

Design and analysis of UW-OFDM signals

Unique word-orthogonal frequency division multiplexing (UW-OFDM) is a novel signaling concept where the guard interval is implemented as a deterministic sequence, the so-called unique word. The UW is generated by introducing a certain level of redundancy in the frequency domain. Different data estimation strategies and the favourable bit error ratio (BER) performance of UW-OFDM, as well as comparisons to competing concepts have already extensively been discussed in previous papers. This work focuses on the different possibilities on how to generate UW-OFDM signals. The optimality of the two-step over the direct approach in systematic UW-OFDM is proved analytically, we present a heuristic algorithm that allows a fast numerical optimization of the redundant subcarrier positions, and we show that our original intuitive approach of spreading the redundant subcarriers in systematically encoded UW-OFDM by minimizing the mean redundant energy is practically also optimum w.r.t. transceiver based cost functions. Finally, we derive closed form approximations of the statistical symbol distributions on individual subcarriers as well as the redundant energy distribution and compare them with numerically found results.     

Fusion of body surface potential and body surface Laplacian signals for electrocardiographic imaging

Various approaches to the solution to the inverse problem of electrocardiography have been proposed over the years. Recently, the use of inverse algorithms using measured body surface Laplacians has been proposed, and in various studies this technique has been shown to outperform the traditional use of body surface potentials in certain model problems. In this paper, we compare the use of body surface potentials and body surface Laplacians on two model problems with different assumed cardiac sources. For the spherical cap model problems with an anterior source, the epicardial estimates using body surface potentials had smaller average relative errors than when body surface Laplacians were used. For the spherical cap model problems with a posterior source, the epicardial estimates using body surface potential or body surface Laplacian sensors generally produced similar relative errors. For the radial dipole model, the epicardial estimates using body surface Laplacians had smaller errors than when body surface potentials were used. We introduce a fusion algorithm that combines the different types of signals and generally produces a good estimate for both model problems.     

Polarisation of waves reflected from the ionosphere

The effect of electron collisions on the polarisation of waves reflected from the ionosphere is calculated by an iteration procedure and shown to be relatively small at night for both normal and oblique incidence, at frequencies above 0.5 MHz.     

Load cells in force sensing analysis -- theory and a novel application

Load cells have long been used to sense and measure force and torque. When properly designed and used, they are very accurate and reliable sensors. Load cells are applied in several different fields, usually for weighing measurements. Among many other things, food, vehicles, and animals are weighed daily with load cells. The gripper of a robotic arm that picks up an object can be equipped with load cells in order to provide compression force feedback to the control system to prevent the object from being damaged or released too early. Also, load cells can be used to sense the compression forces during a robot's walk to provide data for the equilibrium-controlling system. In industrial machinery, rods, beams, wheels and bars are instrumented in order to check the forces exerted on them. The volume or level of a tank can be measured indirectly by means of a load cell that monitors the total weight. Lift units can also have a load's total weight measured to prevent overload. Because of such a variety of possible applications, load cells are very important. This paper describes some of the theory and practice of load cells, including their basic elements and the electronics necessary for measurement. As an application example, the development of a 3-ring spherical load cell is presented which can be used to measure compression forces on fruit during storage and transportation is presented.     

基于分形和测度理论的信号调制识别

为提高信号调制识别的能力 ,提出了一种以最直接、最直观的信号波形的复杂度 -分形维数为特征 ,并运用测度理论来组合多个在小信噪比范围内对通信信号调制类型有较高识别率的分类器 ,从而实现大信噪比范围内识别率明显改善的新方法 ,同时 ,应用该方法也可简化单个分类器的设计 ,提高分类识别效率。计算机模拟结果证实了此方法的有效性