Journal Article•
Mathematical Analysis of Random Noise-Conclusion
About: This article is published in Bell System Technical Journal.The article was published on 1945-01-01 and is currently open access. It has received 807 citations till now.
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TL;DR: In this article, the theoretical saturation spectrum of parametrically excited Langmuir waves in a locally uniform ionosphere is shown to produce, by ohmic dissipation, short-scale field-aligned density striations.
Abstract: The theoretical saturation spectrum of parametrically excited Langmuir waves in a locally uniform ionosphere is shown by the present calculations to produce, by ohmic dissipation, short-scale field-aligned density striations. The spectrum of the calculated striations is not inconsistent with observations of field-aligned scatter of VHF and UHF waves in ionospheric modification experiments if local increases of the pump field due to focusing are invoked.
34 citations
TL;DR: Kempeneers et al. as mentioned in this paper explored the utility of lidar in the lower-canopy ecosystems of the Belgian coastal dune belt, and applied small diameter footprint lidar to derive the canopy height by analyzing the first and last pulse returns simultaneously.
Abstract: Kempeneers, P.; Deronde, B.; Provoost, S., and Houthuys, R., 2009. Synergy of airborne digital camera and lidar data to map coastal dune vegetation. Journal of Coastal Research, SI(53), 73-82. Driven by the successful applications of lidar in forestry and the availability of lidar technology, new research is being carried out in other ecosystems. While lidar data have often been used to study tall forest ecosystems, this study explores the utility of lidar in the lower-canopy ecosystems of the Belgian coastal dune belt. This area is largely covered by marram dune, moss dune, grassland, scrubs and some woodland. Small diameter (0.4 m) footprint lidar was applied to derive the canopy height by analyzing the first and last pulse returns simultaneously. The investigation focused on whether the height of low-canopy ecosystems could be mapped with adequate accuracy. An error analysis was performed first on flat terrain (i.e., tennis court and parking lot) and then on vegetation canopy. The mapping of coastal dune vegetation is necessary to establish the strength of the dune belt. Dune vegetation fixes the sand dunes, protecting them from erosion and from possible breakthroughs threatening the historically reclaimed land (polders) situated inland from the dunes. Next, multispectral data was acquired from a digital camera with visual and near infrared channels. The digital camera overflight was not conducted on the same platform as the lidar. After ortho-rectification of the multispectral image, the data of both sources were fused. The limited spectral information delivered by the digital camera was not able to provide a sufficiently detailed and accurate vegetation map. The fusion with lidar data provided the extra information needed to obtain the desired vegetation and dune strength maps. A total of fourteen classes were defined, of which twelve cover vegetation. It was shown that overall classification accuracy improved 16%, from 55% to 71% after data fusion.
33 citations
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...A Rician distribution (Rice, 1945) was chosen....
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TL;DR: A set of curves that can be used to evaluate in detail over a wide range of operating conditions the performance of systems using envelope detectors to search for CW signals in narrow-band Gaussian noise are presented.
Abstract: This article presents a set of curves that can be used to evaluate in detail over a wide range of operating conditions the performance of systems using envelope detectors to search for CW signals in narrow-band Gaussian noise. The charts discussed relate the probability, P D , of detecting such signals to (i) the signal-power/noise-power ratio, S/N, (ii) the proportion of false detections, P FA , and (iii) the number, M, of independent samples of the envelope of the combined signal and noise that are averaged in making one attempt at detection. The curves and scales were calculated and drawn entirely by computer. The computation program was designed so that nearly linear curves could be produced, thereby increasing the accuracy and ease of interpolation.
33 citations
TL;DR: In this paper, the average frequency of positive slope να+ crossing for the returns of market prices is investigated, based on stochastic processes in which no scaling feature is explicitly required.
Abstract: We investigate the average frequency of positive slope να+ crossing for the returns of market prices. The method is based on stochastic processes in which no scaling feature is explicitly required. Using this method we define a new quantity to quantify the stage of development and activity of stock exchanges. We compare the Tehran and western stock markets and show that some, such as the Tehran (TEPIX) and New Zealand (NZX) stock exchanges, are emerging, and also that TEPIX is a non-active market and is financially motivated to absorb capital.
33 citations
TL;DR: In this article, the statistical properties of the interface between turbulent and nonturbulent fluid in the wake of a heated cylinder are presented, including distributions of the intermittency factor and crossing frequency, probability density functions of the durations of the passages of turbulent and nonsmooth fluid, indicating that the longer durations are exponentially distributed.
Abstract: The statistical properties of the interface between turbulent and nonturbulent fluid in the two‐dimensional wake of a heated cylinder are presented. The following are the principal results: distributions of the intermittency factor and crossing frequency; probability density functions of the durations of the passages of turbulent and nonturbulent fluid, indicating that the longer durations are exponentially distributed; the mean and rms slope angles of the interface at upstream and downstream edges, showing an asymmetry of the mean shape with a steeper downstream edge; and the relative number of overhangs at the two sets of edges, namely, 25% at the downstream edge and only 6% at the upstream edge.
33 citations