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LOFAR sonobuoy localization algorithm based on the measurements of amplitude and frequency
Abstract
In order to estimate the motion parameters of the target before it passes by the CPA (closest point of approach) in the application of the LOFAR (low-frequency acquisition and ranging) sonobuoy, an unbiased estimation method is proposed, which can estimate the motion parameters of the single target using the amplitude and frequency of its radiated noise. For deriving the theoretical formulas for the parameters like the characteristic frequency, absolute speed, CPA and radiated noise amplitude, three measurements of amplitude and frequency that are evenly spaced in the range are used. With consideration to the characteristics of the practical application of LOFAR, the least squares estimation theory was used to enhance the accuracy of the target parameter estimation. The computer simulation results indicate that this method is an unbiased estimation algorithm in theory and the air experiment demonstrates the practicability and effectiveness of this method for use in engineering practice.
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A new algorithm based on sonobuoy Doppler shift CPA (closest point of approach) was proposed. Compared with the original, the new algorithm has two characteristics as follows: (1) the new algorithm is an errorless formula, compared to original algorithm an approximate one; (2) new algorithm is more convenient in used and formula input is easier to get. The relationship between original and new algorithm was compared. The original algorithm used two Doppler shifts which was bilateral symmetry about CPA and the derivative of frequency at CPA point. The new algorithm used Doppler shift and time information added. The experiment shows that the new algorithm is an errorless formula.
The conventional beam‐forming technique cannot be used for source location in a waveguide because of the modal interference structure of the field. In this paper a new method of passive source ranging in a layered waveguide is proposed. The mode filtering processor was used to process the field data of a vertical array to obtain individual modes. The source range information can be extracted by measurement of three individual mode phases. The source range was expressed in terms of the ‘‘mode interference distance’’ as follows: r=L i j *D i j +Δr i j ; Δr i j =D i j ×(δφ i j /2π), where L i j is a certain integer, δφ i j is the phase difference of the ith and jth modes, D i j is the ‘‘mode interference distance’’ defined by D i j =2π/(k i −k j ), and k i is the wavenumber of the ith mode given by a numerical mode code. The information of L i j can be estimated by means of comparison with the phase of the jth mode with another mode, say the mth mode, and then L i j would be estimated by solving the following equation: (δφ j m /2π) =fractional part {(D i j /D j m ) *[L i j +(δφ i j /2π)]}.
The waveguide invariant principle is used to estimate the range to a broadband acoustic source in a shallow-water waveguide using a single acoustic receiver towed along a path directly toward the acoustic source. A relationship between the signal processing parameters and the ocean-acoustic environmental parameters is used to increase the effective signal-to-noise ratio without requiring detailed knowledge of the environment. Heuristics are developed to estimate the minimum source bandwidth and minimum horizontal aperture required for range estimation. A range estimation algorithm is tested on experimental and simulated data for source ranges of 500-2200 m and frequencies from 350 to 700 Hz. The algorithm is accurate to within approximately 25% for the cases tested and requires only a minimal amount of a priori environmental knowledge.
Rhino-orbital-cerebral disease is a significant manifestation of zygomycosis in solid organ transplant (SOT) recipients. However, its characteristics and outcome are not well addressed.
SOT recipients with zygomycosis as per the European Organization for Research and Treatment in Cancer and the Mycoses Study Group criteria in a cohort study at our centers published previously and those identified with a PubMed search from the 1950s to November 2009 were studied. Patients with mycosis involving the sinuses, orbits, or central nervous system (CNS) were included.
Patients comprised a total of 90 SOT recipients with rhino-orbital-cerebral zygomycosis, including 13 in our cohort and 77 in the literature. CNS disease occurred in 57% (51 of 90). Overall mortality was 52.3% (46 of 88), and the mortality in patients with CNS disease was 73.5% (36 of 49). In logistic regression analysis, older age (odds ratio [OR] 1.12, 95% confidence interval [CI] 1.04-1.21, P=0.002) was associated with a higher mortality rate, whereas lipid formulations of amphotericin B compared with amphotericin B deoxycholate (OR 0.09, 95% CI 0.02-0.50, P=0.006) and surgery (OR 0.12, 95% CI 0.01-0.94, P=0.043) were independently associated with an improved survival even when controlled for CNS involvement and the era of diagnosis of disease.
Rhino-orbital-cerebral zygomycosis, particularly CNS disease, is associated with substantial mortality rate in SOT recipients. Older age is a significant risk factor for mortality, whereas lipid formulations of amphotericin B and surgery improved outcomes.
A passive ranging technique based on wavefront curvature is used to estimate the ranges and bearings of impulsive sound sources represented by small arms fire. The discharge of a firearm results in the generation of a transient acoustic signal whose energy propagates radially outwards from the omnidirectional source. The radius of curvature of the spherical wavefront at any instant is equal to the instantaneous range from the source. The curvature of the acoustic wavefront is sensed with a three-microphone linear array by first estimating the differential time of arrival (or time delay) of the acoustic wavefront at each of the two adjacent sensor pairs and then processing the time-delay information to extract the range and bearing of the source. However, modeling the passive ranging performance of the wavefront curvature method for a deterministic transient signal source in a multipath environment shows that when the multipath and direct path arrivals are unresolvable, the time-delay estimates are biased which, in turn, biases the range estimates. The model explains the observed under-ranging of small arms firing positions during a field experiment.