Airborne laser-communication systems require special considerations in size, complexity, power, and weight. We reduce the variability of the received signal by implementing optimized multiple-transmitter systems to average out the deleterious effects of turbulence. We derive the angular laser-beam separation for various isoplanatic and uncorrelated (anisoplanatic) conditions for the phase and amplitude effects. In most cases and geometries, the angles ordered from largest to smallest are: phase uncorrelated angle (equivalent to the tilt uncorrelated angle), tilt isoplanatic angle, phase isoplanatic angle, scintillation uncorrelated angle, and scintillation correlation angle (Theta(psiind) > Theta(TA) > Theta(0) > Theta(chiind) > Theta(chic)). Multiple beams with angular separations beyond Theta(chic) tend to reduce scintillation variations. Larger separations such as Theta(TA) reduce higher-order phase and scintillation variations and still larger separations beyond Theta(psiind) tend to reduce the higher and lower-order (e.g. tilt) phase and scintillation effects. Simulations show two-transmitter systems reduce bit error rates for ground-to-air, air-to-air, and ground-to-ground scenarios.
We introduce novel methods to determine optimum detection thresholds for the Progressive Multi-Channel Correlation (PMCC) algorithm used by the International Data Centre (IDC) to perform infrasound and seismic station-level nuclear-event detection. Receiver Operating Characteristic (ROC) curve analysis is used with real ground truth data to determine the trade-off between the probability of detection ( ) D P and the false alarm rate (FAR) at various detection thresholds.Further, statistical detection theory via maximum a posteriori and Bayes cost approaches is used to determine station-level optimum "family" size thresholds before detections should be considered for network-level processing. These threshold-determining methods are extensible for family-characterizing statistics other than "size," such as a family's collective F-statistic or signal-to-noise ratio (SNR). Therefore, the reliability of analysts' decisions as to whether families should be preserved for network-level processing can only benefit from access to multiple, independent, optimum decision thresholds based upon size, F-statistic, SNR, etc.
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