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Lidar System for Airborne Measurement of Clouds and Aerosols

This is an eye-safe, rugged, all-solid-state system. The figure schematically depicts a lidar system for measuring optical properties of clouds and aerosols at three wavelengths. The system is designed to be operated aboard the NASA ER-2 aircraft, which typically cruises at an altitude of about 20 km — above about 94 percent of the mass of the atmosphere. The system can also be operated aboard several other aircraft, and a version for use on Unmanned Aerial Vehicles (UAVs) is presently under construction. In addition to the requirement for fully autonomous operation in a demanding airborne environment, three other main requirements have governed the design: (1) to make the system eye-safe at the operating altitude; (2) to make the system as lightweight as possible, yet rugged; and (3) to use solid-state photon-counting detectors fiber-coupled to the receiver.

Posted in: Briefs, TSP

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Reduced-Order Kalman Filtering for Processing Relative Measurements

A Kalman filter can be propagated using fewer computations. A study in Kalman-filter theory has led to a method of processing relative measurements to estimate the current state of a physical system, using less computation than has previously been thought necessary. As used here, “relative measurements” signifies measurements that yield information on the relationship between a later and an earlier state of the system. An important example of relative measurements arises in computer vision: Information on relative motion is extracted by comparing images taken at two different times.

Posted in: Briefs

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Fuel Cell Material



Posted in: Blog

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Communicating Underground



Posted in: Blog

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Measuring Positions of Objects Using Two or More Cameras

This method could determine the causes of accidents. An improved method of computing positions of objects from digitized images acquired by two or more cameras (see figure) has been developed for use in tracking debris shed by a spacecraft during and shortly after launch. The method is also readily adaptable to such applications as (1) tracking moving and possibly interacting objects in other settings in order to determine causes of accidents and (2) measuring positions of stationary objects, as in surveying. Images acquired by cameras fixed to the ground and/or cameras mounted on tracking telescopes can be used in this method.

Posted in: Briefs, TSP

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Magnetic Compensation for Second-Order Doppler Shift in LITS

Fractional frequency stability could be the lowest ever achieved. The uncertainty in the frequency of a linear- ion-trap frequency standard (LITS) can be reduced substantially by use of a very small magnetic inhomogeneity tailored to compensate for the residual second-order Doppler shift. An effect associated with the relativistic time dilatation, one cause of the second-order Doppler shift, is ion motion that is attributable to the trapping radio- frequency (RF)electromagnetic field used to trap ions. The second- order Doppler shift is reduced by using a muli-pole trap; however it is still the largest source of systematic frequency shift in the latest generation of LITSs, which are among the most stable clocks in the world. The present compensation scheme reduces the frequency instability of the affected LITS to about a tenth of its previous value.

Posted in: Briefs

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Polarization/Spatial Combining of Laser-Diode Pump Beams

Four beams are combined into two, which are then combined into one. The figure depicts a breadboard version of an optical beam combiner that makes it possible to use the outputs of any or all of four multimode laser diodes to pump a non-planar ring oscillator (NPRO) laser. This apparatus could be an alternative to the one described in the immediately preceding article. Whereas that one utilizes spatial (beam-shaping) beam- combining techniques, this one utilizes a combination of polarization and spatial beam-combining techniques. In both that case and this one, the combined multiple laser-diode pump beams are coupled into an optical fiber for delivery to the NPRO pump optics.

Posted in: Photonics, Briefs

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