Engineering topics

Gentry, Bruce M.

Publications and source records attributed to Gentry, Bruce M..

24 records · Page 2

NASA NTRS1995

High spatial resolution atmospheric wind measurements with the edge technique

The edge technique is a new and powerful method for measuring small frequency shifts such as the Doppler shift of an atmospheric backscattered signal from a pulsed laser. The edge technique can be used for high spatial resolution, high accuracy ground and airborne wind measurements as well as high accuracy spaceborne wind measurements. We have recently made our first ground based wind measurements. These have a spatial resolution of 15 m and an accuracy of 25 cm/s and these measurements are presented in this paper. This is a unique capability and provides valuable information for studies of turbulent processes in the lower atmosphere. It could also be used for high sensitivity detection of wind shear and microbursts in the vicinity of airports. In addition, global wind measurements can be made with the edge technique from space with an accuracy of 1 m/s and a vertical resolution as high as 150 m in the boundary layer and 1 km through the troposphere. Such a system could make eyesafe wind measurements using well developed diode pumped solid state laser technology at 1.06 micron. Multi-pulse averaging would provide a spatially representative wind measurement.

Korb, C. Laurence↗

NASA NTRS1992

Edge technique - Theory and application to the lidar measurement of atmospheric wind

The paper describes the theory of the edge technique, a powerful method for the detection and measurement of small frequency shifts. It can be employed with a lidar to obtain range-resolved measurements of wind with high accuracy and high vertical resolution. The technique can be applied to measure wind with a lidar by using either the aerosol or molecular backscattered signal. Simulations for a ground-based lidar at 1.06 micron using reasonable instrumental parameters show an accuracy of the vector components of the wind which is better than 0.5 m/s from the ground to an altitude of 20 km for a 100-m vertical resolution and a 100-shot average.

Korb, C. L.↗

NASA NTRS1992

Laboratory Velocimeter Measurements Using the Edge Technique

We have developed a simple but powerful measurement methodology using the edge technique to measure the Doppler shift of backscatter laser radiation. With this method, instantaneous velocity information, including wind measurements, can be obtained with sub-meter-per-second accuracy and with high range resolution using a pulsed lidar system. This paper describes laboratory experiments that demonstrate the basic principles of the edge technique. These experiments demonstrate the sensitivity of the technique and the high velocity accuracy which can be obtained. In addition, many of the characteristics which make the edge technique a powerful method for use in lidar wind application were verified. These include the insensitivity of the measurement to laser and/or edge filter frequency jitter and drift, and the ability to make Doppler shift measurements which are of the order of 100 times better than the spectral bandwidth of the measurement (the combined spectral width of the laser and edge filter).

Gentry, Bruce M.↗

NASA NTRS1992

Doppler lidar wind measurement with the edge technique

The edge technique is a new and powerful method for measuring small frequency shifts. Range resolved lidar measurements of winds can be made with high accuracy and high vertical resolution using the edge technique to measure the Doppler shift of an atmospheric backscattered signal from a pulsed laser. The edge technique can be used at near-infrared or visible wavelengths using well developed solid state lasers and detectors with various edge filters. In the edge technique, the laser frequency is located on the steep slope of the spectral response function of a high resolution optical filter. Due to the steep slope of the edge, very small frequency shifts cause large changes in measured signal. The frequency of the outgoing laser pulse is determined by measuring its location on the edge of the filter. This is accomplished by sending a small portion of the beam to the edge detection setup where the incoming light is split into two channels - an edge filter and an energy monitor channel. The energy monitor signal is used to normalize the edge filter signal for magnitude. The laser return backscattered from the atmosphere is collected by a telescope and directed through the edge detection setup to determine its frequency (location on the edge) in a similar manner for each range element. The Doppler shift, and thus the wind, is determined from a differential measurement of the frequency of the outgoing laser pulse and the frequency of the laser return backscattered from the atmosphere. We have conducted simulations of the performance of an edge lidar system using an injection seeded pulsed Nd:YAG laser at 1.06 microns. The central fringe of a Fabry-Perot etalon is used as a high resolution edge filter to measure the shift of the aerosol return.

Korb, C. Laurence↗

NASA NTRS1992

Pulsed laser spectral measurement using a Fabry-Perot interferometer: Limits to resolution

We are developing a Doppler lidar system using the edge technique to measure atmospheric wind profiles. The edge technique requires a laser with a narrow spectral bandwidth and a high resolution optical filter. The lidar system will use a Nd:YAG laser operating at 1.064 microns and a high resolution Fabry-Perot interferometer for the edge filter. The Doppler shift measurement is made by locating the laser on the edge of the filter's spectral response function. Due to the steep slope on the edge, large changes in the filter transmission will be observed for small changes in frequency. The Doppler shift can be determined from a measurement of this change in filter transmission if the filter spectral response function in the region of the measurement is well known. Recently developed injection seeded solid state lasers have made near transform limited laser output readily available for lidar work. Injection-seeded Nd:YAG laser exhibit single mode output with smooth Gaussian temporal pulse shapes. Results of an experiment we conducted to evaluate the effects of a short Gaussian temporal input pulse on the spectral response of a high resolution Fabry-Perot interferometer are presented.

Notari, Anthony↗

NASA NTRS1991

Infrared lidar windshear detection for commercial aircraft and the edge technique, a new method for atmospheric wind measurement

The edge technique, a new method for measuring small frequency shifts, is described. The technique allows high-accuracy measurement of atmospheric winds (0.2-1 m/s) with a high vertical resolution (10 m) using currently available technology. With the edge technique, a lidar system can be used to obtain range resolved measurements of the wind in the atmosphere from the ground, aircraft, or spaceborne platforms. The edge technique can be used with different lasers over a broad range of wavelengths.

Targ, Russell↗