Doctoral Dissertations

Date of Award

5-1990

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Engineering Science

Major Professor

Walter Frost

Committee Members

Robert E. Turner, Kenneth R. Kimble, Frank Collins, Bruce Bomar

Abstract

The capability to measure wind fields has always been a high priority item since man began to fly. This capability has become increasingly significant with the high speeds and values of airborne platforms today. Typically, wind field measurements and reporting is accomplished by ground stations or localized aircraft in the area of interest. The main problem with local aircraft experiencing and reporting problems with wind fields (in this case turbulence) is that it might help the following aircraft in the area but could have caused severe injury to personnel aboard the measurement aircraft and damage to the airframe. The idea of remotely sensing turbulence is not a new idea but has not been achieved to any level of reliability. Severe weather patterns are easy to spot with both Doppler and conventional radar systems. The clear air and otherwise undistinguishable turbulence is the type that has been receiving a lot of publicity lately due to the number of personal injuries suffered aboard aircraft. The purpose of this paper is to investigate the phenomenology and feasibility of remotely sensing and measuring small scale turbulence of this type. The remote sensing device of particular interest in this effort is the lidar (acronym derived from light detection and ranging). Two different field programs were conducted with lidars to research this effort. Also as a proof of concept, some data was collected and reduced in a similar manner as the lidars with a group of pulsed doppler radars. Wind fields were measured with the ground-based NASA Marshall Space Flight Center (NASA/MSFC), Huntsville, Alabama, lidar, NOAA Wave Propagation Lab oratory (NOAA/WPL), Boulder, Colorado, lidar, Stapleton International Airport, Denver, Colorado doppler radars, and with the NASA B-57B instrumented aircraft. The remotely sensed winds are compared in all cases with the in-situ aircraft measurements. It was found from this research that turbulence intensities measured by computing the lidar wind time history for each range gate and then calculating the rms value relative to the mean agree quite well with the aircraft intensities. The spectral width or second moment data from the lidar, however, does not correspond well with the aircraft measured intensities being consistently a factor of 2-3 or more higher. The radar data analyzed also showed promise with the results being very similar to the lidar. Overall, the results of the research show general agreement between winds measured with Doppler lidars/radars and the B-57 instrumented aircraft. Data from these field tests provided unique sets of data to examine the mean wind and turbulence measurements made by remote sensing instruments. It is hoped that the results of this study will prompt increased research into this area and hopefully make our skies safer to fly in.

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