Abstract
Methods to measure wind speed and direction range from simple hot-wire / hot-film anemometers to sophisticated sonic and laser/image-based instrumentation. While these can work well on the ground and to low altitudes, there are challenges in implementation for high altitude measurements at the 20 km and above range, where a near space environment exists. The low pressure, low density environment does not support the conditions needed for all known measurement methods to generate an engineering value for the full velocity vector at the cm/s accuracy and resolution needed to allow for high altitude balloon or platform trajectory correction. The National Oceanic and Atmospheric Administration (NOAA) regularly reports relative wind conditions to the 60 kft (18 km) level. Above this level operators are left to modeling and simulation of the stratified air to determine prevailing wind conditions that can be used to provide trajectory control via altitude changes. An in-situ, on-board sensor that can measure all three components of velocity with resolution and accuracy in the cm/s range can take out the uncertainty that is involved in the software-based approach, and together with other navigation aids, complete a trajectory solution for high altitude platforms and science balloons that will help them extend their mission envelope to greatly benefit operational effectiveness. The development of a novel wind speed sensor solution that can operate at the high altitudes of interest and meet resolution requirements is described. The sensor solution can also be applied in other low density environments to measure flow velocity, as well as, harsh environments that may be challenging for other velocity measurement methods. The paper also includes discussion on the design and fabrication of a special high altitude closed vessel with an integrated wind tunnel, capable of generating wind at altitudes more than 45 km, used in the current project for experimental validation, but could also support future sensor calibration efforts.
