A new high-wind turbulence probe is under development to facilitate study of the atmospheric boundary layer in hurricane-force winds. The design is adapted from pressure-sphere gust probes long used for airborne turbulence measurements. Such a device, exposing neither fragile projections nor moving parts to the flow, has a natural application in the harsh environment of a hurricane at landfall.
The main adaptation from airborne service is expansion of the acceptance angle to a full 360 deg in azimuth and ±15 deg in elevation. The probe will also be hardened against wind-driven rain and other hazards typical of hurricanes' landfall. Water, sand, and the like will be deflected from the pressure ports by back-flushing with air. Back flushing has been successfully used in measurements near the ocean surface in the wave boundary layer.
Omnidirectional acceptance is achieved with multiple pressure sensors, practical because of the small size and power requirements of modern units. Ports are spaced 36 deg around the equator. At each of these ten locations there are also ports 15 deg above and below. The azimuthal pressure differences between adjacent ports on the sphere's equator are measured by differential sensors having ±50 mb capacity. The sensors' error is less than 0.25%. Similar sensors measure the vertical pressure difference. Temperature will be measured by a thermistor in a housing designed to slow the incident wind as it approaches the sensor. This housing will facilitate temperature correction in the strong wind field and help protect the sensor. Five absolute pressure sensors equally spaced around the sphere's equator complete the requirements for wind measurement. Wind speeds up to 100 ms-1 can be measured, sufficient for a category-five hurricane. The direction and speed of the wind are computed using algorithms based on the well-known pressure distribution over a sphere embedded in a flow. Fifty observations will be taken per second.
The sphere will be fully autonomous in its power source and communications capability, controlled by an internal computer. Data will be stored in high-capacity flash memory and transmitted by satellite link to a remote (safe) location.
The prototype is currently under construction. It will be tested in the high-wind, high dust environment of the Idaho desert. Operational use will collaborate with the Hurricane Research Division of NOAA to benefit from their experience with safe, effective deployments. Later applications will sample the wave boundary layer from a pier and perhaps from buoys.
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