DARPA has solved the how to keep stratospheric balloons permanently over one location. They are testing a wind sensor to detect changes in wind speed and direction from large distances. This is part of the Adaptable Lighter-Than-Air (ALTA) balloon program. The balloons can change altitude and position to stay in one spot.
DARPA balloons could provide secure communications and navigation or act as a mother ship for drones.
OAWL shines pulses of laser light into the air. A small fraction of the beam is reflected back, and the reflected laser light is gathered by a telescope. The wavelength of the reflected light is changed slightly depending on how fast the air it bounced back from is moving, a change known as doppler shift. By analyzing this shift, OAWL can determine the speed and direction of the wind.
OAWL looks in two directions at once, giving a better indication of wind speed and direction.
Previous versions of OAWL flown in aircraft have measured winds more than 14 kilometers (8.6 miles) away with an accuracy of better than a meter per second. The main challenge with Strat-OAWL has been shrinking it to fit the space, weight, and power requirements of the ALTA balloons.
The ALTA balloon will operate even higher than Google Loons. They will fly at 75,000 to 90,000 feet (22,900 to 27,400 meters or 14 to 17 miles), where the winds are less predictable. Greater variation in winds will help them have more choices as to which wind they will use.
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