Low Altitude Coyote UAS Missions into Major Hurricane Maria

In September of 2017, scientists from NOAA’s Hurricane Research Division of the Atlantic Oceanic and Atmospheric Laboratory collected valuable and highly unique data from six (6) Coyote Unmanned Aircraft Systems (UAS) deployed into Hurricane Maria. Using NOAA's P-3 reconnaissance aircraft as a mothership and coordinated flight resource, UAS observations of wind speed, wind direction, atmospheric pressure, temperature and moisture were recorded. Remote measurements of sea surface temperature were also collected by the Coyote using an onboard, downward-looking infrared sensor. UAS data were transmitted to the National Hurricane Center and made available to the forecasters in near-real time.

A brief synopsis of the data collected is provided below.

Coyote flight 1 (Friday, September 22nd) Eyewall experiment -
On the first flight, record endurance was attained for a Coyote UAS eyewall mission (43 min). For this experiment, controlled flight was maintained at altitudes as low as 375 feet. Here, the UAS-measured a maximum flight level wind speed of 123mph. As was the case for all six UAS missions, NOAA's P3 hurricane hunter aircraft performed a complementary eye/eyewall pattern that coincided with the UAS track and position. In this particular instance, Coyote UAS observations were noted by NHC forecasters in their forecast discussions of Hurricane Maria.

Coyote flight 2 (Saturday, September 23) Inflow experiment -
Coyote 2 attempted to spiral into the strongest winds of the storm. This mission started ~50 nmi to the WNW of the center while the P3 conducted a 'lawnmower pattern' that kept the manned aircraft within close proximity to the Coyote. UAS stepped descents from 4000ft to 1000 ft were conducted during this 33 minute flight. This experiment is expected to help model parameterizations within the very difficult to observe atmospheric boundary layer and surface layer environment.

Coyote flight 3 (Saturday, September 23rd) Eyewall experiment -
Similar to Coyote flight 1, approximately half of Maria's eyewall was traversed over a 32 minute period. Controlled flight was attained as low as 1100ft (~350m). This experiment was notable in that, to the best of our knowledge, a record was set for UAS-measured wind speed (143 mph at 1115ft). Similar to flight 1 on the 22^nd, these data were used by NHC forecasters as part of their forecast discussion.

Coyote flight 4 (Saturday, September 23rd) Eyewall experiment -
Coyote 4 covered a good portion of Maria's southern eyewall during its 32 minute flight. Separated by less than an hour, flights 3 and 4, when combined, came close to completing an "eyewall orbit" of the powerful storm (which represents the first such pattern of its kind for any aircraft).

Coyote flights 5 and 6 (Sunday, September 24th) UASonde gliders -
These flights were shorter in duration (7-8 minutes) due to engineering challenges that were encountered. Nevertheless, these deployments still retrieved useful data similar to what a dropsonde might collect as the UAS glided to the surface. Unlike a dropsonde however, these Coyotes remained aloft longer and were purposefully guided from a 10k deployment altitude through the transition region between the storm’s eye and the highly turbulent eyewall at very low altitudes. These boundary layer flights are important because they can help us improve understanding of this difficult to observe, yet critically important region of the storm. Horizontal turbulent exchanges of heat, moisture and momentum regularly occur between the eye and eyewall but are rarely, if ever adequately sampled at such low altitudes.

Additional analyses from these groundbreaking UAS missions will be presented.