Final Report:
First-Ever Successful UAS Mission into a Tropical Storm (Ophelia - 2005)

Abstract

On September 16th 2005, NOAA, NASA and Aerosonde partners successfully flew into tropical storm Ophelia. This landmark event marked the first time an autonomous vehicle was flown into the core of a mature tropical system. At the time, Ophelia was a 55kt tropical storm and was located off the North Carolina coastline.

The primary objective of this mission was to utilize the unique capabilities of the Aerosonde platform in order to document areas of the hurricane environment that are either impossible or impractical to routinely observe. A major success of the Ophelia flight was its immediate operational impact. The Aerosonde was able to provide critical near-surface wind speed measurements to the National Hurricane Center in real time. In addition, high-resolution thermodynamic and kinematic observations within Ophelia’s low-level inner core were also collected. It is believed that detailed analyses of these unique data sets will result in improved understanding of the rarely observed hurricane boundary layer environment. The Ophelia Aerosonde data set will also provide invaluable ground truth and should enable detailed comparisons between in-situ observations and airborne as well as satellite-derived estimates. In future years, it is hoped that unique data such as these will also be utilized to initialize and verify operational and research-oriented TC numerical simulations.

Introduction

Hurricanes and tropical storms cause many deaths and average billions of dollars in damages each year. More than 1000 lives were lost in Hurricane Katrina (2005) alone, and the financial impact on the U.S. economy has already exceeded $200 Billion. Improved forecasts and warnings also reduce the costs inherent in responding to the hurricane threat. The devastating impacts of Hurricanes like Katrina or Wilma (2005) require that we make the best possible and most authoritative information available to decision-makers to help them determine whether to implement mandatory evacuations and other costly actions for approaching hurricanes.

NOAA is working with its international and domestic partners to cost-effectively increase the number, breadth, accuracy, and availability of observation systems. As part of this effort, NOAA is investing in new technologies, such as Unmanned Aircraft Systems (UAS) in order to improve the accuracy and timeliness of our Nation’s existing weather observation and forecast system. This experiment plans to demonstrate the capabilities of the versatile Aerosonde UAS within the context of low level hurricane reconnaissance. It will also build upon recent NOAA UAS success (Ophelia 2005).

Ultimately, the value of this proposed work will be measured in lives saved and money not spent from improved understanding, forecasts and preparation. Specific benefits that directly link to NOAA’s stated strategies within the Weather and Water mission goal include detailed documentation of the rarely-observed hurricane boundary layer environment (Monitor and Observe), an improved physical understanding of this critically important region (Understand and Describe), and enhanced observations that directly lead to improved future forecasts of tropical cyclone intensity change (Assess and Predict).

The Aerosonde UAS

The Aerosonde UAS is fully summarized in Holland et al (2000). It has been undertaking civilian operations since 1995, was the first UAV to cross the Atlantic Ocean and has an impressive endurance record of over 32 hrs. It has a sophisticated command and control system and the flexibility to be deployed and commanded from virtually any location. Initially developed for meteorological and environmental applications in remote and dangerous conditions, the Aerosonde has been specifically designed for all-weather operations under harsh conditions and is well suited to the hurricane reconnaissance role. The aircraft has evolved through to the current Mark 4 version and its relevant specifications are provided in Table 1:

Table 1: Specifications of Mark 3 Aerosonde UAV

Specifications
Weight, wing span	26-30 lb, 10 ft
Engine	24 cc, Fuel Injected engine using unleaded petrol
Navigation	GPS
Operation
Staff for Launch and Recovery	3 staff: Controller, Engineer, Pilot/Maintenance
Ground Equipment	Proprietary Staging Box, Personal Computer, GPS, Radio Antennae and Iridium Satellite modem
Flight	Fully autonomous, under Base Command
Launch and Recovery	Launch from car roof rack, or catapult, land on belly. Able to operate from remote and unprepared surfaces
Ground & air communications	UHF or Satcoms to Aerosonde, VHF to field staff and other aircraft, internet or phone to command center and users.
Performance
Speed, Climb	Speed 35-80 kt, Climb 3 m/s at sea level
Endurance, Range	20 to >30 h, up to 3000 km (depending on payload weight and configuration)

Aerosonde Payload

A range of payloads are operational or under development for the Aerosonde. Those that are relevant to the hurricane boundary layer mission are listed in Table 2:

Table 2: Operational Aerosonde instruments of relevance to boundary layer monitoring.

Measurement	Instrument	Manufacturer	Technical	Comments
Air temp, press., hum.	Vaisala RSS901 sensor	Vaisala	P<.5 hPa, T<.2K, RH<2% 0.1 hz standard, capable of 1 hertz	Standard met observations
Winds	Proprietary	AeNA	u,v < .5 m/s	Standard met observations
Surface temperature	IR KT11	Heitronics	SST < 0.5K	Surface ocean and land temperatures.
	IR KT15	Heitronics	SST < 0.5K
Liquid water content and ice crystal concentration	Heymsfield VIPS	NCAR	Video recording of impacts on oiled plastic	Cloud physics and potential spray/ salt distributions
Sea state, ocean surface winds, soil moisture	GPS reflectance	NASA	<10 m resolution. Accuracy unknown	Detailed observations of surface conditions
Surface visible imaging	Digital still camera Olympus 5050	Olympus	5 megapixel 3x Optical zoom	High resolution surface imaging
Surface visible imaging	Sony 555 Video camera, fixed mount	Sony		Video of surface conditions
Infrared imaging	Indigo Omega camera	Indigo Systems	8-12 micron IR imaging	IR surface imagery

Aerosonde Launch, Command and Control

Aerosonde command and control is accomplished by:

• UHF command for LOS up to 120 miles, which may be back to a launch site or can be transferred to a mobile or other site as required;
• Iridium Satcom for OH command to any location on earth.

The required equipment is a lap top computer, a small staging box (briefcase size) and relevant antennae. AeNA has often operated from a vehicle and has transferred control to ships and other sites under operational conditions. All Aerosonde commanders and technicians are fully qualified under Australian Civil Air Operator Certificate Number VT585156-U-01, issued to Aerosonde on 30 May 2003. This is the only current Aviation Authority Certification in the world.

Use of the Aerosonde UAS for Hurricane Reconnaissance

While recent composite analyses from Cione et al (2000) and Cione and Uhlhorn (2003) have led to new insights regarding structural details of the hurricane air-sea interface, sustained and comprehensive observations of the thermodynamic (temperature and moisture) and kinematic (wind) structure of the near-surface hurricane environment have never been undertaken. Yet this environment, where the atmosphere meets the sea, is critically important:

• This is where the critical oceanic energy supply is transferred to the atmosphere
• Here we find the strongest winds in a hurricane and especially those that are most critical for forecasts and warnings

Improved observations in this region will lead to better understanding, and improved capacity for forecasting tropical cyclone intensity change. A major uncertainty in forecasting landfall intensity is the potential for rapid intensification or decay in the critical 24 h period when major response decisions have been already made. Enhancing this predictive capability would save our economy billions of dollars and help reduce the risk of death and injury for vulnerable populations

Successful utilization of the P-3 Orion and Gulfstream 4 aircraft have made NOAA a global leader in the area of hurricane aircraft surveillance and reconnaissance. However, the danger of near-surface operations in the extreme hurricane conditions has precluded comprehensive monitoring of this critical region. Satellites are also unable to monitor this region, so we are currently left with scattered local observations from dropsondes. We propose to use the unique low-flying capacity of the Aerosonde UAS platform to address this significant observational shortcoming. The Aerosonde is capable of flying at altitudes of 500 feet or less within the high-wind hurricane eyewall environment. This is thousands of feet lower than any manned aircraft is able to operate.

We consider that the payoff for using the Aerosonde platform within the hurricane environment would be both significant and immediate. The benefits would include detailed documentation of a heretofore poorly observed region of the tropical cyclone (Monitor and Observe) together with providing real-time, high-resolution, low-level wind observations of the hurricane maximum winds in support of NOAA's Tropical Prediction Center’s (TPC) forecasting requirements (Assess and Predict).; In addition, the low flying Aerosonde would greatly enhance our physical understanding of the rarely observed hurricane air-sea interface (Understand and Describe). Ultimately, this will lead to improved forecasts of tropical cyclone intensity change by enhancing today’s boundary layer parameterization schemes and providing invaluable initialization and verification data sets for numerical models (Assess and Predict). The data also will provide ground truth for aircraft and satellite derived remote measurements.

These observations and related benefits can be obtained at a cost that is quite low by normal hurricane reconnaissance costing standards.

The potential importance of this UAS role in hurricane reconnaissance is emphasized by the findings of the Hurricane Intensity Research Working Group established by the NOAA Science Advisory Board. There preliminary recommendation, presented to the last meeting of the SAB, is that:
“Low and Slow” Unmanned Aircraft Systems (UAS) have demonstrated a capacity to operate in hurricane conditions last season. A full demonstration program should be instituted in 2006 to assess their ability to provide low altitude in situ observations in a critical region where manned aircraft satellite observations are lacking.

UAS Flight into Tropical Storm Ophelia

On September 16th 2005, NOAA, NASA and Aerosonde partners successfully flew into tropical storm Ophelia. This landmark event marked the first time an autonomous vehicle was flown into the core of a mature tropical system (see http://www.noaanews.noaa.gov/stories2005/s2508.htm and http://www.magazine.noaa.gov/stories/mag193.htm) At the time, Ophelia was a 55kt tropical storm and was located off the North Carolina coastline (Figure 1). Winds were reported in near-real time to NOAA’s National Hurricane Center and directly impacted NHC operational forecasts for the tropical system at that time. P-3 Flight level, buoy and SFMR data comparisons are given in Figure 2, while preliminary Doppler radar analysis at the time of closest Aerosonde passage is given in Figure 3.

Figure 1: Aerosonde (blue) and P-3 (red) flight tracks into tropical storm Ophelia on September 16th 2005. This mission marked the first ever successful unmanned flight into a tropical cyclone. Storm intensity at the time was 55kts.

Figure 2: NOAA WP-3D 700 MB winds in dark red, Aerosonde winds in black, buoy winds in dark blue. Peak 700 mb winds of 67 kt were 10 nm SW of center, as opposed to 55 kt SFMR surface winds NE of center near small Inner eye. The Aerosonde flew downwind along major bands to the east and southwest of the storm center.

 

Figure 3: Doppler radar analysis at the time of closest approach of the Aerosonde to the wind center. This occurred just after P-3 WP-3D SFMR penetration across the eye.

 

Tropical Storm Ophelia UAS Lessons Learned:

1. FAA clearances are a major UAS hurdle that needs to be streamlined. We were able to circumnavigate this issue for our lone Ophelia flight but this was in large part due to the fact Ophelia was stalled for 1-2 days prior to mission initiation. This in turn allowed the complicated flight clearance process to play out. In a nutshell, we were very fortunate. One seeming advantage for future UAS Aerosonde missions is that we fly into regions no commercial aircraft will go near let alone fly directly into (i.e. Hurricane environments). That fact alone should play in our favor when asking for future clearances.

2. Real-time data transmission from the Aerosonde to NOAA operational centers (NHC and EMC) was not only possible but occurred without a hitch. NHC forecasters were able to use Aerosonde’s important (and highly unique) low level wind data immediately for consideration in their forecast and warning products that were disseminated to the public.

3. Despite severe budget constraints ($25K- all for flight hour costs), the Ophelia Aerosonde mission of 2005 was a success by any measure. However, follow on efforts in the form of a full UAS Hurricane Demonstration Project will require significant additional resources. This would include financial support for pre-storm (flight planning, clearances, media requests, etc), during storm (coordination with NHC, FAA, CARCAH, Aerosonde flight operators) and post storm efforts (data quality control and in depth post-analysis).

4. Tropical cyclone boundary layer data obtained by the low flying Aerosonde is truly unique and it is now clear that obtaining this information on a regular basis is of high priority for both research (HIRWAG, recent Las Vegas NOAA UAS Workshop) and NOAA operations (NHC and EMC). The fact that Aerosonde thermodynamic and wind observations can be obtained at altitudes unsafe for manned aircraft (as low as 500ft) and can also be obtained in very high spatial resolution (due to the relatively low airspeed of the Aerosonde platform) make these unique data highly desirable. The recently success of the Aerosonde Ophelia flight (2005) has driven this point home to both the research and operational hurricane communities.

Next Step - A 2006 Low Level UAS Hurricane Demonstration?

Objective:

The primary objective of this effort would be to fully demonstrate and utilize the capabilities of a low-flying UAS platform to document areas of the tropical cyclone environment that would otherwise be either unsafe or impractical to observe.  The specific goals of a 2006 demonstration project are given below and are designed to build upon the recent success of the first ever UAS flight into a tropical cyclone (Ophelia 2005) using the Aerosonde.

The immediate focus of this field effort is to significantly improve our understanding of the rarely-observed tropical cyclone boundary layer and undertake detailed comparisons between in-situ and remote-sensing observations. In addition, near-surface wind observations will be transmitted in real-time to the National Hurricane Center in support of NOAA operational requirements. These unique data will also be made available to EMC for both data initialization and forecast verification purposes.

Specific Goals

These goals include:

• In direct support of NOAA operational requirements, continue to transmit real time surface wind, pressure and thermodynamic data to NOAA’s National Hurricane and Environmental Modeling Centers.
• Conduct low level missions into the eyewall region of hurricanes at altitudes as low as 300m
• Use the unique data collected from this demonstration to help develop refined operational model boundary layer parameterization schemes.
• Over the duration of the field program, conduct several low level flights into several low level tropical cyclones (including multiple missions into multiple hurricanes)
• Undertake research aimed at improved understanding of the high-wind boundary layer and the exchanges of heat, moisture and momentum across the oceanic surface.
• Provide initialization, calibration and verification data sets for EMC, NHC and NASA.
• Look to use these unique and critically important data to help establish new NOAA operational goals and requirements.
• Fully explore Aerosonde’s potential to effectively observe critical regions of the tropical cyclone boundary layer environment.

Summary

Many positives have come from the recent UAS Aerosonde mission into tropical storm Ophelia (2005). Besides being a landmark “first” UAS mission into a tropical cyclone it also generated a great amount of interest to establish future low level UAS missions into tropical systems. This interest was broad-based and resonated with the general public, hurricane research scientists and the operational forecast community. As such, we feel that the time is right to continue this strong momentum and conduct a UAS Aerosonde Hurricane Demonstration Project during the summer of 2006. An effort such as this will enable NOAA to plan for the future when UAS observations in hurricanes are an integral and critical part of our nation’s severe weather observational network.

References

Cione, J.J., and E. W. Uhlhorn 2003: Sea surface temperature variability in hurricanes: Implications with respect to intensity change. Mon. Wea. Rev. 131, 1783-1796.

Cione, J.J., P. J. Black and S. Houston 2000: Surface observations in the hurricane environment. Mon. Wea. Rev, 128 1550-1561.

Holland, G.J., P.J. Webster. J. Curry, G. Tyrrell, D.J. Gauntlett, G. Brett, J. Becker, R. Hoag and B. Vaglienti, 2000: The Aerosonde robotic aircraft: A new paradigm for environmental observations. Bull. Amer. Met. Soc. 82, 889–902.