OBSTACLE AWARENESS AND COLLISION AVOIDANCE RADAR SENSOR SYSTEM FOR

LOW-ALTITUDE FLYING SMART UAV

Young K. Kwag and Jung W Kang, Avionics Dept. AERC, Hankuk Aviation University, Seoul, Korea

Presentation by Genya Fridlyand

OBJECTIVE

Obstacle awareness and collision avoidance is consideredthe most important issue in the field of unmanned vehicles.

While this technology is in use for manned vehicles, it is stillin the development and test phase for unmanned vehicles.in the development and test phase for unmanned vehicles.

Objective: propose a suitable radar sensor system for unmanned aircrafts

2

UNMANNED AERIAL VEHICLES

An unmanned aerial vehicle (UAV) is an unpiloted aircraft.UAVs can be remote controlled or fly autonomously based on pre-programmed flight plans or more complex dynamic automation systems [2].

3

PROBLEMS WITH UAVS

In the past seven years, the UAV average mishap ratehas been 4.28; compared to the Air Force mishap rateaverage during that same time of 1.12, UAV mishaps are very high [3].

4

• limited camera angles

• extremely poor pilot-to-airplane interface

• reaction time

• boredom

AVAILABLE TECHNOLOGIES

Current cooperative systems in use for manned aerialvehicles include:

5

• Traffic Alert Collision Avoidance System (TCAS)• Automatic Dependent Surveillance-Broadcast (ADS-B)

Traffic Alert Collision Avoidance System (TCAS)

TCAS involves communication between all aircraft equipped with an appropriate transponder [4].

Each TCAS-equipped aircraft "interrogates" all other aircraftin a determined range about their position and all other craftreply to other interrogations [4].

This interrogation-and-response cycle may occur severaltimes per second [4].

6

Traffic Alert Collision Avoidance System (TCAS)

TCAS I - first generation of collision avoidance technology;Alerts pilot of traffic; no suggestion of remedy [4].

TCAS II - used in commercial aircrafts. Offers all benefits of TCAS I. Offers the pilot direct, vocalized instructions to avoidDanger [4].

TCAS III - "next gen" of collision avoidance technology. Currently suspended; no further plans for development [4].

7

Non-Cooperative Systems

Non-cooperative systems use sensors to measure theavoidance information of the obstacles using active orpassive methods

Active sensors emits energy to obstacles and receives the Active sensors emits energy to obstacles and receives the reflecting energy. Passive sensors only receive energyradiated from obstacles.

• Electro-optical sensors• Electromagnetic radar sensors

8

Sensor Characteristics [1]

Condition Microwave MMW Thermal Imager

Mode Active Active Active

Wavelength cm cm µm

Average Power High Medium Low

Range/Range Available Available Not-Available

9

Range/Range Available Available Not-Available

Detection Range Unlimited 10km 10-15km

Component Large Small Small

Angular Resolution

Large Small Small

AtmosphericEffects

No-degraded Some degraded Degraded

System Requirements

UAV standards/requirementsMaximum speed:

• 500km/hr w/o payload• 440km/hr with payload

Payload limited to 40kg (25kg for optimal collision avoidance)

10

Sensor Requirements Consideration

• Real-time measurement capability (most important)• Operational environment• Payload constraints • Payload constraints • Air safety regulation (ELOS)

11

Real-Time Measurement Capability

• Range/range rate• Bearing in azimuth• Elevation

12

Operation Environment

• Day and night operational capability• Vehicle maneuverability• Endurance time in air• Rain, wind, hail, lightning, etc.• Electronic counter-countermeasures (ECCM) capability

13

Equivalent Level of Safety (ELOS) [1]

Performance Parameter ELOS for See & Avoid

Missed Distance 500 feet

Field of Regard-Azimuth-Elevation

Search Volume+/- 60º+/- 10º-Elevation +/- 10º

VFR Detection Range 1.84 miles

Time to Collision (11 sec avoidance maneuver)

21 sec (10 sec PRT)23.5 sec (12.5 sec PRT)PRT: Pilot Reaction Time

Number of Aircraft in Range Limited (5-10)

14

Most Promising Method

Non-cooperative active radar sensor used as primarycollision avoidance sensor. Specifically the millimeter waveradar (MMW).

However, cooperative methods such as TCAS and/or ADS-Bcould be considered an alternative option for the back-upsystem.

15

Obstacle Awareness and Collision Avoidance System (OACAS) Concept

Consists of CAS radar sensor and OCAS processor.

The CAS radar constitutes the antenna, transmitter/receiver,signal processor, and data processor.

The OCAS processor can be contained in the radar dataprocessor or be part of the Digital Flight Control Computer(DFCC).

16

Concept of OACAS Model [1]

17

Minimum Required Time to Collision Criteria [1]

Velocity (Km/h)

Time to Collision (sec)

5 11 17 23 25 S

500 0.7 1.5 2.3 3.2 3.5 Km

600 0.8 1.8 2.8 3.8 4.2 Km600 0.8 1.8 2.8 3.8 4.2 Km

700 1.0 2.1 3.3 4.5 4.9 Km

800 1.1 2.4 3.8 5.1 5.6 Km

900 1.3 2.8 4.2 5.8 6.3 Km

1000 1.4 3.0 4.7 6.4 6.9 Km

ClosingSpeed

Avoidance Mode

Awareness Mode

18

Key Radar System Design Trade-off Parameters [1]

Parameters To be traded-off

Radar type Coherent or Coherent-on-receiver

Power Module MPM or TRM or Magnetron

Frequency Ka (35 GHz) or Ku band

Antenna Type Dish or Planar type

Range < Max 8 Km

Resolution Range < 5m

PRF Type Low PRF <5 KHz or High PRF> 20KHz

Scan Coverage +/-90 deg in azimuth+20~-80 deg in elevation

Scan Volume +/-60 deg azimuth +/-10 deg elevation

Probability of Detection 90% for SW2, RCS 1 m2, Pfa=10-6

19

CAS Radar Design Model (CAR) [1]

20

CAR Radar Design Parameters[1]

Frequency 35 Ghz Scan Coverage 180º in Azimuth

CAS radar Design parameters meet and exceedrequirements by the FAA

Frequency 35 Ghz Scan Coverage 180º in Azimuth100º in Elevation

Detection Range 6.4 Km Scan Rate 150 deg/sec

PRF 2 KHz Antenna Beam Width 2.5 deg

Pulse Width 33 ns Antenna Gain 38 dB

System Bandwidth 30 MHz RCS 2~30 dBsm

Range Resolution 5 m Prob. of False Alarm 10e-6

Peak Power 3 Kw Prob. of Detection 90%

21

Obstacle Detection Problems

There is slight discrepancy with the shape and actual size ofstationary and moving objects detected by the radar.Problems can arise when extremely high accuracy is needed.

22

Conclusion

After comparing both the cooperative and non-cooperativemethods it was determined the non-cooperative methods arecurrently the most feasible. How ever the OASAS conceptpresented is a promising possibility of future avionics.presented is a promising possibility of future avionics.

QUESTIONS?

23

Cited Sources

[1] Young K and Jung W Kang, “Obstacle Awareness and Collision Avoidance Radar Sensor System For Low-Altitude Flying Smart UAV” Korean Airspace Research Institute. Downloaded Jan 14, 2009

[2] Wikipedia, “Unmanned Arial Vehicle” http://en.wikipedia.org/wiki/Unmanned_aerial_vehicle. Accessed on Jan 23, 2009. Last updated Jan 22, 2009.Jan 23, 2009. Last updated Jan 22, 2009.

[3] Abizer Tyabji, “Unique problems associated with UAV employment” BNET Business Network; Flying Safety. Accessed on Jan 23, 2009 http://findarticles.com/p/articles/mi_m0IBT/is_5_63/ai_n19396165Last Updated May, 2007.

[4] Wikipedia, “Traffic Collision Avoidance System”, http://en.wikipedia.org/wiki/TCAS#TCAS_I Accessed on Jan 24, 2009. Last Updated Jan 23, 2009.

24