Transcript Document 7537350

Radar Systems for
Planetary Exploration
Mike Taylor
[email protected]
Perception in Offroad Environments
• Offroad environment as well as robots themselves are
very harsh on sensors and sensor performance.
Why Radar?
• Radar Positives
– Impervious to rain, mud, fog,
dust.
– Few interference concerns
– Generally physically tough
• Radar Negatives
–
–
–
–
Costly
Wide beams
Slow scan speeds
Very hard to determine target
size or shape
– False Alarms
Key Points:
• Radar provides a generally robust sensing solution.
• Sensor choice: push against technology or push against physics.
Uses
•
•
•
•
Object detection
Terrain mapping
Object tracking
Sensor Fusion
– Camera + radar
• Automotive groups exploring this area
– Laser + radar
• Many robot systems use this. Boss, etc.
Basics
• Standard echo-location
• Radar emits specific radio frequency and
detects reflected waves
– Separate transmit and receive antennas
– Single transmit/receive antenna
• Scan the beam to look in different directions
– Air traffic control radar
• Scanning determines the Field of View (FOV)
– Air traffic control radar: 360°
– Roving from North to East and back: 90°
RF Propagation
• Returned energy proportional to range-4
– Double the range, get only 1/16 the power returned
• RF propagation on transmit:
– Same amount of power would hit each target
• Target 1: 1 W ·m-2
• Target 2: ¼ W ·m-2
– Double the range, ¼ the incident energy
– P α range-2
Target 2:
2 x Range
• Reflected energy suffers same degradation
4 x Area
– Round trip: range-2 · range-2 = range-4
10 m
20 m
Beam Shape
• Beam shape is function of antenna
– High gain vs. omni-directional antennas
– Gain developed by interference
• “Beam Width” estimates
– 3 dB typical
– Contains vast majority of energy
• Relationships:
– Beam Width α frequency -1
– Beam Width α (antenna width)
-1
• Applies in both height and width
Side Lobes
• Result of same interference
pattern that created the main
beam.
– Generally much weaker than
main beam.
• Objects receiving energy from
side lobes can be detected.
– Car off to right as we’re driving
down the road.
Image from appolo.lsc.vsc.edu
• Major issue for terrain mapping.
– Affect confidence of detection.
– See Alex Foessel’s PhD thesis
for further discussion.
10 m
20 m
Beam Shape vs. Resolution
• Beam width affects angular accuracy and ability to separate targets
– Correlates to ‘resolution’
Can the truck fit through?
Only one object reported
with high angular error.
• Comparison to laser
– Laser beam size: usually < 1°
– Radar beam size: most 3 ° to 5°
• Down sides to smaller beams:
– Higher frequency: vegetation opacity & line of site
– Larger antenna: hard to scan, larger form factor
Radar Types
Frequency
Scanning
Data Output
24 GHz
Mechanical
Raw Data
- Antenna or mirror motion
- Powerful
- Resource intensive
Phased / Patch Array
Detections
- Issues with wide views
- Range, Angle, Power
- Simple, Limited
Return Processing
- Beam forming on return
Tracks
77 GHz
94 GHz
- Legal in U.S.?
- Dipole
•
- Traffic use
- Limited
Additional Specs:
– Detection range for certain objects
– Horizontal and vertical beam width
– Horizontal and vertical FOV
– Scan rate
– Number of targets per scan
– Range and angle resolution
Continental ARS-300
• Long range, dual mode ACC-style radar
• Spinning cylindrical reflector
– Grating on cylinder causes different interference patterns
• Specs:
–
–
–
–
Long Range: 200 m, 17°
Mid Range: 60 m, 60°
Beamwidth ~3 degrees
Return limit varies by version
• Reference Information:
– Tartan Racing publications
• Example of steered beam system
–
–
–
–
Unique antenna design
Emitted energy focused on a particular area
Prone to ‘ghost velocities’
Far reaches of FOV have limitations
Delphi ESR
• Long range, dual mode ACC-style radar
• Specs
– Long range: 200 m
– Medium range: 60 m
– Return limit varies by version
•
•
•
•
ESR: Electrically-steered radar
Volvo S60: ESR + Mobileye camera
Launches in 2010
Reference Information:
– http://delphi.com/news/featureStories/fs_2008_06_02_001/
• Example of beam forming on return
–
–
–
–
Beam is not ‘steered’, wide emission pattern
Bearing calculated by phase difference between multiple receive antennas
Provides locations of returns above threshold
Limits available information for processing
ACC Comments
• Cheap, useful, feature-filled radars
– Can be hard to acquire
• Limited to manufacturer’s tools and code
• Not tuned for offroad:
– Incorrect thresholds
– Improper motion models
• Ghost Velocities
– Imperfect noise handling
– Wide beam angles
• Good first step
M/A-Com
•
•
Low cost, low range radar for collision
prevention and blind spot coverage
Specs:
–
–
–
–
•
•
Single Mode
Range: 27 m
FOV: +100°
Limited returns
Particularly good at picking up moving objects
Reference Information:
– http://www.macom.com/macom_prodnews.asp?
ID=1094
•
Example of Dipole Radar
– Two receive antennas
– Returns signals are compared to determine
bearing
– Potential ambiguity in bearing
Path length difference
determines bearing
Angular Ambiguity
• Simple dipole radars have a weakness:
– Both objects below are at roughly the same range
– Simple systems report seeing a single target along the centerline
NavTech
•
•
Spin-off from ACFR
Specs
–
–
–
–
–
FMCW
360 Degree FOV
2 degree beam
2.5 Hz
0.03 meter range
accuracy???
– 200 meter range
•
Initial models could not
measure velocity
•
Reference Information:
–
http://www.nav-tech.com
FMCW Quirk
• Relative velocity causes vertical (frequency) shift in signal
• Range causes horizontal (temporal) shift in signal
• Up and down ramp allows separation of range and Dopper
– Up: Delta = R + D
– Down: Delta = R - D
R+D
R+D
R-D
R-D
Other Suppliers
• Research Houses (for semi-custom radars)
– Militech
•
http://www.millitech.com/
– Epsilon Lambda
•
http://www.epsilonlambda.com/
• Manufacturers
– Eaton-Vorad
•
http://www.roadranger.com/Roadranger/productssolutions/collisionwarningsystems/index.htm
– Bosch
http://rb-kwin.bosch.com/us/en/safety_comfort/driving_comfort/driverassistancesystems/
adaptivecruisecontrolacc/index.html
Reflectivity and RCS
• All objects reflect energy. Two questions:
– How much?
– In which direction?
• Units: dBsm
– Reflected power relative to one square
meter of flat metal sheet
– Human: -10 to 0 dBsm
– Car: +10 dBsm
• Energy reflected depends on
–
–
–
–
Material
Surface structure (clothing wrinkles)
Size….
Shape- Specularity
Radar Return vs. XY Position
Radar Tuning Scene
16” Rock
Senor Origin
6” Dia. Pipe
Radar Return vs. XY Position
Radar Return vs. XY Position
Radar Target Amplitude Curves
Key
Trucks
Amp(dB)
Human
+
Ground
Noise
•
•
•
Ground return is terrible
Objects are specular
“Coke can challenge”
Range(m)
Boss
• Vehicle Tracking
– Radar + Lidar Fusion
– Direct velocity measurements key
– Orientation is challenging
• Veggie Cars
Motion Free Scanning Radar (consortium with CMU)
Motion Free
Scanning
Radar Sensor
•Narrow beam
•High reliability
•Low cost
•Small (30cm  x 20cm L)
High Resolution
Range Map:
Cat AMT
• Radar-based autonomous mining truck (AMT) circa 1995
– Millitech-developed 3D scanning FMCW radar
• Multi-sensor AMT under development with CMU
SSOD
•
•
•
•
•
SSOD: Slow Speed Obstacle Detection
Blind spot detection system
Option on some Caterpillar mining trucks
M/A-Coms compliment WAVS in-cab camera system
Turns off after short distance
Researchers: ACFR
• Australian Center for Field Robotics.
– University of Sydney
•
•
•
•
Rare radar research group
Focused on mining applications
Semi-stationary terrain mapping
Assemble custom systems based on
needs
– Purchase and fabricate components
– Develop own processing
• Paper repository:
– http://www.cas.edu.au/publications
ACFR Radar Mapping
• Stope fill monitoring
– Filling large, mined out voids in
underground mines
– Visibility very limited
• Fill monitoring as well
– Beam width: 1.12°
– 77 Ghz
– 30 cm range resolution
ACFR Radar Mapping
• Drag-line Monitoring
– Poor visibility limits
productivity
– Provides ‘situational
awareness’ for operator
• Terrain
• Bucket
• Ropes
– Allows digging in “zero” vis
Researchers:
•
Steve Shedding, ACFR
– Former Postdoc at R.I
– Working in interesting mobile terrain mapping and map fusion
•
Graham Brooker, ACFR
– Major push behind designing new radar systems at ACFR
•
Alex Foessel
– R.I. PhD, now at John Deere company
•
Research Houses
– Millitech
– Epsilon Lambda
– NavTech
•
Automotive Suppliers
Improvements
• Lower Prices
– Automotive industry: Delphi, Continental, Bosch
• Improved performance
– ACRF, automotive industry
• Sensor fusion
– Automotive, ACFR
– Delphi: Volvo S60 + ESR + Mobileye
• Velodyne for radar
– ABM radar?
Radar Layout Method
• Calculate the number of
radars required to cover all
potential movement.
• Vehicle specs:
–
–
–
–
Top speed
Minimum turning radius
Minimum deceleration
Calculate envelope
• Radar specs:
– Field of view
– Detection Range
• Depends on target
• May vary with heading
Radar Layout Method
• Radar specs
– 60 m range
– 90° FOV
• This radar has
sufficient range but
insufficient FOV.
• Two radars will suffice
Homework
•
Design a radar layout for a ground vehicle exploring a desert region
•
Given:
–
Two radars:
•
•
–
Option 1: ACC-style, $5,000.
Option 2: Raw data, $35,000.
Truck:
•
12 meters long
–
•
•
•
•
•
Rear differential is 2 meters from rear of machine
5 meters wide
Turning radius: 15 meter
Top speed:
12 m · s-1 (assume independent of turning radius)
Deceleration: 1.5 m · s-2
Questions:
–
–
How many of each radar would you need to handle the vehicle?
Which radar would you choose? Write a short blurb on why.
•
•
•
60° FOV, 150 m range for vehicles.
90° FOV, 90 m range for vehicles.
Factors to consider: number of sensors, adjustability, cost, computing and personnel resources.
Assume your team is a typical CMU robotics team in the FRC with the normal skill sets, funding
issues, and compressed timeline. There is no right answer- the key is going through the decision
process and weighting each issue as you see fit.
Extra Credit
–
Which radar would work better for avoiding humans? Think about:
•
•
•
Ability to detect lower power returns
Ability to develop detection algorithms
Stopping distance
References
•
Textbooks: Introduction to Radar Systems by Skolnik
– http://search.barnesandnoble.com/Introduction-to-Radar-Systems/Merrill-ISkolnik/e/9780070579095/?itm=4
•
ACFR Publication Depot
– http://www.cas.edu.au/publications
•
Overview of Delphi ACC systems including ESR Radar:
– http://delphi.com/news/featureStories/fs_2008_06_02_001/
•
M/A-Com
– http://www.macom.com/macom_prodnews.asp?ID=1094
•
NavTech
– http://www.nav-tech.com
•
Boss / Urban Challenge Papers (Continental radar):
– http://www.darpa.mil/GRANDCHALLENGE/TechPapers/Tartan_Racing.pdf
– http://www.ri.cmu.edu/pub_files/pub4/darms_michael_2008_1/darms_michael_2
008_1.pdf
– http://www.tartanracing.org/press/boss-glance.pdf