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Terrain Navigation Principles and Application
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Transcript of Terrain Navigation Principles and Application
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Terrain NavigationPrinciples and Application
Ove Kent Hagen
Geodesi og hydrografidagene
September 19th 2005
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Background and History• TERCOM conceived by Chance-Vought in 1958
– Later and still applied to cruise missiles (e.g. Tomahawk)
• A Kalman filter based system suggested by Hostetler in 1976, developed into SITAN by Sandia National Laboratories– AFTI/SITAN: F16 terrain navigation 1985– HELI/SITAN: helicopter terrain navigation 1990
• TERPROM a fusion of TERCOM (initial mode) and SITAN (track mode)developed by BAE systems during the 80s
• FFI generalisation of SITAN algorithm for bathymetric navigation(developed independently) in 1997 by Heyerdahl and Kloster– Developed into TRIN: AUV terrain navigation with DVL in 2001
• Non-linear Bayesian approach by Bergman in 1999 for aircraft terrain navigation (SAAB)– Point mass filter (PMF) and particle filters
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Why use Terrain Navigation?
• Surface and Air applications: GPS is available– Redundant navigation system in critical systems– Navigation system integrity– Backup navigation system during GPS fall-outs or jamming
INSINS
INSINS
GPS
TerrNav
NavigationIntegrityMonitor
NavigationIntegrityMonitor
PrimaryPosition
Jammer
SecondaryPosition
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Why use Terrain Navigation?
• Underwater applications:
– GPS is not available
– Deepwater: GPS fix not feasible
– Shallow water: GPS fix possible• Not in covert operations
– No infrastructure required• DGPS-USBL requires a mother ship• LBL / UTP requires transponder(s)
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Basic Principles • Lose integration– Navigation system data are
combined with terrain measurements
– Correlated with the expected DTM value in a search area
– A Position solution is produced and passed back to the Navigation System
• Algorithms:– TERCOM– Point Mass Filter– Particle Filters
• Usually batch within ping– Batch over time interval possible– Recursive possible
Nav Sensors
Terrain Sensors
DTM
Nav System
Nav System
TerrNavTerrNav
PositionSolution
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Basic Principles • Tight integration– Terrain sensors are integrated
along with Nav sensors– Correlated with the expected
DTM value of current navigation solution
– Full navigation solution is produced
• Algorithms– Kalman filter based– TRIN– SITAN
• Always recursive in time– Batch within ping possible
Nav Sensors
Terrain Sensors
DTM
Nav SysWith
TerrNav
Nav SysWith
TerrNav
NavigationSolution
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Underwater Measurement Geometry• Sensor ensonifies a
seafloor area– The footprint
• Slant range and angles are computed– Ray bending– The beam vector
• The beam vector is transformed into a body-fixed earth tangent plane system– Relative depth
• Further transformed into a Global Reference System– Global depth
Range and angleerror ellipsoid
Relative depth
Sensor Depth
Across track
MSL
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Underwater Vertical Reference• The vehicle measures
pressure
• Vertical reference error directly adds to seafloor depth estimate error– Correlated between
each beam– Correlated in time
• Slow-changing bias is ok– Tidal wave error– Atmospheric
pressure error– CTD error
• Dynamic pressure error is not ok– Waves
Sea surface
Pressure sensor
Tide over MSL
Tide Level
Mean Sea Level
Vehicle ref point
Atmospheric pressure
Depth
Hydrostatic depth
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Bathymetric sensors• Multibeam Echosounder (MBE)
– Across track profile at each ping, a fan of beamvectors– EM3000 tested from surface ship and Hugin AUVs
• Doppler Velocity Log (DVL)– 4 beamvectors in Janus configuration– RDI WHN 300,600,1200 tested on AUVs (Hugin, OEx, Remus)
• Single Beam Echosounder – Large footprint
• Interferometric SAS– High resolution
• Underwater Laser Camera– High accuracy, low range
• 3D Sonar– Surface at each ping
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Digital Terrain Models
• Algorithm requirements– Random access– Fast access
• In memory representation– Regular grid– Bilinear interpolation
• Resolution requirement– Terrain navigation accuracy is in the order of DTM resolution– For typical AUV operations: at least 10 m
• Accuracy description requirement– Ideally a spatial statistical description ( grid node depth error )– Usually not available in exchanged DTMs
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Sensor/DTM measurement model
• We only have a model of true terrain h(x)– Horizontal node spacing– Interpolation– Node depth estimates
• Measurements are made towards true terrain
h(x)
Deterministic
Stochastic
x
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Extended Kalman Filter (EKF) approach (TRIN, SITAN)
• Linearization for EKF requires gradient map– Ok in linear and
weekly non-linear topography
• Highly non-linear topography handled by stochastic linearization– Best fit surface
tangent plane within uncertainty area
– Automatically detects non suitable terrain
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Terrain Contour Matching (TERCOM)
• For each grid point:– Calculate mean
absolute distance (MAD) between measured and expected profile
• Position fix from minimum of the MAD correlation matrix
• No inherent accuracy of fix is available
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Point Mass Filter (PMF) from TerrP
• The position error probability density function (pdf) is estimated on a grid
• An initial pdf, depending on INS accuracy, can be used
• Each measurement is blended with current pdfusing Bayes’ rule, and a sensor error pdf
• INS drift diffuses the pdfbetween each ping
Ping 0Ping 1Ping 4Ping 8
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Particle Filters (PF) from TerrLab
• Position error pdfrepresented by free particles
• Initial state is simulated from INS position error distribution
• Measurement: Each particle is weighted using the sensor error pdf
• Resampling• Dynamic update
through simulation on INS drift distribution
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Terrain Suitability?
TRIN, SITAN
• Clearly defined gradients
• Linear beach
• Parabolic beach
• Fjord
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Terrain Suitability?
TERCOM, PMF, PF
• Rough topography
• Not self similar
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Tactical Use of Terrain Navigation
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Applications
• Cruise missiles– Backup system– Independent of GPS, cannot be jammed
• Fighter aircrafts– Redundant navigation system– Terrain following aid for low altitude flying
• AUVs– Autonomous missions– Covert operations
• Submarines– Always covert– Transmission of sound is restricted– “Man in the loop”
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FFI Developed Systems
• Terrain Referenced Integrated Navigation (TRIN)– MatLab implementation of FFI’s EKF based algorithm– Verified in 2 NATO experiments for different AUVs and a
surface vessel
• Terrain Navigation Processor (TerrP)– Real-time terrain navigation system (TERCOM, PMF)– Primarily designed for HUGIN– Verified on playback of real data from HUGIN
• Terrain Navigation Laboratory (TerrLab)– MatLab toolkit for terrain navigation algorithm development,
simulation and post processing– TERCOM, PMF, Particle Filters