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Comparison Of Elevation Collection Technologies
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Comparison Of Elevation Collection Technologies

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  • 1.
    • Flood modelling and management
    • Glasgow University
    • 8 September 2004
    • Paul Shaw - GeoVision
  • 2.
    • Format for morning session
    • 9-30 – 10.30 Comparison of modern data collection technologies
    • 10.30 – 10.45 Coffee
    • 10.45 – 11.45 Comparison of modern data collection technologies (cont)
    • 11.45 - 12.00 Coffee
    • 12.00 – 1.00 Remote sensing for environmental monitoring
    • 1.00 – 2.00 Lunch
  • 3.
    • How important are heights in flood modelling?
  • 4.
    • Comparison of data collection technologies
    • GPS - Global Positioning Systems
    • Aerial Photography
    • LIDAR - Light Detection and Ranging
    • SAR– Synthetic Aperture Radio Detection and Ranging
    • Multi Spectral Satellite Imagery
  • 5.
    • Comparison of data collection technologies
    • For each technology a summary on
    • Process of data collection
    • Potential sources of error
    • Benefits and concerns
    • General comments
  • 6.
    • Comparison of data collection technologies
    • GPS - Global Positioning Systems
    • Aerial Photography
    • LIDAR - Light Detection and Ranging
    • SAR– Synthetic Aperture Radio Detection and Ranging
    • Multi Spectral Satellite Imagery
  • 7.
    • GPS
    • Process
    • Use technique called RTK or kinematic
    • Requires base station and rover
    • Requires radio link
    • Software converts to grid and geoid heights
    • Collect mapping data (as points, polylines,polygons and attributes)
    • May require post-plotting using survey infill techniques
  • 8.
    • GPS
    • Potential sources of error
    • Grid transformation and geoid model – Link
    • Satellite azimuth, number, quality and spread (measured as DOP’s) - Link
    • Radio range
    • Base station problems
  • 9.
    • Benefits
    • Accurate to 10mm
    • Certainty with ground heights
    • Accurate definition of break lines
    • Data collected in useable format
    GPS
    • Concerns
    • Slow at 0.2 sq km/day
    • Not allowed in all countries
    • Radio strength
    • Foliage and infrastructure
    • No image
    • Access restrictions
  • 10.
    • GPS
    • General comments
    • Many UK companies - Link
    • In GB OS have active and passive stns – Link
    • OS trig and BM system redundant
    • NAVSTAR (US) – 29 operational at present - Link
    • GLONASS (Russian) - 8 operational at present – ( Link )
    • GALILEO (European) – operational from 2008 – 30 in total – ( Link )
    • Started becoming available in the mid nineties
    • Further details on how GPS works at ( Link )
  • 11.
    • Comparison of data collection technologies
    • GPS - Global Positioning Systems
    • Aerial Photography
    • LIDAR - Light Detection and Ranging
    • SAR– Synthetic Aperture Radio Detection and Ranging
    • Multi Spectral Satellite Imagery
  • 12.
    • Aerial Photography
    • Process
    • Route planning; weather forecasting; flying permission; possible pre-mark; control network
    • Film processing
    • Possible Scanning
    • Photo/Imagery control
    • Aerial triangulation
    • DEM generation; possible vector digitising; post plotting; integration
    • Ortho production/mosaicing
  • 13.
    • Aerial Photography
    • Potential sources of error
    • Crabbing, fore and aft overlap
    • Lens calibration
    • Film quality
    • Verticality
    • Scale problems through large terrain change
    • Forward Motion
    • Photo control errors
  • 14.
    • Concerns
    • Flying permission required
    • Seasonal
    • Weather dependency
    • Heights to top of foliage
    • Restrictions by government
    • Matching of orthos
    • Automated DEM’s
    Aerial Photography
    • Benefits
    • Large areas covered in one flight
    • Height generated from the imagery
    • Infrared available
    • Orthophotos
    • 3D visualisations
    • Automated DEM’s
  • 15.
    • Aerial Photography
    • General comments
    • Was used by the EA – replaced by LIDAR in 1998
    • Increasingly sophisticated on-board systems
    • Approx 10 UK companies
    • Fixed Wing or helicopter, hard copy or digital
    • Large archive at larger scales through BKS, Simmons Aerofilms, OS, OSNI and others
    • Getmapping have GB covered at 1:10,000 – Link Imagery £25 per sq km at 1:10,000 scale, heights extra
  • 16.
    • Comparison of data collection technologies
    • GPS - Global Positioning Systems
    • Aerial Photography
    • LIDAR - Light Detection and Ranging
    • SAR– Synthetic Aperture Radio Detection and Ranging
    • Multi Spectral Satellite Imagery
  • 17.
    • LIDAR
  • 18.
    • LIDAR
    • Process
    • Route planning; weather forecasting; flying permission; control network
    • Processing – last reflection
    • DEM generation;
    • Post survey infill
    • Integration
  • 19.
    • LIDAR
    • Potential sources of error include
    • GPS and IMU calibration
    • IMU and laser head calibration
    • Lazer pulse rate
    • GPS baseline length
    • Level of uncertainty with ground height
    • No break line definition
    • Details available at ( Link )
  • 20.
    • Benefits
    • Accurate to 50mm
    • Large areas covered in one flight (30 sq km in one hour)
    • Can be flown at night
    • Not dependent on sun
    • Water height
    LIDAR
    • Concerns
    • No image
    • Weather dependency
    • Flying permission required
    • Processing time – up to 4 months for a few days data collection
  • 21.
    • LIDAR
    • General comments
    • 4 UK companies – global directory at ( Link )
    • QinetiQ have combined with digital cameras to create ATLAS system – ( Link )
    • General information about LIDAR can be found at ( Link and Link )
    • Used extensively by the EA - archive coverage - Link . Catalogue - Link
  • 22.  
  • 23.
    • Coffee break
  • 24.
    • Comparison of data collection technologies
    • GPS - Global Positioning Systems
    • Aerial Photography
    • LIDAR - Light Detection and Ranging
    • SAR– Synthetic Aperture Radio Detection and Ranging
    • Multi Spectral Satellite Imagery
  • 25.
    • SAR
    • Process (InterMap)
    • Aircraft has 2 antennae, receive slightly different return signals, phase difference determines height
    • Synthetic aperture digitally enhances the data in real time
    • Rigorous QC processing checks
    • DEM
    • DSM by interpolation
    • Intermap SAR description at ( Link )
  • 26.
    • SAR
    • Potential sources of error
    • Shadow
    • Rain shadow
    • S ignal saturation
    • Missing data
    • Specular reflection
    • DSM generation
    • Details at ( Link )
  • 27.
    • Benefits
    • Can cover 100 sq km in a few hours
    • Generates height (up to 0.3m) and image (up to 2.5m)
    • All weather capability
    SAR
    • Concerns
    • Flying permission required
    • Gives height to first reflection
    • Accuracy of DSM
    • No break lines - Nextmap products are 5 and 10m grid spacing
  • 28.
    • SAR
    • General comments
    • No UK companies
    • Accuracy comparison by EA available at ( Link )
    • Nextmap data for UK has 2 accuracy levels – 0.6m for the SE and 1.5m for the rest
    • QinetiQ have just gained reseller status
    • Nextmap archive at Link
    • Intermap global archive and prices at Link
  • 29.
    • Comparison of data collection technologies
    • GPS - Global Positioning Systems
    • Aerial Photography
    • LIDAR - Light Detection and Ranging
    • SAR– Synthetic Aperture Radio Detection and Ranging
    • Multi Spectral Satellite Imagery
  • 30.
    • Multi Spectral Satellites Imagery
    • Process
    • Order and collect basic imagery
    • Image control points
    • Rectification
    • DEM generation
    • Possible vector digitising
    • Map completion
  • 31.
    • Multi Spectral Satellites Imagery
    • Potential sources of error
    • Cloud
    • Other atmospheric interference
    • Off-nadir angle of separate image
    • Sun
    • Shadow
    • Incorrect sensor calibration details
  • 32.
    • Multi Spectral Satellites Imagery
    • Benefits
    • No restrictions
    • Large archives
    • Large area coverage
    • Repeatability
    • Concerns
    • Problems with automated DEM’s
    • Weather dependency
    • Heights to top of foliage/buildings
    • Height accuracy still at research stage
  • 33.
    • Satellites
    • General comments
    • Wide range of sensors with stereo capability
    • On-going program of launch of new satellites
    • Quickbird ( Link ), IKONOS ( Link ), SPOT ( Link ), IRS ( Link ).
    • Recent research by a Japanese University has shown 0.5m height accuracy possible – Link
    • Quickbird archive at Link
  • 34.  
  • 35.  
  • 36.  
  • 37.
    • Comparison
    50cm 50 days new Min 100 sq km £0.03k Quickbird 30cm Global archive £0.064k (Hts only) SAR 15cm 120 days new GB archive £0.35k LIDAR (No image) 4cm 50 days new Global archive £3-5k Aerial Photography 1cm 50 days/sq km new £5-10k GPS (No image) Accuracy Delivery Cost/sq km Technology
  • 38.
    • Summary
    • There is an increasing amount of height data for flood modelling. The skill is to select the correct one for a given application. Considerations include:-
    • How accurate do you want the heights?
    • How regular do you want it monitored?
    • What intensity of information do you want?
    • How much money have you got?
    • How quickly do you want it?
    • but.................
  • 39.
    • Other considerations
    • Global warming – 10 - 20cm msl rise last century, estimated 50 cm this century - ( Link )
    • Glacial Isostatic Adjustment – 2 mm per annum (- in South, + in North) – ( Link ). General Info at ( Link )
    • OS recently adjusted UK geoid – up to 10cm variance
    • Spring tides – up to 12m range - ( Link and Link )
    • Tidal loading – up to 6cm variance in 1 day
  • 40.  
  • 41.
    • Coffee break

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