Comparison Of Elevation Collection Technologies
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Transcript of Comparison Of Elevation Collection Technologies
www.geovision.co.uk Global Solutions
Flood modelling and management
Glasgow University
8 September 2004
Paul Shaw - GeoVision
www.geovision.co.uk Global Solutions
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
How important are heights in flood modelling?
www.geovision.co.uk Global Solutions
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
www.geovision.co.uk Global Solutions
Comparison of data collection technologies
For each technology a summary on• Process of data collection• Potential sources of error• Benefits and concerns
• General comments
www.geovision.co.uk Global Solutions
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
www.geovision.co.uk Global Solutions
GPSProcess• 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
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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
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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
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GPSGeneral 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 ninetiesFurther details on how GPS works at (Link)
www.geovision.co.uk Global Solutions
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
www.geovision.co.uk Global Solutions
Aerial PhotographyProcess• 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
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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
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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
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Aerial PhotographyGeneral 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
www.geovision.co.uk Global Solutions
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
LIDAR
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LIDAR
Process • Route planning; weather forecasting; flying
permission; control network• Processing – last reflection • DEM generation;• Post survey infill• Integration
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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)
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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
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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
Coffee break
www.geovision.co.uk Global Solutions
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
www.geovision.co.uk Global Solutions
SARProcess (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 interpolationIntermap SAR description at (Link)
www.geovision.co.uk Global Solutions
SAR
Potential sources of error• Shadow• Rain shadow• Signal saturation• Missing data• Specular reflection • DSM generation
Details at (Link)
www.geovision.co.uk Global Solutions
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
SARConcerns
• Flying permission required
• Gives height to first reflection
• Accuracy of DSM• No break lines -
Nextmap products are 5 and 10m grid spacing
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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
www.geovision.co.uk Global Solutions
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
www.geovision.co.uk Global Solutions
Multi Spectral Satellites Imagery
Process • Order and collect basic imagery• Image control points• Rectification• DEM generation• Possible vector digitising• Map completion
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Multi Spectral Satellites Imagery
Potential sources of error • Cloud• Other atmospheric interference• Off-nadir angle of separate image• Sun• Shadow• Incorrect sensor calibration details
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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
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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 – LinkQuickbird archive at Link
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Comparison Technology Cost/sq km Delivery Accuracy
GPS
(No image)
£5-10k 50 days/sq km new
1cm
Aerial Photography £3-5k 50 days new
Global archive
4cm
LIDAR
(No image)
£0.35k 120 days new
GB archive
15cm
SAR £0.064k
(Hts only)
Global archive 30cm
Quickbird £0.03k 50 days new
Min 100 sq km
50cm
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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.................
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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
Coffee break