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WORKSHOP PLAN … (MORNING)
A. Introductions
B. Applications of Change Detection
C. Review of Topographic Surveys & Data
D. Review of Building DEMs
E. Essential Best Practices to Support GCD
F. Traditional Approaches to Change Detection
G. Change Detection in GCD
H. Thresholding AlternativesA Plan.. Not a Contract
GEOMORPHIC CHANGE DETECTIONESPRESSO WORKSHOP
C. REVIEW OF TOPOGRAPHIC SURVEYS & DATA
CONCLUSION
• Hire a surveyor
THE END
PURPOSE
• Remind ourselves where all these DEMs come from
• Highlight differences in acquisition techniques that result in DEMs of varying degree of quality
• Clarify what different techniques can and cannot do
Review of Topographic Surveys & Data
YOU GUYS… LIKE MANY
• LiDaR• Aerial Photogrammetry• SFM
• Total Station Surveys• GPS• Terrestrial Laser Scanning
Ground-Based Surveys
Remotely Sensed or Aerial Surveys
• Multibeam Sonar• Singlebeam Sonar
Boat-Based Bathymetry Surveys
Has many ways of acquiring high-resolution topography
TYPICAL EXTENT & RESOLUTION
TECHNOLOGY EXTENT (Reach Lengths) RESOLUTION (pt./m2)
Airborne LiDaR 10’s – 100’s km 1-8
Bathymetric LiDaR 10’s – 100’s km 0.5 – 4
Aerial Photogrammetry 10’s – 100’s km 0.1 – 1
Total Station Surveying 100 – 5,000 m 0.1 – 4
rtkGPS Surveying 100 – 5,000 m 0.1 - 4
Terrestrial Laser Scanning (aka ground-based LiDaR)
100 – 5,000 m 10 – 10,000
SFM 100 – 1000 m 100 – 10,000
Multi-beam Sonar 1 – 25 km? 10- 10,000
Single-beam Sonar 5 – 100 km? 0.05 – 5
BAR-SCALE
GRAIN-SCALE
WATERSHED
REACH-SCALE
THREE KEY SAMPLING QUESTIONS
1. Is the sampling smart(i.e. requires judgment) or systematic?
2. Is higher density result of judgement or brute force?
3. Do I have to see the point to record it?
NIR AIRBORNE LiDAR
MORE IS BETTER?
Is higher point density always better?
• If high point density is result of single pass, yes
• If high point density is result of multiple passes
With LiDaR we attempt to make up for smart sampling with brute force…
See LiDaR Tools for ENVI: http://bcal.geology.isu.edu/node/10
NOT ALL LiDAR IS EQUAL!
• Co-registration of imagery & LiDaR
• Ground Control
• Hydro-Enforced Breaklines
• Co-registration of flight linesSee Watershed Sciences (2011): Available on OpenTopography
Streutker et al (2011): Photogrammetric Engineering & Remote Sensing
GREEN LiDaR… PROMISING BUT
See McKeen et al (2010): Remote Sensing
2004 20042007 2007
AERIAL IMAGERY – e.g. SPECTRAL
• Aerial imagery can be used in at least three ways to derive topography
– Aerial photogrammetry (requires overlapping stereo pairs)
– Bathymetric topography from spectral-based depth correlations (requires on the ground depth sample)
– Structure from motion (e.g. Photosynth, SFM Toolkit)
From Legleiter (2003)
From Bangen et al. (2011)
PHOTOGRAMETRY - VISIBLE
• Vertical measured from overlapping stereo pairs
• I can measure what I see…
STRUCTURE FROM MOTION
See Fonstad, Dietich et al. (2013): ESPL ESEX
DOI: 10.1002/esp.3366
See also: Westaboy et al. (2012): Geomorphology,
DOI: 10.1016/j.geomorph.2012.08.021
STRUCTURE FROM MOTION
• d
From Fonstad et al (2013)
From airborne or ground-based platforms (or both)
COMMERCIAL & OPEN SOURCE
• Agisoft PhotoScan
• Microsoft Photosynth
• SFM Toolkit
• Visual SFM
Point cloud of a debris fan and sand bar in Grand Canyon – from Becca Rossi
SFM WORKFLOWFOR RIVERS
• Combination of SFM& spectral-depth correlation to paint complete picture…
From: Javernick L, Brasington J and Caruso B. 2014. Modelling the topography of shallow braided rivers using Structure-from-Motion photogrammetry. Geomorphology. 213: 166-182. DOI: 10.1016/j.geomorph.2014.01.006.
SURVEY GRADE GPS• Antennae is external
• Typical Quality:
– Real-time Kinematic:
• +/- 10 to 20 mm Horizontal
• +/- 20 to 30 mm Vertical
– Static:
• +/- 5 mm Horizontal
• +/- 5 mm Vertical
TOTAL STATION: A GUN AND A ROD…
• Technically an example of active remote sensing…
• Gun shoots and record
• Prism on rod reflects
2 PERSON CREW…
• Who’s the smarter one?
Dumb end of a stick…
WHAT IS TLS?
• LiDaR from the ground…
• Terrestrial Laser Scanner (a.k.a. ground-based LiDaR)
SORT OF LIKE A RELFECTORLESS TS…
• Normal total station needs a reflector target…
• Reflectorless, just looks for a return off any surface
• TLS, like reflectorless… on speed.
TLS SCALE-FREE?REACH-SCALE
BAR-SCALE
GRAIN-SCALE
From James Brasington
SONAR (DEPTH SOUNDING)
• Multi-Beam & Single-Beam
• Position tracking based on GPS (or TS) & IMU
• Multi-Beam similar data density to TLS
SINGLE BEAM SONAR TRACKS…
• How good does someone mow the lawn? Mission Lake, Kansas
MULTI-BEAM – EASIER TO MOW LAWN
• Still need to get overlap
BUT WHICH TOY DO I USE?
From Bangen et al. (2014) Geomorphology
DOI: 10.1016/j.geomorph.2013.10.010
Which topographic survey techniques will work best where?
ERROR MODELS…
• Greater extent on TLS & ALS
• ALS & TLS worthless in water
• ALS best on floodplain
Total Station
rtkGPS
TLSALS
DEM UNCERTAINTY BY SITE & METHOD
From Bangen et al. (2014) Geomorphology
DOI: 10.1016/j.geomorph.2013.10.010
AND THE WINNER(s) IS(ARE)…
• Total station most versatile and reliable (but slow)
• rtkGPS faster, but limited in areas with trees or deep canyons (also slow compared to remote sensing)
• TLS & ALS provide nothing in channel
• TLS is pretty useless in vegetated riparian areas
• No SILVER BULLET →
TYPICAL EXTENT & RESOLUTION
BAR-SCALE
GRAIN-SCALE
WATERSHEDREACH-SCALE
NO SUCH