c. review of topographic surveys & dataetalweb.joewheaton.org.s3-us-west-2.amazonaws.com/... ·...

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