Argus as an Coastal Engineering Tool - Validation through Comparisons with Traditional Methods Joan...
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Transcript of Argus as an Coastal Engineering Tool - Validation through Comparisons with Traditional Methods Joan...
Argus as an Coastal Engineering Tool -
Validation through Comparisons with Traditional Methods
Joan Oltman-Shay,
Matt Pruis, and Dave BerlinerSponsored (Requested) by: USACE Portland District
Background: Argus Monitoring at North Head
• Sponsor: US Army Corps of Engineers – Portland District
• Project Objectives:
• Survey the intertidal zone of Benson Beach, north of the Mouth of the Columbia River
• Develop a process understanding of sediment transport on Benson Beach
• Provide an “informed” opinion of best location(s) for dredge material disposal within the littoral cell (beneficial use of dredged sands)
Eight cameras looking south
50mm lenses
Jetties, MCR, and the great state of Oregon in the distance
Site E
2 miles; 3.22 km
1km
4km
MCR
North HeadLighthouse
USACE District Experience with Argus
• The bosses of Corps project engineers do not “know” Argus from Adam
• Proof of Argus methods is therefore needed
– e.g., comparison with “traditional” survey methods like RTK GPS
• Comparison #1: Where is the painted rock?
• Comparison #2: Intertidal bathmetry comparision with RTK GPS
– Result: Identification of “best-use” images and parameters for intertidal bathymetry mapping
• Only use images collected during flood tides
• “Measure” foreshore beach slope for each survey day
Comparison #1:GPS vs Argus:
Location of the White Rocks 2005 Request: Location ofPainted Stones ?
Argus Answer:
A creative X,Y, Z solution
Results:
The contract has continued.
Comparison #2: Traditional vs ArgusIntertidal Bathymetry Surveys
• RTK GPS “Traditional” Surveys– Peter Ruggiero and George
Kaminsky • USACE Portand District funding
– Bi-annual surveys of Benson Beach and the larger Columbia River Littoral Cell
• 6 surveys between Feb 2004 and Nov 2005 coincide with Argus acquisition of good images– No fog, Hrms < 2m, large tidal
range
Argus intertidal bathymetry surveys:• Tools from Delft’s ARE
Shoreline Detection: Pixel Intensity Clustering Method of Aarninkof and Roelvink (1999)
Shoreline Elevation:
Zwl = Ztide + Zwvsetup + (Kosc)Zswash
(Battjes&Jannsen, 1978; Svendsen, 1984; Stive and DeVriend, 1994; Aarninkof&Roelvink, 1999)
Note: Zwvsetup and Zswash are a function of Hrms, Tpk, and foreshore beach slope)
Contours span 4m elevation
Sept 2005
Sept 2006
Warning: Foreshore beach slope can changea lot…and often
Date Intertidal Beach Slope Comments
20 February 2004 0.044 0.053 slope for 1.5-2.5m elev
30 July 2004 0.016 0.042 slope for 1.5-2.5m elev
20 September 2004 0.026 0.028 slope for 1.5-2.5m elev
20 February 2005 0.022 0.026 slope for 1.5-2.5m elev
23 August 2005 0.01 0.015 slope for 1.5-2.5m elev
15 November 2005 0.042 0.042 slope for 1.5-2.5m elev
The alongshore average (2km) intertidal (0.5-1.5m NAVD88) beach slope determined from an initial (beach slope fixed at 0.025) Argus intertidal bathymetry
Argus and RTK GPS Comparisons: Flood vs Flood & Ebb Tide Images
Flood & ebb images
Flood only images
Argus contour elevations compared with the average elevation of the interpolated GPS-Buggy data along each of the Argus x,y contours (Aarninkhof method).
Argus and RTK GPS Comparisons: Flood vs Flood & Ebb Tide Images
DATE FLOOD TIDE ONLY FLOOD & EBB TIDE
Mean Error (cm)
RMS Error (cm)
Mean Error (cm)
RMS Error (cm)
20 Feb 2004 -1.4 10.6 11.7 30.6
30 July 2004 -3.4 8.9 -10 18.8
20Sep 2004 -5.2 9.3 -21.2 26.7
20 Feb 2005 8.9 11.5 10.1 14
23Aug 2005 0.2 9.3 -11.3 20
15Nov 2005 -7.3 10.9 -10.2 30.6
Argus and RTK GPS Comparisons: Fixed vs “Measured” Foreshore Slope
DATE MEASURED BEACH SLOPE FIXED 0.025 BEACH SLOPE
Mean Error (cm)
RMS Error (cm)
Mean Error (cm)
RMS Error (cm)
20 Feb 2004 -1.4 10.6 25.2 26.5
30 July 2004 -3.4 8.9 -20.6 22
20 Sep 2004 -5.2 9.3 -4.1 8.6
20 Feb 2005 8.9 11.5 5.3 8.9
23 Aug 2005 0.2 9.3 -24.8 26.4
15 Nov 2005 -7.3 10.9 -6.3 10.8
A Picture is Worth A Thousand Words
Alongshore (m)
Cro
ss-s
hore
(m
)
Feb. 21, 2004
1000 1500 2000 2500 3000
300
350
400
450
500
550
Buggy
Argus
MHW Shoreline
Alongshore (m)
Cro
ss-s
hore
(m
)
Jul. 28, 2004
1000 1500 2000 2500 3000
300
350
400
450
500
550
Buggy
Argus
Alongshore (m)
Cro
ss-s
hore
(m
)
Feb. 20, 2004
1000 1500 2000 2500 3000
300
350
400
450
500
550
Buggy
Argus
Alongshore (m)
Cro
ss-s
hore
(m
)
Aug. 23, 2005
1000 1500 2000 2500 3000
300
350
400
450
500
550
Buggy
Argus
Summary
• RMS errors of O(10cm) between RTK GPS and Argus surveys at North Head can be achieved if:– Argus uses only images acquired during flood tides
• rms errors reduced by as much as 20cm
– the Argus waterline elevation model uses a timely “measured” foreshore slope
• An one-step, iterative method of first estimating foreshore slope from Argus contour elevations estimated with a fixed beach slope and then corrected with the “measured” foreshore slope improved comparisons
– rms errors reduced by as much as 15cm
– you don’t have to re-pick contours to do this
Reprocessing North Head Contour Data
• We’re going back through 30+ months of Argus images and constraining (“filtering”) our contour for:– Flood tide images– Flood tidal ranges spanning nominally 1 to 3m NAVD88– Hrms < nominally 2m*– Tpk < nominally 15sec*
• We use autogeom to also help us identify and filter good quality images (good geometry solutions = good images … no fog at North Head)– This is a critically important time saver
* Minimizing Hrms and Tpk reduces the magnitude of wave setup and swash (model error); we presently use Hrms < 1m in summer, < 2.5m in winter and do not constrainTpk.
This exercise has given us great confidence in the ARE waterline elevation model
NorthWest Research Associates (NWRA)
Bellevue, WA
NWRA is a scientific
research group, owned
and operated by its
Principal Investigators,
with expertise in the
geophysical and related
sciences.