Silvia Medri University of Bologna

CoastView Meeting Lisbon 18 – 19 Sept 2004 Analysis of the accuracy of Argus in identifying shoreline position: comparison of two procedures with in-situ measurements in Lido di Dante Silvia Medri University of Bologna

Contents 1. Comparison of two procedures to find waterline • Description of the two procedures • Justification of the use of the two procedures • Results presentation • Comments 2. Comparison of the two procedures in the study of shoreline evolution • Results presentation • Comments 3. Comparison of the two procedures with in-situ measurements • Fieldwork description: GPS Survey, 15-22 July 2004 • GPS survey data • GPS-Argus Comparison • Conclusions

1.Comparison of the two procedures • Description: first procedure • First merge images with AMT • Then find WL with IBM

1.Comparison of the two procedures • Description: second procedure • First find WL with IBM on single oblique images • Then “merge” single cameras WLs in a unique WL with Matlab.

1st procedure: First merge then use IBM 2nd procedure: First use IBM then merge • Advantages: • - accurate in the ROI overlap • accurate in identifying obstacles in the far • field • - at the present level of implementation fast Advantages: - proper tidal level for each image - accurate in identifying details, due to the greater pixel resolution Disadvantages: - approximated tidal levels - decrease of visualization of small objects (persons, umbrellas, etc..) - less image definition • Disadvantages: • - not accurate in the region of cameras overlap • - decrease of the possibility of identifying • oblique obstacles • pixel resolution loss in the far field • - at the present level of implementation slow 1.Comparison of the two procedures • Justification of the use of the two procedures • Discrepancies at a qualitative inspection between obtained WLs • Tidal levels assignment • Operative differences

1.Comparison of the two procedures Shoreline at the same hour obtained with the two procedures. [20 July 2004 06 GMT] • Presentation of results

Reduced area Whole area 1.Comparison of the two procedures • Reasons for a reduced area of calculations • Decreasing pixel resolution • worse representation of far field pixel intensities in dry/wet separation procedure • increase of the difficulty for the operator to visually distinguish the shoreline itself • WL position differences are calculated on the X axis of Argus reference system • overestimate these differences where the shoreline is not parallel to Y axis • Systematic tidal data delay

1.Comparison of the two procedures WLs at the same hour obtained with the two procedures for one day of the fieldwork. [20 July 2004 from 06 to 14:00 GMT] • Statistics of differences

1.Comparison of the two procedures • Statistics of differences WLs at the hour obtained with the two procedures for the whole period of the fieldwork. [ From 15 July to 22 July 2004] The Mean value of the Median of the absolute values of the differences between shorelines obtained with the two procedures indicates the two procedures disagree of about 0.58 m in both the whole and the reduced areas.

1.Comparison of the two procedures • Comments • The quantified disagreement between the two procedures (of 0.6 m) is not so important if compared with shoreline dynamics itself. • Against the expectation there aren’t significant improvements/variations in reducing the area of work. ? Probably the two systematic errors in timing the merged images and tide hide the differences. • There is a recurrent presence of outliers especially at the end of the area (due to unavoidable decreasing pixel resolution in the far field) and near the central groin (due to a significant density in that area of tourists and big umbrellas).

2.Comparison of the two procedures in the study of shoreline evolution Shoreline evolution during 1 day of the fieldwork with the two procedures. [20 July 2004 from 06 to 15 GMT] • Presentation of results

2.Comparison of the two procedures Shoreline evolution during 1 day of the fieldwork with the two procedures calculated for the whole area and for the reduced area [20 July 2004 from 06 to 15 GMT] • Statistics of shoreline evolution

2.Comparison of the two procedures • Analysis of WL displacements quality • 1st criterion: to verify if the WL variation is coherent in sign with the corresponding tidal level variation, indicating a clear trend of WL evolution (minimum requirement). • 2nd criterion: to verify, in the unavoidable presence of small discrepancies (only few points in against trend), if however: |Median - Median abs| < 0.1 m indicating a low percentage and a small entity of values in against trend. In these cases the signs of shoreline displacements are concordant among them, reproducing a mean intertidal beach profile with a constant sign slope (further requirement).

2.Comparison of the two procedures Estimated mean intertidal beach profiles The profiles show a qualitative good agreement with the realistic situation, in particular it is shown a simple morphology with lack of significant bars and throughs (Lido di Dante protected area)

2.Comparison of the two procedures • Statistics of shoreline evolution WLs evolution for every day of the fieldwork with the two procedures calculated for both the whole and the reduced area

2.Comparison of the two procedures • Comments on shoreline evolution • In the whole area: • The 1st procedure (First merge then use IBM) gives results in very good agreement with the tidal excursion in about 60% of the instances, and fairly good results in about 30% of the instances in whom it was used. • The 2nd procedure (First use IBM then merge) gives results in very good agreement with the tidal excursion in about 79% of the instances and fairly good results in about 15% of the instances on whom it was used. • In the reduced area: • The 1st procedure (First merge then use IBM) gives results in very good agreement with the tidal excursion in about 64% of the instances in whom it was used, with a small improvement with respect to the whole area. • The 2nd procedure (First use IBM then merge) gives results in very good agreement with the tidal excursion in about 88% of the instances in whom it was used, with a small improvement with respect to the whole area.

2.Comparison of the two procedures • Conclusions on shoreline evolution • Considering only ‘very good’ results, the 2nd procedure (SINGLE) is better then the 1st one (MERGE). • Considering the whole of ‘very good’ + ‘fairly good’ results, both the procedures are equivalently of high quality in the great part (about 90%) of the instances. • Both the procedures improve their performance in the reduced area. • Robustness test: the 2nd procedure is the most robust because it gives better results even in the whole area where there are the great part of outliers.

3. Comparison with in-situmeasurements Objectives • To validate video derived data • To provide demonstration CSIs for the Lido di Dante site. • To check what is the best way to use Argus IBM. Strategy • To compare a significant set of surveyed shorelines with the corresponding Argus waterlines, in order to evaluate the capability of Argus in identifying WLs for both the analysed procedures • To measure a significant set of surveyed cross-shore transects in order to have a more realistic estimate of intertidal beach slope.

3. Comparison with in-situ measurements 15-22 July 2004 GPS Survey Available data set 60 transects • 15 July ( 2 transects) • 19July (11 transects) • 20 July (10 transects) • 21 July (12 transects) • 22 July (25 transects) 40 shorelines • 15 July (GMT 09:00, 11:00, 12:00 = 3 WL) • 19July (from GMT 09:00 to GMT 16:00 = 7 WL) • 20 July (from GMT 06:00 to GMT 15:00 = 10 WL) • 21 July (from GMT 07:00 to GMT 16:00 = 10 WL) • 22 July (from GMT 06:00 to GMT 15:00 = 10 WL) Area of interest

3. Comparison with in-situ measurements 15-22 July 2004 GPS Survey GPS Technical Specifications: LEICA SR510 Receiver Satellite Reception: single-frequency Receiver Channels: 12 L1 continuous tracking L1 channels: Carrier phase, C/A narrow L1 Carrier Tracking: reconstructed carrier phase via C/A code Satellites tracked: up to 12 simultaneously Kinematic Mode : after a static or known point initialisation, kinematic surveys can be carried out and with dynamic procedures in post processing yields 10 to 20mm + 2ppm rms Antenna The AT501 is a small precision centered L1 antenna , L1 microstrip with Built-in groundplane . CORS: Continously Operating Reference Station Manager: Prof.Susanna Zerbini, Dept. of Geophysic, University of Bologna. Position: Marina di Ravenna (8 Km far from Lido di Dante site) Data collection rate: 30 sec

3. Comparison with in-situ measurements 15-22 July 2004 GPS Survey Shoreline surveyed hourly basis, simultaneously with the recording of time-averaged video images by the 4-cameras of Argus video station in LdD.

3. Comparison with in-situ measurements 15-22 July 2004 GPS Survey Offshore Wave Heights range: (0.07 ÷ 0.5) meters

3. Comparison with in-situ measurements 15-22 July 2004 GPS Survey Tidal level range: -0.5 ÷ +0.3 meters Sea Water Level (m) Atmospheric Pressure (hPa) Water temperature (°C) Temperature (°C) Wind Direction (°N) Wind Direction (°N) Wind Intensity (m/s)

Presentation of results

3. Comparison with in-situ measurements • 1st procedure (First merge then use IBM) – GPS Comparison

3. Comparison with in-situ measurements • 2nd procedure (First use IBM then merge) – GPS Comparison

3. Comparison with in-situ measurements • GPS - Argus Comparison • Results • The two procedures are equivalent on a set of normal (without spurious results) data. • If there are significant outliers the 1st procedure seems better than the 2nd one.

3. Comparison with in-situ measurements • Comments • Result interpretation: the combined effect of two systematic errors in timing the merged images and tide results in hiding the great part of differences on merged images (1st procedure), while frustrating the precision in the synchronism with tidal data of oblique images (2nd procedure). • Result judgement: there is a good agreement of both the used Argus procedures to find shoreline location with ground truth data of GPS survey, considered the shoreline dynamics itself and the time shift in tidal data. (With correct tide data the 1st procedure is expected to give the better results (with a dispersion <0.5 m )).

3. Comparison with in-situ measurements • Future work • To estimate the systematic error in our tide data by comparison with local measured data (past intensive fieldwork). • To estimate intertidal beach slope through the analysis of GPS intertidal transects. • To compare the two Argus procedures with GPS data even in the reduced area. • To carry out another GPS survey in October to have “cleaner” shorelines.

Nourishment works Topographers 2. Shoreline Variation due to a stormTopographical Survey - O8 Oct 2003

3. Comparison with in-situ measurements July 2004 GPS Survey

3. Comparison with in-situ measurements 15-22 July 2004 GPS Survey Available data set 40 shoreline : • 15 July (GMT 09:00, 11:00, 12:00 = 3 WL) • 19July (from GMT 09:00 to GMT 16:00 = 7 WL) • 20 July (from GMT 06:00 to GMT 15:00 = 10 WL) • 21 July (from GMT 07:00 to GMT 16:00 = 10 WL) • 22 July (from GMT 06:00 to GMT 15:00 = 10 WL) 60 transects • 15 July ( 2 transects) • 19July (11 transects) • 20 July (10 transects) • 21 July (12 transects) • 22 July (25 transects)

Silvia Medri University of Bologna