Lidar and Pressure Measurements of Inner-Surfzone Waves and Setup

Abstract

Observations of waves and setup on a steep, sandy beach are used to identify and assess potential applications of spatially dense lidar measurements for studying inner-surf and swash-zone hydrodynamics. There is good agreement between lidar-and pressure-based estimates of water levels (r 2 5 0.98, rmse 5 0.05 m), setup (r 2 5 0.92, rmse 5 0.03 m), infragravity wave heights (r 2 5 0.91, rmse 5 0.03 m), swell-sea wave heights (r 2 5 0.87, rmse 5 0.07 m), and energy density spectra. Lidar observations did not degrade with range (up to 65 m offshore of the lidar) when there was sufficient foam present on the water surface to generate returns, suggesting that for narrow-beam 1550-nm light, spatially varying spot size, grazing angle affects, and linear interpolation (to estimate the water surface over areas without returns) are not large sources of error. Consistent with prior studies, the lidar and pressure observations indicate that standing infragravity waves dominate inner-surf and swash energy at low frequencies and progressive swell-sea waves dominate at higher frequencies. The spatially dense lidar measurements enable estimates of reflection coefficients from pairs of locations at a range of spatial lags (thus spanning a wide range of frequencies or wavelengths). Reflection is high at low frequencies, increases with beach slope, and decreases with increasing offshore wave height, consistent with prior studies. Lidar data also indicate that wave asymmetry increases rapidly across the inner surf and swash. The comparisons with pressure measurements and with theory demonstrate that lidar measures inner-surf waves and setup accurately, and can be used for studies of inner-surf and swash-zone hydrodynamics.

Observations of runup and energy flux on a low‐slope beach with high‐energy, long‐period ocean swell

“…Scans were rectified using independently surveyed targets and coregistered hourly to an accurate baseline scan, accounting for movement of the lidar platform owing to solar heating and other effects. Lidar line scans (7.122 Hz) were gridded at 0.1 m cross‐shore resolution [ Brodie et al , ], producing an ( x , t , elevation) matrix (Figure a) visually similar to a video ( x , t , intensity) “timestack” [e.g., Stockdon et al , ].…”

Extreme Water Levels for Australian Beaches Using Empirical Equations for Shoreline Wave Setup

“…Shoreline wave setup has been measured (as the mean elevation at the shoreline relative to the SWL) by pressure sensors, resistance wires, photogrammetry (video cameras), and remote SONAR or LIDAR ping‐return range finder sensors (Brodie et al, ; Gourlay, ; Stockdon et al, , and references therein). Accompanying this, regression analysis has shown relationships between empirical parameterizations and measurements of shoreline wave setup, wave and beach characteristics.…”

FRF Wave Test Bed and Bathymetry Inversion

“…The shallowest gauges are in the active morphology evolution zone, and the depths change continually. A dune-mounted lidar is used to measure runup and wave statistics within the inner 100 m of the surf zone (Brodie et al 2015). The FRF also has acoustic altimeters placed at three of the cross-shore array stations (Table 1).…”