Airborne Remote Sensing of Surface and Internal Wave Processes on the Inner Shelf

Transcription

1 Airborne Remote Sensing of Surface and Internal Wave Processes on the Inner Shelf Ken Melville, Luc Lenain Scripps Institution of Oceanography North Wind/Wave NDBC Station N W 19 Oct 2011 C 600m Airborne infrared imagery showing a temperature front at the northern Spatial resolution boundary of the loop current 0.25x0.25m

2 Overview To investigate the role of surface and internal wave processes on the dynamics, transport and mixing in the water column on the inner shelf and their measurement using an airborne platform. Phenomenon/Process Surface waves Sea surface temperature (SST) Surface wave breaking & mixing Langmuir Circulation, turbulence Internal waves, internal tides Surface currents, eddies Instrument Scanning lidars IR camera, radiometer Visible & IR video Visible & IR video, hyperspectral imager Scanning lidars, visible and IR video, hyperspectral imager IR and hyperspectral imagers

3 SIO Modular Aerial Sensing System (MASS) Hyperspectral (Specim EagleAISA) GPS/IMU (NovAtel LN200 SPAN) Power distribution, synchronization, data acquisition Operator touchscreen 54 cm 8 Mpx digital color camera Long Wave IR Camera (FLIR SC6000 LWIR) Scanning waveform lidar (RIEGL Q680i)

4 SIO Modular Aerial Sensing System (MASS) NDBC Station N W 19 Oct 2011 Example of surface elevation as measured from the MASS during a recent experiment in the Gulf of Mexico, flying above NDBC buoy # (wind~12m/s, Hs = 3.1m) Instrumentation Measurement Spatial resolution 0.25x0.25m Scanning Waveform Lidar Riegl Q680i Surface wave, surface slope, directional wave spectra (vert. accuracy ~2-3cm) Long-wave IR Camera FLIR SC6000 (QWIP) Ocean surface processes, wave kinematics and breaking, frontal processes High-Resolution Video JaiPulnix AB-800CL Ocean surface processes, wave kinematics and breaking, frontal processes Hyperspectral Camera Specim EagleAISA Ocean surface and biogeochemical processes GPS/IMU Novatel SPAN-LN200 Georeferencing, trajectory

5 MASS Example of High-Resolution Measurements of Breaking Waves (IR & Visible) Sample georeferenced images of a breaking wave in the visible and infrared (8-9.2μm) bands during a recent experiment in the Gulf of Mexico. Note that the foam is colder (blue) due to rapid cooling (T water - T atm 8 C) while the active breaker is warmer (red), disrupting the surface skin layer and bringing warmer water from below. Also shown is a perspective view of the sea surface elevation for the same breaking wave color coded for WGS84 height (World Geodetic System 1984 datum). The lower panel shows the profile of the transect A-B marked in the georeferenced visible image.

6 MASS - Wave Observations down to wavelengths of <0.6m over a wide range of conditions

7 MASS Surface wave processes wave breaking Sutherland & Melville (2013): Nondimensional breaking length distribution binned by wave age in color. The solid lines are using IR data from R/P FLIP, the dash-dot lines are using visible imagery from FLIP, and the dashed lines are using airborne visible imagery from Kleiss & Melville (2010).

8 MASS Characterization of surface kinematics from airborne thermal imagery Sea surface temperature estimated from TERRA level 3 daily product ( C) on October 30, 2011, 10hr prior to the airborne survey conducted the same day. The flight track is shown in blue. The average surface velocities derived from the thermal imagery are shown as vectors along the flight track (red, positive easterly velocity, black, positive westerly velocity). Note the sharp change in surface velocities as the aircraft went across the LC.

9 Wave Enhancement at SST Front Northern edge of the LC (left) Sea surface temperature imagery of the northern edge of the Gulf of Mexico Loop Current on October (right) Evolution of the omnidirectional wavenumber spectrum as the aircraft flew across the Loop Current. The color scale represents the average SST over the length of the wave record (4 km) used in the spectral analysis, also shown as a function of latitude in the upper panel. Note the wave enhancement going into the LC

10 SSHA from Airborne and Satellite Altimetry ssha ssh mean _ sea _ surface lidar lidar Satellite ocean _ tides Tidal_ loading solid _ earth _ tides pole _ tide Ocean tides: Corrections for solid earth and sea surface height variations due to the attraction of the Sun and Moon (FES2004 model) Solid earth tides: Corrections for solid earth variations due to the attraction of the Sun and Moon (McCarthy and Petit, IERS Conventions 2003) Pole tides: Corrections for variations due to the attraction of the Sun and Moon. Tidal loading: Corrections for height variations due to changes in tide-induced forces acting on the Earth's surface (FES2004 model)

11 High-Resolution SSHA from Airborne Altimetry

12 From Ata s talk

13 Airspace and proposed flight operations for the pilot experiment 5-6 flights planned for the pilot experiment (4.5 hrs endurance) Base of operations: Oxnard,CA & San Luis Obispo, CA Two 1-week field period to sample spring/neap cycle within the in-situ sampling period (June (deploy) and August 2-6 (recovery))

14 Airspace and proposed flight operations for the pilot experiment 2 km

15 NAWCWD PT. MUGU SEA TEST RANGE SUA USN FACSFAC SAN DIEGO 6 5 W-283 6D W-532N 7D 7E W-532S 7C 6E W-285 5D E D C 6C E M M W-537 W-289S 28

16 NOAA monthly tide predictions JUNE 2015

17 NOAA monthly tide predictions JULY 2015

18 Wind climatology Dorman & Winant 1995

19 Wind/Wave climatology NDBC 46011

20 Wind/Wave climatology NDBC 46011

21 SST front climatology Castelao JGR 2006

22 SST front climatology Castelao JGR 2006

23 Notes on Airborne Measurements of Surf Zone Surface Kinematics in the Gulf of Mexico Perspective view of the 3D Lidar point cloud color-coded for height (referenced to WGS84) as the aircraft went across the surf zone in Gulf Shores, AL on October The wind direction is shown as blue arrows, with wind waves propagating in the same direction off the beach. Note the lack of returns while flying over slicks, also apparent in the IR imagery (see figure 3) Composite uncalibrated infrared image measured from the MASS on October as the aircraft went across the shores on its way back to the airport. Temperature range in the water is +/-0.3C. Note the abundance of temperature structures, ranging from smaller scales close to shore, the apparent colder slicks ( m) and signatures of Langmuir circulation aligned with the wind direction offshore ( m). Distances are in meters, relative to a reference point located at the Gulf Shores Airport (KJKA).

24 Notes on Airborne Measurements of Surf Zone Surface Kinematics in the Gulf of Mexico

25 Notes on Airborne Measurements of Surf Zone Surface Kinematics in the Gulf of Mexico Sample high-resolution visible image collected from the MASS (top) and the corresponding vertical vorticity computed from the velocity field derived from pair of subsequent visible images using optical flow techniques, and apparent at each end of the segments of the breaking waves. Note that that this aerial coverage over large sections of beach complements the local in situ measurements of currents and vorticity by Dave Clark et al. (GRL 2013). The IR imagery can be processed using PIV and optical flow techniques to measure surface velocity fields in the surf zone.

26 Notes on Airborne Measurements of Surf Zone Surface Kinematics in the Gulf of Mexico