Modular Aerial Sensing System

Airborne Lidar in support of Ocean Topography Missions and Science

With the growing interest in understanding air-sea interaction, upper ocean dynamics and thermodynamics, increasing emphasis has been placed on submesoscale ocean processes. Meanwhile the interest in coastal oceanography also requires both spatial and temporal resolution beyond the typical (ten-day) repeat cycle of satellite altimetry. As we move to higher spatial resolution, for example, the 2-km requirement and 500-m goal of the Surface Water and Ocean Topography (SWOT) mission, the surface wave field will become of more significance both for the dynamics and for the sea-state bias corrections since the wave field correlates with the submesoscale dynamics through wave-current interaction. As the community moves into this regime of ocean dynamics, some of these needs can be met by the use of airborne lidar for the measurement of ocean topography from mesoscales of O(100) km to gravity-capillary waves of wavelengths O(1) cm. Thus airborne lidar can be used in the pre-launch and calibration/validation phases and to supplement the science goals of the mission. In this talk we present the results of airborne lidar measurements synchronized with Jason 1 altimeter tracks in the Gulf of Mexico. We compare the airborne lidar measurements of the sea-surface topography and significant wave height (SWH) with Jason 1 data. In the Gulf of Mexico we also use coincident airborne hyperspectral and infrared imagery to characterize the gradients in sea surface topography and surface wave variables across the Loop Current boundary and eddies.

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High-Resolution Airborne Waveform Lidar for Oceanographic Research

It is now accepted that to better understand the coupling between the atmosphere and the ocean, surface-wave processes must be taken into account. Traditional airborne lidar systems and in situ instrumentation have limited directional and frequency responses and do not have the resolution required to fully test modern theories of directional wave spectra. Directional observations at lower and higher wavenumbers, the latter being close to the end of the gravity-wave range, are especially limited, but are important as they need to be resolved in current wind-wave models.

Over the past two years, we have integrated a novel, portable, high-resolution airborne topographic lidar with video and hyperspectral imaging systems. The scanning waveform lidar is coupled to a highly accurate GPS/inertial measurement unit permitting airborne measurements of the sea surface elevation and whitecap coverage with swath widths of up to 800m under the aircraft track over water, and horizontal spatial resolution as low as 0.2m. We describe system performance, and present preliminary results from recent measurements, where we obtained wave directional spectra down to wavelengths of 0.8m.

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Quantitative comparison of airborne remote-sensed and in situ Rhodamine WT dye during RIVET & IB09

The transport and evolution of temperature, sediment, chlorophyll, fluorescent dye, and other tracers is of significant oceanographic interest, particularly in complex coastal environments such as the nearshore river mouths, and tidal inlets. The fate of littoral pollutants and contaminants is of significant interest to the Navy. Tracer transport in the nearshore is relevant to chemically detecting mines, avoiding contact with dangerous substances, and predicting where optical clarity will be clouded by fine sediments and silt.

Remote sensing improves spatial coverage over in situ observations, and ground truthing remote sensed observations is critical for its use. Here, we present remotely sensed observations of Rhodamine WT dye using the SIO Modular Aerial Sensing System (MASS) and compare them with in situ observations; from the IB09 (0-300)m seaward of the surfzone, (Imperial Beach, CA, October 2009) and RIVET (New River Inlet NC, May 2012) field experiments. During RIVET, dye is also characterized using a pushbroom hyperspectral imaging system (SPECIM AISAEagle VNIR 400-990 nm). During IB09 and RIVET, in situ dye was measured with two GPS-tracked jet skis, a small boat and moored observations. The in situ observations are compared with the remotely sensed data in these two complex coastal environments.

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