Abstract
This study takes on the challenge of resolving upper ocean surface currents with a suite of airborne remote sensing methodologies, simultaneously imaging the ocean surface in visible, infrared, and microwave bands. A series of flights were conducted over an air-sea interaction supersite established 63 km offshore by a large multi-platform CASPER-East experiment. The supersite was equipped with a range of in situ instruments resolving air-sea interface and underwater properties, of which a bottom-mounted acoustic Doppler current profiler was used extensively in this paper for the purposes of airborne current retrieval validation and interpretation. A series of water-tracing dye releases took place in coordination with aircraft overpasses, enabling dye plume velocimetry over 100 m to 10 km spatial scales. Similar scales were resolved by a Multichannel Synthetic Aperture Radar, which resolved a swath of instantaneous surface velocities (wave and current) with 10 m resolution and 5 cm/s accuracy. Details of the skin temperature variability imprinted by the upper ocean turbulence were revealed in 1–14,000 m range of spatial scales by a mid-wave infrared camera. Combined, these methodologies provide a unique insight into the complex spatial structure of the upper ocean turbulence on a previously under-resolved range of spatial scales from meters to kilometers. However, much attention in this paper is dedicated to quantifying and understanding uncertainties and ambiguities associated with these remote sensing methodologies, especially regarding the smallest resolvable turbulent scales and reference depths of retrieved currents.
Highlights
Capabilities for spatial measurements of ocean surface turbulence are highly desirable for a wide variety of needs ranging from basic studies of upper ocean mixing processes to data assimilation into high-resolution coastal and ocean circulation models
The objective of this study is to evaluate the ability of the airborne remote sensing to accurately measure ocean surface currents on spatial scales of 10 s to 1000 s of meters
The experiment described in this paper simultaneously employs some of the above-mentioned methodologies of ocean surface current retrieval, : (1) hyperspectral visible-near infrared (VNIR) imaging of fluorescent dye releases; (2) mid-wave infrared (MWIR) imaging of sea surface temperature modulations by subsurface turbulence; and (3) active microwave surface imaging with a Multichannel Synthetic Aperture Radar (MSAR)
Summary
Capabilities for spatial measurements of ocean surface turbulence are highly desirable for a wide variety of needs ranging from basic studies of upper ocean mixing processes to data assimilation into high-resolution coastal and ocean circulation models. Much anticipated launches of the Surface Water and Ocean Topography (SWOT) and Coastal and Ocean measurement Mission with Precise and Innovative Radar Altimeter (COMPIRA) satellite missions will provide some submesoscale altimetry coverage; many smaller scale processes, such as non-geostrophic submesoscale turbulence, frontal instabilities, or Langmuir circulations will remain unresolved. Some of these processes are unresolved even by the dense horizontal resolution of surface currents from shore-based high frequency (HF) radars. The hypothesis pursued in this study is that this range of scales can potentially be resolved with an airborne imaging approach
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