Airborne Remote Sensing of the Upper Ocean Turbulence during CASPER-East

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.Keywords: airborne remote sensing; ocean surface currents; upper ocean turbulence BackgroundCapabilities 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. On the global scale, presently available observations of the ocean currents are provided by satellite altimeters, which are limited to mesoscales and resolve only the geostrophic component of the surface current. Much anticipated launches of the

An Empirical Evaluation of Turbulence Closure Models in the Coastal Ocean

“…While the shape of the velocity spectrum (not shown) dictated 20 s to be a good cutoff for the high frequency noise, the choice of the low frequency cutoff was less obvious. In agreement with the observations of the airborne survey (Savelyev et al., 2018), frequencies corresponding to submesoscales were found to be far more energetic, and therefore a slight change in the low frequency cutoff choice could easily double the total amount of TKE in the leftover signal. The same was observed for the fifth beam of the tilted instrument: the amount of low frequency TKE dominated over the useful higher frequency signal, although not as much as in the side beams.…”

“…However, as was shown with a variety of airborne remote sensing methods by Savelyev et al. (2018), CASPER‐East study area around the ASI‐2 location was rich with multi‐scale submesoscale activity. The submesoscale structures were often associated with sharp fronts, which can introduce abrupt change in the stratification profile.…”

“…It is assumed that the glider can capture this background stratification and the model can be slowly relaxed to it with a 30 min e-folding time scale. However, as was shown with a variety of airborne remote sensing methods by Savelyev et al (2018), CASPER-East study area around the ASI-2 location was rich with multi-scale submesoscale activity. The submesoscale structures were often associated with sharp fronts, which can introduce abrupt change in the stratification profile.…”

“…But each flight lasts only a few hours and is nearly instantaneous in the context of a month-long survey. Savelyev et al (2018) analyzed data from five flights over ASI-2 during year days 296, 302, 303, 308, and 309. The airborne sampling during each flight was done by means of tracking dye plume deformations, infrared mapping of spatial SST structures, and surface velocity mapping by means of a synthetic aperture radar.…”

Spatial Structure, Short-temporal Variability, and Dynamical Features of Small River Plumes as Observed by Aerial Drones: Case Study of the Kodor and Bzyp River Plumes

“…Many previous works used airborne data to study various marine processes including mapping of coastal topography [7,8] and bathymetry [9][10][11][12], surveying of marine flora and fauna [13][14][15][16][17][18][19][20][21][22], and monitoring of water quality and anthropogenic pollution [23][24][25][26][27][28]. Several works used airborne data to study physical properties of sea surface layer including estimation of turbulence [29] and reconstruction of surface currents [30,31]. However, applications of aerial remote sensing are still rare in physical oceanography, especially in comparison with numerous studies based on satellite remote sensing.…”