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Shudong He, Youduo Peng, Yongping Jin, Jian Yan, and Buyan Wan

Abstract

Deep-sea sediments hold evolutionary records of the oceanic environment—records of great significance for scientific fields investigating marine sedimentary processes, structural evolution, and seabed mineral resource exploration. However, the acquisition of original samples from deep-sea sediments is completely dependent on advanced seabed sediment collection methods and technical equipment. In this paper, a novel sampler is proposed to obtain intact sediment samples at full ocean depth. It mainly consists of a sampling device, pressure-retaining device, pressure-compensating device, and sample transfer device. The sampler can collect samples at full ocean depth (11 000 m) with a maximum core diameter of 54 mm and core length of 350 mm, and samples can be maintained at near–in situ pressures during recovery. The sampler can be installed on a remote-operated vehicle or human-occupied vehicle, and it can be operated with a single mechanical arm to collect pressure-retained samples. The experimental test showed that the novel sampler had good pressure-retaining performance and suitability with a mechanical arm, and can be applied to pressure-retaining sampling of seabed sediments at depth of 11 000 m.

Open access
F. Joseph Turk, Ramon Padullés, Estel Cardellach, Chi O. Ao, Kuo-Nung Wang, David D. Morabito, Manuel de la Torre Juarez, Mayra Oyola, Svetla Hristova-Veleva, and J. David Neelin

Abstract

Observationally, a major source of uncertainty in evaluation of climate models arises from the difficulty in obtaining globally distributed, fine-scale profiles of temperature, pressure, and water vapor that probe through convective precipitating clouds, from the boundary layer to the upper levels of the free troposphere. In this manuscript, a 2-yr analysis of data from the Radio Occultations through Heavy Precipitation (ROHP) polarimetric radio occultation (RO) demonstration mission onboard the Spanish Paz spacecraft is presented. ROHP measures the difference in the differential propagation phase delay (Δϕ) between two orthogonal polarization receive states that is induced from the presence of nonspherically shaped hydrometeors along the Global Navigation Satellite System (GNSS) propagation path, complementing the standard RO thermodynamic profile. Since Δϕ is a net path-accumulated depolarization and does not resolve the precipitation structure along the propagation path, orbital coincidences between ROHP and the Global Precipitation Measurement (GPM) constellation passive microwave (MW) radiometers are identified to provides three-dimensional precipitation context to the RO thermodynamic profile. Passive MW-derived precipitation profiles are used to simulate the Δϕ along the ROHP propagation paths. Comparison between the simulated and observed Δϕ are indicative of the ability of ROHP to detect threshold levels of ray-path-averaged condensed water content, as well as to suggest possible inferences on the average ice-phase hydrometeor nonsphericity. The use of the polarimetric RO vertical structure is demonstrated as a means to condition the lower-tropospheric humidity by the topmost height of the associated convective cloud structure.

Open access
Free access
Armand Neukermans, Gary Cooper, Jack Foster, Lee Galbraith, and Sudhanshu Jain

Abstract

Two methods for the laboratory-scale formation of aerosols of nanosized particles of precipitated calcium carbonate (PCC), for potential use in stratospheric aerosol injection as a solar radiation management technique, are described. The first uses the coarse fluidization of bulk PCC in a simple vessel, followed by dispersal using a commercially available two-fluid nozzle. The manufacturer’s measured particle mass distribution for the bulk material and sprayed aerosol particle mass distributions are compared, indicating that the sprayed particles are well separated despite a notoriously problematic agglomeration tendency. The method is suitable for scale-up. A second dispersal method, useful for small laboratory experiments, using liquid carbon dioxide as a dispersant as well as spray propellant, gave similar results. The mass mode diameters measured here (0.89–1.4 μm) differ from that stated by the manufacturer (0.7 μm), but the distributions are consistent in showing complete separation of the particles.

Open access
Seth F. Zippel, J. Thomas Farrar, Christopher J. Zappa, Una Miller, Louis St. Laurent, Takashi Ijichi, Robert A. Weller, Leah McRaven, Sven Nylund, and Deborah Le Bel

Abstract

Upper-ocean turbulence is central to the exchanges of heat, momentum, and gases across the air–sea interface and therefore plays a large role in weather and climate. Current understanding of upper-ocean mixing is lacking, often leading models to misrepresent mixed layer depths and sea surface temperature. In part, progress has been limited by the difficulty of measuring turbulence from fixed moorings that can simultaneously measure surface fluxes and upper-ocean stratification over long time periods. Here we introduce a direct wavenumber method for measuring turbulent kinetic energy (TKE) dissipation rates ϵ from long-enduring moorings using pulse-coherent ADCPs. We discuss optimal programming of the ADCPs, a robust mechanical design for use on a mooring to maximize data return, and data processing techniques including phase-ambiguity unwrapping, spectral analysis, and a correction for instrument response. The method was used in the Salinity Processes Upper-Ocean Regional Study (SPURS) to collect two year-long datasets. We find that the mooring-derived TKE dissipation rates compare favorably to estimates made nearby from a microstructure shear probe mounted to a glider during its two separate 2-week missions for O(10−8) ≤ ϵO(10−5) m2 s−3. Periods of disagreement between turbulence estimates from the two platforms coincide with differences in vertical temperature profiles, which may indicate that barrier layers can substantially modulate upper-ocean turbulence over horizontal scales of 1–10 km. We also find that dissipation estimates from two different moorings at 12.5 and at 7 m are in agreement with the surface buoyancy flux during periods of strong nighttime convection, consistent with classic boundary layer theory.

Open access
Cesar M. Salazar Aquino, Boonleng Cheong, and Robert D. Palmer

Abstract

In this paper, a novel technique is proposed to mitigate the so-called blind range on radars that use pulse compression. It is well known that the blind range is caused by the strong leak through into the receiver during the transmission cycle. The proposed technique is called progressive pulse compression (PPC) and is based on partial decoding. PPC uses a portion of the uncontaminated received signal in conjunction with pulse compression to estimate the echoes from the incomplete signal. The technique does not require the use of a fill pulse or any hardware modifications. PPC can be divided into three steps. The first step is to discard all the received signals during the transmit cycle and apply a smooth taper for continuous transition from zero to one. The second step is to perform the pulse compression using matched filter. The combination of these two steps is equivalent to performing pulse compression using a progressively changing template to partially extract the uncontaminated received signal for compression. The third step is to compensate for the progressively changing template so that proper reflectivity values can be recovered. This technique has been tested on the PX-1000 and will be implemented on PX-10k in the near future. These two radars are designed and operated by the Advanced Radar Research Center at the University of Oklahoma and are both X-band software-defined solid-state systems. The results presented in this paper are collected using the PX-1000 radar.

Open access
Björn Lund, Ruben Carrasco, Hanjing Dai, Hans C. Graber, Cédric M. Guigand, Brian K. Haus, Jochen Horstmann, John A. Lodise, Guillaume Novelli, Tamay Özgökmen, Michael A. Rebozo, Edward H. Ryan, and Michael Streßer

Abstract

Our unmanned aerial system (UAS) current mapping is based on optical video data of the sea surface. We use three-dimensional fast Fourier transform and least squares fitting to measure the surface waves’ phase velocities and the currents via the linear dispersion relationship. Our UAS is a low-cost off-the-shelf quadcopter with inaccurate camera position and attitude measurements, which may cause spurious currents as large as the signal. We present a novel wave-based UAS heading and position correction, improving the image rectification accuracy by a factor of ~3.5 and the current measurements’ temporal repeatability by factors of 1.8–4.8. This validation study maps the currents at high spatiotemporal resolution (5 m and 4 s) across the ~700-m-wide tidally dominated Bear Cut channel in Miami, Florida. The UAS currents are compared to flotsam tracks, obtained through automated UAS video object detection and tracking, drifter tracks, and acoustic Doppler current profiler measurements. The root-mean-square errors of the cross- and along-channel currents are better than 0.03 m s−1 for the flotsam comparison and better than 0.06 m s−1 for the drifter comparison; the latter revealed a 0.06 m s−1 along-wind bias due to wind- and wave-driven vertical current shear. UAS current mapping could be used to monitor river discharge, buoyant pollutants, or submesoscale fronts and eddies; the proposed wave-based heading and position correction enables its use in areas without ground control points.

Open access
Free access
Travis Miles, Wayne Slade, and Scott Glenn

Abstract

Suspended particle size and concentration are critical parameters that are necessary to understand water quality, sediment dynamics, carbon flux, and ecosystem dynamics, among other ocean processes. In this study we detail the integration of a Sequoia Scientific, Inc., Laser In Situ Scattering and Transmissometry (LISST) sensor into a Teledyne Webb Research Slocum autonomous underwater glider. These sensors are capable of measuring particle size, concentration, and beam attenuation by particles in size ranges from 1.00 to 500 μm at a resolution of 1 Hz. The combination of these two technologies provides the unique opportunity to measure particle characteristics persistently at specific locations or to survey regional domains from a single profiling sensor. In this study we present the sensor integration framework, detail quality assurance and control procedures, and provide a case study of storm-driven sediment resuspension and transport. Specifically, Rutgers glider RU28 was deployed with an integrated LISST-Glider for 18 days in September of 2017. During this period, it sampled the nearshore environment off coastal New Jersey, capturing full water column sediment resuspension during a coastal storm event. A novel method for in situ background corrections is demonstrated and used to mitigate long-term biofouling of the sensor windows. In addition, we present a method for removing schlieren-contaminated time periods utilizing coincident conductivity temperature and depth, fluorometer, and optical backscatter data. The combination of LISST sensors and autonomous platforms has the potential to revolutionize our ability to capture suspended particle characteristics throughout the world’s oceans.

Open access
J. C. Hubbert, G. Meymaris, U. Romatschke, and M. Dixon

Abstract

Ground clutter filtering is an important and necessary step for quality control of ground-based weather radars. In this paper, ground clutter mitigation is addressed using a time-domain regression filter. Clutter filtering is now widely accomplished with spectral processing where the times series of data corresponding to a radar resolution volume are transformed with a discrete Fourier transform after which the zero and near-zero velocity clutter components are eliminated by setting them to zero. Subsequently for reflectivity, velocity, and spectrum width estimates, interpolation techniques are used to recover some of the power loss due to the clutter filter, which has been shown to reduce bias. The spectral technique requires that the in-phase (I) and quadrature (Q) time series be windowed to reduce clutter power leakage away from zero and near-zero velocities. Unfortunately, window functions such as the Hamming, Hann, and Blackman attenuate the time series signal by 4.01, 4.19, and 5.23 dB for 64-point times series, respectively, and thereby effectively reduce the number of independent samples available for estimating the radar parameters of any underlying weather echo. In this paper, a regression filtering technique is investigated, through simulated data, that does not require the use of such window functions and thus provides for better weather signal statistics. In a follow-on paper that is in preparation the technique will be demonstrated using both S-band polarimetric radar (S-Pol) and NEXRAD data. Here, it is shown that the regression filter rejects clutter as effectively as the spectral technique but has the distinct advantage that estimates of the radar variables are greatly improved. The technique is straightforward and can be executed in real time.

Open access