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David T. Walker and Kelsey Brunner

Abstract

This paper describes a variational data assimilation algorithm based on the SWAN near shore wave-spectrum model. The approach allows single-point wave spectrum observations to be used to estimate the wave field for a nearshore region under stationary conditions, assuming a spatially uniform incident wave spectrum at the offshore boundary. The assimilated data are in the form of Fourier directional coefficients, the standard output from operational wave buoys, and are used directly by incorporating the relationship between directional spectrum and the Fourier coefficients into the formulation. The algorithm was tested on data from nearshore buoys deployed off the coast of North Carolina in May 2012, and the estimated wave field is compared to both the input data and to independent observation data. The results compare favorably to the independent data with overall RMS errors of 10–20 percent for significant wave height, about half a second for mean wave period, and as much as 3–4 SWAN spectral grid cells for mean direction. Overall, the results show that the algorithm can be effectively used to estimate the offshore boundary spectrum and accurately reproduce wave conditions in the domain.

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Douglas Mach and Katrina Virts

Abstract

We have developed a technique to estimate the three-dimensional (3D) location of lightning optical pulses based on the stereo view of common lightning pulses from two different orbital instruments. The technique only requires the satellite position and the look vector to the lightning optical source. An example dataset of the Geostationary Lightning Mappers (GLMs) on GOES-16 and GOES-17 from 10 June 2019 is used to illustrate the technique. For this dataset, we find that the values for the stereo determination of cloud top altitudes are on average lower by 740 m than the ones calculated from the lightning ellipsoid that is currently applied during geolocation. When we compare the locations to the Advanced Baseline Imager (ABI) Cloud Height Algorithm (ACHA), we find that our technique also produces slightly lower altitude values by 240 m. There is greater spread in our technique than either the lightning ellipsoid or the ABI cloud-top height that is likely due to the incorrect pairing of Groups between the two GLMs and the 8 to 14 km resolution in the Group locations. Based on GLM location errors derived from comparisons to ground truth sources, the uncertainty in the radial location determined by the stereo location technique is 5.2 km, while the altitude uncertainty is 4.0 km. The technique can be used to 3D map lightning or other optical sources such as bolides and other upper atmospheric optical phenomena from any two orbital sensors with overlapping fields of view.

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Charles-Antoine Guérin, Dylan Dumas, Anne Molcard, Céline Quentin, Bruno Zakardjian, Anthony Gramoullé, and Maristella Berta

Abstract

We report on the installation and first results of one compact oceanographic radar in the region of Nice for a long-term observation of the coastal surface currents in the North-West Mediterranean Sea. We describe the specific processing and calibration techniques that were developed at the laboratory to produce high-quality radial surface current maps. In particular, we propose an original self-calibration technique of the antenna patterns, which is based on the sole analysis of the database and does not require any shipborne transponder or other external transmitters. The relevance of the self-calibration technique and the accuracy of inverted surface currents have been assessed with the launch of 40 drifters that remained under the radar coverage for about 10 days.

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Christopher Daly, Matthew K. Doggett, Joseph I. Smith, Keith V. Olson, Michael D. Halbleib, Zlatko Dimcovic, Dylan Keon, Rebecca A. Loiselle, Ben Steinberg, Adam D. Ryan, Cherri M. Pancake, and Eileen M. Kaspar

Abstract

There is a great need for gridded daily precipitation datasets to support a wide variety of disciplines in science and industry. Production of such datasets faces many challenges, from station data ingest to gridded dataset distribution. The quality of the dataset is directly related to its information content, and each step in the production process provides an opportunity to maximize that content. The first opportunity is maximizing station density from a variety of sources, and assuring high quality through intensive screening, including manual review. To accommodate varying data latency times, the PRISM Climate Group releases eight versions of a day’s precipitation grid, from 24 hours after day’s end to six months elapsed time. The second opportunity is to distribute the station data to a grid using methods that add information and minimize the smoothing effect of interpolation. We use two competing methods, one that utilizes the information in long-term precipitation climatologies, and the other using weather radar return patterns. Finally, maintaining consistency among different time scales (monthly vs. daily) affords the opportunity to exploit information available at each scale. Maintaining temporal consistency over longer time scales is at cross purposes with maximizing information content. We therefore produce two datasets, one that maximizes data sources, and a second that includes only networks with long-term stations and no radar (a short-term data source). Further work is underway to improve station metadata, refine interpolation methods by producing climatologies targeted to specific storm conditions, and employ higher-resolution radar products.

Open access
Agustinus Ribal, Ali Tamizi, and Ian R. Young

Abstract

Four scatterometers, namely, MetOp-A, MetOp-B, ERS-2, and OceanSat-2 were recalibrated against combined National Data Buoy Center (NDBC) data and aircraft Stepped Frequency Microwave Radiometer (SFMR) data from hurricanes. As a result, continuous calibration relations over the wind speed range from 0 to 45 m s−1 were developed. The calibration process uses matchup criteria of 50 km and 30 min for the buoy data. However, due to the strong spatiotemporal wind speed gradients in hurricanes, a method that considers both scatterometer and SFMR data in a storm-centered translating frame of reference is adopted. The results show that although the scatterometer radar cross section is degraded at high wind speeds, it is still possible to recover wind speed data using the recalibration process. Data validation between the scatterometers shows that the calibration relations produce consistent results across all scatterometers and reduce the bias and root-mean-square error compared to previous calibrations. In addition, the results extend the useful range of scatterometer measurements to as high as 45 m s−1.

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Lillian Muir, Chris Roman, David Casagrande, and Steven D’Hondt

Abstract

The Deep Autonomous Profiler (DAP) is a full-ocean-depth profiler rated to 11 km. Its hydrographic profiles and water samples can provide information on physical oceanographic properties, seawater composition, and biological communities at every depth in the ocean. Designed around a 24-bottle rosette, the DAP is an untethered system able to autonomously collect temperature, salinity, and oxygen profiles, as well as water samples. An adaptive sampling method was developed to analyze the water-column data to identify and sample desired features while under way. Acoustic ranging-only tracking is used to monitor and geolocate the system underwater. In September 2018 the vehicle was tested to 8377 m in the Puerto Rico Trench. The DAP was able to generate full-ocean-depth profiles and collect water samples at both preset and adaptively determined depths. To demonstrate the utility of the DAP, we radiocarbon dated the deepest water sampled in the Puerto Rico Trench, providing the first direct evidence of hadal water-mass age in the trench: 318 ± 25 yr. This paper presents an overview of the DAP system and the Puerto Rico Trench sea trials.

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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
Suzhou Pang, Zheng Ruan, Ling Yang, Xiantong Liu, Zhaoyang Huo, Feng Li, and Runsheng Ge

Abstract

Doppler spectra measured by vertically pointing radars are inherently linked to raindrop size distributions (DSDs). But accurate estimation of DSDs remains challenging because raindrop spectra are broadened by atmospheric turbulence and shifted by vertical air motions. This paper presents a novel method to estimate vertical air motions in which there is no need to assume a model for DSD at each range gate. The theory of the new method is that the spectral difference between the adjacent range gates is contributed by vertical air motions and the variability of DSDs. The contribution of the change of DSDs is estimated by looking up the prepared tables [lookup tables (LUTs)] of raindrop velocity difference and shape function difference. Then the vertical air motions can be estimated by minimizing the cost function of the two spectra between the adjacent range gates. The retrieval algorithm is applied to three cases including a stratiform case and two convective cases observed by a C-band vertically pointing radar in Longmen, Guangdong Province, China, in June 2016. Before that, the spectrum broadening effect is removed by the traditional deconvolution method with a wind profiler. The vertical profiles of precipitation parameters are also retrieved to investigate the microphysical process. The precipitation parameters retrieved near the surface are compared with the ground data collected by a two-dimensional video disdrometer (2DVD), and the results show good agreement.

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Zaid R. Al-Attabi, George Voulgaris, and Daniel C. Conley

Abstract

An examination of the applicability and accuracy of the empirical wave inversion method in the presence of swell waves is presented. The ability of the method to invert Doppler spectra to wave directional spectra and bulk wave parameters is investigated using 1-month data from a 12-MHz Wellen Radar (WERA) high-frequency (HF) radar system and in situ data from a wave buoy. Three different swell inversion models are evaluated from Lipa et al. (LPM), from Wang et al. (WFG), and empirical (EMP), an empirical approach introduced in this study. The swell inversions were carried out using two different scenarios: 1) a single beam from a single radar site and two beams from a single radar site, and 2) two beams from two sites (a single beam per site) intersecting each other at the buoy location. The LPM method utilizing two beams from two different sites was found to provide the best estimations of swell parameters (swell height RMS error: 0.24 m) and showed a good correlation with the partitioned swell in situ values. For the wind-wave inversion, the empirical method presented here is used with an empirical coefficient of 0.3, which seems to be suitable for universal application for all radar operating frequencies. The inverted swell parameters are used to create a swell spectrum that is combined with the inverted wind-wave spectrum to create a full directional wave spectrum. The wave inversion method presented in this study although empirical does not require calibration with in situ data and can be applied to any beam-forming system and operating frequency.

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Zichen Wang, Jian Xu, Xuefeng Zhang, Can Lu, Kangkang Jin, and Yinquan Zhang

Abstract

This paper proposes a two-dimensional underwater sound propagation model using the discontinuous Galerkin finite-element method (DG-FEM) to investigate the influence of current on sound propagation. The acoustic field is calculated by the convected wave equation with the current speed parameter. Based on the current speed data from an assimilation model, a two-dimensional coupled acoustic propagation model in the Fram Strait water area is established to observe the variability in propagation loss under different seasonal velocities in the real ocean environment. The transmission loss and signal time structure are examined. The results obtained in different source frequencies are also compared. It appears that the current velocity, time, and range variation all have an effect on underwater sound propagation.

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