On Shipboard Marine X-Band Radar Near-Surface Current ‘‘Calibration’’

2015 ◽  
Vol 32 (10) ◽  
pp. 1928-1944 ◽  
Author(s):  
Björn Lund ◽  
Hans C. Graber ◽  
Katrin Hessner ◽  
Neil J. Williams
Keyword(s):  
Surface Current ◽  
Differential Gps ◽  
Near Surface ◽  
The Pacific ◽  
X Band ◽  
Correction Technique ◽  
Order Of Magnitude ◽  
Cross Track ◽  
The Impact ◽  
Ship Speed

AbstractThe ocean wave signatures within conventional noncoherent marine X-band radar (MR) image sequences can be used to derive near-surface current information. On ships, an accurate near-real-time record of the near-surface current could improve navigational safety. It could also advance understanding of air–sea interaction processes. The standard shipboard MR near-surface current estimates were found to have large errors (of the same order of magnitude as the signal) that are associated with ship speed and heading. For acoustic Doppler current profilers (ADCPs), ship heading errors are known to induce a spurious cross-track current that is proportional to the ship speed and the sine of the error angle. Conventional mechanical gyrocompasses are very reliable heading sensors, but they are too inaccurate for shipboard ADCPs. Within the ADCP community, it is common practice to correct the gyrocompass measurements with the help of multiantenna carrier-phase differential GPS systems. This study shows how a similar multiantenna GPS-based ship heading correction technique stands to improve the accuracy of MR near-surface current estimates. Changes to the standard MR near-surface current retrieval method that are necessary for high-quality results from ships are also introduced. MR and ADCP data collected from R/V Roger Revelle during the Impact of Typhoons on the Ocean in the Pacific (ITOP) program in 2010 are used to demonstrate the MR currents’ accuracy and reliability.

scholarly journals Near-Surface Current Mapping by Shipboard Marine X-Band Radar: A Validation

2018 ◽  
Vol 35 (5) ◽  
pp. 1077-1090 ◽  
Author(s):  
Björn Lund ◽  
Brian K. Haus ◽  
Jochen Horstmann ◽  
Hans C. Graber ◽  
Ruben Carrasco ◽  
...  
Keyword(s):  
Mississippi River ◽  
Oil Spills ◽  
Surface Current ◽  
Current Profile ◽  
Near Surface ◽  
Sea Surface Roughness ◽  
X Band ◽  
Effective Depth ◽  
The Mean ◽  
Potential Impact

AbstractThe Lagrangian Submesoscale Experiment (LASER) involved the deployment of ~1000 biodegradable GPS-tracked Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) drifters to measure submesoscale upper-ocean currents and their potential impact on oil spills. The experiment was conducted from January to February 2016 in the Gulf of Mexico (GoM) near the mouth of the Mississippi River, an area characterized by strong submesoscale currents. A Helmholtz-Zentrum Geesthacht (HZG) marine X-band radar (MR) on board the R/V F. G. Walton Smith was used to locate fronts and eddies by their sea surface roughness signatures. The MR data were further processed to yield near-surface current maps at ~500-m resolution up to a maximum range of ~3 km. This study employs the drifter measurements to perform the first comprehensive validation of MR near-surface current maps. For a total of 4130 MR–drifter pairs, the root-mean-square error for the current speed is 4 cm and that for the current direction is 12°. The MR samples currents at a greater effective depth than the CARTHE drifters (1–5 m vs ~0.4 m). The mean MR–drifter differences are consistent with a wave- and wind-driven vertical current profile that weakens with increasing depth and rotates clockwise from the wind direction (by 0.7% of the wind speed and 15°). The technique presented here has great potential in observational oceanography, as it allows research vessels to map the horizontal flow structure, complementing the vertical profiles measured by ADCP.

scholarly journals Using Lidar and Historical Similar Meteorological Fields to Evaluate the Impact of Anthropogenic Control on Dust Weather During COVID-19

2021 ◽  
Vol 9 ◽  
Author(s):  
Bin Chen ◽  
Yue Huang ◽  
Jianping Huang ◽  
Li Dong ◽  
Xiaodan Guan ◽  
...  
Keyword(s):  
Optical Properties ◽  
Human Activities ◽  
Control Measures ◽  
Anthropogenic Emissions ◽  
Chinese Government ◽  
Near Surface ◽  
Dust Aerosols ◽  
The Pacific ◽  
Dust Weather ◽  
The Impact

Asian dust can be transported at least one full circuit around the globe. During the transportation, dust can interact with local air-borne dust and pollutants, and has a profound impact on the environment. A novel coronavirus (COVID-19) has been affecting human activities worldwide since early 2020. The Chinese government has implemented emergency control measures. Since April 2020, control measures to reduce anthropogenic emissions have been gradually reduced. The optical properties of aerosols during the dust transport were affected by meteorological conditions, local environmental conditions and human activities. Therefore, two dust weather processes in March 2018 and March 2020 were screened under similar meteorological fields and transportation paths, which were mainly affected by human activities. Based on lidar data, in East China, compared with 2018, the average aerosol optical depth (AOD) of all types of aerosols at 0–4 km in 2020 decreased by 55.48%, while the AOD of dust aerosols decreased by 43.59%. The average particle depolarization ratio and color ratio decreased by 40.33 and 10.56% respectively. Due to the reduction of anthropogenic emissions in China (detected by lidar), the concentration of surface PM2.5 decreased by 57.47%. This indicated that due to the decrease in human activities caused by COVID-19 control measures, the optical properties of aerosols were significantly reduced during dust weather process in eastern China. However, in the Pacific region, compared with 2018, the AOD values of 0–1 km layer and 1–6 km layer in 2020 increased by 56.4% and decreased by 29.2% respectively. The difference between the two contributions of dust aerosols was very small. Meanwhile, compared with 2018, China’s near surface pollutants decreased significantly in 2020, indicating that the near surface AOD of the Pacific in 2020 was mainly contributed by local pollutants. This study was of great significance to the study of long-range and cross regional transport of pollutants.

scholarly journals Impact of surface and near-surface processes on ice crystal concentrations measured at mountain-top research stations

2018 ◽  
Vol 18 (12) ◽  
pp. 8909-8927 ◽  
Author(s):  
Alexander Beck ◽  
Jan Henneberger ◽  
Jacob P. Fugal ◽  
Robert O. David ◽  
Larissa Lacher ◽  
...  
Keyword(s):  
Ice Crystals ◽  
Surface Processes ◽  
Blowing Snow ◽  
Ice Crystal ◽  
Turbulent Layer ◽  
Near Surface ◽  
Microphysical Properties ◽  
Order Of Magnitude ◽  
The Impact

Abstract. In situ cloud observations at mountain-top research stations regularly measure ice crystal number concentrations (ICNCs) orders of magnitudes higher than expected from measurements of ice nucleating particle (INP) concentrations. Thus, several studies suggest that mountain-top in situ cloud microphysical measurements are influenced by surface processes, e.g., blowing snow, hoar frost or riming on snow-covered trees, rocks and the snow surface. This limits the relevance of such measurements for the study of microphysical properties and processes in free-floating clouds. This study assesses the impact of surface processes on in situ cloud observations at the Sonnblick Observatory in the Hohen Tauern region, Austria. Vertical profiles of ICNCs above a snow-covered surface were observed up to a height of 10 m. The ICNC decreases at least by a factor of 2 at 10 m if the ICNC at the surface is larger than 100 L−1. This decrease can be up to 1 order of magnitude during in-cloud conditions and reached its maximum of more than 2 orders of magnitudes when the station was not in cloud. For one case study, the ICNC for regular and irregular ice crystals showed a similar relative decrease with height. This suggests that either surface processes produce both irregular and regular ice crystals or other effects modify the ICNCs near the surface. Therefore, two near-surface processes are proposed to enrich ICNCs near the surface. Either sedimenting ice crystals are captured in a turbulent layer above the surface or the ICNC is enhanced in a convergence zone because the cloud is forced over a mountain. These two processes would also have an impact on ICNCs measured at mountain-top stations if the surrounding surface is not snow covered. Conclusively, this study strongly suggests that ICNCs measured at mountain-top stations are not representative of the properties of a cloud further away from the surface.

scholarly journals The impact of the Pacific Decadal Oscillation on springtime dust activity in Syria

2016 ◽  
Vol 16 (21) ◽  
pp. 13431-13448 ◽  
Author(s):  
Bing Pu ◽  
Paul Ginoux
Keyword(s):  
Middle East ◽  
Optical Depth ◽  
North Africa ◽  
Pacific Decadal Oscillation ◽  
Large Scale ◽  
Arabian Peninsula ◽  
Dust Storms ◽  
Near Surface ◽  
The Pacific ◽  
The Impact

Abstract. The increasing trend of aerosol optical depth in the Middle East and a recent severe dust storm in Syria have raised questions as to whether dust storms will increase and promoted investigations on the dust activities driven by the natural climate variability underlying the ongoing human perturbations such as the Syrian civil war. This study examined the influences of the Pacific Decadal Oscillation (PDO) on dust activities in Syria using an innovative dust optical depth (DOD) dataset derived from Moderate Resolution Imaging Spectroradiometer (MODIS) Deep Blue aerosol products. A significantly negative correlation is found between the Syrian DOD and the PDO in spring from 2003 to 2015. High DOD in spring is associated with lower geopotential height over the Middle East, Europe, and North Africa, accompanied by near-surface anomalous westerly winds over the Mediterranean basin and southerly winds over the eastern Arabian Peninsula. These large-scale patterns promote the formation of the cyclones over the Middle East to trigger dust storms and also facilitate the transport of dust from North Africa, Iraq, and Saudi Arabia to Syria, where the transported dust dominates the seasonal mean DOD in spring. A negative PDO not only creates circulation anomalies favorable to high DOD in Syria but also suppresses precipitation in dust source regions over the eastern and southern Arabian Peninsula and northeastern Africa.On the daily scale, in addition to the favorable large-scale condition associated with a negative PDO, enhanced atmospheric instability in Syria (associated with increased precipitation in Turkey and northern Syria) is also critical for the development of strong springtime dust storms in Syria.

Remote measurement of near-surface currents via wave spectra: currents varying vertically and horizontally

2020 ◽  
Author(s):  
Benjamin K Smeltzer ◽  
Ida Seip Gundersen ◽  
Simen Ådnøy Ellingsen
Keyword(s):  
Surface Current ◽  
Window Size ◽  
Wave Dispersion ◽  
Remote Measurement ◽  
Wave Spectra ◽  
Surface Currents ◽  
Improved Method ◽  
Near Surface ◽  
X Band ◽  
Spatially Varying

<p>Remote sensing of ocean near-surface currents based on measurements of the wave spectrum is an attractive means of mapping currents over a large area simultaneously. The most common wave measurement method involves marine X-band radar (Lund et al. 2015), with optical video measurements using drones more recently being used as an alternative (Streßer, Carrasco & Horstmann, 2017). In both cases, analysis of the wave dispersion within a subset window of the spatial domain is performed to determine the spatially varying near-surface current. An improved method for determining the depth-dependence of sub-surface currents from measured wave spectra was recently developed by our group (Smeltzer et al 2019).</p><p>Our long-term goal is to develop methods whereby the best possible representation of the three-dimensional sub-surface current can be obtained from remote measurement of waves. Methods based on current retrieval from wave spectra must assume that horizontal current variations are slow compared to a typical wavelength, but this is not always so. To resolve horizontal space, retrieved images must be subdivided into windows and the velocity vector at the midpoint is determined from the 3D spectrum of the waves within the window only.</p><p>In this work we examine the dependence of the spatial window size on the results of the current reconstruction. When the window size is decreased, greater spatial resolution is achieved being able to capture currents that vary on a faster horizontal length scale, at the expense of lower resolution in wavevector spectral space which may decrease the accuracy of the reconstructed currents, especially when information as the depth-dependence of the flow is desired. When the window size is larger, the reconstructed current may not be representative of the average current within the window. We present experiments conducted in a laboratory where spatially varying currents and waves of can be well-controlled and measured in situ, a valuable test-bed setup compared to field measurements. We investigate the factors involved which determine the optimal choice of window size.</p><p><strong>References</strong></p><p>Lund, B., et al. A new technique for the retrieval of near-surface vertical current shear from marine X-band radar images. J. Geophys. Res.: Oceans (2015) <strong>120 </strong>8466-8496.</p><p>Smeltzer, B.K., Æsøy, E., Ådnøy, A. and Ellingsen S.Å., An improved method for determining near-surface currents from wave dispersion measurements. J. Geophys. Res.: Oceans. (2019) <strong>124</strong>, https://doi.org/10.1029/2019JC015202.</p><p>Streßer, M., Carrasco, R. and Horstmann, J., Video-based estimation of surface currents using a low-cost quadcopter, IEEE Geosci. Remote Sens. Lett. (2017) <strong>14 </strong>2027-2031.</p>

Pound Wise and Penny Foolish? Weight Loss and The Dynamics of Health Care Spending

2011 ◽  
Vol 14 (2) ◽  
Author(s):  
Thomas G Koch
Keyword(s):  
Weight Loss ◽  
Cost Savings ◽  
Cost Effective ◽  
Economic Consequences ◽  
Health Care Spending ◽  
Order Of Magnitude ◽  
Dynamic Measures ◽  
The Cost ◽  
The Impact ◽  
The Relationship

Current estimates of obesity costs ignore the impact of future weight loss and gain, and may either over or underestimate economic consequences of weight loss. In light of this, I construct static and dynamic measures of medical costs associated with body mass index (BMI), to be balanced against the cost of one-time interventions. This study finds that ignoring the implications of weight loss and gain over time overstates the medical-cost savings of such interventions by an order of magnitude. When the relationship between spending and age is allowed to vary, weight-loss attempts appear to be cost-effective starting and ending with middle age. Some interventions recently proven to decrease weight may also be cost-effective.

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