Visibility of River Plume Fronts with an X-Band Radar

A land-based X-band radar was employed to observe river plume fronts at the mouth of the Tenryu River, Japan. Time-averaged radar images captured fronts extending offshore from the river’s mouth as bright streaks. Comparisons between satellite optical images and radar images confirm that streaky features in the radar image represent color river plume fronts. Further corroboration comes from field observations of water temperature, salinity, and turbidity conducted simultaneously with the radar measurements. When a survey ship crossed the front, the measured properties varied discontinuously, suggesting that water from the river and sea converged there and also that a downwards current was present. Variation of visibility of the fronts was assessed and compared with the rate of variation of water level and the wind speed and direction. The radar is able to image fronts when the water level is decreasing during ebb tide and the wind speed is over 3 m/s along shore. Surface ripple waves are generated by the local wind, and if they propagate across the front, wave heights increase, causing higher backscatter of the emitted radar beam. This observation gives further evidence on the imaging mechanism of river plume fronts with X-band radars in relation to wind direction

A study on the longshore sediment transport rate around a headland

This study tries to estimate the variation of longshore sediment transport rates (LSTR) around a jetty, or a headland, from observational data and numerical computation. X-band radar was installed to observe hourly waves and morphology around the headland at Kashima Coast, Ibaraki, Japan. Several features, such as the surfzone, shoreline positions, and wave crest locations, are digitized from the radar images. Then the intertidal beach slopes were evaluated with shoreline positions and tidal records. Incident wave height, period, and direction were measured at NOWPHAS wave station at Kashima Port with 2 hours interval. Annual variation of shoreline position, intertidal slope, and incident wave height and direction are summarized to analyze LSTR in the vicinity of the headland. Annual variations of the shoreline positions and the intertidal slopes were analyzed at the northern and southern sides of the headland. Northern sides of the headland are generally accumulating in winter season and are eroding in summer season, and at the southern side, the opposite is observed. These features are corresponding to seasonal wave characteristics. Incident wave directions are primary from the northern; to the headland in winter season and from southern in summer season. From the shoreline positions and the intertidal slopes, cross sectional areas and beach volumes are estimated, and then LSTR are evaluated from change rates of beach volumes. To compute LSTR, wave and current fields were computed for every 2 hours. The numerical results are verified by comparing widths of the surfzone and wave directions read from radar images. Wave breaking height, widths of the surfzone and current speeds from the numerical computation are used to estimate LSTR with several formulas. For the period with fair wave climate, reasonable agreement is obtained for LSTR estimation between observation and computation

Automatic Shoreline Position and Intertidal Foreshore Slope Detection from X-Band Radar Images using Modified Temporal Waterline Method with Corrected Wave Run-up

Automatic and accurate shoreline position and intertidal foreshore slope detection are challenging and significantly important for coastal dynamics. In the present study, a time series shoreline position and intertidal foreshore slope have been automatically detected using modified Temporal Waterline Method (mTWM) from time-averaged X-band radar images captured throughout the course of two-week tidal cycle variation over an area spanning 5.6 km on the Hasaki coast between 12 April 2005 and 31 December 2008. The methodology is based on the correlation map between the pixel intensity variation of the time-averaged X-band radar images and the binary signal of the tide level ranging from −0.8 m to 0.8 m. In order to ensure the binary signal represented each of the water levels in the intertidal shore profile, determining the water level direction-wise bottom elevation is considered as the modification. Random gaps were detected in the captured images owing to the unclear or oversaturation of the waterline signal. A horizontal shift in the detected shoreline positions was observed compared to the survey data previously collected at Hasaki Oceanographical Research Station (HORS). This horizontal shift can be attributed to wave breaking and high wave conditions. Wave set-up and run-up are the effects of wave breaking and high wave conditions, respectively. The correction of the wave set-up and run-up is considered to allow the upward shift of the water level position, as well as shoreline position, to the landward direction. The findings indicate that the shoreline positions derived by mTWM with the corrected wave run-up reasonably agree with the survey data. The mean absolute bias (MAB) between the survey data and the shoreline positions detected using mTWM with the corrected wave run-up is approximately 5.9 m, which is theoretically smaller than the spatial resolution of the radar measurements. The random gaps in the mTWM-derived shoreline positions are filled by Garcia’s data filling algorithm which is a Penalized Least Squares regression method by means of the Discrete Cosine Transform (PLS-DCT). The MAB between survey data and the gap filled shoreline positions detected using TWM with corrected wave run-up is approximately 5.9 m. The obtained results indicate the accuracy of the mTWM with corrected wave run-up integrated with Garcia’s method compared to the survey observations. The executed approach in this study is considered as an efficient and robust tool to automatically detect shoreline positions and intertidal foreshore slopes extracted from X-band radar images with the consideration of wave run-up correction

Estimation of Shoreline Positions by Combining X-band Radar and SAR Observations

Shoreline positions of Kashima Coast facing the Pacific Ocean, which is approximately 16 km long with Hasaki Fishery Port at the south end and Kashima Port at the north end, have been observed with four land-based X-band radars and Synthetic Aperture Radar (SAR) satellite. X-band radars observe shoreline positions continuously in time but do not cover the whole coast. On the other hand, SAR covers the whole spatial domain, but data is available only a few times in a year. The purpose of the present work is to propose a data fusion method which combines different shoreline data observed by X-band radars and SAR satellite with the help of Garcia\u27s method, a Penalized Least Square (PLS) regression based on Discrete Cosine Transform (DCT). Garcia\u27s method is initially applied to shoreline positions dataset derived from X-band radars, and its performance has been checked for this dataset with artificial gaps. Then Garcia\u27s method is executed to combine Radar and SAR shoreline positions dataset together. The data fusion result is verified by survey data, and we confirm that our fusion method performs reasonably well to process shoreline data set

Collapse and recovery process of the sand spit at the Tenryu River mouth on the Pacific Coast of Japan

This paper investigates the collapse and recovery processes of the sand spit at the Tenryu River mouth on the Pacific Coast of Japan, when two characteristic typhoons, Man-Yi and Fitow, passed over the study site in the year 2007. Although these two typhoons caused equally high storm waves, these two events were different in principal wave directions and in the amount of river discharges. As a result, Man-Yi collapsed the sand spit, while Fitow rather enhanced the recovery of the sand spit. Successive still images recorded by six field cameras were analyzed to investigate the dynamic morphology change of the river mouth for 2 months during which these two events had occurred. Comparisons of obtained topography changes and various hydrodynamic characteristics yielded several findings: (i) the sand spit was breached approximately 6 h after the peak of flow velocity and 2 h after the peak of the water head difference across the sand spit; (ii) the breached part of the sand spit was refilled by wave-induced shoreward sediment transport; and (iii) a core sample showed three clear layers of graded sedimentary structures of gravel, which correspond to the number of observed high waves overtopping the sand spit

SAR衛星による高頻度観測結果を用いた鹿島灘南部の汀線変動解析

合成開口レーダ（Synthetic Aperture Radar）衛星はマイクロ波レーダを搭載した衛星であり，雲天時，夜間にも観測可能である．そのため光学（可視）衛星に比べ同一地点のシーンを高頻度に取得できる．年に複数回取得されたシーンより汀線位置を読み取り，漂砂系内の季節的な汀線変動を追跡した．高頻度に観測されたデータの解析結果を示し，その優位性を検討する．具体的には地球観測衛星ALOS (PALSAR)（運用期間：2006～2011年）とALOS-2 (PALSAR-2)（2014年～現在）が取得した鹿島灘南部（鹿島港～利根川河口）の32シーンを分析した．2006年から2016年にかけての約10年間の汀線変動の特徴を議論し，年に1回取得される観測結からは抽出できない汀線変動特性を説明する

Responsive behaviour of galvanic anodes in concrete and the basis for its utilisation

This article was published in the journal, Corrosion Science [© Elsevier]. The definitive version is available at: http://www.sciencedirect.com/science/article/pii/S0010938X11003441In this study, a unique concrete specimen was used to analyse the response of embedded sacrificial zinc and steel anodes to rainfall and fluctuations in temperature. Current from the zinc and steel anodes increased when the environment was aggressive, showing that the required protection current depends on the present level of corrosion risk. A basis for using the ‘responsive behaviour’ of galvanic anodes is provided by the protective effects of pit re-alkalisation and pH maintenance. By contrast, protection based on achieving adequate polarisation inhibits the use of responsive behaviour and galvanic anodes might only deliver adequate polarisation in aggressive environments

Membrane expansion alleviates endoplasmic reticulum stress independently of the unfolded protein response

Increasing the size of the ER by lipid synthesis helps the cell deal with ER stress

An experimental study of cathodic protection for chloride contaminated reinforced concrete

Cathodic protection (CP) is being increasingly used on reinforced concrete structures to protect steel reinforcing bars from corrosion in aggressive conditions. Due to the complexity of environmental conditions, the design specifications in national and international standards are still open to discussion to achieve both sufficient and efficient protection for reinforced concrete structures in engineering practices. This paper reports an experimental research to investigate the influence of chloride content on concrete resistivity, rebar corrosion rate and the performance of CP operation using different current densities. It aims to understand the correlation between the chloride content and concrete resistivity together with the CP current requirement, and to investigate the precision of the CP design criteria in standards