L-Band Analysis of the Effects of Oil Slicks on Sea Wave Characteristics

The purpose of this study was to investigate the characteristics of sea surface waves as they pass through oil slicks.The parameterized first-guess spectrum method(PFSM)theory-based wave retrieval algorithm was applied to 20 images of horizontal-horizontal(HH)polarization obtained using the phased-array L-band synthetic aperture radar(SAR)(PALSAR)on the Advanced Land Observing Satellite(ALOS-1).The images were collocated with simulations from the WAVEWATCH-Ⅲ(WW3)model in a 0.1°grid using the European Centre for Medium-Range Weather Forecasts(ECMWF)reanalysis(ERA-5)winds data as the forcing field.The validation of the model-simulated significant wave height(SWH)against the measurements from the Jason-2 altimeter produced a 0.66m root mean square error(RMSE)for the SWH,with a coefficient(COR)0.74.In this sense,the WW3-simulated waves were reliable for our work.A comparison between the SAR retrieval results and the WW3 simulations was performed using the dataset for the regions without oil slicks,which produced a 0.34m RMSE for the SWH,with a COR of 0.79,which is less than a the RMSE of 0.52 m and the COR of 0.70 for the regions with oil slicks.Moreover,it was found that the SAR-derived SWHs were significantly underestimated by about 0.2m in the areas with oil slicks.This difference is probably due to the underestimation of the SAR-derived wind speeds at moderate wind speeds(i.e.,at wind speeds of greater than 5ms^(-1)).An additional analysis compared the SAR-derived wave spectra with those from the WW3 model as waves passed through the oil slicks.The interesting finding is that the wave energy at short wave lengths(about 30m)is reduced by the oil slicks,causing the movement of the dominant wave spectrum to shift to longer wave lengths(about 80 m).

An alternative approach to determine critical angle of contrast reversal and surface roughness of oil slicks under sunglint

The critical angle is the angle at which the contrast of oil slicks reverse their contrasts against the surrounding oil-free seawater under sunglint.Accurate determination of the critical angle can help estimate surface roughness and refractive index of the oil slicks.Although it’s difficult to determine a certain critical angle,the potential critical angle range help to improve the estimation accuracy.In this study,the angle between the viewing direction and the direction of mirror reflection is used as an indicator for quantifying the critical angle and could be calculated from the solar/viewing geometry from observations of the Moderate Resolution Imaging Spectroradiometer(MODIS).The natural seep oil slicks in the Gulf of Mexico were first delineated using a customized segmentation approach to remove noise and apply a morphological filter.On the basis of the histograms of the brightness values of the delineated oil slicks,the potential range of the critical angle was determined,and then an optimal critical angle between oil slicks and seawater was then determined from statistical and regression analyses in this range.This critical angle corresponds to the best fitting between the modeled and observed surface roughness of seep oil slicks and seawater.

An oil slick spectral experiment of nearshore sea water in the East China Sea

Along with the rapid advance in global industrialization, oil spill events caused by offshore operations, trans- portation and accidents are increasing. Compared with ship surveys, monitoring oil spills through remote sensing has real-time, comprehensive, low-cost advantages, which can effectively guide cleaning and evalu- ation, and reduce the marine ecological destruction resulting from oil spills. Therefore, studying the remote sensing mechanism used to monitor marine oil spills is of great significance for ecological environmen- tal protection. This paper describes an experiment and corresponding analysis based on the above-water method, using the East China Sea coastal turbid water. The analysis shows that ＂upward short-wave＂ in ultraviolet and blue-purple bands and its displacement, along with the changing thickness, are important characteristics for distinguishing between the oil slick and the sea water, and also to differentiate oil slicks of different thicknesses. From blue to near-infrared bands, the spectrum of lube oil is flatter than that of diesel, and the diesel spectrum rises faster than the lube spectrum on the right side of the trough at 400 nm. These two features form an important basis for differentiating diesel from lube oil. These analyses will further the development of oil spill remote sensing in the East China Sea.

一种新型多用途污染控制船的研发及其球鼻艏的优化

Controlling marine pollution caused by hydrocarbons spilling from oil tanker accidents and oil rigs is urgently needed.Conventional pollution control vessels currently in service worldwide do not meet certain safety criteria,storage capacities,and response times owing to their technical shortcomings.This study proposes a new concept of multimission and autonomous antipollution vessels capable of acting quickly and efficiently to counter such pollution threats.The objective of this study is to carry out a total and rapid recovery of the spilled oil slick in complete safety.Hence,optimizing the bulbous bow adapted to the pollution control vessel during its displacement is necessary to horizontally straighten the accompanying waves formed around the hull and to laminate the flow upstream of the side openings for the recovery of spilled oil.This optimization improves the nautical qualities specific to this ship to reduce the total resistance to progress and to standardize the flow upstream of the side openings to allow the collection of spilled oil at high speed.This optimization study can open a field of application for the construction of modern multi-mission pollution control vessels.Tests in hull basins will be planned to validate and adjust the results obtained from the simulations.

MATHEMATICAL MODELING OF OIL SPILL ON THE SEA AND APPLICATION OF THE MODELING IN DAYA BAY

Through the study of the theory of oil spill model, a mathematical modeling of oil spill on the sea is developed which with the consideration of spread, diffusion, drifting and attenuation of oil slick is influenced by evaporation and emulsification factors. A model that under the effect of ocean dynamic condition of tide, wind and wave, using Monte Carlo method to simulate the movement of oil slick is established. The modeling is applied to calculate and predict pollution range of oil spill at oil quay and oil ship in Daya Bay. The prediction results have basically shown the pollution situation by emergency of oil spill on the sea.

Determining oil slick thickness using hyperspectral remote sensing in the Bohai Sea of China

Determining oil slick thickness plays an important role in assessing oil spill volume and its environmental impacts on the ocean.In this study,we used a Hyperion image of an oil spill accident area and seawater and fresh crude oil samples collected in the Bohai Sea of China.A well-controlled laboratory experiment was designed to simulate spectral responses to different oil slick thicknesses.Spectral resampling and normalization methods were used to reduce the differences in spectral reflectances between the experimental background seawater sample and real background seawater.Fitting the analysis with laboratory experimental data results showed a linear relationship between normalized oil slick reflectance and normalized oil slick thickness[20th band(R^(2)-0.92938,n=49,pB0.01),26th band(R^(2)=0.93806,n=49,pB0.01),29th band(R^(2)=0.93288,n=49,pB0.01)].By using these statistical models,we successfully determined the normalized oil slick thickness with the Hyperion image.Our results indicate that hyperspectral remote sensing technology is an effective method to monitor oil spills on water.The spectral ranges of visible green and red light were the optimal bands for estimating oil slick thickness in case 2 water.The high,stabilized spectral reflectance of background seawater will be helpful in oil slick thickness inversion.

SIMULATION OF THE OIL SLICK MOVEMENT IN TIDAL WATER-WAYS

Based on particle approach and tidal flow model this article studies the behavior of the oil slick on the water surface in the Huangpu River, a tidal waterway in Shanghai. In order to track the oil slick motion, a two-dimensional oil trajectory model is used. The dynamical properties of spilled oil characterized by advection, oil spreading and turbulent diffusion are considered in the model. The simulation results consistent with the flume experimental data show that the model is applicable. Both simulation and experiment illustrate that the tidal flow has a great influence on the oil slick motion. The calculated results can be used as a reference for the response to oil spill accidents in rivers.