Yukio Koibuchi

Statistical Combination of Spatial Interpolation and Multispectral Remote Sensing for Shallow Water Bathymetry

There is often a need for making a high-resolution or a complete bathymetric map based on sparse point measurements of water depth. Well-known feasible methods for this problem include spatial interpolation and passive remote sensing using readily available multispectral imagery, whose accuracies depend strongly on geometric and optical conditions, respectively. For a more accurate and robust water-depth mapping, in this letter, the two methods are combined into a new method in a statistically reasonable and beneficial manner. The new method is based on a semiparametric regression model that consists of a parametric imagery-based term and a nonparametric spatial interpolation term that complement one another. An accuracy comparison in a test site shows that the new method is more accurate than either of the existing methods when sufficient training data are available and far more accurate than the spatial interpolation method when the training data are scarce.

SHALLOW WATER BATHYMETRY FROM MULTISPECTRAL SATELLITE IMAGES: EXTENSIONS OF LYZENGA'S METHOD FOR IMPROVING ACCURACY

A high-resolution or complete bathymetric map of shallow water based on sparse point measurements (depth soundings) is often needed. One possible approach to such maps is passive remote sensing of water depth by using multispectral imagery in the popular method proposed by Lyzenga et al. [2006]; however, its application has been limited due to insufficient accuracy. To improve accuracy, we have developed 3 extensions of Lyzengas method by addressing unrealistic optical and statistical assumptions in the method. The purpose of this paper is to compare the accuracy of Lyzengas method, the 3 extensions, and the combination of the 3 extensions. The accuracy comparison test was performed for 2 coral reef sites by using cross validation. The results indicated that for both sites, the extended methods were more accurate than Lyzengas method when sufficient training data were available. The most accurate extension was the one derived by modeling the spatial autocorrelation in the error term of the regression model used in Lyzengas method. The combination of the 3 extensions was even more accurate than the extensions. The implementations of the extended methods are not difficult in terms of software availability and computational cost.

Occurrence and partition ratios of radiocesium in an urban river during dry and wet weather after the 2011 nuclear accident in Fukushima.

After the 2011 nuclear accident in Fukushima, radiocesium was released from the Fukushima Dai-ichi Nuclear Power Plant and contaminated waters in urban areas near Tokyo. By intensive field monitoring during 3 years, this study investigated the temporal trends and the occurrence of radiocesium during dry and wet weather, and analyzed the variations in radiocesium during rainfall events and factors controlling them. Concentrations of particulate radiocesium decreased rapidly from May 2012 to March 2013 and reached an equilibrium in 2014. Concentrations of particulate (137)Cs during wet weather were almost double those during dry weather in the same period. In contrast to the small variations in (137)Cs concentrations in the particulate phase on a suspended solids (SS) weight basis during events, those in the dissolved phase on a liquid-volume basis fluctuated greatly, resulting in variations in the partition coefficient (apparent Kd). The apparent Kd of (137)Cs during wet weather ranged from 30,000 to 150,000 L kg(-1) and showed a significant negative correlation with SS concentrations during wet weather. Specific surface area in solids contributed to the variations in apparent Kd.

Microbial Response to Benthic Environment in Trench and Flat Seabed Sediments in Tokyo Bay, Japan

Abstract In order to elucidate microbial response to the benthic environment in trench and flat seabed sediments, dynamic changes in the sediment microbial community and the water quality of overlying water were evaluated during summer and autumn in Tokyo Bay, Japan. A large amount of nutrients accumulated in the trench during summer when stratification occurred, which stimulated the sediment microbial growth, resulting in higher microbial density compared to the flat seabed sediment. Additionally, predominant ubiquinone species in the two sediments were ubiquinone with 9 isoprene units (Q-9) and Q-8, respectively, while menaquinone with 6 isoprene units (MK-6) dominated. Hence, the different bottom shapes were expected to produce distinct microbial environments. In autumn, the convective mixing of seawater resulted in the disappearance of stratification and the deposition of nutrients onto the flat seabed sediment, which contributed to excessive microbial growth. During this transition period, Q-containing bacteria dominated with lag time instead of MK-containing bacteria. At the same time, the molar fraction of MK-6 that might correspond to sulfate-reducing bacteria also rapidly decreased. However, this microbial change was not observed in the trench since it kept anaerobic conditions longer. Multidimensional scaling analysis indicated that dissolved oxygen of the bottom water can drive microbial community shift.

Development of standard test methods for evaluation of ROV/AUV performance for emergency response applications

This paper discusses the National Institute of Standards and Technology (NIST) and the Department of Homeland Security (DHS) efforts to develop standard test methods for aquatic response robot performance. Different remotely operated vehicles (ROVs) and autonomous underwater vehicles (AUVs) were used to evaluate the test methods and the tests were refined accordingly. Experiments were conducted in order to evaluate the validity of the test methods. Results of those experiments as well as future work are discussed herein.

Environmental Monitoring in Urban Coastal Zone

Coastal water receives a large number of pollutants from urban area which have a potentially adverse effect on water quality and aquatic ecosystems. The sources of the discharge of such pollutants are categorized into two types: point and non-point sources. Point source means pollutant sources which are easily identified facilities discharging pollutants to the environment. Factories, housings and sewage treatment plants are included in this category. In many countries, the quality of the discharged water from these point sources is regulated by laws and is controlled by a wide range of treatment technologies. Diffuse sources of pollutants such as vehicles and urban surface materials are called non-point sources. Non-point source pollution occurs with rainfall or snowmelt. The water from rain or snow dissolves the atmospheric pollutants, washes off the pollutants on the impervious surfaces and finally flows into rivers, lakes and coastal waters. Naturally, the non-point source pollution is difficult to control, since the water is irregularly discharged. The monitoring or sampling of such irregular water discharge requires special devices and/or incurs high labor costs. The source responsible for the pollution is often unclear, not least because the water runoff itself is a natural phenomenon and the pollutant sources are diverse; responsibility is thus difficult to assign. As such, the significance of non-point source pollution in the water environment tends only to be recognized after the controlling system of the point sources has been spread well in the society.

Source analysis of radiocesium in river waters using road dust tracers

Following the Fukushima Dai-ichi Nuclear Power Station accident, regional road dust, heavily contaminated with radiocesium, now represents a potential source of radiocesium pollution in river water. To promote effective countermeasures for reducing the risk from radiocesium pollution, it is important to understand its sources. This study evaluated the utility of metals, including Al, Fe, and Zn as road dust tracers, and applied them to analyze sources of 137Cs in rivers around Fukushima during wet weather. Concentrations of Zn in road dust were higher than agricultural and forest soils, whereas concentrations of Fe and Al were the opposite. Concentrations of Zn were weakly but significantly correlated with benzothiazole, a molecular marker of tires, indicating Zn represents an effective tracer of road dust. Al, Fe, and Zn were frequently detected in suspended solids in river water during wet weather. Distribution coefficients of these metals and 137Cs exceeded 104, suggesting sorptive behavior in water. Although concentrations of Al, Fe, Zn, and 137Cs were higher in fine fractions of road dust and soils than in coarse fractions, use of ratios of 137Cs to Al, Fe, or Zn showed smaller differences among size fractions. The results demonstrate that combinations of these metals and 137Cs are useful for analyzing sources of radiocesium in water. These ratios in river water during wet weather were found to be comparable with or lower than during dry weather and were closer to soils than road dust, suggesting a limited contribution from road dust to radiocesium pollution in river water.

Numerical Simulation of Urban Coastal Zones

Numerical modeling is an essential technique for the understanding and management of water quality in urban coastal zones. This may be because urban coastal zones are characterized by an extremely wide variety of environments with complicated geographical features, such as urban areas that intersect with outer oceans, and hence are affected by both. The phenomena in this area are not only physical, but also biological or chemical, and they interfere with each other. Therefore, the ecosystem and the water quality of urban coastal zones are highly complicated. The quality of water has long been deteriorating at many of the world’s urban coastal zones (Walker 1990) . Damage caused by events such as red tides, harmful algal bloom, and decreased amounts of dissolved oxygen in bottom water occur frequently. Such phenomena induce the degradation of aquatic ecosystems and the loss of aquatic resources such as sea grass beds, as well as fish and shellfish. These phenomena – caused by an excessive inflow of nutrients that has been accelerated by urban populations, resulting in the increase of concentrations called eutrophication (Caperon et al. 1971) – have been causing many problems for fisheries and recreation areas in urban coastal zones. However, these events are also influenced by weather conditions, ocean currents, household and industrial wastes, nutrients coming from agricultural lands, sewage treatment plants, acid rain and other such phenomena (Ærtebjerg et al. 2003) . Furthermore, the interactions between all of these factors are quite complicated. Actually, distinguishing between natural and anthropogenic effects is not easy (Jøgensen and Richardson 1996) . This makes the improvement of water quality and the management of resources in this area even more difficult.

Chapter 7 Study on change of bottom topography and sediment characteristics around a reclaimed land in Sanbanze

Abstract In recent years, Sanbanze has been drawing focussing attention on environmental rehabilitation. This study provides a more comprehensive understanding of coastal topographic change and variation of sediment conditions in this area. This understanding leads to a significant contribution to the rehabilitation of Sanbanze. The sedimentation processes occurring over the past 30 years were identified from surface sediment and column core samples, which were analyzed for the particle size distribution, carbon ratio, electrical conductivity and radioactivity in a total of 43 stations. It was concluded that the change in sedimentation processes was caused by reclamation as well as the formation of sandbars in the vicinity of Urayasu City.

Field Observation to evaluate Function of Yatsu Tidal Flat in Nutrients Budget of Tokyo Bay in Autumn

In order to estimate nutrients budget of a tidal flat, a field observation was conducted in autumn in Yatsu tidal flat which is connected to Tokyo Bay only through two rivers. Measured water level showed asymmetric variation with relatively longer duration for low tide, due to nonlinear effect of the semi-enclosed water body connected to the open sea by narrow and shallow rivers. It was also found that the Yatsu tidal flat was the source of nutrients for Tokyo Bay in autumn, owing to the overgrowth of ulva in spring and summer. Thus, Yatsu tidal flat is considered to be a temporal buffer for storing nutrients. The outflow of SS exceeds the inflow, resulting in the change of surface sediments from mud to sand.