Multi-angle backscatter classification and sub-bottom profiling for improved seafloor characterization     

Evangelos Alevizos  Mirjam Snellen  Dick Simons  Kerstin Siemes  Jens Greinert 《Marine Geophysical Researches》2018,39(1-2):289-306

This study applies three classification methods exploiting the angular dependence of acoustic seafloor backscatter along with high resolution sub-bottom profiling for seafloor sediment characterization in the Eckernförde Bay, Baltic Sea Germany. This area is well suited for acoustic backscatter studies due to its shallowness, its smooth bathymetry and the presence of a wide range of sediment types. Backscatter data were acquired using a Seabeam1180 (180 kHz) multibeam echosounder and sub-bottom profiler data were recorded using a SES-2000 parametric sonar transmitting 6 and 12 kHz. The high density of seafloor soundings allowed extracting backscatter layers for five beam angles over a large part of the surveyed area. A Bayesian probability method was employed for sediment classification based on the backscatter variability at a single incidence angle, whereas Maximum Likelihood Classification (MLC) and Principal Components Analysis (PCA) were applied to the multi-angle layers. The Bayesian approach was used for identifying the optimum number of acoustic classes because cluster validation is carried out prior to class assignment and class outputs are ordinal categorical values. The method is based on the principle that backscatter values from a single incidence angle express a normal distribution for a particular sediment type. The resulting Bayesian classes were well correlated to median grain sizes and the percentage of coarse material. The MLC method uses angular response information from five layers of training areas extracted from the Bayesian classification map. The subsequent PCA analysis is based on the transformation of these five layers into two principal components that comprise most of the data variability. These principal components were clustered in five classes after running an external cluster validation test. In general both methods MLC and PCA, separated the various sediment types effectively, showing good agreement (kappa >0.7) with the Bayesian approach which also correlates well with ground truth data (r²?>?0.7). In addition, sub-bottom data were used in conjunction with the Bayesian classification results to characterize acoustic classes with respect to their geological and stratigraphic interpretation. The joined interpretation of seafloor and sub-seafloor data sets proved to be an efficient approach for a better understanding of seafloor backscatter patchiness and to discriminate acoustically similar classes in different geological/bathymetric settings.  相似文献   

Petrophysical properties of bioclastic platform carbonates: implications for porosity controls during burial     

Delphine Croizé  Stephen N. Ehrenberg  Knut Bjørlykke  François Renard  Jens Jahren 《Marine and Petroleum Geology》2010

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Importance of geological information for assessing drain flow in a Danish till landscape     

Anne Lausten Hansen  Anne Storgaard  Xin He  Anker Lajer Hjberg  Jens Christian Refsgaard  Bo Vangs Iversen  Charlotte Kjaergaard 《水文研究》2019,33(3):450-462

There has, in recent years, been an increasing interest in developing nutrient load mitigation measures focussing on tile drains. To plan the location of such tile drain measures, it is important to know where in the landscape drain flow is generated and to understand the key factors governing drain flow dynamics. In the present study, we test two approaches to assess spatial patterns in drain flow generation and thereby assess the importance of including geological information. The approaches are the widely used topographical wetness index (TWI), based solely on elevation data, and hydrological models that include the subsurface geology. We set‐up an ensemble of 20 hydrological models based on 20 stochastically generated geological models to predict drain flow dynamics in the clay till Norsminde catchment in Denmark and test the results against TWI. We find that the hydrological models predict observed daily drain flow reasonably well. High drain flow volumes were found in stream valleys and in wetlands and lower drain flow volumes in the more hilly parts of the catchment. In spite of the apparent connection to the landscape, there was no statistically significant correlation between TWI and drain flow at grid scale (100 × 100 m). TWI was therefore not found to be a sufficient index on its own to assess where drain flow is generated, especially in the highlands of the catchment. The geology below 3 m was found to have a large impact on the drain flow, and correlations between sand percentage in the subsurface geology and drain flow volume were found to be statistically significant. Geological uncertainty therefore give rise to uncertainty on simulated drain flow, and this uncertainty was found to be high at the model grid scale but decreasing with increasing scale.  相似文献   

Catchment chemostasis revisited: Water quality responds differently to variations in weather and climate     

Sarah E. Godsey  Jens Hartmann  James W. Kirchner 《水文研究》2019,33(24):3056-3069

Solute concentrations in streamflow typically vary systematically with stream discharge, and the resulting concentration–discharge relationships are important signatures of catchment biogeochemical processes. Solutes derived from mineral weathering often exhibit decreasing concentrations with increasing flows, suggesting dilution of a kinetically limited weathering flux by a variable flux of water. However, previous work showed that concentration–discharge relationships of weathering‐derived solutes in 59 headwater catchments were much weaker than this simple dilution model would predict. Instead, catchments behaved as chemostats, with rates of solute production and/or mobilization that were nearly proportional to water fluxes, on both event and interannual timescales. Here, we re‐examine these findings using data for a wider range of solutes from 2,186 catchments, ranging from ~10 to >1,000,000 km² in drainage area and spanning a wide range of lithologic and climatic settings. Concentration–discharge relationships among this much larger set of larger catchments are broadly consistent with the previously described chemostatic behaviour, at least on event and interannual timescales for weathering‐derived solutes. Among these same catchments, however, site‐to‐site variations in mean concentrations of weathering‐derived solutes exhibit strong negative correlations with long‐term average precipitation and discharge, reflecting strong climatic control on long‐term leaching of the critical zone. We use multiple regression of site characteristics including discharge to identify potential controls on long‐term mean concentrations and find that lithologic and land cover controls are significant predictors for many analytes. The picture that emerges is one in which, on event and interannual timescales, weathering‐derived stream solute concentrations are chemostatically buffered by groundwater storage and fast chemical reactions, but each catchment's chemostatic “set point” reflects site‐to‐site differences in climatically driven evolution of the critical zone. In contrast to these weathering products, some nutrients and particulates are often near‐chemostatic across all timescales, and their long‐term mean concentrations correlate more strongly with land use than climatic characteristics.  相似文献   

New method of quantitatively describing drainage areas     

Lars HÅkanson  Tord Andersson  Ake Nilsson 《Environmental Geology》1990,15(1):61-69

The aim was to introduce a new method, the DAZ method (drainage area zonation), to quantify environmental parameters, such as bedrocks, soil type, and land use in drainage areas. The work was carried out within the framework of the Swedish project Liming—mercury. Two important points in the project are that there are quantifiable relationships between the character of the drainage area and the lake and that several limnological and morphometric parameters may have an impact on the Hg content in fish. The DAZ method accounts for the fact that, for example, a certain soil type does not have an even distribution in the whole drainage area. To get a simple yet relevant measure of the influence of, for example, soil type on the lake character, the drainage areas were divided into zones using a special transparent paper placed on the map. The method gives normalized values depending on: (1) distance between the object and the given lake, (2) the main direction of water flow in the drainage area, and (3) the area of the environmental parameter (for example, area of bedrock). In the DAZ method, dot counting is used for determination of area. The dot-counting method has been compared with other methods for area determination (planimeter and square counting). Dot counting is the fastest and the counting of squares the most time consuming. The statistical reliabilities of the dot method and the planimeter method were compared. The planimeter is best for large homogeneous objects. Dot counting, on the other hand, is very well suited for heterogeneous objects. The statistical certainty of area determination depends on size, heterogeneity, and form of the objects, as well as the time dedicated to the determination. A nomogram is also given, which illustrates the relationship between the number of counts, that is, the number of times the transparent dotted paper is put on the map and the dots counted, the error in the area determination, and the statistical reliability.  相似文献   

Improving BeiDou real-time precise point positioning with numerical weather models   总被引：1，自引：1，他引：0  

Cuixian Lu  Xingxing Li  Florian Zus  Robert Heinkelmann  Galina Dick  Maorong Ge  Jens Wickert  Harald Schuh 《Journal of Geodesy》2017,91(9):1019-1029

Precise positioning with the current Chinese BeiDou Navigation Satellite System is proven to be of comparable accuracy to the Global Positioning System, which is at centimeter level for the horizontal components and sub-decimeter level for the vertical component. But the BeiDou precise point positioning (PPP) shows its limitation in requiring a relatively long convergence time. In this study, we develop a numerical weather model (NWM) augmented PPP processing algorithm to improve BeiDou precise positioning. Tropospheric delay parameters, i.e., zenith delays, mapping functions, and horizontal delay gradients, derived from short-range forecasts from the Global Forecast System of the National Centers for Environmental Prediction (NCEP) are applied into BeiDou real-time PPP. Observational data from stations that are capable of tracking the BeiDou constellation from the International GNSS Service (IGS) Multi-GNSS Experiments network are processed, with the introduced NWM-augmented PPP and the standard PPP processing. The accuracy of tropospheric delays derived from NCEP is assessed against with the IGS final tropospheric delay products. The positioning results show that an improvement in convergence time up to 60.0 and 66.7% for the east and vertical components, respectively, can be achieved with the NWM-augmented PPP solution compared to the standard PPP solutions, while only slight improvement in the solution convergence can be found for the north component. A positioning accuracy of 5.7 and 5.9 cm for the east component is achieved with the standard PPP that estimates gradients and the one that estimates no gradients, respectively, in comparison to 3.5 cm of the NWM-augmented PPP, showing an improvement of 38.6 and 40.1%. Compared to the accuracy of 3.7 and 4.1 cm for the north component derived from the two standard PPP solutions, the one of the NWM-augmented PPP solution is improved to 2.0 cm, by about 45.9 and 51.2%. The positioning accuracy for the up component improves from 11.4 and 13.2 cm with the two standard PPP solutions to 8.0 cm with the NWM-augmented PPP solution, an improvement of 29.8 and 39.4%, respectively.  相似文献   

Enhanced incoherent scatter plasma lines     

H. Nilsson  S. Kirkwood  J. Lilensten  M. Galand 《Annales Geophysicae》1997,14(12):1462-1472

Detailed model calculations of auroral secondary and photoelectron distributions for varying conditions have been used to calculate the theoretical enhancement of incoherent scatter plasma lines. These calculations are compared with EISCAT UHF radar measurements of enhanced plasma lines from both the E and F regions, and published EISCAT VHP radar measurements. The agreement between the calculated and observed plasma line enhancements is good. The enhancement from the superthermal distribution can explain even the very strong enhancements observed in the auroral E region during aurora, as previously shown by Kirk-wood et al. The model calculations are used to predict the range of conditions when enhanced plasma lines will be seen with the existing high-latitude incoherent scatter radars, including the new EISCAT Svalbard radar. It is found that the detailed structure, i.e. the gradients in the suprathermal distribution, are most important for the plasma line enhancement. The level of superthermal flux affects the enhancement only in the region of low phase energy where the number of thermal electrons is comparable to the number of suprathermal electrons and in the region of high phase energy where the suprathermal fluxes fall to such low levels that their effect becomes small compared to the collision term. To facilitate the use of the predictions for the different radars, the expected signal-to-noise ratios (SNRs) for typical plasma line enhancements have been calculated. It is found that the high-frequency radars (Søndre Strømfjord, EISCAT UHF) should observe the highest SNR, but only for rather high plasma frequencies. The VHP radars (EISCAT VHP and Svalbard) will detect enhanced plasma lines over a wider range of frequencies, but with lower SNR.  相似文献   

Recovery of Danish Coastal Ecosystems After Reductions in Nutrient Loading: A Holistic Ecosystem Approach     

Bo Riemann  Jacob Carstensen  Karsten Dahl  Henrik Fossing  Jens W. Hansen  Hans H. Jakobsen  Alf B. Josefson  Dorte Krause-Jensen  Stiig Markager  Peter A. Stæhr  Karen Timmermann  Jørgen Windolf  Jesper H. Andersen 《Estuaries and Coasts》2016,39(1):82-97

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Intersex in feral marine and freshwater fish from northeastern Germany   总被引：1，自引：0，他引：1  

Gercken J  Sordyl H 《Marine environmental research》2002,54(3-5):651-655

A histopathological assessment of the gonad of male fish was performed as part of biological field studies carried out in coastal waters and small rivers in Mecklenburg-Western Pomerania, northeastern Germany. In the marine environment the eelpout (Zoarces viviparus) was selected as sentinel species. The three spined stickleback (Gasterosteus aculeatus) and perch (Perca fluviatilis) were chosen at freshwater locations. Histopathology of the testis revealed the presence of intersexuality in specimens of all three species. The intersex condition was defined by the simultaneous presence of primary oocytes within the apparently normal testis tissue. In comparison to stickleback and perch the eelpout exhibited the highest intersex prevalence and the most severe histological alterations. Fish with intersex were found at contaminated marine and freshwater stations as well as at sites with apparently little pollution. The findings suggest that feminised male fish were exposed to endocrine disrupting substances in the aquatic environment.  相似文献   

62kaBP以来湖光岩玛珥湖沉积物有机碳同位素记录及古气候环境意义   总被引：18，自引：1，他引：18  

刘强  顾兆炎  刘嘉麒  游海涛  吕厚远  储国强  祁向雷  Jens Mingram  Georg Schettler 《海洋地质与第四纪地质》2005,25(2):115-126

湖光岩玛珥湖HUG-B孔岩心记录了62kaBP以来的古气候、古环境变化信息。全岩有机碳同位素组成(δ^13CTOC)分析表明，62kaBP以来δ^3CTOC值变化比较明显，其变化范围为-28．5‰～-15．5％0。结合孢粉和有机地球化学指标进行综合分析，湖光岩玛珥湖δ^13CTOC变化曲线可划分为6个演化阶段：62～58和48～40．5kaBP两个时段的δ^13CTOC值偏负，沉积物中有机质主要来源于热带-亚热带地区的陆生C13森林植被，反映了温暖潮湿的气候环境；58～48和40．5～17．2kaBP期间δ^13CTOC值明显偏正，沉积物中有机质主要源自C4草本植物，反映了湖光岩地区有效降水量减少、干旱程度增加导致湖光岩玛珥湖湖面下降，大量C4草本植物生长在暴露的湖滨岸；17．2～4kaBP时段内δ^13CTOC值尽管存在更加频繁的波动，但总体呈现逐渐偏负的趋势，反映了暖湿和冷干气候多次交替但总体上逐渐变暖、变湿的气候环境；4kaBP以来δ^13CTOC值存在逐渐偏正的趋势，虽然不排除人类活动的影响，但很可能反映了干旱程度的再次增加。综合分析表明，有效降水量(降水量-蒸发量)是控制湖光岩玛珥湖地区C3／C4植物相对生物量变化的主导因素。湖光岩玛珥湖有机碳同位素的研究结果支持区域气候环境而不是大气CO2浓度变化是末期冰期以来热带低纬度地区C3／C4植被相对生物量变化的主要原因。  相似文献