Impact of fish distribution and species composition on the relationship between acoustic and swept-area estimates of fish density     

Aglen  Asgeir 《ICES Journal of Marine Science》1996,53(2):501-505

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Particulate n-alkanes and fatty acids in the Changjiang river system     

WU Ying  ZHANG Jing  LIU Sumei  ZHANG Zaifeng  CHEN Hongtao  XIONG Hui 《海洋学报(英文版)》2007,26(2):36-48

Particulate samples were collected from the Changjiang river system during a flood period, in May 1997, and POC, stable isotope and lipids associated with particles were examined. Results showed the decrease (0.84% ～ 1.88%) of organic carbon content from the upper reaches to the estuary.δ13C values of particulate organic carbon was in the range of -24.9×10-3 to -26.6×10-3, which were close to the isotopic signature of continental C3 vegetation. Total particulate n-alkanes concentrations varied from 1.4 to 10.1μg/dm3,or from 23.7 to 107μg/g of total suspended matter. Fatty acids were present in all the samples, from 1.4 to 5.4μg/dm3, with saturated and unsaturated straight-chain and branched compounds in the carbon number range from C12 to C30. Both δ13C and the ratio of carbon content to nitrogen content indicate the predominance of terrestrial inputs (soil organic matter) among the particles. The biomarker approach has been used to identify the relative portion of terrigenous and autochthonous fraction in the particulate samples. The distribution of fatty acids suggests a striking phytoplanktonic and microbial signal in most particle samples. The terrestrial alkanes are used to estimate the contribution of terrestrial inputs along the mainstream.  相似文献   

The retrieval of the nonlinear random waves from the non-Gaussian characteristics of the sea surface elevation distribution     

Liu Xin''an  Huang Peiji 《海洋学报(英文版)》1993,12(4):499-510

In this paper, without recourse to the nonlinear dynamical equations of the waves, the nonlinear random waves are retrieved from the non-Gaussian characteristic of the sea surface elevation distribution. The question of coincidence of the nonlinear wave profile, spectrum and its distributions of maximum (or minimum) values of the sea surface elevation with results derived from some existing nonlinear theories is expounded under the narrow-band spectrum condition. Taking the shoaling sea wave as an example, the nonlinear random wave process and its spectrum in shallow water are retrieved from both the non-Gaussian characteristics of the sea surface elevation distribution in shallow water and the normal sea waves in deep water and compared with the values actually measured. Results show that they can coincide with the actually measured values quite well, thus, this can confirm that the method proposed in this paper is feasible.  相似文献   

Profile Evolution and Energy Dissipation for Internal Soliton Transmitting over Different Submarine Ridges     

Chen-Yuan CHEN I-Fan TSENG Hsien-Chueh Peter YANG Cheng-Wu CHEN Tsung-Hao CHEN 《中国海洋工程》2006,20(4):585-594

1 .IntroductionWhile surface solitary waves arefoundin many physical phenomena (Chouand Shih,1996 ;Chouand Quyang,1999 ;Chouet al .,2003 ; Chenet al .,2004 ; Wang,2004 ;Tsenget al .,2005) ,internal solitary waves (ISWs) have been observed since the beginning of the 20th century.In fact ,some internal waves have alarge enoughamplitudeto cause consequence onthe surface .Hence obser-vation of the oceansurface may helpto detect the activities of internal waves . We require observationsthrough…  相似文献   

Shenzhou-4 spaceborne altimeter waveform processing and significant wave height retrieval     

JI Yonggang  ZHANG Jie  ZHANG Youguang  MENG Junmin 《海洋学报(英文版)》2006,25(3):40-47

1IntroductionSZ-4spaceborne,launched on30December2002,is the fourth unmanned spaceborne of China.Multimode microwave remote sensor is its primaryload,of which the altimeter mode is the most impor-tant one.During about five months,a large numberofSZ-4altim…  相似文献   

Determination of wave energy dissipation factor and numerical simulation of wave height in the surf zone     

Y. H. Zheng  Y. M. Shen  X. G. Wu  Y. G. You 《Ocean Engineering》2004,31(8-9):1083-1092

Based on the time-dependent mild slope equation including the effect of wave energy dissipation, an expression for the energy dissipation factor is derived in conjunction with the wave energy balance equation. The wave height of regular and irregular waves is numerically simulated by use of the parabolic mild slope equation considering the energy dissipation due to wave breaking. Comparison of numerical results with experimental data shows that the expression for the energy dissipation factor is reasonable. The effects of the wave breaking coefficient on the breaking point and the distribution of wave height after breaking are discussed through the study of a specific experimental topography.  相似文献   

黄河三角洲区域地表形变监测研究          下载免费PDF全文

韩红花 《山东国土资源》2020,36(11)

由于地壳运动、地下水使用及矿床开采等因素的影响,会造成地表的形变,特别是垂直（高程）方向影响更大。为了维持高程基准的现势性,本文提出了一种以InSAR地表形变监测和水准测量相结合的方法,实现地表形变区高程基准动态维持。并以黄河三角洲区域为例,对2种成果精度进行了对比验证,水准测量和InSAR监测结果基本相符,可实现2种技术手段融合以获取点、面综合的高程变化信息。  相似文献   

Nonlinear response of runoff to atmospheric freezing level height variation based on hybrid prediction models     

Yanhua Qin  Xun Sun  Yaning Chen  Xun Shi 《水文科学杂志》2013,58(13):1556-1572

ABSTRACT

We use data on the freezing level height (FLH) and summer runoff in the Hotan River, China, from 1960 to 2013, to analyse the nonlinear relationships of atmospheric and hydrological factors at different time scales, by employing three nonlinear decomposition methods. Six hybrid prediction models are established by combining linear regression and back-propagation artificial neural network (BPANN) models. The decomposition results by three nonlinear methods are compared, indicating that the extreme-point symmetric mode decomposition (ESMD) method ensures the best prediction capacity. The runoff and FLH have periods of 3 and 6 years, respectively, at the inter-annual scale, which pass the significance test of 0.05 (P < 0.05) by using the Monte Carlo method, although there were slight differences in the periods at the inter-decadal scale. Among the six models, ESMD-BPANN exhibits the highest accuracy, with good reliability and resolution, according to several performance indicators. The ESMD-BPANN model is thus selected for the simulation and prediction of runoff.  相似文献   

Measuring snow ablation rates in alpine terrain with a mobile multioffset ground‐penetrating radar system          下载免费PDF全文

Nena Griessinger  Franziska Mohr  Tobias Jonas 《水文研究》2018,32(21):3272-3282

Ground‐penetrating radar (GPR) has become a promising technique in the field of snow hydrological research. It is commonly used to measure snow depth, density, and water equivalent over large distances or along gridded snow courses. Having built and tested a mobile lightweight set‐up, we demonstrate that GPR is capable of accurately measuring snow ablation rates in complex alpine terrain. Our set‐up was optimized for efficient measurements and consisted of a multioffset radar with four pairs of antennas mounted to a plastic sled, which was small enough to permit safe and convenient operations. Repeated measurements at intervals of 2 to 7 days were taken during the 2014/2015 winter season along 10 profiles of 50 to 200 m length within two valleys located in the eastern Swiss Alps. Resulting GPR‐based data of snow depth, density, and water equivalent, as well as their respective change over time, were in good agreement with concurrent manual measurements, in particular if accurate alignment between repeated overpasses could be achieved. Corresponding root‐mean‐square error (RMSE) values amounted to 4.2 cm for snow depth, 17 mm for snow water equivalent, and 22 kg/m³ for snow density, with similar RMSE values for corresponding differential data. With this performance, the presented radar set‐up has the potential to provide exciting new and extensive datasets to validate snowmelt models or to complement lidar‐based snow surveys.  相似文献   

How to evaluate the quality of coarse‐resolution DEM‐derived drainage networks          下载免费PDF全文

Thâmara Martins Ismael Sousa  Adriano Rolim Paz 《水文研究》2017,31(19):3379-3395

The quality of digital elevation model (DEM)‐derived river drainage networks (RDNs) is influenced by DEM quality, basin physical characteristics, scale, and algorithms used; these factors should not be neglected. However, few research studies analyse the different evaluation approaches used in the literature with respect to adequacy, meaning of the results, advantages, and limitations. Focusing on coarse‐resolution networks, this paper reviews the use of these techniques and offers new insights on these issues. Additionally, we propose adaptations for selected metrics and discuss distinct interpretations for the evaluation of RDNs derived at different spatial resolutions (1, 5, 10, 20, and 30 km) considering the Uruguay River basin (206,000 km²) as a case study. The results demonstrate that lumped basin/river characteristics and basin delineation analysis should not be used as evaluation criteria for RDN quality; however, some of these metrics offer useful complementary information. Percentage of the DEM‐derived RDN within a uniform buffer placed around a river network considered as reference and mean separation distance between these two networks are more suitable metrics, but the former is insensitive to serious errors. The change in reference from a fine‐scale network to a coarse‐resolution manual tracing network significantly augments the discrepancy of these largest errors when the mean distance metric was applied, and visual comparison analysis is necessary to interpret the results for other metrics. We recommend the use of the mean distance metric in combination with a detailed visual assessment, the importance of which increases as the resolution coarsens. In both cases, the impact of network quality can be further refined by quantifying the basin shape and river length errors.  相似文献