Exact asymmetric slope distributions in stochastic Gauss–Lagrange ocean waves     

Georg Lindgren   《Applied Ocean Research》2009,31(1):65-73

The stochastic Lagrange wave model is a realistic alternative to the Gaussian linear wave model, which has been successfully used in ocean engineering for more than half a century. This paper presents exact slope distributions and other characteristic distributions at level crossings for symmetric and asymmetric Lagrange space and time waves. These distributions are given as expectations in a multivariate normal distribution, and they have to be evaluated by simulation or numerical integration. Interesting characteristic variables are: slopes obtained by asynchronous sampling in space or time, slopes in space or time, and horizontal particle velocity, when waves are observed when the water level crosses a predetermined level.  相似文献   

Effect of observation method on the perception of community structure and water quality in a brackish water ecosystem     

Tiia Möller  Jonne Kotta  & Georg Martin 《Marine Ecology》2009,30(S1):105-112

The EU Water Framework Directive is a Community legislative instrument in the field of environmental protection that establishes a common framework for keeping water quality at a favourable level. To implement the directive, classification systems need to be established that allow detection of human impacts at early stages and, thus, more effective management of coastal communities. Due to the spatial variability of communities, however, the results of any assessment are highly dependent on the selection of data. In this study we identified local spatial scales in which variability of macrophyte communities was maximised, quantified links between observed patterns of sediment types and communities and estimated how selection criteria impacted the outcome of the assessment of indicator class value in four different communities of the Northern Baltic Sea. The main findings of the study were that: (i) there were no clear local spatial scales in which the variability of benthic communities was maximised; (ii) hard-bottom communities were better predicted by the spatial arrangement of sediment characteristics than soft-bottom communities; (iii) the selection of method had no effect on the estimates of macrophyte cover and indicator class; but (iv) method impacted independently of habitat type on error estimates of macrophyte cover and indicator class. To conclude, in such homogeneous and low diversity macrophyte communities it is preferable to use methods that result in lower error estimates of algal coverage and, thus, result in lower uncertainties of estimates in the water quality class.  相似文献   

Carrier phase wind-up in GPS reflectometry   总被引：1，自引：0，他引：1  

Georg Beyerle 《GPS Solutions》2009,13(3):191-198

Changes in GPS transmitter and receiver antenna orientations induce variations in observed carrier phase values. An analytic formula for this well-known carrier phase wind-up correction is derived which generalizes a previous result. In addition, it is shown that in GPS reflectometry the wind-up values of direct and coherently reflected rays may differ by up to several centimeters. The results are discussed on the basis of simulated measurements.  相似文献