Line transect abundance estimation with uncertain detection on the trackline

Bibliography: leaves 225-233.After critically reviewing developments in line transect estimation theory to date, general likelihood functions are derived for the case in which detection probabilities are modelled as functions of any number of explanatory variables and detection of animals on the trackline (i.e. directly in the observer's path) is not certain. Existing models are shown to correspond to special cases of the general models. Maximum likelihood estimators are derived for some special cases of the general model and some existing line transect estimators are shown to correspond to maximum likelihood estimators for other special cases. The likelihoods are shown to be extensions of existing mark-recapture likelihoods as well as being generalizations of existing line transect likelihoods. Two new abundance estimators are developed. The first is a Horvitz-Thompson-like estimator which utilizes the fact that for point estimation of abundance the density of perpendicular distances in the population can be treated as known in appropriately designed line transect surveys. The second is based on modelling the probability density function of detection probabilities in the population. Existing line transect estimators are shown to correspond to special cases of the new Horvitz-Thompson-like estimator, so that this estimator, together with the general likelihoods, provides a unifying framework for estimating abundance from line transect surveys

Nonparametric Stochastic Generation of Daily Precipitation and Other Weather Variables

Traditional stochastic approaches for synthetic generation of weather variables often assume a prior functional form for the stochastic process, are often not capable of reproducing the probabilistic structure present in the data, and may not be uniformly applicable across sites. In an attempt to find a general framework for stochastic generation of weather variables, this study marks a unique departure from the traditional approaches, and ushers in the use of data-driven nonparametric techniques and demonstrates their utility. Precipitation is one of the key variables that drive hydrologic systems and hence warrants more focus . In this regard, two major aspects of precipitation modeling were considered: (I) resampling traces under the assumption of stationarity in the process, or with some treatment of the seasonality, and (2) investigations into interannual and secular trends in precipitation and their likely implications. A nonparametric seasonal wet/dry spell model was developed for the generation of daily precipitation. In this the probability density functions of interest are estimated using non parametric kernel density estimators. In the course of development of this model, various nonparametric density estimators for discrete and continuous data were reviewed, tested, and documented, which resulted in the development of a nonparametric estimator for discrete probability estimation. Variations in seasonality of precipitation as a function of latitude and topographic factors were seen through the non parametric estimation of the time-varying occurrence frequency. Nonparametric spectral analysis, performed on monthly precipitation, revealed significant interannual frequencies and coherence with known atmospheric oscillations. Consequently, a non parametric, nonhomogeneous Markov chain for modeling daily precipitation was developed that obviated the need to divide the year into seasons. Multivariate nonparametric resampling technique from the nonparametrically fitted probability density functions, which can be likened to a smoothed bootstrap approach, was developed for the simulation of other weather variables (solar radiation, maximum and minimum temperature, average dew point temperature, and average wind speed). In this technique the vector of variables on a day is generated by conditioning on the vector of these variables on the preceding day and the precipitation amount on the current day generated from the wet/dry spell model

A geostatistical approach for quantification of contaminant mass discharge uncertainty using multilevel sampler measurements

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95058/1/wrcr11058.pd

Modelação numérica do impacto dos esporões na hidrodinâmica costeira

Mestrado em Meteorologia e Oceanografia FísicaA hidrodinâmica costeira engloba uma variedade de processos ligados à propagação das ondas em direcção à costa, empolamento e eventual rebentação. Fenómenos como a refracção, difracção, reflexão e a própria rebentação possuem características não lineares, o que dificulta o seu estudo e modelação. A hidrodinâmica influencia também a morfodinâmica das praias, área de investigação em grande foco actualmente. A modelação numérica constitui uma ferramenta importante na investigação dessas dinâmicas e fenómenos envolvidos. Torna-se, então, necessário calibrar os modelos para que sejam capazes de representar correctamente os processos que actuam na costa e simular alterações futuras. Numa primeira fase desta tese, resultados obtidos com o modelo COULWAVE são comparados com dados de campo de alturas significativas de onda e de velocidades horizontais, recolhidos na praia da Cornélia, na Costa da Caparica. Os resultados são bastante promissores, particularmente para as alturas significativas de onda medidas antes da rebentação. Os esporões são estruturas transversais à costa projectadas para reter sedimentos em transporte na corrente de deriva litoral, com o objectivo de minorar a erosão em trechos específicos da linha de costa. Estas estruturas são frequentemente colocadas em costas arenosas e têm associado um importante impacto na hidro e morfodinâmica costeira, uma vez que se estendem perpendicularmente à costa, em direcção ao largo. Diversos constrangimentos estruturais e ambientais, entre os quais o comprimento e orientação do esporão, a altura das ondas incidentes e o nível da superfície do mar, determinam esse impacto. Neste contexto, a segunda fase desta tese consiste na avaliação, através da modelação numérica com o já referido modelo COULWAVE, do impacto dos esporões na altura significativa das ondas e velocidade horizontal junto à costa, considerando diferentes cenários. Os vários cenários correspondem a diferentes comprimentos (L=200 m, L=250 m, L=300 m e L=400 m) e orientações ( 10º, 15º, 25º e 30º) do esporão, diferentes alturas significativas das ondas incidentes (Hs=1 m, Hs=1.5 m, Hs=2.0 m e Hs=3.0 m) e diferentes níveis da superfície do mar (SSL=0.50 m, SSL=0.75 m, SSL=1.50 m e SSL=2.40 m). Verifica-se que a altura das ondas incidentes é o factor que adquire uma maior relevância no impacto do esporão na hidrodinâmica costeira, seguido do nível da superfície do mar, comprimento do esporão e, finalmente, da orientação do esporão.Nearshore hydrodynamics involves a variety of processes as waves propagate towards the coast, start shoaling and eventually break. Phenomena such as refraction, diffraction, reflection and the breaking itself are highly nonlinear, and thus difficult to study and model. The hydrodynamics will further play a role on the morphodynamics of beaches, a subject undergoing intensive research nowadays. Numerical modelling presents a useful tool to investigate these dynamics and involved phenomena. It is then necessary to calibrate models to accurately represent the processes acting on the coast and be able of simulating future changes. This thesis begins with the comparison of COULWAVE model results with field data from Cornélia beach, in Costa da Caparica, for both significant wave height and horizontal velocity. Results are quite promising, especially for significant wave height values measured before wave breaking. Groins are cross-shore structures projected to retain sediments from the longshore drift, to attenuate the erosion of specific coastline stretches. Frequently employed in sandy coasts, these structures are expected to have an important impact on nearshore hydrodynamics and morphodynamics, as they extend seawards, approximately perpendicularly to the coast. Several structural and environmental factors condition that impact, such as groin length and orientation relatively to the shoreline, and incident wave height and sea-surface level. Hence, in the second phase of this thesis, it is performed an evaluation, through numerical modelling with COULWAVE model, of the impact of groins in significant wave height and horizontal velocity nearshore, under different scenarios. The different scenarios assumed different groin lengths (L=200 m, L=250 m, L=300 m and L=400 m) and orientations ( 10º, 15º, 25º and 30º), different significant heights of incident waves (Hs=1.0 m, Hs=1.5 m, Hs=2.0 m and Hs=3.0 m) and different sea-surface levels (SSL=0.50 m, SSL=0.75 m, SSL=1.50 m e SSL=2.40 m). Incident wave height is found to be a preponderant factor on groin impact in nearshore hydrodynamics, followed by sea-surface level, groin length and, finally, groin orientation

Exploring the possible role of small scale terrain drag on stable boundary layers over land

This paper addresses the possible role of unresolved terrain drag, relative to the turbulent drag on the development of the stable atmospheric boundary layer over land. Adding a first-order estimate for terrain drag to the turbulent drag appears to provide drag that is similar to the enhanced turbulent drag obtained with the so-called long-tail mixing functions. These functions are currently used in many operational models for weather and climate, although they lack a clear physical basis. Consequently, a simple and practical quasi-empirical parameterization of terrain drag divergence for use in large-scale models is proposed and is tested in a column mode. As an outcome, the cross-isobaric mass flow (a measure for cyclone filling) with the new scheme, using realistic turbulent drag, appears to be equal to what is found with the unphysical long-tail scheme. At the same time, the new scheme produces a much more realistic less-deep boundary layer than is obtained by using the long-tail mixing function

Effects of the 2003 European heatwave on the Central Mediterranean Sea: surface fluxes and the dynamical response

International audienceThe effects of the 2003 European heatwave on the sea surface layer of the Central Mediterranean were studied using a regional 3-D ocean model. The model was used to simulate the period 2000 to 2004 and its performance was validated using remotely-sensed and in situ data. Analysis of the results focused on changes in the Sea Surface Temperature (SST) and on changes to the surface and sub-surface current field. This permitted us to identify and quantify the anomalies of atmospheric and sea surface parameters that accompanied the heatwave. The dominant annual cycle in each variable was first removed and a wavelet analysis then used to locate anomalies in the time-frequency domain. We found that the excess heating affecting the sea surface in the summer of 2003 was related to a significant increase in air temperature, a decrease in wind stress and reduction of all components of the upward heat flux. The monthly averages of the model SST were found to be in good agreement with remotely-sensed data during the period studied, although the ocean model tended to underestimate extreme events. The spatial distribution of SST anomalies as well as their time-frequency location was similar for both the remotely-sensed and model temperatures. We also found, on the basis of the period of the observed anomaly, that the event was not limited to the few summer months of 2003 but was part of a longer phenomenon. Both the model results and experimental data suggest the anomalous heating mainly affected the top 15 m of ocean and was associated with strong surface stratification and low mixing. The skill of the model to reproduce the sub-surface hydrographic features during the heatwave was checked by comparison with temperature and salinity measurements. This showed that the model was generally in good agreement with observations. The model and observations showed that the anomalous warming also modified the currents in the region, most noticeably the Atlantic Ionian Stream (AIS) and the Atlantic Tunisian Current (ATC). The AIS was reduced in intensity and showed less meandering, mainly due to the reduced density gradient and low winds, while the ATC was enhanced in strength, the two currents appearing to modulate each other in order to conserve the total transport of Modified Atlantic Water