Statistical analysis of low-flow based on short time series. The case of Wallonia

in Geophysical Research Abstracts (2011), 13

The floods have always been the main concern resulting of extreme weather conditions. Now droughts and low flows are more and more recognized as risk situations due to the huge consequences of water ... [more ▼]

The floods have always been the main concern resulting of extreme weather conditions. Now droughts and low flows are more and more recognized as risk situations due to the huge consequences of water shortage. Furthermore, the changing climate context constitutes a new threat even if the uncertainty in low-flows evolution remains high. In Wallonia (Southern part of Belgium), a knowledge gap remains on statistical analysis of low-flows. In this paper, we present a study of historical data in Walloon Region and the first steps of their statistical analysis. Wallonia is one of the three regions of Belgian federal state. It covers an area of 17000 km² and spreads on 4 districts (Meuse, Escaut, Rhin, Senne). The watercourses are divided in navigable watercourses (700km), not navigable watercourses that are listed in 3 categories (14300km) and streams that are not navigable and not listed (4000km). Hydrological monitoring has a short history in Wallonia. The first monitoring site was installed in 1960. It consisted in a limnimetric scale and daily manual readings. Since 1974, hourly data are recorded. The number of measurement sites reached 244 stations in 2011. About 60 % of the monitoring sites have less than 20 years of hourly data. A qualitative analysis of monitoring stations led us to disregard 184 stations. The main quality problems were important discharge rating curve extrapolation, algae development in summer or low flow inferior to 5l/s. In preparation for a statistical analysis of low-flows, the old manual daily readings were analyzed. Unusable in high flow situations, they still hold practical and usable information during drought. This analysis allowed us to extend the registration period up of 7 stations and to recover 16 stations. There were lots of missing data during the 1960-1994 period, due to a poor management of the monitoring network. A yearly hydrograph analysis leads us to keep years of partial measurement when the gaps were found to be out of the low-flow period. The monitoring sites presenting more than 20 years of readings were selected for the statistical analysis. A homogeneity test was performed. Finally 64 out of 244 monitoring sites are kept for the frequency analysis. The indicators used to characterize low-flows are the popular Q95 and MAM7. Five below bounded distributions are tested with the HYFRAN software: Weibull (2 parameters), log-normal 2 parameters and 3 parameters, Gamma and Pearson type III. The parameters of the laws are estimated by the maximum likelihood estimation. The selection of the three best laws is performed for each site thanks to three Bayesian criterions proposed by HYFRAN. Then the distribution that fits the best the data is visually chosen. The results of the adjustment method are the same for the two indicators. The Gamma distribution is the most used followed by the lognormal with 2 parameters. However in some cases a law of three parameters is more appropriate. This preliminary work gives a first analysis of low-flows statistics in Wallonia. Yet a lot of missing data or short recording duration still limits our knowledge, this analysis allows us to progress towards best management practices in rivers and watersheds. [less ▲]

Statistical analysis of modulated codes for robot positioning -- Application to BeAMS

Report (2013)

Positioning is a fundamental issue for mobile robots. Therefore, a performance analysis is suitable to determine the behavior of a system, and to optimize its working. Unfortunately, some systems are only ... [more ▼]

Positioning is a fundamental issue for mobile robots. Therefore, a performance analysis is suitable to determine the behavior of a system, and to optimize its working. Unfortunately, some systems are only evaluated experimentally, which makes the performance analysis and design decisions very unclear. In [4], we have proposed a new angle measurement system, named BeAMS, that is the key element of an algorithm for mobile robot positioning. BeAMS introduces a new mechanism to measure angles: it detects a beacon when it enters and leaves an angular window. A theoretical framework for a thorough performance analysis of BeAMS has been provided to establish the upper bound of the variance, and to validate this bound through experiments and simulations. It has been shown that the estimator derived from the center of this angular window provides an unbiased estimate of the beacon angle. This document complements our paper by going into further details related to the code statistics of modulated signals in general, with an emphasis on BeAMS. In particular, the probability density function of the measured angle has been previously established with the assumption that there is no correlation between the times a beacon enters the angular window or leaves it. This assumption is questionable and, in this document, we reconsider this assumption and establish the exact probability density function of the angle estimated by BeAMS (without this assumption). The conclusion of this study is that the real variance of the estimator provided by BeAMS was slightly underestimated in our previous work. In addition to this speci c result, we also provide a new and extensive theoretical approach that can be used to analyze the statistics of any angle measurement method with beacons whose signal has been modulated. To summarize, this technical document has four purposes: (1) to establish the exact probability density function of the angle estimator of BeAMS, (2) to calculate a practical upper bound of the variance of this estimator, which is of practical interest for calibration and tracking (see Table 1, on page 13, for a summary), (3) to present a new theoretical approach to evaluate the performance of systems that use modulated (coded) signals, and (4) to show how the variance evolves exactly as a function of the angular window (while re- maining below the upper bound). [less ▲]

Statistical analysis of spherical data -- N. I. Fisher et al.

in Ciel et Terre (1988), 104

Not Available

A statistical analysis of the location and width of Saturn's aurora, and implications for magnetospheric dynamics

Conference (2006, September)

We present the results of a statistical analysis of the location of commonly-occurring auroral features in Saturn's southern polar ionosphere. Using a magnetospheric model, modified for Saturn from a data ... [more ▼]

We present the results of a statistical analysis of the location of commonly-occurring auroral features in Saturn's southern polar ionosphere. Using a magnetospheric model, modified for Saturn from a data-based terrestrial model (Tsyganenko, 1996), we estimate the region in the equatorial plane of the outer magnetosphere that maps to the observed aurora. We then discuss the possible magnetospheric processes that may cause these auroral emissions. [less ▲]

Statistical Analysis of the night weather conditions favouring the epidemic of the brown rust in the Grand-Duchy of Luxemburg.

in Italian Journal of Agronomy [=IJA] = Rivista di Agronomia (2008), 3(3), 611-612

A statistical analysis of the theoretical results obtained for concerted 1,3-dipolar cycloaddition

in Journal of Molecular Structure : Theochem (1982), 89(1-2), 147-163

Statistical analysis of validation method revisited : the need to use the total error

Conference (2003)

Statistical and Non-statistical Reactions in Energy Selected Fluoromethane Ions.

in Chemical Physics (1995), 201

The unimolécular reactions of the fluoromethane ion have been investigated by the threshold photoelectron photoion coincidence technique (TPIPECO). The breakdown curves have been measured in the energy ... [more ▼]

The unimolécular reactions of the fluoromethane ion have been investigated by the threshold photoelectron photoion coincidence technique (TPIPECO). The breakdown curves have been measured in the energy range between the adiabatic ionization potential of 12.53 eV and 21 eV. In this enery range the formation of the CH2F+, CHF+, CH2+, CH3+, and CF+ fragment ions is observed. The appearance energies (AE) for these ions at 300K are 13.2, 13.91, 13.93, 14.51 and <17.7 eV respectively. The 0K threshold energy for the formation of CH2F+ ions is 13.37 eV. Two different pathways for the unimolecular reaction of the fluoromethane ion can be distinguished.The reaction proceeding through the electronic ground state of the ion is entirely statistical. In contrast to this the reaction occurring through the first electronic excited state shows non-statistical behaviour. The two pathways are distinguished via the kinetic energy released in the respective dissociation channels. While all thermodynamically allowed reaction channels are observed on the ion ground state potential, the first excited state seems to decay predominantly by F loss reaction. [less ▲]

Statistical approximations in the study of wave packet dynamics for non-adiabatic intramolecular processes induced by a coherent excitation

in Molecular Physics (1987), 61(4), 981-997

Statistical considerations for the validation of an ELISA assay as biomarker

Conference (2007)