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Previous issue date: 2015-08-17 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico (CNPq) / Gases-tra?o s?o importantes para nosso ambiente, mesmo se manifestando apenas em ?tra?os?, mas suas concentra??es devem ser monitoradas, para que quaisquer interven??es necess?rias sejam tomadas a tempo. Condi??es apropriadas para nossas vidas residem dentro de limites inferiores e superiores destes gases, por isso seu monitoramento ? essencial hoje em dia e diversas t?cnicas podem ser usadas para este fim. Uma delas ? a espectroscopia de absor??o ?ptica diferencial (DOAS), que consiste de uma regress?o - o m?todo cl?ssico usa m?nimos quadrados - para determinar a concentra??o dos gases-tra?o. Para melhorar os resultados, diversos estudos buscaram abordagens alternativas. Alguns tentaram pr?-processar o sinal, atrav?s de uma remo??o de ru?do, e.g., usando transformada wavelet discreta (DWT). Este trabalho apresenta um estudo semi-emp?rico para encontrar a DWT com o melhor desempenho para remo??o de ru?do. Dentre diversas fam?lias conhecidas, buscou-se aquelas cuja remo??o de ru?do foram melhor, preservando caracter?sticas principais do sinal original, ent?o com a redu??o do ru?do, o res?duo ap?s a regress?o tamb?m diminui. A an?lise leva em conta o n?vel de decomposi??o wavelet, o limiar aplicado nos coeficientes de detalhe e como aplic?-los - limiariaza??o abrupta ou suave. Os sinais usados prov?m de um banco de dados aberto e online com sinais caracter?sticos de gases-tra?o usualmente estudados. / Trace gases are important to our environment even though their presence comes
only by ?traces?, but their concentrations must be monitored, so any necessary interventions
can be done at the right time. There are some lower and upper boundaries
which produce nice conditions for our lives and then monitoring trace gases comes
as an essential task nowadays to be accomplished by many techniques. One of them
is the differential optical absorption spectroscopy (DOAS), which consists mathematically
on a regression - the classical method uses least-squares - to retrieve the trace
gases concentrations. In order to achieve better results, many works have tried out
different techniques instead of the classical approach. Some have tried to preprocess
the signals to be analyzed by a denoising procedure - e.g. discrete wavelet transform
(DWT). This work presents a semi-empirical study to find out the most suitable DWT
family to be used in this denoising. The search seeks among many well-known families
the one to better remove the noise, keeping the original signal?s main features,
then by decreasing the noise, the residual left after the regression is done decreases
too. The analysis take account the wavelet decomposition level, the threshold to be
applied on the detail coefficients and how to apply them - hard or soft thresholding.
The signals used come from an open and online data base which contains characteristic
signals from some trace gases usually studied.
| Identifer | oai:union.ndltd.org:IBICT/oai:repositorio.ufrn.br:123456789/21039 |
| Date | 17 August 2015 |
| Creators | Ara?jo, Boanerges Victor Soares de |
| Contributors | 79090095420, http://lattes.cnpq.br/1982228057731254, Martins, Allan de Medeiros, 01979076448, http://lattes.cnpq.br/4402694969508077, Braz, Erico Cadineli, 01324025484, http://lattes.cnpq.br/9382571991103772, Silveira, Luiz Felipe de Queiroz, 02863206494, http://lattes.cnpq.br/4139452169580807, Campos, Antonio Luiz Pereira de Siqueira |
| Publisher | Universidade Federal do Rio Grande do Norte, PROGRAMA DE P?S-GRADUA??O EM ENGENHARIA EL?TRICA E DE COMPUTA??O, UFRN, Brasil |
| Source Sets | IBICT Brazilian ETDs |
| Language | Portuguese |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, info:eu-repo/semantics/masterThesis |
| Source | reponame:Repositório Institucional da UFRN, instname:Universidade Federal do Rio Grande do Norte, instacron:UFRN |
| Rights | info:eu-repo/semantics/openAccess |
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