In this study, a one-dimensional model based on the Mellor and Yamada level 2.5 turbulence closure model was coupled with a biogeochemical model to investigate the inter-annual variation of biogeochemistry at the South-East Asian Time-series Study (SEATS) Site in the northern South China Sea (SCS) from 1997 to 2003. During the study period there were two El Niño Events and two La Niña Events. This study was focused on the hydrographic and biogeochemical conditions during these events. In order to better understand the model performance in the physical and biogeochemical aspects, numerical experiments were conducted to investigate the key processes. Numerical experiments by using idealized forcing conditions revealed that stronger wind stresses resulted in stronger cooling and deeper mixed layer. The model results were as sensitive to the initial density structure of the water column as to wind stress. Numerical experiments with the coupled model revealed that the biogeochemical results are insensitive to the initial biogeochemical conditions except the nitrate profile. Sensitivity tests indicated that primary production was sensitive to the remineralization rate constant for the detritus and parameters related to zooplankton, such as growth rate, grazing constant and mortality rate constant. It is less sensitive to iv aggregation constant of phytoplankton. The SEATS project of the National Center for Ocean Research provided data of sea surface chlorophyll-a (S-chl) concentrations, which were derived from SeaWiFS data for the period from Jan. 1997 to Dec. 2003 by calibrating against shipboard observations. The time-series showed decreases of mean S-chl by 35% and 9% below the climatological mean in the winter months (DJF) of the two El Niño Events. The negative S-chl anomalies corresponded to elevated sea surface temperature (SST) by 1.4oC and 0.4oC above the climatological mean, while the mean wind speed (WS) was reduced by 20% and 13%, and the surface heat exchange reverted from net loss to net gain or null. It is hypothesized that the anomalously low S-chl may have been caused by the weakened wind mixing and strengthened stratification. A 1-dimensional coupled physical-biogeochemical model was developed to test this hypothesis. The model driven by wind stress and surface heat fluxes successfully reproduced the seasonal cycles of S-chl and integrated primary productivity (IPP) as compared to shipboard observations and SeaWiFS data derived values, and predicted the negative anomalies of S-chl and IPP under the 1997-98 and 2002-03 El Niño conditions. However, the model-predicted strong positive anomalies of S-chl and IPP under the 1998-99 and 1999-2000 La Niña conditions, which brought v stronger wind and heat loss, were not substantiated by observations. Hydrographic conditions at the SEATS station indicated that, under La Niña conditions, unusual accumulation of warm and nutrient-depleted water occurred in the upper water column cancelled out the effect of stronger mixing. Therefore, the biogeochemical responses of the northern SCS to surface forcing during the recent El Niño/La Niña conditions displayed in a highly asymmetrical manner.

The single greatest uncertainty in seasonal water supply forecasts is the amount of precipitation falling after the forecast issue date. There has been a long history of attempting to incorporate seasonal climate forecasts into operational water supply forecasts. The skill of these precipitation forecasts remains low especially compared to highly confident snow-based streamflow forecasts. Early in the season (e.g., September-December), however, large-scale climate indices are the best available predictors of future water supplies. This dissertation suggests practical methods for issuing climate-based operational streamflow forecasts.This study also documents the existence of strong decadal trends in water supply forecast skill. Across the Western US, 1 April forecast skill peaked in the 1960-1970s and has been on the decline more recently. The high skill period was a very calm period in the Western US, with a near absence of extreme (wet or dry) spring precipitation events. In contrast, the period after 1980 has had the most variable, persistent, and skewed spring and summer streamflows in the modern record. Spring precipitation is also now more variable than it has been since at least the 1930s. This rise in spring precipitation variability in the Colorado/Rio Grande Basins and the Pacific Northwest is the likely cause behind the recent decline in water supply forecast skill.

Determination of safe yield of a water source is a basic aspect of water supply planning. In this report, the safe yield is defined as the maximum constant release from a reservoir that is possible during a selected drought period. The yield depends on drought magnitude and duration controlled by nature and ability to manipulate the releases through man made controls in the form of impoundment structures and regulations. A water supply system with two reservoirs in series and one in parallel in Spotsylvania County — the Hunting Run Reservoir, the Motts Run Reservoir (in series), and the Ni River Reservoir is considered to demonstrate the yield calculations. When several reservoirs are considered, the critical periods (defined as the period from full storage to empty condition) may not coincide and the system must be analyzed for the binding critical duration. A zero-one linear integer programming formulation is proposed to compute the system yield. The formulation accommodates the various storage and river flow dependent instream flow requirements. It is found that the water treatment plant capacity, instream flow requirements, and flows themselves limit the yield. Inflows to the reservoir are very important factor in determination of safe yield for any system of reservoirs. Changes in the precipitation hence inflows may cause a significant effect on the operation of reservoir. El Nino and La Nina phenomena, which occur due to changes in the atmospheric condition over the equatorial Pacific region, are found to affect the global climate in different studies. To examine the changes in the precipitation / streamflows due to El Nino and La Nina events on the safe yield, studies are done on the streamflows in the study area and four regions across the world during El Nino and LA Nina events. Lag correlation studies and descriptive analysis of the streamflows in the study region in Northern Virginia fail to show any pattern in the streamflow changes due to El Nino and La Nina events, based on the available data. However, this observation is not conclusive and further research if needed. / Master of Science

With the launch of CloudSat, direct observations of cloud vertical structure became possible on the global scale. This thesis utilizes over two years of CloudSat data to study large-scale variations of clouds. We compose a global data set of contiguous clouds (echo objects, EOs) and the individual pixels comprising each EO. For each EO many attributes are recorded. EOs are categorized according to cloud type, time of day, season, surface type, and region. From the categorization we first look at gross global climatology of clouds. Maps of cloud cover are subdivided by EO (cloud) type, and results compare well with previous CloudSat work. The seasonality of cloud cover is also examined. Focus topics studied in this thesis include: (1) mid-level clouds, (2) stratocumulus clouds, and (3) clouds across the Madden-Julian Oscillation (MJO). The mid-level cloud work found an unexpected frequency peak in EO top heights between 7-8 km in the tropics, further shown to correspond to a global peak in EO top temperature between -15°C ? -20°C. Hypotheses are discussed regarding cause of this feature. Stratocumulus clouds are defined as low-level (tops < 4.5 km), wide (width > 11 km) EOs. Stratocumulus cloud cover agrees (with understandable differences) with other estimates (ISCCP and CALIPSO). The seasonal cycle of stratocumulus over the main stratocumulus decks is examined. The Peruvian and Namibian decks have increased cloud cover in austral spring in 2007 vs. 2006, corresponding sensibly to sea surface temperature differences and changes in lower static stability. Looking at rain and drizzle statistics, wider EOs are found to drizzle more. Clouds across the MJO are defined relative to temporally filtered OLR data. Cloud cover (volume) doubles (triples) from suppressed to active MJO phases, with some shifts of the relative contributions of different EO types from the front to back of the MJO. Pixel statistics in dBZ-height space correspond to these cloud-type shifts. High anvils and low clouds in front lead deep convection followed by relatively lower anvils in the back.

No description available.

Le phénomène El Niño est le mode dominant de la variabilité du climat aux échelles de temps interannuelles dans le Pacifique tropical. Il modifie considérablement le climat régional dans les pays voisins, dont le Pérou pour lequel les impacts socio-économiques peuvent être dramatiques. Comprendre et prévoir El Niño reste un enjeu prioritaire pour la communauté climatique. Des progrès significatifs dans notre compréhension du phénomène El Niño et dans notre capacité à le prédire ont été réalisés dans les années 80, en particulier grâce à la mise en place du système d'observation dans le Pacifique tropical (programme de TOGA, en particulier, ainsi que l'émergence de l'ère des satellites). À la fin du XXe siècle, alors que de nouvelles théories scientifiques ont été proposées et testées, les progrès réalisés dans le domaine de la modélisation numérique et de l'assimilation de données ont conduit à l'idée que le phénomène El Niño pourrait être prévu avec au moins deux ou trois saisons à l'avance. Or, depuis le début du 21ième siècle, les manifestations du phénomène El Niño ont réduit cette expectative: un nouveau type d'El Niño est a été découvert - identifié par des anomalies de température moins intenses et localisées dans le centre du Pacifique équatorial. Ce phénomène, connu sous le nom CP El Niño pour El Niño Pacifique Central ou El Niño Modoki a placé la communauté scientifique devant un nouveau défi. Cette thèse est une contribution à l'effort international actuel pour comprendre la dynamique de ce nouveau type d'El Niño, dans le but de proposer des mécanismes expliquant sa présence accrue au cours des dernières décennies. Plus précisément, l'objectif de cette thèse est d'étudier le rôle des ondes longues équatoriales dans le Pacifique tropical sur la dynamique océanique et la thermodynamique associées au phénomène El Niño de type Pacifique Central. Cette thèse s'intéresse tout d'abord au premier CP El Niño du 21ième siècle, le phénomène El Niño 2002/03, à partir des sorties d'un modèle de circulation océanique général. Ensuite, nous documentons les caractéristiques des ondes équatoriales de Kelvin aux fréquences Intra Saisonnières (ISKw) sur la période 1990-2011, fournissant une statistique de l'activité des ondes ISKw durant l'évolution des événements El Niño de type Central Pacifique. Nos résultats montrent que l'onde ISKw subit une forte dissipation dans le Pacifique Est, qui est interprétée comme provenant de la dispersion des ondes lorsqu'elles rencontrent le front zonal de la stratification dans l'Est du Pacifique (i.e. la pente de la thermocline d'Ouest en Est). Une réflexion partielle de l'onde ISKw en onde de Rossby équatoriale de près de 120°W est également identifiée, ce qui peut expliquer le confinement dans le Pacifique central des anomalies de température de surface associées aux événements El Niño de type Central Pacifique. Nous suggérons que la fréquence accrue au cours des dernières années des événements CP El Niño peut être associée à l'état froid - de type La Niña - observé dans le Pacifique Equatorial depuis les années 90 et les changements dans la variabilité saisonnière de la profondeur de la thermocline depuis les années 2000. / The El Niño phenomenon is the dominant mode of climate variability at interannual timescales in the tropical Pacific. It modifies drastically the regional climate in surrounding countries, including Peru for which the socio-economical impacts can be dramatic. Understanding and predicting El Niño remains a top-priority issue for the climatic community. Large progress in our understanding of El Niño and in our ability to predict it has been made since the 80s thanks to the improvement of the observing system of the tropical Pacific (TOGA program and emergence of the satellite era). At the end of the Twentieth century, whereas new theories were proposed and tested, progress in numerical modeling and data assimilation led to the idea that El Niño could be predicted with at least 2 or 3 seasons in advance. The observations since the beginning of the 21st century have wiped out such expectation: A new type of El Niño, known as the Central Pacific El Niño (CP El Niño) or Modoki El Niño has put the community in front of a new challenge. This thesis is a contribution to the current international effort to understand the dynamics of this new type of El Niño in order to propose mechanisms explaining its increased occurrence in recent decades. More specifically, the objective of the thesis is to study the role of the oceanic equatorial waves in the dynamic and thermodynamic along the equatorial Pacific Ocean, focusing on the CP El Niño. This thesis first takes a close look at the first CP El Niño of the 21st century of this type, i.e. the 2002/03 El Niño, based on an Oceanic General Circulation Model. Then it documents the characteristics of the IntraSeasonal Kelvin waves (ISKws) over the period 1990-2011, providing a statistics on the ISKws activity during the evolution of CP El Niño events. We find that the ISKw experiences a sharp dissipation in the eastern Pacific that is interpreted as resulting from the scattering of energy associated to the zonal contrast in stratification (i.e. sloping thermocline from west to east). Partial reflection of the ISKw as Rossby waves near 120°W is also identified, which may explain the confinement of CP El Niño warming in the central Pacific. We suggest that the increased occurrence of CP El Niño in recent years may be associated to the La Niña-like state since the 90s and changes in the seasonality of the thermocline since the 2000s.

[pt] A energia eólica é hoje uma das mais promissoras fontes de energia do mundo por ser limpa e abundante. O estudo de fenômenos que estão relacionados com alterações na circulação atmosférica, como o El Niño, são de extrema importância pela possibilidade de afetarem a geração eólica. A fim de explorar o possível efeito de tais fenômenos nos ventos da região Nordeste do Brasil, a qual possui a maior capacidade eólica instalada, é realizada uma análise estatística para a quantificação desse efeito através dos modelos Generalized Autoregressive Score (GAS). Estes permitem a modelagem de séries temporais para diferentes distribuições de probabilidade. Nesse estudo, o GAS é aplicado às séries de velocidade do vento a partir das distribuições Weibull, Gama e Beta. Os resultados mostram que a distribuição Beta produz o melhor ajuste quando se considera o efeito do El Niño através da Temperatura da Superfície do Mar (TSM), na velocidade do vento de uma usina eólica no Nordeste do Brasil. Em particular estes mostram que, o maior impacto do El Niño ocorre nos meses de abril e maio, onde para um aumento de 1 grau Celcius da TSM é observada uma variação de aproximadamente 1.3 por cento na velocidade do vento. / [en] Wind energy is now one of the most promising energy sources of the world being both clean and abundant. The study of phenomena that are related to changes in atmospheric circulation, such as El NiÑo, are extremely important for its ability to affect wind generation. In order to explore the possible effect of such phenomena in the winds of the Northeast region of Brazil which has the largest installed wind capacity, a statistical analysis is performed to quantify this effect through the Generalized Autoregressive Score (GAS) models. These allows the modeling of time series for different probability distributions. In this study, GAS models are applied to the wind speed series using Weibull, Gamma and Beta distributions. The results shows that the Beta distribution produces the best fit when considering the effect of El Niño through Sea Surface Temperature (SST) in the wind speed of an wind farm in the Northeast of Brazil. In particular these show that the greatest impact of the El Niño occurs in the months of April and May, where for an increase of 1 degrees Celcius of SST is observed a variation of approximately 1.3 per cent in wind speed.

Made available in DSpace on 2015-03-26T13:50:16Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1518212 bytes, checksum: 37651f0e365918ff9d0f80d2eaf8ac5d (MD5) Previous issue date: 2003-07-10 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / The daily precipitation data referring to 134 localities in the State of Minas Gerais, supplied by the Agência Nacional de Águas (ANA), were analyzed in order to characterize the rainy period (RP), as well as the event and duration of the dry spells occurring over the climatic events El Niño (EN) and La Niña (LN). At first, the beginning of the rainy periods (BRP) and the precipitation amount of the rainy period were analyzed, respectively based on the averages and normalized standard deviations of three annual series: El Niño, La Niña and neutral years. The influence of these phenomena on each 15-day period over the months from November to February were analyzed, by using the average and the standardized precipitation rate, as well as the behavior of each RP based on precipitation anomalies. For both analyses, seven stations were chosen according to the climatically homogeneous areas in Minas Gerais. Then, the frequency of dry spells was determined to intervals with four durations in these three series, and the dry spell was defined as a period with at least three dry consecutive days (precipitation &#8804; 1 mm) during the rainy period. The method of Regression Analysis was used to relate the duration of the rainy period (RPD) and, or, BRP with the dry spells lasting from three to six days (A) and from seven to ten days (B), as well as the BRP and the total precipitation amount during RP with the dry spells classified as classes A and B, respectively. The results obtained for the influence of the EN and LN phenomena were georeferrenced by the interpolation method that materialized them into thematic maps generated by the Geographic Information System (GIS). The thematic maps were obtained, by involving of Minas Gerais State Digital Elevation Model (DEM) with the classification concerning to the total precipitation and RPD with the average frequencies of the dry spells. A characteristic of La Niña is to cause rains below the average on an extensive part of the State, as well as on half-Northeastern over events El Niño, and rains above the average on half- Southwestern Minas Gerais. The dry spells caused by LN on the North-Northeastern part of the State are due to the periods lasting more than 15 days, whereas on the South-Southwestern are due to the dry spells lasting from three to six days. Similarly, the dry spells on North-Northeastern of Minas Gerais during El Niño events, and the rains above the average on the half-Southwestern of the State cause an influence of the dry spells lasting three to six days. / Dados diários de precipitação de 134 localidades do estado de Minas Gerais, fornecidos pela Agência Nacional de Águas (ANA), foram analisados com o intuito de caracterizar o período chuvoso (PC) e o comportamento na ocorrência e duração dos veranicos em anos de eventos climáticos El Niño (EN) e La Niña (LN). Inicialmente, foram classificados o início dos períodos chuvosos (IPC) e a quantidade pluviométrica do PC, baseados, respectivamente, nas médias e desviospadrão normalizados de três séries, sendo elas: anos de El Niño, anos de La Niña e anos neutros. Conjuntamente, foram analisadas a influência destes fenômenos nas quinzenas dos meses de novembro a fevereiro, com a utilização da média e do índice padronizado de precipitação e o comportamento de cada PC baseando-se nas anomalias de precipitação. Ambas análises, para sete estações distribuídas por regiões climaticamente homogêneas de Minas Gerais. Em seguida, determinou-se a freqüência de ocorrência de veranicos para quatro intervalos de duração nas três séries, sendo definido, como veranico, o período de pelo menos três dias secos (precipitação &#8804; 1 mm) consecutivos durante o período chuvoso. Foi utilizado o método de análise de regressão, para relacionar a duração do período chuvoso (DPC) e, ou, IPC com os veranicos com duração de três a seis dias (A) e de sete a dez dias (B), e o IPC, total pluviométrico durante o PC com os veranicos de classes A e B. Os resultados referentes à influência dos fenômenos EN e LN foram geoespacializados, utilizando-se método de interpolação que os materializou em forma de mapas gerados por intermédio de um Sistema de Informações Geográficas (SIG). Foram efetuadas sobreposições de temas, envolvendo o relevo do Estado com a classificação referente ao total pluviométrico e da DPC com as freqüências médias de veranicos. A La Niña possui uma característica marcante de ocasionar chuvas abaixo da média em grande parte do Estado, da mesma forma para a metade nordeste em episódios do El Niño e chuvas acima da média na metade sudoeste de Minas Gerais. As estiagens ocasionadas pela LN, no Norte- Nordeste do Estado, são devidas a períodos superiores a 15 dias de duração e no sul-sudoeste aos veranicos com duração de três a seis dias. Da mesma forma, ocorre para as estiagens no Norte-Nordeste de Minas Gerais, durante eventos El Niño e as chuvas acima da média na metade sudoeste ocasionam uma influência, somente, por parte dos veranicos com duração de três a seis dias.

Orientador: Rogério Caetano da Costa / Banca: Antonio Leão Castilho / Banca: Jandira Liria Biscalquini Talamoni / Resumo: O presente estudo foi dividido em dois capítulos e tiveram como objetivos: cap.1- verificar a distribuição espaço-temporal de L. schmitti em três baías do litoral norte do estado de São Paulo, Ubatumirim (UBM), Ubatuba (UBA) e Mar Virado (MV); testar a relação dos fatores ambientais com a distribuição dos camarões durante um período de 2 anos (1998 e 1999) e cap. 2- averiguar a variação anual e sazonal da biomassa e do número de indivíduos do camarão, durante 4 anos de estudo (1998, 1999, 2002, 2006), com enfoque no período reprodutivo e de recrutamento juvenil informando qual a melhor época para a pesca. Os camarões foram capturados com um barco camaroneiro equipado com redes do tipo "double-rig" em profundidades até os 20 metros. Em 1998 e 1999, um total de 5658 indivíduos foi coletado, sendo 4437 no primeiro ano e 1221 no segundo ano. Em MV obteve-se a maior abundância (n= 2747), seguido de UBM (n= 1649) e UBA (n=1262). A salinidade da água variou de 28 a 37 com média de 34,6 ± 1,44, porém não houve correlação significativa desse fator com a abundância (p=0,90). A média da temperatura de fundo foi de 24,8 ± 2,84 °C com valor máximo de 31,4 °C e mínimo de 19 °C. Apesar dessa grande variação nos valores obtidos, não houve correlação significativa desse fator com a abundância (p= 0,11). A maior captura de camarões foi registrada em áreas onde silte + argila correspondem mais de 70 % do sedimento e em locais com maior porcentagem de matéria orgânica. Houve relação inversa da abundância com a pluviosidade, com as maiores abundâncias nos meses posteriores a temporada de chuvas. Porém, no ano em que houve maior pluviosidade, também houve uma maior captura de indivíduos. A quantidade de camarões seguiu uma tendência sazonal, sendo maior durante o outono e inverno... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The present study was divided in two chapters, which aimed: chapter 1 - to verify the spatiotemporal distribution of L. schmitti in three bays of north littoral of São Paulo State, Ubatumirim (UBM), Ubatuba (UBA) e Mar Virado (MV); to test the relation between environmental factors and shrimp distribution, during a 2-year period (1998 and 1999) and chapter 2 - to investigate the annual and seasonal variation of biomass and of the number of shrimp individuals, focusing reproductive period and juvenile recruitment; which is the best period for the open season; the rainfall influence on abundance during 4 years of study (1998, 1999, 2002 and 2006). Shrimps were captured with a shrimp fishing boat equipped with two double-rig nets at depths up to 20m. In 1998 and 1999, a total of 5658 individuals was collected, being 4437 on first year and 1221 on second year. The highest abundance was obtained at MV (n=2747), followed by UBM (n=1649) and then by UBA (n=1262). Water salinity has varied from 28 to 37, with average of 34.6 ± 1.44, although abundance has not had a significant correlation with this factor (p=0,90). The average bottom temperature was of 24,8 ± 2,84 °C, with a maximum of 31.4 °C and a minimum of 19°C. Besides the great variation on these values, abundance has not had a significant correlation with this factor (p=0.11). The higher shrimp capture was registered in areas where sediment was composed by more than 70% of silt + clay and at areas with highest percentage of organic-matter. There was an inverse correlation between abundance and rainfall, with the highest abundances on months after the rainy season. However, the highest individual catch occurred in the year with highest rainfall rates. Shrimp amount had a seasonal tendency, being higher during autumn and winter in both years. A total of 566 (13,171 g) individuals... (Complete abstract click electronic access below) / Mestre

Nonlinear dynamical systems theory has inspired a new set of useful tools to be applied in climate studies. In this work we presented specific examples where information has been gained by the application of methods from nonlinear dynamical systems theory. The main goal is to understand the relative importance of stochastic forcing versus deterministic coupling within the context of Coupled General Circulation Models. This work address this important subject by approaching this goal through the development of a hierarchy of models with increasing complexity that we assert contain the essential dynamics of ENSO. We examined the effect of noise in a low order model and found that it is not restricted to blurring the attractor trajectories in phase space, but includes important changes in the dynamics of the system. The main results indicate that the presence of noise in a nonlinear system has two different effects. The presence of noise acts to increase the maximum Lyapunov exponent and can result in noise induced chaos if the system was originally stable. However, the same arguments are not valid if the original system is already in the chaotic regime, where the noise inclusion acts to decrease the maximum Lyapunov exponent, therefore increasing the system stability. The system of interest includes coupled ocean-atmosphere interactions and here we mimic this interaction by coupling two low order models with very different dominant time scales. These subsystems interact in a complex, nonlinear way and the behavior of the whole system cannot be explained by a linear summation of dynamics of the system parts. We used information theory concepts to detect the influence of the slow system dynamics in synchronizing the fast system in coupled models. We introduced a fast-slow coupled system, where both the slowness of the ocean model and the intensity of the boundary forcing anomalies contribute to the asymmetry and phase locking of both subsystems. The mechanisms controlling the fast modelspread were uncovered revealing uncertainty dynamics depending on the location of ensemble members in the model’s phase space. As an intermediate step between low order models and CGCMs we study the effect of noise on an intermediate complexity model. The addition of gaussian noise to the Zebiak-Cane model in order to understand the effects of noise on its attractor led to a way of estimating the noise level based on the effects of noise on the correlation dimension curves. We investigate the intrinsic predictability of the coupled models used here, and the different time scales associated with fast and slow modes were detected using the Finite Size Lyapunov Exponents. We found new estimates for the prediction horizon of ENSO for the Zebiak-Cane model as well as for the NCAR CCSM3 model and observations. The whole analysis of observations and CCSM3 was possible after applying noise reduction techniques. We also improved our understanding of three different noise reduction techniques by comparing the Local Projective Noise Reduction, the Interactive Ensemble strategy, and a Random Interactive Ensemble applied to CCSM3. The main difference between these two noise reduction techniques is when the process is applied. The Local Projective Noise Reduction can be applied to both model and observations, and it is done a posteriori in phase space, therefore the trajectories to be adjusted already posses the physical mechanisms embedded in them. The Interactive Ensemble approach can only be applied to model simulations and has shown to be a very useful technique for noise reduction since its done a priori while the system evolves instead of a posteriori, besides the fact that it allows to retrieve the spatial distribution of the noise level in physical space.