Snow albedo is one of the most important factors for atmosphere-surface energy exchange in high latitude areas. Remote sensing provides continual observations of snow albedo. However, the reliability of snow albedos obtained from remotely sensed images can be problematic, especially when acquired over heterogeneous land surfaces. This research examines spatial variations in snow albedo observed under different conditions in order to assess how accurate an individual in situ observation of snow albedo is when compared to the Moderate Resolution Imaging Spectroradiometer (MODIS) daily snow albedo product (MOD10A1) and its relationship with land surface types. In addition to the field observations, albedos retrieved from two SURFRAD stations are also examined. The overall Root Mean Square Error (RMSE) between the in situ and MODIS albedos is 8%. Semivariogram analysis of Landsat ETM+ snow albedo retrievals on January 26th, 2010 over an ice and snow covered lake indicates spatial autocorrelation lengths of approximately 260 m, suggesting limited in situ observation can be considered fairly representative of albedos retrieved from MODIS images. To further reveal what parameters could influence the spatial representativeness, this research examined landscape metrics based on seven binary snow maps created from Landsat images for three areas of differing roughness and for different snow cover conditions. There are two Landscape metrics, Mean Shape Index (MSI) and Area Weighted Shape Index (AWMSI), were found to be correlated the spatial autocorrelation lengths of snow albedo as measured from the range distance of the modeled semivariograms. In addition, this research also introduced a method of using multi-angle mast to measure the surface bidirectional reflectance distribution function (BRDF). This method could be used for further research to build the BRDF library of the snow-covered canopies.

A l’heure des études sur le changement climatique, un certain nombre d’inconnues subsiste comme la caractérisation des propriétés radiatives des aérosols à l’échelle globale. Différents moyens d’observations, depuis la surface ou l’espace, ont été développés ces dernières années et nous nous focalisons ici sur les mesures spatiales océaniques et notamment sur celles issues de deux instruments, MODIS/AQUA (Moderate Resolution Imaging Spectroradiometer de la NASA) et POLDER/PARASOL (POLarization and Directionality of Earth Reflectances du CNES) qui appartiennent à la constellation de satellites « A-Train ». Ces deux instruments nous permettent, à partir des luminances réfléchies par le système « Terre-Atmosphère », d’observer quotidiennement différents types d’aérosols (brûlis, poussières désertiques, pollution) en fonction de la zone géographique et d’en effectuer le suivi temporel.En première analyse, on peut comparer les résultats obtenus par chaque capteur qui ont des techniques d’observations privilégiant pour l’un, le domaine spectral pour l’autre, le caractère angulaire et polarisé des luminances. Utiliser ensuite en synergie les deux types d’informations nécessite de comparer les mesures brutes des instruments et d’assurer la cohérence des traitements. Nous avons ainsi examiné les étapes nécessaires à cette inversion: étalonnage des instruments, corrections apportées aux mesures et validité des modèles d’aérosols utilisés. Enfin, nous avons sélectionné quelques cas d’études afin d’analyser les caractéristiques des aérosols (quantité, taille, nature) d’origine désertique au-dessus de l’océan Atlantique et leur évolution au cours de leur transport. / Within climatic change issues, one of the unknowns remains the characterization of the aerosol radiative properties at global scale. Different ways of monitoring aerosols from surface or space have been developed during the recent years and our present study is especially focused on observations over ocean from two satellite instruments, MODIS/AQUA (Moderate Resolution Imaging Spectroradiometer of NASA) and POLDER/PARASOL (POLarization and Directionality of Earth Reflectances of CNES), that are both part of the “A-Train” constellation. From the radiances reflected by the “Earth-Atmosphere” system, we can monitor the distribution of different aerosol types (smoke, dust, pollution) over specific regions and with a good temporal frequency.We can first compare results obtained by each sensor that are using different techniques, MODIS favor spectral domain when POLDER considers the angular and polarized character of radiances. In a second step, it looks attractive to combine both data sets into a single inversion scheme. To do so, it requires to ensure that the radiances of the two instruments are consistent and to control the coherency of the assumptions used along the retrieval processing. We analyze the different steps: calibration, gaseous absorption and molecular scattering correction as well as the validity of the aerosol models. Lastly, we select specific events to analyze the evolution of aerosol plumes (content, size, composition) transported over the Atlantic Ocean.

Abstract In the present study, the height of internal solitary wave is derived by combining the theoretical fluid flow field from perturbation method and MODIS images. The flow field is derived by assuming two-layer fluid system. Note that it is difficult to determine the interface depth from CTD measurement because sea water density changes continuously with depth. Moreover, changing the upper layer thickness will significantly affect the estimate of wave height. Thus, a proper method should be used so that the two-layer fluid system can represent the continuously stratified sea water. The resulting parameters for the two-layer system are the upper and lower layer thickness h1 and h2 and the corresponding densities £l1 and £l2 . Another important parameter dpp derived from MODIS images is the distance from dark-band to light-band. The dark-band and light-band are due to the interaction of surface and internal waves that changes roughness on the ocean surface. These processes are discussed in detail in this thesis. Finally, the parameters h1, h2, £l1, £l2 and dpp are combined to estimate internal solitary waves height in the deep ocean. According to the estimate for deep ocean with 3000m depth, the wave height is about 100m which is quite reasonable by comparing with in-situ observation.

This thesis applies a numerical model to study the propagation of internal solitary wave based on a two-dimensional model developed by Lynett and Liu (2002) and modified by Cheng et al. (2005).The numerical model derived assumes weak nonlinearity and weak dispersion in a two-layer inviscid fluid system. The governing continuity and momentum equations are solved and the real topography is included in the wave model. In order to improve the accuracy of simulation, mixed-layer thickness is allowed to change from place to place. Initial conditions are modified so that wave forms of non-hyperbolic -secant functions and wave fronts taken by satellite can be used. The diffraction near the island of Dongsha is simulated, and results of both fixed and variable mixed-layer thickness are compared. Simulated waveform in MODIS images after 24 hours are compared with other wave fronts of the same image. Laterally, internal waves can become very wide when it is far away from its origin. The extra energy can be explained by nonlinear wave-wave interaction because the energy of large amplitude internal wave increases after interacting with smaller internal waves.

Thesis (M.Sc). / Title from title page of PDF (viewed 2008/01/28). Written for the Dept. of Physics. Includes bibliographical references.

Chemnitz, Techn. Univ., Studienarb., 2001.

Many traditional drought assessments are conducted based on climate and hydrologic data. The availability and precision of data limit the spatial and temporal resolution and accuracy of derived drought indices. In this study, Vegetation Condition Index (VCI) and Temperature Condition Index (TCI) were generated from Moderate Resolution Imaging Spectroradiometer (MODIS) products. The VCI was derived from Normalized Difference Vegetation Index (NDVI) that was calculated with near infrared and visible red band reflectance from MOD09Q1. The TCI was derived from land surface temperature (LST) product MOD11A2. The VCI and TCI were then combined with reference to the vegetation coverage information from MOD44B to generate the modified Vegetation Health Index (VHI). The modified VHI was applied to quantify the intensity of drought that took place in Illinois from 2000 to 2012. The results showed that the modified VHI identified the major droughts that occurred in Illinois from 2000 to 2012, especially the extreme one taking place in 2012. Moreover, the modified VHI led to the spatial distributions and temporal trends of drought severity, which were overall similar to those from the U.S. Drought Monitor (USDM) maps, but had more detailed spatial variability and much higher spatial resolution. The modified VHI also differentiated the drought impacts between the vegetated and non-vegetated areas, being a lack of the original VHI. Thus, the modified VHI takes advantage of spatially continuous and timely data from satellites and can be applied to conduct the monitoring and detection of drought intensity at local, regional, and national scales. The modified VHI can effectively synthesize the drought information of LST and NDVI to differentiate the effects of land use and land cover (LULC) types and provide the detailed spatial variability of drought intensity and thus enhance the understanding of relationship between drought condition and LULC types.

Submitted by Eduarda Figueiredo (eduarda.ffigueiredo@ufpe.br) on 2015-03-05T13:32:41Z No. of bitstreams: 2 Oliveira_LMM_2012_Tese.pdf: 7226231 bytes, checksum: 2d0e9aa85bcb012deb83914db596293c (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-05T13:32:41Z (GMT). No. of bitstreams: 2 Oliveira_LMM_2012_Tese.pdf: 7226231 bytes, checksum: 2d0e9aa85bcb012deb83914db596293c (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2012-09-03 / CNPq / Informações quantitativas da evapotranspiração, que constitui importante componente do ciclo hidrológico, são utilizadas na resolução de numerosos problemas que envolvem o manejo da água. Nesta pesquisa utilizou-se o algoritmo Surface Energy Balance Algorithm for Land – SEBAL aplicado a imagens de satélite do Moderate Resolution Imaging Spectroradiometer – MODIS, para estimar os balanços de radiação e energia, bem como, a evapotranspiração real diária – ET em escala regional. O estudo foi realizado na bacia hidrográfica do rio Tapacurá no estado de Pernambuco, com doze imagens MODIS dos satélites Terra e Aqua entre os anos de 2010 e 2011. Instalou-se na área de estudo uma estação meteorológica experimental destinada à determinação do balanço de energia pela técnica de Razão de Bowen. Foram processadas cartas temáticas georreferenciadas do albedo da superfície, saldo de radiação, fluxos de calor no solo, sensível, latente e evapotranspiração real. Os resultados evidenciaram boa correlação entre o saldo de radiação medido e o estimado por sensoriamento remoto (R2 = 0,9355). A ET pela Razão de Bowen variou de 3,6 a 4,9 mm dia-1 e pelo algoritmo SEBAL utilizando produtos MODIS foi de 0,0 a 6,0 mm dia-1, sendo seus menores valores registrados em áreas urbanas e os maiores no reservatório do Tapacurá. A validação da ET pelo SEBAL com o Balanço de Energia pela razão de Bowen apresentou Erro Absoluto Médio de 0,38 W m-2, Erro Relativo Médio de 9,15% e Raiz do Erro Quadrático Médio de 0,49 W m-2. Esta pesquisa demonstrou a eficiência da aplicabilidade desta metodologia para estudos da distribuição espacial da ET. O modelo SEBAL pode ser aplicado de forma prática, econômica e eficiente na geração de subsídios à adequada gestão dos recursos hídricos da região.

This thesis investigates the variation of the chlorophyll-a concentration near Dongsha Atoll derived from MODIS Aqua and Terra satellite images, and their relationship to physical environments including sea surface temperature, CTD water qualities, tides, currents and surface winds for the period 2005 to 2008. The results revealed that the seasonal variation of chlorophyll-a concentration was higher in the winter than in the summer, and had inverse relationship with sea surface temperature. The increased chlorophyll-a concentration was due to entrainment of lower layer cold water with high nutrient. The upwelling water was induced by mixing of surface wind and internal wave shoaling. When the internal waves propagated westward to the Dongsha Atoll, the bottom topography and coastline oriented the cold deep water surged up slope to the northeastern corner of the Atoll, which produced high chlorophyll-a concentration a few days after. The comparison of MODIS images and CTD data revealed that the chlorophyll-a concentration didn¡¦t increase immediately after the passage of internal waves.

Rapid population growth in Arizona is leading to increasing demand and decreasing availability of water, requiring a detailed quantification of hydrological processes. The integration of detailed spatial water fluxes information from remote sensing platforms, and hydrological models is one of the steps towards this goal. One example step is the use of MODIS Snow Cover Area (SCA) information to update the snow component of a land surface model (LSM). Because cloud cover obscures the images, this project explores a rule-based method to remove the clouds. The rules include: combination of SCA maps from two satellites; time interpolation method; spatial interpolation method; and the probability of snow occurrence in a pixel based on topographic variables. The application in sequence of these rules over the Upper Salt River Basin for WY 2005 resulted in a reduction of cloud obscuration by 93.7878% and the resulting images' accuracy is similar to the accuracy of the original SCA maps. The results of this research will be used on a LSM to improve the management of reservoirs on the Salt River. This research seeks to improve SCA data for further use in a LSM to increase the knowledge base used to manage water resources. It will be relevant for regions were snow is the primary source of water supply.