A radiative transfer model for a homogeneous plane parallel vegetative canopy is developed. A method to decompose and calculate the uncollided, once scattered, and multiply scattered radiation components is also presented based on the turbid medium approach. The new model accounts for the some effects exhibited only by homogenous vegetation canopies. This allows the simulation of the scattering processes within the plant canopy as a function of the traditional canopy architecture parameters such as leaf area index (LAI), leaf reflectance and transmittance, and also the canopy height and leaf size, stem etc... This model integrates two different approaches: the turbid medium approach and an approach that takes into account the finite size of the leaves. Furthermore, a state of the art leaf radiation transfer model (PROSPECT) is incorporated into the new model that provides leaf scattering properties as inputs (transmittance and reflectance vs. wavelength). Based on the proposed canopy model, a computer code in MATLAB was formulated using the discrete ordinates numerical method. This was used to calculate the bi-directional reflectance factor for a given geometry and a viewing angle from a plant canopy. The code for the new model is modular and very simple to use. The new model has been validated against other radiative transfer models, and compared with measured data. The results obtained using the model are in good agreement with the measured data.

The investigations contained in this body of work detail a viable proof-of-concept model for monitoring seasonal snow pack propensity for melt release based on time-variant snow surface optical and thermal properties. The model has been called the Near Surface Moisture Index- (Snow) (NSMI). The NSMI was developed based on time-variant snow surface optical and thermal properties. This research achieved three primary objectives: 1).development of theoretical foundation and surface moisture sensitive algorithm used to track both surface melt and pack discharge potential; 2.) time-dependent phases of coupling and decoupling between snow surface properties and melt discharge were characterized through analysis of long-term surface and sub-surface state variables; 3.) and sensitivity of optical satellite systems specifically, EOS TERRA-MODIS, to melting were was examined through radiative transfer simulations. Simulated at-sensor radiance was produced for various grain size changes to determine MODIS capacity to track melt onset. MODIS wavelengths greater than 667nm were sensitive to large changes in grain sizes, particularly bands with coarse spatial resolution (1000m). Longer wavelengths showed greater sensitivity to small changes in smaller grains than to small changes in larger grains. Shorter wavelengths at 500m spatial resolution appeared less effective overall for monitoring changes in grain size. NMSI feature space using Normalized Difference Snow Index (NDSI) on the abscissa and brightness temperature (Tb) on the ordinate was simulated. Simulated NDSI as a function of grain radius saturated approximately around 400-450 μm. ASTER derived NSMI demonstrated behavior consistent with simulations with deviations due to topography, vegetation, and regional heterogeneity. We examined NSMI performance during an entire melt season through tracking phases of coupling between snow surface properties and propensity for melt using two ground-base approaches; one with higher snow surface spectral information and low temporal resolution, the other with high temporal resolution and coarse spectral information. Phases of decoupling exhibited within ground-based time varying simulated NSMI were regulated by the temporal resolution specified to construct the feature space. Coarser temporal intervals on surface optical/thermal variables correlated the NSMI feature space various components of surface radiative variability. Coarser temporal optical and thermal resolution will tend to reduce variability within the NSMI feature space due to specific snowfall events.

Improved knowledge of landscape seasonal variations and phenology at the regional scale is needed for carbon and water flux studies, and biogeochemical, hydrological, and climate models. Amazon vegetation mechanisms and dynamics controlling biosphere-atmosphere interactions are not entirely understood. To better understand these processes, vegetation photosynthetic activity and canopy water and temperature dynamics were analyzed over various types of vegetation in Amazon using satellite data from the Terra-Moderate Resolution Imaging Spectroradiometer (MODIS). The objectives of this dissertation were to 1) assess the spatial and temporal variations of satellite data over the Amazon as a function of vegetation physiognomies for monitoring and discrimination, 2) investigate seasonal vegetation photosynthetic activity and phenology across the forest-cerrado ecotone and conversion areas, and 3) investigate seasonal variations of satellite-based canopy water and land surface temperature in relation to photosynthetic activity over the Amazon basin.The results of this study showed the highly diverse and complex cerrado biome and associated cerrado conversions could be monitored and analyzed with MODIS vegetation index (VI) time series data. The MODIS enhanced vegetation index (EVI) seasonal profiles were found useful in characterizing the spatial and temporal variability in landscape phenology across a climatic gradient of rainfall and sunlight conditions through the rainforest-cerrado ecotone. Significant trends in landscape phenology were observed across the different biomes with strong seasonal shifts resulting from differences in vegetation physiognomic responses to rainfall and sunlight. We also found unique seasonal and temporal patterns of the land surface water index (LSWI) and land surface temperature (LST), which in combination with the EVI provided improved information for monitoring the seasonal ecosystem dynamics of the Amazon rainforest, cerrado, ecotone, and conversion areas. In conclusion, satellite-based, regional scale studies were found to aid in understanding land surface processes and mechanisms at the ecosystem level, providing a "big picture" of landscape dynamics. Coupling this with ground, in-situ measurements, such as from flux towers, can greatly improve the estimation of carbon and water fluxes, and our understanding of the biogeochemistry and climate in very dynamic and changing landscapes.

<p> Ultra-spectrometers with a spectral resolution better than 1 cm_-1, such as AIRS on the AQUA, IASI on the Metop-A/B, and CrIS on the Suomi-NPP, have become operational during the past decade. The radiance spectra measured by these satellite-borne spectrometers provide soundings of the atmosphere with relatively high vertical resolution and high accuracy except for the lower atmosphere. Meanwhile, many ground-based ultra-spectrometers based on the Michelson Interferometer have been incorporated into the Department of Energy Atmospheric Radiation Measurement facilities and aboard NOAA research vessels. These instruments provide temperature and water vapor soundings within the planetary boundary layer continuously with very high vertical resolution. This dissertation develops a retrieval procedure which can combine the radiance measured by ground-based spectrometers and coincident observation from satellite-borne instruments to improve retrieval results throughout the lower atmosphere. </p><p> To verify the feasibility and improved accuracy of the combined retrieval, 90 clear sky cases from four in-situ radiosonde measurement locations or geographical regions, were selected for this study. Each region consists of radiosonde measurements of temperature and water vapor, downwelling radiance spectra measured at approximately the balloon launch time, and upwelling radiance observation by IASI at the location and time coincident with the surface radiance and radiosonde measurements. </p><p> These cases indicate, that when compared with the retrieval from upwelling radiance or downwelling radiance spectra only, there is a significant improvement of the retrieval using combined upwelling and downwelling radiance spectra is observed. At altitude below the 800 hPa pressure level, the errors using the combined retrieval are about 0.5 &ndash; 1 K in temperature, and 20 &ndash; 40 % for water vapor mixing ratio. These errors are approximately one-third the magnitude of errors for the sounding retrieval obtained using satellite upwelling radiance alone.</p>

<p>Typical imaging systems rely on the interactions of matter with electromagnetic radiation, which can lead to scattered waves that are radiated away from the imaging area. The goal such an imaging device is to collect these radiated waves and focus them onto a measurement detector that is sensitive to the wave's properties such as wavelength (or color) and intensity. The detector's measurements of the scattered fields are then used to reconstruct spatial information about the original matter such as its shape or location. However, when a scattered wave is collected by the imaging device, it diffracts and inteferes with itself. The resulting interference pattern can blur spatial information of the reconstructed image. This leads to a so-called diffraction limit, which describes the minimum sizes of spatial features on a scatterer that can be resolved using conventional imaging techniques. The diffraction limit scales with the wavelength &lambda; of the illuminating field, where the limit for conventional imaging with visible light is approximately 200 nm. Investigating subwavelength objects (< &lambda;) requires more advanced measurement techniques, and improving the resolving capabilities of imaging devices continues to be an active area of research.</p><p>Here, I describe a new sensing technique for resolving the position of a subwavelength scatterer (< &lambda;) with vastly subwavelength resolution (<< &lambda;). My approach combines two separate fields of scientific inquiry: time-delayed nonlinear feedback and wave chaos. In typical time-delayed nonlinear feedback systems, the output of a nonlinear device is delayed and fed back to its input. In my experiment, the output of a radio-frequency (&lambda; ~ 15 cm) nonlinear circuit is injected into a complex scattering environment known as a wave-chaotic cavity. Inside the cavity, the field interacts with a subwavelength dielectric object from all sides, and a portion of the scattered waves are coupled out of the cavity, amplified, and fed back to the input of the nonlinear circuit. The resulting closed-feedback loop generates its own radio-frequency illumination field (> 1 GHz), which contains multiple wavelengths and is sensitive to location of the scattering object. Using the dynamical changes in the illumination field, I demonstrate subwavelength position-sensing of the scatterer's location in the cavity with a one-dimensional resolution of ~&lambda;/10,000 and a two-dimensional resolution of ~ &lambda;/300. </p><p>This novel method demonstrates that the dynamical changes of a feedback oscillator can be exploited for resolving subwavelength spatial features. Unlike conventional imaging techniques, it uses a single scalar measurement of the scattered field and takes advantage of a complex scattering environment. Furthermore, this work demonstrates the first application of quasiperiodic dynamics (oscillations with incommensurate frequencies) from a nonlinear system. Using the key ingredients from my radio-frequency system, I extend my method to an experiment that uses optical frequencies (&lambda; = 1550 nm) to demonstrate subwavelength sensing in two dimensions with a resolution of approximately 10 nm. Because this new sensing technique can be adapted to multiple experiments over vastly different length scales, it represents a potential platform for creating a new class subwavelength imaging devices.</p> / Dissertation

No description available.

The purpose of this research was development of a geographic information system (GIS) and linkage with existing ground-water models to expedite wellhead protection area (WHPA) delineation within a wellhead protection (WHP) program. Research objectives included: (1) incorporation of relevant data from federal, state, and local agencies into the database; (2) delineation of WHPAs utilizing linkage established at Rice University between the GIS and WHPA (a ground-water model which delineates capture zones); (3) evaluation of model input parameter sensitivities to address effects of parameter input on the shape of delineated WHPAs; (4) demonstration of the utility of the GIS to facilitate WHPA delineation; and (5) development of a prototype ground-water management system. Harris County, Texas, already identified as a critical ground-water supply area, was selected as the project area. Public water well data on 224 City of Houston wells served as the initial dataset for the development of a county-wide WHP program.

Soil erosion is a complex, natural process that often is accelerated by such human activities as land clearance, agriculture, construction, and surface mining. Accurate soil erosion type/intensity maps can be effective tools in aid of soil erosion control efforts. / The principal objective of this research was to use geographic information system (GIS) and remotely sensed data to extract and define erosion types/intensities over a large area (4,511.8 km2) in Iran. The study proceeded in three major steps: (i) a 10-m resolution digital elevation model (DEM), land slope, elevation range, and stream network pattern were created. These basic identifying parameters plus Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images were used to differentiate various landforms, (ii) a land use and land cover map was created based on analysis of three Landsat Enhanced Thematic Mapper (ETM+) images from the growing season plus use of a landform map and climatic zones as ancillary information, and (iii) in order to extract and identify various erosion types/intensities, the difference in brightness combination over two growing season intervals derived from the Landsat ETM+ images were used. Further, land slope, landform, land use, and land cover layers were used to assist in the classification of the erosion types (interrill and rill). / The approach presented produced soil erosion type/intensity maps with an overall accuracy of 93.4%. Considering only rangeland and forest a unique relationship exists between seasonal brightness combinations and erosion intensity. It was found that for the lower erosion levels it is the later season or second brightness combination (BJS) which indicates degree of erosion intensity, but for the areas of severe and very severe erosion it is the early season or first brightness combination (BMJ) that differentiates degree of erosion intensity. Further, this study illustrated that land use, land cover, landform, and land slope layers can be used for differentiating erosion types. / The approach presented has been shown to be an effective tool for the creation of soil erosion maps over a large area of Iran and is expected to be useful for aiding in the development of soil conservation and watershed management plans in other areas. The main advantages of this approach are accuracy, lower demands on time and funds for field work and ready availability of required data for many regions of the world. / Processus naturel complexe, l'érosion du sol est fréquemment exacerbée par les activités anthropiques telles le défrichage, l'agriculture, la construction, et l'exploitation minière à ciel ouvert. Une cartographie précise du type et de l'intensité d'érosion du sol peut s'avérer un outil efficace dans une lutte contre l'érosion. / Les présentes recherches visèrent l'utilisation de SIG et de données de télédétection dans la localisation et l'identification de divers types d'érosion sur une aire de grande étendue (4,511.8 km2) en Iran. L'étude s'échelonna sur trois étapes: (i) un modèle altimétrique numérique (MAN) d'une résolution de 10 m servit à créer des plans de pente du terrain, d'altitude, et du tracé hydrographique. Différentes formes de relief furent différenciés grâce à ces paramètres identificateurs et à des images provenant de radiomètre spatial de pointe pour l'étude de la réflectance et des émissions thermiques terrestres (ASTER), (ii) une carte d'affectation et de couvert du sol fut tracée selon l'analyse de trois images Landsat ETM+ prises durant la saison de croissance ainsi que des informations supplémentaires tirés de cartes de relief et de zones climatiques, et (iii) la différence dans la combinaison de brillances provenant d'images Landsat ETM+, lors de deux intervalles de la saison de croissance, servit à extraire et identifier les différents types et intensités d'érosion. Les plans de pente du terrain, de relief, ainsi que ceux d'affectation et couvert du sol, appuyèrent l'identification du type d'érosion (rigoles et entre-rigoles). / Cette approche généra des cartes de type et d'intensité d'érosion d'une exactitude globale de 93.4%. Ne prenant en compte que les parcours et forêts, il devient apparent qu'il existe un lien tout particulier entre la combinaison de brillances saisonnières et le taux d'érosion. Pour les niveaux d'érosions moins élevés c'est la seconde combinaison de brillances (BJS), qui prévale en fin de saison, qui est la plus fortement liée au niveau d'intensité de l'érosion, tandis que pour les zones d'érosion sévères et très sévères c'est la première combinaison de brillances (BMJ), qui prévale en début de saison, qui permet de différencier le niveau d'intensité de l'érosion. Cette étude indique que l'affectation et le couvert du sol, le relief et les pentes du terrain peuvent servir à différencier divers types d'érosion. / Nous avons démontré que la démarche préconisée représente un outil efficace dans la création de cartes d'érosion à grande échelle pour l'Iran, et nous nous attendons qu'elle s'avèrera utile au développement de politiques de conservation du sol et de gestion des bassins versants dans d'autres régions. Les principaux avantages de cette démarche sont sa précision, ses moindres exigences au niveau du temps sur le terrain et coûts associés, ainsi que la disponibilité accrue des données nécessaires de par le monde.

The photochemical reflectance index (PRI) is a remotely sensed vegetation index that detects a decrease in spectral reflectance at 531nm associated with xanthophyll cycle activity. PRI has been shown to track light use efficiency (LUE) in a number of plant species. PRI shows great promise in improving our ability to sense photosynthetic fluxes of CO2 remotely. However, it has not been tested in all environments, and its applicability is particularly uncertain for peatland environments dominated by mosses. This research investigates the ability of PRI to track LUE in a boreal forest and peatland, and examines the spectral signal associated with xanthophyll cycle activity in heterogeneous peatland plots. This research also investigates the relationship between PRI and leaf area index (LAI) over space and time in a peatland. We found most plots examined in the peatland site did not exhibit a spectral signal associated with xanthophyll cycle activity when exposed to a transition from dark conditions to full sunlight. This transition should lead to a de-epoxidation of xanthophylls in leaf tissues and a decrease in reflectance at 531nm. Plots that did show the decrease in reflectance at 531nm after this change in light conditions also displayed a decrease in PRI. This indicates that PRI effectively detects the 531nm signal as well as xanthophyll cycle activity and light stress in these plots. However, the variability in the strength of the spectral response to changing light conditions may confound the PRI signal in practice, and make it difficult to interpret results of airborne or satellite data. We also found PRI at the peatland site to be sensitive to and directly correlated with spatial variability in LAI, and negatively correlated with temporal variability in LAI. These characteristics may result in further difficulties applying PRI in peatlands. PRI and LUE were correlated at both the forest and peatland site, however at both sites the PRI signal saturated around 500 µmol m-2 s-1 of photosynthetically active radiation (PAR). This saturation effect has not, to our knowledge, been reported in other studies. Saturation of the PRI signal may limit our ability to determine carbon fluxes from airborne or satellite based remotely sensed data which is generally collected under clear skies during the brightest parts of the day when PAR exceeds 500 µmol m-2 s-1. / L'indice de réflectance photochimique (IRP) est un indice de végétation par télédétection qui détecte une diminution de la réflectance spectrale à 531nm associée à l'activité du cycle des xanthophylles. Il a été démontré que l'IRP est associé à l'efficacité d'utilisation de lumière (EUL) dans un certain nombre d'espèces végétales. L'IRP permet donc d'améliorer notre capacité à détecter les flux photosynthétiques du CO2 à distance. Cependant, il n'a pas été testé dans tous les environnements, et son applicabilité est particulièrement incertaine pour les écosystèmes tels que les tourbières dominées par les mousses. Cette étude examine la capacité des IRP de déceler l'EUL dans une forêt boréale et une tourbière, et examine le signal spectral associé à l'activité du cycle xanthophylle dans des parcelles hétérogènes d'une tourbière. Cette étude explore également la relation entre l'IRP et l'indice de surface foliaire (ISF) dans l'espace et le temps dans une tourbière.Nous avons trouvé que la plupart des parcelles examinées dans la tourbière ne présentent pas un signal spectral associé à l'activité du cycle de xanthophylle lorsqu'exposées à des conditions passant de l'obscurité à la lumière du soleil. Cette transition de luminosité devrait mener à la de-époxydation des xanthopylles dans les tissus foliaires et à une diminution de la réflectance à 531 nm. Les parcelles qui ont montré une telle diminution de la réflectance à 531 nm après les changements de luminosité ont aussi affiché une baisse de l'IRP. Ceci indique que l'IRP peut détecter le signal à 531 nm ainsi que l'activité du cycle de xanthophylle et le stress lumineux dans ces parcelles. Par contre, la variabilité de la réponse spectrale à l'évolution des conditions de lumière peuvent confondre le signal de l'IRP, ce qui rend difficile d'interpréter les résultats provenant de données aériennes ou satellitaires. Nous avons également constaté que l'IRP dans la tourbière est sensible et directement corrélé avec la variabilité spatiale de l'ISF, et négativement corrélé avec la variabilité temporelle de l'ISF. Ces caractéristiques peuvent entraîner des difficultés supplémentaires quant à l'application de l'IRP dans les tourbières.L'IRP et l'EUL étaient corrélés à la forêt et à la tourbière, mais il y avait saturation du signal de l'IRP autour de 500 µmol m-2 s-1 du rayonnement photosynthétiquement actif (RPA) aux deux sites. Cet effet de saturation n'a pas, à notre connaissance, été signalé dans d'autres études. La saturation du signal de l'IRP peut limiter notre capacité à déterminer les flux de carbone provenant de données aériennes ou satellitaires qui sont généralement recueillies sous un ciel clair pendant les parties les plus brillantes de la journée où la RPA dépasse 500 µmol m-2 s-1.

In this work, the various sources of errors in radar rain estimation are quantified and procedures are developed to reduce them. The few topics explored here are: the variability of drop size distributions (DSDs), radar calibration, and errors in polarimetric rain estimation. The findings resulting from this study include 1) a new filtering technique that reduces the spurious DSD sampling variability while maintaining the physical variability, 2) a generalization of previously suggested DSD models in terms of scaling concepts, 3) the experimental evidence of the physical interpretation of DSD evolution and of R-Z relationships, 4) the time scale dependence of the DSD variability and its implication for radar rain estimation, 5) the quantification of error sources in polarimetric rain estimation and its feasibility in operational environment, and 6) a complete set of stable radar calibration methods and their theoretical limits. All error statistics from this work will be used as a guideline in radar rain estimation.