Snow and lake ice have very high albedos compared to other surfaces found in nature. Surface albedo is an important component of the surface energy budget especially when albedos are high since albedo governs how much shortwave radiation is absorbed or reflected at a surface. In particular, snow and lake ice albedos have been shown to affect the timing of lake ice break-up. Lakes are found throughout the Northern Hemisphere and lake ice has been shown to be sensitive to climatic variability. Therefore, the modelling of lake ice phenology, using lake ice models such as the Canadian Lake Ice Model (CLIMo), is important to the study of climatic variability in the Arctic and sub-Arctic regions and accurate snow and lake ice albedo measurements are required to ensure the accuracy of the simulations. However, snow and lake ice albedo can vary from day-to-day depending on factors such as air temperature, presence of impurities, age, and composition. Some factors are more difficult than others to model (e.g. presence of impurities). It would be more straight forward to just gather field measurements, but such measurements would be costly and lakes can be in remote locations and difficult to access. Instead, CLIMo contains an albedo parameterization scheme that models the evolution of snow and lake ice albedo in its simulations. However, parts of the albedo parameterization are based on sea-ice observations (which inherently have higher albedos due to brine inclusions) and the albedo parameterization does not take ice type (e.g. clear ice or snow ice) into account. Satellite remote sensing via the Moderate Resolution Imaging Spectroradiometer (MODIS) provides methods for retrieving albedo that may help enhance CLIMo’s albedo parameterization. CLIMo’s albedo parameterization as well the MODIS daily albedo products (MOD10A1 and MYD10A1) and 16-day product (MCD43A3) were evaluated against in situ albedo observations made over Malcolm Ramsay Lake near Churchill, Manitoba, during the winter of 2012. It was found that the snow albedo parameterization of CLIMo performs well when compared to average in situ observations, but the bare ice parameterization overestimated bare ice albedo observations. The MODIS albedo products compared well when evaluated against the in situ albedo observations and were able to capture changes in albedo throughout the study period. The MODIS albedo products were also compared against CLIMo’s melting ice parameterization, because the equipment had to be removed from the lake to prevent it from falling into the water during the melt season. Cloud cover interfered with the MODIS observations, but the comparison suggests that MODIS albedo products retrieved higher albedo values than the melting ice parameterization of CLIMo. The MODIS albedo products were then integrated directly into CLIMo in substitution of the albedo parameterization to see if they could enhance break-up date (ice off) simulations. MODIS albedo retrievals (MOD10A1, MYD10A1, and MCD43A3) were collected over Back Bay, Great Slave Lake (GSL) near Yellowknife, Northwest Territories, from 2000-2011. CLIMo was then run with and without the MODIS albedos integrated and compared against MODIS observed break-up dates. Simulations were also run under three difference snow cover scenarios (0%, 68%, and 100% snow cover). It was found that CLIMo without MODIS albedos performed better with the 0% snow cover scenario than with the MODIS albedos integrated in. Both simulations (with and without MODIS albedos) performed well with the snow cover scenarios. The MODIS albedo products slightly improved CLIMo break-up simulations when integrated up to a month in advance of actual lake ice break-up for Back Bay. With the MODIS albedo products integrated into CLIMo, break-up dates were simulated within 3-4 days of MODIS observed break-up. CLIMo without the MODIS albedos still performed very well simulating break-up within 4-5 days of MODIS observed break-up. It is uncertain whether this was a significant improvement or not with such a small study period and with the investigation being conducted at a single site (Back Bay). However, it has been found that CLIMo performs well with the original albedo parameterization and that MODIS albedos could potentially complement lake-wide break-up simulations in future studies.

Variation in snow albedo feedback (SAF) among CMIP5 climate models has been shown to explain much of the variation in projected 21st Century warming over Northern Hemisphere land. Prior studies using observations and models have demonstrated both considerable spread in the albedo, and a weak bias in the simulated strength of SAF, over snow-covered boreal forests. Boreal evergreen needleleaf forests are capable of intercepting snowfall throughout the snow season, which has a significant impact on seasonal albedo. Two satellite data products and tower-based observations of albedo are compared with simulations from multiple configurations of the Community Climate System Model (CCSM4) to investigate the causes of weak simulated SAF over the boreal forest. The largest bias occurs in April-May when simulated SAF is one-half the strength of SAF in observations. This is traced to two canopy snow parameterizations in the land model. First, there is no mechanism for the dynamic removal of snow from the canopy when temperatures are below freezing, which results in albedo values in midwinter that are biased high. Second, when temperatures do rise above freezing, all snow on the canopy is melted instantaneously, which results in an unrealistically early transition from a snow-covered to a snow-free canopy. These processes combine to produce large differences between simulated and observed monthly albedo, and are the sources of the weak bias in SAF. This analysis highlights the importance of canopy snow parameterizations for simulating the hemispheric scale climate response to surface albedo perturbations. A number of new experiments are described as recommendations for future work.

Canadian High Arctic terrestrial ice masses and the polar atmosphere evolve co-dependently, and interactions between the two systems can lead to feedbacks, positive and negative. The two primary positive cryosphere-atmosphere feedbacks are: 1) The snow/ice-albedo feedback (where area changes in snow and/or ice cause changes in surface albedo and surface air temperatures, leading to further area changes in snow/ice); and 2) The elevation - mass balance feedback (where thickness changes in terrestrial ice masses cause changes to atmospheric circulation and precipitation patterns, leading to further ice thickness changes). In this thesis, numerical experiments are performed to: 1) quantify the magnitudes of the two feedbacks for chosen Canadian High Arctic terrestrial ice masses; and 2) to examine the direct and indirect consequences of surface air temperature changes upon englacial temperatures with implications for ice flow, mass flux divergence, and topographic evolution. Model results show that: a) for John Evans Glacier, Ellesmere Island, the magnitude of the terrestrial snow/ice-albedo feedback can locally exceed that of sea ice on less than decadal timescales, with implications for glacier response times to climate perturbations; b) although historical air temperature changes might be the direct cause of measured englacial temperature anomalies in various glacier and ice cap accumulation zones, they can also be the indirect cause of their enhanced diffusive loss; c) while the direct result of past air temperature changes has been to cool the interior of John Evans Glacier, and its bed, the indirect result has been to create and maintain warm (pressure melting point) basal temperatures in the ablation zone; and d) for Devon Ice Cap, observed mass gains in the northwest sector of the ice cap would be smaller without orographic precipitation and the mass balance – elevation feedback, supporting the hypothesis that this feedback is playing a role in the evolution of the ice cap.

Thesis (doctoral)--Universität Hannover, 2004. / Includes bibliographical references (p. 129-137). Also available in color version in PDF format.

Submitted by Nathália Faria da Silva (nathaliafsilva.ufv@gmail.com) on 2017-07-26T15:49:38Z No. of bitstreams: 1 texto completo.pdf: 8862607 bytes, checksum: 1abea5aa5010bb199162254036d1c345 (MD5) / Made available in DSpace on 2017-07-26T15:49:38Z (GMT). No. of bitstreams: 1 texto completo.pdf: 8862607 bytes, checksum: 1abea5aa5010bb199162254036d1c345 (MD5) Previous issue date: 1993-12-15 / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Realizou-se um estudo comparativo do microclima de uma área de floresta com o de uma área de pastagem, em Marabá, PA. Como consequência do desmatamento, observaram-se alterações nos componentes do balanço total de radiação. O albedo diário foi mais elevado na área de pastagem, com 18,3%, enquanto na área de floresta foi equivalente a 15,7% na estação seca. Na estação chuvosa, o albedo variou de 13,2% na floresta a 18,2% na pastagem. O saldo total de radiação foi superior na área de floresta, principalmente, na estação seca. As maiores amplitudes térmicas diárias do ar foram observadas na área de pastagem, em todo o período estudado. A velocidade do vento foi comparável entre as duas áreas no período diurno, porém, à noite, o vento, na área de pastagem, diminuiu bastante. Esta situação, associada com o maior resfriamento do ar na pastagem, proporcionou um menor déficit de umidade específica, em comparação com a floresta. As alterações apresentadas contribuíram para menores estimativas de evapotranspiração potencial na pastagem, pelos métodos de Penman e Priestley-Taylor. As diferenças nas variáveis meteorológicas entre as áreas de floresta e de pastagem poderão induzir alterações no clima, em escala local ou regional, dependendo da extensão da área desmatada.

abstract: Remote sensing in visible to near-infrared wavelengths is an important tool for identifying and understanding compositional differences on planetary surfaces. Electronic transitions produce broad absorption bands that are often due to the presence of iron cations in crystalline mineral structures or amorphous phases. Mars’ iron-rich and variably oxidized surface provides an ideal environment for detecting spectral variations that can be related to differences in surface dust cover or the composition of the underlying bedrock. Several imaging cameras sent to Mars include the capability to selectively filter incoming light to discriminate between surface materials. At the coarse spatial resolution provided by the wide-angle Mars Color Imager (MARCI) camera aboard the Mars Reconnaissance Orbiter (MRO), regional scale differences in reflectance at all wavelengths are dominated by the presence or absence of Fe3+-rich dust. The dust cover in many regions is highly variable, often with strong seasonal dependence although major storm events can redistribute dust in ways that significantly alter the albedo of large-scale regions outside of the normal annual cycle. Surface dust reservoirs represent an important part of the martian climate system and may play a critical role in the growth of regional dust storms to planet-wide scales. Detailed investigation of seasonal and secular changes permitted by repeated MARCI imaging coverage have allowed the surface dust coverage of the planet at large to be described and have revealed multiannual replenishing of regions historically associated with the growth of storms. From the ground, rover-based multispectral imaging acquired by the Mastcam cameras allows compositional discrimination between bedrock units and float material encountered along the Curiosity rover’s traverse across crater floor and lower Mt. Sharp units. Mastcam spectra indicate differences in primary mineralogy, the presence of iron-bearing alteration phases, and variations in iron oxidation state, which occur at specific locations along the rover’s traverse. These changes represent differences in the primary depositional environment and the action of later alteration by fluids circulating through fractures in the bedrock. Loose float rocks sample materials brought into the crater by fluvial or other processes. Mastcam observations provide important constraints on the geologic history of the Gale Crater site. / Dissertation/Thesis / Supplemental Animations for Chapter 2 / Doctoral Dissertation Geological Sciences 2018

Submitted by Eduarda Figueiredo (eduarda.ffigueiredo@ufpe.br) on 2015-03-13T15:05:19Z No. of bitstreams: 2 dissertação.pdf: 6455224 bytes, checksum: ef9156322dda8d7f46ffd83a38e15fa7 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) / Made available in DSpace on 2015-03-13T15:05:19Z (GMT). No. of bitstreams: 2 dissertação.pdf: 6455224 bytes, checksum: ef9156322dda8d7f46ffd83a38e15fa7 (MD5) license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Previous issue date: 2012-08-14 / CAPES / A evapotranspiração é um dos componentes mais importantes do ciclo da água, diante desse aspecto, com intuito de contribuir para a compreensão das estimativas e análises da Evapotranspiração, este estudo tem como objetivo obter o balanço de energia e a evapotranspiração real diária na área de preservação ambiental Ilha de Santa Rita - Alagoas. As técnicas de sensoriamento remoto mediante as imagens orbitais crescem como uma alterativa rápida de coletar informações sobre os fenômenos existentes na superfície da terra, como a evapotranspiração. Logo, A metodologia a ser utilizada envolve o uso do algoritmo SEBAL, imagens do satélite TM Landsat 5 e dados complementares de estação meteorológica localizada na área de estudo. A distribuição espacial da ET24h real foi analisada em combinação com o mapa de cobertura da terra. A estimativa diária de ET24h real variou de 0 a 1 mm.dia-1 para solo exposto e cidade; a 6 mm.dia-1 para corpos d’água e mangue, com um valor médio de 3,78 mm.dia-1, 3,45 mm, dia-1 e 4,75mm.dia-1 para os dias 03/09/2003, 26/08/2006 e 17/03/2011, respetivamente, para toda área estudada. A variação da ET24h real estimado em diferentes tipos de uso da terra foi concedida com a teoria da evapotranspiração, o que sugere a aplicação da abordagem SEBAL com algumas informações detalhadas, como campo de cultura ou de uso da terra.

Au niveau global, il a été estimé qu’une augmentation de 4% de l’albédo (ou réflectivité) de la surface provoquerait une diminution de 0,7° de la température d’équilibre de la Terre. Or les propriétés des surfaces (dont l’albédo) changent sous la pression climatique et l’action de l’homme. Parallèlement à ce changement des propriétés de surface un débat divise la communauté scientifique sur une éventuelle diminution ou augmentation du rayonnement incident à la surface depuis le milieu des années 1980 (conséquence d’une augmentation ou diminution de la concentration d’aérosols dans l’atmosphère). La Terre est un système complexe piloté en sa surface par 3 cycles (énergie, eau et carbone). Ces cycles ne sont pas insensibles à ces changements de propriété de réflectivité de surface, de rayonnement solaire incident ou de concentration en aérosols. Certains avancent ainsi qu’une augmentation du rayonnement diffus durant les dernières décennies aurait déjà entraîné un excédent de captation de carbone par la végétation de 9.3%. La problématique ici soulevée est d’évaluer l’apport de la connaissance du flux solaire absorbé par la surface (combinaison du rayonnement solaire et de l’albédo de surface) et plus particulièrement par sa partie végétative pour le suivi des flux d’énergie, d’eau et de carbone. Dans ce travail, j’ai fait appel à l’observation satellitaire et à la modélisation du transfert radiatif pour cartographier la dynamique du rayonnement solaire absorbé par la surface et sur la verticale de la végétation. Dans un premier temps, chacune des sources d’incertitudes sur le rayonnement incident, sur l’albédo de surface mais aussi sur la répartition du rayonnement entre les hétérogénéités horizontales et verticales à la surface furent quantifiées. Puis tout en discutant l’effet de ces incertitudes, j’ai mesuré l’apport de l’utilisation de cette cartographie par satellite du rayonnement solaire absorbé pour estimer les flux d’énergie et d’eau en surface ; ce qui améliora les scores de prévision du temps à court terme et permis également de suggérer des rétroactions à l’échelle climatique sur des zones sensibles tel le Sahel. Aussi une correction de biais de 15% sur l’estimation de la production primaire brute de carbone à l’échelle planétaire démontra l’importance des développements réalisés afin de caractériser les hétérogénéités verticales dans le couvert. Finalement, ce travail m’a conduit à chiffrer l’impact de la méconnaissance des variabilités spatiales et temporelles des propriétés des aérosols (concentration et type). J’ai montré que le suivi au cours du temps des propriétés de directionalité de la réflectivité de surface (tel abordé dans la première partie de mon étude) pouvait aussi permettre de remonter à la quantité d’aérosol dans l’atmosphère. L’utilisation d’observations issues de satellite géostationnaire permet d’estimer la concentration en aérosol avec la même qualité mais avec une fréquence de détection plus élevée (x5 environ) que les méthodes classiques. Enfin, ce travail dresse des pistes pour améliorer la détection des changements des propriétés de réflectivité de surface et d’aérosols de l’atmosphère, et atteindre un suivi encore meilleur des cycles biogéochimiques de la biosphère terrestre. / It is known that a global 4% increase of land surface albedo (also called reflectivity) may result approximately in a decrease of 0.7°C in the Earth’s equilibrium temperature. Nowadays the surface properties (including albedo) are changing under climatic and human pressure. At the same time, there is a debate that divides the scientific community about the potential trends (increase or decrease) affecting the surface incoming solar radiation since mid-1980 (resulting of a decrease or increase of aerosol concentration in the atmosphere, respectively). The Earth is a complex system driven at the surface level by three cycles (energy, water, and carbon). These cycles are not insensitive to changes of surface reflectivity, incoming radiation, or aerosol properties. For example, some argue that the increase of diffuse radiation during the last decades would have led to an exceed of carbon uptake by the Earth’s vegetation of 9.3%. The main issue raised here is to assess the added value of the knowledge in absorbed solar radiation by the surface (combination of incoming solar radiation with surface albedo) and, especially, by the vegetation for the monitoring of energy, water and carbon fluxes.In this work, I have used satellite observations and modeled the radiative transfer theory in order to make dynamic mapping of solar radiation absorbed by the surface and through the vertical dimension of the vegetation. First, I quantified each uncertainty source affecting incoming solar radiation, surface albedo and the way radiation is split between horizontal and vertical heterogeneity. In a second step, I measured the added value of using this absorbed radiation mapping of the surface by satellite to estimate the energy and water fluxes at the surface. The resulting improved scores of weather forecast models in the short-range time scale suggested potential feedbacks at the climatic time scale over sensible areas such as the Sahel region. Another significant outcome is that the developments proposed to better characterize the vertical heterogeneity within the canopy led to an improvement of 15% of annual global terrestrial gross primary production (GPP). Moreover, this study has led to measure the impact of the lack of knowledge of spatial and temporal variability of aerosol properties (concentration and type). I have shown that the tracking of temporal changes of directional properties of reflectance allows me to retrieve to the amount of aerosols in the atmosphere as precisely as other widely used methods but with a higher frequency (5 times more) by using data from geostationary satellite. Finally, this study addresses some possibilities to better track temporal changes of properties of reflectivity of surface and aerosol of atmosphere, and to access to a better monitoring of biogeochemical cycles of the terrestrial biosphere.

This study focuses on comparing six different marine optical models, field measurements, and laboratory measurements. Inherent Optical Properties (IOPs) of the water column depend only on the constituents within the water, not on the ambient light field. Apparent Optical Properties (AOPs) depend both on IOPs and the geometric underwater light field resulting from solar irradiance. Absorption (a) and scattering (b) are IOPs. Scattering can be partitioned into backscattering (b[subscript b]). Remote Sensing Reflectance (R[subscript rs]), the ratio of radiant light leaving the water to the light entering the water surface plane (E[subscript d]), is an AOP. R[subscript rs] is proportional to b[subscript b]/(a + b[subscript b]). Using this relationship, R[subscript rs] is inverted to determine both absorption and backscattering. The constituents contributing to both absorption and backscattering can then be further deconvolved using modeling techniques. The in situ instruments usually have a fixed path length while AOP measurement path length depends on the penetration and/or return of downwelling solar irradiance. As a consequence, AOP measurements use a longer path length than in situ instruments. If the path length of a direct IOP measurement instrument is too short, there may not be sufficient signal to determine a change in value. While the AOP inversions require more empirical assumptions to determine IOP values than in situ instruments, they provide a higher signal to noise ratio in clearer waters. This study defines closure as the statistical agreement between instruments and methods in order to determine the same optical property. No method is considered absolute truth. An R[subscript rs] inversion algorithm was best under most of the test stations for measuring IOP values. One exception was when bottom reflectance was significant, an inversion of diffuse attenuation (the change in the natural log of E[subscript d] over depth) was better for determining absorption and a field instrument was better for determining backscattering. The relationships between AOPs and IOPs provide estimates of unmeasured optical properties. A method was developed to determine the spectral reflectance of the bottom using IOP estimates and R[subscript rs].

Land surface albedo describes the proportion of incident solar radiant flux that is reflected from the Earth's surface and therefore is a crucial parameter in modeling and monitoring attempts to capture the current climate, hydrological, and biogeochemical cycles and predict future scenarios. Due to the temporal variability and spatial heterogeneity of land surface albedo, remote sensing offers the only realistic method of monitoring albedo on a global scale. While the distribution of bright, highly reflective surfaces (clouds, snow, deserts) govern the vast majority of the fluctuation, variations in the intrinsic surface albedo due to natural and human disturbances such as urban development, fire, pests, harvesting, grazing, flooding, and erosion, as well as the natural seasonal rhythm of vegetation phenology, play a significant role as well. The development of times series of global snow-free and cloud-free albedo from remotely sensed observations over the past decade and a half offers a unique opportunity to monitor and assess the impact of these alterations to the Earth's land surface. By utilizing multiple satellite records from the MODerate-resolution Imaging Spectroradiometer (MODIS), the Multi-angle Imaging Spectroradiometer (MISR) and the Visible Infrared Imaging Radiometer Suite (VIIRS) instruments, and developing innovative spectral conversion coefficients and temporal gap-filling strategies, it has been possible to utilize the strengths of the various sensors to improve the spatial and temporal coverage of global land surface albedo retrievals. The availability of these products is particularly important in tropical regions where cloud cover obscures the forest for significant periods. In the Amazon, field ecologists have noted that some areas of the forest ecosystem respond rapidly with foliage growth at the beginning of the dry season, when sunlight can finally penetrate fully to the surface and have suggested this phenomenon can continue until reductions in water availability (particularly in times of drought) impact the growth cycle. While it has been difficult to capture this variability from individual optical satellite sensors, the temporally gap-filled albedo products developed during this research are used in a case study to monitor the Amazon during the dry season and identify the extent of these regions of foliage growth.