A multispectral retrieval method is developed on the 100 km regional scale to extract the temperature, particle size, fractional cover and 11-μm emissivity of clouds which may be semitransparent in the infrared based on emitted radiances. The scheme utilizes the nonlinear relationship between emitted radiances when clouds are semitransparent and form a single-layered system. The retrieval method has the limitation that the particle size must be sufficiently small that the extinction and absorption cross sections at the different wavelengths are significantly different. For combinations of emission at 11 and 12 μm, the droplets must have radii less than 20 μm for both ice and water; for 3.7 and 12 μm the droplets must have radii less than 60 μm for ice and less than 100 μm for water; for 3.7 and 8 μm the droplets must have radii less than l50 μm for both ice and water. The retrieval scheme together with the spatial coherence method is applied to the analysis of NOAA-11 4-km Advanced Very High Resolution Radiometer 3.7, 11 and 12-μm observations obtained during the First ISCCP Regional Experiment Intensive Field Observations, Kansas, 1991. The results indicate that clear skies, single-layered and multi-layered cloud systems constitute equal proportions of 100-km scale regions. For the upper-level, single-layered clouds, 100-km scale emissivity and fractional cloud cover are correlated and the average effective radius of ice particles in semitransparent clouds is about 10 μm. Numerical simulations are performed to determine the sensitivity of the retrieved results to errors in observations and model assumptions and to compare the results of the current algorithm to those obtained with a threshold algorithm like that used by ISCCP. For effective radii less than 15 μm, errors in the retrieved effective radius are less than 1.5 μm and errors in cloud temperature are less than 5 K. The fractional cloud cover may be underestimated by 0.15. The 11-μm emissivity may be overestimated by 0.30. For upper-level, semitransparent/broken clouds, the current algorithm is superior to the threshold algorithm in the determination of cloud temperature and effective radius. / Graduation date: 1996

Realistic assessment of the vertical distribution of clouds, particularly the occurrence of multi-layered systems, is critical for accurate calculations of radiative transfer in general circulation models. Such information is also useful in the design and improvement of satellite retrieval techniques. Current methods for retrieving cloud properties from satellite data assume that the clouds reside in single-layered systems. These methods are not expected to be successful for multi-layered systems. Attempts to specifically address the question of cloud layering have thus far been limited, due in part to the difficulties of inferring vertical cloud structure from either surface or satellite data. In situ observations, such as those provided by aircraft, are available only for localized regions and are limited in time. This study uses data from a lidar instrument flown onboard the space shuttle and satellite imagery data to identify the frequencies of occurrence of layered cloud systems at different spatial scales over various regions of the globe. The Lidar In-Space Technology Experiment (L1TE) was flown on Space Shuttle Discovery in September 1994 and provided global-scale, high vertical resolution profiles of the earth's troposphere and lower stratosphere. Analysis of the LITE observations requires distinguishing clouds residing in organized, well-defined layers from clouds that are distributed in altitude throughout the troposphere. The analysis employs a histogram technique in which peaks having some critical number of observations are considered to correspond to observations belonging to well-defined cloud layers. Advanced Very High Resolution Radiometer (AVHRR) data for the 11-day duration of the LITE mission are analyzed using the spatial coherence method. This method identifies regions of locally uniform emission which are associated either with cloud-free pixels or with overcast pixels corresponding to clouds in a single layer at a well-defined altitude. The number of layers present is determined by the number of overcast radiances associated with pixel arrays exhibiting locally uniform emission within the region. Layer statistics are compiled for the Pacific, Atlantic, and Indian Oceans and the North and South American, African, European, Asian, and Australian continents using horizontal scales of 60 and 250 km. The results indicate a strong dependence on the spatial scale chosen for the analysis, with two- and three-layered systems more prevalent at the 250-km scale. Analysis of cloud-top altitudes from LITE and AVHRR show that low-level cloud systems comprise the majority of the observations over both ocean and land. / Graduation date: 1998

No description available.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1972. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1971. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Improvements have been made to the spatial coherence method for automatically determining cloud-free ocean radiances in satellite imagery by incorporating the spectral signatures of reflecting surfaces. The spatial coherence method relies on the fact that small-scale cloud-free regions typically exhibit uniform emission and uniform reflection. While small-scale overcast regions typically exhibit uniform emission, they often exhibit considerable variability in reflectance. On rare occasions the requirements of spatial uniformity are not met and errors are produced in estimated cloud-free radiances. The frequency of errors in identification of cloud-free and overcast pixels was assessed using two years of Advanced Very-High Resolution Radiometer (AVHRR) data from six regions of the globe. Significant improvement in the identification of cloud-free radiances is obtained by including a test of Q, the ratio of the AVHRR channel 2 (0.83-μm) reflectance to channel 1 (0.63-μm) reflectance. Q varies depending on whether the reflecting surface is cloud-free ocean, cloud-free land, or overcast by clouds. A study was conducted to determine the dependence of Q for overcast pixels on changes in season and geography. While some variation is evident due to satellite viewing angle and differences in atmospheric water vapor content, these effects are sufficiently small that constant thresholds may be used to help separate cloud-free and overcast pixels. The modified spatial coherence method uses the threshold for Q and radiance uniformity thresholds at 0.63-μm and 11-μm to identify cloud-free and overcast pixels. A sensitivity study was performed to determine the dependence of cloud-free ocean radiance estimates on the values of the uniformity thresholds. The results of the study indicate that using thresholds of 0.5% for the 0.63-μm reflectivity and 0.5 mWm⁻²sr⁻¹cm for the 11-μm radiance, produces cloud-free radiances that are rarely biased by more than 0.4% for reflectances at 0.63 μm and 0.4 K for the 11-μm brightness temperature. The uniformity and Q thresholds may be used for a large variety of scenes from different seasons and geographic areas. / Graduation date: 2000

A ground-based near-infrared spectroradiometer was built and used to measure relative spectral reflectance from cumulus congestus and cumulonimbus clouds during the 1985 and 1986 Arizona summer monsoon seasons. Thermodynamic phase was inferred from spectral features in the regions between 1.55-1.75μm and 2.1-2.3μm where there are distinct differences between absorption in liquid water and ice and absorption by water vapor is very weak. Although liquid water and ice are nearly transparent in the visible, they absorb weakly in the near-infrared and that absorption is amplified by multiple scattering in clouds. Reflectance measurements are simple to make, requiring neither high spectral resolution nor absolute detector response. Three distinct aspects of differences between absorption in liquid water and ice were used to infer phase: (a) Ratio of the signal at 1.65 μm to that at 2.2 μm; (b) Wavelength of peak signal in the 1.65 μm water vapor transmission window; (c) Half-bandwidth of the 2.1-2.3 μm feature. Representative spectra are presented and analyzed on the basis of the predicted behavior of liquid water and ice cloud absorption. The results are consistent with young cumuli rapidly glaciating as they reach cooler levels, well before evidence of anvil formation or fibrous structure, contrary to the notion that phase can be inferred from visible cloud features.

The accurate determination of cloud cover amount is important for characterizing the role of cloud feedbacks in the climate system. Clouds have a large influence on the climate system through their effect on the earth's radiation budget. As indicated by the NASA Earth Radiation Budget Experiment (ERBE), the change in the earth's radiation budget brought about by clouds is ~-15 Wm⁻² on a global scale, which is several times the ~4 Wm⁻² gain in energy to the troposphere-surface system that would arise from a doubling of CO₂ in the atmosphere. Consequently, even a small change in global cloud amount may lead to a major change in the climate system. Threshold methods are commonly used to derive cloud properties from satellite imagery data. Here, in order to quantify errors due to thresholds, cloud cover is obtained using three different values of thresholds. The three thresholds are applied to the 11 μm, (4 km)² NOAA-9 AVHRR GAC satellite imagery data over four oceanic regions. Regional cloud-cover fractions are obtained for two different scales, (60 km)² and (250 km)². The spatial coherence method for obtaining cloud cover from imagery data is applied to coincident data. The differences between cloud cover derived by the spatial coherence method and by the threshold methods depends on the setting of the threshold. Because the spatial coherence method is believed to provide good estimates of cloud cover for opaque, single-layered cloud systems, this study is limited to such systems, and the differences in derived cloud cover are interpreted as errors due to the application of thresholds. The threshold errors are caused by pixels that are partially covered by clouds and the errors have a dependence on the regional scale cloud cover. The errors can be derived from the distribution of pixel-scale cloud cover. Two simple models which assume idealized distributions for pixel-scale cloud cover are constructed and used to estimate the threshold errors. The results show that these models, though simple, perform rather well in estimating the differences between cloud cover derived by the spatial coherence method and those obtained by threshold methods. / Graduation date: 1992

Recentemente, as nuvens cirrus tem sido reconhecidas como importantes agentes do sistema climático global por funcionarem como cobertores térmico e poderem alterar signicativamente o balanço de radiação atmosférico, afetando o sistema climático em escalas de tempo que vão desde condições do tempo até mudanças climáticas. Elas são encontradas perto da tropopausa e são formadas principalmente por cristais de gelo não esféricos, com tempo de vida que pode ir de horas a alguns dias. Apesar de serem relativamente transparentes à radiação solar (profundidade óptica < 3,0), elas são opacas à radiação infravermelha, aprisionado radiação que seria perdida para o espaço, e, assim, podendo ter uma forçante radiativa positiva. Sua importância cresce devido a sua grande área de cobertura. A cobertura global de nuvens cirrus tem sido estimada em cerca de 20-25% e sua ocorrência pode ser mais de 70 % nos trópicos ( LIOU , 2002). No inicio de 2011, uma estação de UV-Raman Lidar se tornou operacional na região central da Amazônia, instalado 30 km a NE de Manaus-AM (2,89 °S 59,97 °W). Usando um laser de 95 mJ Nd-Yag em 355 nm e um telescópio Cassegrain com 400 e 4000 mm de distancia focal, este sistema detecta remotamente a troposfera com 7,5 m e 1-min de resolução espacial e temporal, respectivamente. Para analisar esse grande volume de dados, um algoritmo automatizado para detecção de nuvens cirrus foi desenvolvido com base no método descrito por ( BARJA , 2002), que determina a altitude da base, topo, máximo retro espalhamento e espessura. Os resultados mostram uma boa concordância entre o método visual de costume, não havendo diferença signicativa nas alturas de base. Um método baseado no fator de transmitância da equação do lidar foi utilizado para derivar a profundidade óptica dos cirrus. Pers de temperatura e pressão foram obtidos através de radiosondagens disponíveis duas vezes por dia do aeroporto militar de Ponta Pelada (28 km ao sul do sitio exerimental). Os métodos de Klett e Raman foram utilizados para derivar os coeciente de retroespalhamento e estimar a razão lidar das nuvens cirrus. Como resultados da analise dos dados dos dois primeiros anos de medidas (2011 e 2012), encontramos que a ocorrência de nuvens cirrus foi cerca de 71,0 % do tempo de observação total, sendo cerca de 24,2 % de todos os cirrus foram cirrus subvisuais (<0,03), 40,7 % eram cirrus nos (0,03< <0,3) e 35,1 % eram cirrus stratus ( > 0,3). Encontramos tambem os valores médios de 12,4 ± 2.k km , 14,3 ± 2,2 km para as altitudes de base e topo, respectivamente, residindo entre a temperaturas de até -90 °C e frequentemente encontradas próximas a tropopausa. A razão lidar para estas nuvens cirrus foi estimada em 20,0 ± 6,8 sr. Além disso, estudamos o comportamento destas grandezas com relação a temperatura. Enquanto as nuvens cirrus observadas mostraram uma redução da espessura e da profundidade óptica com a diminuição da temperatura (aumento da altitude), a razão lidar mostrou-se constante, indicando uma composição constante em termos da mistura de cristais de gelo. / Recently, cirrus clouds have been recognized as important agents of global climate system by functioning as a thermal blanket and can signicantly alter the radiation balance of the atmosphere, aecting the climate system from the weather to climate change timescales. They are found near the tropopause and are formed mainly by non spherical ice crystals, with lifetime that can go from hours to a few days. Despite being relatively transparent to solar radiation (optical depth < 3.0), they are opaque to the infrared radiation that would be lost to space, and thus have a positive radiative forcing. Its importance grows due to its large coverage area. The global cirrus cover has been estimated to be about 20-25% and their occurrence can be more than 70% over the tropics ( LIOU , 2002). In mid-2011 a UV Raman Lidar station become operational in the central Amazon region, installed 30 km up-wind from Manaus-AM (2.89 °S 59.97 °W). Using a 95 mJ Nd-Yag laser at 355 nm and a cassegrain telescope with 400 mm and 4000 mm focal length, this system remotely senses the troposphere with 7.5 m and 1-min height and time resolution respectively. To analyze this large amount of data, an automated algorithm for the detection of cirrus clouds was developed based on the method described for( BARJA , 2002), which determine the cloud base, top and maximum light backscattering heights, and cloud thickness. The results show a good agreement between the usual visual method, with no signicant dierence in the base heights. The transmittance factor of the lidar signal was used to derive the optical depth cirrus. Proles of temperature and pressure were obtained by radiosondes available twice daily from the military airport of Ponta Pelada (28 km south from the experimental site). The Klett and Raman methods were used to derive the backscattering coecient and to estimate the lidar ratio of the cirrus clouds. As the results for the analysis of data from the rst two years of measurements (2011 and 2012 ), we found that the occurrence of cirrus clouds was approximately 71.0 % of the total time of observation, being approximately 24.2 % of all cirrus were subvisual ( < 0.03), 40.7 % were thin cirrus (0.03 < < 0.3 ) and 35.1 % were cirrus stratus ( > 0.3). Also found the average values of 12.4 ± 2.4 km 14.3 ± 2.2 km for altitudes of the base and top height, respectively, residing between the temperatures down to -90 °C and frequently found near the tropopause. The lidar-ratio was estimated as 20.0 ± 6.8 sr . Also, the behavior of these quantities with respect to temperature was studied.

Recentemente, as nuvens cirrus tem sido reconhecidas como importantes agentes do sistema climático global por funcionarem como cobertores térmico e poderem alterar signicativamente o balanço de radiação atmosférico, afetando o sistema climático em escalas de tempo que vão desde condições do tempo até mudanças climáticas. Elas são encontradas perto da tropopausa e são formadas principalmente por cristais de gelo não esféricos, com tempo de vida que pode ir de horas a alguns dias. Apesar de serem relativamente transparentes à radiação solar (profundidade óptica < 3,0), elas são opacas à radiação infravermelha, aprisionado radiação que seria perdida para o espaço, e, assim, podendo ter uma forçante radiativa positiva. Sua importância cresce devido a sua grande área de cobertura. A cobertura global de nuvens cirrus tem sido estimada em cerca de 20-25% e sua ocorrência pode ser mais de 70 % nos trópicos ( LIOU , 2002). No inicio de 2011, uma estação de UV-Raman Lidar se tornou operacional na região central da Amazônia, instalado 30 km a NE de Manaus-AM (2,89 °S 59,97 °W). Usando um laser de 95 mJ Nd-Yag em 355 nm e um telescópio Cassegrain com 400 e 4000 mm de distancia focal, este sistema detecta remotamente a troposfera com 7,5 m e 1-min de resolução espacial e temporal, respectivamente. Para analisar esse grande volume de dados, um algoritmo automatizado para detecção de nuvens cirrus foi desenvolvido com base no método descrito por ( BARJA , 2002), que determina a altitude da base, topo, máximo retro espalhamento e espessura. Os resultados mostram uma boa concordância entre o método visual de costume, não havendo diferença signicativa nas alturas de base. Um método baseado no fator de transmitância da equação do lidar foi utilizado para derivar a profundidade óptica dos cirrus. Pers de temperatura e pressão foram obtidos através de radiosondagens disponíveis duas vezes por dia do aeroporto militar de Ponta Pelada (28 km ao sul do sitio exerimental). Os métodos de Klett e Raman foram utilizados para derivar os coeciente de retroespalhamento e estimar a razão lidar das nuvens cirrus. Como resultados da analise dos dados dos dois primeiros anos de medidas (2011 e 2012), encontramos que a ocorrência de nuvens cirrus foi cerca de 71,0 % do tempo de observação total, sendo cerca de 24,2 % de todos os cirrus foram cirrus subvisuais (<0,03), 40,7 % eram cirrus nos (0,03< <0,3) e 35,1 % eram cirrus stratus ( > 0,3). Encontramos tambem os valores médios de 12,4 ± 2.k km , 14,3 ± 2,2 km para as altitudes de base e topo, respectivamente, residindo entre a temperaturas de até -90 °C e frequentemente encontradas próximas a tropopausa. A razão lidar para estas nuvens cirrus foi estimada em 20,0 ± 6,8 sr. Além disso, estudamos o comportamento destas grandezas com relação a temperatura. Enquanto as nuvens cirrus observadas mostraram uma redução da espessura e da profundidade óptica com a diminuição da temperatura (aumento da altitude), a razão lidar mostrou-se constante, indicando uma composição constante em termos da mistura de cristais de gelo. / Recently, cirrus clouds have been recognized as important agents of global climate system by functioning as a thermal blanket and can signicantly alter the radiation balance of the atmosphere, aecting the climate system from the weather to climate change timescales. They are found near the tropopause and are formed mainly by non spherical ice crystals, with lifetime that can go from hours to a few days. Despite being relatively transparent to solar radiation (optical depth < 3.0), they are opaque to the infrared radiation that would be lost to space, and thus have a positive radiative forcing. Its importance grows due to its large coverage area. The global cirrus cover has been estimated to be about 20-25% and their occurrence can be more than 70% over the tropics ( LIOU , 2002). In mid-2011 a UV Raman Lidar station become operational in the central Amazon region, installed 30 km up-wind from Manaus-AM (2.89 °S 59.97 °W). Using a 95 mJ Nd-Yag laser at 355 nm and a cassegrain telescope with 400 mm and 4000 mm focal length, this system remotely senses the troposphere with 7.5 m and 1-min height and time resolution respectively. To analyze this large amount of data, an automated algorithm for the detection of cirrus clouds was developed based on the method described for( BARJA , 2002), which determine the cloud base, top and maximum light backscattering heights, and cloud thickness. The results show a good agreement between the usual visual method, with no signicant dierence in the base heights. The transmittance factor of the lidar signal was used to derive the optical depth cirrus. Proles of temperature and pressure were obtained by radiosondes available twice daily from the military airport of Ponta Pelada (28 km south from the experimental site). The Klett and Raman methods were used to derive the backscattering coecient and to estimate the lidar ratio of the cirrus clouds. As the results for the analysis of data from the rst two years of measurements (2011 and 2012 ), we found that the occurrence of cirrus clouds was approximately 71.0 % of the total time of observation, being approximately 24.2 % of all cirrus were subvisual ( < 0.03), 40.7 % were thin cirrus (0.03 < < 0.3 ) and 35.1 % were cirrus stratus ( > 0.3). Also found the average values of 12.4 ± 2.4 km 14.3 ± 2.2 km for altitudes of the base and top height, respectively, residing between the temperatures down to -90 °C and frequently found near the tropopause. The lidar-ratio was estimated as 20.0 ± 6.8 sr . Also, the behavior of these quantities with respect to temperature was studied.