A constante evolução dos equipamentos e softwares na área de topografia propiciou um ganho considerável em produtividade e qualidade na confecção dos mapas que servem de base aos projetos de Engenharia. O propósito deste trabalho é a analise comparativa dos dados de altimetria obtidos por três diferentes equipamentos de grande uso no mercado nacional, ou seja, a Estação total, GPS geodésico e GPS navegação, a fim de podermos avaliar a possibilidade do uso dos equipamentos rastreadores GPS para elaboração da hipsometria terrestre. Á área em estudo encontra-se no Campus “Luiz de Queiroz” da Universidade de são Paulo, no município de Piracicaba, Estado de São Paulo, cujas coordenadas aproximadas são: latitude de 22 o 42´40 “S e longitude de 47 o 37´30” W, sendo os dados coletados no mês de julho de 2002. Para avaliar o desempenho dos receptores GPS de Navegação e Geodésico em levantamentos altimétricos para fim de sistematização de terras, foram levantadas áreas com declividades diferentes (0 a 1%; 2 a 4% e 5 a 8%), simultaneamente pelo método topográfico convencional, utilizado uma Estação Total, de acordo com a NBR 13.133 – Execução de Levantamento Topográfico, e com os receptores GPS, sendo posteriormente calculados os volumes de terras para a comp aração dos resultados. De acordo com a metodologia empregada e os resultados obtidos, as principais conclusões foram: a) foi possível avaliar o erro cometido pelos equipamentos descritos, confirmando assim a possibilidade de uso do GPS Geodésico e descartando o uso do GPS de navegação para fins de sistematização de terras; b) com o uso do GPS diferencial os volumes entre os MDTs (Estação Total x GPS Geodésico) analisados em nove áreas com declividades diferentes esta em média 0,67% quando comparada as superfícies geradas, o que pode ser considerado como aceitável, e não significativo quando da execução dos serviços de sistematização terras o que vem ratificar o uso do equipamento GPS geodésico, se utilizados conforme a metodologia adotada. / The constant evolution of the equipments and softwares in the surveing field has brought a lot of gain in productivity and quality to make maps that are the foundation for the engineering projects. The purpose of this work is the comparative analyses of the data obtained by 3 different equipments that are very used in the national market - the Total Station, the Geodetic GPS and the Navigation GPS- in order to be able to evaluate the possibility of the use of the tracking GPS equipments for the elaboration of the terrestrial hypsometry. The studied area is in the “Luiz de Queiroz” Campus, in the University of São Paulo, in the city of Piracicaba, São Paulo state, whose approximate coordinates are: 22 42’40”S of latitude, and 47 37’30” W of longitude, these datum are from July 2002. According to the applied methodology and the obtained result, the main conclusions are: a) it was possible to evaluate the mistake by the described equipments, confirming the possibility of the use of Geodesic GPS and discarding the use of the Navigation GPS for land systematization; b) with the use of the differential GPS, the volume between the MDTs (Total Station x Geodesic GPS) analyzed in three different areas, the average is 067%, which can be considered acceptable, and not meaningful when from the execution of the land systematization services, what ratifies the use of the Geodesic GPS equipment, if used according to the applied methodology.

A common way to measure height in aerial vehicles is to use a radar height altimeter (RHM). Since the RHM transmits radar pulses that can be detected, a passive alternative would be desirable in military applications. The idea to use reflected signals from the Global Positioning System (GPS) as a bistatic radar, has been established over the last years. The GPS signals are already present and would not reveal aeroplanes in covert operations. In this thesis, the use of reflected GPS signals as a bistatic, passive altimeter is examined. A simulation model has been developed and implemented, and simulations using the model have been done. Different types of ground cover have been investigated, both water and land types, with varying reflectivity and scattering behaviour. For larger terrain variations, e.g. mountains and valleys, a ground elevation database has been used. Furthermore, several parameters, like the antenna coverage and the satellite elevation angle, have been varied and the result of this examined. The results of these simulations show that measuring height is possible for bothsea and land surfaces. The accuracy depends on several error factors, like a bias originating from surface roughness and measurement errors due to noise in the receiver. The simulations also show that the most important design parameter is the antenna, which must be designed to give a sufficiently large SNR, capture the specular reflection and avoid unwanted reflections.

Dans le contexte de la hausse actuelle du niveau marin, la détermination du mouvement vertical à la côte est cruciale pour deux principales raisons. D’une part, parce qu’il est enregistré dans la mesure marégraphique et constitue une source d’incertitude dans l’estimation des variations long terme du niveau marin (suivant les auteurs ces variations sont de l’ordre de 1 à 2 mm/an de montée au cours du siècle passé). Et d’autre part, parce que les processus de subsidence à la côte sont un facteur aggravant des effets de la montée du niveau marin avec parfois des taux qui résultent en une montée relative du niveau marin de l’ordre de 1 cm/an, soit des projections de 1 mètre en un siècle, sans accélération des contributions climatiques actuelles. Cette thèse de doctorat s’attaque à la détermination des mouvements verticaux à la côte par GPS et par une méthode originale de combinaison des données de marégraphie et d’altimétrie radar embarquée sur satellite. La méthode proposée ici est basée sur celle de Kuo et al. (2004), reprise et étendue en appliquant un filtrage spatio-temporel issu de l’analyse EOF des deux types de séries de données. La méthode est appliquée dans le Golfe du Mexique sur la période 1950-2009 en utilisant les quinze séries marégraphiques de plus de 40 ans d’observations disponibles dans la région au PSMSL et les séries altimétriques mises à disposition dans AVISO sur la période 1992-2009. La comparaison avec les mouvements verticaux issus des cinq séries de positions de stations GPS co-localisées avec marégraphes montre un écart moyen quadratique sur les différences de 0.60 mm/an révélant la grande précision de la nouvelle approche. Les séries temporelles GPS ont préalablement fait l’objet d’une analyse poussée du bruit et des incertitudes associées, légitimant l’utilisation des séries GPS dans la correction des tendances du niveau marin obtenues des marégraphes. Les incertitudes obtenues des vitesses verticales GPS sont de l’ordre de 0.5 mm/an ce qui est significativement inférieur à d’autres analyses de ce type. La méthode altimétrie moins marégraphie mise au point offre donc des perspectives intéressantes dans la détermination précise des mouvements verticaux côtiers où il n’existe pas de mesures géodésiques. / In the context of the current sea level rise, the determination of coastal vertical land motion is crucial for two main reasons. In one hand, tide gauge measurements are affected by vertical displacements and this is a source of uncertainties for the estimation of long-term sea level variations ( those variations are in the order of 1 to 2 mm/yr of sea level rise during the last century according to different authors). On the other hand, coastal subsiding processes could aggravate the effects of sea level rise with rates leading sometimes to 1 cm/yr of relative sea level rise, that is 1 meter over a century, without any acceleration of climatic contribution. This PhD thesis addresses the determination of coastal vertical land movement by GPS and by an original method combining the data from both tide gauge and satellite radar altimetry. The method which is suggested here is based on those of Kuo et al., (2004), repeated and extended by spatio-temporal filtering from EOF analysis of the two kinds of series. The method is applied in the Gulf of Mexico over the period 1950-2009 using the available fifteen tide gauge series of more than 40 years of observations selected from the PSMSL and altimetric series selected from AVISO over the period 1992-2009. The comparison between vertical land movements from the five position time series of the GPS stations collocated at tide gauge locations shows a root mean square error of 0.60 mm/an over the difference , highlighting the high accuracy of the new approach. Beforehand, GPS time series underwent a detailed noise analysis and their associated uncertainties, legitimating the use of GPS series in the correction of tide gauge sea level trends. The uncertainties from GPS vertical velocities are in the order of 0.5 mm/yr which is significantly lower than other analysis of this type. The adjusted method altimetry minus tide gauge presents interesting prospects for the accurate determination of coastal land motion where there are not geodetic measurements.

<p>The spaceborne lidar Ice, Cloud, and land Elevation Satellite (ICESat)-2 provides the ATL13 data product for inland water bodies. However, its quality characteristics are not yet fully understood. This study presents a robust method for extracting lake water level data and makes a comprehensive evaluation on the determined water levels. The selected study areas are Lake Huron and Lake Superior, which are part of the Great Lakes. The extracted water levels from ATL13 over a period of four years are validated by using the field measurements at the closest NOAA hydrological stations. The evaluation is carried out in terms of data specifications, wind speed, frozen precipitation, distance of photon segments to hydrological stations, data acquisition time, and beam intensity. The determined water levels are then further used for seasonal monitoring and modeling of water surface. This work demonstrates the critical need for outlier removal and the capability of the ATL13 data. A total bias of 9 - 10 cm is found in the ATL13 product. It is found that frozen precipitation can lead to an overestimation (~ 5 cm) of the water level. However, the uncertainty of water level determination is not found to be significantly related to the laser beam intensity and data acquisition time. We expect that these findings will be valuable for users employing the ATL13 inland water body product and for developers producing future versions of the ATL13 product.</p>

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The Arctic cryosphere is experiencing a higher rate of warming compared to the rest of the world due to Arctic amplification. As glacier elevation change provide reliable evidence of climate change it is routinely measured by satellite altimeters. Satellite altimetry, while a valuable tool for monitoring elevation change over time, is subject to inherent uncertainties caused by, among other factors, the small scale surface roughness of the target surfaces. Previous studies have identified surface roughness as a key source of uncertainty when measuring sea ice freeboard and studies suggest the surface roughness strongly influences the Synthetic Aperture Radar (SAR) signatures of sea ice. Similar studies over snow- and glacier surfaces, are rare. In this context, we attempt to conduct a small scale calibration and validation (cal/val) campaign over glacier surfaces, using the ideal location and infrastructure of the University Centre in Svalbard. We demonstrate the process, from planning through field data collection and data analysis. By doing so, we identify good as well as bad practices. Using high resolution in-situ LiDAR data, collected under two ICESat-2 (IS2) overpasses in Svalbard we generated Digital Elevation Models (DEM) and calculated surface roughness estimates across glacier- and snow surfaces. The surface roughness was quantified by calculating the Root Mean Square (RMS) of deviations from the overall topography of the surfaces. The DEMs were used for direct comparison with the satellite elevation retrievals and the observed elevation differences were tested for correlation with surface roughness at different length scales. We then investigated the effect of surface roughness on the photon cloud of the lower level ATL03 ICESat-2 data products, by quantifying the precision in the data. We found little to no correlation between RMS roughness and the observed elevation differences between in-situ and satellite data sets, possibly explained by errors in georeferencing the DEMs. We show moderate to strong correlation between photon cloud precision and along- and across-track absolute surface slopes, with correlation coefficients of 0.6–0.8. Correlation between photon cloud precision and RMS roughness was found, with a maximum correlation coefficient of 0.9 for a roughness length scale of 1m. The results suggest IS2 is sensitive to surface roughness at similar length scales but we identify a need for more data, covering a wider range of surfaces and potential roughness scenarios, to draw strong conclusions. We demonstrate how a small team can carry out a cal/val campaign in the high arctic and collect coincident data under satellite overpasses, data which is typically rare for the remote high Arctic regions.

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