analysis of two years of ascat and smos derived soil moisture estimates over europe and north africa

More than two years of soil moisture data derived from the Advanced SCATterometer (ASCAT) and from the Soil Moisture and Ocean Salinity (SMOS) radiometer are analysed and compared. The comparison has been performed within the framework of an activity aiming at validating the EUMETSAT Hydrology Satellite Application Facility (H-SAF) soil moisture product derived from ASCAT. The available database covers a large part of the SMOS mission lifetime (2010, 2011 and partially 2012) and both Europe and North Africa are considered. A specific strategy has been set up in order to enable the comparison between products representing a volumetric soil moisture content, as those derived from SMOS, and a relative saturation index, as those derived from ASCAT. Results demonstrate that the two products show a fairly good degree of correlation. Their consistency has some dependence on season, geographical zone and surface land cover. Additional factors, such as spatial property features, are also preliminary investigated

On Small Satellites for Oceanography: A Survey

The recent explosive growth of small satellite operations driven primarily from an academic or pedagogical need, has demonstrated the viability of commercial-off-the-shelf technologies in space. They have also leveraged and shown the need for development of compatible sensors primarily aimed for Earth observation tasks including monitoring terrestrial domains, communications and engineering tests. However, one domain that these platforms have not yet made substantial inroads into, is in the ocean sciences. Remote sensing has long been within the repertoire of tools for oceanographers to study dynamic large scale physical phenomena, such as gyres and fronts, bio-geochemical process transport, primary productivity and process studies in the coastal ocean. We argue that the time has come for micro and nano satellites (with mass smaller than 100 kg and 2 to 3 year development times) designed, built, tested and flown by academic departments, for coordinated observations with robotic assets in situ. We do so primarily by surveying SmallSat missions oriented towards ocean observations in the recent past, and in doing so, we update the current knowledge about what is feasible in the rapidly evolving field of platforms and sensors for this domain. We conclude by proposing a set of candidate ocean observing missions with an emphasis on radar-based observations, with a focus on Synthetic Aperture Radar.Comment: 63 pages, 4 figures, 8 table

Tendance et variabilité de la vapeur d'eau atmosphérique : un enjeu pour l'étude du niveau moyen océanique

La mesure du niveau de la mer par altimétrie satellitaire est perturbée par la présence de vapeur d'eau dans l'atmosphère. Un radiomètre micro-onde, sur les missions altimétriques, est chargé de corriger les mesures de ces perturbations. Les exigences quant à la qualité de cette correction, appelée correction troposphérique humide, sont particulièrement fortes pour l'étude des changements climatiques. Cette thèse a pour objet l'étude des corrections troposphériques humides utilisées dans le cadre des missions altimétriques Jason-1 et Envisat. L'objectif est de caractériser les incertitudes liées à la correction et d'identifier les potentielles anomalies présentes. L'étude faire ressortir une potentielle dérive dans l'étalonnage du radiomètre de la mission Jason-1 après 2008. Pour la mission Envisat, l'analyse met en avant des biais régionaux à l'approche des côtes. Ces derniers sont probablement liés au traitement de la donnée radiométrique.Measurements of the sea surface height are disturbed by the presence of water vapor in the atmosphere. A microwave radiometer, on altimetric missions, is used to correct the measurements from theses disturbances. Requirements on the quality of this correction, called the wet tropospheric correction, are stringent for the survey of climate changes. This thesis concerns the monitoring of the wet tropospheric correction used in the altimetry missions, Jason-1 and Envisat. The aim is to characterize uncertainties related to this correction and to identify potential anomalies. The analysis brings out a potential drift in the radiometer used on Jason-1, after 2008. For the Envisat missions, the presence of biases near coastlines suggests processing related issues

Relationship between aquarius L-band active and passive multi-year observations over Australia

This PFC is focused in evaluating the feasibility of doing a combined changed algorithm to simplify the process of low resolution downscaling using high resolution.The aim of this Thesis is to further our understanding of the geophysical information that can be estimated from active and passive L-band sensors. All data was obtained from NASA's satellite Aquarius durin the period Sept. 2011- August 2014

Earth Resources, A Continuing Bibliography with Indexes

This bibliography lists 460 reports, articles and other documents introduced into the NASA scientific and technical information system between July 1 and September 30, 1984. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economical analysis

Ocean surface currents reconstruction from microwave radiometers measurements

Premi Extraordinari de Doctorat, promoció 2014-2015. Àmbit d'Enginyeria de les TICOcean currents are a key component to understanding many oceanic and climatic phenomena and knowledge of them is crucial for both navigation and operational applications. Therefore, a key problem in oceanography is the estimation of the synoptic velocity field. Currently, global ocean surface velocities are routinely estimated from Sea Surface Height (SSH) measurements provided by altimeters. However, the separation between passes, as well as and the limited number of available altimeters leads to errors in the accurate location of oceanic currents when these measurements are used exclusively. Contrarily, satellite images of Sea Surface Temperature (SST) provide a good qualitative view of the location of ocean patterns, which has encouraged the investigation of alternative methodologies to reconstruct the velocity field based on these observations. This Ph.D. thesis has assessed the capability of SST microwave radiometers observations to retrieve ocean surface currents. The reconstruction of the ocean surface currents from SST observations can be expressed in terms of a transfer function notation, that allows to convert SST maps into SSH, and thus into currents. Because under geostrophic balance, the slope of SSH is proportional to ocean surface currents. This transfer function can be theoretically derived using the Surface Quasi-Geostrophic equations (SQG). Two different approaches were analyzed at a global scale: on one side, the analysis of the validity of the SQG approach has been performed, and on the other, an approach based on the synergetic properties between simultaneous SST and SSH observations has been analyzed. Both approaches have been compared with ocean surface currents retrieved from merged altimetric observations. The study has been focused on the period from October 2002 to May 2005, since during that period there were available four different altimeters, and the quality of the merged altimetric observations was enhanced. The analysis of the validity of SQG at a global scale revealed that this dynamical model is valid near the major extratropic current system such us the Gulf Stream, the Antartic Circumpolar Current, Kuroshio currents. Besides, the potential of MW SST observations to reconstruct ocean surface currents was analyzed using a synergetic approach: the combination of the SST phase with the SSH spectra. Actually, we explored under which environmental conditions the phase of the MW SST is close to the SSH phase. Results showed that the phase of the MW SST can be used to retrieve ocean currents during winter, near the major extratropical current systems, which are characterized by an intense mesoscale activity and the presence of strong thermal gradients, and deep ML. Furthermore, the reconstruction of the velocity fields from an ideal transfer function built up from simultaneous SST and SSH observations revealed that the SQG approach can be enhanced. The spectral properties of this ideal transfer function derived from simultaneous SST and SSH observations were characterized at a global scale. The analysis of spectral properties of the transfer function between SST and SSH observations revealed that despite daily spectral can be flatter or steeper than the k^{-1} predicted by SQG theory, in mean eSQG is a good statistically approach to retrieve ocean currents, when no simultaneous observations of SSH and SST are available.Las corrientes oceánicas son clave en muchos procesos oceánicos y climáticos, y su conocimiento es crucial para aplicaciones operacionales y de navegación. Por lo tanto, un aspecto importante en oceanografía es la estimación de campos sinópticos del campo de velocidades superficiales del mar. Actualmente, las velocidades superficiales el mar se estiman rutinariamente a partir de medidas del nivel del mar proporcionadas por altimetros, denotadas a partir de ahora con sus siglas en inglés SSH. Sin embargo, la llocalización de las corrientes puede no ser la correcta si solo se utilizan este tipo de medidas para su estimación, debido a la separación entre trazas del satélite. Por contra, las imágenes de temperatura superficial del mar, SST, proporiconan una visión cualitativa de la localización de las estructruas oceánicas. Este hecho ha motivado la investigación de metodologías alternativas para reconstruir los campos de velocidades superficiales del mar basados en estas observaciones. Esta tesis doctoral ha investigado la capacidad de las observaciones de SST proporcionadas por radiometros de microondas para recuperar las corrientes oceánicas superficiales. La reconstrucción de estas velocidades a partir de observaciones de SST se puede expresar en términos de una función de transferencia que relacione las observaciones de SST con las observaciones de SSH. Con lo que la estimación del campo de velocidades es directa, puesto que bajo la condición de equilibrio geostrófico la pendiente de la SSH es proporcional a las corrientes oceánicas. Esta función de transferencia se puede derivar teóricamente mediante las equaciones superficiales cuasi-geotróficas, denotadas con sus siglas en inglés SQG a partir de ahora. Una pregunta clave, es si las ecuaciones de este modelo dinámico son válidas. En esta tesis, se han llevado a cabo dos aproximaciones diferentes para la reconstrucción del campo de velocidades superficiales del mar: por un lado, el análisis de la validez de las ecuaciones SQG, y por otro, una aproximación basada en las propiedades espectrales de medidas simultáneas de SST y SSH. El estudio se ha centrado en el período comprendido entre Octubre del 2002 y Mayo del 2005, puesto que durante este período había disponibles hasta cuatro altmímetros, y consecuentemente la calidad de las observaciones es mayor. El análisis de la validez de SQG a escala global reveló que este modelo dinámico es válido en las regiones cerca de los sistemas de corrientes extratropicales, como la corriente del Golfo, la Corriente Circumpolar Antártica (ACC), o la Kuroshio. Además, el potencial de las observaciones de SST en el rango de las microondas para la recuperación del campo de velocidades superficiales del mar, ha sido analizado utilizando un método que combina la fase de la SST con el espectro de SSH. En realidad, se ha investigado bajo que condiciones la SST y SSH están en fase. Los resultados mostraron que la fase de la SST de microondas puede utilizarse para para la reconstrucción en invierno, cerca de los sistemas de corrientes extratropicales, caracterizados por una intensa actividad de mesoscala y la presencia de fuertes gradientes termales, así como de capas de mezcla profundas. Asimismo, la reconstrucción del campo de velocidades a partir de una función de transferencia ideal, construida a partir de imágenes simultaneas de SST y SSH, reveló que la aproximación SQG puede ser mejorada. Las propiedades espectrales de esta función de tranferencia ideal han sido estudiadas., así como su variabilidad temporal. Este análisis desveló que para escalas pequeñas y zonas enegéticas, la aproximación SQG es una buena aproximación, al menos, desde un punto de vista estádistico.Award-winningPostprint (published version

Earth resources: A continuing bibliography with indexes (issue 51)

This bibliography lists 382 reports, articles and other documents introduced into the NASA scientific and technical information system between July 1 and September 30, 1986. Emphasis is placed on the use of remote sensing and geophysical instrumentation in spacecraft and aircraft to survey and inventory natural resources and urban areas. Subject matter is grouped according to agriculture and forestry, environmental changes and cultural resources, geodesy and cartography, geology and mineral resources, hydrology and water management, data processing and distribution systems, instrumentation and sensors, and economic analysis

Correcting Multiyear Sea Ice Concentration Estimates from Microwave Satellite Observations with Air Temperature, Sea Ice Drift and Dynamic Tie Points

Arctic sea ice cover is a sensitive climate indicator. Due to the warming climate, it has decreased dramatically in the Arctic over the past three decades. Moreover, multiyear ice (MYI), ice which has survived at least one summer, is decreasing at a much higher rate. MYI concentration can be retrieved from microwave remote sensing data. However, the retrieval shows flaws under specific weather conditions. The current thesis is motivated by the need of better estimates of MYI distribution. It introduces three methods to improve/correct the MYI concentration estimates from microwave satellite observations. The first method builds upon the NASA Team algorithm and uses dynamic tie points to compensate the temporal variations of tie points (typical brightness temperatures of each surface type at all the channels). The MYI retrievals in winters (Oct-May) of the years 1989-2012 show that the method with dynamic tie points yields higher estimates than the original method in most years. Both methods show clear declining trends of the MYI area from 1989 to 2012, which is consistent with the sea ice extent minimum. The MYI concentration retrieval with the NASA Team algorithm is most sensitive to the tie points of MYI and FYI at 19 GHz vertical polarized channel. These tie points should be treated with more caution when dynamic tie points are used. The second and third methods are two correction schemes used to account for radiometric anomalies that trigger the erroneous MYI concentration retrievals from microwave satellite observations. The correction based on air temperature is introduced to restore the underestimated MYI concentration under warm conditions. It utilizes the fact that the warm spell in autumn lasts for a few days and replaces the erroneous MYI concentrations with interpolated ones. It is applied to MYI retrievals from the Environment Canada Ice Concentration Extractor (ECICE) using inputs from QuikSCAT and AMSR-E data, acquired over the Arctic in a series of autumn seasons (Sep-Dec) from 2003 to 2008. The correction works well by identifying and correcting the anomalous MYI concentrations. For September of the six years, it introduces over 1.0x105 km2 MYI area, except for 2005. The correction based on ice drift is designed to correct the overestimated MYI concentrations that are impacted by factors such ice deformation, snow wetness and metamorphism. It utilizes ice drift records to constrain the MYI changes within a predicted contour and uses two thresholds of passive microwave radiometric parameters to account for snow wetness and metamorphism. It is applied to the MYI concentration retrievals from ECICE in winters (Oct-May) from 2002 to 2009. Qualitative comparison with Radarsat-1 SAR images and quantitative comparison against results from previous studies show that the correction works well by removing the anomalous high MYI concentrations. On average, the correction reduces 5.2x105 km2 of the estimated MYI area in Arctic except for the April-May time frame, when the reduction is larger as the warmer weather prompts the condition of the anomalous snow radiometric signatures. Both corrections can be used as post-processings to all the microwave-based MYI concentration retrieval algorithms. Due to the regional effect of weather conditions, they could be important in the operational applications. In addition, both corrections take the spatial and temporal continuity of MYI into account, which gives a new insight that instantaneous observations alone of sea ice may lead to ambiguities in determination of partial ice concentrations. This approach may be applicable to the retrieval of other sea ice parameters as well