Polarimetric Formulation Of The Visibility Function Equation Including Cross-Polar Antenna Patterns

The European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission will be the first one using two-dimensional aperture synthesis radiometry for Earth observation. This study presents the formulation that relates instrument observables and brightness temperature maps including cross-polar antenna voltage patterns, which may be also different from element to element. Finally, the radiometric accuracy degradation if cross-polar patterns are neglected in the image reconstruction is studied.Peer Reviewe

Polarimetric formulation of the visibility function equation including cross-polar antenna patterns

The European Space Agency’s Soil Moisture and Ocean Salinity (SMOS) mission will be the first one using two-dimensional aperture synthesis radiometry for earth observation. This study presents the formulation that relates instrument observables and brightness temperature maps including cross-polar antenna voltage patterns, which may be also different from element to element. Finally, the radiometric accuracy degradation if cross-polar patterns are neglected in the image reconstruction is studied.Postprint (published version

Contribution to advanced sensor development for passive imaging of the Earth

This work has been formally undertaken within the frame of the scholarship number BES-2012-053917 of 1 December 2012, by the "Secretario de Estado de Investigación del Ministerio de Economía y Competitividad" related to the program "Formación de Personal Investigador (FPI)". The scholarship is related to the research project at the Universitat Politècnica de Catalunya (UPC) number TEC2011-25865. In a more general scope, this thesis is related to the Remote Sensing Laboratory (Signal Theory & Communication Department, UPC) on-going activities, within the SMOS (Soil Moisture and Ocean Salinity) mission by the European Space Agency (ESA). These activities have been organized to provide original advances in the following four main topics: 1) SMOS calibration and performance. Since the launch of the instrument in 2009, SMOS imaging has been performing exclusively in co-polar mode. However, SMOS measurements are fully polarimetric. This feature was not operationally exploited due to the large errors yielded by full-pol images. In this context my work was addressed to support better characterization of the antenna. Based on the idea that SMOS polarization mode was recently implemented using Full-pol measurements, the so-called relative phases have been recomputed by using co-polar and cross-polar measurements. SMOS moderate Side Lobe Level (SLL) is caused by the limited coverage of the measured visibility samples in the frequency domain, so another objective of this work has been devoted to assess the impact of calibration errors into SMOS side lobes level (SLL). The main objective on this topic has been to reproduce by simulation SMOS measured side-lobe levels (SLL) by adding errors to a point source response, in order to identify the dominant source of error. During commissioning phase it was detected that SMOS heater system were introducing small and random sporadic PMS offset steps (jumps) in several units. Another work during this thesis has been devoted to mitigate those PMS jumps by trimming calibration date from single LICEF averaged TA jumps over the ocean. 2) SMOS spatial bias assessment. SMOS measurements still have mathematical image reconstruction errors that must be properly assessed. The aim of this work is to focus on the so-called "floor error", defined in an error free end-to-end image reconstruction simulation. In order to reduce this error, different inversion approaches have been implemented and tested, as the so-called Gibbs 2 approach 3) SMOS improved imaging. One of the problems of most concern within the SMOS mission is related to the so-called "land-sea contamination" (LSC), an artificial increase of ocean brightness temperature close to land masses. Therefore, a systematic assessment has been performed in this thesis in order to understand and mitigate this artifact. This subject is related to one of the main original outcomes of the thesis, since it has a relevant impact on the quality of SMOS imaging. The LSC mitigation technique developed during the work of the thesis has been presented and validated by different methods. 4) SMOS follow-on missions advanced configurations. This work is devoted to assess the impact of instrumental errors on the radiometric accuracy (pixel bias) of one of the selected array configurations of the so-called Super-MIRAS instrument. The aim of this work has been focused on the assessment of different array geometries and instrument architectures of future L-band synthetic aperture radiometers to improve spatial resolution while maintaining radiometric sensitivity.Esta tesis se ha llevado a cabo en el marco de la beca FPI BES-2012-053917 del 1 de diciembre de 2012, por el "Secretario de Estado de Investigación del Ministerio de Economía y Competitividad", asociada al proyecto TEC2011-25865 (Universidad Politècnica de Catalunya). En un sentido más amplio, el trabajo se engloba dentro de las actividades del Grupo de Teledetección (RSLab) del Departamento de Teoría de la Señal y Comunicaciones, UPC, en el marco de la misión SMOS (Soil Moisture and Ocean Salinity) de la Agencia Espacial Europea del Espacio (ESA). El trabajo se divide en: 1) Calibración y prestaciones del sensor SMOS Desde el lanzamiento del instrumento en 2009, la imagen de SMOS se ha obtenido utilizando medidas en modo co-polar. Sin embargo, las medidas en SMOS se realizan en full-pol. Esto no se había llevado a cabo debido a los grandes errores que se obtenían con imágenes en full-pol. En este contexto mi trabajo se ha enfocado en la realización de una mejor caracterización de la antena. Basado en la idea de que el modo full-pol ha sido recientemente implementado en SMOS, las fases relativas entre antenas han sido recalculadas utilizando medidas co-polares y cross-polares. Los lóbulos secundarios de SMOS (SLL) son causados por la cobertura limitada de las visibilidades medidas en el dominio frecuencial, así que otro de los objetivos de este trabajo ha sido analizar el impacto de errores de calibración en los lóbulos secundarios de SMOS. Básicamente se han reproducido los lóbulos secundarios de SMOS mediantes simulaciones añadiendo errores a una fuente puntual, identificando las principales fuentes de error. Durante la fase de comisionado se detectó que el sistema de calentamiento de SMOS introducía pequeños saltos aleatorios del offset del PMS en diferentes unidades. Para hacer un seguimiento y corregir estos saltos se realizaron calibraciones de offset semanales justo después de la fase de comisionado, así que otro de los trabajos realizados en esta tesis ha sido dirigido a mitigar estos saltos introduciendo calibraciones adicionales antes de los mismos a partir de medir la temperatura de antena media calculada en el océano. 2) Técnicas de reducción de los errores espaciales SMOS tiene un error matemático de reconstrucción en la imagen que ha sido investigado en este trabajo. Así que este trabajo se ha focalizado en el "floor error" definido como el error de reconstrucción en un instrumento ideal libre de errores. Para reducir este error se han utilizado diferentes aproximaciones como Gibbs 2. 3) Mejoras en la inversión de imagen Uno de los mayores problemas durante los primeros cinco años de misión SMOS ha sido la llamada "land-sea contamination" (contaminación tierra-mar). Así pues, se ha realizado un estudio sistemático para comprender y mitigar este artefacto. Este tema está relacionado con uno de los descubrimientos más importantes de esta tesis ya que este tiene un gran impacto en la calidad de la imagen de SMOS. La técnica encontrada para mitigar este error es presentada y validada mediante diferentes métodos. 4) Misiones futuras Este trabajo está enfocado en la investigación del impacto de errores instrumentales en la precisión radiométrica de errores espaciales de una de las posibles nuevas configuraciones de array propuestas para construir un nuevo instrumento llamado Super-MIRAS. El propósito principal de este trabajo está orientado en el desarrollo de diferentes geometrías de arrays y arquitecturas de instrumentos para una futura misión en banda L, en la que se diseñaría un nuevo radiómetro de apertura sintética para mejorar la resolución espacial manteniendo la sensibilidad radiométrica.Postprint (published version

Contribution to advanced sensor development for passive imaging of the Earth

This work has been formally undertaken within the frame of the scholarship number BES-2012-053917 of 1 December 2012, by the "Secretario de Estado de Investigación del Ministerio de Economía y Competitividad" related to the program "Formación de Personal Investigador (FPI)". The scholarship is related to the research project at the Universitat Politècnica de Catalunya (UPC) number TEC2011-25865. In a more general scope, this thesis is related to the Remote Sensing Laboratory (Signal Theory & Communication Department, UPC) on-going activities, within the SMOS (Soil Moisture and Ocean Salinity) mission by the European Space Agency (ESA). These activities have been organized to provide original advances in the following four main topics: 1) SMOS calibration and performance. Since the launch of the instrument in 2009, SMOS imaging has been performing exclusively in co-polar mode. However, SMOS measurements are fully polarimetric. This feature was not operationally exploited due to the large errors yielded by full-pol images. In this context my work was addressed to support better characterization of the antenna. Based on the idea that SMOS polarization mode was recently implemented using Full-pol measurements, the so-called relative phases have been recomputed by using co-polar and cross-polar measurements. SMOS moderate Side Lobe Level (SLL) is caused by the limited coverage of the measured visibility samples in the frequency domain, so another objective of this work has been devoted to assess the impact of calibration errors into SMOS side lobes level (SLL). The main objective on this topic has been to reproduce by simulation SMOS measured side-lobe levels (SLL) by adding errors to a point source response, in order to identify the dominant source of error. During commissioning phase it was detected that SMOS heater system were introducing small and random sporadic PMS offset steps (jumps) in several units. Another work during this thesis has been devoted to mitigate those PMS jumps by trimming calibration date from single LICEF averaged TA jumps over the ocean. 2) SMOS spatial bias assessment. SMOS measurements still have mathematical image reconstruction errors that must be properly assessed. The aim of this work is to focus on the so-called "floor error", defined in an error free end-to-end image reconstruction simulation. In order to reduce this error, different inversion approaches have been implemented and tested, as the so-called Gibbs 2 approach 3) SMOS improved imaging. One of the problems of most concern within the SMOS mission is related to the so-called "land-sea contamination" (LSC), an artificial increase of ocean brightness temperature close to land masses. Therefore, a systematic assessment has been performed in this thesis in order to understand and mitigate this artifact. This subject is related to one of the main original outcomes of the thesis, since it has a relevant impact on the quality of SMOS imaging. The LSC mitigation technique developed during the work of the thesis has been presented and validated by different methods. 4) SMOS follow-on missions advanced configurations. This work is devoted to assess the impact of instrumental errors on the radiometric accuracy (pixel bias) of one of the selected array configurations of the so-called Super-MIRAS instrument. The aim of this work has been focused on the assessment of different array geometries and instrument architectures of future L-band synthetic aperture radiometers to improve spatial resolution while maintaining radiometric sensitivity.Esta tesis se ha llevado a cabo en el marco de la beca FPI BES-2012-053917 del 1 de diciembre de 2012, por el "Secretario de Estado de Investigación del Ministerio de Economía y Competitividad", asociada al proyecto TEC2011-25865 (Universidad Politècnica de Catalunya). En un sentido más amplio, el trabajo se engloba dentro de las actividades del Grupo de Teledetección (RSLab) del Departamento de Teoría de la Señal y Comunicaciones, UPC, en el marco de la misión SMOS (Soil Moisture and Ocean Salinity) de la Agencia Espacial Europea del Espacio (ESA). El trabajo se divide en: 1) Calibración y prestaciones del sensor SMOS Desde el lanzamiento del instrumento en 2009, la imagen de SMOS se ha obtenido utilizando medidas en modo co-polar. Sin embargo, las medidas en SMOS se realizan en full-pol. Esto no se había llevado a cabo debido a los grandes errores que se obtenían con imágenes en full-pol. En este contexto mi trabajo se ha enfocado en la realización de una mejor caracterización de la antena. Basado en la idea de que el modo full-pol ha sido recientemente implementado en SMOS, las fases relativas entre antenas han sido recalculadas utilizando medidas co-polares y cross-polares. Los lóbulos secundarios de SMOS (SLL) son causados por la cobertura limitada de las visibilidades medidas en el dominio frecuencial, así que otro de los objetivos de este trabajo ha sido analizar el impacto de errores de calibración en los lóbulos secundarios de SMOS. Básicamente se han reproducido los lóbulos secundarios de SMOS mediantes simulaciones añadiendo errores a una fuente puntual, identificando las principales fuentes de error. Durante la fase de comisionado se detectó que el sistema de calentamiento de SMOS introducía pequeños saltos aleatorios del offset del PMS en diferentes unidades. Para hacer un seguimiento y corregir estos saltos se realizaron calibraciones de offset semanales justo después de la fase de comisionado, así que otro de los trabajos realizados en esta tesis ha sido dirigido a mitigar estos saltos introduciendo calibraciones adicionales antes de los mismos a partir de medir la temperatura de antena media calculada en el océano. 2) Técnicas de reducción de los errores espaciales SMOS tiene un error matemático de reconstrucción en la imagen que ha sido investigado en este trabajo. Así que este trabajo se ha focalizado en el "floor error" definido como el error de reconstrucción en un instrumento ideal libre de errores. Para reducir este error se han utilizado diferentes aproximaciones como Gibbs 2. 3) Mejoras en la inversión de imagen Uno de los mayores problemas durante los primeros cinco años de misión SMOS ha sido la llamada "land-sea contamination" (contaminación tierra-mar). Así pues, se ha realizado un estudio sistemático para comprender y mitigar este artefacto. Este tema está relacionado con uno de los descubrimientos más importantes de esta tesis ya que este tiene un gran impacto en la calidad de la imagen de SMOS. La técnica encontrada para mitigar este error es presentada y validada mediante diferentes métodos. 4) Misiones futuras Este trabajo está enfocado en la investigación del impacto de errores instrumentales en la precisión radiométrica de errores espaciales de una de las posibles nuevas configuraciones de array propuestas para construir un nuevo instrumento llamado Super-MIRAS. El propósito principal de este trabajo está orientado en el desarrollo de diferentes geometrías de arrays y arquitecturas de instrumentos para una futura misión en banda L, en la que se diseñaría un nuevo radiómetro de apertura sintética para mejorar la resolución espacial manteniendo la sensibilidad radiométrica

Performance of sea surface salinity and soil moisture retrieval algorithms with different auxiliary datasets in 2-D L-band aperture synthesis interferometric radiometers

The Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Opportunity Mission was selected in May 1999 by the European Space Agency Earth Observation Programme Board to provide global and frequent soil moisture (SM) and sea surface salinity (SSS) maps. SMOS' single payload is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) sensor, an L-band two-dimensional aperture synthesis interferometric radiometer with multiangular and polarimetric imaging capabilities. The definition of the SMOS Level 2 Processor requires the selection of the optimum operation mode (dual-polarization or full-polarimetric) for each application, the specification of the required auxiliary data, and the optimum retrieval algorithms. Using the SMOS simulator and based on the experience gained in previous works, this paper presents a study of the SM and SSS retrieval capabilities over homogeneous pixels, in the two modes of operation with different auxiliary data. It is found that SSS retrievals using the first Stokes parameter measured in the dual-polarization mode perform somewhat worse than using the vertical (T/sub vv/) and horizontal (T/sub hh/) brightness temperatures measured in the full-polarimetric mode, and the performance degrades for cold waters due to the lower sensitivity of the brightness temperature to SSS at low sea surface temperature (SST). Due to the larger angular variation of T/sub hh/ and T/sub vv/, SM retrievals using T/sub hh/ and T/sub vv/ measured in the full-polarimetric mode exhibit a significant better performance over bare soils than over vegetation-covered soils. Over vegetation-covered soils vegetation parameters (opacity and albedo) can be inferred over a 550-km swath width in the full-polarimetric mode. However, since the first Stokes parameter is independent of both geometric and Faraday rotations, it is very robust in the presence of instrumental and geophysical errors. In the SSS retrieval problem and in the SM retrieval problem (with T/sub hh/ and T/sub vv/ measured in the full-polarimetric mode), the performance of the retrieval algorithms tested is not significantly altered if the model parameters are not exactly known, but are left as adjustable parameters in the optimization process.Peer Reviewe

Performance Of Sea Surface Salinity And Soil Moisture Retrieval Algorithms With Different Auxiliary Datasets In 2-D L-Band Aperture Synthesis Interferometric Radiometers

The Soil Moisture and Ocean Salinity (SMOS) Earth Explorer Opportunity Mission was selected in May 1999 by the European Space Agency Earth Observation Programme Board to provide global and frequent soil moisture (SM) and sea surface salinity (SSS) maps. SMOS' single payload is the Microwave Imaging Radiometer by Aperture Synthesis (MIRAS) sensor, an L-band two-dimensional aperture synthesis interferometric radiometer with multiangular and polarimetric imaging capabilities. The definition of the SMOS Level 2 Processor requires the selection of the optimum operation mode (dual-polarization or full-polarimetric) for each application, the specification of the required auxiliary data, and the optimum retrieval algorithms. Using the SMOS simulator and based on the experience gained in previous works, this paper presents a study of the SM and SSS retrieval capabilities over homogeneous pixels, in the two modes of operation with different auxiliary data. It is found that SSS retrievals using the first Stokes parameter measured in the dual-polarization mode perform somewhat worse than using the vertical (T/sub vv/) and horizontal (T/sub hh/) brightness temperatures measured in the full-polarimetric mode, and the performance degrades for cold waters due to the lower sensitivity of the brightness temperature to SSS at low sea surface temperature (SST). Due to the larger angular variation of T/sub hh/ and T/sub vv/, SM retrievals using T/sub hh/ and T/sub vv/ measured in the full-polarimetric mode exhibit a significant better performance over bare soils than over vegetation-covered soils. Over vegetation-covered soils vegetation parameters (opacity and albedo) can be inferred over a 550-km swath width in the full-polarimetric mode. However, since the first Stokes parameter is independent of both geometric and Faraday rotations, it is very robust in the presence of instrumental and geophysical errors. In the SSS retrieval problem and in the SM retrieval problem (with T/sub hh/ and T/sub vv/ measured in the full-polarimetric mode), the performance of the retrieval algorithms tested is not significantly altered if the model parameters are not exactly known, but are left as adjustable parameters in the optimization process.Peer Reviewe

The impact of Antenna Pattern Frequency Dependence in Aperture Synthesis Microwave Radiometers

The effect of the frequency dependence of the antenna voltage patterns within the bandwidth of an aperture synthesis interferometric radiometer is studied and quantified using actual antenna voltage patterns measured at different frequencies for the first nine receivers of the Microwave Imaging Radiometer with Aperture Synthesis instrument aboard the European Space Agency's Soil Moisture and Ocean Salinity mission. A technique is proposed to mitigate this effect.Peer Reviewe

The impact of antenna pattern frequency dependence in aperture synthesis microwave radiometers

The effect of the frequency dependence of the antenna voltage patterns within the bandwidth of an aperture synthesis interferometric radiometer is studied and quantified using actual antenna voltage patterns measured at different frequencies for the first nine receivers of the Microwave Imaging Radiometer with Aperture Synthesis instrument aboard the European Space Agency's Soil Moisture and Ocean Salinity mission. A technique is proposed to mitigate this effect.Peer Reviewe

Electromagnetic Wave Theory and Applications

Contains table of contents for Section 3 and reports on five research projects.U.S. Department of Transportation Contract DTRS-57-88-C-00078TTD13U.S. Department of Transportation Contract DTRS-57-88-C-00078TTD30Defense Advanced Research Projects Agency Contract MDA972-90-C-0021Digital Equipment CorporationIBM CorporationJoint Services Electronics Program Contract DAAL03-89-C-0001Joint Services Electronics Program Contract DAAL03-92-C-0001Schlumberger-Doll ResearchU.S. Navy - Office of Naval Research Grant N00014-90-J-1002U.S. Navy - Office of Naval Research Grant N00014-89-J-1019National Aeronautics and Space Administration Grant NAGW-1617National Aeronautics and Space Administration Grant 958461National Aeronautics and Space Administration Grant NAGW-1272U.S. Army Corp of Engineers Contract DACA39-87-K-0022U.S. Navy - Office of Naval Research Grant N00014-89-J-110