TriHex: combining formation flying, general circular orbits and alias-free imaging, for high resolution L-band aperture synthesis

The Soil Moisture and Ocean Salinity (SMOS) mission of the European Space Agency (ESA), together with NASA’s Soil Moisture Active Passive (SMAP) mission, is providing a wealth of information to the user community for a wide range of applications. Although both missions are still operational, they have significantly exceeded their design life time. For this reason, ESA is looking at future mission concepts, which would adequately address the requirements of the passive L-band community beyond SMOS and SMAP. This article proposes one mission concept, TriHex, which has been found capable of achieving high spatial resolution, radiometric resolution, and accuracy, approaching the user needs. This is possible by the combination of aperture synthesis, formation flying, the use of general circular orbits, and alias-free imaging.Peer ReviewedPostprint (author's final draft

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

Wideband corrugated feedhorns, for radar, communications, radiometry and quasi-optics

This work was supported in part by Engineering and Physical Sciences Research Council, U.K., under Grant EP/R013705/1, and in part by IAA Funding.A wide variety of desirable antenna beam patterns can be synthesized by optimal excitation and phasing of the HE11 and HE12 modes in scalar corrugated feedhorns. However, the bandwidth of such two-mode horns is often limited by modal dispersion. In this paper we introduce a class of low dispersion, two-mode feedhorns that can operate, in some cases, over operating bandwidths of 40-50%. We provide example designs that include horns with high coupling efficiency to: 1) a pure HE11 mode for single-mode excitation of corrugated pipe transmission lines; 2) a LG00 and LG02 combination for radiometry, with narrow beams; 3) a pure Laguerre Gaussian LG00 mode for quasi-optical instrumentation with constant phase centers; 4) a constant gain antenna for uniform illumination with frequency; 5) Airy patterns or “top hat” patterns for radar or communications applications, designed to maximize aperture efficiencies when used with larger reflect or lens antennas. More generally, we show methods to generate and phase multiple HE1n modes, to synthesize symmetric output beams at any desired frequency or gain.Publisher PDFPeer reviewe

Microwave performance characterization of large space antennas

Performance capabilities of large microwave space antenna configurations with apertures generally from 100 wavelengths upwards are discussed. Types of antennas considered include: phased arrays, lenses, reflectors, and hybrid combinations of phased arrays with reflectors or lenses. The performance characteristics of these broad classes of antennas are examined and compared in terms of applications

Remote Sensing Of Asteroid Surface Mineralogy

A major research question in asteroid science centres on how fragments from main belt asteroids, which are located between the orbits of Mars and Jupiter, end up in Earth crossing orbits. Advances in infrared astronomy have made it possible to test the validity of solar system dynamical models using observational data. Specifically, near-infrared (NIR) reflectance spectroscopy can be employed to search the main asteroid belt for possible mineralogical analogues of Near Earth asteroids. Two asteroids, 3628 Božněmcová and 2002 JB9, were studied using the NASA Infrared Telescope Facility. 3628 Božněmcová had been suggested as a possible parent body for ordinary chondrite meteorites due to its unique spectral characteristics and the fact that it orbits in the vicinity of the 3:1 Kirkwood gap. A more recent suggestion by Cloutis et al. (2006) is that 3628 Božněmcová is a type A clinopyroxene and possible parent body for the angrite meteorites. The spectrum of 3628 Božněmcová obtained during the observing run of June 2011 shows distinct absorption features at 1.02 and 2.16 microns. It is therefore possible to effectively rule out an ordinary chrondrite or howardite-eucrite-diogenite (HED) mineralogy for this asteroid. While not entirely conclusive, the implied mineralogy for 3628 Božněmcová, i.e., a high calcium type B clinopyroxene with a possible fassite component, suggests it may be a possible parent body for the angrite meteorites

The microwave radiometer spacecraft: A design study

A large passive microwave radiometer spacecraft with near all weather capability of monitoring soil moisture for global crop forecasting was designed. The design, emphasizing large space structures technology, characterized the mission hardware at the conceptual level in sufficient detail to identify enabling and pacing technologies. Mission and spacecraft requirements, design and structural concepts, electromagnetic concepts, and control concepts are addressed

A design study for the use of a multiple aperture deployable antenna for soil moisture remote sensing satellite applications

The instrumentation problems associated with the measurement of soil moisture with a meaningful spatial and temperature resolution at a global scale are addressed. For this goal only medium term available affordable technology will be considered. The study while limited in scope, will utilize a large scale antenna structure, which is being developed presently as an experimental model. The interface constraints presented by a singel Space Transportation System (STS) flight will be assumed. Methodology consists of the following steps: review of science requirements; analyze effects of these requirements; present basic system engineering considerations and trade-offs related to orbit parameters, number of spacecraft and their lifetime, observation angles, beamwidth, crossover and swath, coverage percentage, beam quality and resolution, instrument quantities, and integration time; bracket the key system characteristics and develop an electromagnetic design of the antenna-passive radiometer system. Several aperture division combinations and feed array concepts are investigated to achieve maximum feasible performacne within the stated STS constraints

Microwave radiometric thermometry in layered tissue structures.

Non-invasive thermal imaging and temperature measurement by microwave radiometry is investigated for medical diagnostic applications and monitoring hyperthermia treatment of cancer, in the context of the heterogeneous body structure. The temperature measured by a radiometer is a function of the emission and propagation of microwaves in tissue and the receiving characteristics of the radiometric probe. Propagation of microwaves in lossy media is analysed by a spectral diffraction approach. Extension of this technique via a cascade transmission line model provides an efficient algorithm for predicting the field patterns of aperture antennas contacting multi-layered tissue. Comparisons of computer simulations with field measurements in homogeneous and bi-layered tissue-equivalent media confirm the validity of the algorithm. A coherent radiative transfer analysis is used to relate the field pattern of a radiating antenna to its receiving characteristics when used as a radiometer probe, leading to a method for simulating radiometric data. The design and construction of a 4.6 GHz radiometer is described and good agreement is found between computer simulations and radiometer measurements in tissue equivalent phantoms. Measurements and simulations are used to assess the effect of overlying fat layers upon radiometer response to temperature hot-spots in muscle-type media. It is shown that dielectric layering in tissue greatly influences measured temperatures and should be accounted for in the interpretation of radiometric data. The feasibility of employing microwave radiometry for tomographic mapping of differential temperature distributions induced by hyperthermia is examined. A suitable reconstruction algorithm is proposed; however the limited 'depth of view' in lossy tissue is shown to restrict the volume which can be imaged and thus its use for monitoring deep hyperthermia is doubtful. Alternative applications of this technique in medical diagnostics are proposed