New Passive Instruments Developed for Ocean Monitoring at the Remote Sensing Lab—Universitat Politècnica de Catalunya

Lack of frequent and global observations from space is currently a limiting factor in many Earth Observation (EO) missions. Two potential techniques that have been proposed nowadays are: (1) the use of satellite constellations, and (2) the use of Global Navigation Satellite Signals (GNSS) as signals of opportunity (no transmitter required). Reflectometry using GNSS opportunity signals (GNSS-R) was originally proposed in 1993 by Martin-Neira (ESA-ESTEC) for altimetry applications, but later its use for wind speed determination has been proposed, and more recently to perform the sea state correction required in sea surface salinity retrievals by means of L-band microwave radiometry (TB). At present, two EO space-borne missions are currently planned to be launched in the near future: (1) ESA's SMOS mission, using a Y-shaped synthetic aperture radiometer, launch date November 2nd, 2009, and (2) NASA-CONAE AQUARIUS/SAC-D mission, using a three beam push-broom radiometer. In the SMOS mission, the multi-angle observation capabilities allow to simultaneously retrieve not only the surface salinity, but also the surface temperature and an “effective” wind speed that minimizes the differences between observations and models. In AQUARIUS, an L-band scatterometer measuring the radar backscatter (σ0) will be used to perform the necessary sea state corrections. However, none of these approaches are fully satisfactory, since the effective wind speed captures some sea surface roughness effects, at the expense of introducing another variable to be retrieved, and on the other hand the plots (TB-σ0) present a large scattering. In 2003, the Passive Advance Unit for ocean monitoring (PAU) project was proposed to the European Science Foundation in the frame of the EUropean Young Investigator Awards (EURYI) to test the feasibility of GNSS-R over the sea surface to make sea state measurements and perform the correction of the L-band brightness temperature. This paper: (1) provides an overview of the Physics of the L-band radiometric and GNSS reflectometric observations over the ocean, (2) describes the instrumentation that has been (is being) developed in the frame of the EURYI-funded PAU project, (3) the ground-based measurements carried out so far, and their interpretation in view of placing a GNSS-reflectometer as secondary payload in future SMOS follow-on missions

Study of maize plants effects in the retrieval of soil moisture using the interefence Ppttern GNSS-R technique

The use of Global Navigation Satellite Signals Reflections (GNSS-R) techniques to retrieve geophysical parameters from surfaces has been increased in the recent years. These techniques have resulted in suitable tools to obtain information about the sea state of oceans, which is very useful to improve the ocean salinity retrieval, and also, information about the soil moisture of lands. The present work focuses on the use of the Interference Pattern Technique (IPT), a particular type of GNSS-R technique, to study vegetation-covered soils. The IPT consists mainly of the measurement of the interference pattern between the GPS direct and reflected signals (the interference power), after they impinge over the ensemble soil surface and vegetation layer. The measured interference signal provides information on the soil moisture of the surface and also, on the vegetation height.Peer ReviewedPostprint (published version

Sistemas de teledetección activos y pasivos embarcados en sistemas aéreos no tripulados para la monitorización de la tierra

La comunidad científica ha mostrado gran interés por estudiar los fenómenos que ocurren sobre la superficie de la tierra, específicamente los que suceden en la atmósfera, los océanos, o la superficie del suelo, y que afectan el clima o modifican la superficie de la tierra. Para poder analizar y predecir estos fenómenos, se monitorizan parámetros que se relacionan de manera directa o indirecta con procesos biofísicos y geofísicos. Es en este punto donde la teledetección entra en juego, puesto que es la técnica que permite medir tales parámetros de forma remota sin necesidad de entrar en contacto directo con un objeto o una superficie. En particular, la teledetección por microondas permite la detección de energía electromagnética casi bajo cualquier condición climática y a cualquier hora del día, debido a que a esta longitud de onda la energía electromagnética puede penetrar a través de las nubes, polvo, neblina y lluvia, y es menos susceptible a la dispersión atmosférica, que afecta en gran medida a las señales ópticas. Actualmente existen varios sistemas de teledetección por microondas que se han embarcado en satélites, para monitorizar parámetros biofísicos y geofísicos sobre la superficie de la tierra de manera global. También se han desarrollado estos sistemas para ser transportados en plataformas aéreas tripuladas para realizar estudios a nivel local o regional, donde se desea obtener información de una zona en particular en tiempos relativamente cortos. Sin embargo, ambas plataformas representan, entre otras cosas, un alto coste, no solo económico sino de infraestructura, equipo, grupos de trabajo, permisos de operación, y varios requerimientos más. El creciente desarrollo de los sistemas aéreos no tripulados (Unmanned Aerial Vehicle, UAV), ha hecho posible su uso para transportar sensores de teledetección. Los sistemas UAV presentan las mismas ventajas que los sistemas aéreos tripulados, pero además añaden otras ventajas adicionales. Por ejemplo, pueden ser operados durante varias horas de forma autónoma, el coste de explotación y desarrollo puede ser menor que el de un avión tripulado si se emplea un UAV de bajas prestaciones. Por tal motivo en este trabajo se propone el uso de un aeromodelo de control por radio como plataforma UAV para monitorizar diversos parámetros geofísicos y biofísicos de la tierra mediante sensores activos y pasivos de teledetección por microondas. Para realizar las medidas de teledetección pasiva se ha desarrollado el sensor denominado Airborne RadIometEr at L-Band (ARIEL) que es un radiómetro Dicke de bajo peso y pequeñas dimensiones, y que trabaja en Banda L (≈1.4 GHz). En la presenta memoria se muestra el diseño del sensor, las características principales de funcionamiento, y las técnicas de procesamiento de datos. Posteriormente se presentan las campañas de medida realizadas en zonas de cultivo, suelo descubierto, y zonas costeras. En tales campañas se han conseguido generar mapas de temperatura de brillo y de humedad de suelo. Con el fin de llevar a cabo medidas de teledetección activa se ha desarrollado el sistema denominado AiR Based REmote Sensing ARBRES, que consta de dos sensores radar de apertura sintética SAR diseñados a dos frecuencias diferentes, uno en Banda C (≈ 5.3 GHz) y otro en Banda X (≈ 9.65 GHz). Ambos radares son de onda continua FMCW, además son de bajo peso, bajo consumo de potencia y de pequeñas dimensiones. Ambos sensores tienen la capacidad de realizar medidas de interferometría SAR. En esta memoria se muestran las características de funcionamiento del sistema, así como algunos algoritmos de focalización de imágenes SAR, y una técnica para compensar los movimientos de la plataforma de vuelo. Finalmente se presentan medidas en campo para obtener imágenes de reflectividad de un escenario, y se muestran también los resultados para medidas realizadas en configuración de interferometría de simple pasada, la cual está relacionada con la topografía del terreno

Guidelines for the assessment and planning of estuarine barrages

Also known as Environment Agency R and D technical report W211Available from British Library Document Supply Centre-DSC:7514.030(491) / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

ARBRES: Light-weight CW/FM SAR sensors for small UAVs

This paper describes a pair of compact CW/FM airborne SAR systems for small UAV-based operation (wingspan of 3.5 m) for low-cost testing of innovative SAR concepts. Two different SAR instruments, using the C and X bands, have been developed in the context of the ARBRES project, each of them achieving a payload weight below 5 Kg and a volume of 13.5 dm3 (sensor and controller). Every system has a dual receiving channel which allows operation in interferometric or polarimetric modes. Planar printed array antennas are used in both sensors for easy system integration and better isolation between transmitter and receiver subsystems. First experimental tests on board a 3.2 m wingspan commercial radio-controlled aircraft are presented. The SAR images of a field close to an urban area have been focused using a back-projection algorithm. Using the dual channel capability, a single pass interferogram and Digital Elevation Model (DEM) has been obtained which agrees with the scene topography. A simple Motion Compensation (MoCo) module, based on the information from an Inertial+GPS unit, has been included to compensate platform motion errors with respect to the nominal straight trajectory.Peer Reviewe

Design and first results of an UAV-borne L-band radiometer for multiple monitoring purposes

UAV (unmanned Aerial Vehicle) platforms represent a challenging opportunity for the deployment of a number of remote sensors. These vehicles are a cost-effective option in front of manned aerial vehicles (planes and helicopters), are easy to deploy due to the short runways needed, and they allow users to meet the critical requirements of the spatial and temporal resolutions imposed by the instruments. L-band radiometers are an interesting option for obtaining soil moisture maps over local areas with relatively high spatial resolution for precision agriculture, coastal monitoring, estimation of the risk of fires, flood prevention, etc. This paper presents the design of a light-weight, airborne L-band radiometer for deployment in a small UAV, including the hardware and specific software developed for calibration, geo-referencing, and soil moisture retrieval. First results and soil moisture retrievals from different field experiments are presented.Peer Reviewe

Numerical modelling of the deformation of elastic material by the TLM method

SIGLEAvailable from British Library Document Supply Centre-DSC:DXN022625 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Altimetry study performed using an airborne GNSS-reflectometer

The Global Navigation Satellite Signals Reflections (GNSSR)techniques have been widely used for remote sensing purposes retrieving geophysical parameters over different types of surfaces. Over the ocean, altimetry or sea state can be retrieved. Over land, soil moisture can be inferred and over ice, altimetry, and ice age are also retrieved. This paper presents the results of using GNSS-R techniques to retrieve altimetry from the measurements of an airborne GNSS-Reflectometer.Peer Reviewe

Study of maize plants effects in the retrieval of soil moisture using the interefence Ppttern GNSS-R technique

The use of Global Navigation Satellite Signals Reflections (GNSS-R) techniques to retrieve geophysical parameters from surfaces has been increased in the recent years. These techniques have resulted in suitable tools to obtain information about the sea state of oceans, which is very useful to improve the ocean salinity retrieval, and also, information about the soil moisture of lands. The present work focuses on the use of the Interference Pattern Technique (IPT), a particular type of GNSS-R technique, to study vegetation-covered soils. The IPT consists mainly of the measurement of the interference pattern between the GPS direct and reflected signals (the interference power), after they impinge over the ensemble soil surface and vegetation layer. The measured interference signal provides information on the soil moisture of the surface and also, on the vegetation height.Peer Reviewe

Review of the CALIMAS Team Contributions to European Space Agency’s Soil Moisture and Ocean Salinity Mission Calibration and Validation

This work summarizes the activities carried out by the SMOS (Soil Moisture and Ocean Salinity) Barcelona Expert Center (SMOS-BEC) team in conjunction with the CIALE/Universidad de Salamanca team, within the framework of the European Space Agency (ESA) CALIMAS project in preparation for the SMOS mission and during its first year of operation. Under these activities several studies were performed, ranging from Level 1 (calibration and image reconstruction) to Level 4 (land pixel disaggregation techniques, by means of data fusion with higher resolution data from optical/infrared sensors). Validation of SMOS salinity products by means of surface drifters developed <em>ad-hoc</em>, and soil moisture products over the REMEDHUS site (Zamora, Spain) are also presented. Results of other preparatory activities carried out to improve the performance of eventual SMOS follow-on missions are presented, including GNSS-R to infer the sea state correction needed for improved ocean salinity retrievals and land surface parameters. Results from CALIMAS show a satisfactory performance of the MIRAS instrument, the accuracy and efficiency of the algorithms implemented in the ground data processors, and explore the limits of spatial resolution of soil moisture products using data fusion, as well as the feasibility of GNSS-R techniques for sea state determination and soil moisture monitoring