Ocean monitoring using GNSS-R techniques and microwave radiometry: The pau instrument concept

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El uso de señales de oportunidad GPS para observación de la Tierra

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Calibration of Correlation Radiometers Using Pseudo-Random Noise Signals

The calibration of correlation radiometers, and particularly aperture synthesis interferometric radiometers, is a critical issue to ensure their performance. Current calibration techniques are based on the measurement of the cross-correlation of receivers’ outputs when injecting noise from a common noise source requiring a very stable distribution network. For large interferometric radiometers this centralized noise injection approach is very complex from the point of view of mass, volume and phase/amplitude equalization. Distributed noise injection techniques have been proposed as a feasible alternative, but are unable to correct for the so-called “baseline errors” associated with the particular pair of receivers forming the baseline. In this work it is proposed the use of centralized Pseudo-Random Noise (PRN) signals to calibrate correlation radiometers. PRNs are sequences of symbols with a long repetition period that have a flat spectrum over a bandwidth which is determined by the symbol rate. Since their spectrum resembles that of thermal noise, they can be used to calibrate correlation radiometers. At the same time, since these sequences are deterministic, new calibration schemes can be envisaged, such as the correlation of each receiver’s output with a baseband local replica of the PRN sequence, as well as new distribution schemes of calibration signals. This work analyzes the general requirements and performance of using PRN sequences for the calibration of microwave correlation radiometers, and particularizes the study to a potential implementation in a large aperture synthesis radiometer using an optical distribution network

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

Ocean monitoring using L-Band microwave radiometry and GNSS-R

The knowledge of sea surface salinity (SSS) is a key issue to understand and monitor the Earth¿s water cycle. Accurate and systematic measurement of SSS was not possible until the ESA¿s Soil Moisture and Ocean Salinity (SMOS) mission was launched in 2009. The SMOS mission uses L-band microwave radiometry to infer SSS from measurements of the ocean¿s emis- sivity. However, the ocean surface emissivity is not only dependent on SSS, but also on sea surface temperature (SST), incidence angle, polarization, and sea surface roughness (i.e. sea-state). While the dependence on most of these parameters is well-known, and can be properly accounted for, the accurate estimation and correction of the sea surface roughness contribution remains a challenge. The Passive Advanced Unit (PAU) project was born in 2003 with the main objective of studying how to correct ocean L-band brightness temperature for the sea-state effect by using an emerging technology such as reflectome- try of opportunity GNSS signals (GNSS-R). GNSS-R is based on measuring the forward scattered GNSS signals so as to infer geophysical properties of the scattering surface. Particularly, the PAU project proposed to use direct observables from the reflected signal¿s Delay-Doppler Map (DDM) to parame- terize sea surface roughness, and link those observables to the brightness tem- perature variations induced by sea-state, without using scattering/emissivity models. In this line, prior work was performed by J.F. Marchan-Hernandez in his PhD. Thesis (UPC, Barcelona, 2009). In that work, a first version of the PAU GNSS-R receiver was developed, and first experimental results were obtained that supported the hypothesis that direct GNSS-R observables can be used to describe sea-state. This PhD. Thesis follows on that research, and steps into the use of GNSS- R observables for estimation of the sea-state contribution to the ocean L-band brightness temperature. The work presented here was undertaken between 2008 and 2012, and comprises contributions to three main fields: GNSS-R hardware development, experimental results, and theoretical studies. Firstly, the PAU GNSS-R instrument was re-designed and re-implemented for im- proved sensitivity and stability. Secondly, results from ground-based and airborne experiments were obtained, that prove the hypothesis that GNSS-R observables can be used to successfully correct L-band brightness tempera- ture for the sea-state effect, resulting in an improvement in the SSS retrieval accuracy. Finally, theoretical studies to foresee the performance of the PAU concept in a future spaceborne mission were conducted, along with the de- velopment of a new technique to obtain ocean surface scattering coefficient images from measured DDMs

Renormalisation of a hierarchical PHI43 model

SIGLEAvailable from British Library Document Supply Centre- DSC:3630.84(DIAS-STP--87-55) / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Impact of doppler frequency compensation errors on spaceborne GNSS-R altimetry

The compensation of the Doppler frequency error is important to accurately estimate the sea height in spaceborne GNSSR altimetry. This work presents the impact of the residual Doppler error on the altimetric performance. The GNSS-R altimetric observables (waveforms) are simulated with various observation parameters, and the degradation is analyzed vs. the Doppler errors. It is shown that the Doppler error causes a bias, a decrease of the waveform value, and consequently the altimetric performance degradation in accuracy and precision.Peer Reviewe

Preliminary error budget of a GNSS-r spaceborne mission

Reflectometry using Global Navigation Satellite System's (GNSS) opportunity signals was originally conceived for altimetry [1], but it has been demonstrated today that it can be applied to sea state determination, soil moisture, vegetation, snow monitoring... So far, GPS signals scattered over the Earth's surface have been cross-correlated with a local replica of the transmitted signal (typically the only GPS available: the C/A code) shifted in frequency (Δfd) and in delay (τ). However, to achieve the full potential (bandwidth) of these signals the direct and reflected signals can be directly cross-correlated, but in this case, high gain antennas are required to increase the signal-to-noise ratio. Therefore these antennas must be steerable so as to track the direct satellite and the specular reflection point. This is the concept of the European Space Agency PARIS In Orbit Demonstrator (IoD) mission [2], a new concept that was demonstrated experimentally for the first time in 2010 [3]. This work deals with the analysis of the preliminary instrument error budget of this mission to address the critical design parameters.Peer ReviewedPostprint (published version

Management of radical change A case study of Hungarian telecommunications

SIGLEAvailable from British Library Document Supply Centre- DSC:DX184640 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Preliminary error budget of a GNSS-r spaceborne mission

Reflectometry using Global Navigation Satellite System's (GNSS) opportunity signals was originally conceived for altimetry [1], but it has been demonstrated today that it can be applied to sea state determination, soil moisture, vegetation, snow monitoring... So far, GPS signals scattered over the Earth's surface have been cross-correlated with a local replica of the transmitted signal (typically the only GPS available: the C/A code) shifted in frequency (Δfd) and in delay (τ). However, to achieve the full potential (bandwidth) of these signals the direct and reflected signals can be directly cross-correlated, but in this case, high gain antennas are required to increase the signal-to-noise ratio. Therefore these antennas must be steerable so as to track the direct satellite and the specular reflection point. This is the concept of the European Space Agency PARIS In Orbit Demonstrator (IoD) mission [2], a new concept that was demonstrated experimentally for the first time in 2010 [3]. This work deals with the analysis of the preliminary instrument error budget of this mission to address the critical design parameters.Peer Reviewe