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This work was supported by the “la Caixa” Foundation (ID 100010434) under Grant LCF/PR/MIT19/51840001 (MIT-Spain Seed Fund), by MISTI-Germany and MISTI-Belgium Seed Funds, by the XXXIII Ramón Areces Postdoctoral Fellowship, by the NASA (Grant 1510842), by grants PID2020-114623RB-C32 and MDM-2016-0600 funded by MCIN/AEI/10.13039/501100011033, by the European Regional Development Fund (ERDF), and by the NASA Postdoctoral Program at the NASA Goddard Space Flight Center. D. Chaparro thanks the AKS department (DLR) and the CEE department (MIT) for hosting and supervision., Postprint (author's final draft)

The vegetation optical depth (VOD) variable contains information on plant water content and biomass. It can be estimated alongside soil moisture from currently operating satellite radiometer missions, such as SMOS (ESA) and SMAP (NASA). The estimation of water fluxes, such as plant water uptake (PWU) and transpiration rate (TR), from these earth system parameters (VOD, soil moisture) requires assessing water potential gradients and flow resistances in the soil, the vegetation and the atmosphere. Yet water flux estimation remains an elusive challenge especially on a global scale. In this concept study, we conduct a field-scale experiment to test mechanistic models for the estimation of seasonal water fluxes (PWU and TR) of a winter wheat stand using measurements of soil moisture, VOD, and relative air humidity (RH) in a controlled environment. We utilize microwave L-band observations from a tower-based radiometer to estimate VOD of a wheat stand during the 2017 growing season at the Selhausen test site in Germany. From VOD, we first extract the gravimetric moisture of vegetation and then determine the relative water content (RWC) and vegetation water potential (VWP) of the wheat field. Although the relative water content could be directly estimated from VOD, our results indicate this may be challenging for the phenological phases, when rapid biomass and plant structure development take place within the wheat canopy. We estimate water uptake from the soil to the wheat plants from the difference between the soil and vegetation potentials divided by the flow resistance from soil into wheat plants. The TR from the wheat plants into the atmosphere was obtained from the difference between the vegetation and atmosphere water potentials divided by the flow resistances from plants to the atmosphere. For this, the required soil matric potential (SMP), the vapor pressure deficit (VPD), and the flow resistances were obtained from on-site observations of soil, plant, and atmosphe, David Chaparro has received funding by “la Caixa” Foundation (ID 100010434), under agreement LCF/PR/MIT19/51840001, by the MIT-MISTI, by the XXXIII Ramón Areces Postdoctoral Fellowship, and by grants PID2020-114623RB-C32 and MDM-2016-0600 funded by MCIN/AEI/10.13039/501100011033 and by the European Regional Development Fund (ERDF, EU). María Piles was supported by grant RTI2018-096765-A-100 funded by MCIN/AEI/10.13039/501100011033 and by the European Regional Development Fund (ERDF, EU). The article processing charges for this open-access publication were covered by the German Aerospace Center (DLR)., Peer Reviewed, Postprint (published version)

The MTDCA soil moisture and VOD datasets are freely available at https://doi.org/10.5281/zenodo.5579549. The DCA retrievals generated for this study are freely available from the authors upon request., Satellite soil moisture and vegetation optical depth [(VOD); related to the total vegetation water mass per unit area] are increasingly being used to study water relations in the soil-plant continuum across the globe. However, soil moisture and VOD are typically jointly estimated, where errors in the optimization approach can cause compensation between both variables and confound such studies. It is thus critical to quantify how satellite microwave measurement errors propagate into soil moisture and VOD. Such a study is especially important for VOD given limited investigations of whether VOD reflects in situ plant physiology. Furthermore, despite new approaches that constrain (or regularize) VOD dynamics to reduce soil moisture errors, there is limited study of whether regularization reduces VOD errors without obscuring true vegetation temporal dynamics. Here, we find that, across the globe, VOD is less robust to measurement error (more difficult for optimization methods to find the true solution) than soil moisture in their joint estimation. However, a moderate degree of regularization (via time-constrained VOD) reduces errors in VOD to a greater degree than soil moisture and reduces spurious soil moisture-VOD coupling. Furthermore, despite constraining VOD time dynamics, regularized VOD variations on subweekly scales are both closer to simulated true VOD time series and have global VOD post-rainfall responses with reduced error signatures compared to VOD retrievals without regularization. Ultimately, we recommend moderately regularized VOD for use in large scale studies of soil-plant water relations because it suppresses noise and spurious soil moisture-VOD coupling without removing the physical signal., Peer Reviewed, Postprint (published version)

The attenuation of microwave emissions through the canopy is quantified by the vegetation optical depth (VOD), which is related to the amount of water, the biomass and the structure of vegetation. To provide microwave-derived plant water estimates, one must account for biomass/structure contributions in order to extract the water component from the VOD. This study uses Aquarius scatterometer data to build an L-band global seasonality of vegetation volume fraction (d), representative of biomass/structure dynamics. The dynamic range of d is adapted for its application in a gravimetric moisture (Mg) retrieval model. Results show that d ranging from 0 to 3.35.10- 4 is needed for modelling physically reasonable Mg values. The global average of d shows consistent spatial patterns across vegetation distributions, and d seasonality is coherent with the phenology of the studied vegetation types. These findings enable the separation of information on vegetation water and biomass/structure inherent within VOD., This work was supported by “la Caixa” Foundation (ID 100010434), under agreement LCF /PR/MIT19/51840001 (MIT -Spain Seed Fund), and by the Spanish Ministry of Science, Innovation and Universities and the European Regional Development Fund (ERDF, EU) through projects ESP2017-89463-C3-3-R, RTI2018-096765-A-100, CAS19/00264 and MDM-2016-0600. Also, the authors are grateful to MIT for supporting this research with the MIT-Germany Seed Fund (D. Entekhabi, T. Jagdhuber)., Peer Reviewed, Postprint (published version)

Vegetation Optical Depth (VOD) is highly sensitive to Above-ground Biomass (AGB), particularly at L-band, as this band is more sensitive to the canopy layer and has greater ca pacity to penetrate the vegetation. However, higher frequen cies, such as C- and X-bands are more related to smaller veg etation structures. Then a combination of these three bands is expected to be relevant to accurate AGB retrievals. This study presents a comparison of three VOD products at three bands and evaluates the performance of a multi-frequency VOD combination by applying a Principal Component Re gression (PCR) to Forest biomass. Results show that L-band VOD captures the 84% of the biomass and the PCR is built, mainly, for this band meaning that higher frequencies do not contribute substantially to the AGB retrieval in this study, still they do not affect the retrievals negatively., Peer Reviewed, Postprint (author's final draft)

Vegetation canopy height (CH) is one of the important remote-sensing parameters related to forests’ structure, and it can be related to the biomass and the carbon stock. Global navigation satellite system-reflectometry (GNSS-R) has proved capable to retrieve vegetation information at a moderate resolution from space (20–65 km) using L1 C/A signals. In this study, data retrieved by the airborne microwave interferometric reflectometer (MIR) GNSS-R instrument at L1 and L5 are compared to the Global Forest CH product, with a spatial resolution of 30 m. This work analyzes the waveforms (WFs) measured at both bands, and the correlation of the waveform width and the reflectivity values to the CH product. A neural network algorithm is used for the retrieval, showing that the combination of the reflectivity and the waveform width allows to estimate the CH information at a very high resolution, with a root-mean-square error (RMSE) of 4.25 and 4.07 m at L1 and L5, respectively, which is an error about 14% of the actual CH., Postprint (updated version)

The Microwave Interferometric Reflectometer (MIR) is an airborne GNSS-R instrument developed by Universitat Politècnica de Catalunya. In 2018, it was flown twice over the agricultural Yanco area, New South Wales, Australia, once after a very dry period, and a further time the day after a strong rain event. This rain event resulted in many crop fields being entirely flooded, producing a saturation in the GNSS-R reflectivity value. In this work, the received data set is processed to identify the optimum integration time with the goal to minimize pixel blurring. This issue is assessed for airborne conditions, and then extra-polated to the spaceborne case. The presented results show that the blurring of the GNSS waveform is produced even from an airborne sensor with short integration times. Following the determination of an optimal integration time for the platform in use, the surface roughness term in the reflectivity equation can be isolated due to the signal saturation during very wet surface conditions. The final results from the two channels (L1 C/A and L5) are subsequently presented. In this case, it is shown that most reflectivity variations in GNSS-R measurements are linked to surface roughness and Speckle noise fluctuations rather than soil moisture changes., Postprint (updated version)

At L-band (1–2 GHz), and particularly in microwave radiometry (1.413 GHz), vegetation has been traditionally modeled with the τ-ω model. This model has also been used to compensate for vegetation effects in Global Navigation Satellite Systems-Reflectometry (GNSS-R) with modest success. This manuscript presents an analysis of the vegetation impact on GPS L1 C/A (coarse acquisition code) signals in terms of attenuation and depolarization. A dual polarized instrument with commercial off-the-shelf (COTS) GPS receivers as back-ends was installed for more than a year under a beech forest collecting carrier-to-noise (C/N0) data. These data were compared to different ground-truth datasets (greenness, blueness, and redness indices, sky cover index, rain data, leaf area index or LAI, and normalized difference vegetation index (NDVI)). The highest correlation observed is between C/N0 and NDVI data, obtaining R2 coefficients larger than 0.85 independently from the elevation angle, suggesting that for beech forest, NDVI is a good descriptor of signal attenuation at L-band, which is known to be related to the vegetation optical depth (VOD). Depolarization effects were also studied, and were found to be significant at elevation angles as large as ~50°. Data were also fit to a simple τ-ω model to estimate a single scattering albedo parameter (ω) to try to compensate for vegetation scattering effects in soil moisture retrieval algorithms using GNSS-R. It is found that, even including dependence on the elevation angle (ω(θe)), at elevation angles smaller than ~67°, the ω(θe) model is not related to the NDVI. This limits the range of elevation angles that can be used for soil moisture retrievals using GNSS-R. Finally, errors of the GPS-derived position were computed over time to assess vegetation impact on the accuracy of the positioning., This work has been funded by the Spanish MCIU and EU ERDF project (RTI2018-099008-B-C21) “Sensing with pioneering opportunistic techniques” and grant to “CommSensLab-UPC” Excellence Research Unit Maria de Maeztu (MINECO grant MDM-2016-600)., Peer Reviewed, Postprint (published version)

© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., As compared to the using L1C/A signals, L5/E5a Global Navigation Satellite System - Reflectometry (GNSS-R), gives improved resolution over the Earth's surface due to the sharper auto-correlation function. Furthermore, the larger transmitted power (+3dB with respect to L1 C/A), and correlation gain (+40dB) allows the reception of weaker reflected signals. If high directivity antennas are used, very short incoherent integration times are needed to have enough signal-to-noise (SNR) ratios, allowing the reception of multiple specular reflection points such as crest of consecutive waves without the blurring induced by long incoherent integration times. This study presents for the first time experimental evidence of the wind and swell waves signatures in the GNSS-R waveforms, and compares them with models., Postprint (author's final draft)

© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Global Navigation Satellite Systems Reflected (GNSS-R) signals exhibit an incoherent and a coherent components [1], [2]. Current models assume that one or the other are dominant, and the calibration, and geophysical parameter retrieval (eg. wind speed, soil moisture ...) are developed accordingly. Even the presence itself of the coherent component of a GNSS reflected signal has been a matter of discussion in the last years. In this work, the method used in [3] to separate the leakage of the direct signal from the reflected one is applied to a set of GNSS signals reflected collected over the ocean by the MIR [4], [5], an airborne dual-band (L1/E1 and L5/E5a), multi-constellation (GPS and Galileo) GNSS-R instrument with two 19-elements array with 4 beam-steered each. The results presented demonstrate the feasibility of the proposed technique to untangle the coherent and incoherent components in GNSS reflected signals. This technique allows the processing of these components separately, which will increase the calibration accuracy (as today both are mixed together), and allows high resolution applications since the spatial resolution of the coherent component is determined by the size of the first Fresnel zone [6] (300-500 meters from a LEO satellite), and not by the size of the glistening zone (~25 km from a LEO satellite)., This work was supported by the Spanish Ministry of Science, Innovation and Universities, “Sensing with Pio- neering Opportunistic Techniques”, grant RTI2018-099008- B-C21, and the grant for recruitment of early-stage research staff FI-DGR 2015 and 2018 of the AGAUR - Generalitat de Catalunya (FEDER), Postprint (author's final draft)

As compared to GPS L1C/A signals, L5/E5a Global Navigation Satellite System-Reflectometry (GNSS-R) improves the spatial resolution due to the narrower auto-correlation function. Furthermore, the larger transmitted power (+3 dB), and correlation gain (+10 dB) allow the reception of weaker reflected signals. If directive antennas are used, very short incoherent integration times are enough to achieve good signal-to-noise ratios, allowing the reception of multiple specular reflection points without the blurring induced by long incoherent integration times. This study presents for the first time experimental evidence of the wind and swell waves signatures in the GNSS-R waveforms, and it performs a statistical analysis, a time-domain analysis, and a frequency-domain analysis for a unique data set of waveforms collected by the UPC MIR instrument during a series of flights over the Bass Strait, Australia, This work was founded by the Spanish Ministry of Science, Innovation and Universities, “Sensing with Pioneering Opportunistic Techniques”, grant RTI2018-099008-B-C21, and the grant for recruitment of early-stage research staff FI-DGR 2015 of the AGAUR - Generalitat de Catalunya (FEDER), Spain, and the grant for recruitment of early-stage research staff FI 2018 of the AGAUR - Generalitat de Catalunya (FEDER), Spain, and Unidad de Excelencia María de Maeztu MDM-2016-060., Peer Reviewed, Postprint (published version)

This work analyzes the quality of the soil moisture L3 (25 km) and L4 (1 km) products generated at the Barcelona Expert Center (BEC) in two sites located in distinct semi-arid regions, where measurement networks are installed: “Red de Estaciones de Medición de la Humedad del Suelo” (REMEDHUS), which is located in the central part of the Duero basin (Spain), and National Center for Monitoring and Early Warning of Natural Disasters (CEMADEN), at Northeast of the Brazil. REMEDHUS has been used as a calibration/validation site for SMOS and SMAP missions. It is a dense network covering 35 x 35 km2 and it has 22 stations. The CEMADEN network provides a database for the development of early warnings for natural disasters that occurs in Brazil, such as droughts and floods. It is a sparse network covering 1000 x 1000 km2 with more than 500 station. Results show good correspondence between SMOS L4 data and the in situ soil moisture data for REMEDHUS and CEMADEN networks. Correlations mean range from 0.3 to 0.8, and depend mainly on the station situation, soil type, and land cover on both Spain and Brazil networks. For the average data of both series, the correlation coefficient is higher than 0.6. Results show that the L4 product are better correlated than the L3 product, although L4 and L3 products are quite similar. This indicates that both products are ready for its operational use, with L4 providing a better representation of the soil moisture status at finer scales., Este trabalho analisa a qualidade dos produtos L3 (25 km) e L4 (1 km) de umidade do solo gerados no Barcelona Expert Center (BEC) em dois locais localizados em regiões semi-áridas distintas, onde estão instaladas redes de medição: Estações de Medição de Umidade do Solo” (REMEDHUS), localizado na parte central da bacia do Douro (Espanha), e Centro Nacional de Monitoramento e Aviso Prévio de Desastres Naturais (CEMADEN), no nordeste do Brasil. O REMEDHUS foi usado como um local de calibração / validação para missões SMOS e SMAP. É uma rede densa cobrindo 35 x 35 km2 e possui 22 estações. A rede CEMADEN fornece um banco de dados para o desenvolvimento de alertas precoces de desastres naturais que ocorrem no Brasil, como secas e inundações. É uma rede esparsa cobrindo 1000 x 1000 km2 com mais de 500 estações. Os resultados mostram boa correspondência entre os dados SMOS L4 e os dados de umidade do solo in situ para as redes REMEDHUS e CEMADEN. As correlações variam de 0,3 a 0,8 e dependem principalmente da situação da estação, tipo de solo e cobertura do solo nas redes da Espanha e do Brasil. Para os dados médios de ambas as séries, o coeficiente de correlação é superior a 0,6. Os resultados mostram que o produto L4 está melhor correlacionado que o produto L3, embora os produtos L4 e L3 sejam bastante semelhantes. Isso indica que ambos os produtos estão prontos para seu uso operacional, com L4 fornecendo uma melhor representação do status de umidade do solo em escalas mais refinadas, This work was supported by the Spanish Ministry of Economy and Competitiveness, through the project PROMISES: Productos y servicios innovadores con sensores de microondas, SMOS y Sentinels para tierra ESP2015-67549-C3- 1-R and the ERDF (European Regional Development Fund). And though the award “Unidad de Excellencia María de Maetzu MDM2016-0600, financed by the Agencia Estatal de Investigación (Spain)., Peer Reviewed, Postprint (published version)

As opposed to monostatic radars where incoherent backscattering dominates, in bistatic radars, such as Global Navigation Satellite Systems Reflectometry (GNSS-R), the forward scattered signals exhibit both an incoherent and a coherent component. Current models assume that either one or the other are dominant, and the calibration and geophysical parameter retrieval (e.g., wind speed, soil moisture, etc.) are developed accordingly. Even the presence of the coherent component of a GNSS reflected signal itself has been a matter of discussion in the last years. In this work, a method developed to separate the leakage of the direct signal in the reflected one is applied to a data set of GNSS-R signals collected over the ocean by the Microwave Interferometer Reflectometer (MIR) instrument, an airborne dual-band (L1/E1 and L5/E5a), multi-constellation (GPS and Galileo) GNSS-R instrument with two 19-elements antenna arrays with 4 beam-steered each. The presented results demonstrate the feasibility of the proposed technique to untangle the coherent and incoherent components from the total power waveform in GNSS reflected signals. This technique allows the processing of these components separately, which increases the calibration accuracy (as today both are mixed and processed together), allowing higher resolution applications since the spatial resolution of the coherent component is determined by the size of the first Fresnel zone (300–500 meters from a LEO satellite), and not by the size of the glistening zone (25 km from a LEO satellite). The identification of the coherent component enhances also the location of the specular reflection point by determining the peak maximum from this coherent component rather than the point of maximum derivative of the incoherent one, which is normally noisy and it is blurred by all the glistening zone contributions, This work was founded by the Spanish Ministry of Science, Innovation and Universities, “Sensing withPioneering Opportunistic Techniques”, grant RTI2018-099008-B-C21, and the grant for recruitment of early-stageresearch staff FI-DGR 2015 of the AGAUR—Generalitat de Catalunya (FEDER), Spain, and Unidad de ExcelenciaMaría de Maeztu MDM-2016-060., Peer Reviewed, Postprint (published version)

Global navigation satellite system reflectometry (GNSS-R) is a group of techniques that uses satellite navigation signals as signals of opportunity for remote sensing applications. In GNSS-R, large amounts of data are acquired and have to be processed. Computation time is typically the bottleneck for ground and airborne experiments. This article presents an efficient solution for off-line GNSS-R processing data taking advantage of graphics processing units (GPUs). After comparing to the typically used CPU languages, such as MATLAB and C++, the advantage of using parallel processing on the GPU is clear. GPU-based computation can reduce the processing time by as much as 95% of the acquisition time of the data. An implementation taking advantage of a home-use GPU is proposed for the data processing units. Thanks to its efficiency, even real-time processing experiments are feasible., This work was supported in part bythe Spanish Ministry of Economy and Competitiveness and FEDER EU underthe project “AGORA: Técnicas Avanzadas en Teledetección Aplicada UsandoSeñales GNSS y Otras Señales de Oportunidad” (MINECO/FEDER) ESP2015-70014-C2-1-R by the Agencia Estatal de Investigación; in part by the SpanishMinistry of Science, Innovation, and Universities, “Sensing with Pioneering Opportunistic Techniques,” under Grant RTI2018-099008-B-C21; in part by the Collaboration under Grant 998142 by the Spanish Ministry of Education; inpart by Unidad de Excelencia María de Maeztu MDM-2016-0600; and in partby Prof. Camps ICREA Academia 2015 award of the Generalitat de Catalunya., Peer Reviewed, Postprint (published version)

The objective of this paper is to explore the performance of a miniature 3D spherical wind sensor for Mars atmosphere, working under extreme wind speeds, up to the Dust Devil scale. The experimental campaign has been made for winds in the range Reynolds 1000-2000, which for typical Mars conditions and the dimensions of the sensor, represent 65-130m/s wind velocities. The experimental results further confirm high-fidelity numerical simulations of the fluid dynamics and heat transfer from a sphere for Reynolds 1000-104 and Prandtl 0.7, recently published in, which indicate that it is possible to measure in this regime., Peer Reviewed, Postprint (published version)

This manuscript describes the Microwave Interferometric Reflectometer (MIR) instrument, a multi-beam dual-band GNSS-Reflectometer with beam-steering capabilities built to assess the performance of a PAssive Reflectrometry and Interferometry System—In Orbit Demonstrator (PARIS-IoD) like instrument and to compare the performance of different GNSS-R techniques and signals. The instrument is capable of tracking up to 4 different GNSS satellites, two at L1/E1 band, and two at L5/E5 band. The calibration procedure of the up- and down-looking arrays is presented, the calibration performance is evaluated, and the results of the validation experiments carried out before the field experiments are shown in this paper., Peer Reviewed, Postprint (author's final draft)

This work analyzes the satellite cross-talk observed by the microwave interferometric reflectometer (MIR), a new global navigation satellite system (GNSS) reflectometer, during an airborne field campaign in Victoria and New South Wales, Australia. MIR is a GNSS reflectometer with two 19-element, dual-band arrays, each of them having four steerable beams. The data collected during the experiment, the characterization of the arrays, and the global positioning system (GPS) and Galileo ephemeris were used to compute the expected delays and power levels of all incoming signals, and the probability of cross-talk was then evaluated. Despite the MIR highly directive arrays, the largest ever for a GNSS-R instrument, one of the flights was found to be contaminated by cross-talk almost half of the time at the L1/E1 frequency band, and all four flights were contaminated ~5–10% of the time at the L5/E5a frequency band. The cross-talk introduces an error of up to 40 cm of standard deviation for altimetric applications and about 0.24 dB for scatterometric applications, Peer Reviewed, Postprint (published version)

Global Navigation Satellite System (GNSS) reflected signals can be used to remotely sense the Earth’s surface, known as GNSS reflectometry (GNSS-R). The GNSS-R technique has been applied to numerous areas, such as the retrieval of wind speed, and the detection of Earth surface objects. This work proposes a new application of GNSS-R, namely to detect objects above the Earth’s surface, such as low Earth orbit (LEO) satellites. To discuss its feasibility, 14 delay Doppler maps (DDMs) are first presented which contain unusually bright reflected signals as delays shorter than the specular reflection point over the Earth’s surface. Then, seven possible causes of these anomalies are analysed, reaching the conclusion that the anomalies are likely due to the signals being reflected from objects above the Earth’s surface. Next, the positions of the objects are calculated using the delay and Doppler information, and an appropriate geometry assumption. After that, suspect satellite objects are searched in the satellite database from Union of Concerned Scientists (UCS). Finally, three objects have been found to match the delay and Doppler conditions. In the absence of other reasons for these anomalies, GNSS-R could potentially be used to detect some objects above the Earth’s surface., Peer Reviewed, Postprint (published version)

An optimal payload selection conducted in the frame of the H2020 ONION project (id 687490) is presented based on the ability to cover the observation needs of the Copernicus system in the time period 2020–2030. Payload selection is constrained by the variables that can be measured, the power consumption, and weight of the instrument, and the required accuracy and spatial resolution (horizontal or vertical). It involved 20 measurements with observation gaps according to the user requirements that were detected in the top 10 use cases in the scope of Copernicus space infrastructure, 9 potential applied technologies, and 39 available commercial platforms. Additional Earth Observation (EO) infrastructures are proposed to reduce measurements gaps, based on a weighting system that assigned high relevance for measurements associated to Marine for Weather Forecast over Polar Regions. This study concludes with a rank and mapping of the potential technologies and the suitable commercial platforms to cover most of the requirements of the top ten use cases, analyzing the Marine for Weather Forecast, Sea Ice Monitoring, Fishing Pressure, and Agriculture and Forestry: Hydric stress as the priority use cases., Peer Reviewed, Postprint (published version)

Attenuation of surface microwave emission due to the overlying vegetation is proportional to the density of the canopy and to its water content. The vegetation optical depth (VOD) parameter measures this attenuation. VOD could be a valuable source of information on agroecosystems, especially at lower frequencies for which greater portion of the vegetation canopy contributes to the observed brightness temperature. In the past, visible-infrared indices have been used to provide yield estimates based on measuring the photosynthetic activity from the surface canopy layer. These indices are affected by clouds and apply only in the presence of solar illumination. In this study we instead use the L-band microwave radiometer on board of the SMAP mission that provides VOD estimates in all weather and regardless of illumination. This study proposes a series of L-band VOD metrics for crop yield assessment using the first annual cycle of SMAP data (April 2015 to March 2016) over north-central United States. Maps of yield and crop proportion from the US Department of Agriculture are compared to VOD retrieved from SMAP with the Multi-Temporal Dual Channel Algorithm (MT-DCA). The yield-VOD relationship is explored using principal components regressions. Results show that 66% of yield variance is explained over the whole region by the first principal component (PC1). In corn-soy crops, PC1 explains 78% of yield amount, and maximum, standard deviation, and range of VOD capture the yield spatial patterns. Mixture of crops and scene heterogeneity reduced the unique relationships between VOD metrics and yield for specific crops. Hence, in wheat and mixed crops, PC1 explains 43% of yield variance. Results suggest that complementary information on maximum biomass, growth rate, and VOD amplitude can provide robust yield estimates, and that the uncertainty of these estimates depends on crop composition and heterogeneity. This study provides evidence that L-band VOD metrics can potentially, Peer Reviewed, Postprint (published version)

As the TDS-1 and CYGNSS spaceborne GNSS-R missions progress, a large number of Delay-Doppler Maps (DDM) is being collected, from the land scattered as well as from the ocean. Based on those data, the feasibility study on the retrieval of land geophysical parameters such as soil moisture and vegetation is being studied. This work presents the E2E simulator that generates the synthesized DDM reflected over land. For the efficient development, the existing simulator for ocean scattering has been upgraded to accommodate the specific functionalities for land scattering: topography, surface roughness, vegetation effects, in addition to surface soil moisture, obviously. The developed end-to-end (E2E) simulator is used to conceive the retrieval algorithms and assess their performance. In this work, the upgraded items are described and illustrated with some simulation results., Peer Reviewed, Postprint (published version)

Radio-Frequency Interference (RFI) is one of the most concerning topics in Global Navigation Satellite Systems (GNSS) and GNSS - Reflectometry (GNSS-R) because any undesired signal present at the antenna can corrupt the received signal and the eventual geophysical measurements. The purpose of this paper is two-fold. First, an RFI analysis is performed to the raw data obtained from an airborne dual-band GNSS reflectometer. Finally, the Front-End GNSS Interference eXcisor (FENIX) mitigation algorithm is applied to the raw data, and then the Signal-to-Noise Ratio (SNR) improvement at the Delay-Doppler Map (DDM) is obtained. From the analysis of one of the datasets, two RFI signals were detected and characterized. Moreover, FENIX output signal was revealed to be much cleaner than before. The mean SNR improvement with coherent DDMs of 1 ms is 0.72 dB, whereas the SNR improvement increases to 1.49 dB when considering 50 incoherent averages. This improvement represents a reduction in the geophysical parameter estimation uncertainty., Peer Reviewed, Postprint (published version)

The potential of GNSS-R techniques to estimate land surface parameters such as Soil Moisture (SM) is experimentally studied using 2014-2017 global data from the UK TechDemoSat-1 (TDS-1) mission. The approach is based on the analysis of the sensitivity to Soil Moisture of different observables extracted from the Delay Doppler Maps (DDM) computed by the SGR-ReSI instrument using the L1 (1575.42 MHz) left-hand circularly-polarized (LHCP) reflected signals emitted by navigation satellites. After quality-filtering the data (spacecraft not `in eclipse' and the direct signal not present in the DDM), topography filtering the data, correction for background noise, antenna pattern gain, different distance propagation factors, and vegetation attenuation, the sensitivity of different GNSS-R observables to SM and its dependence with incidence angle is analyzed., Peer Reviewed, Postprint (published version)

©2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., The maximum coherent integration time of GNSS reflected (GNSS-R) signals over sea depends on the sea state, as well as on the geometry formed by the receiver, the GNSS satellite and the reflection point. In this paper, real data obtained with a dedicated airborne instrument named MALYGNSS (Multi-band Airborne L-Band reflectometrY with GNSS) is used to acquire GPS L1 C/A and L2C, and Galileo E1OS signals. The direct signals are used as a reference to detect any phase shift due to data bits changes and the presence of a residual Doppler frequency. These phase transitions are removed in the reflected signals, and coherent correlations of different lengths are performed in order to study sea correlation time., Peer Reviewed, Postprint (published version)

The 3 Cat-3/MOTS mission is a joint initiative between the Institut Cartogràfic i Geològic de Catalunya (ICGC) and the Universitat Politècnica de Catalunya-BarcelonaTech (UPC) to foster new and innovative technologies on Earth Observation (EO) based on the data fusion of Global Navigation Satellite Systems Reflectometry (GNSS-R) and optical payloads on a 6U CubeSat platform. The final objective of the mission is to provide soil moisture mapping through the GNSS-R payload and improve its resolution by data fusion with the multi-spectral optical data acquired. This technique has been successfully applied to SMOS, but never performed from a 6U CubeSat carrying both payloads. An airborne optical and GNSS-R field experiment has been carried out to test/develop the algorithm and to analyze the results both separately (GNSS-R + optical data) and as a soil moisture product, once performed the data fusion., Peer Reviewed, Postprint (published version)

Global Navigation Satellite Systems - Reflectometry (GNSS-R) has shown his potential for remote sensing. Since new wider band signals are being broadcasted, and new systems are becoming available, a performance comparison in fair conditions between signals and system is required. For this purpose, the Universitat Politecnica de Catalunya has been developing the MIR instrument, an airborne GNSS reflec-to meter that mimics PARIS-IOD, and that also aims to better understand some GNSS-R techniques, the RFI analysis and mitigation, and the use of beamforming techniques to improve the GNSS-R capabilities. This work presents the advances in the instrument, the end-to-end tests, and the field campaign being planned in Australia for Spring, 2018., Peer Reviewed, Postprint (published version)

In order to provide high resolution soil moisture maps, the Institut Cartografic i Geológic de Catalunya (ICGC) in colab-oration with Universitat Politecnica de Catalunya are planing to deploy the 3 Cat-3 picosatellite, which aims to estimate soil moisture from space using Global Navigation Satellite Systems - Reflectometry (GNSS-R) and to downscale it using data fusion with a multi-spectral camera. As a proof of concept, a field campaign is being carried out in Lleida, Catalunya. MALYGNSS is a GNSS reflectometer flying as an opportunity sensor that will validate the main reflectometer of the project: the CORTO instrument., Peer Reviewed, Postprint (published version)

© 2018 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., Radio Frequency Interference (RFI) is one of the problems causing the performance degradation in passive microwave radiometry. Especially, Synthetic Aperture Interferometric Radiometer (SAIR) is quite vulnerable to strong RFI. The Soil Moisture Ocean Salinity (SMOS) brightness temperature images show serious contamination by the RFI. The RFI affection in SAIR images should be mitigated or filtered out to retrieve the geophysical parameters. This work presents a method to RFI mitigation/filtering for SAIRs. Different from the existing method processing the brightness temperature image directly, RFI filtering of the subspace of covariance matrix is introduced, and the results are shown. The proposed method shows decent results for strong RFI with efficiency compared to the existing methods. © 2018 IEEE., Peer Reviewed, Postprint (published version)

The purpose of this paper is to present the experimental results obtained with a prototype of a 4-sector spherical anemometer, in the Aarhus Wind Tunnel Simulator II (AWTSII) reproducing Martian conditions. The main objective of the experimental campaign has been to measure wind velocity for a wide number of yaw and pitch angles, in an environment in the range of typical Mars conditions. The experimental results indicate that wind speed and angle recovery can be achieved with the proposed spherical sensor. The obtained responses are close to the empirical models found in the literature., Authors want to show their gratefulness to the Planetary Environment Facilities at Aarhus University (DK) for their hostage and professional approach. This laboratory is a member of Europlanet 2020 RI which has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 654208. This work was partially supported by the Spanish Ministry MINECO under Project grant no. ESP2016-79612-C3-2R., Peer Reviewed, Postprint (published version)

Global Navigation Satellite Systems – Reflectometry (GNSS-R) is a relatively new remote sensing technique that benefits from GNSS signals as signals of opportunity as a bistatic radar. These signals can be processed as a scatterometer by measuring the relative scattered power, as an altimeter by measuring the relative delay between the direct and the scattered signals, and as an unfocused Synthetic Aperture Radar (SAR) with very short coherent integration times (typically a few millisecons). Wider bandwidth signals provide an opportunity to increase the performance of some GNSS reflectometry applications (i.e. altimetry). The Microwave Interferometric Reflectometer (MIR) is an instrument developed at UPC to compare different GNSS-R techniques, notably the conventional and interferometric ones, and assess the capabilities of these new signals and bands of the GPS and Galileo systems (L1/E1 and L5/E5). This paper describes the MIR beamforming system., Peer Reviewed, Postprint (published version)

This work is part of “Operational Network of Individual Observation Nodes” (ONION). ONION is an H2020 project devoted to identify solutions and to satisfy emerging needs of the European Earth Observation (EO) market. In this regard, this work presents a review and analysis of the potential payloads and next generation of sensors in order to cover the measurements gaps of the top ten use cases of the European EO infrastructure. For each use case the potential instruments to support stakeholder requirements are identified, pointing out the aspects in which they represent an innovation with respect to existing technological solutions. This identification of instruments is based on existing, operational, under development, and demonstration missions. The capability of the instrument technologies is evaluated according to the trends in the design for small EO satellites (payload mass <; 500 kg). This work concludes with a set the potential instruments to be possibly developed as part of the future European space infrastructure, proposing an integrated set of instruments and measurements to optimize the performances, simplifying the implementation, and reducing the costs., Peer Reviewed, Postprint (published version)

Global change is increasing the risk of forest decline worldwide, impacting carbon and water cycles. Hence, there is an urgent need for predicting forest decline occurrence. To that purpose, this study links forest decline events in Catalonia, detected by the DEBOSCAT forest monitoring program, with information from the Soil Moisture and Ocean Salinity (SMOS) satellite. Firstly, this study reviews the role of the SMOS soil moisture in a previous forest decline episode occurred in 2012, where the authors concluded that dry soils increased the probability of observing decline in broadleaved forests. Secondly, the present study detects that forest decline in 2012 and 2016 was linked to very dry soil conditions (generally with SM<;0.06 m 3 ·m -3 ). A similar analysis is proposed using SMOS Vegetation Optical Depth (VOD) data, which is a proxy of vegetation hydric status. Results and preliminary models will be presented at IGARSS 2018., Peer Reviewed, Postprint (published version)

The characterization of the ionosphere and its impact on the propagation of radio-wave signals has received an increasing interest for satellite communications, Global Navigation Satellite Systems (GNSS) applications (i.e. navigation and timing), and Earth Observation (EO) missions, especially low frequency SAR missions and GNSS-Reflectometry (GNSS-R). Although the main climatological models for the mean stable part of the electron density in the ionospheric layers (e.g. IRI or NeQuick) or for the magnetic field (e.g. WMM) have been significantly improved in the past years, the inhomogeneous part, responsible for scintillation effects, can still be significantly improved, since models are based on relatively old data (e.g. WBMOD), or the climatological inputs are limited to properly characterize all latitudes and solar conditions (e.g. GISM or WAM). ESA's CLIM IONO study aims to use the experimental observations of the ionosphere collected in the past years to assess the performance of climatological ionosphere models, with the focus on scintillation models, in order to evaluate their ability to properly support future needs, to identify weak areas if any, to propose recommendations for improvements and to implement these improvements whenever possible in existing models. This work focuses on the capabilities of GNSS-R techniques to characterize ionospheric scintillation, notably at low and high latitudes., Peer Reviewed, Postprint (published version)

After more than 8 years in orbit the Soil Moisture and Ocean Salinity (SMOS) satellite is still in good health and several algorithms for improving its spatial resolution have been proposed and validated in a variety of catchments. However, none of them has yet been applied at the global scale. In this article we present: i) a review of the latest SMOS-BEC downscaling algorithm, which allows for its global application using an adaptive moving window and ii) a thorough validation of the resulting maps over two in-situ networks: REMEDHUS in Spain and OzNet in Australia. The proposed algorithm combines SMOS brightness temperatures (at ~40 km spatial resolution), and MODIS-derived Land Surface Temperature and Normalized Differenced Vegetation Index (at 1 km), into 1km soil moisture maps. This paper also presents a variant of the algorithm, which allows for cloud-free retrievals. A statistical comparison has been carried out when the MODIS Land Surface Temperature is replaced in the algorithm by the one provided by the ERA5 reanalysis. Fine-scale estimates show good agreement in terms of correlation and root-mean-squared error with in-situ soil moisture., Peer Reviewed, Postprint (published version)

This work describes a software tool developed for ESA within the project BIBLOS-2 (BuIlding BLOcks for earth observation mission performance simulator) to model typical conical scanning microwave radiometers in a generic Earth Observation mission. It consists of functional modules: Geometry, Scene Generator, Instrument, and Level 1 data generation modules. This structure follows the architecture for generic Earth Observation mission simulator study, ARCHEO-E2E (ARCHitecture of Earth Observation). The improvement in the BIBLOS-2 Passive Microwave is developing the Radio Frequency Interferences (RFI) generation and mitigation functionality. The developed simulation modules will be provided soon via the BIBLOS web page (https://gmv-biblos.gmv.com/). In this paper, the functions of the BIBLOS-2 passive microwave are described module by module, including the RFI generation/mitigation examples., This work describes a software tool developed for ESA within the project BIBLOS-2 (BuIlding BLOcks for earth observation mission performance simulator) to model typical conical scanning microwave radiometers in a generic Earth Observation mission. It consists of functional modules: Geometry, Scene Generator, Instrument, and Level 1 data generation modules. This structure follows the architecture for generic Earth Observation mission simulator study, ARCHEO-E2E (ARCHitecture of Earth Observation). The improvement in the BIBLOS-2 Passive Microwave is developing the Radio Frequency Interferences (RFI) generation and mitigation functionality. The developed simulation modules will be provided soon via the BIBLOS web page (https://gmv-biblos.gmv.com/). In this paper, the functions of the BIBLOS-2 passive microwave are described module by module, including the RFI generation/mitigation examples. © 2018 IEEE., Peer Reviewed, Postprint (published version)

Vegetation Optical Depth (VOD) at L-band is highly sensitive to the water content and above-ground biomass of vegetation. Hence, it has great potential for monitoring crop phenology and for providing crop yield forecasts. Recently, the Multi-Temporal Dual Channel Algorithm (MT -DCA) has been proposed to retrieve L-band VOD from Soil Moisture Active Passive (SMAP) measurements. In previous research, SMAP VOD has been compared to crop phenology and has been used to derive crop yield estimates. Here, we review and expand these initial research studies. In particular, we quantify the capability of VOD to detect different crop stages, and test different VOD metrics (i.e., maximum, range and integrals of VOD) to provide crop yield estimates in the United States Corn Belt. Results show that VOD captures 50% to 70% of crop changes during growing and maturing phases, and that it explains between 44% (in heterogeneous crop regions) and 74% (in homogenous croplands) of final crop yields., Peer Reviewed, Postprint (published version)

The potential of Global Navigation Satellite Systems-Reflectometry (GNSS-R) techniques to estimate land surface parameters such as soil moisture (SM) is experimentally studied using 2014-2017 global data from the UK TechDemoSat-1 (TDS-1) mission. The approach is based on the analysis of the sensitivity to SM of different observables extracted from the Delay Doppler Maps (DDM) computed by the Space GNSS Receiver-Remote Sensing Instrument (SGR-ReSI) instrument using the L1 (1575.42 MHz) left-hand circularly-polarized (LHCP) reflected signals emitted by the Global Positioning System (GPS) navigation satellites. The sensitivity of different GNSS-R observables to SM and its dependence on the incidence angle is analyzed. It is found that the sensitivity of the calibrated GNSS-R reflectivity to surface soil moisture is ~ 0.09 dB/% up to 30° incidence angle, and it decreases with increasing incidence angles, although differences are found depending on the spatial scale used for the ground-truth, and the region. The sensitivity to subsurface soil moisture has been also analyzed using a network of subsurface probes and hydrological models, apparently showing some dependence, but so far results are not conclusive. © 2018 by the authors., Peer Reviewed, Postprint (published version)

This work was developed as part of the European H2020 ONION (Operational Network of Individual Observation Nodes) project, aiming at identifying the technological opportunity areas to complement the Copernicus space infrastructure in the horizon 2020–2030 for polar region monitoring. The European Earth Observation (EO) infrastructure is assessed through of comprehensive end-user need and data gap analysis. This review was based on the top 10 use cases, identifying 20 measurements with gaps and 13 potential EO technologies to cover the identified gaps. It was found that the top priority is the observation of polar regions to support sustainable and safe commercial activities and the preservation of the environment. Additionally, an analysis of the technological limitations based on measurement requirements was performed. Finally, this analysis was used for the basis of the architecture design of a potential polar mission., Peer Reviewed, Postprint (published version)

Radio-Frequency Interference (RFI) and jamming are increasing problems for timing applications based on Global Navigation Satellite Systems (GNSS). FENIX-lite is a real-time pre-correlation anti-jamming system designed to provide increased resilience against RFI/jamming in critical GNSS-enabled applications. This work aims to evaluate the combined performance of FENIX-lite and a timing setup composed by two GNSS disciplined oscillators named DOWR. The results show that FENIX provides an anti-jamming resilience of 10-30 dB, at the expense of introducing a small bias and an additional jitter of 2-4 ns., Peer Reviewed, Postprint (published version)

Lambert's problem is the two-point boundary-value problem resulting from a two-body orbital transfer between two position vectors in a given time. It lies at the very heart of several fundamental astrodynamics and space engineering problems and, as such, it has attracted the interest of scientists over centuries. In this work, we revisit the solution of Lambert's problem based on Levi-Civita regularization developed by Carles Simó in 1973. We offer an exhaustive derivation of the theory, including proofs of all the results and the formulae employed, and we extend the algorithm to deal with multi-revolution transfers. Then, after investigating a range of initial guess search techniques and testing different numerical methods to approximate the solution, we propose a procedure in which the initial guess is assigned very efficiently by querying a pre-defined interpolating table. Then, in order to achieve both speed and robustness, we combine Newton-Raphson with safety checks to avoid out of boundary deviations to approximate the solution. We validate the method through several tests and applications, and we assess its convergence and performance. The algorithm presents no singularities, converges in all realistic scenarios and its computational cost is comparable with state of the art algorithms., Peer Reviewed, Postprint (author's final draft)

Peer Reviewed, Postprint (published version)

End-to-end mission performance simulators for Earth Observation missions are one of the prominent tools for system design and scientific validation in early mission phases. The European Space Agency (ESA)has promoted efforts to exploit synergies between activities and reduce engineering costs. Some of these activities are the ARCHEO study, the BIBLOS project, the OpenSF frameworkandthe EO CFI library, the. The main goal of BIBLOS is to provide a library of software units called “Building Blocks”, or simply “Blocks”,that can be used to build an end-to-end simulator. Many Blocks are common across simulators, for example the geometry-related ones. Some Blocks are common for a certain type of instrument, like the Radiative Transfer Model, or parts of theInstrument model. BIBLOS targets the Blocks mostfrequently used by the engineering and scientific community. The user can access the library through the BIBLOS website, download the Blocks and use them directly, in combination with their own developments, or modify them. All of the Blocks are provided with the source code, and are under ESA Software Community License. The first stage of this activity focused on Passive Optical instruments, mainly imagers, which are one of the most frequent types of instrument on Earth Observation satellites. The models already developedinclude the geometry, scene generation and instrument modelling of an optical imager. These Blocks can be combined into a full chain that produces raw data. ESA is currently developing the Level-1 processing, which may be includedinto BIBLOS in the future. Themodels, documentation and demos can be downloaded from the BIBLOS website: https://gmv-biblos.gmv.com/.A second stage of the activity is currently ongoing with the purpose of expanding this library to include Passive Microwave instruments and Active Microwave instruments. Severalsimulators for Passive and Active Microwave payloads are currently being developed for ESA missions and it is foreseen that, Peer Reviewed, Postprint (published version)

The impact of Radio Frequency Interference (RFI) is a very serious problem for spaceborne microwave radiometry. Many Soil Moisture Ocean Salinity (SMOS) images show serious contamination by the RFI. SMOS is even more impacted by the RFI than real aperture case because the grating lobes are usually higher in Synthetic Aperture Interferometric Radiometer (SAIR) compared to real aperture one. RFI effects should properly be mitigated or filtered out to retrieve the geophysical parameters from SMOS measurements. This work presents a feasibility study of RFI mitigation/filtering for SAIRs. Instead of dealing with brightness temperature image directly, RFI filtering of the subspace of covariance matrix is introduced., Peer Reviewed, Postprint (published version)

Ships and ice monitoring is of key importance in numerous applications, such as maritime traffic control, prevention of illegal activities, climate change studies, and maritime security. In this work, the feasibility of near real-time ocean target detection from a constellation of spaceborne Global Navigation Satellite System-Reflectometry (GNSS-R) images is demonstrated by addressing the two following points: 1) simulation of the revisit time allowed by constellations of GNSS-R instruments; 2) derivation and implementation of an ocean target detector aimed at identifying inhomogeneous features inside the delay-Doppler map. The revisit time is computed by simulating a realistic mission as a function of the constellation size and the number of receiving channels of the GNSS-R instrument. The proposed ocean target detection algorithm consists of four steps - pre-processing, pre-screening, selection, and geolocation - and is validated using actual U. K. TechDemoSat-1 data., Peer Reviewed, Postprint (published version)

© 2017 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works., This study addresses a novel application of global navigation satellite system-reflectometry (GNSS-R) delay-Doppler maps (DDMs), namely sea target detection. In contrast with other competing remote sensing technologies, such as synthetic aperture radar and optical systems, typically exploited in the field of sea target detection, GNSS-R systems could be employed as satellite constellations, so as to fulfill the temporal requirements for near real-time ships and sea ice sheets monitoring. In this study, the revisit time offered by GNSS-R systems is quantitatively evaluated by means of a simulation analysis, in which three different realistic GNSS-R missions are simulated and analyzed. Then, a sea target detection algorithm from spaceborne GNSS-R DDMs is described and assessed. The algorithm is based on a sea clutter compensation step and uses an adaptive threshold to take into account spatial variations in the sea background and/or noise statistics. Finally, the sea target detector algorithm is tested and validated for the first time ever using experimental GNSS-R data from the U.K. TechDemoSat-1 dataset. Performance is assessed by providing the receiver operating characteristic curves, and some preliminary experimental results are presented., Peer Reviewed, Postprint (published version)

This work addresses the accuracy of the Global Navigation Satellite Systems (GNSS)-Reflectometry (GNSS-R) scatterometric measurements considering the presence of both coherent and incoherent scattered components, for both conventional GNSS-R (cGNSS-R) and interferometric GNSS-R (iGNSS-R) techniques. The coherent component is present for some type of surfaces, and it has been neglected until now because it vanishes for the sea surface scattering case. Taking into account the presence of both scattering components, the estimated Signal-to-Noise Ratio (SNR) for both techniques is computed based on the detectability criterion, as it is done in conventional GNSS applications. The non-coherent averaging operation is considered from a general point of view, taking into account that thermal noise contributions can be reduced by an extra factor of 0.88 dB when using partially overlapped or partially correlated samples. After the SNRs are derived, the received waveform’s peak variability is computed, which determines the system’s capability to measure geophysical parameters. This theoretical derivations are applied to the United Kingdom (UK) TechDemoSat-1 (UK TDS-1) and to the future GNSS REflectometry, Radio Occultation and Scatterometry on board the International Space Station (ISS) (GEROS-ISS) scenarios, in order to estimate the expected scatterometric performance of both missions., Peer Reviewed, Postprint (published version)

In this paper, is presented a method for estimation of the effect of the transport process to aerosol optical properties. Aerosol optical data retrieved by lidars and sun-photometer measurements, are applied to Saharan dust events observed simultaneously at the two EARLINET/AERONET sites of Barcelona and Granada during the periods of June–September of 2012 and 2013. For this purpose, elastic lidar profiles and sun-photometer columnar retrievals are analyzed together with satellite observations and dust forecast models. Granada presents more than twice Saharan dust outbreaks compared to Barcelona. The scenarios favoring the Saharan dust outbreaks are identified in both places. The mineral dust originating in the Sahara region and arriving at both stations is usually transport wither over the Atlas Mountains or through an Atlantic pathway. Analyses of dust events affecting both stations reveal how differences in the transport process lead to differences in the aerosol optical properties measured at each station. Mean dust related Ångström exponent is 1.8 times higher in Barcelona than in Granada. This difference is a result of the additional contribution of anthropogenic aerosol, mainly in the aerosol fine mode, during the transport of the mineral dust plume over the Iberian Peninsula., Peer Reviewed, Postprint (author's final draft)

This paper investigates a novel application of Global Navigation Satellite System-Reflectometry (GNSS-R) in the fields of maritime surveillance and safety, and climate change analysis, namely sea target detection in near real-time. Potentialities of the recent GNSS-R technology in the detection of targets over the sea (large ships, sea ice sheets) in near real-time are explored by: 1) computing the revisit time achieved with constellations of GNSS-R satellites; 2) deriving, implementing and testing a sea target detection algorithm. The global average revisit time is evaluated by mission simulation in two realistic scenarios and is shown as a function of the number of parallel receiver channels and the number of GNSS-R satellites in orbit. The sea target detection algorithm consists of four steps - pre-processing, pre-screening, selection, and geolocation - and is tested using actual UK TechDemoSat-1 data., Peer Reviewed, Postprint (published version)

This work reviews and analyses potentially relevant technologies to ensure that the gaps and stakeholder needs for sea ice products are covered. Each variable related to sea ice that presenting gaps using the European EO infrastructure on the horizon (2020-2030) is revised according the stakeholder requirements, together with the feasibility of deploying available technologies on small satellites. A survey of instruments oriented towards sea ice observations in the past and current is presented. Based on this survey technological capabilities in terms of the spatial resolution, swath, mass, power, and data rate are obtained. In order to identify the technologies, numerical scores are assigned based on instrument capabilities. This works concludes with a set of the technologies compatible with small platforms, with the objective to complement the sea ice data products of Copernicus Services., Peer Reviewed, Postprint (published version)

The ESA's Soil Moisture and Ocean Salinity (SMOS, 2009-2017) is the first mission using L-band radiometry to monitor the Earth's global surface soil moisture (SM). After more than 7 years in orbit, many studies have contributed to improving the quality and applicability of SMOS-derived SM maps. In this research, a novel downscaling algorithm is proposed for retrieving high resolution (1 km) SM. This model is an extension of the “universal triangle” technique, and also introduces the concept of adaptive moving window. Its inputs are the low resolution SMOS BEC L3 SM and the brightness temperatures at vertical and horizontal polarizations (SMOS L1C), and the high resolution NDVI and LST from optically-based sensors. The proposed method allows obtaining high resolution SM maps worldwide, with no limitation in extension., Peer Reviewed, Postprint (published version)