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Papers by Nazzareno Pierdicca

Spaceborne X-band synthetic aperture radars (SARs) represent a well-established tool for Earth re... more Spaceborne X-band synthetic aperture radars (SARs) represent a well-established tool for Earth remote sensing at very high spatial resolution (order of meters). Until now, SAR has not been exploited for hydrological cycle modelling and numerical weather forecast, however, there are scientific evidences that at X band and beyond: i) atmospheric precipitation in liquid and ice phase affect SAR imagery and its intensity can be retrieved, ii) snow areal extent and mass (water-equivalent) can be detected and estimated. KydroSAT mission concept foresees a miniaturised fully-digital SAR at Ku and Ka band (KydroSAR), specifically devoted to detecting and estimating atmospheric precipitation and surface snow; its baseline includes dual-polarization capability, high orbit duty cycle (>75%), flexible ground resolution (5-150 m), and a large variable swath (50-150 km), doubled with formation of two minisatellites both carrying a KydroSAR. Moreover, the mission concept foresees the along-track convoy with the COSMO-SkyMed and SAOCOM SAR platforms, allowing the observation of the same scene at L, X, Ku and Ka bands. The challenging requirements of this architecture require the development of new technologies such as Digital Beam Forming and Direct Digital to RF Conversion. In order to exploit the synergic approach of the KydroSAT convoy for precipitation, in this work we will simulate and discuss the SAR response at X, Ku and Ka bands of the same scene, using the SAR forward model described in Mori et al. (2017). Subsequently, an example retrieval of Snow Equivalent Water (SWE) by Ku-SAR will be given.

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018

Work funded by European Space Agency (ESA) under Contract No. 4000121670/17/NL/AF

Unlike space-based near-nadir viewing radars, X-SARs will mainly measure the slant-path integrate... more Unlike space-based near-nadir viewing radars, X-SARs will mainly measure the slant-path integrated scattering and attenuation of precipitation in orthogonal oblique directions.. A microwave model for simulating the normalized Radar Cross Section (NRCS) SAR response was set up in this work and exploited to train the proposed X-SAR retrieval algorithms. The rain-cloud 2-D shape was modeled as product of a horizontal and a vertical distribution function. An inversion approach, based on the Volterra Integral Equatio (VIE), was applied to a X-SAR/SIR-C case study. The VIE approach is a mathematically elegant way to treat the SAR inverse problem, but it needs to be generalized to vertically- inhomogeneous media to be useful in atmospheric applications

A comparison of three different electromagnetic scattering models for land surface delay-Doppler ... more A comparison of three different electromagnetic scattering models for land surface delay-Doppler maps (DDMs) obtained from global navigation satellite system reflectometry (GNSS-R) along a Cyclone Global Navigation Satellite System (CYGNSS) track in the San Luis Valley, Colorado, USA, is presented. The three models are the analytical Kirchhoff solutions (AKS), the Soil And VEgetation Reflection Simulator (SAVERS), and the improved geometrical optics with topography (IGOT). Common inputs to the three models were defined by using field samples of soil moisture and texture, soil surface roughness measurements, and a digital elevation model (DEM). The resulting peak reflectivity profiles of the models and the CYGNSS data all had a dynamic range of 10 dB along the selected track, mainly due to the influence of topography. The reflectivities obtained from all three models agreed with one another to within 2.4 dB along the full length of the track. The models also showed general agreement ...

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2021

HydroGNSS (Hydrology using Global Navigation Satellite System reflections) has been selected as t... more HydroGNSS (Hydrology using Global Navigation Satellite System reflections) has been selected as the second European Space Agency (ESA) Scout earth observation mission to demonstrate the capability of small satellites to deliver science. This article summarizes the case for HydroGNSS as developed during its system consolidation study. HydroGNSS is a high-value dual small satellite mission, which will prove new concepts and offer timely climate observations that supplement and complement the existing observations and are high in ESAs earth observation scientific priorities. The mission delivers the observations of four hydrological essential climate variables as defined by the global climate observing system using the new technique of GNSS reflectometry. These will cover the world's land mass to 25 km resolution, with a 15-day revisit. The variables are soil moisture, inundation or wetlands, freeze/thaw state, and above-ground biomass.

Abstract: This paper presents a theoretical study of microwave remote sensing of vegetated surfac... more Abstract: This paper presents a theoretical study of microwave remote sensing of vegetated surfaces. The purpose of this study is to find out if satellite bistatic radar systems can provide a performance, in terms of sensitivity to vegetation geophysical parameters, equal to or greater than the performance of monostatic systems. Up to now, no suitable bistatic data collected over land surfaces are available from satellite, so that the electromagnetic model developed at Tor Vergata University has been used to perform simulations of the scattering coefficient of corn, over a wide range of observation angles at L- and C-band. According to the electromagnetic model, the most promising configuration is the one which measures the VV or HH bistatic scattering coefficient on the plane that lies at the azimuth angle orthogonal with respect to the incidence plane. At this scattering angle, the soil contribution is minimized, and the effects of vegetation growth are highlighted.

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2020

The article of the freeze/thaw dynamic of highlatitude Earth surfaces is extremely important and ... more The article of the freeze/thaw dynamic of highlatitude Earth surfaces is extremely important and informative for monitoring the carbon cycle, the climate change, and the security of infrastructures. Current methodologies mainly rely on the use of active and passive microwave sensors, while very few efforts have been devoted to the assessment of the potential of observations based on signals of opportunity. This article aims at assessing the performance of spaceborne Global Navigation Satellite System Reflectometry (GNSS-R) for high-spatial and high-temporal resolution monitoring of the Earth-surface freeze/thaw state. To this aim, reflectivity values derived from the TechDemoSat-1 (TDS-1) data have been collected and elaborated, and thus compared against the soil moisture active passive (SMAP) freeze/thaw information. Shallow subsurface soil temperature values recorded by a network of in situ stations have been considered as well. Even if an extensive and timeliness cross availability of both types of experimental data is limited by the spatial coverage and density of TDS-1 observations, the proposed analysis clearly indicates a significant seasonal cycle in the calibrated reflectivity. This opens new perspectives for the bistatic L-band high-resolution satellite monitoring of the freeze/thaw state, as well as to support the development of next-generation of GNSS-R satellite missions designed to provide enhanced performance and improved temporal and spatial coverage over high latitude areas. Index Terms-Bistatic radars, Freeze thaw (FT), global positioning system (GPS), GNSS reflectometry (GNSS-R), soil moisture active passive (SMAP), TechDemoSat-1 (TDS-1) mission. I. INTRODUCTION AND BACKGROUND T HE freeze/thaw (FT) state of the ground describes the seasonal landscape transition between predominantly frozen and thawed conditions [1]-[5]. It affects several environmental Manuscript

IEEE Geoscience and Remote Sensing Letters, 2021

Previous studies have shown that the decrease of temporal interferometric synthetic aperture rada... more Previous studies have shown that the decrease of temporal interferometric synthetic aperture radar (InSAR) coherence could be exploited to detect the appearance of floodwater in urban areas. However, as of today, approaches based on this principle only make use of single co-polarization images for identifying the presence of floodwater in the double-bounce feature. In this study, we take advantage of both co-and cross-polarization images to detect significant decreases of the multitemporal InSAR coherence in order to enhance the mapping of floodwater in urban areas. We consider that not only doublebounce scattering, but also multiple-bounce may occur in urban areas depending on how the building facades are oriented with respect to the synthetic aperture radar (SAR) sensor's line of sight. The Sentinel-1 (S-1) mission is particularly well suited for applying and testing this kind of approach due to the systematic availability of dual-polarization data. Using as a test case, the widespread flooding in the city of Houston, USA, caused by Hurricane Harvey in 2017, we demonstrate that the proposed methodology leads to an increase of the accuracy of the urban flood maps from 75.2% when only using the VV polarization, to 82.9% when using the dual polarization information.

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2020

In this study, the capability of Global Navigation Satellite System Reflectometry in evaluating f... more In this study, the capability of Global Navigation Satellite System Reflectometry in evaluating forest biomass from space has been investigated by using data coming from the TechDemoSat-1 (TDS-1) mission of Surrey Satellite Technology Ltd. and from the Cyclone Satellite System (CyGNSS) mission of NASA. The analysis has been first conducted using TDS-1 data on a local scale, by selecting five test areas located in different parts of the Earth's surface. The areas were chosen as examples of various forest coverages, including equatorial and boreal forests. Then, the analysis has been extended by using CyGNSS to a global scale, including any type of forest coverage. The peak of the Delay Doppler Map calibrated to retrieve an "equivalent" reflectivity has been exploited for this investigation and its sensitivity to forest parameters has been evaluated by a direct comparison with vegetation optical depth (VOD) derived from the Soil Moisture Active Passive L-band radiometer, with a pantropical aboveground biomass (AGB) map and then with a tree height (H) global map derived from the Geoscience Laser Altimeter System installed on-board the ICEsat satellite. The sensitivity analysis confirmed the decreasing trend of the observed equivalent reflectivity for increasing biomass, with correlation coefficients 0.31 ≤ R ≤ 0.54 depending on the target parameter (VOD, AGB, or H) and on the considered dataset (local or global). These correlations were not sufficient to retrieve the target parameters by simple inversion of the direct relationships. The retrieval has been therefore based on Artificial Neural Networks making it possible to add other inputs (e.g., the incidence angle, the signal to noise ratio, and the lat/lon information in case of global maps) to the algorithm. Although not directly correlated to the biomass, these inputs helped in improving the retrieval accuracy. The algorithm was tested on both the selected areas and globally,

Remote Sensing, 2018

The next generation of synthetic aperture radar (SAR) systems could foresee satellite missions ba... more The next generation of synthetic aperture radar (SAR) systems could foresee satellite missions based on a geosynchronous orbit (GEO SAR). These systems are able to provide radar images with an unprecedented combination of spatial (≤1 km) and temporal (≤12 h) resolutions. This paper investigates the GEO SAR potentialities for soil moisture (SM) mapping finalized to hydrological applications, and defines the best compromise, in terms of image spatio-temporal resolution, for SM monitoring. A synthetic soil moisture–data assimilation (SM-DA) experiment was thus set up to evaluate the impact of the hydrological assimilation of different GEO SAR-like SM products, characterized by diverse spatio-temporal resolutions. The experiment was also designed to understand if GEO SAR-like SM maps could provide an added value with respect to SM products retrieved from SAR images acquired from satellites flying on a quasi-polar orbit, like Sentinel-1 (POLAR SAR). Findings showed that GEO SAR systems p...

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2016

GEROS-ISS stands for GNSS REflectometry, radio occultation, and scatterometry onboard the Interna... more GEROS-ISS stands for GNSS REflectometry, radio occultation, and scatterometry onboard the International Space Station (ISS). It is a scientific experiment, successfully proposed to the European Space Agency in 2011. The experiment as the name indicates will be conducted on the ISS. The main focus of GEROS-ISS is the dedicated use of signals from the currently available Global Navigation Satellite Systems (GNSS) in L-band for remote sensing of the Earth with a focus to study climate change. Prime mission objectives are the determination of the altimetric sea surface height of the oceans and of the ocean surface mean square slope, which is related to sea roughness and wind speed. These geophysical parameters are derived using reflected GNSS signals (GNSS reflectometry, GNSS-R). Secondary mission goals include atmosphere/ionosphere sounding using refracted GNSS signals (radio occultation, GNSS-RO) and remote sensing of land surfaces using GNSS-R. The GEROS-ISS mission objectives and its design, the current status, and ongoing activities are reviewed and selected scientific and technical results of the GEROS-ISS preparation phase are described.

Remote Sensing of Environment, 2015

A comparison of soil moisture products derived from satellite data, in-situ measurements and land... more A comparison of soil moisture products derived from satellite data, in-situ measurements and land models was performed in the frame of the EUMETSAT H-SAF project. In particular, soil moisture retrievals of ASCAT/H-SAF and SMOS were compared with two other independent datasets, that are the NCEP/NCAR volumetric soil moisture content reanalysis developed by NOAA, and the ERA-Interim/Land soil moisture produced by ECMWF. In situ data available through the International Soil Moisture Network and distributed in regions comprising Denmark,

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015

In this study, a technique developed to retrieve integrated water vapor from interferometric synt... more In this study, a technique developed to retrieve integrated water vapor from interferometric synthetic aperture radar (InSAR) data is described, and a three-dimensional variational assimilation experiment of the retrieved precipitable water vapor into the mesoscale weather prediction model MM5 is carried out. The InSAR measurements were available in the framework of the European Space Agency (ESA) project for the "Mitigation of electromagnetic transmission errors induced by atmospheric water vapor effects" (METAWAVE), whose goal was to analyze and possibly predict the phase delay induced by atmospheric water vapor on the spaceborne radar signal. The impact of the assimilation on the model forecast is investigated in terms of temperature, water vapor, wind, and precipitation forecast. Changes in the modeled dynamics and an impact on the precipitation forecast are found. A positive effect on the forecast of the precipitation is found for structures at the model grid scale or larger (1 km), whereas a negative effect is found on convective cells at the subgrid scale that develops within 1 h time intervals. The computation of statistical indices shows that the InSAR assimilation improves the forecast of weak to moderate precipitation (<15 mm/3 h).

Remote Sensing, 2013

This paper presents a theoretical study of microwave remote sensing of vegetated surfaces. The pu... more This paper presents a theoretical study of microwave remote sensing of vegetated surfaces. The purpose of this study is to find out if satellite bistatic radar systems can provide a performance, in terms of sensitivity to vegetation geophysical parameters, equal to or greater than the performance of monostatic systems. Up to now, no suitable bistatic data collected over land surfaces are available from satellite, so that the electromagnetic model developed at Tor Vergata University has been used to perform simulations of the scattering coefficient of corn, over a wide range of observation angles at Land C-band. According to the electromagnetic model, the most promising configuration is the one which measures the VV or HH bistatic scattering coefficient on the plane that lies at the azimuth angle orthogonal with respect to the incidence plane. At this scattering angle, the soil contribution is minimized, and the effects of vegetation growth are highlighted.

Italian Journal of Remote Sensing, 2009

Space-borne X-band synthetic aperture radars (SARs) provide a unique opportunity to measure rainf... more Space-borne X-band synthetic aperture radars (SARs) provide a unique opportunity to measure rainfall over land with unsurpassed spatial resolution of about few hundred meters. This work explores the potential of space-borne X-SARs to estimate rainfall over land from both a model and retrieval point of view. The main objective is to provide a framework for a physically-based inversion of SARs measurements at X (9.6 GHz), Ku (14 GHz) and Ka (30 GHz) band over land. A forward model of SAR response will be illustrated for X, Ku and Ka bands. We will present an inversion methodology, a quantitative application to X-SAR data of the SIR-C mission in 1994, and a qualitative application to TerraSAR-X data over France, 2008.

Italian Journal of Remote Sensing, 2009

The objective of this study is to evaluate the possibility to identify floods when soil is covere... more The objective of this study is to evaluate the possibility to identify floods when soil is covered by vegetation, recognizing differences in backscattering between SAR measurements acquired before and after the event. To this end, the electromagnetic model developed at Tor Vergata University is run for an early stage and a fully grown wheat field, at L, C and X band. Theoretical results show that flooding can be detected at all frequencies in presence of short vegetation, while L band is the most suitable one for developed crops. Results obtained in the case of early stage are in reasonable agreement with ERS data collected over grass fields before and after the strong flooding occurred in Alessandria (North Italy) in 1994.

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2014

Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique usefu... more Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique useful in many land applications, such as tectonic movements, landslide monitoring and digital elevation model extraction. One of its major limitation is the atmospheric effect, and in particular the high water vapour spatial and temporal variability which introduces an unknown delay in the signal propagation. This paper describes the general approach and some results achieved in the framework of an ESA funded project devoted to the mapping of the water vapour with the aim to mitigate its effect in InSAR applications. Ground based (microwave radiometers, radiosoundings, GPS) and spaceborne observations (AMSR-E, MERIS, MODIS) of columnar water vapour were compared with Numerical Weather Prediction model runs in Central Italy during a 15-day experiment. A dense network of GPS receivers was deployed close to Como, in Northern Italy, to complement the operational network in order to derive Zenith Total Delay as well as Slant Delay which can support InSAR processing. A comparison with Atmospheric Phase Screens (APS) derived from a sequence of Envisat multi pass interferometric acquisitions processed using the Permanent Scatters technique on the two test sites has been also performed. The acquired experimental data and their comparison give a valuable idea of what can be done to gather information on water vapour, which, besides InSAR applications, plays a fundamental role in weather prediction and radio propagation studies. The work has been carried out in the framework of an ESA funded project, named "Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects" (METAWAVE). This paper presents the general approach an the various methodologies exploited in the project, together with the overall intercomparison of the results. In deep details on the comparison with the InSAR APS maps derived by the PS technique, as well as on GPS receiver processing and water vapour tomography are reported in two companion papers.

International Geoscience and Remote Sensing Symposium (IGARSS), 2009

2010 IEEE International Geoscience and Remote Sensing Symposium, 2010

Spaceborne X-band synthetic aperture radars (SARs) represent a well-established tool for Earth re... more Spaceborne X-band synthetic aperture radars (SARs) represent a well-established tool for Earth remote sensing at very high spatial resolution (order of meters). Until now, SAR has not been exploited for hydrological cycle modelling and numerical weather forecast, however, there are scientific evidences that at X band and beyond: i) atmospheric precipitation in liquid and ice phase affect SAR imagery and its intensity can be retrieved, ii) snow areal extent and mass (water-equivalent) can be detected and estimated. KydroSAT mission concept foresees a miniaturised fully-digital SAR at Ku and Ka band (KydroSAR), specifically devoted to detecting and estimating atmospheric precipitation and surface snow; its baseline includes dual-polarization capability, high orbit duty cycle (>75%), flexible ground resolution (5-150 m), and a large variable swath (50-150 km), doubled with formation of two minisatellites both carrying a KydroSAR. Moreover, the mission concept foresees the along-track convoy with the COSMO-SkyMed and SAOCOM SAR platforms, allowing the observation of the same scene at L, X, Ku and Ka bands. The challenging requirements of this architecture require the development of new technologies such as Digital Beam Forming and Direct Digital to RF Conversion. In order to exploit the synergic approach of the KydroSAT convoy for precipitation, in this work we will simulate and discuss the SAR response at X, Ku and Ka bands of the same scene, using the SAR forward model described in Mori et al. (2017). Subsequently, an example retrieval of Snow Equivalent Water (SWE) by Ku-SAR will be given.

IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium, 2018

Work funded by European Space Agency (ESA) under Contract No. 4000121670/17/NL/AF

Unlike space-based near-nadir viewing radars, X-SARs will mainly measure the slant-path integrate... more Unlike space-based near-nadir viewing radars, X-SARs will mainly measure the slant-path integrated scattering and attenuation of precipitation in orthogonal oblique directions.. A microwave model for simulating the normalized Radar Cross Section (NRCS) SAR response was set up in this work and exploited to train the proposed X-SAR retrieval algorithms. The rain-cloud 2-D shape was modeled as product of a horizontal and a vertical distribution function. An inversion approach, based on the Volterra Integral Equatio (VIE), was applied to a X-SAR/SIR-C case study. The VIE approach is a mathematically elegant way to treat the SAR inverse problem, but it needs to be generalized to vertically- inhomogeneous media to be useful in atmospheric applications

A comparison of three different electromagnetic scattering models for land surface delay-Doppler ... more A comparison of three different electromagnetic scattering models for land surface delay-Doppler maps (DDMs) obtained from global navigation satellite system reflectometry (GNSS-R) along a Cyclone Global Navigation Satellite System (CYGNSS) track in the San Luis Valley, Colorado, USA, is presented. The three models are the analytical Kirchhoff solutions (AKS), the Soil And VEgetation Reflection Simulator (SAVERS), and the improved geometrical optics with topography (IGOT). Common inputs to the three models were defined by using field samples of soil moisture and texture, soil surface roughness measurements, and a digital elevation model (DEM). The resulting peak reflectivity profiles of the models and the CYGNSS data all had a dynamic range of 10 dB along the selected track, mainly due to the influence of topography. The reflectivities obtained from all three models agreed with one another to within 2.4 dB along the full length of the track. The models also showed general agreement ...

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2021

HydroGNSS (Hydrology using Global Navigation Satellite System reflections) has been selected as t... more HydroGNSS (Hydrology using Global Navigation Satellite System reflections) has been selected as the second European Space Agency (ESA) Scout earth observation mission to demonstrate the capability of small satellites to deliver science. This article summarizes the case for HydroGNSS as developed during its system consolidation study. HydroGNSS is a high-value dual small satellite mission, which will prove new concepts and offer timely climate observations that supplement and complement the existing observations and are high in ESAs earth observation scientific priorities. The mission delivers the observations of four hydrological essential climate variables as defined by the global climate observing system using the new technique of GNSS reflectometry. These will cover the world's land mass to 25 km resolution, with a 15-day revisit. The variables are soil moisture, inundation or wetlands, freeze/thaw state, and above-ground biomass.

Abstract: This paper presents a theoretical study of microwave remote sensing of vegetated surfac... more Abstract: This paper presents a theoretical study of microwave remote sensing of vegetated surfaces. The purpose of this study is to find out if satellite bistatic radar systems can provide a performance, in terms of sensitivity to vegetation geophysical parameters, equal to or greater than the performance of monostatic systems. Up to now, no suitable bistatic data collected over land surfaces are available from satellite, so that the electromagnetic model developed at Tor Vergata University has been used to perform simulations of the scattering coefficient of corn, over a wide range of observation angles at L- and C-band. According to the electromagnetic model, the most promising configuration is the one which measures the VV or HH bistatic scattering coefficient on the plane that lies at the azimuth angle orthogonal with respect to the incidence plane. At this scattering angle, the soil contribution is minimized, and the effects of vegetation growth are highlighted.

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2020

The article of the freeze/thaw dynamic of highlatitude Earth surfaces is extremely important and ... more The article of the freeze/thaw dynamic of highlatitude Earth surfaces is extremely important and informative for monitoring the carbon cycle, the climate change, and the security of infrastructures. Current methodologies mainly rely on the use of active and passive microwave sensors, while very few efforts have been devoted to the assessment of the potential of observations based on signals of opportunity. This article aims at assessing the performance of spaceborne Global Navigation Satellite System Reflectometry (GNSS-R) for high-spatial and high-temporal resolution monitoring of the Earth-surface freeze/thaw state. To this aim, reflectivity values derived from the TechDemoSat-1 (TDS-1) data have been collected and elaborated, and thus compared against the soil moisture active passive (SMAP) freeze/thaw information. Shallow subsurface soil temperature values recorded by a network of in situ stations have been considered as well. Even if an extensive and timeliness cross availability of both types of experimental data is limited by the spatial coverage and density of TDS-1 observations, the proposed analysis clearly indicates a significant seasonal cycle in the calibrated reflectivity. This opens new perspectives for the bistatic L-band high-resolution satellite monitoring of the freeze/thaw state, as well as to support the development of next-generation of GNSS-R satellite missions designed to provide enhanced performance and improved temporal and spatial coverage over high latitude areas. Index Terms-Bistatic radars, Freeze thaw (FT), global positioning system (GPS), GNSS reflectometry (GNSS-R), soil moisture active passive (SMAP), TechDemoSat-1 (TDS-1) mission. I. INTRODUCTION AND BACKGROUND T HE freeze/thaw (FT) state of the ground describes the seasonal landscape transition between predominantly frozen and thawed conditions [1]-[5]. It affects several environmental Manuscript

IEEE Geoscience and Remote Sensing Letters, 2021

Previous studies have shown that the decrease of temporal interferometric synthetic aperture rada... more Previous studies have shown that the decrease of temporal interferometric synthetic aperture radar (InSAR) coherence could be exploited to detect the appearance of floodwater in urban areas. However, as of today, approaches based on this principle only make use of single co-polarization images for identifying the presence of floodwater in the double-bounce feature. In this study, we take advantage of both co-and cross-polarization images to detect significant decreases of the multitemporal InSAR coherence in order to enhance the mapping of floodwater in urban areas. We consider that not only doublebounce scattering, but also multiple-bounce may occur in urban areas depending on how the building facades are oriented with respect to the synthetic aperture radar (SAR) sensor's line of sight. The Sentinel-1 (S-1) mission is particularly well suited for applying and testing this kind of approach due to the systematic availability of dual-polarization data. Using as a test case, the widespread flooding in the city of Houston, USA, caused by Hurricane Harvey in 2017, we demonstrate that the proposed methodology leads to an increase of the accuracy of the urban flood maps from 75.2% when only using the VV polarization, to 82.9% when using the dual polarization information.

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2020

In this study, the capability of Global Navigation Satellite System Reflectometry in evaluating f... more In this study, the capability of Global Navigation Satellite System Reflectometry in evaluating forest biomass from space has been investigated by using data coming from the TechDemoSat-1 (TDS-1) mission of Surrey Satellite Technology Ltd. and from the Cyclone Satellite System (CyGNSS) mission of NASA. The analysis has been first conducted using TDS-1 data on a local scale, by selecting five test areas located in different parts of the Earth's surface. The areas were chosen as examples of various forest coverages, including equatorial and boreal forests. Then, the analysis has been extended by using CyGNSS to a global scale, including any type of forest coverage. The peak of the Delay Doppler Map calibrated to retrieve an "equivalent" reflectivity has been exploited for this investigation and its sensitivity to forest parameters has been evaluated by a direct comparison with vegetation optical depth (VOD) derived from the Soil Moisture Active Passive L-band radiometer, with a pantropical aboveground biomass (AGB) map and then with a tree height (H) global map derived from the Geoscience Laser Altimeter System installed on-board the ICEsat satellite. The sensitivity analysis confirmed the decreasing trend of the observed equivalent reflectivity for increasing biomass, with correlation coefficients 0.31 ≤ R ≤ 0.54 depending on the target parameter (VOD, AGB, or H) and on the considered dataset (local or global). These correlations were not sufficient to retrieve the target parameters by simple inversion of the direct relationships. The retrieval has been therefore based on Artificial Neural Networks making it possible to add other inputs (e.g., the incidence angle, the signal to noise ratio, and the lat/lon information in case of global maps) to the algorithm. Although not directly correlated to the biomass, these inputs helped in improving the retrieval accuracy. The algorithm was tested on both the selected areas and globally,

Remote Sensing, 2018

The next generation of synthetic aperture radar (SAR) systems could foresee satellite missions ba... more The next generation of synthetic aperture radar (SAR) systems could foresee satellite missions based on a geosynchronous orbit (GEO SAR). These systems are able to provide radar images with an unprecedented combination of spatial (≤1 km) and temporal (≤12 h) resolutions. This paper investigates the GEO SAR potentialities for soil moisture (SM) mapping finalized to hydrological applications, and defines the best compromise, in terms of image spatio-temporal resolution, for SM monitoring. A synthetic soil moisture–data assimilation (SM-DA) experiment was thus set up to evaluate the impact of the hydrological assimilation of different GEO SAR-like SM products, characterized by diverse spatio-temporal resolutions. The experiment was also designed to understand if GEO SAR-like SM maps could provide an added value with respect to SM products retrieved from SAR images acquired from satellites flying on a quasi-polar orbit, like Sentinel-1 (POLAR SAR). Findings showed that GEO SAR systems p...

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2016

GEROS-ISS stands for GNSS REflectometry, radio occultation, and scatterometry onboard the Interna... more GEROS-ISS stands for GNSS REflectometry, radio occultation, and scatterometry onboard the International Space Station (ISS). It is a scientific experiment, successfully proposed to the European Space Agency in 2011. The experiment as the name indicates will be conducted on the ISS. The main focus of GEROS-ISS is the dedicated use of signals from the currently available Global Navigation Satellite Systems (GNSS) in L-band for remote sensing of the Earth with a focus to study climate change. Prime mission objectives are the determination of the altimetric sea surface height of the oceans and of the ocean surface mean square slope, which is related to sea roughness and wind speed. These geophysical parameters are derived using reflected GNSS signals (GNSS reflectometry, GNSS-R). Secondary mission goals include atmosphere/ionosphere sounding using refracted GNSS signals (radio occultation, GNSS-RO) and remote sensing of land surfaces using GNSS-R. The GEROS-ISS mission objectives and its design, the current status, and ongoing activities are reviewed and selected scientific and technical results of the GEROS-ISS preparation phase are described.

Remote Sensing of Environment, 2015

A comparison of soil moisture products derived from satellite data, in-situ measurements and land... more A comparison of soil moisture products derived from satellite data, in-situ measurements and land models was performed in the frame of the EUMETSAT H-SAF project. In particular, soil moisture retrievals of ASCAT/H-SAF and SMOS were compared with two other independent datasets, that are the NCEP/NCAR volumetric soil moisture content reanalysis developed by NOAA, and the ERA-Interim/Land soil moisture produced by ECMWF. In situ data available through the International Soil Moisture Network and distributed in regions comprising Denmark,

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2015

In this study, a technique developed to retrieve integrated water vapor from interferometric synt... more In this study, a technique developed to retrieve integrated water vapor from interferometric synthetic aperture radar (InSAR) data is described, and a three-dimensional variational assimilation experiment of the retrieved precipitable water vapor into the mesoscale weather prediction model MM5 is carried out. The InSAR measurements were available in the framework of the European Space Agency (ESA) project for the "Mitigation of electromagnetic transmission errors induced by atmospheric water vapor effects" (METAWAVE), whose goal was to analyze and possibly predict the phase delay induced by atmospheric water vapor on the spaceborne radar signal. The impact of the assimilation on the model forecast is investigated in terms of temperature, water vapor, wind, and precipitation forecast. Changes in the modeled dynamics and an impact on the precipitation forecast are found. A positive effect on the forecast of the precipitation is found for structures at the model grid scale or larger (1 km), whereas a negative effect is found on convective cells at the subgrid scale that develops within 1 h time intervals. The computation of statistical indices shows that the InSAR assimilation improves the forecast of weak to moderate precipitation (<15 mm/3 h).

Remote Sensing, 2013

This paper presents a theoretical study of microwave remote sensing of vegetated surfaces. The pu... more This paper presents a theoretical study of microwave remote sensing of vegetated surfaces. The purpose of this study is to find out if satellite bistatic radar systems can provide a performance, in terms of sensitivity to vegetation geophysical parameters, equal to or greater than the performance of monostatic systems. Up to now, no suitable bistatic data collected over land surfaces are available from satellite, so that the electromagnetic model developed at Tor Vergata University has been used to perform simulations of the scattering coefficient of corn, over a wide range of observation angles at Land C-band. According to the electromagnetic model, the most promising configuration is the one which measures the VV or HH bistatic scattering coefficient on the plane that lies at the azimuth angle orthogonal with respect to the incidence plane. At this scattering angle, the soil contribution is minimized, and the effects of vegetation growth are highlighted.

Italian Journal of Remote Sensing, 2009

Space-borne X-band synthetic aperture radars (SARs) provide a unique opportunity to measure rainf... more Space-borne X-band synthetic aperture radars (SARs) provide a unique opportunity to measure rainfall over land with unsurpassed spatial resolution of about few hundred meters. This work explores the potential of space-borne X-SARs to estimate rainfall over land from both a model and retrieval point of view. The main objective is to provide a framework for a physically-based inversion of SARs measurements at X (9.6 GHz), Ku (14 GHz) and Ka (30 GHz) band over land. A forward model of SAR response will be illustrated for X, Ku and Ka bands. We will present an inversion methodology, a quantitative application to X-SAR data of the SIR-C mission in 1994, and a qualitative application to TerraSAR-X data over France, 2008.

Italian Journal of Remote Sensing, 2009

The objective of this study is to evaluate the possibility to identify floods when soil is covere... more The objective of this study is to evaluate the possibility to identify floods when soil is covered by vegetation, recognizing differences in backscattering between SAR measurements acquired before and after the event. To this end, the electromagnetic model developed at Tor Vergata University is run for an early stage and a fully grown wheat field, at L, C and X band. Theoretical results show that flooding can be detected at all frequencies in presence of short vegetation, while L band is the most suitable one for developed crops. Results obtained in the case of early stage are in reasonable agreement with ERS data collected over grass fields before and after the strong flooding occurred in Alessandria (North Italy) in 1994.

IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, 2014

Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique usefu... more Spaceborne Interferometric Synthetic Aperture Radar (InSAR) is a well established technique useful in many land applications, such as tectonic movements, landslide monitoring and digital elevation model extraction. One of its major limitation is the atmospheric effect, and in particular the high water vapour spatial and temporal variability which introduces an unknown delay in the signal propagation. This paper describes the general approach and some results achieved in the framework of an ESA funded project devoted to the mapping of the water vapour with the aim to mitigate its effect in InSAR applications. Ground based (microwave radiometers, radiosoundings, GPS) and spaceborne observations (AMSR-E, MERIS, MODIS) of columnar water vapour were compared with Numerical Weather Prediction model runs in Central Italy during a 15-day experiment. A dense network of GPS receivers was deployed close to Como, in Northern Italy, to complement the operational network in order to derive Zenith Total Delay as well as Slant Delay which can support InSAR processing. A comparison with Atmospheric Phase Screens (APS) derived from a sequence of Envisat multi pass interferometric acquisitions processed using the Permanent Scatters technique on the two test sites has been also performed. The acquired experimental data and their comparison give a valuable idea of what can be done to gather information on water vapour, which, besides InSAR applications, plays a fundamental role in weather prediction and radio propagation studies. The work has been carried out in the framework of an ESA funded project, named "Mitigation of Electromagnetic Transmission errors induced by Atmospheric Water Vapour Effects" (METAWAVE). This paper presents the general approach an the various methodologies exploited in the project, together with the overall intercomparison of the results. In deep details on the comparison with the InSAR APS maps derived by the PS technique, as well as on GPS receiver processing and water vapour tomography are reported in two companion papers.

International Geoscience and Remote Sensing Symposium (IGARSS), 2009

2010 IEEE International Geoscience and Remote Sensing Symposium, 2010