Pia Addabbo

Stochastic Modeling and Simulation of Delay–Doppler Maps in GNSS-R Over the Ocean

A stochastic model for delay-Doppler map (DDM) simulation from global navigation satellite system reflectometry (GNSS-R) systems is presented. The aim is to provide a useful tool for investigating the performance of estimation and retrieval algorithms that are based on finite time series. The scattering inside a delay-Doppler cell is modeled as the sum of a random number of contributions from inner specular points that, as the mean number of such contributions gets larger, tends to a compound-Gaussian process. The statistical averages reveal that the model is fully consistent with the previous results provided by Zavorotny and Voronovich. Numerical simulations of large airborne and spaceborne DDMs are easily practicable and show the clear patterns due to signal fluctuations and thermal noise that fade away when the number of averaged observations increases. Comparisons with TechDemoSat-1 data show that the model and the simulation scheme provide accurate realizations of the onboard-processed DDMs.

The Unmixing of Atmospheric Trace Gases From Hyperspectral Satellite Data

A new approach for the retrieval of the vertical column concentrations of trace gases, from hyperspectral satellite reflectances, is presented. The investigation moves from the general rationale of independent component analysis, but the constraint of perfect independence among sources is replaced by a minimum dependence concept that proves more reasonable for the application at hand. The unmixing of the gas spectra and their concentrations is achieved from linear mixtures obtained from the logarithm of the spectral reflectance. After a proper preprocessing stage aimed at reducing major residual dependences caused by atmospheric scattering, trace-gas retrieval is carried out through a minimization of a statistical cost function, subject to the physical constraint that the resulting spectra must be nonnegative. The experimental analysis relies on the retrieval of sulfur dioxide during volcanic emissions using data from the National Aeronautics and Space Administration Ozone Monitoring Instrument. To validate the procedure, reference reflectance spectra having a known profile of sulfur dioxide are generated with the MODerate resolution atmospheric TRANsmission software, and the retrieved concentration is compared with the theoretical one. Performance in the presence of shot and detector noise has also been analyzed starting from pure simulated spectral reflectances.

The Hyperspectral Unmixing of Trace-Gases From ESA SCIAMACHY Reflectance Data

Atmospheric concentrations of trace-gases are retrieved from hyperspectral data using a blind source separation method. The algorithm relies on the assumption that the absorption cross sections of the gas components are weakly dependent on the overall atmospheric background. The unmixing of contributions from the logarithm of the spectral reflectance provides estimates of both individual trace-gas absorption cross sections and their concentrations. In the experimental analysis, nadir reflectances received by SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY are considered in two scenarios: the sulfur dioxide emissions from a volcanic eruption and the nitrogen dioxide production from anthropogenic pollution. In both cases, it is demonstrated that the algorithm performs very similarly to the Differential Optical Absorption Spectroscopy algorithm but with very little ancillary information.

Simulation of stochastic GNSS-R waveforms based on a novel time-varying sea scattering model

We propose a new stochastic model governing bistatic returns from GNSS-R systems. The main mechanism exploited in the model is the scattering from specular points and the fluctuations of their number. The scattering inside a delay-Doppler cell is modelled as the sum of a random number of contribution from specular points that, when the number of such contribution is large, converges to a compound-Gaussian process. This process is simple to simulate and is able to model both the spatial and temporal dynamics of the sea surface. After simulation of the waveform received by the receiver, averaging over long time sequences produces results that fully resembles the theoretical results predicted by the Zavorotny and Voronovich model [1].

Land cover classification and monitoring through multisensor image and data combination

Authors in this work aim to present new analysis methods for Earth Observation, developed by processing Sentinel-1 and Landsat-8 satellite data and combining them in an original way. Comparing SAR and Optical/Multispectral data is a procedure already in use because they are two acquisition systems that provide very different and therefore complementary and useful information. Even if the combination of such different data is not a simple process, the overall information greatly improves when both satellite data are jointly used, as application of our procedure to some case studies demonstrates.

Wind retrieval for GNSS reflectometry from techdemosat-1

The main purpose of this study is to propose and validate a new algorithm for wind speed retrieval over the ocean using Global Navigation Satellite System-Reflectometry (GNSS-R). The proposed method is based on a Least Squares (LS) estimation from the volume of the scattered power function. Real DDMs collected by the space GNSS receiver-remote sensing instrument (SGR-ReSI) on board the TechDemoSat-1 (TDS-1) satellite and the Advanced SCATterometer (ASCAT) wind speed measurements are used for validation.

Analysis of GPS signals backscattered from a target on the sea surface

In this paper the Two-Scale Model has been used to derive the theoretical Normalized Radar Cross Section (NRCS) for sea clutter in the L-band, taking into account also the circular polarization of GPS signals. Using this theoretical model and the theoretical formula for NRCS, authors aim to investigate the possibility to extend target detection through GPS signals in backscattering configuration by varying the incidence angle and the wind speed, whereas results obtained previously were related only to a single value of the incidence angle and to two values of the wind speed. Target Scattered Power and Sea Clutter Power are derived and compared finding that: 1) smaller targets can be detected as the incidence angle increases; 2) the Sea Clutter Power is lower than the one estimated when the “worst case” of a VV-polarization signal is chosen to derive the NRCS value from experimental data. Some final considerations are made as future work.

Simulation of TechDemoSat-1 Delay-Doppler Maps for GPS Ocean Reflectometry

The increasing diffusion of spaceborne GNSS reflectometry as a remote sensing technique has motivated, recently, the development of end-to-end delay-Doppler map simulators. We present here the most relevant issues involved in the design of a simulator for applications of ocean wind remote sensing with a conventional acquisition technique. The approach is based on the stochastic Monte Carlo simulation of the scattered signal followed by a 2-D convolution and filtering accounting for the Doppler processing implemented on the TechDemoSat-1 platform. Simulation accuracy is assessed in the validation setup, where ensemble runs are supported by the estimation of the empirical cumulative distribution function.

The hyperspectral unmixing of nitrogen dioxide from the ESA-SCIAMACHY Nadir measurements

The Nadir reflectances, measured by the SCIAMACHY hyperspectral sensor, are used to retrieve vertical column concentrations of nitrogen dioxide (NO2), resulting from anthropogenic pollution. The estimation process is realized via a blind source separation method: the unmixing of the NO2 spectral waveform from the overall atmospheric absorption contribution within the logarithmic reflectance spectra is realized.

Combination of LANDSAT and EROS-B satellite images with GPS and LiDAR data for land monitoring. A case study: The Sant'Arcangelo Trimonte dump

In this work, authors outline how measurements from different types of sensors can be put together to characterize in an extensive way a sensitive waste dump site. Terrestrial surveying systems and aerial images have been combined with satellite remote sensing techniques to get a complete overview of the surface stability and its thermal characteristics in conjunction with geomorphological conditions and water distribution. The objective has been to implement a broad monitoring system to control the area under observation. Interesting observations have been deducted from the comparison among different data since surface temperature retrievals and variations can be correlated to soil moisture and water exchange by showing that the proposed monitoring system performs correctly in taking under control deformation, terrain displacements, temperature and water surface modifications.