Prof.
Nazzareno Pierdicca
(Sapienza University of Rome)
Ka-band RADAR frequency range has not yet been used for Synthetic Aperture Radar (SAR) from space so far, but this technology may lead to important applications for the next generation of SAR space sensors. First of all the small wavelength makes small baseline suitable for interferometric applications, thus enabling a relatively simple implementation of single pass interferometry from a spaceborne platform. However, a better knowledge is required on backscatter at Ka-band in order to assess the realistic performance of a spaceborne SAR for the envisaged applications.
The research presented in this paper was supported by an ESA project (Ka-band SAR backscatter analysis in support of future applications) aimed at investigating the wave interaction at Ka-band for a widely varying range of targets, both natural and manmade. The main objective was to establish a reference for the range of sigma nought expected from the earth surface and its variability as function of incidence angle and target conditions, to be used for system performance assessment and design. An additional outcome of the project was a better understanding on the sensitivity of Ka sigma nought to surface parameters as compared to other frequency bands.
In particular, it was investigated the radar response of bare soil, crops, forests, sea surface and snow covered soil. The investigation was based both on the analysis of experimental data and on the exploitation of electromagnetic scattering models. Actually the available experimental data are quite scarce and in some cases not consistent, so that the electromagnetic models revealed themselves essential to enlarge the range of conditions (e.g., incidence angle and range of target bio-geophysical parameters) to be investigated.
In the presentation the results of the models are showed and critically compared to the available data. The model outputs are then presented to assess the sensitivity to the target parameters of Ka backscatter in comparison to other radar frequency bands currently exploited from space for different applications. Namely, modelling of Ka backscatter of bare soil is discussed and the limitation of state of art asymptotic solutions demonstrated. The sensitivity to soil parameters was finally showed using a semi-empirical model. As for vegetated target both crops, shrubs and few types of forests were considered. A solution of the Radiative Transfer Equation was used to investigate the polarimetric response of those targets, their range of sigma nought at Ka band, and the sensitivity to vegetation type and biomass. As for the seas surface, backscatter is manly determined by Bragg scattering at the higher frequency range of the capillary wave spectrum, thus echibiting some modelling challenges and some differences with respect to the commonly used frequency band for sea applications (e.g., C and Ku).
Summary
In the presentation the results of electromagnetic models of earth scattering at Ka band are showed and critically compared to the available data. The model outputs are then presented to assess the sensitivity to the target parameters of Ka backscatter in comparison to other radar frequency bands currently exploited from space for different applications. Namely, modelling of Ka backscatter of bare soil is discussed and the limitation of state of art asymptotic solutions demonstrated. The sensitivity to soil parameters was finally showed using a semi-empirical model. As for vegetated target both crops, shrubs and few types of forests were considered. A solution of the Radiative Transfer Equation was used to investigate the polarimetric response of those targets, their range of sigma nought at Ka band, and the sensitivity to vegetation type and biomass. As for the seas surface, backscatter is manly determined by Bragg scattering at the higher frequency range of the capillary wave spectrum, thus echibiting some modelling challenges and some differences with respect to the commonly used frequency band for sea applications (e.g., C and Ku).
Prof.
Nazzareno Pierdicca
(Sapienza University of Rome)
Dr
Antonio Repucci
(STARLAB)
Mr
Björn Rommen
(ESA)
Dr
Daniele Mapelli
(Aresys s.r.l. – a Polimi spin off)
Prof.
Leila Guerriero
(Università di Roma, Tor Vergata, DICII)
Dr
Luca Pulvirenti
(Cima Foundation)
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