Space and airborne remote sensing of natural surfaces have been demonstrated to provide valuable information for several applications in different fields, such as climatology, oceanography, flooding and agricultural monitoring, just to mention but a few. In this frame, an accurate and flexible characterization of the electromagnetic scattering is considered a fundamental step, requiring a sound electromagnetic background as well as interdisciplinary expertise.
Based on numerical and experimental modeling, this research project proposes an extensive study of the bistatic scattering generated by natural surfaces, such as the ocean, the anisotropic and vegetated soils. Extensive investigations on the theoretical capabilities of different configurations, designed by considering a transmitting and receiving antenna not located in the same place, will be conducted. Moving from the activities developed in the framework of the ESA mission SAOCOM-CS, on which this investigator is concluding a 1-year research assignment, the potential improvement offered by bistatic configurations with respect to much known monostatic surveys onto the soil moisture estimation, will be investigated. Improvements achievable on wind fields characterization over the ocean and on the vegetation biomass monitoring will be considered as well. In this frame, based on the extension of well-established electromagnetic models, whose validity has not yet accurately investigated for bistatic geometry, efficient and reliable numerical codes will be developed, taking into account different polarizations.
Overall, the proposed research represents a fundamental step towards the assessment of the capabilities offered by bistatic radar observations, and to gather valuable information for the design of future, high-science and high-application value, spatial missions. This project is in line with the next 1-year assignment for which the proposer has been already declared winner (procedure no. 8/2017, DIET Dpt).
As discussed in the previous sections the modeling of the scattering generated by ocean and lands is nowadays considered fundamental for a wide class of interdisciplinary scientific areas.
Bistatic satellite systems are presently devoted only to interferometric applications (e.g., Tandem-X for extraction of Digital Elevation Model) which foresees small baselines (i.e., the distance between platforms), whereas polarimetric applications with large baselines are presently scarcely investigated. The investigation of innovative bistatic configurations taking into account different polarization and the role of anisotropy for bare and vegetated soils is an original distinctive feature of the research topic here under investigation. In addition, the possibility of providing laboratory-scale measurements, as detailed next, by means of an experimental setup already exploited in the past for ground penetrating radar survey, is highly desirable for the validation of the codes developed in the first stage, in particular to assess the accuracy and the effectiveness of the proposed anisotropic model for the tilled agricultural soil.
One of the innovative aspects of the proposed research would consist in the analysis of the sensitivity of anisotropic surfaces to the illumination direction, a feature that it is not predicted by electromagnetic models usually applied to simulate the response of bare and vegetated areas.
In addition, the role of coherent scattering phenomena, which may extend across significant areas of an agricultural field, will be investigated, being potentially able to significantly improve the accuracy of the soil moisture estimation of agricultural soils. An accurate modeling and understanding of coherent phenomena for both monostatic and bistatic observation would be considered a clear innovation and advancement for the field.
Among other possible bistatic technique that can benefits from the proposed research, we mention the Global Navigation Satellite System (GNSS)-Reflectometry (GNSS-R) [1]. It is a technique consisting in detecting the signal of opportunity coming from one of the GNSS satellites and scattered off the Earth surface using an antenna looking down to the surface and possibly another one looking up to collect the incoming signal to use as reference. Only receivers need to be deployed since a large number of transmitters are already in place as part of the GNSS network. This feature makes the technique intrinsically inexpensive and the instrumentation generally simpler and smaller with respect to active radar systems. Potential advancements in this field cannot be developed without a comprehensive understanding of the electromagnetic bistatic scattering phenomenon, that is the main goal of the proposed research.
The use of a bistatic radar for measuring land bio-geophysical parameters such the vegetation biomass has also not received enough attention in the last decades. As discussed in [2, 3] the attenuation by vegetation of the coherent reflection from the soil enables the estimation of vegetation biomass by using a specular bistatic configuration. However, the proposed model relies on a simplified assumption that considers the vegetation as positioned on a flat infinite soil. In this frame, a potential advancement would be generated by considering a truncated model for the soil support along with a realistic topographical profile for the earth surface. Exploiting the analysis on the coherent scattering made for the anisotropic soil, these two realistic features for the vegetated surface could be effectively integrated in the numerical algorithm. Overall, the understanding of the role of the topography for the bistatic scattering generated by vegetated areas would represent a significant advancement in the field.
More applications could emerge in the course of the activity; the implemented models will provide tools to further investigate newer application domains in the future.
References
[1] Pierdicca N, Guerriero L, Giusto R, Brogioni M, Egido A. "SAVERS: A simulator of GNSS reflections from bare and vegetated soils," IEEE Trans. Geosci. Remote Sens. 2014 Oct; 52 (10): 6542-54.
[2] P. Ferrazzoli, L. Guerriero, C. I. Del Monaco, and D. Solimini, "A further insight into the potential of bistatic SAR in monitoring the Earth surface," Proc. IEEE IGARSS, Jul. 2003, vol. 2, pp. 776-777.
[3] Guerriero L, Pierdicca N, Pulvirenti L, Ferrazzoli P, "Use of satellite radar bistatic measurements for crop monitoring: A simulation study on corn fields," Remote Sensing. 2013 Feb 20; 5(2): 864-90.