Current Frontiers in the Modelling of Scattering, Propagation and Emission for Microwave Remote Sensing

Dear Colleagues,

Classical Electromagnetic Theory is the most fundamental basis of the interaction between matter and electromagnetic fields at microwave frequencies, with the important exception of thermal emission, which involves quantum aspects. All the sensors that observe the Earth from Space or their equivalent systems that do so from airborne platforms rely on the laws of electromagnetism, except for the case of gravimeters. In the context of Remote Sensing of the Earth, most of the theoretical work for the formal description of propagation, scattering and absorption of electromagnetic waves was done in the 80s and 90s of the twentieth century.  The complexity of the Earth natural scenarios, either land, ocean or atmosphere, leads to cumbersome analytical formulas, which are seldom used in its full shape for the practical purpose of inferring the Earth features that we pursue to evaluate. The upcoming missions to other planets and moons in the solar system extends the challenge. On the other hand, some very simple models have been exploited largely, with relatively minor differences among the variations that have been devised for them by different authors. In particular, much of the work done in Radar Polarimetry is based on such simple models. In addition to the work on analytical solutions for scattering, propagation and emission problems in the natural extended targets that form the observable scenarios of the Earth, a great deal of fundamental work is achieved by Computational Electromagnetics. In this case, traditionally at the cost of heavy computation efforts, the same situations can be simulated in their geometry and radiometric characteristics and the fields to be measured can be numerically computed. A new generation of computational techniques overcome the burden of large computing, often parallelized resources by including elements of the aforementioned analytical models.

There is an obvious necessity of obtaining geophysical information from the measurements of the increasingly complex and more precise instruments deployed by national or international space agencies and a gradually larger number of private companies. This need is currently attracting the application of new information extraction tools, including the successful resources provided by Machine Learning and Data Science. Furthermore, there are other more traditional approaches for the inverse problem of evaluating geophysical parameters and essential climate variables, based on optimization algorithms and direct estimation methods, that can still play an important role. Both strategies will be considered in this issue as long as they incorporate physically based models for the interaction between electromagnetic fields and matter at radio frequencies.

General topics include:

+ Propagation, scattering and absorption modelling for random media in Earth Observation

+ Inverse modelling techniques and the role of Big Data and Bayesian Learning

+ Evolution of electromagnetic models for random media, randomly rough surfaces and layered structures in the last fifty years

+ Optimal geometric and radiometric modelling of sea, land, atmosphere, and cryosphere for electromagnetic analysis

+ New computational solutions for direct and inverse electromagnetic modelling

+ Availability of open-source computational methods and interfacing with performance simulators for microwave sensors

+ Propagation in disturbed media conditions (fire, smoke, ionized media)

+ Coherence theory for Microwave Remote Sensing

+ Electromagnetic modelling in Planetary Radar Remote Sensing

In addition to this, a number of more specific research areas are especially welcome:

+ The sufficiency of the Kirchhoff approximation and the SPM for practical Radar Remote Sensing models and the role of more sophisticated models.

+ The physics of current Radar Polarimetry and the potential need for future improvements

+ The physics of coherence in Radar Interferometry and potential lessons from optics and quantum mechanics

+ Scattering by arrays of oriented lossy structures (typically in crops and forests)

+ Electromagnetic modelling of the scattered phase from vegetation targets

+ Scattering by multi-layered media (typically in snow and arid soils)

Dr. Jose Luis Alvarez-Perez
Dr. Abdelhamid Tayebi Tayebi
Dr. Angelo Liseno
Dr. Matias Barber
Guest Editors

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• Radar Remote Sensing Electromagnetic Modelling
• Scattering and Propagation in Random Media
• Emission by Random Media
• Computational Electromagnetics
• Coherence Modelling
• Polarimetry