Stand-off sensing of material characteristics by polarimetric MMW radiometry

ABSTRACT The characterization of dielectric materials is of great importance for many applications, being for instance quality control during product fabrication or status control of outside constructions over time. In many outside situations the objects of interest have limited accessibility, and the investigation has to be done without destruction of any part of the object and without any health risks for an operator. Hence remote sensing from stand-off position is desirable, and the use of microwaves, millimeter-waves or THz waves offers some penetration capability into matter, depending on its chemical and physical decomposition and of course frequency. Many objects of interest consist of a dielectric coating or enclosure, which can electromagnetically be treated as a dielectric layered structure or a dielectric slab surrounded by air. Radar as an active remote sensing technology has great potential with respect to precise range measurements and spatial resolution. However, its mostly mono-static implementation suffers from low or no back reflection of signals in case of plane and tilted surfaces, delivering hence no information. In contrast radiometric imaging as passive remote sensing technology uses naturally generated noise-like radiation of thermal origin, being available everywhere and from all directions. Quite often the sky can be used as large illumination source, providing rather low radiation power compared to objects on Earth, using frequencies up to few hundred GHz. Furthermore, thermal radiation originally is un-polarized, but becomes polarized when reflected partly on a dielectric surface. Hence, the use of polarimetric measurements at various incidence angles can provide information on the type and structure of the reflecting object. The approach and the measurement setup are described. Experimental results of polarimetric measurements are shown and discussed

Performance of the Copernicus Imaging Microwave Radiometer On-Board RFI Processor

This paper presents the simulations needed to assess the performance of the Radio Frequency Interference (RFI) processor for the Copernicus Imaging Microwave Radiometer (CIMR). A brief description of the common RFI processor used for all radiometer bands in CIMR and of the system parameters is given in sections 2 and 3, respectively. Hereafter follows a description of the simulations and how the performance can be obtained in sections 4 and 5. Conclusion is in section 6

Impact of permittivity patterns on fully polarimetric brightness temperature signatures at l-band

—This study investigates the sensitivity of L-band (1.41 GHz) polarimetric brightness temperature signatures to oriented permittivity patterns, which can occur for example in the case of row and interrow soil moisture differences in agricultural fields. A field experiment and model simulations are conducted to verify the effects of such patterns on all four Stokes parameters. We find that for an artificial target resembling idealized model conditions, permittivity patterns lead to systematic brightness temperature modulations in dependency of the azimuthal look angle. For the specific field setup, modulations reach amplitudes of ∼ 4 K and mostly affect h-polarized brightness temperatures as well as the first, second, and third Stokes parameters. Simulations of soil moisture patterns under idealized model conditions indicate even higher amplitudes (up to 60 K for extreme cases). However, the effects occur only for permittivity layer widths of up to 8 cm (given the observing wavelength of 21 cm), which is lower than the row and interrow widths typically observed in agricultural settings. For this reason, and due to the idealized model geometry investigated here, future studies are needed to transfer the findings of this study to potential applications such as the sensing of oriented soil moisture patterns. Particular interest might lie in radiometry and reflectometry in lower frequency ranges such as P-band, where according to the threshold established here (8/21 wavelengths), permittivity layer widths of up to ∼ 45 cm could be observed. © 2019, Electromagnetics Academy. All rights reserved

Ultra-High Performance C & L-Band Radiometer System for Future Spaceborne Ocean Missions

A next generation spaceborne radiometer system for hi-quality ocean measurements is discussed. Instead of a classical horn, a focal plane array is used as antenna feed. The antenna beam is created by adding the outputs from many small antenna elements, thus providing an antenna beam of unsurpassed quality. This solves the classical polarization purity and land/sea contamination issues. The concept requires many microwave receivers and fast analog-to-digital converters as well as fast digital signal processing on-board the satellite. This is discussed, and resource budgets, especially concerning power, are provided