Electromagnetic Multi–Gaussian Speckle

Generalizing our prior work on scalar multi-Gaussian (MG) distributed optical fields, we introduce the two-dimensional instantaneous electric-field vector whose components are jointly MG distributed. We then derive the single-point Stokes parameter probability density functions (PDFs) of MG-distributed light having an arbitrary degree and state of polarization. We show, in particular, that the intensity contrast of such a field can be tuned to values smaller or larger than unity. We validate our analysis by generating an example partially polarized MG field with a specified single-point polarization matrix using two different Monte Carlo simulation methods. We then compute the joint PDFs of the instantaneous field components and the Stokes parameter PDFs from the simulated MG fields, while comparing the results of both Monte Carlo methods to the corresponding theory. Lastly, we discuss the strengths, weaknesses, and applicability of both simulation methods in generating MG fields.

Polarization Tomography with Stokes Parameters

We present a simple but powerful technique for the analysis of polarized emission from radio galaxies and other objects. It is based on the fact that images of Stokes parameters often contain considerably more information than is available in polarized intensity and angle maps. In general, however, the orientation of the Stokes parameters will not be matched to the position angles of structures in the source. Polarization tomography, the technique presented in this paper, consists of making a series of single linear Stokes parameter images, S(ρ), where each image is rotated by an angle ρ from the initial orientation of Q and U. Examination of these images, in a series of still frames or a movie, reveals often hidden patterns of polarization angles, as well as structures that were obscured by the presence of overlapping polarized emission. We provide both cartoon examples and a quick look at the complex polarized structure in Cygnus A.

Features of the Propagation of Microwave Radiation in a Freshwater Ice Cover

When scanning fresh ice cover in the microwave range at a frequency of 13 GHz, the transmitted radiation power was investigated at four linear polarizations (vertical, horizontal, and polarizations rotated at an angle of +-45) for a long period of time. The measurements were carried out on the ice cover of the lake. Arakhley (Transbaikal region) at a distance of 120 m from the coast in March 2021. We also measured the external parameters of the studied environment, namely, the temperature of the ice cover, meteorological parameters (wind speed, air temperature, pressure). The distance between the generator and the receiver of electromagnetic radiation was 40 meters. The orientation of the instruments is West-East. As a result, variations in the power of the transmitted microwave radiation were detected. These variations are related to the temperature deformations of the ice cover, which were recorded using a deformation sensor installed in the ice cover. Also revealed a feature that was observed earlier in the spring. This is a different temporal behavior of the first Stokes parameter, which is determined by the sum of the powers of two orthogonal polarizations, namely, the sum of the received signals at the vertical and horizontal polarizations, and the sum of the received signals of the two polarizations rotated at an angle of +45 and -45. This difference is also associated with temperature deformations of the fresh ice cover in the spring. Keywords: microwave range, fresh ice cover, Stokes parameters, temperature deformation

A study of polarimetric error induced by satellite motion: application to the 3MI and similar sensors

This study investigates the magnitude of the error introduced by the co-registration and interpolation in computing Stokes vector elements from observations by the Multi-viewing, Multi-channel, Multi-polarisation Imager (3MI). The Stokes parameter derivation from the 3MI measurements requires the syntheses of three wide-field-of-view images taken by the instrument at 0.25 s interval with polarizers at different angles. Even though the synthesis of spatially or temporally inhomogeneous data is inevitable for a number of polarimetric instruments, it is particularly challenging for 3MI because of the instrument design, which prioritizes the stability during a long life cycle and enables the wide-field-of-view and multiwavelength capabilities. This study therefore focuses on 3MI's motion-induced error brought in by the co-registration and interpolation that are necessary for the synthesis of three images. The 2-D polarimetric measurements from the Second-generation Global Imager (SGLI) are weighted and averaged to produce two proxy datasets of the 3MI measurements, with and without considering the effect of the satellite motion along the orbit. The comparison of these two datasets shows that the motion-induced error is not symmetric about zero and not negligible when the intensity variability of the observed scene is large. The results are analyzed in five categories of pixels: (1) cloud over water, (2) clear sky over water, (3) coastlines, (4) cloud over land, and (5) clear sky over land. The most spread distribution of normalized polarized radiance (Lp) difference is in the cloud-over-water class, and the most spread distribution of degree of linear polarization (DOLP) difference is in the clear-sky-over-water class. The 5th to 95th percentile ranges of Lp difference for each class are (1) [-0.0051,0.012], (2) [-0.0040,0.0088], (3) [-0.0033,0.012], (4) [-0.0033,0.0062], and (5) [-0.0023,0.0032]. The same percentile range of DOLP difference for each class are (1) [-0.023,0.060], (2) [-0.043,0.093], (3) [-0.019,0.082], (4) [-0.0075,0.014], and (5) [-0.011,0.016]. The medians of the Lp difference are (1) 0.00035, (2) 0.000049, (3) 0.00031, (4), 0.000089, and (5) 0.000037, whereas the medians of the DOLP difference are (1) 0.0014, (2) 0.0015, (3) 0.0025, (4) 0.00027, and (5) 0.00014. A model using Monte Carlo simulation confirms that the magnitude of these errors over clouds are closely related to the spatial correlation in the horizontal cloud structure. For the cloud-over-water category, it is shown that the error model developed in this study can statistically simulate the magnitude and trends of the 3MI's motion-induced error estimated from SGLI data. The obtained statistics and the simulation technique can be utilized to provide pixel-level quality information for 3MI Level 1B products. In addition, the simulation method can be applied to the past, current, and future spaceborne instruments with a similar design.

Optimal Demodulation Algorithm of Spatially Modulated Full-Polarization Imaging System

Spatially modulated full-polarization imaging systems can obtain full Stokes parameter information by single imaging, with strong characteristics of real-time execution and stability. Since all the polarization information is modulated into an interferogram, demodulation becomes an essential step. As the resolution of the obtained image continuously increases, the data to be calculated also increase. Therefore, a higher speed for the demodulation process is requisite. This article proposes a local filtering method and bypasses the frequency centralization method in the frequency domain to improve the speed of demodulation. The demodulation time of an interferogram of size 1024×1024 pixels was reduced from 3.027 473 s to 0.134 637 s, increasing the speed of demodulation by 97.72%. Meanwhile, the demodulation time of an interferogram of size 6144×6144 pixels was reduced from 444.329 92 s to 4.637 069 s, increasing the speed of demodulation by 98.75%.

Evaluating Simulated RADARSAT Constellation Mission (RCM) Compact Polarimetry for Open-Water and Flooded-Vegetation Wetland Mapping

When severe flooding occurs in Canada, the Emergency Geomatics Service (EGS) is tasked with creating and disseminating maps that depict flood extents in near real time. EGS flood mapping methods were created with efficiency and robustness in mind, to allow maps to be published quickly, and therefore have the potential to generate high-repeat water products that can enhance frequent wetland monitoring. The predominant imagery currently used is synthetic aperture radar (SAR) from RADARSAT-2 (R2). With the commissioning phase of the RADARSAT Constellation Mission (RCM) complete, the EGS is adapting its methods for use with this new source of SAR data. The introduction of RCM’s circular-transmit linear-receive (CTLR) beam mode provides the option to exploit compact polarimetric (CP) information not previously available with R2. The aim of this study was to determine the most effective CP parameters for use in mapping open water and flooded vegetation, using current EGS methodologies, and compare these products to those created by using R2 data. Nineteen quad-polarization R2 scenes selected from three regions containing wetlands prone to springtime flooding were used to create reference flood maps, using existing EGS tools. These scenes were then used to simulate 22 RCM CP parameters at different noise floors and spatial resolutions representative of the three RCM beam modes. Using multiple criteria, CP parameters were ranked in order of importance and entered into a stepwise classification procedure, for evaluation against reference R2 products. The top four CP parameters —m-chi-volume or m-delta-volume, RR intensity, Shannon Entropy intensity (SEi), and RV intensity—achieved a maximum agreement with baseline R2 products of upward of 98% across all 19 scenes and three beam modes. Separability analyses between flooded vegetation and other land-cover classes identified four candidate CP parameters—RH intensity, RR intensity, SEi, and the first Stokes parameter (SV0)—suitable for flooded-vegetation-region growing. Flooded-vegetation-region-growing CP thresholds were found to be dependent on incidence angle for each of these four parameters. After region growing using each of the four candidate CP parameters, RH intensity was deemed best to map flooded vegetation, based on our evaluations. The results of the study suggest a set of suitable CP parameters to generate flood maps from RCM data, using current EGS methodologies that must be validated further as real RCM data become available.