Polarimetry is one of the most promising types of remote sensing for improved characterization of atmospheric aerosol. Indeed, aerosol particles constitute a highly variable atmospheric component characterized by a large number of parameters describing particle sizes, morphologies (including shape and internal structure), absorption and scattering properties, amounts, horizontal and vertical distribution, etc. Reliable monitoring of all these parameters is very challenging, and therefore the aerosol effects on climate and environment are considered to be among the most uncertain factors in climate and environmental research. In this regard, observations that provide both the angular distribution of the scattered atmospheric radiation as well as its polarization state at multiple wavelengths covering the UV–SWIR spectral range carry substantial implicit information on the atmospheric composition. Therefore, high expectations in improving aerosol characterization are associated with detailed passive photopolarimetric observations. The critical need to use space-borne polarimetry for global accurate monitoring of detailed aerosol properties was first articulated in the late 1980s and early 1990s. By now, several orbital instruments have already provided polarization observations from space, and a number of advanced missions are scheduled for launch in the coming years by international and national space agencies. The first and most extensive record of polarimetric imagery was provided by POLDER-I, POLDER-II, and POLDER/PARASOL multi-angle multi-spectral polarization sensors. Polarimetric observations with the POLDER-like design intended for collecting extensive multi-angular multi-spectral measurements will be provided by several instruments, such as the MAI/TG-2, CAPI/TanSat, and DPC/GF-5 sensors recently launched by the Chinese Space Agency. Instruments such as the 3MI/MetOp-SG, MAIA, SpexOne and HARP2 on PACE, POSP, SMAC, PCF, DPC–Lidar, ScanPol and MSIP/Aerosol-UA, MAP/Copernicus CO2 Monitoring, etc. are planned to be launched by different space agencies in the coming decade. The concepts of these future instruments, their technical designs, and the accompanying algorithm development have been tested intensively and analyzed using diverse airborne prototypes. Certain polarimetric capabilities have also been implemented in such satellite sensors as GOME-2/MetOp and SGLI/GCOM-C. A number of aerosol retrieval products have been developed based on the available measurements and successfully used for different scientific applications. However, the completeness and accuracy of aerosol data operationally derived from polarimetry do not yet appear to have reached the accuracy levels implied by theoretical sensitivity studies that analyzed the potential information content of satellite polarimetry. As a result, the dataset provided by MODIS is still most frequently used by the scientific community, yet this sensor has neither polarimetric nor multi-angular capabilities. Admittedly polarimetric multi-angular observations are highly complex and have extra sensitivities to aerosol particle morphology, vertical variability of aerosol properties, polarization of surface reflectance, etc. As such, they necessitate state-of-the-art forward modeling based on first-principles physics which remains rare, and conventional retrieval approaches based on look-up tables turn out to be unsuitable to fully exploit the information implicit in the measurements. Several new-generation retrieval approaches have recently been proposed to address these challenges. These methods use improved forward modeling of atmospheric (polarized) radiances and implement a search in the continuous space of solutions using rigorous statistically optimized inversions. Such techniques provide more accurate retrievals of the main aerosol parameters such as aerosol optical thickness and yield additional parameters such as aerosol absorption. However, the operational implementation of advanced retrieval approaches generally requires a significant extra effort, and the forward-modeling part of such retrievals still needs to be substantially improved. Ground-based passive polarimetric measurements have also been evolving over the past decade. Although polarimetry helps improve aerosol characterization, especially of the fine aerosol mode, the operators of major observational networks such as AERONET remain reluctant to include polarimetric measurements as part of routine retrievals owing to their high complexity and notable increase in effort required to acquire and interpret polarization data. In addition to remote-sensing observations, polarimetric characteristics of aerosol scattering have been measured in situ as well as in the laboratory using polar nephelometers. Such measurements constitute direct observations of single scattering with no contributions from multiple scattering effects and therefore provide unique data for the validation of aerosol optical models and retrieval concepts. This article overviews the above-mentioned polarimetric observations, their history and expected developments, and the state of resulting aerosol products. It also discusses the main achievements and challenges in the exploitation of polarimetry for the improved characterization of atmospheric aerosols.

https://hal.archives-ouvertes.fr/hal-03009287/document

Polarimetric remote sensing of atmospheric aerosols: Instruments, methodologies, results, and perspectives

Preface Acknowledgements 1. Introduction 2. The macroscopic Maxwell equations and monochromatic fields 3. Fundamental homogeneous-medium solutions of the macroscopic Maxwell equations 4. Basic theory of frequency-domain electromagnetic scattering by a fixed finite object 5. Far-field scattering 6. The Foldy equations 7. The Stokes parameters 8. Poynting-Stokes tensor 9. Polychromatic electromagnetic fields 10. Polychromatic scattering by fixed and randomly changing objects 11. Measurement of electromagnetic energy flow 12. Measurement of the Stokes parameters 13. Description of far-field scattering in terms of actual optical observables 14. Electromagnetic scattering by a small random group of sparsely distributed particles 15. Statistically isotropic and mirror-symmetric random particles 16. Numerical computations and laboratory measurements of electromagnetic scattering 17. Far-field observables: qualitative and quantitative traits 18. Electromagnetic scattering by discrete random media: far field 19. Near-field scattering by a sparse discrete random medium: microphysical radiative transfer theory 20. Radiative transfer in plane-parallel particulate media 21. Weak localization 22. Epilogue Appendix A. Dyads and dyadics Appendix B. Free-space dyadic Green's function Appendix C. Euler rotation angles Appendix D. Spherical-wave expansion of a plane wave in the far zone Appendix E. Integration quadrature formulas Appendix F. Wigner d-functions Appendix G. Stationary phase evolution of a double integral Appendix H. Hints and answers to selected problems Appendix I. List of acronyms References Index.

Electromagnetic Scattering by Particles and Particle Groups: An Introduction

https://ntrs.nasa.gov/api/citations/20170004359/downloads/20170004359.pdf

First-Principles Modeling Of Electromagnetic Scattering By Discrete and Discretely Heterogeneous Random Media

CELES is a freely available MATLAB toolbox to simulate light scattering by many spherical particles. Aiming at high computational performance, CELES leverages block-diagonal preconditioning, a lookup-table approach to evaluate costly functions and massively parallel execution on NVIDIA graphics processing units using the CUDA computing platform. The combination of these techniques allows to efficiently address large electrodynamic problems (>104 scatterers) on inexpensive consumer hardware. In this paper, we validate near- and far-field distributions against the well-established multi-sphere T-matrix (MSTM) code and discuss the convergence behavior for ensembles of different sizes, including an exemplary system comprising 105 particles.

/pdf/celes-cuda-accelerated-simulation-of-electromagnetic-1uoqnndxkh.pdf

CELES: CUDA-accelerated simulation of electromagnetic scattering by large ensembles of spheres

This Essay traces the centuries-long history of the phenomenological disciplines of directional radiometry and radiative transfer in turbid media, discusses their fundamental weaknesses, and outlines the convoluted process of their conversion into legitimate branches of physical optics.

/pdf/directional-radiometry-and-radiative-transfer-the-convoluted-52jo23n13g.pdf

Directional radiometry and radiative transfer: The convoluted path from centuries-old phenomenology to physical optics

We report the results of high-accuracy controlled laboratory measurements of the Stokes reflection matrix for suspensions of submicrometer-sized latex particles in water and compare them with the results of a numerically exact computer solution of the vector radiative transfer equation (VRTE). The quantitative performance of the VRTE is monitored by increasing the volume packing density of the latex particles from 2% to 10%. Our results indicate that the VRTE can be applied safely to random particulate media with packing densities up to ∼2%. VRTE results for packing densities of the order of 5% should be taken with caution, whereas the polarized bidirectional reflectivity of suspensions with larger packing densities cannot be accurately predicted. We demonstrate that a simple modification of the phase matrix entering the VRTE based on the so-called static structure factor can be a promising remedy that deserves further examination.

/pdf/radiative-transfer-theory-verified-by-controlled-laboratory-2yniqdpy2m.pdf

Radiative transfer theory verified by controlled laboratory experiments

A method and system for determining a new orientation and/or position of an object comprises a sky polarimeter configured to record image data of the sky. a signal processing unit, and logic configured to receive and store in memory the image data received from the sky polarimeter. The logic calculates the Stokes parameters (SO, S1, S2,), DoLP, and AoP from the image data, detects obscurants and filters the obscurants (such as clouds and trees) from the image data to produce a filtered image. The logic is further configured to find the Sun and zenith in the filtered image, and to determine the roll, pitch, yaw, latitude and longitude of the object using the filtered image.

Sky Polarization and Sun Sensor System and Method

Development of reliable imaging polarimeters and the models that predict their performance is dependent on the ability to assess their accuracy. Field tests frequently result in contradictory data and laboratory measurements are often not representative of materials in the field. To address these concerns, we have built a device with which the calibration of imaging polarimeters (both stationary and moving) can be verified and the polarimetric properties of materials in the field can be measured with accuracy. The device is a handheld, non-imaging polarimeter that is capable of highly calibrated phenomenology measurements in both the lab and field. Multiple optical heads enable monitoring of samples from a variety of angles in order to characterize polarimetric signatures as a function of source, sample, and sensor geometry. The device may also be used in unattended diurnal monitoring of polarimetric signatures of the sky, backgrounds, and targets of interest, providing a correlation between observed polarization phenomenology and weather conditions. The handheld device and the associated data acquisition system is small and portable enough that it can be taken to the field readily and is simple enough that calibration and system performance is predictable and verifiable. In this paper, we describe the design and performance of the non-imaging handheld polarimeter, performance specifications, and measurement results to date.

Handheld Polarimeter for Phenomenology Studies

Polarization data of a SM gyroscope coil may correlate to drift that provides a method to statically predict a performance range of a coil during manufacturing or at a minimum before integration into a FOG assembly. The Crossover Free (CF) coils described here are thermally symmetric and lack fiber crossovers. This design allows possible expansion of depolarized FOGs beyond the research environment. To that end a series of double sided CF gyroscope coils were manufactured and analyzed using a 4 channel fiber coupled polarimeter. In addition the coils were tested on a single axis rate table in a FOG testbed. A polarimeter was used to measure the output polarization state of the stand-alone coils and when integrated into an experimental FOG testbed. In addition Shupe data of the CF coils was taken to determine the thermal sensitivity of the coils. Coil geometry and construction, polarimetric and traditional drift data, and Shupe performance will be presented.

Polarization and drift analysis of thermally symmetric double sided crossover free SM fiber coils

We describe the design, construction, calibration, and validation of a Stokes vector polarimeter for investigating the polarization characteristics of fiber optic gyroscope coils. The device measures the complete Stokes vector, and reports conventional polarization properties including the Degree of Polarization (DoP), the orientation and Degree of Linear Polarization (DoLP), and the handedness and Degree of Circular Polarization (DoCP). The sensor operates at 1550 nm and employs a division of aperture optical architecture to acquire full Stokes vectors at 8 kHz while calculating polarization properties at a rate of 200 Hz. Preliminary measurements performed on both traditionally and unconventionally wound gyroscope coils are also presented.

Arthur Lompado

Papers

Radiative transfer theory verified by controlled laboratory experiments

Sky Polarization and Sun Sensor System and Method

Handheld Polarimeter for Phenomenology Studies

Polarization and drift analysis of thermally symmetric double sided crossover free SM fiber coils

Full Stokes polarimeter for characterization of fiber optic gyroscope coils