Polarimetric Calibration and Characterization of the Telops Field Portable Polarimetric-Hyperspectral Imager

The Telops polarimetric-hyperspectral imager combines polarimetric and hyperspectral technologies to enable enhanced scene characterization. The Defense Threat Reduction Agency funded research at AFIT to leverage this capability to provide more accurate scene information to radiation transport models that will allow for more effective location of radiation sources within a region of interest. To support the objectives of the DTRA effort, there is a requirement for highly accurate radiometric, polarimetric, and spectral data on a pixel-by-pixel basis. The complex nature of the Telops instrument combined with working in the thermal IR waveband makes achieving this accuracy a challenge. This thesis develops a calibration methodology that enables high data accuracy in all three domains. In the process, a mathematical calibration framework was developed that links standard Fourier transform spectrometer (FTS) calibration with standard polarimetric calibration in a straightforward manner. This provided a framework for understanding the influence of various instrument parameters (both ideal and non-ideal) on ultimate calibration performance. The framework developed is utilized to quantify the non-idealities of the system and to characterize the performance of the spectro-polarimetric calibration. Additionally, fundamental performance limits are characterized including the noise equivalent spectral radiance and noise equivalent degree of linear polarization of the system

Exploration of a Polarized Surface Bidirectional Reflectance Model Using the Ground-Based Multiangle Spectropolarimetric Imager

Accurate characterization of surface reflection is essential for retrieval of aerosols using downward-looking remote sensors. In this paper, observations from the Ground-based Multiangle SpectroPolarimetric Imager (GroundMSPI) are used to evaluate a surface polarized bidirectional reflectance distribution function (PBRDF) model. GroundMSPI is an eight-band spectropolarimetric camera mounted on a rotating gimbal to acquire pushbroom imagery of outdoor landscapes. The camera uses a very accurate photoelastic-modulator-based polarimetric imaging technique to acquire Stokes vector measurements in three of the instrument's bands (470, 660, and 865 nm). A description of the instrument is presented, and observations of selected targets within a scene acquired on 6 January 2010 are analyzed. Data collected during the course of the day as the Sun moved across the sky provided a range of illumination geometries that facilitated evaluation of the surface model, which is comprised of a volumetric reflection term represented by the modified Rahman-Pinty-Verstraete function plus a specular reflection term generated by a randomly oriented array of Fresnel-reflecting microfacets. While the model is fairly successful in predicting the polarized reflection from two grass targets in the scene, it does a poorer job for two manmade targets (a parking lot and a truck roof), possibly due to their greater degree of geometric organization. Several empirical adjustments to the model are explored and lead to improved fits to the data. For all targets, the data support the notion of spectral invariance in the angular shape of the unpolarized and polarized surface reflection. As noted by others, this behavior provides valuable constraints on the aerosol retrieval problem, and highlights the importance of multiangle observations.NASAJPLCenter for Space Researc

Intercomparison of Airborne Multi-Angle Polarimeter Observations from the Polarimeter Definition Experiment (PODEX)

In early 2013, three airborne polarimeters were flown on the high altitude NASA ER-2 aircraft in California for the Polarimeter Definition Experiment (PODEX). PODEX supported the pre-formulation NASA Aerosol-Cloud-Ecosystem (ACE) mission, which calls for an imaging polarimeter in polar orbit (among other instruments) for the remote sensing of aerosols, oceans and clouds. Several polarimeter concepts exist as airborne prototypes, some of which were deployed during PODEX as a capabilities test. Two of those instruments to date have successfully produced Level 1 (georegistered, calibrated radiance and polarization) data from that campaign: the Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) and the Research Scanning Polarimeter (RSP). We compared georegistered observations of a variety of scene types by these instruments to test if Level 1 products agree within stated uncertainties. Initial comparisons found radiometric agreement, but polarimetric biases beyond measurement uncertainties. After subsequent updates to calibration, georegistration, and the measurement uncertainty models, observations from the instruments now largely agree within stated uncertainties. However, the 470nm reflectance channels have a roughly +6% bias of AirMSPI relative to RSP, beyond expected measurement uncertainties. We also find that observations of dark (ocean) scenes, where polarimetric uncertainty is expected to be largest, do not agree within stated polarimetric uncertainties. Otherwise, AirMSPI and RSP observations are consistent within measurement uncertainty expectations, providing credibility for subsequent creation of Level 2 (geophysical product) data from these instruments, and comparison thereof. The techniques used in this work can also form a methodological basis for other intercomparisons, such as of the data gathered during the recent Aerosol Characterization from Polarimeter and Lidar (ACEPOL) field campaign, carried out in October and November of 2017 with four polarimeters (including AirMSPI and RSP)

Incorporation of Polarization Into the DIRSIG Synthetic Image Generation Model

The Digital Imaging and Remote Sensing Synthetic Image Generation (DIRSIG) model uses a quantitative first principles approach to generate synthetic hyperspectral imagery. This paper presents the methods used to add modeling of polarization phenomenology. The radiative transfer equations were modified to use Stokes vectors for the radiance values and Mueller matrices for the energy-matter interactions. The use of Stokes vectors enables a full polarimetric characterization of the illumination and sensor reaching radiances. The bi-directional reflectance distribution function (BRDF) module was rewritten and modularized to accommodate a variety of polarized and unpolarized BRDF models. Two new BRDF models based on Torrance- Sparrow and Beard-Maxwell were added to provide polarized BRDF estimations. The sensor polarization characteristics are modeled using Mueller matrix transformations on a per pixel basis. All polarized radiative transfer calculations are performed spectrally to preserve the hyperspectral capabilities of DIRSIG. Integration over sensor bandpasses is handled by the sensor module

Design and construction of a snapshot full-Stokes polarimetric camera : seeing through fog

Tesi amb menció internacionalA la portada: Centre for Sensors, Instruments and Systems Development (CD6-UPC). Faculty of Optics and Optometry of Terrassa (FOOT)(English) Polarization is one of the properties of light and it is often put aside. Human beings receive light beams and process only the intensity and wavelength information. Our optical system lacks the capability of ’seeing’ polarization in comparison to other animals. The vectorial nature of polarization is uncorrelated to the intensity and colour information and this can unveil additional information for improving the current technology. This Thesis aims to develop a camera capable of measuring the full polarization in a 2D scene. In particular, it focuses on the design and construction of a prototype that measures in the visible waveband the full-Stokes vector in a snapshot such that the acquisition time and noise equalization are balanced while reducing movement and registration artefacts. The Thesis starts with the revision of the current state of the art in the polarimetric imaging field. Based on this, the optomechanical design of the polarimetric camera is developed ensuring a faster acquisition of polarization since it integrates optimum states to immunize the system from Gaussian and Poisson noise. Accordingly, this Thesis proposes a general calibration methodology addressed to the radiometry of the sensor, the geometrical aberrations from optics and the polarization elements in the system to transform the intensity measurements into polarization information. Besides, this Thesis studies two imaging modes of polarization, Stokes imaging and Mueller matrix imaging, for different applications. The novelty of this system consists of the use of optimal polarization states in a division of aperture architecture for noise immunization. Finally, this Thesis studies the application of the system to improve detection in the real-world problem of seeing through the fog. Polarization information can improve the range of detection due to the polarization memory effect. This system could be employed inside a multimodal system to ensure detection when others are hampered due to external conditions.(Català) La polarització és una de les propietats de la llum i que sovint es prescindeix d’ella. Els éssers humans reben els raigs de llum i únicament processen la informació provinent de la intensitat i la longitud d’ona de la llum. El nostre sistema òptic no té la capacitat de "veure" la polarització en comparació a altres animals. La natura vectorial de la polarització està no correlada amb la informació donada per la intensitat i el color, i això pot revelar informació addicional per millorar la tecnologia actual. Aquesta Tesi té com a objectiu desenvolupar una càmera per mesurar la polarització d’una escena 2D. En particular, es centra en el disseny i construcció d’un prototip que mesuri a l’espectre visible el vector de Stokes complert en un sol tret de manera que el temps d’adquisició i la equalització del soroll siguin compensats a la vegada que es redueixen els artefactes causats pel moviment i pel registre. La Tesi comença revisant l’actual estat de l’art en el camp de la imatge polarimètrica. Arran d’això, es realitza el disseny optomecànic de la càmera polarimètrica garantint una adquisició ràpida, ja que el disseny implementa uns estats òptims de polarització per immunitzar el sistema de soroll gaussià i de Poisson. Per tant, aquesta Tesi proposa una metodologia general de calibratge dirigida a la radiometria del sensor, a les aberracions geomètriques de l’òptica i als elements de polarització en el sistema per transformar les mesures d’intensitat en informació polarimétrica. A més, aquesta Tesi estudia dos maneres d’imatge de la polarització, imatge de Stokes i imatge de la matriu de Mueller, per diferents aplicacions. La novetat d’aquest sistema radica en la utilització d’estats de polarització òptims basant-se en una arquitectura de divisió d’apertura per la immunització al soroll. Finalment, aquesta tesi estudia les aplicacions del sistema per millorar la detecció en un problema del món real com és veure a través de la boira. La informació de la polarització pot millorar el rang de detecció degut a l’efecte de memòria de la polarització. Aquest sistema, doncs, podria utilitzar-se dins d’un altre sistema multimodal per assegurar la detecció quan la resta de sistemes estiguin perjudicats per les condicions externes.(Español) La polarización es una de las propiedades de la luz y de la que a menudo se prescinde. Los seres humanos percibimos los rayos de luz y solo procesamos la información proveniente de la intensidad y de las longitudes de onda de la luz. Nuestro sistema óptico carece de la capacidad de "ver" la polarización en comparación con otros animales. La naturaleza vectorial de la polarización está no correlacionada con la información aportada por la intensidad y el color, y esto puede desvelar información adicional para mejorar la tecnología actual. Esta Tesis tiene como objetivo desarrollar una cámara para medir la polarización en una escena 2D. En particular, se centra en el diseño y construcción de un prototipo que mida en el espectro visible el vector de Stokes completo en un solo disparo de manera que el tiempo de adquisición y la ecualización del ruido estén compensados a la vez que se reduzcan los artefactos debidos al movimiento y al registro. La Tesis comienza revisando el actual estado del arte en el campo de imagen polarimétrica. A partir de esto, se realiza el diseño optomecánico de la cámara polarimétrica garantizando una adquisición rápida ya que el diseño implementa unos estados óptimos de polarización para inmunizar el sistema del ruido de gaussiano y de Poisson. Por consiguiente, esta Tesis propone una metodología general de calibración dirigida a la radiometría del sensor, a las aberraciones geométricas de la óptica y a los elementos de polarización en el sistema para transformar las medidas de intensidad en información polarimétrica. Además, esta Tesis estudia dos modos de imagen de la polarización, imagen de Stokes e imagen de la matriz de Mueller, para diferentes aplicaciones. La novedad de este sistema radica en la utilización de estados de polarización óptimos basándose en una arquitectura de división de apertura para la inmunización al ruido. Finalmente, esta Tesis estudia las aplicaciones del sistema para mejorar la detección en un problema del mundo real como es ver a través de la niebla. La información de la polarización puede mejorar el rango de detección debido al efecto de memoria de la polarización. Este sistema podría utilizarse dentro de un sistema multimodal para asegurar la detección cuando el resto de sistemas están perjudicados por las condiciones externas.DOCTORAT EN ENGINYERIA ÒPTICA (Pla 2013

A review of RFI mitigation techniques in microwave radiometry

Radio frequency interference (RFI) is a well-known problem in microwave radiometry (MWR). Any undesired signal overlapping the MWR protected frequency bands introduces a bias in the measurements, which can corrupt the retrieved geophysical parameters. This paper presents a literature review of RFI detection and mitigation techniques for microwave radiometry from space. The reviewed techniques are divided between real aperture and aperture synthesis. A discussion and assessment of the application of RFI mitigation techniques is presented for each type of radiometer.Peer ReviewedPostprint (published version

Estimating Index of Refraction from Polarimetric Hyperspectral Imaging Measurements

Current material identification techniques rely on estimating reflectivity or emissivity which vary with viewing angle. As off-nadir remote sensing platforms become increasingly prevalent, techniques robust to changing viewing geometries are desired. A technique leveraging polarimetric hyperspectral imaging (P-HSI), to estimate complex index of refraction, N̂(ν̃), an inherent material property, is presented. The imaginary component of N̂(ν̃) is modeled using a small number of “knot” points and interpolation at in-between frequencies ν̃. The real component is derived via the Kramers-Kronig relationship. P-HSI measurements of blackbody radiation scattered off of a smooth quartz window show that N̂(ν̃) can be retrieved to within 0.08 RMS error between 875 cm−1 ≤ ν̃ ≤ 1250 cm−1. P-HSI emission measurements of a heated smooth Pyrex beaker also enable successful N̂(ν̃) estimates, which are also invariant to object temperature