The sixteen elements of the Mueller matrix are associated with sixteen degrees of freedom, seven nonpolarizing, and nine depolarizing degrees of freedom. Combinations of polarization elements are associated with all the degrees of freedom demonstrating that physically realizable polarization elements span all sixteen degrees. Two alternative polarization basis states are introduced.

This paper deals with the depolarization properties of rough surface back-scattering at visible and infra-red wavelengths. It is well known that rough surfaces depolarize incident light. In this paper we analyze the structure of surface depolarization using a coherency matrix approach and show that quantitative estimates of roughness may be obtained from a single Mueller matrix parameter, the scattering anisotropy A. Multi-spectral backscatter Mueller matrix data has been obtained for a set of controlled laboratory measurements on roughened Aluminum surfaces. The surfaces were manufactured using a bead-blasting process and the surface statistics have been carefully measured. We then applied a technique first developed for applications in radar scattering, which involves transformation of the Mueller matrix into a complex hermitian coherency matrix with subsequent eigenanalysis. These eigenvalues are then used to characterize the depolarizing properties of the surface. We show how important surface information is contained in the eigenvalue variation with angle of incidence and conclude as to the possibility for quantitative surface roughness measurements using this technique.

We describe efficient beam splitters for the equi-partition of infrared input power using combined reflection and transmission by a strip-coated all-dielectric slab. Because no metal coating is used, high efficiency is achieved. The beam splitters use a fused silica parallel-slab that is strip coated with germanium on the front and back sides. Specific designs for operation at 1.55, 2.02 and 5.0 µm wavelengths are presented.

External-reflection phase retarders with high reflectance have been of interest for many years. 1-7 By selecting the angle of incidence, film thickness, and refractive indices of both the film and metallic substrate, the p- and s-polarized components of incident monochromatic light can be reflected equally and with a specified differential reflection phase shift introduced beween them. In general, these studies involved isotropic films. Azzam and Perilloux1 discussed the constraint on the optical constants of a film-substrate system such that it functions as a quarter-wave retarder (QWR) or half-wave retarder (HWR) at incidence angles of 70° and 45°, respectively.

There are presented results of theoretical investigation of self-depolarization effect resulting in variation of space distribution of polarization-ellipse parameters of high-power focused laser beam. In particular, both linear and circular initial polarizations are shown to change and turn into elliptic polarization with inhomogeneous distribution of polarization-ellipse parameters in focal area. Detailed results and calculations are presented for particular case of Gaussian beams of low order (TE00, TE0i, TEi0 and TEn). Bearing in mind obtained results, we discuss specific symmetry structure of self-depolarization effect allowing experimental checking of described phenomenon. Possibility of observing polarization dependence for damage and self-focusing thresholds in transparent materials is also considered.

The Liquid Crystal based Stokes Polarimeter (LCSP) was developed for high resolution full Stokes spectropolarimetry of solar vector magnetic fields. A prototype version was operated at the Gregory Coud? Telescope (GCT) at the Observatorio del Teide (Tenerife). The low voltage polarimeter consists of two nematic crystal variable retarders in front of a polarizing beam splitter. The voltage tunable variable retardance of the crystals is used for the in situ compensation of cross-talk inside the polarimeter. Other parts of instrumental polarization are removed by a method using the full spectral information contained in the observed Stokes profiles.

Accurately calibrating an infrared polarimeter presents several challenges. Some of these challenges include characterization of the polarization elements within the polarimeter, overcoming the effects of thermal emissions within the polarimeter, and developing a test setup and procedure for conclusively verifying the instrument calibration. We describe our efforts to absolutely calibrate our imaging Stokes polarimeter that operates in the mid-wave infrared band (3 to 5 microns). We have developed a generator that provides well-controlled polarization states for calibrating the polarimeter. This generator overcomes problems associated with thermal emissions, stray reflections, and narcissus effects. While the polarization state emitted by the generator is not known with extreme accuracy, we are able to rotate the generated state without affecting its degree of polarization or ellipticity. We show that we can create a complete set of input states to allow a full calibration of the polarimeter, and we describe a technique for optimizing the calibration based on a variance-minimization. Results of our calibration are presented, indicating that our polarimeter precision is better than 0.1%. This technique is not limited to infrared polarimeters and should therefore have broad applicability.

The relationship between system condition and SNR in reconstructed Stokes parameter images is investigated for rotating compensator, variable retardance, and rotating analyzer Stokes vector polarimeters. A variety of optimal configurations are presented for each class of systems. The operation of polarimeters is discussed in terms of a 4-dimensional vector space, and the concept of non-orthogonal bases, frames, and tight frames are introduced to describe this class of devices. While SNR is an important consideration, performance of a polarimeter in the presence of systematic error is also important. Here, the relationship between system condition and error performance is investigated, and it is shown that an optimum system from the point of view of SNR is not always an optimum system with respect to error performance. Finally, the concepts used to optimize Stokes vector polarimeters are extended to be useful for full Mueller matrix polarimeters.

Figures of merit for optimization of a complete Stokes polarimeter based on its measurement matrix are described which are not limited in their application to cases in which four measurements are used in the determination of a single Stokes vector. Singular value decomposition and probability theory are used to investigate the behavior and significance of these figures of merit. Their use to optimize a system consisting of a rotatable retarder and fixed polarizer indicates that a retardance of 132° (approximately three-eighths wave) and retarder orientation angles of ±51.7° and ±15.1° are favorable when four measurements are used. The performance of this system is demonstrated with experimental data.

We have investigated the degree of polarization (DOP) of infrared radiation reflected from rough white and black materials. Mueller matrices for these materials have been measured with an out-of-plane scatterometer with full polarization optics. We have compared the Mueller matrix data to the microfacet model. These results may have applications for stray light coatings for imaging polarimetric instruments.

The incorporation of polarisation sensitive optics offers considerable potential for improving the utility of remote sensing imaging systems operating within the visible or infrared wavebands. Systems now exist allowing measurement of the four components of Stokes vector arising from each pixel in the image. In order to develop the interpretation of polarimetric images, knowledge is required of the polarised directional reflectance properties of the materials in the scene, which determine the radiation reaching the sensor. Natural vegetation forms a significant element of many scenes observed with remote sensing systems. Although the size of a leaf may be below the spatial resolution of a system, the reflectance properties of individual leaves will affect the polarimetric data observed. This paper will report the results of measurements of the linear polarised bidirectional reflectance distribution function (BRDF) from two examples of leaves. The polarimetric properties of the directional reflectance from an individual leaf will depend on the surface and volume scattering properties. We report data on two leaves representing extreme cases of the leaf structure. Laurel (prunus laurecatious) has a nacreous surface creating a gloss finish to the leaf. Mullein (verbascum thapsus) has a highly pubescent surface, creating a highly diffuse surface reflectance. Measurements of the linear polarisation BRDF are reported at 632.8nm, 1064nm, 3.39pm and 10.6µm as a function of the polar scatter angles. These wavelengths characterise the polarised reflectance from the leaves under different conditions of absorption and scattering. In both cases the body of the leaf acts a highly diffuse reflector through multiple scattering, but this mechanism is only important when the absorption by the leaf constituents is low. In the spectral regions of moderate and high absorption the surface reflectance dominates. In the case of laurel the surface is relatively smooth, with an associated Brewster angle, whereas the data suggests the layer of hair covering a mullein leaf acts as an array of scattering sources.

Measurements of circular dichroism (CD) in the UV and vacuum UV have used photoelastic modulators (PEMs) for high sensitivity (to about 10-6). While a simple technique for wavelength calibration of the PEMs has been used with good results, several features of these calibration curves have not been understood. The authors have calibrated a calcium fluoride PEM and a lithium fluoride PEM using the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory as a light source. These experiments showed calibration graphs that are linear but do not pass through the graph origin. A second “multiple pass” experiment with laser light of a single wavelength, performed on the calcium fluoride PEM, demonstrates the linearity of the PEM electronics. This implies that the calibration behavior results from intrinsic physical properties of the PEM optical element material. An algorithm for generating calibration curves for calcium fluoride and lithium fluoride PEMs has been developed. The calibration curves for circular dichroism measurement for the two PEMs investigated in this study are given as examples.

A limited polarimetric characterization of paint samples on aluminum substrates is presented. Twelve painted aluminum panels, representing various colors, reflectances, and surface finishes, were examined in a spectropolarimetric reflectometer. Data were analyzed in detail for the 0.9 to 1.0 micrometer wavelength region, although data were taken over a wider spectral range. Polarizance was measured for the twelve samples at eight input beam incidence angles. All observations were made from normal to the sample. Characterization of the surface roughness of the samples was done using profilometers. It was found that as the incidence beam angle increases, the polarizance increases; and as the reflectance of the sample decreases, the polarizance increases.

In recent years there has been an increasing interest in optical imaging through scattering media, including through body tissue, battlefield smoke, fog, rain, and mist, and muddy water. When an image is formed of an object embedded in a scattering medium, the image is comprised of the superposition of a sharp image plus a diffuse background. The light that propagates the shortest distance between the object and image plane forms the sharp image. The diffuse image is the result of the scattered light taking a random path between the object and image. In order to observe the sharp image formed by the weakly scattered light, the diffuse background must be removed from the image. Polarization based discrimination between weakly scattered and scattered light is based on the fact that weakly scattered light retains its incident polarization state whereas diffuse scattered light carries a random polarization state. In this paper, we will describe a polarimetric sensor and laboratory setup for imaging through scattering media. We will report the results from the laboratory measurements demonstrating imaging through several types of scattering media. Finally, we will discuss application of this technique to medical imaging, imaging through battlefield obscurants, and wireless communications.

The paper covers an issue of method and device for measurement of two-dimensional retardance with high-order and azimuthal direction. The system based on the use of a crossed polarizer by changing spectroscopic polarized light. Sixty-four sets of images are used for birefringence analysis. The spectroscopic interferogram change sinusoidal with wave number and the period is in proportion to birefringence of specimen. The measured results of the two dimensional birefringence distribution of a plastic and standard phase plate of retardation are shown. Fourier transform method and maximum entropy method enable to measure birefringence with high resolution. Two examples, measurement of aligned polymer film, which is laminated as steps, and that of birefringence distribution, are demonstrated.

The high-accuracy universal polarimeter (HAUP) uses a technique (HAUP method) for simultaneous measurement of optical anisotropy (birefringence, optical activity, rotation of optical indicatrix, dichroism, electro-optic coefficients,...) of crystals. The HAUP method has been applied to determining linear birefringence and optical activity of Quartz as a function of temperature in the range 25-300 °C at 632.8 nm of wavelenght. The measurements are affected by modulation in the fitted parameters of HAUP method and optical properties when the sample temperature is changed. This effect can be explained by the multiple reflections within the slab that give rise to a temperature-dependent interference pattern. The same effect has been observed in Lithium Niobate and Calcite samples of great plane-parallelism. Good agreement was found between our experimental values and the HAUP method equations in the presence of multiple reflections.

The problem of determination of main demands to which modem Mueller-polarimeter has to correspond have been widely addressed in polarimetric literature existed now. However, at our opinion there exists one more conceptual demand to which modem Mueller-polarimeter has to correspond and that of has not been addressed in polarimetric literature yet. This is the developed functional elasticity of polarimeter. This means that the modem Mueller-polarimeter must have the possibility to realize the various approaches to the Mueller matrix measurement (say, fully dynamic, four, three and two probating polarization) and some other functions, in particular, the producing of any needed state of polarization (whole Poincare sphere in general) of probating radiation. It is greatly important to note that all above functions the polarimeter have to realize only by correspondent software. In the paper the analysis and optimization of automatic Mueller-polarimeter utilizing general- purpose controlled polarization transformer based on electro-optical effect in probing channel and that of meets the requirement determined above is presented.

Focal plane wideband infrared digital polarization imagery will be compared with visual wideband focal plane digital imagery of a camouflaged C-130 aircraft to show the extreme enhancement possible using digital imagery. The experimental observations will be compared with theoretical calculations and modeling results of both specular and shadowed areas. The relationship of both the specular and the shadowed areas to surface structure, orientation, specularity, roughness, shadowing, orientation and complex index of refraction will be illustrated. The imagery was obtained in four plane polarized directions with axes oriented vertically, horizontally and at plus and minus 45 degrees to the vertical. Nine locations on the aircraft were chosen (tail, fuselage, wing and propeller as well as five sky locations to establish sky background. Both sunlit and shadowed locations were examined. The direction of the dominant plane of polarization was obtained, but not the existence of circular polarization, which requires a quarter wave plate to resolve temporal coherence. Unpolarized radiation exists in the imagery,but its coherence is not evident without a phase resolving element.

Digital cameras can be used as imaging polarimeters, as previously reported. Comparisons of the radiometric characteristics of three-band digital cameras with eight- and ten- bit radiometric precision, which we have used as imaging polarimeters are made. We also discuss preliminary calibrations on a hyperspectral imaging polarimeter based upon a 16-bit camera and an LCD tunable filter. Examples are shown to illustrate the camera radiometric characteristics and the types of calibration procedure needed for imaging polarimetry in natural and in artificial light. Procedures using primary and secondary calibration standards are discussed. The impacts of radiometric fall-off with increasing field angle and band-dependent and intensity-dependent asymmetries experienced with the hyperspectral polarimeter are discussed. We present some examples of the detail afforded in artificial illumination by cameras offering 8-bit and 12-bit radiometric depth. The importance of multiband polarimetric images, which has been stressed before is again demonstrated for artificially illuminated scenarios.

In this study, we try to improve the understanding of the polarization of the signal reflected by the water body for which an accurate knowledge is necessary in remote-sensing applications. We only detail the Opol factor defined as the ratio between the vertically polarized to the total (unpolarized) marine reflectance. In the validation plans of many ocean color sensors, some above-water measurements of the diffuse marine reflectance, such as the SIMBAD measurements, use polarized observation of the sea which reduce the skylight reflection effects. Consequently, to access the marine reflectance, a correction by the Opol factor is made and for which an accuracy better than 2% is required. Another goal is to better consider polarization in the computation of the Top of the Atmosphere signal in the absolute calibration of satellite sensors over Rayleigh scattering (POLDER for instance). Measurements were collected for various conditions by REFPOL and SIMBAD radiometers. The results were confronted to computations performed using two different transfer radiative codes, a Monte-Carlo code and a Successive Order of Scattering code. The radiative transfer into the sea is computed considering the water index, the concentration and polarized phase function for the phytoplankton. As the upwelling signal observed just above the sea surface depends strongly to the radiance downwelling onto the sea surface, the presence of molecules and aerosol in the atmosphere which induce a polarized signature, have to be considered.

Previous infrared polarization imaging research has shown manmade objects to be sources of emitted and reflected polarized radiation while natural backgrounds are predominantly unpolarized. The prior work underscored the dramatic improvements in signal to clutter ratio that could be achieved in a typical target acquisition scenario using polarization sensing techniques. Initial investigations into the polarization signatures of surface scattered mines have also shown polarization techniques are able to provide strong cues to mine presence. The US Army Night Vision and Electronics Sensors Directorate has developed complete Stokes imaging polarimeters in the midwave infrared (MWIR, 3-5 µm)1,2, the short wave infrared (SWIR, 1-2 µm) and the visible wavebands in order to investigate polarization phenomenology and to quantify expected improvements to target acquisition and mine detection. This paper will review the designs of the polarization cameras and will summarize efforts to calibrate them. An example phenomenology study of MWIR polarization from surface scattered landmines will be presented.

The Space Dynamics Laboratory at Utah State University has built and flown an airborne infrared Hyperspectral Imaging Polarimeter (HIP) as a proof-of-principle sensor for a satellite-based polarimeter. This paper briefly reviews the instrument design that was presented in previous SPIE papers1,2, details the changes and improvements made between the 1998 and 1999 measurements, and presents measurement data from the flights. Measurement data from a series of flights in 1998 indicated the need for wider-band measurements than could be made with our ferroelectric liquid crystal polarimeter design. For this reason, the existing sensor was modified to use a rotating wire-grid polarization filter. The reasons for this choice, equipment design, and measurement equations will be given. A short description of the 1999 flights aboard FISTA3 (Flying Infrared Signatures Technology Aircraft), an Air Force KC-135 based at Edwards Air Force Base will be given, as well as a small sample of the four-dimensional data set will be presented.

The Space Dynamics Laboratory at Utah State University (SDL/USU) has built and flown an airborne hyperspectral imaging polarimeter (HIP)1,2 as a proof-of-principle sensor for a satellite-based polarimeter. This paper discusses measurement limitations and uncertainties associated with imaging polarimetric measurements in remote sensing applications, using experience and lessons learned from the HIP program and the design study for the proposed satellite demonstration sensor.

The visual detection of vehicles and personnel depend upon a number of factors: reflected/emitted color (photometry) contrast (spectral resolution), shapes and motion. Optical polarization has not been used although its relative radar has been readily been accepted and applied. There are clear analogs between radar optics and light optics.

There is evidence that polarimetric as well as intensity contrast differences in images are band-dependent. Some previous evidence is reviewed. We are currently fabricating and testing a hyperspectral imaging polarimeter to assess and to take advantage of subtle spectral detail in hyperspectral polarimetric images. This device uses a tunable liquid crystal filter and a 16-bit camera. New and varied calibration challenges have occurred and are discussed. We consider it important to present the problems as well as the successes.

The emitted polarization signature of materials is of interest for use in discriminating targets from cluttered backgrounds. In addition, spectrally varying polarization signatures might be used for material identification or to separate target and environment radiance contributions. A spectrally filtered LWIR Imaging Polarimeter (LIP) has been constructed and used in the lab and in the field to make signature measurements of controlled targets. In addition, a full-stokes FTIR Polarization Spectrometer (FSP) has been constructed for higher spectral resolution measurements of materials. This paper will discuss the instruments, calibration methods, general operation, and results characterizing the emitted polarization properties of materials as a function of wavelength.

In this paper we propose a new polarimetric formalism - Doppler polarimetry that includes the conventional polari- metric radar target description as a special case. Using this new formalism the problem of staggered polarimetric measurements is solved. Then it is shown how polarimetric basis transformation can influence the spectral properties of radar targets. Doppler polarimetry is applied for ground clutter suppression in atmospheric remote sensing. Two new clutter suppression techniques are illustrated using radar measurements of precipitation and ground clutter. The first ground suppression method uses co-polar correlation to reduce ground clutter reflections and increase the contrast between ground clutter and atmospheric signals. And the second technique is used to reduce the width of the ground clutter and thus to optimize the known Doppler clutter suppression technique.

We are applying a novel LWIR (long-wavelength infrared: 8-12 micrometers) hyperspectral polarimetric imager to geophysical ocean surface sensing. The sensor is an embodiment of an invention by Aerodyne Research known as P-SIM (for Polarimetric Spectral Intensity Modulation). The design enables instantaneous ”snapshot” spectropolarimetric imaging with perfect channel registration and full elliptical polarimetry. The optical polarimetry enables retrieval of the phenomenologically rich capillary wave structure morphology (roughness). The spectrally resolved polarimetry additionally allows disambiguation of downwelling from emitted components. Such data supports improved retrievals of sea surface temperature, emissivity, and surface wind vector. We discuss the sensor design, and the analytic means for the geophysical retrievals.

The infrared monochromatic image of corona was reported in 1975. The Solar Infrared electric field observing and researching was proposed in 1986 and infrared solar magnetic field observing was suggested in 1987. These observing data describes various states of solar atmosphere. To varying degrees, compared with traditional system, near infrared system have its special characteristics. In this paper, we present a vacuum solar telescope with a near-infrared (at 8438 angstrom ~ 10830 angstrom) filter system which is designed to measure the solar electric field and monochromatic image in Huairou workstation of Beijing Astronomical Observatory (BAO). The vacuum optical telescope will be consist of a primary mirror in 35cm Diameter, a Gregorian mirror, two vacuum windows, a collimating lens and an imagine lens. The filter with polarizing analyzer will be consist of two pre-filters, one liquid crystal analyzers, a universal birefringent filter which spectral range is in 8000 angstrom ~ 11000 angstrom and pass-band 0.25 angstrom at 10830 angstrom. The birefringent filter and the optical system of the telescope are described in details. We expect to achieve an electric field observing system, two-dimensional monochromatic image observational system of corona. It also can be turned across the spectral line to obtain line profiles of two-dimensional of the field.

To derive the polarization characteristics of a remotely sensed object, a time-sequential polarimeter must create multiple polarization response states during the course of each measurement set. A common method of creating these states is to rotate a polarizer element to a discrete location and hold that position while the detectors integrate and are sampled. The polarizer element is then rotated to the next position and the process is repeated. This time-sequential, advance-and-hold technique is widely used and easily understood because of its simplicity. However, it is not well suited for remote sensing applications where time delays caused by the advance-and-hold mechanism can limit measurement speed and reduce measurement accuracy. This paper introduces a continuously spinning polarizer (CSP) technique that eliminates the time delays and associated problems of an advance-and-hold polarimeter. A performance model for a linear Stokes polarimeter containing a CSP is derived, and a demonstration of the CSP technique based on the performance of the hyper-spectral imaging polarimeter (HIP) is presented.

Polarimetric remote sensing dates back to the early 1900s, when French astronomers Lyot and Dollfus used it in astronomical observations of the planets. They realized that with its unique properties, polarization could accomplish what photometry alone could not, as well as supplementing photometric observations of the planets.