An objective analysis is carried out of the matricial models representing the polarimetric properties of light and material media leading to the identification and definition of their corresponding physical quantities, using the concept of the coherency matrix. For light, cases of homogeneous and inhomogeneous wavefront are analyzed, and a model for 3D polarimetric purity is constructed. For linear passive material media, a general model is developed on the basis that any physically realizable linear transformation of Stokes vectors is equivalent to an ensemble average of passive, deterministic nondepolarizing transformations. Through this framework, the relevant physical quantities, including indices of polarimetric purity, are identified and decoupled. Some decompositions of the whole system into a set of well-defined components are considered, as well as techniques for isolating the unknown components by means of new procedures for subtracting coherency matrices. These results and methods constitute a powerful tool for analyzing and exploiting experimental and industrial polarimetry. Some particular application examples are indicated.

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Polarimetric characterization of light and media - Physical quantities involved in polarimetric phenomena

Chlorophyll fluorescence techniques are used widely in both laboratory and field studies to assess the abundance and physiological responses of cyanobacteria, microalgae, macroalgae and vascular plants, as described in other chapters in this volume. Most of the instruments used in these studies excite fluorescence in the blue region of the spectrum and measure chlorophyll fluorescence (peak ca. 685 nm) at ambient temperature. Fluorescence is generally detected using a photomultiplier tube (PMT), which is very sensitive to intensity but insensitive to spectral quality. Cross-talk between the light source used to excite fluorescence and the detector is prevented by the use of cut-off filters on both the emitter and the PMT, or by the use of emitters with narrow wavebands, such as light-emitting diodes (LEDs) or lasers, and a long-pass filter on the detector. With the advent of LEDs, which have a very high efficiency (intensity of light output per unit power input) compared to the xenon flash-lamps used in many older instruments, commercially-available fluorometers can have very low power demands and be both small and sensitive (detection limits are typically <1 mg m−3 of Chla). This makes them ideal for unattended monitoring such as on platforms, moorings or gliders.

Taxonomic Discrimination of Phytoplankton by Spectral Fluorescence

We consider target detection in images perturbed with additive noise. We determine the conditions in which polarimetric imaging, which consists of analyzing of the polarization of the light scattered by the scene before forming the image, yields better performance than classical intensity imaging. These results give important information to assess the interest of polarimetric imaging in a given application.

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When is polarimetric imaging preferable to intensity imaging for target detection

Further to the irradiation of pig with cobalt, the polarimetric properties of skin samples were experimentally investigated, and the Mueller matrices were measured at different wavelengths. Whatever the studied sample, both increase of irradiation rate and reduction of wavelengths decreased the depolarization. Finally, we demonstrate that, 70 days after irradiation, polarization measurements allow one to distinguish a healthy pig skin sample from a 15 Gy- or 20 Gy-irradiated one.

Analysis of the depolarizing properties of irradiated pig skin

We consider active polarimetric imaging systems that illuminate a scene with an incident polarization state and project the backscattered light on another polarization state in order to produce a scalar intensity image. We present and analyze a method for determining the configuration of illumination and analysis polarization states that maximizes the observed contrast between a target and the background when the scene is partially depolarizing and in the presence of additive Gaussian detection noise.

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Optimization of the contrast in polarimetric scalar images.

The possibility of correctly detecting immersed targets with a lidar through the air-water interface is discussed in this paper. The water surface roughness, in relation with wind direction, greatly disturbs light dispersion. Nevertheless, a detection of immersed targets is always possible. This paper reports on an attempt to improve the quality of detection. It was carried out by a polarimetric coding of optical signals based upon the Stokes-Mueller polarimetric formalism, and by choosing a special orientation for the transceiver.

http://iopscience.iop.org/article/10.1088/0963-9659/7/6/011/pdf

Polarimetric considerations to optimize lidar detection of immersed targets

Up to now, no technique was available to perform inventories and surveys of immersed macroalgae. This article presents a method making it possible to discriminate between macroalgae and seafloor and to identify the various macroalgae groups (green, brown or red). To our knowledge, this is the first excitation-emission matrix (EEM) of macroalgae ever carried out allowing the identification of the spectral characteristics of each macroalgae group. Fluorescence imaging provides the spatial dimension besides spectral properties. An optical parametric oscillator (OPO) laser excites a test scene of macroalgae in a seawater aquarium. Laser-induced fluorescence images from 400 to 640 nm displayed by steps of 10 nm are filtered at 680 nm. Their analysis, combined with the water depth parameter, leads to an identification method for macroalgae groups in a false-colour image: each of the three macroalgae groups is enhanced by one defined threshold on this false-colour image.

http://iopscience.iop.org/article/10.1088/0022-3727/34/16/324/pdf

Laser induced fluorescence imaging: application to groups of macroalgae identification

Up to now, no technique was available to perform inventories and surveys of immersed macroalgae. This article presents a method making it possible to discriminate between macroalgae and sea-floor and to identify the various macroalgae groups. To our knowledge, this is the first EEM of macroalgae ever carried out allowing the identification of the spectral characteristics of each macroalgae group. Fluorescence imaging provides the spatial dimension besides spectral properties. An OPO laser excites a test scene of macroalgae in a sea-water aquarium. Laser-induced fluorescence images from 400 nm to 640 nm displayed by steps of 10 nm are filtered at 680 nm. Their analysis, combined to the water depth parameter, leads to an identification method for macroalgae groups in a false-color image: each of the three macroalgae groups is enhanced by one defined threshold on this false-color image.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Laser-induced fluorescence imaging: application to groups of macroalgae identification

This paper presents an adaptive polarimetric filtering method to optimize target scattering behaviour in laser imagery Knowledge of a target's Mueller matrix permits one to calculate its polarization signature Analysing this signature outlines some particular states of polarization These states are directly related to the scattering properties of the given target Using these optimum polarizations for transmission and reception either enhances or removes the associated scattering behaviour

C Kieleck

Papers

Polarimetric considerations to optimize lidar detection of immersed targets

Laser induced fluorescence imaging: application to groups of macroalgae identification

Laser-induced fluorescence imaging: application to groups of macroalgae identification

Adaptive polarimetric filtering: application to laser imagery