Vitalii S. Shamanaev

Laser Sensing of a Subsurface Oceanic Layer. II. Polarization Characteristics of Signals.

In Part I of this paper we calculated depth profiles and polarization characteristics of airborne lidar return signals by the Monte Carlo method. Here we calculate the polarization characteristics of lidar return signals for different types of water. We demonstrate the feasibility of polarization lidar application to the detection of underwater inhomogeneities of different origins. It is shown that simultaneous analysis of depth profiles of the lidar return signal power and signal depolarization ratio substantially increases the information content of airborne lidar sensing of seawater. We compare calculated results with the data of airborne lidar measurements for lambda = 0.53 mum.

Optik-É AN-30 Aircraft Laboratory for Studies of the Atmospheric Composition

AbstractThe scientific instrumental complex of the Optik-E AN-30 aircraft laboratory developed at the Institute of Atmospheric Optics of the Siberian Branch of the Russian Academy of Sciences is described in detail. Specifications of the main units of the instrumental complex are presented. Special attention is given to the metrological support of measurements of the atmospheric parameters. Experimental capabilities of the aircraft laboratory are illustrated by the results obtained in recent flights over various regions of the Russian Federation.

Laser sensing of a subsurface oceanic layer. I. Effect of the atmosphere and wind-driven sea waves.

Depth profiles and polarization characteristics of airborne lidar return signals have been calculated by the Monte Carlo method. We analyze some peculiarities of depth profiles of lidar return signals for a rough air-water interface. The distorting effect of the atmosphere on the lidar return signal structure is evaluated as a function of the geometry of the observations. Calculated results are compared with the data of airborne lidar measurements for lambda = 0.53 mum.

Airborne Laser Sensing of Scottish Coastal Waters

An Nd:YAG-based airborne lidar system has been used to measure the optical properties of littoral waters off the northwest Scottish coast. The small-scale structure of subsurface scattering layers was also investigated. Methods of solving the Lidar Sensing Equation in the single scattering approximation are described and the values of the derived extinction indices presented. The extinction index averaged over a series of five flights to the northeast of the Gulf Stream was k = 0.224 m -1 with a standard deviation of 0.212 m -1 . Further, it was demonstrated that, in coastal waters, optical inhomogeneities with dimensions between 50 m and 200 km obey the power law Sp k ~ k -P with the parameter P close to two. In turbid or transparent areas, the water extinction index can change by several tenths of a percent with respect to the surrounding water mass. This suggests that the observed nonmonotonic behavior of the power spectra of the water extinction index fluctuations is caused by the outer scale of turbu...An Nd:YAG-based airborne lidar system has been used to measure the optical properties of littoral waters off the northwest Scottish coast. The small-scale structure of subsurface scattering layers was also investigated. Methods of solving the Lidar Sensing Equation in the single scattering approximation are described and the values of the derived extinction indices presented. The extinction index averaged over a series of five flights to the northeast of the Gulf Stream was k = 0.224 m -1 with a standard deviation of 0.212 m -1 . Further, it was demonstrated that, in coastal waters, optical inhomogeneities with dimensions between 50 m and 200 km obey the power law Sp k ~ k -P with the parameter P close to two. In turbid or transparent areas, the water extinction index can change by several tenths of a percent with respect to the surrounding water mass. This suggests that the observed nonmonotonic behavior of the power spectra of the water extinction index fluctuations is caused by the outer scale of turbulence, in particular, by the bottom depth at the measurement site.

Influence of Air Bubbles in Seawater on the Formation of Lidar Returns

Abstract Air bubbles arising in water under the action of wind-driven sea waves or as a result of the vital activity of pelagic microorganisms and concentrated in the subsurface water layer change the optical properties of seawater. In the present paper, numerical experiments are performed to investigate the influence of the air bubbles on the characteristics of lidar returns in airborne sensing of seawater with both linearly polarized and unpolarized radiation. The dependencies of the lidar return characteristics on the air bubble concentration, their microstructure, and optical and geometrical conditions of observations are examined for the radiation wavelength λ = 0.53 μm.

Expanding the dynamic range of a lidar receiver by the method of dynode-signal collection

A method of lidar data collection by simultaneous registration of signals from the anode and several dynodes of the photomultiplier is suggested. The dynamic range of the receiver has been extended as many as 5 orders of magnitude in the case of cloud sensing. The stable operation under strong background illumination is possible without losses in fine signal structure.

Influence of the air–water interface on hydrosol lidar operation

The results of seawater sensing by use of an airborne lidar with a changeable field of view (FOV) are presented, together with the results of numerical simulation of lidar operation by the Monte Carlo method. It is demonstrated that multiple scattering and wind-driven sea waves have opposite effects on the measured attenuation coefficient. At small FOVs the wind-driven sea waves cause the lidar signal decay rate to increase compared with the size of the plane surface and hence result in an overestimation of the retrieved attenuation coefficient. Inefficient operation of lidars with small FOVs is caused by strong fluctuations of lidar signal power that cannot be described by a normal distribution. Specific features of the fluctuations can be interpreted as manifestations of the well-known effect of backscattered signal amplification caused by the double passage of radiation through the same inhomogeneities. As for the plane air-water interface, multiple scattering is significant for large FOVs and compensates for the effect of wind-driven sea waves. The applicability of simple sea-surface models to a description of lidar signal power fluctuations is discussed.

Influence of multiscattering on the results of airborne hydro-optical sensing

Experimental data on seawater laser sensing with an airborne lidar having a changeable field of view are presented. Wind-driven sea waves and microwaves lead to Fresnels splitting of a sounding beam into smaller sized beams, fluctuations, and escape of a number of signal photons from the detector field-of-view (FOV) cone, that is, to an apparent increase in the attenuation coefficient. Multiple scattering leads to the arrival of additional signal photons in the detector FOV, that is, to an apparent decrease in the attenuation coefficient. For the described lidar, two opposite processes provide its reliable operation at the FOV no less than 6 mrad.

Polarization structure of lidar signals reflected from ice crystal clouds

Polarization characteristics of signals of a monostatic lidar intended for sensing of homogeneous ice crystal clouds are calculated by the Monte Carlo method. Clouds are modeled as monodisperse ensembles of randomly oriented hexagonal ice crystals. The polarization state of multiply scattered lidar signal components is analyzed for different scattering orders depending on the crystal shapes and sizes as well as on the optical and geometrical conditions of observation. Light-scattering phase matrices (SPMs), calculated by the beam splitting method (BSM), are used as input data for solving the vector radiative transfer equation. The principles of the BSM method are briefly described, and the SPM components are given for hexagonal ice plates and columns of different sizes and linearly polarized incident radiation with the wavelength lambda = 0.55 microm.

Polarization Structure of Multiply Scattered Background Components of Lidar Signals Reflected from Cloud Ice Crystals

A numerical experiment is performed to obtain the polarization characteristics of signals of a monostatic lidar intended for homogeneous cloud sensing. It is assumed that clouds consist of monodisperse randomly-oriented hexagonal ice crystals. To solve the vector radiative transfer equation, the light scattering phase matrices, preliminary calculated with the help of the beam splitting technique, are used as input data. The formation of the polarization structure of multiply scattered background signal component is studied for different scattering orders depending on crystal shapes and sizes and optical and geometrical conditions of the experiment.