Iosif L. Katsev

Monte Carlo and multicomponent approximation methods for vector radiative transfer by use of effective Mueller matrix calculations

For single scattering in a turbid medium, the Mueller matrix is the 4 x 4 matrix that multiplies the incident Stokes vector to yield the scattered Stokes vector. This matrix contains all the information that can be obtained from an elastic-scattering system. We have extended this concept to the multiple-scattering domain where we can define an effective Mueller matrix that, when operating on any incident state of light, will yield the output state. We have calculated this matrix using two completely different computational methods and compared the results for several simple two-layer turbid systems separated by a dielectric interface. We have shown that both methods give reliable results and therefore can be used to accurately predict the scattering properties of turbid media.

Efficient technique to determine backscattered light power for various atmospheric and oceanic sounding and imaging systems

A new technique that efficiently simplifies the estimations of backscattered light power is presented. This technique allows one to consider real inhomogeneous scattering media with an underlying surface and to account for all the features both of media phase functions and of the reflection of underlying surfaces. It is assumed that the phase function has a sharp forward peak. Different sounding, vision, and location systems can be considered. The image transfer equation is derived for any observed object, including three-dimensional and non-Lambertian objects. A few examples of the successful use of the developed approach to solve various problems are given.

Demodulation techniques for the amplitude modulated laser imager

A new technique has been found that uses in-phase and quadrature phase (I/Q) demodulation to optimize the images produced with an amplitude-modulated laser imaging system. An I/Q demodulator was used to collect the I/Q components of the received modulation envelope. It was discovered that by adjusting the local oscillator phase and the modulation frequency, the backscatter and target signals can be analyzed separately via the I/Q components. This new approach enhances image contrast beyond what was achieved with a previous design that processed only the composite magnitude information.

Iterative procedure for retrieval of spectral aerosol optical thickness and surface reflectance from satellite data using fast radiative transfer code and its application to MERIS measurements

The retrieval of aerosol characteristics over land from satellite data has been a challenge up to now. Currently, several well known techniques for retrieving aerosol optical thickness (AOT) have been developed for satellite instruments including MODIS (Kaufman et al., 1997; Remer et al., 2005), MERIS (Santer et al., 1999, 2000), POLDER (Deuze et al, 2001), and MISR (Martonchik et al., 2002). While each technique has its own merits, the accuracy of AOT retrieval still needs further clarification and improvement. From this point of view the inter-comparison and verification of these techniques undertaken recently (Kokhanovsky et al., 2007) is of a great importance.

Lidar returns from multiply scattering media in multiple-field-of-view and CCD lidars with polarization devices: comparison of semi-analytical solution and Monte Carlo data

Quite recently, a semi-analytical approach to the sounding of multiply scattering media (clouds, seawaters) using multiple-field-of-view and CCD lidars with polarization devices was developed. The angular distributions of polarized components of the lidar returns from multiply scattering media computed on the basis of this theory using the small-angle approximation are presented and discussed. The semi-analytical nature of the solution makes the computation procedure faster. The obtained data are compared with results provided by the most advanced Monte Carlo algorithms for simulation of modern lidar performance. The good agreement between data provided by the semi-analytical approach and Monte Carlo computations assures one that these approaches can serve as a reliable theoretical base for interpretation and inversion of cloud lidar sounding data obtained with polarized lidars, including polarized multiple-field-of-view and CCD lidars.

Simple model of the optical characteristics of bubbles and sediments in seawater of the surf zone

The development of a simple model of the seawater inherent optical properties (IOPs) associated with bubbles and sediments would represent a great advance in surf zone optics. We present one solution for this problem using a combination of geometrical optics and Fraunhofer diffraction. An analytic model of the IOPs of bubbles and sediments (the extinction and absorption coefficients, and phase function) is developed in terms of the moments of the particle size distribution and the complex refractive index of particles.

Analytical and computer modeling of the oceanic lidar performance

This work overviews recent advances that have been made in an analytical theory of elastic and Raman lidar returns with multiple scattering and polarization from clouds and seawaters and outlines newly developed software for computer simulation of airborne oceanic lidar performance.

Simulating the performance of airborne and in-water laser imaging systems

The real-time simulation of broken and distorted images of a submerged target observed through a random realization of wind roughened sea surface produced by airborne gating imaging lidar is presented. The user is allowed to watch the sequence of images at the computer screen, which the lidar operator vies sat the TC screens of an operating airborne imaging lidar. Th inclusion of all types of noise as well as spatial correlation of receiver noise and noise due to a windy roughened sea surface with detailed treatment of seawater scattering provides a very realistic model. Two image processing techniques to deal with actual images - Matched Filter and Optimal Integration - are compared as to signal-to-noise ratio and probability of detection. Optimal Integration is appropriate for use by an experienced lidar operator.

Modulated lidar system: experiment versus theory

A modulated light detecting and ranging system has been developed to improve underwater imaging. This system uses the modulation information encoded on an optical signal to distinguish between the backscatter signal and the signal reflected from an underwater target. Through choice of the appropriate modulation frequency, this technique has the ability to improve underwater target contrasts by reducing backscatter noise. Both laboratory tank experiments and in- situ pier measurements have been completed with a modulated lidar prototype. The results show that the target contrast improved as the modulation frequency. Concurrent with the experimental measurements, a theoretical model is being developed for the modulated lidar system. This analytical model incorporates both the Small Angle Diffusion Approximation and the Multi-Component Method developed by Zege et al to solve the radiative transfer equation. The various experimental characteristics are included in the model and the results are compared with relevant experimental data. Preliminary results show good agreement with experimental data, including the reduction of backscatter with increasing modulation frequency.

Retrieval of optical characteristics of the aerosol atmosphere and Earth’s surface by the joint processing of different satellite information

Methods and algorithms for the retrieval of optical characteristics of the aerosol atmosphere and underlying surface by data from a multispectral satellite sensor (MSSS) are described. A procedure for the joint processing of MSSS and multizonal imaging system (MZIS) data is proposed and described with the aim of retrieving the albedo of the Earth’s surface with a high spatial resolution. In this case the spectral optical characteristics of the aerosol atmosphere are retrieved by MSSS data in the visible range of 400–700 nm. According to these results, transmission functions of the atmosphere in MZIS spectral channels are calculated and an atmospheric correction of MZIS data is performed. The accuracy of determining the albedo of the underlying surface in spectral channels of MZIS with high-spatial-resolution is estimated.