Autoquenching of spherical photon density waves during propagation in a turbid medium.

The effect of the formation of deep minima in frequency characteristics of photon density waves (PDWs) during their propagation in scattering media with different optical characteristics has been studied by statistical Monte Carlo modeling. The simulation was performed for the Henyey-Greenstein scattering phase function with the anisotropy factor value varying in the range of 0-0.93.

Angular distribution of photon density waves radiance in media with different scattering anisotropy.

Statistical modeling of pulsed frequency responses of the light field radiance by an isotropic point source was performed by Monte Carlo technique. Scattering properties of the medium were simulated by the Henyey-Greenstein phase function with different anisotropy factor values. Angular distributions of the pulsed field and amplitudes of the photon density waves in a certain range of parameters were shown to have a qualitatively different character for media with quasi-isotropic and strongly anisotropic scattering.

Effect of scattering anisotropy on the properties of photon density waves.

The frequency characteristics of spherical photon density waves excited in media with different degrees of scattering anisotropy are studied. Statistical modeling of the frequency and phase responses of the spatial irradiance of the light field emitted by a point-sized isotropic source were performed employing the Monte Carlo technique. The scattering anisotropy of the medium was determined by the Henyey-Greenstein phase function with different values of the mean scattering cosine.

Nonstationary angular distribution of optical field radiance from an isotropic source in sea water.

The spatial-angular and temporal characteristics of the radiance of the light field emitted by a nonstationary point isotropic source in sea water are studied. Using the Monte Carlo method, we calculated the pulse transfer functions and frequency responses of the angular radiance distributions at various distances from the source. Particular integral characteristics of the angular radiance distributions are estimated.

Time delay and width variation caused by temporal dispersion of a complex modulated signal in underwater lidar.

The parameters of an echo signal from the underwater lidar are studied for the case of modulation of a probing pulse by a high frequency signal with a frequency linearly varying with time. The analysis is based on the statistical Monte Carlo simulations of the frequency and phase responses of a signal propagating along the emitter-water-reflector-water-receiver path and an analytical representation of the signal as a pulse described by a Gaussian function with intrapulse modulation. Delays and pulse shape changes caused by temporal dispersion of the photon-density waves are estimated.

Comparative evaluation of signal-to-noise ratio and resolution of underwater imaging systems with artificial illumination.

Characteristics of different underwater imaging systems are compared based on the results of Monte Carlo simulations of light transport in the sea water. The consideration includes systems with continuous-wave illumination, modulated illumination, pulsed systems with time gating detection, and hybrid systems with probing pulse modulated at high frequency. To generalize the study, the ratio of SNRs of different systems when imaging a sinusoidal test pattern is analyzed.

Backscatter signals in underwater lidars: temporal and frequency features.

Backscatter signal formation in underwater lidar systems is studied and temporal and frequency characteristics are analyzed using the Monte Carlo technique. Both frequency and phase responses of the backscattered signal demonstrate similar dependencies, showing stronger frequency dependence in the high-frequency range. The beats of the frequency response due to dephasing of corresponding spectral harmonics are shown in the high-frequency range.

Nonstationary optical transfer functions of underwater imaging systems.

Optical transfer functions of underwater imaging systems employing narrow pulses or sinusoidally modulated beams for image formation are studied. A modified Monte Carlo technique allowing for direct statistical modeling of these functions accounting for temporal dispersion is proposed and implemented. The optical transfer functions are calculated for various modulation frequencies of the illumination beam and for the case of pulsed illumination.

Temporal and frequency characteristics of a narrow light beam in sea water.

The structure of a light field in sea water excited by a unidirectional point-sized pulsed source is studied by Monte Carlo technique. The pulse shape registered at the distances up to 120 m from the source on the beam axis and in its axial region is calculated with a time resolution of 1 ps. It is shown that with the increase of the distance from the source the pulse splits into two parts formed by components of various scattering orders.

Light pulse propagation along the path atmosphere-rough-surface-sea water.

The influence of surface waves and multiple scattering in water on the parameters of light pulses from an airborne source is studied. The contributions of various mechanisms to variations in delay of pulse and its variance are estimated. It is shown that waves make the main contribution to these values at small depths.

Water-scattered signal to compensate for the rough sea surface effect on bottom lidar imaging.

We investigate the possibility of using the water-backscattered radiation from a bottom sounding airborne imaging light detection and ranging (lidar) system to determine the surface slope at the point where the laser beam intersects the surface. We show that the refraction angle of the beam can be determined using receivers whose sensitivities vary linearly over their field of view. Equations are derived to estimate the statistical mean and variance values of this refracted angle.