Iosif M. Levin

Influence of illumination conditions on the sea-bottom visibility

Statistical models of the useful and background signals forming an image of the sea bottom observed through a rough sea surface are constructed. The methods for estimating the signal-to-noise ratio in the image of the bottom with the test distribution of the reflectance are described. The dependence of the signal-to-noise ratio on observational conditions, in particular, on the mutual orientation of the directions of sighting, wind, and solar vertical, is analyzed. Recommendations on the choice of optimal conditions for bottom observations from airborne carriers are given.

Image transfer through rough sea surface: computer simulations

This paper is devoted to computer simulation of random realizations of bottom images. Simulations of random images are considered to be a straightforward way to predict bottom visibility under realistic conditions. A simplified version of a bottom imaging model using a fast simulation algorithm has been developed. Simulated results presented here allow the visual evaluation of image quality for different signal/noise ratio (SNR) values. We show how the simulation of random images can be used to predict bottom visibility over a variety of environmental conditions and also determine an optimal observation strategy.

Secchi disk theory : a reexamination

The possibility of the retrieval of the waters inherent optical properties (IOP) from Secchi disk observations is discussed. The paper directly addresses objections to the use of Secchi disks raised by Preisendorfer in 1986. A new version of Secchi depth theory is given, which in contrast to conventional Secchi disk theories includes the effects of light reflection from the sea surface and treats measurements from both the sunny and shaded sides of a vessel. Empirical correlations between different IOP are used to estimate not only the attenuation coefficient, but also the single scattering albedo and the backscattering probability at 550 nm from Secchi depth data. The theory is compared with measurements made in the Black Sea.

Inverse problems of lidar sensing of the ocean

We consider the inverse problems in the retrieval of the waters inherent optical properties (IOP) and the properties of the hydro-physical processes taking place in a water body using the returned signal of an oceanic lidar. An algorithm for the retrieval of the depth distributions of IOPs from a lidar signal was developed using correlations between IOPs in the middle of the visual spectrum. Our algorithm gives simple equations for the attenuation coefficients depth profile using narrow and wide lidar receiving angles. We also show how to find this profile for an arbitrary lidar receiving angle. Analysis of the algorithms accuracy demonstrated that the probabilistic nature of the correlations between IOPs produces large errors in the retrieved lOPs. These errors increase with the optical depth of the sensed layer. The suggested adaptive algorithm improves retrieval accuracy by processing the lidar signal itself. It is shown how a two-channel lidar with specific directivity diagrams can be used to well-determine one water optical property, and then find the other TOPs with correlations. We also consider the possibility of detecting hydro-physical processes in water by the example of lidar images of internal waves.

Front Matter: Volume 6615

This PDF file contains the front matter associated with SPIE Proceedings Volume 6615, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Application of an advanced stochastic bottom imaging model for airborne hyperspectral imager data collection

Collection of airborne dat can be an expensive exercise. Data flights should optimize the quality and quantity of the data collected at minimal cost. Although the site to be surveyed is fixed, a mission planner has some freedom in formulating collection strategies. Choices may include the season, the time of day, the altitude and directions of the data run flights, the spectral bands, and the spectral and spatial resolutions used for the survey. A stochastic model has been developed to simulate and quantitatively estimate the statistical performance of airborne hyper- and multi- spectral systems in imaging a littoral sea bottom through a wavy sea surface. Results include mean and variance of various measures of system performance. Candidate collection plans can be tested with the stochastic model. This paper demonstrates the use of the stochastic model in examining the effect of flight direction on the quality of imagery for a variety of zenith sun angles and surface wave conditions. The calculations show the extreme sensitivity of data quality in terms of image signal to noise ratios to flight direction, sun angle, and sea wave direction.

Potential for determining the sea water absorption coefficient by satellite pulsed lidar

Abstract The problem of the present-day methods for determining the sea water absorption coefficient from space is the fact that the valid signal is an order of magnitude lower than the noise. In the present work, the pulse-gating method is considered as a means to increase the ratio of valid to spurious signals. A theoretical model is developed in order to estimate the radiance of the atmosphere–ocean system irradiated by a lidar in the pulse-gating regime in the range of sea-water transmittance (0.400–0.550 μm). The model makes it possible to formulate technical requirements to the lidar (the emergent beam angle, pulse power, etc.), which prove to be quite achievable at the present time. Three typical situations are considered when the method under discussion can be used: 1) at night, with clear skies; 2) daytime, with clear skies; 3) at night, with thin clouds. The estimates are given for each case. The primary emphasis is placed on the expediency of constructing and testing an equipment for measuring optical properties of sea water by the pulse gating method from space.

Theory of satellite observation of the sea bottom in coastal waters: maximal sighting range and resolution

The paper deals with some aspects of the underwater imaging theory. The first effect discussed is the increasing of sighting range of sea bottom with an observers altitude over the sea surface. Calculations show that the maximal sighting range from the space under the most favorable conditions does not exceed 500 meters. Secondly, the dependence of the sighting range and the resolution on size of target elements and target itself is considered. It is shown that the apparent contrast of target elements equal in size is higher for smaller targets. Computations prove the nonmonotone dependence of contrast on distance between the observer and the target. Finally, we consider the possibility of observation of the ocean bottom in coastal waters through clouds and show that large details of the bottom, such as sand spots against the seaweeds background, can be seen through continuous clouds with an optical thickness under 10.

Spectral contrast of oil films on the sea surface: influence of water type, wind velocity, and solar altitude

Contrast of oil film against the rough sea surface background was estimated for the wavelength range from 300 - 800 nm in various observation conditions. Morel and Prieurs experimental data on water reflectance in the visible spectrum were used as the basis for computations. Extrapolations of these data to the UV and IR regions are based on the well-known low- parametric models for water properties. The computations show that the contrast magnitude varies depending on the water type, wavelength, wind velocity and solar altitude from -90% to +60% (plus relates to the case when oil is brighter than water, minus relates to the opposite case). To avoid small or zero contrasts, observations apparently should be fulfilled in several spectral channels. Calculation method was verified during a flight over the Black Sea when predicted oil-water contrast was obtained with two airborne TV-cameras operating in the visible and UV spectral regions.