This paper describes the depth sounding activities in Sweden. These include the development of a helicopter borne lidar called FLASH as well as instrumentation for in situ measurement of the optical water parameters as well as modeling efforts of depth sounding lidar performance. The FLASH system has been further developed into two operational systems called Hawk Eye with Saab Dynamics as the main contractor and Optech Inc. as the main subcontractor. Data collection and evaluation from Hawk Eye will be discussed. The Swedish Defence Research Establishment (FOA) was a member of the Hawk Eye project team together with the National Maritime Administration, the Royal Swedish Navy and the Defence Material Administration. Together with the Swedish Maritime Administration, FOA has been engaged in analysis of lidar data to determine system performance and possible ways to optimize that in relation to lidar parameters and anticipated bottom depth and topography. Examples from that analysis will be presented. The test analysis so far strongly supports the depth sounding lidar technology as being a rapid and accurate sounder fulfilling the requirement by International Maritime Office on depth accuracy.

This paper presents the history of development, testing, and two years operation of the Scanning Hydrographic Operational Airborne Lidar Survey (SHOALS) system. The SHOALS system was developed for the US Army Corps of Engineers (USACE) as part of an objective to facilitate private sector investment in lidar bathymetry by demonstrating the technology and commercial applications. The system services the USACE by providing hydrographic surveys of many of its projects, as well as providing services to other US government agencies including the National Ocean Service and Navy. Laboratory development was completed in November 1993 and field tests were conducted January through February 1994 to determine performance and compliance with contract specifications. Since acceptance in March 1994, and as of April 1996, SHOALS has surveyed over 50 projects covering more than 1,500 km² and faced many technical and operational challenges.

Airborne lidar is being considered as a tool for fish detection and for fisheries surveys. Detection has been demonstrated, and an imaging lidar has been developed to detect and identify fish for commercial fisheries. For survey work, a simpler radiometric lidar is being investigated, and preliminary results suggest that such a lidar can be very useful for biomass estimation.

The ultimate accuracy of depths from an airborne laser hydrography system depends both on careful hardware design aimed at producing the best possible accuracy and precision of recorded data, along with insensitivity to environmental effects, and on post-flight data processing software which corrects for a number of unavoidable biases and provides for flexible operator interaction to handle special cases. The generic procedure for obtaining a depth from an airborne lidar pulse involves measurement of the time between the surface return and the bottom return. In practice, because both of these return times are biased due to a number of environmental and hardware effects, it is necessary to apply various correctors in order to obtain depth estimates which are sufficiently accurate to meet International Hydrographic Office standards. Potential false targets, also of both environmental and hardware origin, must be discriminated, and wave heights must be removed. It is important to have a depth confidence value matched to accuracy and to have warnings about or automatic deletion of pulses with questionable characteristics. Techniques, procedures, and algorithms developed for the SHOALS systems are detailed here.

In Australia airborne laser hydrography has been researched and developed over a period of 18 years from a concept into a fully integrated operational unit in the Royal Australian Navy. This paper reviews the first three years of operation and considers recent developments and findings. These include surface reflections as a surface reference level, depth accuracy and detection capability over small shoals and the effect of turbidity on depth measurement. Also discussed are operational aspects relevant to laser hydrography.

During the CZCS era chlorophyll retrieval algorithms were developed with a very limited number of oceanic spectral radiance and pigment pairs obtained at individual ship stations. Recent results suggest that copious airborne active-passive data can now be used to validate oceanic water-leaving radiances, incident downwelling irradiance, phytoplankton chlorophyll, and the chromophoric dissolved organic matter absorption coefficient. Furthermore, these data can be used to develop and validate 1) oceanic radiance models, 2) inherent optical property (IOP) models, and 3) inversion methods for retrieval of IOP's.

In theory, depth profiles of received power from ocean remote sensing airborne lidar data with a wide filed of view can be related to the diffuse attenuation coefficient, K_d. Preliminary results from clear open ocean waters in the Sargasso Sea and in the North Pacific Ocean indicate that a wavelength dependent discrepancy may exist, and that the 532 nm lidar K_d values are approximately 33 percent lower values than those derived from sunlight. If the discrepancies can be resolved, then a lidar system could provide a way to remotely measure the spatial variability of K_d over synoptic scales that can not be achieved within a reasonable time interval from a surface vessel.

A novel laser cavity design was proposed to compensate for thermally induced stress birefringence in cylindrical laser rods. The use of this optical schematic of the cavity allows lasers to operate efficiently at high average power levels. Experimentally a Nd:YAG oscillator has been operated in an electro-optically Q-switched mode giving 55 mJ linearly polarized output pulses at a pulse repetition rate of 500 Hz. Other features of the laser design include the ability to produce second and third harmonics with high efficiency.

In the present work some results of work carried out in LASER CENTER of St. Petersburg State Institute of Fine Mechanics and Optics are represented. This R and D work has been aimed on creation of powerful flash-lamp pumped solid- state lasers with advanced exploitation parameters that may be installed on different kind of moving stations. The main attention with be paid to two laser systems that are quite different but indicate practically all the field of development of powerful solid-state lasers.

The recent developments in manufacturing of various types of lasers, including new modifications of Nd:YAG, Cu⁺ vapor, and dye lasers, are considered from the point of view of application in airborne systems designed for remote sensing of natural water bodies. The general expressions are given to analyze the effect of laser source wavelength on expressions and general optical detection theory based on Sakett's D-index of discriminability, a criterion is formulated for optical choice of sounding radiation wavelength for airborne lidar systems which takes into account the sun light composition as well as spectral dependencies of PMT photocathod sensitivity, hydro-optical characteristics of sea water and bottom reflectivity. Several results are presented to compare the effectiveness of different laser sources for lidar bathymetry applications for various types of ocean waters and meteorological conditions.

The design and performance characteristics of a tunable, six stage Lyot filter for use with the Australian laser airborne depth sounder are described. It is predicted that the filter will significantly reduce the effect of sky reflection from the sea surface thereby allowing an increase in the operational hours of the LADS system by up to six hours per day.

Measurements of ocean-water optical properties that are directly relevant to airborne oceanographic lidar (AOL) systems are rare. The two most important water optical properties to AOL systems are the volume scattering function (VSF) at 180 degrees and the lidar beam attenuation coefficient. An instrument has been developed, called Beta Pi, which measures, in situ, these two optical parameters. It is a self-calibrating instrument that provides an accurate measurement of both the VSF at 180 degrees and the lidar attenuation coefficient. Results from a deployment in the Gulf of Mexico near Panama City, Florida, during a Navy lidar test, are given. It was found that the VSF increases by more than 50 percent from 179 degrees to 180 degrees. A sharp enhancement, possible due to coherent backscattering, was also observed at 180 degrees with an angular width of about 0.03 degrees. Measurements made at six discrete wavelengths from 457 to 532 nm revealed that the spectral dispersion of backscattering at and near 180 degrees was substantially greater than the dispersion at 135 degrees measured with multispectral bi-static backscattering sensors. All of these results have important implications to the sea truth calibration of AOL systems.

The equations of small angle scattering theory for obtaining a point spread function from the volume scattering function f a scattering medium are derived following the pattern given by Wells with additional explanation and comments on application. THe scattering phase function is also discussed along with the Hankel transform that are required by the theory. Finally, some suggestions are given for further work in the area of point spread function modeling and measurement.

The present work consists of two parts. In the first part the principal results of the scattering theory of ultra short light pulses (USLP) by a small spherical particle, ar briefly outlined. In the second part, the peculiarities of the USLP scattering by marine suspension are examined.

In the present work the difference between light pulses optics and conventional marine optics are examined. In the first part we consider the absorption of ultra short light pulses in sea water; in the second, three regimes of propagation of light pulses in sea water.

Airborne lidars systems have progressed to the point where they are increasingly being used in surveys and bathymetric studies of coastal and littoral zones. Scattered laser pulse light in these turbid regions hurt the performance of lidar system s as photons delayed by multiple scattering simultaneously return with the signal from a distant target. This phenomenon is called 'optical ringing' and is analogous to reverberation in acoustics. A Monte Carlo model was used to examine the effect of water turbidity on the temporal storage of photons in increasing scattering orders for an airborne lidar. The lidars modeled had combinations of both wide and narrow source and receiver fields. The lidar looked at nadir into a flat clam sea with optical properties ranging from clear to turbid water. The amount of optical ringing present in a return was proportional to the size of the pulse-illuminated in water volume. The results showed multiple scattered light surpassing single scattered light returns for all cases of source-receiver field combinations for even the clearest water studied.

We have performed Monte Carlo calculations to investigate the effect of multiple scattering on the frequency spectra due to Brillouin scattering in the ocean. The use of the frequency spectra to determine the speed of sound and temperature profiles and the hydrosol backscattering probability is shown to be stable in turbid multiple scattering waters.