Bottom Map Research Articles

Application of hydroacoustic technology to marine fishery management in Washington State

The Washington Department of Fisheries has utilized hydroacoustic stock assessment techniques since the early 1970s for research and management of state marine fish resources. The objectives of these applications have been to provide estimates of harvestable biomass, which drive in-season management of Pacific whiting ( Merluccius productus) and Pacific herring ( Clupea harengus pallasi) in Puget Sound, and to develop a new assessment technique for estimation of the population of black rockfish ( Sebastes melanops) off the coast of Washington and Oregon. During the early years of hydroacoustic assessment, there was considerable uncertainty from a manager's perspective concerning biomass estimates because of inconsistencies with the electronics, lack of target strength verification, inadequate data for determination of species and fish age composition, and inconsistent sampling designs. Continued improvements in methodology and equipment have resulted in better estimates of biomass which have substantially reduced the risk of making poor management decisions for herring and whiting. Because the sport and commercial line fisheries for black rockfish off the coast of Washington have emerged in recent years, estimates of harvestable biomass of this nearshore semi-pelagic species have been required for purposes of conservation and allocation between user groups. Results from the first 3 years of a 5 year project to develop a hydroacoustic survey plan have resulted in a coastwide bottom habitat map and characterization of fish distribution and densities. However, methodology for identification of species composition must still be developed before the population size of black rockfish can be estimated and applied to management.

Measurement of seabed topography by multibeam sonar using CFFT

A precise ocean bottom map for ocean surveying and dredging is desired. Especially in dredging, it is essential to know the seabed topography in real time without being affected by scatterers (for example floating sand and mud) in the seawater during work. To meet these requirements, the multi-narrow-beam sonar system (MBSS) has been developed. The MBSS forms beams with the use of the complex fast Fourier transform (CFFT) algorithm. In the MBSS, arithmetic mean processing is employed to eliminate echo from scatterers and the measurement error due to the oblique incident angle is reduced by peak value detection processing. By using these processes, an ocean bottom map can be accurately obtained. It is both theoretically and experimentally shown that the distribution of echo intensity from scatterers is approximated by the Rayleigh probability density function. The arithmetic mean of four to eight successively received echoes from scatterers reduces the variance of the echo intensity distribution by 6 to 12 dB.

Heave-roll-pitch correction for hydrographic and multi-beam survey systems

Abstract The development of a new generation of Hydrographic and Bathymetric Survey Systems by the U.S. National Ocean Survey (NOS), is described. New Instrumentation in the form of Multi-Beam Swath Sonars, Heave-Roll-Pitch (HRP) Instrumentation, and power computer systems have been merged to provide a quantum step forward in bathymetric and hydrographic survey techniques. These new systems provide the capability to achieve 100 percent bottom coverage as compared to the 2–5 percent coverage typically achieved by conventional narrow beam survey techniques. Two Bathymetric Swath Survey Systems (BS 3 ) are now under development and approaching operational status within NOS. One utilizes the General Instrument Corporation BO'SUN Sonar as its principal sensor and is optimized for mapping water depths from 20 to 300 fathoms. BO'SUN/BS 3 has been in use for over a year on the NOAA Ship “Davidson” in Alaska and West Coast waters. The second system utilizes the General Instrument Corporation SEABEAM Sonar as its principal sensor. This sonar is designed for deep ocean mapping. SEABEAM/BS 3 is currently undergoing grooming and initial sea trials on board the NOAA Ship “Surveyor”. Functionally, the two systems are very similar. They both employ similar computer hardware and software. Software has been developed that automates the real time survey data acquisition and control as well as the post time processing and production of bottom maps. These systems, when fully groomed and operational, will provide a new dimension to hydrographic and bathymetric Surveys. Results to date have shown a significant improvement in the accuracy and completeness of survey data as compared to more conventional techniques.

A One-Parameter Subsemigroup which meets many Regular -Classes

We give an example which answers affirmatively the following problem posed by Hofmann and Mostert (1, p. 200):P. 10. Let S be a compact semigroup with identity 1, zero 0, and totally ordered -class space . Suppose that there is a one-parameter semigroup containing 0 and 1. Can S have any regular -classes aside from D(0) and D(1)?I am indebted to Professor K. H. Hofmann and Professor P. S. Mostert for their many helpful suggestions.1. We first give a method of embedding a given semigroup S in a semigroup R so that in the commutative diagramthe bottom map is an isomorphism of partially ordered spaces and some non-regular -class of S is embedded into a regular -class of R.