Abstract
Possibilities of lidar detection of fish and plankton are overviewed on cited results of nature experiments in the sea. Volume-backscattering coefficients for the lidar with wave-length 532 nm and the acoustic sonar are compared for schools of some fish species. Examples of effective detecting of fish schools and assessment of their abundance by lidar are demonstrated for cases of sardine and anchovy at California coast, capelin and herring in the North Pacific, mullet at the west coast of Florida, juvenile mackerel in the coastal Atlantic waters of southern Europe, menhaden in the Chesapeake Bay, and others. In some experiments, the per-kilometer costs of airborne lidar surveys are estimated as 10 % or less as compared to ship-based sampling. Besides, the lidar surveys take a shorter time and their results are not distorted by avoidance behavior of fish caused by ship and sampling gear noises. Experimental surveys of thin scattering layers (probably formed by plankton) made by NOAA fish lidar are overviewed, as well, including the first tests of the system in the South California Bay in April 1997, the tests in the North-West Atlantic at Iberian coast in August-September 1998, in the Gulf of Alaska in July-September 2001 and May-August 2002, in the Norwegian Sea in July 2002, in the North-East Pacific at the coast of Oregon and Washington in July 2003, and in the Gulf of Alaska in July 2003. Some aspects of future development for improvement of school-detecting capabilities of lidar are discussed, as additional scanning for 2D-images and adding of second receiver co-polarized with the laser light for better identification of fish species and other scatterers in the sea.
Highlights
Рассмотрены возможности современных средств активной лазерной локации при дистанционном обнаружении концентраций рыб и других водных животных
Possibilities of lidar detection of fish and plankton are overviewed on cited results of nature experiments in the sea
Volume-backscattering coefficients for the lidar with wave-length 532 nm and the acoustic sonar are compared for schools of some fish species
Summary
При дистанционных исследованиях пелагических видов рыб, таких как мойва, с использованием указанных средств весьма существенными являются акустические измерения с надводных судов и буксируемых систем для интерпретации распределения объектов ниже глубины проникновения излучения лидара. Это было определено во время судовых испытаний лидара, где деполяризация возврата света от рыбы была примерно 30 %, а деполяризация от водной среды составляла только около 10 % (Churnside et al, 1997). При применении этого алгоритма использовались данные средней интенсивности обратного рассеяния по глубине для 500 импульсов лидара или его световых «пятен». 1 приведены некоторые результаты лидарных и акустических измерений косяков с указанием количества проходов лидара над косяком, средней отражательной способности и средними стандартными девиациями (при трех и более проходах — в остальных случаях удалось получить лишь одно хорошее измерение для каждого косяка). Таблица 1 Некоторые результаты лидарных (2–4) и акустических (5–7) измерений косяков
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