The possibility of passive whale tracking with the use of an hyperspectral sensor

摘要

According to the 1972Marine Mammal Protection Act, the National Marine Fisheries Service has the responsibility to monitor and protect marine mammals including the great whales. To effectively implement this act NMFS must routinely observe whalesto measure the size and health of their population. The Act further stipulates that observations of whales be done from a distance far enough away to ensure that the whales not be disturbed. Thus a need exists for an accurate method to sense the whalesfrom an airplane at an altitude sufficient to not trouble the animals while still making accurate measurements of their size and other features. This paper describes a study conducted in the spring of 1996 in the waters off the western coast of theHawaiian Island of Maui to evaluate the utility of an airborne Hyperspectral Imaging (HSI) Sensor to detect and recognize whales. This area serves as a spring mating and calving area for a population of humpback whales who winter in Alaskan waters. AScience and Technology, Inc. (STI) Hyperspectral Imaging (HSI) camera was mounted in a Piper Aztec aircraft moving at a ground velocity ranging from 80 to 100 miles/hour. The aircraft flew at an altitude of 1000 m above the whales. The HSI camera wasoperated in a "pushbroom" mode and was framed at a nominal 40 frame per second rate to image in each downtrack frame a strip on the sea surface beneath the aircraft. The strip was of width 190 m wide with a 1 m down track extent. The frame rate of thecamera and the altitude and speed of the aircraft ensured that successively framed downtrack strips were contiguous in space. A spectral dispersion element in the camera divided the white light strip image into 72 contiguous spectral bands that fell on aCharge Coupled Device (CCD) array located in the focal plane of the camera. The system had sufficient data storage capacity to be able to image an ocean area of width 190-m by 2 km in length. The size of a single pixel imaged on the ocean surface was 1m{sup}2. An internal Global Positioning System was used to reference the image of the sea surface and the whales to the local navigational charts. The paper gives a detailed discussion of the sensor, describes the spectral image processing used to detectand enhance the whale images, provides sample imagery products, and finally discusses the potential utility of the method to conduct a rapid and accurate whale population survey at sea.