Meteorology and elephant infrasound at Etosha National Park, Namibia
作者:
David Larom,
Michael Garstang,
Malan Lindeque,
Richard Raspet,
Mark Zunckel,
Yvonne Hong,
Kevin Brassel,
Sean O’Beirne,
Frank Sokolic,
期刊:
The Journal of the Acoustical Society of America
(AIP Available online 1997)
卷期:
Volume 101,
issue 3
页码: 1710-1717
ISSN:0001-4966
年代: 1997
DOI:10.1121/1.418180
出版商: Acoustical Society of America
数据来源: AIP
摘要:
Measured vertical profiles of temperature and wind are used to model infrasound propagation over a representative high savanna habitat typically occupied by the African elephant,Loxodonta africana, to predict calling distance and area as a function of the meteorological variables. The profiles were measured up to 300 m above the surface by tethered balloon-borne instruments in Etosha National Park, Namibia, during the late dry season. Continuous local surface layer measurements of wind and temperature at 5 and 10 m provide the context for interpreting the boundary layer profiles. The fast field program (FFP) was used to predict the directionally dependent attenuation of a 15-Hz signal under these measured atmospheric conditions. The attenuation curves are used to estimate elephant infrasonic calling range and calling area. Directionality and calling range are shown to be controlled by the diurnal cycle in wind (shear) and temperature. Low-level nocturnal radiative temperature inversions and low surface wind speeds make the early evening the optimum time for the transmission of low-frequency sound at Etosha, with range at a maximum and directionality at a minimum. As the night progresses, a nocturnal low-level wind maximum (jet) forms, reducing upwind range and calling area. The estimated calling area drops rapidly after sunrise with the destruction of the inversion. Daytime calling areas are usually less than 50 km2, while early evening calling areas frequently exceed 200 km2and are much less directional. This marked diurnal cycle will be present in any dry savanna climate, with variations due to local topography and climate. Calling range and low-frequency sound propagation cannot be effectively understood without knowledge of meteorological controls.
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