Abstract
The natural electric field at the depth of 0 ∼ 1500 m in high seas of South China Sea is obtained by using a new type of measuring device. The electric field data in the 0.01 ∼ 0.5 Hz and 0.5 ∼ 30 Hz frequency range are analyzed respectively. The results show that the induced electric field generated by the surface wave (about 0.14 Hz in the experiment) is obvious at the depth of 50 m but can be ignored at the depth greater than 100 m. When the depth increases from 50 m to 1500 m, the peak-to-peak value of the natural electric field gradually decreases. At the depth of 1000 m, the peak-to-peak values are 0.04 ∼ 0.08 μV/m in the 0.01 ∼ 0.5 Hz range, and 0.07 ∼ 0.1 μV/m in the 0.5 ∼ 30 Hz range. At last, the natural electric field in coastal water near Sanya City, where the water depth is 15 m, is measured by means of a sinking device. The results show that the peak-to-peak values are about 2 ∼ 4 μV/m in the 0.01 ∼ 0.5 Hz range and 2 μV/m in the 0.5 ∼ 30 Hz range. By comparing the natural electric field in high seas with that of coastal water, we find the latter has a larger peak-to-peak value at nearly the same water depth. In addition, line spectrum noise often occurs in coastal water, while it is rarely observed in high seas when the water depth is more than 50 m.
Highlights
The shaft-rate electric field originated from the rotation of ship’s propeller has characteristics of low frequency and obvious line spectrum, which make it become an important source for ship detection and recognition (Young,2012;Tatavarti,2013; LI,2015;Yu, 2019)
Comparing the electric field measured at the bottom of coastal waters with that measured at m depth of high seas, we can find that they have the same level of peak values in 0.01~0.5 Hz, but the peak value of the former is nearly 2 times larger than the latter in 0.5~30 Hz
The natural electric field in the depth range of 0~1500 m in South China Sea is obtained by using an electric field measuring device based on the autonomous profiling drifter
Summary
The shaft-rate electric field originated from the rotation of ship’s propeller has characteristics of low frequency (generally between 0.5~30Hz) and obvious line spectrum, which make it become an important source for ship detection and recognition (Young,2012;Tatavarti,2013; LI,2015;Yu, 2019). The experiment was conducted in the high-seas area of South China Sea. The natural electric field in the depth range of 0~1500 m was measured by this device.
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