RE-WRITE Essay Example | Topics and Well Written Essays - 1500 words

RE-WRITE - Essay Example The usual assumption is that ambient noise is isotropic (equal on all directions). This is commonly considered in sonar equations. We therefore attempt to reduce the effective noise level by utilising of the directional capabilities of the hydrophone (NL-DI). However, in deep waters the sea surface is considerably the principal source of ambient noise. It these areas the ambient level is not truly isotropic. Conversely, in shallow waters ambient noise is essentially isotropic due to reflections from the sea floor (Davidson, 2006). The features of the parametric approach are best illustrated on an example taken from a hypothetical sonar application. The approach was to apply time-frequency circumstances for detection. The detection conditions are simply: The second level, in particular, enables signal detection of a very low false alarm rate on narrow-band sonar signals. It acts as a narrow band pass filter at the input of detection algorithm, which efficiently eliminates out-of-band noise. Figure 1 shows a 50 kHz sonar return from shallow water. Simulated water-depth is 3 m. the transmit pulse has a duration of 0.4 Ms. The noise is of uniform distribution restricted to the signal band. Signal to noise ratio (S/N) is 20 dB while the signal’s full waveform was digitised at the rate of 1 MHz. Only the envelope of the signal is shown in Figure 1. Without any further processing, the echo time series, which consists of 1000 sample, is now submitted to the detection algorithm. While the parametric model is calculated for every sample, the spectrum from 48 kHz to 52 kHz is computed for every 10th interval. The 4 kHz band is evaluated at 200 frequencies with a resolution of 20 Hz. A three dimensional view of the sonogram (Figure 2) may illustrate how well the spectral peaks in the sonar return are defined in a time-frequency representation. The algorithm is very fast and real time processing capable. It does not require that the