Table 4 User-defined attenuated signal removal parameters in Echoview®.
From: Sounding out life in the deep using acoustic data from ships of opportunity
Filter parameter | Unit | Description | Value used |
|---|---|---|---|
Exclude above depth | Metre | Nominal upper limit of deep scattering layer (DSL) depth. \({S}_{v}\) samples between surface and this depth were not included in the algorithm (i.e. Eq. 3). Note that this depth line (in synchronous with ‘exclude below depth’ line) was adjusted to track high signal homogeneous regions for all frequencies. Ryan, et al.5 observed robust performance of attenuated signal algorithm in the DSL where SNR and ping overlap is generally high. | 500 |
Exclude below depth | Metre | Nominal lower limit of DSL depth. \({S}_{v}\) samples below this depth were not included in the algorithm (i.e. Eq. 3). Note that this depth line (in synchronous with ‘exclude above depth’ line) was adjusted to track high signal homogeneous regions for all frequencies. | 600 |
Vertical size of context window (\(m\)) | Metre | Vertical size of the context window used to identify pings with attenuated signal. This window size defines the vertical separation between ‘exclude above’ and ‘exclude below’ depth lines (see above). | 100 |
Horizontal size of context window (\(n\)) | Number | Horizontal size of the context window (i.e. number of pings) used to identify pings with attenuated signal. | 301 |
Detection percentile (\(p\)) | Percentile | The percentile value used for comparison between the current ping and context window. | 50 |
Detection threshold (\(\delta \)) | dB re 1 m2 m−3 | The threshold value used to identify pings with attenuated signal. | 8 |
