How do I find the equivalent two-way beam angle Ψ for my echo sounder?
The Equivalent TWBA is frequency and transducer-specific, and the value can be calculated (in Steradians) for the circular transducer through the following equation (when ka>10):
or in dB format:
Where k is the wave number [k=2π/λ] and λ is the wavelength (m), and a is the active radius of the transducer.
The calculated Equivalent two-way beam angle for each instrument with monochromatic setup is given in the table below:
| Instrument/Frequency |
a |
Ψ [sr] |
Ψ [dB] |
| Signature 1000 | 15 | 0.0015 | -28.3443 |
| Signature 500 | 30 | 0.0015 | -28.3443 |
| Signature 250/500kHz | 40 | 8.23e-04 | -30.8431 |
| Signature 100/70kHz | 43.5 | 0.0355 | -14.4942 |
| Signature 100/90kHz | 43.5 | 0.0215 | -16.6771 |
| Signature 100/120kHz | 43.5 | 0.0121 | -19.1759 |
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