All transducers should have a measured beam pattern, showing the magnitude of the main lobe and associated side lobes. Performed by the manufacturer, these transducer-specific measurements also provide measures for Ψ (equivalent beam angle) and the 3-dB angle used in data collection and processing. The active radius (a) of a circular transducer, the half-intensity beam angle (θ3dB) and the equivalent beam angle (Ψ) are related and can be calculated from each other through the following equations (when ka>10):
θ3dB is the half power beam angle (º)
k is the wave number [k=2π/λ] and λ is the wavelength (m).