Resolvable Target Distance Calculation
Organisms must be sufficiently separated to be resolved as individual targets for valid TS measurements to be obtained. Pulse duration (τ, s) and sound speed (c, m•s-1) affect the separation of echoes through the relationship:
where ∆R is the range between two resolvable targets (R1 and R2, m). Targets that are closer together cannot be separated (Simmonds and MacLennan 2005). Although frequency is not a factor in the calculation of acoustic resolution, higher frequencies can generally operate at shorter pulse durations (e.g., 0.2-0.3 ms), thus allowing the resolution of targets closer together.
If data are collected at c = 1450 m•s-1,with τ = 0.0003 s (≡0.3 ms), then
Targets must be separated by at least 21.8 cm to be individually resolvable.