a |
Transducer active radius (cm or m) |
A |
Survey area (km2 or nmi2) |
BD |
Water column depth (bottom depth, m) |
b(θ) or B(θ) |
Transducer directivity in the direction defined by angle θ (linear or dB scale) |
c |
Sound speed (m•s-1) |
D |
Cruise track length (Distance, km or nmi) |
f |
Frequency (Hz or kHz) |
heq |
Height of the bottom deadzone (m) |
i |
Ping interval (sec) |
k |
Wave number (k=2π/λ) |
L |
Target scattering size (e.g., body length or swimbladder length) (cm or m) |
R |
Range between two targets or between a target and the transducer (m) |
Rnf |
Near-field range (m) |
sa , ABC |
Area backscattering coefficient (m2•m-2) |
sA, NASC |
Nautical area backscattering coefficient (sA = sa/(1852)2 4 π), unit m2•nm-2) |
Sa |
Area back scattering strength (Sa = 10 log10(sa), dB) |
sv |
Volume backscattering coefficient (m2•m-3) |
SV |
Volume backscattering strength (Sv = 10log10(sv), dB) |
T |
Temperature (ºC) |
TS |
TS (dB), TS = 10log10(σbs), dB) |
TSu |
Measured value in the TS echogram (dB). Also called uncompensated TS |
V |
Sampling volume (m3) |
w |
Fish mass (gm or kg) |
W |
System transmit power (W) |
α |
Absorption coefficient (dB•m-1 or dB•km-1) |
Ψ or EBA, Ψ |
Equivalent beam angle (steradians or dB re: 1 sr) |
λ |
Wavelength (m) |
σbs |
Backscattering cross section (m2) |
θ3dB |
Half-beam angle to the -3 dB point (º) |
Λ |
Degree of coverage (no units) |
ρv |
Volumetric fish density (#•m-3) |
ρa |
Areal fish density (#•m-2) |
τ |
Pulse duration (s) |