# Array gain / design (MURRELET)

Array gain (ideal, uncorrelated noise) AG = 10*log10(N).
N=64 -> 18.1 dB. nice. real AG lower w/ correlated flow noise.

Element spacing d = lambda/2 at design freq to avoid grating lobes.
c ~ 1500 m/s. at 5 kHz lambda = 0.3 m -> d = 0.15 m. at 30 kHz d=0.025 m.
can't satisfy both -> nested/sparse array or accept grating above design freq.
design freq pick: cavitation tonals of interest sit low (blade rate harmonics).
go low (d=0.15) and live with HF limitation, MURRELET is about prop noise anyway.

aperture L = (N-1)*d = 63*0.15 = 9.45 m. that's long for a UUV mount. fold? tow?
flag: ROCKFISH integration — hull won't take 9.45 m rigid. talk hull w/ David.