# Interpretation of minimum discernible signal (MDS) in sonar equation

I am working on modelling and simulations of synthetic aperture sonar at component/subsystem level. I have started with standard sonar equations for calculating detection ranges for different environmental conditions. One parameter I calculated is Minimum Discernible Signal (MDS) which is difference between detection threshold (DT) and array gain/directivity index (AG/DI) (beam forming). According to book definition, MDS is SNR at array's hydrophone face required for detection at some preassigned level of correctness.

After hydrophones, there are of course pre-amplifiers (PA) and ADCs before beam former stage (DI/AG). My confusion is how to interpret this MDS/SNR in terms of PA and ADC specifications?. I have defined and fixed receiving sensitivity of hydrophones, however I need to drive PA and ADCs specifications from calculated MDS especially in terms of noise levels so that same MDS/SNR appearing at array's hydrophones face can appear at beam former input without distortion.

NOTE:

Suppose my MDS/SNR (in terms of acoustic/sound pressure) for certain conditions came out to be $-20\textrm{ dB}$. Using hydrophone sensitivity, I think same SNR (in terms of voltage) will appear at each hydrophone output (if I am not wrong). Does it mean that even if echo level at input of PA /ADC of each hydrophone in array is 20 dB below PA/ADC noise floor, beam former and post processing will still be able to detect this echo???