acoustic   signal   may   be   attenuated   by   overlying sediment. . Bottom clutter —  This  phenomena  results  in non-mine targets being detected by a minehunting sonar system.  This  makes  it  difficult  for  the  operator  to identify  targets  from  the  ambient  noise. .  Sediment  resistivity  —  This  is  the  ability  of sediment  to  conduct  electrical  current. Resistivity depends upon salinity, electrical conductivity of the sediment,  and  the  thickness  of  the  sediment. MAGNETIC ENVIRONMENT The  factors  that  affect  the  sensitivity  of  magnetic sweep equipment are as follows: l  The  effectiveness  of   magnetic  sweep  equipment is influenced by the water depth and the conductivity of the water (salinity and temperature). .  Magnetic  storms  cause  momentary  fluctuations in the earth’s magnetic field. These storms sometimes closely resemble the magnetic signature of a ship and may   result   in   magnetic   influences   firing   mines prematurely. ACOUSTIC ENVIRONMENT Ambient  noise  can  create  problems  for  mines  and MCMs in shallow water. . High ambient noise levels present a problem for the performance of acoustic influence mines, since the target must be discriminated from ambient noise over relatively   long   ranges. .  High-frequency  components  of  ambient  noise tend to have little effect on minehunting operations because  of  the  high  receiver  directivity  characteristics of  minehunting  sonar  systems. PRESSURE ENVIRONMENT Water pressure can play a significant role in MIW operations. l The effective pressure change caused by wave heights at the surface diminishes with increasing depth. l   Generally,   pressure   mines   require   other influences,  such  as  acoustic  or  magnetic  influences  to be present simultaneously in order for the mine to explode. BIOLOGICAL   ENVIRONMENT Biologics   may   influence   sonar   detection,   the neutralization  of  mines  by  EOD  divers,  and  the performance  of  acoustic  influence  mines. l  Marine  biofouling  —  Both  plant  and  animal forms constitute major fouling agents in shallow waters, animal  forms  being  dominant  in  deeper  waters. .  Marine  life  —  Divers  can  be  exposed  to dangerous  marine  life  in  open  waters. .  Bioluminescence  —  Bioluminescent    displays may reveal minedrops or outline moored mines and cables. l Biological ambient noise —  Minehunting  sonars and  most  acoustic  mines  are  not  seriously  affected  by this  type  of  ambient  noise. PHYSICAL  CHARACTERISTICS Water  temperature,  and  temperature  profile  versus depth can play a significant role in MIW operations. Temperature Strong negative temperature gradients found in shallow water will result in strong bottom reverberation. Detection  ranges  may  be  sharply  reduced. Variable  Depth  Sonar  (VDS)  Transducers Depth and tilt angles can be adjusted to be optimally tuned  to  existing  environmental  conditions. Diving  Operations Diver performance is affected by water temperature as well as water clarity. . In cold water, a diver’s ability to concentrate and work efficiently will be greatly reduced. . The possibility of exhaustion exists when diving operations  are  conducted  in  the  vicinity  of  industrial outflow due to higher temperature waste water. Salinity There  are  salinity  considerations  that  must  be addressed  in  the  planning  and  conducting  of  MIW operations. 13-6