ar ▁systems ▁where ▁the ▁anten na ▁is ▁typically ▁drawn ▁under ▁the ▁water . ▁In ▁active ▁son ar , ▁the ▁son ar ▁system ▁em its ▁sound ▁waves ▁( ac oust ic ▁energy ) ▁then ▁listening ▁and ▁monitoring ▁any ▁existing ▁echo ▁( the ▁reflected ▁waves ). ▁The ▁reflected ▁sound ▁waves ▁can ▁be ▁used ▁to ▁estimate ▁parameters , ▁such ▁as ▁velocity , ▁position ▁and ▁direction ▁etc . ▁D iff icult ies ▁and ▁limitations ▁in ▁son ar ▁systems ▁comparing ▁to ▁rad ar ▁systems ▁emer ged ▁from ▁the ▁fact ▁that ▁the ▁propag ation ▁speed ▁of ▁sound ▁waves ▁under ▁the ▁water ▁is ▁slower ▁than ▁the ▁radio ▁waves . ▁Another ▁source ▁of ▁limitation ▁is ▁the ▁high ▁propag ation ▁losses ▁and ▁scatter ing . ▁Despite ▁all ▁these ▁limitations ▁and ▁difficulties , ▁son ar ▁system ▁remains ▁a ▁reliable ▁technique ▁for ▁range , ▁distance , ▁position ▁and ▁other ▁parameters ▁estimation ▁for ▁under water ▁applications . ▁▁ ▁N ORS AR ▁is ▁an ▁independent ▁ge o - s cient ific ▁research ▁facility ▁that ▁was ▁founded ▁in ▁Norway ▁in ▁ 1 9 6 8 . ▁N ORS AR ▁has ▁been ▁working ▁with ▁array ▁processing ▁ever ▁since ▁to ▁measure ▁se ism ic ▁activity ▁around ▁the ▁glo be . ▁They ▁are ▁currently ▁working ▁on ▁an ▁International ▁Mon itor ing ▁System ▁which ▁will ▁compr ise ▁ 5 0 ▁primary ▁and ▁ 1 2 0 ▁auxili ary ▁se ism ic ▁stations ▁around ▁the ▁world . ▁N ORS AR ▁has ▁on going ▁work ▁to ▁improve ▁array ▁processing ▁to ▁improve ▁monitoring ▁of ▁se ism ic ▁activity ▁not ▁only ▁in ▁Norway ▁but ▁around