▁Washington ▁County , ▁Missouri ▁ ▁See ▁also ▁ ▁Bel grade ▁( disambiguation ) ▁ ▁Category : T own ship ▁name ▁dis ambiguation ▁pages <0x0A> </s> ▁In ▁physics , ▁coh er ent ▁back sc atter ing ▁is ▁observed ▁when ▁coh er ent ▁radiation ▁( such ▁as ▁a ▁las er ▁beam ) ▁propag ates ▁through ▁a ▁medium ▁which ▁has ▁a ▁large ▁number ▁of ▁scatter ing ▁cent ers ▁( such ▁as ▁milk ▁or ▁a ▁thick ▁cloud ) ▁of ▁size ▁compar able ▁to ▁the ▁w avel ength ▁of ▁the ▁radiation . ▁ ▁The ▁waves ▁are ▁scattered ▁many ▁times ▁while ▁travel ing ▁through ▁the ▁medium . ▁Even ▁for ▁in co her ent ▁radiation , ▁the ▁scatter ing ▁typically ▁reaches ▁a ▁local ▁maximum ▁in ▁the ▁direction ▁of ▁back sc atter ing . ▁For ▁coh er ent ▁radiation , ▁however , ▁the ▁peak ▁is ▁two ▁times ▁higher . ▁ ▁C oh er ent ▁back sc atter ing ▁is ▁very ▁difficult ▁to ▁detect ▁and ▁measure ▁for ▁two ▁reasons . ▁The ▁first ▁is ▁fairly ▁obvious , ▁that ▁it ▁is ▁difficult ▁to ▁measure ▁the ▁direct ▁back sc atter ▁without ▁blocking ▁the ▁beam , ▁but ▁there ▁are ▁methods ▁for ▁over coming ▁this ▁problem . ▁The ▁second ▁is ▁that ▁the ▁peak ▁is ▁usually ▁extremely ▁sharp ▁around ▁the ▁back ward ▁direction , ▁so ▁that ▁a ▁very ▁high ▁level ▁of ▁angular ▁resolution ▁is ▁needed ▁for ▁the ▁det ector ▁to ▁see ▁the ▁peak ▁without ▁aver aging ▁its ▁intensity ▁out ▁over ▁the ▁surrounding ▁angles ▁where ▁the ▁intensity ▁can ▁under go ▁large ▁di ps . ▁At ▁angles ▁other ▁than ▁the