▁of ▁em itting ▁area ▁into ▁one ▁of ▁W ▁observed ▁on ▁the ▁det ector . ▁ ▁The ▁broad - band ▁respons ivity , ▁is ▁then ▁just ▁the ▁signal ▁weight ed ▁by ▁this ▁w att age . ▁ ▁Where , ▁▁ ▁is ▁the ▁respons ivity ▁in ▁units ▁of ▁Sign al ▁/ ▁W , ▁( or ▁sometimes ▁V / W ▁or ▁A / W ) ▁▁ ▁is ▁the ▁out going ▁rad iance ▁from ▁the ▁black ▁body ▁( or ▁light ▁source ) ▁in ▁W / sr / cm ² ▁of ▁em itting ▁area ▁▁ ▁is ▁the ▁total ▁integrated ▁et end ue ▁between ▁the ▁em itting ▁source ▁and ▁det ector ▁surface ▁▁ ▁is ▁the ▁det ector ▁area ▁▁ ▁is ▁the ▁solid ▁angle ▁of ▁the ▁source ▁project ed ▁along ▁the ▁line ▁connecting ▁it ▁to ▁the ▁det ector ▁surface . ▁ ▁From ▁this ▁metric ▁noise - equ ivalent ▁power ▁can ▁be ▁computed ▁by ▁taking ▁the ▁noise ▁level ▁over ▁the ▁respons ivity . ▁ ▁Similarly , ▁noise - equ ivalent ▁ir rad iance ▁can ▁be ▁computed ▁using ▁the ▁respons ivity ▁in ▁units ▁of ▁phot ons / s / W ▁instead ▁of ▁in ▁units ▁of ▁the ▁signal . ▁Now , ▁the ▁detect ivity ▁is ▁simply ▁the ▁noise - equ ivalent ▁power ▁normal ized ▁to ▁the ▁band width ▁and ▁det ector ▁area . ▁ ▁References ▁▁ ▁Category : Phys ical ▁quantities ▁Category : In fra red ▁imag ing <0x0A> </s> ▁Fra och y ▁Bay ▁is ▁a ▁Scottish ▁G ael ic ▁cart oon ▁created ▁by ▁Ne illy d ub h ▁An imation ▁Limited ▁and