SNR in a processing gain system (i.e., the GPS signal) is somewhat of a manufactured value and may be taken or defined in different ways, but it is known each t

SNR in a processing gain system (i.e., the GPS signal) is somewhat of a manufactured value and may be taken or defined in different ways, but it is known each time you take an observation for each satellite. In fact you may have more than one signal for a given satellite due to multipath. SNR is one way to decide which of those signals to report.