A plethysmography (“PPG”) measurement system may include at least one source of PPG radiation and at least one auxiliary sensor for detection of PPG radiation. The radiation source emits a portion of the PPG radiation toward a subject and another portion along an optical path for direct communication between the PPG radiation source and the auxiliary sensor. The auxiliary sensor may develop a profile against which measurements from primary PPG sensors, which receive light returning from the subject, may be compared. From this comparison, new PPG signals may be generated that exhibit lower noise than the PPG signals output by PPG sensors. These noise mitigation techniques may be used advantageously by a PPG system to generate more accurate measurements and also to reduce power consumption by the radiation sources.
