Multi-channel photoplethysmography sensor

An activity monitoring apparatus comprising:

• one or more first light sources that are configured to emit light having a first light wavelength corresponding to a green light wavelength;
• one or more second light sources that are configured to emit light having a second light wavelength corresponding to a red light wavelength, wherein one or more of the one or more first light sources and one or more of the one or more second light sources are co-located;
• one or more processors;
• a non-transitory computer-readable storage medium coupled to the one or more processors and storing instructions which, when executed using the one or more processors, cause the one or more processors to:
• obtain one or more first photoplethysmography (PPG) signals based on light emitted from the one or more first light sources;
• obtain one or more second PPG signals based on light emitted from the one or more second light sources;
• determine that a majority of the one or more second PPG signals are comprised of motion signals;
• responsive to determining that the majority of the one or more second PPG signals are comprised of motion signals, remove corresponding motion signals from the one or more first PPG signals;
• generate an estimated heart rate value based on only the one or more first PPG signals after the corresponding motion signals have been removed from the one or more first PPG signals;
• and
• cause the estimated heart rate value to be displayed via a user interface.