Suppression of sunlight interference for fluorescence in situ measurement

Except for system noise, the sunlight interference can severely influence the result of fluorescence in situ measurement. In this paper, we analyzed the noise sources of the fluorescence in situ measurement system, discussed the characteristics of sunlight interference, and studied the performances of three sunlight interference suppression methods that respectively based on pulse width modulation, lock-in amplifier and pseudorandom sequence modulation. Experiment results show that methods based on lock-in amplifier and pseudorandom sequence modulation can effectively suppress sunlight interference.