An apparatus for in-situ calibration of a photoacoustic sensor is provided. The apparatus includes a calibration unit that includes at least one processor configured to calculate calibration information. A light emitter of the photoacoustic sensor is configured to emit an electromagnetic spectrum and the photoacoustic sensor is configured to provide at least two measurement signals based on at least two electromagnetic spectra. The calibration unit is configured to compare the at least two measurement signals to obtain the calibration information and apply the calibration information to the photoacoustic sensor to perform the in-situ calibration.