Abstract: Aspects relate to a self-calibrated and self-referenced spectral sensor. The spectral sensor includes an optical head that includes a light source configured to produce input light, an optical window above the light source and through which the input light is directed towards a sample in a sample measurement mode, and a reflection flag (for self-calibration and self-referencing) that is moveable between a first position beneath the optical window within a light path of the input light in a reference measurement mode and a second position away from the light path in the sample measurement mode. The spectral sensor further includes an optical core module and a processor configured to produce a reference PSD in the reference measurement mode and a sample PSD in the sample measurement mode. The processor is further configured to correct the sample PSD based on the reference PSD to produce a sample spectrum.