A thermal processing system (100, 200, 300) for performing thermal processing of semiconductor workpieces, the thermal processing system comprising: a workpiece support plate configured to support a workpiece; one or more heat sources (130, 140) configured to heat the workpiece; one or more windows (106, 108) disposed between the workpiece support plate and the one or more heat sources, the one or more windows comprising one or more transparent regions that are transparent to at least a portion of electromagnetic radiation within a measurement wavelength range and one or more opaque regions that are opaque to electromagnetic radiation within the portion of the measurement wavelength range; and a temperature measurement system configured to obtain a temperature measurement indicative of a temperature of the workpiece, the temperature measurement system comprising: a plurality of infrared emitters (150, 152, 154) configured to emit infrared radiation; a plurality of infrared sensors (165, 166, 167, 168), each infrared sensor corresponding to one of the plurality of infrared emitters, each of the plurality of infrared sensors configured to measure infrared radiation within the measurement wavelength range and disposed such that at least one of the one or more transparent regions is at least partially within a field of view of at least one of the plurality of infrared sensors; and a controller configured to perform operations, the operations comprising: obtaining, from the plurality of infrared sensors, at least one first transmittance measurement, at least one second transmittance measurement, and at least one reflectance measurement associated with the workpiece; determining, based at least in part on the at least one first transmittance measurement, the at least one second transmittance measurement, and the at least one reflectance measurement, a temperature of the workpiece when the temperature of the workpiece is less than about 600 °C. a workpiece support plate configured to support a workpiece; one or more heat sources (130, 140) configured to heat the workpiece; one or more windows (106, 108) disposed between the workpiece support plate and the one or more heat sources, the one or more windows comprising one or more transparent regions that are transparent to at least a portion of electromagnetic radiation within a measurement wavelength range and one or more opaque regions that are opaque to electromagnetic radiation within the portion of the measurement wavelength range; and a temperature measurement system configured to obtain a temperature measurement indicative of a temperature of the workpiece, the temperature measurement system comprising: a plurality of infrared emitters (150, 152, 154) configured to emit infrared radiation; a plurality of infrared sensors (165, 166, 167, 168), each infrared sensor corresponding to one of the plurality of infrared emitters, each of the plurality of infrared sensors configured to measure infrared radiation within the measurement wavelength range and disposed such that at least one of the one or more transparent regions is at least partially within a field of view of at least one of the plurality of infrared sensors; and a plurality of infrared emitters (150, 152, 154) configured to emit infrared radiation; a plurality of infrared sensors (165, 166, 167, 168), each infrared sensor corresponding to one of the plurality of infrared emitters, each of the plurality of infrared sensors configured to measure infrared radiation within the measurement wavelength range and disposed such that at least one of the one or more transparent regions is at least partially within a field of view of at least one of the plurality of infrared sensors; and a controller configured to perform operations, the operations comprising: obtaining, from the plurality of infrared sensors, at least one first transmittance measurement, at least one second transmittance measurement, and at least one reflectance measurement associated with the workpiece; determining, based at least in part on the at least one first transmittance measurement, the at least one second transmittance measurement, and the at least one reflectance measurement, a temperature of the workpiece when the temperature of the workpiece is less than about 600 °C. obtaining, from the plurality of infrared sensors, at least one first transmittance measurement, at least one second transmittance measurement, and at least one reflectance measurement associated with the workpiece; determining, based at least in part on the at least one first transmittance measurement, the at least one second transmittance measurement, and the at least one reflectance measurement, a temperature of the workpiece when the temperature of the workpiece is less than about 600 °C.