We developed a method that enables one to correct solar blind pyrometer cavity temperature measurements for the system-sensor reflection error. The method is valid for measurements made on diffusely emitting and reflecting cavity surfaces when there is no participating medium between the pyrometer and the surface of interest. The surfaces' emissivities must be known. The procedure gives the uncertainty interval associated with the correction. The procedure was validated by measuring surface temperatures in a solar reactor insulated with Yttria-stabilized Zirconia felt receiving concentrated solar radiation. The temperature range of the experimental study was from 1100-1600 K. Temperature measurements made with a pyrometer having a narrow band filter centered at 1.398 Am were compared to temperatures measured with Zirconia felt shielded thermocouples. Uncorrected pyrometer measurements differed from the thermocouple measurements by as much as 350 K. The thermocouple measurements mostly fell within the system-sensor uncertainty interval of the corrected temperature measurements. The uncertainty interval depends both on the number of surfaces probed with the pyrometer and the nature of the solar blind filter A numerical simulation study showed that a UV filter centered at a wavelength near 0.285 mu m gives tighter system-sensor uncertainty intervals than an IR filter centered at 1.398 mu m.