On-orbit absolute blackbody emissivity determination using the heated halo method

We present a novel method to measure the absolute spectral emissivity of a blackbody cavity in situ using the heated halo, a broadband thermal source. Laboratory demonstrations have yielded spectral emissivity measurements of a 0.999 emissivity blackbody that are in agreement with results based on Monte Carlo ray trace modelling. The combined uncertainty of the measurement is less than 4 x 10(-4) (k = 3) in the 580 cm(-1) to 2800 cm(-1) spectral range. This is equivalent to a detection limit of 11 mK in the error in radiance temperature for a calibration blackbody (at 330 K, 1500 cm(-1)) due to blackbody cavity emissivity drift. These results provide the experimental foundation for this technology to be implemented on satellite instruments and thus eliminate a key, time-dependent, systematic error from future measurements on-orbit.