Development of Transfer Standard Spectrographs: Implications for Earth Remote Sensing

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CONFERENCE: Conference on Characterization and Radiometric Calibration for Remote Sensing (CALCON)

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Woodward, John T.; Brown, Steven W.; Shaw, Ping-Shine; Lykke, Keith R.
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During NASA’s Earth Observing System-era, a series of source radiance validation campaigns were planned and executed by the EOS Project Office with the goal of validating the radiances assigned to laboratory calibration sources, principally lamp-illuminated integrating spheres, and establishing uncertainty budgets for the disseminated radiance scale. Based on an analysis of 7 years’ worth of data, Butler et al.1 assigned an uncertainty in disseminated radiance scales of 2% to 3% in the Vis/NIR (silicon) region, increasing to 5% in the short-wave infrared region. The uncertainty in the radiance scale met EOS requirements. For example, the radiance uncertainty requirement for MODIS was 5% in the Vis/NIR spectral region and the uncertainty in disseminated radiance scales met or exceeded sensor calibration requirements. Looking to the future, uncertainty requirements for radiance are reduced below 1% [2]. Uncertainties in the radiance scale in disseminated sources from NIST cannot be reduced and alternate approaches need to be considered to meet future satellite sensor uncertainty requirements.In this presentation, the radiometric characterization and calibration of a spectrograph along with its uncertainty budget are discussed. Its long-term stability is presented and its potential use as a transfer standard radiometer is discussed. The combined standard uncertainty in the spectrograph responsivity is estimated to be 0.25% (k=1), representing a potential order of magnitude reduction in the uncertainty in the radiance of laboratory calibration sources.[1] Butler, J. J., et al., Validation of radiometric standards for the laboratory calibration of reflected-solar Earth observing satellite instruments, Proc. SPIE 6677, 667707 (2007).[2] Ohring, G., et al. (eds.), Satellite Instrument Calibration for Measuring Global Climate Change, NISTIR 7047 (2004).