P1.2
Error in FTIR spectrometer radiances due to noise at high levels
Penny M. Rowe, University of Idaho, Moscow, ID; and S. P. Neshyba, C. J. Cox, and V. P. Walden
A significant contribution to error in calibrated spectra measured by Fourier transform IR spectrometers is random noise in uncalibrated spectra of the scene and hot and cold calibration sources (with standard deviations σs, σh and σc). For low noise, the well-known equation for the variance in the calibrated radiance (σL2) is related simply to σs, σh, σc and the instrument responsivity (r). An estimate of σL2 is needed at higher noise levels for setting a practical limit for the low noise threshold and for measurements that exceed it. Additionally, a criterion is needed for rejection of spectral data points having unacceptably large errors. Such errors can occur at wavenumbers where the absorption coefficient is so strong that trace gases between source and detector absorb and re-emit all source radiation. The expression for the error in the calibrated spectrum is found to have a singularity for a particular pair of uncalibrated source-spectrum errors, making σL2 infinite; the median error is suggested as an alternative. Errors and biases in calibrated radiances at high noise levels are shown for two FTIR instruments used for atmospheric radiation measurements: the Atmospheric Emitted Radiance Interferometer (AERI) and the Interferometric Monitor for Greenhouse Gases (IMG). A criterion (σr/r < 0.3) is suggested for identification of spectral data points having unacceptably large errors and is applied to AERI data.
Poster Session 1, Radiation Poster Session I: Earth Radiation Budget
Monday, 28 June 2010, 5:30 PM-8:30 PM, Exhibit Hall
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