Quantification and mitigation of the instrument effects and uncertainties of the airborne limb imaging FTIR GLORIA

Abstract

Abstract. The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) is an infrared imaging FTS (Fourier transform spectrometer) with a 2-D infrared detector that is operated on two high-flying research aircraft. It has flown on eight campaigns and measured along more than 300 000 km of flight track. This paper details our instrument calibration and characterization efforts, which, in particular, almost exclusively leverage in-flight data. First, we present the framework of our new calibration scheme, which uses information from all three available calibration sources (two blackbodies and upward-pointing “deep space” measurements). Part of this scheme is a new algorithm for correcting the erratically changing nonlinearity of a subset of detector pixels and the identification of the remaining bad pixels. Using this new calibration, we derive a 1σ bound of 1 % on the instrument gain error and a bound of 30 nW cm−2 sr−1 cm on the instrument offset error. We show how we can examine the noise and spectral accuracy for all measured atmospheric spectra and derive a spectral accuracy of 5 ppm on average. All these errors are compliant with the initial instrument requirements. We also discuss, for the first time, the pointing system of the GLORIA instrument. Combining laboratory calibration efforts with the measurement of astronomical bodies during the flight, we can achieve a pointing accuracy of 0.032∘, which corresponds to one detector pixel. The paper concludes with a brief study of how these newly characterized instrument parameters affect temperature and ozone retrievals. We find that the pointing uncertainty and, to a lesser extent, the instrument gain uncertainty are the main contributors to the error in the result.

Non‐Orographic Gravity Waves and Turbulence Caused by Merging Jet Streams

“…The performance and processing of the GLORIA measurements have been improved continuously over the last years. The GLORIA observations during SouthTRAC are characterized by instrumental gain and offset errors as low as 1% and 30 nW cm −2 sr −1 cm, respectively (Ungermann et al., 2022). From the GLORIA observations, vertical profiles and 3D distributions of temperature, trace gas volume mixing ratios, and clouds are retrieved (e.g., Johansson et al., 2018; Krasauskas et al., 2021; Krisch et al., 2017; Wetzel et al., 2021).…”

Ammonia (NH3) in the UTLS: GLORIA airborne measurements for CAMS model evaluation in the Asian Monsoon and in biomass burning plumes above the South Atlantic

“…The resulting calibrated spectra at each detector pixel are screened, filtered, and finally horizontally binned into 127 spectra per recorded measurement sampled in the vertical direction (with one horizontal line of spectra beeing disregarded completely due to detector artifacts; Kleinert et al, 2014;Ungermann et al, 2022). All GLORIA retrievals in this study are based on version v03.02 of GLORIA level 1 data (calibrated spectral radiances).…”