Characterization of blackbody inhomogeneity and its effect on the retrieval results of the GLORIA instrument

Kleinert, Anne; Krisch, Isabell; Ungermann, Jörn; Adibekyan, Albert; Gutschwager, B.; Monte, C.

doi:10.5194/amt-11-3871-2018

Cited by 4 publications

(6 citation statements)

References 21 publications

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“…The standard deviations and correlation lengths used for the different systematic errors are summarised in Table 2. The effects of instrument errors on the GLORIA retrieval are discussed in detail by Kleinert et al (2018). The covariance matrix for measurement noise is taken from theoretical estimates given by Friedl-Vallon et al (2014) that agree As most systematic errors are fully correlated over all measurements of one flight and the noise terms are negligible in magnitude compared to the wave perturbation terms, the error term G(a a ) is disregarded in the simulation study.…”

Section: Tomographic Temperature Retrievalmentioning

confidence: 99%

“…These factors are chosen ad hoc and cannot be interpreted directly as physically meaningful correlation lengths. A more physical regularisation scheme is currently under development and will be described by Krasauskas et al (2018). This minimisation problem is solved with a truncated conjugate gradient-based trust region scheme.…”

Section: Tomographic Temperature Retrievalmentioning

confidence: 99%

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Limited angle tomography of mesoscale gravity waves by the infrared limb-sounder GLORIA

et al. 2018

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Abstract. Three-dimensional measurements of gravity waves are required in order to quantify their directionresolved momentum fluxes and obtain a better understanding of their propagation characteristics. Such 3-D measurements of gravity waves in the lowermost stratosphere have been provided by the airborne Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) using full angle tomography. Closed flight patterns of sufficient size are needed to acquire the full set of angular measurements for full angle tomography. These take about 2 h and are not feasible everywhere due to scientific reasons or air traffic control restrictions. Hence, this paper investigates the usability of limited angle tomography for gravity wave research based on synthetic observations. Limited angle tomography uses only a limited set of angles for tomographic reconstruction and can be applied to linear flight patterns. A synthetic end-toend simulation has been performed to investigate the sensitivity of limited angle tomography to gravity waves with different wavelengths and orientations with respect to the flight path. For waves with wavefronts roughly perpendicular to the flight path, limited angle tomography and full angle tomography can derive wave parameters like wavelength, amplitude, and wave orientation with similar accuracy. For waves with a horizontal wavelength above 200 km and vertical wavelength above 3 km, the wavelengths can be retrieved with less than 10 % error, the amplitude with less than 20 % error, and the horizontal wave direction with an error below 10 • . This is confirmed by a comparison of results obtained from full angle tomography and limited angle tomography for real measurements taken on 25 January 2016 over Iceland. The reproduction quality of gravity wave parameters with limited angle tomography, however, depends strongly on the orientation of the waves with respect to the flight path. Thus, full angle tomography might be preferable in cases in which the orientation of the wave cannot be predicted or waves with different orientations exist in the same volume and thus the flight path cannot be adjusted accordingly. Also, for low-amplitude waves and short-scale waves full angle tomography has advantages due to its slightly higher resolution and accuracy.

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Section: Tomographic Temperature Retrievalmentioning

confidence: 99%

Section: Tomographic Temperature Retrievalmentioning

confidence: 99%

Limited angle tomography of mesoscale gravity waves by the infrared limb-sounder GLORIA

et al. 2018

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“…To estimate the effect of parameter errors on the result, repeated retrieval calculations have been performed with varying parameters. The effect of radiometric calibration uncertainties has been modelled by an additive spectrally constant offset error of 30 nW (cm −1 sr cm 2 ) −1 and a multiplicative scaling error of 1% [35]. A temperature error of 1 K is applied to test its effect on the resulting water vapour profile.…”

Section: Retrieval Diagnosticsmentioning

confidence: 99%

Retrieval of Water Vapour Profiles from GLORIA Nadir Observations

et al. 2021

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We present the first analysis of water vapour profiles derived from nadir measurements by the infrared imaging Fourier transform spectrometer GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere). The measurements were performed on 27 September 2017, during the WISE (Wave driven ISentropic Exchange) campaign aboard the HALO aircraft over the North Atlantic in an area between 37°–50°N and 20°–28°W. From each nadir recording of the 2-D imaging spectrometer, the spectral radiances of all non-cloudy pixels have been averaged after application of a newly developed cloud filter. From these mid-infrared nadir spectra, vertical profiles of H2O have been retrieved with a vertical resolution corresponding to five degrees of freedom below the aircraft. Uncertainties in radiometric calibration, temperature and spectroscopy have been identified as dominating error sources. Comparing retrievals resulting from two different a priori assumptions (constant exponential vs. ERA 5 reanalysis data) revealed parts of the flight where the observations clearly show inconsistencies with the ERA 5 water vapour fields. Further, a water vapour inversion at around 6 km altitude could be identified in the nadir retrievals and confirmed by a nearby radiosonde ascent. An intercomparison of multiple water vapour profiles from GLORIA in nadir and limb observational modes, IASI (Infrared Atmospheric Sounding Interferometer) satellite data from two different retrieval processors, and radiosonde measurements shows a broad consistency between the profiles. The comparison shows how fine vertical structures are represented by nadir sounders as well as the influence of a priori information on the retrievals.

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“…Over the course of processing and evaluating data from these campaigns, our understanding of the instrument has constantly improved (Kleinert et al, 2014;Guggenmoser et al, 2015;Kleinert et al, 2018). We have consequently adapted and standardized our in-flight calibration scenario.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2022

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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.

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Characterization of blackbody inhomogeneity and its effect on the retrieval results of the GLORIA instrument

Cited by 4 publications

References 21 publications

Limited angle tomography of mesoscale gravity waves by the infrared limb-sounder GLORIA

Limited angle tomography of mesoscale gravity waves by the infrared limb-sounder GLORIA

Retrieval of Water Vapour Profiles from GLORIA Nadir Observations

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

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