GLORIA dataset from the PGS Airbone campaign

Instrument description

The GLORIA instrument (Friedl-Vallon et al., 2014; Riese et al., 2014) is a cryogenic limb-imaging spectrometer deployed on board high-altitude aircraft. Measurements are performed in limb mode to the right-hand side of the flight track. Using 128 vertical×48 horizontal pixels of a HgCdTe detector, GLORIA passively observes the thermal radiation of the atmosphere in the spectral range from 780 to 1400 cm−1. The pointing of GLORIA is stabilized using a gimballed frame, aided by an inertial navigation system (Figure 1, Figure 2). During each interferometer sweep, GLORIA records data cubes of interferograms with all pixels simultaneously. Thereby, the detector rows correspond with limb-viewing geometries with tangent altitudes typically between ∼ 5 km and flight level.

Low tangent points are situated further away from the observer than high tangent points. The regions around the tangent points contribute the major part of the information derived in atmospheric parameter retrievals. Upward viewing observations have no tangent points along the line of sight and contribute limited information on the scenario above the flight track (Figure 3). In post-flight data processing, spectra of the detector rows within each data cube are binned to reduce uncertainties. The spectra are quantitatively calibrated using in-flight blackbody measurements (Kleinert et al., 2014)

Measurement campaign

GLORIA can be operated with different spectral sampling rates. Thereby, a higher spectral sampling results in a lower along-track sampling. Here, the measurements in high spectral-resolution mode (“chemistry mode”) with a spectral sampling of 0.0625 cm−1 are provided. The resulting apodized spectral resolution of 0.121 cm−1 (full width at half maximum using the Norton-Beer ‘strong’ apodization function (Norton and Beer, 1976; Norton and Beer, 1977)) is particularly useful for resolving weak and narrow spectral signatures of minor species. In this measurement mode, one data cube resulting in one vertical sequence of calibrated spectra is recorded within 13 s. This corresponds with a net along-track sampling of ∼ 3 km (Figure 4).

Figure 4: The GLORIA data analysis chain from the airborne observations (1st column) via the spectral images (2nd column) and the calibration and spectral binning (3rd column) to the trace gas profiles (4th column) as well as the cross sections of atmospheric parameters (5th column). Figure courtesy of W. Woiwode.

The aircraft campaigns POLSTRACC, GW-LCYCLE II, GWEX, and SALSA were conducted together as the PGS campaign during the Arctic winter 2015/16 from bases in Oberpfaffenhofen, Germany, and Kiruna, Sweden (Oelhaf et al., 2019). In total, 18 research flights from 17 December 2015 to 18 March 2016 were performed, covering regions between 80°W and 30°E longitude and 25 and 87°N latitude. Aboard the German research aircraft HALO, nine in situ and three remote-sensing instruments were deployed. The flight paths of flights with GLORIA measurements are depicted in Figure 5. Here we provide calibrated and geo-located limb-imaging hyperspectral infrared radiance data from flight 19 on 13 March 2016. Several papers discussing results of the PGS campaign using GLORIA data have been published (Johansson et al., 2018; Krisch et al., 2017; Krisch et al., 2018; Woiwode et al., 2018; Braun et al., 2019; Johansson et al., 2019).

The provided dataset belongs to one of the central flights discussed by Johansson et al., 2018. It is for example characterized by the detection of strongly enhanced volume mixing ratios of HNO3 at low altitudes.

Figure 5 : Flight paths of all PGS flights with GLORIA measurements. The parts of the flights with GLORIA high-spectral-resolution-mode measurements are represented in bold lines. Flight PGS19 (13 March 2016) is discussed in detail in this paper and is highlighted on the map, together with flight PGS12, which is discussed incidentally. Figure from Johansson et al., 2018.

These were caused by sedimentation of polar stratospheric cloud particles during the cold temperatures in the stratosphere during winter 2015/16. A comparison with in-situ data from the aircraft as well as Microwave Limb Sounder (MLS) satellite data is shown in Figure 6 (Johansson et al., 2018).

Figure 6 : HNO3 as derived from GLORIA for HALO PGS flight 19 on 3 March 2016: cross section of (a) retrieved HNO3 volume mixing ratio (the flight altitude is marked with a gray line, the ECMWF potential vorticities of 2 and 4PVU are marked with magenta dashed lines, and way points are marked with gray vertical dashed lines). Cross section of (b) MLS HNO3 data interpolated to the GLORIA tangent points and above the aircraft. Regions with no corresponding GLORIA measurement are marked with fainter colors. Cross sections of (c) total estimated error, (d) vertical resolution and (e) comparison of the GLORIA measurements (green) to the AIMS in situ measurement (blue). Figure taken from Johansson et al., 2018.