A 3-D tomographic retrieval approach with advection compensation for the air-borne limb-imager GLORIA

Abstract

Abstract. Infrared limb sounding from aircraft can provide 2-D curtains of multiple trace gas species. However, conventional limb sounders view perpendicular to the aircraft axis and are unable to resolve the observed airmass along their line-of-sight. GLORIA (Gimballed Limb Observer for Radiance Imaging of the Atmosphere) is a new remote sensing instrument that is able to adjust its horizontal view angle with respect to the aircraft flight direction from 45 • to 135 • . This will allow for tomographic measurements of mesoscale structures for a wide variety of atmospheric constituents.Many flights of the GLORIA instrument will not follow closed curves that allow measuring an airmass from all directions. Consequently, it is examined by means of simulations, what spatial resolution can be expected under ideal conditions from tomographic evaluation of measurements made during a straight flight. It is demonstrated that the achievable horizontal resolution in the line-of-sight direction could be reduced from over 200 km to around 70 km compared to conventional retrievals and that the tomographic retrieval is also more robust against horizontal gradients in retrieved quantities in this direction. In a second step, it is shown that the incorporation of channels exhibiting different optical depth can further enhance the spatial resolution of 3-D retrievals enabling the exploitation of spectral samples usually not used for limb sounding due to their opacity.A second problem for tomographic retrievals is that advection, which can be neglected for conventional retrievals, plays an important role for the time-scales involved in a tomographic measurement flight. This paper presents a method to diagnose the effect of a time-varying atmosphere on a 3-D Correspondence to: J. Ungermann (j.ungermann@fz-juelich.de) retrieval and demonstrates an effective way to compensate for effects of advection by incorporating wind-fields from meteorological datasets as a priori information.

Airborne limb-imaging measurements of temperature, HNO<sub>3</sub>, O<sub>3</sub>, ClONO<sub>2</sub>, H<sub>2</sub>O and CFC-12 during the Arctic winter 2015/2016: characterization, in situ validation and comparison to Aura/MLS

“…This assures the best possible match of sampled air masses with the in situ instrument. It is important to keep in mind that the data sets do not probe exactly the same air masses, since GLORIA measures at the limb and thus collects the radiation from a long path of ≈ 100 km through the atmosphere Ungermann et al, 2011). In Fig.…”

“…These different azimuth pointing angles are desired to avoid stray sunlight, to correct for movements of the carrying aircraft due to cross winds or to adopt the measurement line of sight (LOS) for expected horizontal gradients in temperature or trace gases. Another application of the adjustable azimuth angle is the feasibility of tomographic measurements (Ungermann et al, 2011).…”

Transport of Antarctic stratospheric strongly dehydrated air into the troposphere observed during the HALO-ESMVal campaign 2012

“…The gimbal mount and inertial altitude control system allows GLORIA to maintain a steady pointing on a moving aircraft; it can also be used to point the instrument at a range of azimuth angles with respect to the aircraft, covering about 70 • . This allows for tomographic measurement patterns and 3-D reconstruction of fine-scale filamentary structures (Ungermann et al, 2011;Kaufmann et al, 2015). The vertical location of retrieved quantities approximately follows the tangent points of the measurement geometry (parabola curve through the atmosphere).…”

A large-area blackbody for inflight calibration of an infrared interferometer deployed on board a long-duration balloon for stratospheric research

“…GLORIA makes novel information on small-scale atmospheric dynamics available, e.g. STE, the StratosphereTroposphere Exchange and other important phenomena (Riese et al, 2014;Ungermann et al, 2011Ungermann et al, , 2015.…”