Airborne lidar observations of wind, water vapor, and aerosol profiles during the NASA Aeolus calibration and validation (Cal/Val) test flight campaign

Abstract

Abstract. Lidars are uniquely capable of collecting high-precision and high spatiotemporal resolution observations that have been used for atmospheric process studies from the ground, aircraft, and space for many years. The Aeolus mission, the first space-borne Doppler wind lidar, was developed by the European Space Agency (ESA) and launched in August 2018. Its novel Atmospheric LAser Doppler INstrument (ALADIN) observes profiles of the component of the wind vector and aerosol/cloud optical properties along the instrument's line-of-sight (LOS) direction on a global scale. A total of two airborne lidar systems have been developed at NASA Langley Research Center in recent years that collect measurements in support of several NASA Earth Science Division focus areas. The coherent Doppler Aerosol WiNd (DAWN) lidar measures vertical profiles of LOS velocity along selected azimuth angles that are combined to derive profiles of horizontal wind speed and direction. The High Altitude Lidar Observatory (HALO) measures high resolution profiles of atmospheric water vapor (WV) and aerosol and cloud optical properties. Because there are limitations in terms of spatial and vertical detail and measurement precision that can be accomplished from space, airborne remote sensing observations like those from DAWN and HALO are required to fill these observational gaps and to calibrate and validate space-borne measurements. Over a 2-week period in April 2019, during their Aeolus Cal/Val Test Flight campaign, NASA conducted five research flights over the eastern Pacific Ocean with the DC-8 aircraft. The purpose was to demonstrate the following: (1) DAWN and HALO measurement capabilities across a range of atmospheric conditions, (2) Aeolus Cal/Val flight strategies and comparisons of DAWN and HALO measurements with Aeolus, to gain an initial perspective of Aeolus performance, and (3) ways in which atmospheric dynamic processes can be resolved and better understood through simultaneous observations of wind, WV, and aerosol profile observations, coupled with numerical model and other remote sensing observations. This paper provides a brief description of the DAWN and HALO instruments, discusses the synergistic observations collected across a wide range of atmospheric conditions sampled during the DC-8 flights, and gives a brief summary of the validation of DAWN, HALO, and Aeolus observations and comparisons.

Boundary layer water vapour statistics from high-spatial-resolution spaceborne imaging spectroscopy

“…It is reasonable to ask whether this finding that the PBL variance dominates the TCWV variance is representative of the real atmosphere. Indeed, the LES results are supported by the same statistics calculated from High Altitude Lidar Observatory (HALO) flights over the Pacific Ocean in April 2019 (Bedka et al, 2021), as presented in Thompson et al (2021) and shown in Fig. 2f.…”

“…Correlation coefficient between clear-sky partial column water vapour (PCWV) integrated up to given capping altitudes, and the TCWV. (a)-(e) contain the snapshots of each individual LES run and (f) reproduces the values calculated from High Altitude Lidar Observatory flights over the Pacific(Bedka et al, 2021) as presented inThompson et al (2021). The LES profiles also have a horizontal bar appended at the derived PBL top height.…”

“…Retrievals will include a range of surfaces in a subset of the snapshots (to identify sensitivity to surface type) and then a fixed surface type across all snapshots (to identify sensitivity to atmospheric conditions). Sensitivity tests will be performed on individual subsets of snapshots as required, and a correction method for identifying the random component (Bedka et al, 2021) as presented in Thompson et al (2021). The LES profiles also have a horizontal bar appended at the derived PBL top height.…”

“…More TCWV leads to increasing depth of H 2 O absorption features relative to other wavelengths. This applies to TCWV VSWIR from missions including MERIS (Bennartz and Fischer, 2001;Guanter et al, 2008), MODIS (Diedrich et al, 2015;Gao and Kaufman, 2003), TROPOMI (Borger et al, 2020;Schneider et al, 2020), SCIAMACHY (Noël et al, 2004), GOME (Noël et al, 1999), GOME-2 (Grossi et al, 2015) and OCO-2 (Nelson et al, 2016).…”

Retrieval improvements for the ALADIN Airborne Demonstrator in support of the Aeolus wind product validation

“…Since the start of the mission, the quality of the Aeolus wind data product has been assessed by a number of calibration and validation (Cal/Val) activities based on model comparisons (Martin et al, 2021) and ground-based or suborbital instruments (Bedka et al, 2021;Iwai et al, 2021;Fehr et al, 2020Baars et al, 2020;Khaykin et al, 2020). Within the framework of this international effort, the German Aerospace Center (Deutsches Zentrum für Luft-und Raumfahrt, DLR) has conducted three airborne validation campaigns between November 2018 and October 2019 (Lux et al, 2020a), deploying its highaccuracy, coherent 2-µm DWL (Weissmann et al, 2005;Witschas et al, 2017;Witschas et al, 2020) in combination with the ALADIN Airborne Demonstrator (A2D) on-board the DLR Falcon research aircraft.…”