Benjamin Witschas

The HEterodyne Detection Wind lIdar Gadget (HEDWIG) is a new airborne Doppler wind lidar developed at the German Aerospace Center (DLR) for high-resolution observations of atmospheric wind profiles. The instrument operates at an eye-safe wavelength of 1617 nm. A newly developed double-wedge scanner provides rapid and flexible beam steering, enabling both conical scanning for horizontal wind retrieval and parallel nadir-pointing observations for direct measurements of the vertical wind component. The complete instrument, including laser transmitter, receiver, scanner, data acquisition system and wind retrieval chain, is described in detail. Particular emphasis is placed on the optical and mechanical design of the scanner, the synchronized data acquisition, as well as the retrieval algorithms for line-of-sight (LOS) Doppler velocities and atmospheric wind vectors. The instrument was successfully deployed for the first time aboard the German research aircraft HALO during the North Atlantic Waveguide, Dry Intrusion and Downstream Impact Campaign (NAWDIC) in winter 2026. Surface-return analyses demonstrate a systematic wind speed error below 0.1 m s ⁻¹ and a random error of about 0.2 m s ⁻¹ for single LOS measurements under high-SNR conditions. First airborne observations further demonstrate the capability of HEDWIG to retrieve horizontal wind vectors together with high-resolution vertical wind profiles. The instrument therefore provides a unique observational capability for airborne studies of atmospheric dynamics as well as for satellite instrument validation as for instance the Doppler velocity products of the cloud profiling radar on EarthCARE, but also for future missions as WIVERN and Aeolus-2.

Mineral dust is a major component of atmospheric aerosol mass, yet its role in cloud processes remains poorly understood. While laboratory studies have explored its ability to act as cloud condensation nuclei (CCN) and ice nucleating particles (INPs), in situ atmospheric measurements are scarce. This study presents unique in situ and remote sensing observations of dust-embedded clouds from the A-LIFE campaign in the Eastern Mediterranean. In situ observations on 20 April 2017 including shadow images and size distributions of aerosol and cloud particles combined with Doppler wind lidar (DWL) measurements were used to characterize dust and cloud microphysical properties. A novel size distribution retrieval for the second-generation Cloud, Aerosol, and Precipitation Spectrometer (CAPS) was developed – accounting for instrumental uncertainties, particle non-sphericity, and refractive index via a Monte Carlo method – and a machine learning-based calibration of the CAPS hotwire sensor for LWC measurements was introduced. Using the newly developed analysis tools, this study presents a quantitative assessment of two different aerosol-cloud interaction processes in dust-embedded clouds: Measurements at the cloud-top indicated heterogeneous ice nucleation, in accordance with laboratory experiments and INP parameterizations. Furthermore, small-scale CCN activation of mineral dust particles into liquid droplets (~10 µm) was observed in the middle part of the cloud, with activation diameters as small as 0.13–0.23 µm, consistent with laboratory findings. DWL observations revealed vertical lifting as the driver of increased water supersaturation, enabling CCN activation. These findings provide new insights into the microphysical processes of dust-embedded clouds and their interactions with the atmosphere.

Mineral dust is a major component of atmospheric aerosol mass, yet its role in cloud processes remains poorly understood. While laboratory studies have explored its ability to act as cloud condensation nuclei (CCN) and ice nucleating particles (INPs), in situ atmospheric measurements are scarce. This study presents unique in situ and remote sensing observations of dust-embedded clouds from the A-LIFE campaign in the Eastern Mediterranean. In situ observations on 20 April 2017 including shadow images and size distributions of aerosol and cloud particles combined with Doppler wind lidar (DWL) measurements were used to characterize dust and cloud microphysical properties. A novel size distribution retrieval for the second-generation Cloud, Aerosol, and Precipitation Spectrometer (CAPS) was developed – accounting for instrumental uncertainties, particle non-sphericity, and refractive index via a Monte Carlo method – and a machine learning-based calibration of the CAPS hotwire sensor for LWC measurements was introduced. Using the newly developed analysis tools, this study presents a quantitative assessment of two different aerosol-cloud interaction processes in dust-embedded clouds: Measurements at the cloud-top indicated heterogeneous ice nucleation, in accordance with laboratory experiments and INP parameterizations. Furthermore, small-scale CCN activation of mineral dust particles into liquid droplets (~10 µm) was observed in the middle part of the cloud, with activation diameters as small as 0.13–0.23 µm, consistent with laboratory findings. DWL observations revealed vertical lifting as the driver of increased water supersaturation, enabling CCN activation. These findings provide new insights into the microphysical processes of dust-embedded clouds and their interactions with the atmosphere.

The Heterodyne Detection Wind lidar Gadget (HEDWIG) is a new airborne Doppler wind lidar developed at the German Aerospace Center (DLR) for high-resolution observations of atmospheric wind profiles. The instrument operates at an eye-safe wavelength of 1617 nm. A newly developed double-wedge scanner provides rapid and flexible beam steering, enabling both conical scanning for horizontal wind retrieval and parallel nadir-pointing observations for direct measurements of the vertical wind component. The complete instrument, including laser transmitter, receiver, scanner, data acquisition system and wind retrieval chain, is described in detail. Particular emphasis is placed on the optical and mechanical design of the scanner, the synchronized data acquisition, as well as the retrieval algorithms for line-of-sight (LOS) Doppler velocities and atmospheric wind vectors. The instrument was successfully deployed for the first time aboard the German research aircraft HALO during the North Atlantic Waveguide, Dry Intrusion and Downstream Impact Campaign (NAWDIC) in winter 2026. Surface-return analyses demonstrate a systematic wind speed error below 0.1 m s^-1 and a random error of about 0.2 m s^-1 for single LOS measurements. First airborne observations further demonstrate the capability of HEDWIG to retrieve horizontal wind vectors together with high-resolution vertical wind profiles. The instrument therefore provides a unique observational capability for airborne studies of atmospheric dynamics as well as for satellite instrument validation as for instance the Doppler velocity product of the cloud profiling radar on EarthCARE, but also for future missions as WIVERN and Aeolus-2.

The Heterodyne Detection Wind lidar Gadget (HEDWIG) is a new airborne Doppler wind lidar developed at the German Aerospace Center (DLR) for high-resolution observations of atmospheric wind profiles. The instrument operates at an eye-safe wavelength of 1617 nm. A newly developed double-wedge scanner provides rapid and flexible beam steering, enabling both conical scanning for horizontal wind retrieval and parallel nadir-pointing observations for direct measurements of the vertical wind component. The complete instrument, including laser transmitter, receiver, scanner, data acquisition system and wind retrieval chain, is described in detail. Particular emphasis is placed on the optical and mechanical design of the scanner, the synchronized data acquisition, as well as the retrieval algorithms for line-of-sight (LOS) Doppler velocities and atmospheric wind vectors. The instrument was successfully deployed for the first time aboard the German research aircraft HALO during the North Atlantic Waveguide, Dry Intrusion and Downstream Impact Campaign (NAWDIC) in winter 2026. Surface-return analyses demonstrate a systematic wind speed error below 0.1 m s^-1 and a random error of about 0.2 m s^-1 for single LOS measurements. First airborne observations further demonstrate the capability of HEDWIG to retrieve horizontal wind vectors together with high-resolution vertical wind profiles. The instrument therefore provides a unique observational capability for airborne studies of atmospheric dynamics as well as for satellite instrument validation as for instance the Doppler velocity product of the cloud profiling radar on EarthCARE, but also for future missions as WIVERN and Aeolus-2.

This feasibility study demonstrates, through modelling and simulation, that a Versatile Atmospheric Laser Doppler Instrument (VALDI), based on a single Fizeau interferometer and imaging detector, has the potential for precise, high-sensitivity, simultaneous measurements of wind speeds, temperature and atmospheric scattering ratio (ASR). In simple principle, the linear frequency dispersion of the Fizeau interferometer creates in the fringe plane an extended spectrum of atmospheric scattering. This is made up of broadband molecular scattering resulting in a Rayleigh-Brillouin spectral component of ≈4 GHz full width at half maximum (at 355 nm wavelength), and a narrow band spectral component originating from aerosol (Mie) scattering with spectral characteristics defined by the laser source and Fizeau design parameters. For the present investigation, a 16 channel detector, similar to those employed in ESA’s Aeolus spaceborne lidar is considered, together with an adapted Fizeau interferometer of specifications (plate separation, wedge angle, finesse, etc.) well within current practice. Extensive modelling and simulation demonstrates that the 16 detector channels of spectral information provide versatile, high sensitivity operation, for widely varying atmospheric scattering and attenuation conditions throughout the troposphere and lower stratosphere. Drawing on operational data and experience of the ESA Aeolus spaceborne lidar systems, simulations indicate that a spaceborne VALDI could achieve wind speed uncertainties σvHLOS in the range of ±1.4 m s−1 to ±3.2 m s−1, from the aerosol signal in central detector channels (with ASR ≈ 2 and 12 km observational path). The outer channels, dominated by molecular signal, should give wind speed uncertainties between ±2.4 m s−1 and ±3.4 m s−1 (for 87 km observation path length). It is further shown that fast analytical ratio techniques provide Doppler frequency analysis with accuracy approaching the Cramér-Rao ultimate quantum limit within 10 % to 20 %. Finally, questions of practical design, construction and operation are considered. In this regard the single interferometer and detector, with single optical delivery train, offers considerable advantages of optical simplicity, high signal throughput efficiency, robustness and good long term alignment control and stability, plus wide frequency/wind speed capability extending well above 100 m s−1.

The Heterodyne Detection Wind lidar Gadget (HEDWIG) is a new airborne Doppler wind lidar developed at the German Aerospace Center (DLR) for high-resolution observations of atmospheric wind profiles. The instrument operates at an eye-safe wavelength of 1617 nm. A newly developed double-wedge scanner provides rapid and flexible beam steering, enabling both conical scanning for horizontal wind retrieval and parallel nadir-pointing observations for direct measurements of the vertical wind component. The complete instrument, including laser transmitter, receiver, scanner, data acquisition system and wind retrieval chain, is described in detail. Particular emphasis is placed on the optical and mechanical design of the scanner, the synchronized data acquisition, as well as the retrieval algorithms for line-of-sight (LOS) Doppler velocities and atmospheric wind vectors. The instrument was successfully deployed for the first time aboard the German research aircraft HALO during the North Atlantic Waveguide, Dry Intrusion and Downstream Impact Campaign (NAWDIC) in winter 2026. Surface-return analyses demonstrate a systematic wind speed error below 0.1 m s^-1 and a random error of about 0.2 m s^-1 for single LOS measurements. First airborne observations further demonstrate the capability of HEDWIG to retrieve horizontal wind vectors together with high-resolution vertical wind profiles. The instrument therefore provides a unique observational capability for airborne studies of atmospheric dynamics as well as for satellite instrument validation as for instance the Doppler velocity product of the cloud profiling radar on EarthCARE, but also for future missions as WIVERN and Aeolus-2.

The Heterodyne Detection Wind lidar Gadget (HEDWIG) is a new airborne Doppler wind lidar developed at the German Aerospace Center (DLR) for high-resolution observations of atmospheric wind profiles. The instrument operates at an eye-safe wavelength of 1617 nm. A newly developed double-wedge scanner provides rapid and flexible beam steering, enabling both conical scanning for horizontal wind retrieval and parallel nadir-pointing observations for direct measurements of the vertical wind component. The complete instrument, including laser transmitter, receiver, scanner, data acquisition system and wind retrieval chain, is described in detail. Particular emphasis is placed on the optical and mechanical design of the scanner, the synchronized data acquisition, as well as the retrieval algorithms for line-of-sight (LOS) Doppler velocities and atmospheric wind vectors. The instrument was successfully deployed for the first time aboard the German research aircraft HALO during the North Atlantic Waveguide, Dry Intrusion and Downstream Impact Campaign (NAWDIC) in winter 2026. Surface-return analyses demonstrate a systematic wind speed error below 0.1 m s^-1 and a random error of about 0.2 m s^-1 for single LOS measurements. First airborne observations further demonstrate the capability of HEDWIG to retrieve horizontal wind vectors together with high-resolution vertical wind profiles. The instrument therefore provides a unique observational capability for airborne studies of atmospheric dynamics as well as for satellite instrument validation as for instance the Doppler velocity product of the cloud profiling radar on EarthCARE, but also for future missions as WIVERN and Aeolus-2.

The Heterodyne Detection Wind lidar Gadget (HEDWIG) is a new airborne Doppler wind lidar developed at the German Aerospace Center (DLR) for high-resolution observations of atmospheric wind profiles. The instrument operates at an eye-safe wavelength of 1617 nm. A newly developed double-wedge scanner provides rapid and flexible beam steering, enabling both conical scanning for horizontal wind retrieval and parallel nadir-pointing observations for direct measurements of the vertical wind component. The complete instrument, including laser transmitter, receiver, scanner, data acquisition system and wind retrieval chain, is described in detail. Particular emphasis is placed on the optical and mechanical design of the scanner, the synchronized data acquisition, as well as the retrieval algorithms for line-of-sight (LOS) Doppler velocities and atmospheric wind vectors. The instrument was successfully deployed for the first time aboard the German research aircraft HALO during the North Atlantic Waveguide, Dry Intrusion and Downstream Impact Campaign (NAWDIC) in winter 2026. Surface-return analyses demonstrate a systematic wind speed error below 0.1 m s-1 and a random error of about 0.2 m s-1 for single LOS measurements. First airborne observations further demonstrate the capability of HEDWIG to retrieve horizontal wind vectors together with high-resolution vertical wind profiles. The instrument therefore provides a unique observational capability for airborne studies of atmospheric dynamics as well as for satellite instrument validation as for instance the Doppler velocity product of the cloud profiling radar on EarthCARE, but also for future missions as WIVERN and Aeolus-2.

Mineral dust is a major component of atmospheric aerosol mass, yet its role in cloud processes remains poorly understood. While laboratory studies have explored its ability to act as cloud condensation nuclei (CCN) and ice nucleating particles (INPs), in situ atmospheric measurements are scarce. This study presents unique in situ and remote sensing observations of dust-embedded clouds from the A-LIFE campaign in the Eastern Mediterranean. In situ observations on 20 April 2017 including shadow images and size distributions of aerosol and cloud particles combined with Doppler wind lidar (DWL) measurements were used to characterize dust and cloud microphysical properties. A novel size distribution retrieval for the second-generation Cloud, Aerosol, and Precipitation Spectrometer (CAPS) was developed – accounting for instrumental uncertainties, particle non-sphericity, and refractive index via a Monte Carlo method – and a machine learning-based calibration of the CAPS hotwire sensor for LWC measurements was introduced. Using the newly developed analysis tools, this study presents a quantitative assessment of two different aerosol-cloud interaction processes in dust-embedded clouds: Measurements at the cloud-top indicated heterogeneous ice nucleation, in accordance with laboratory experiments and INP parameterizations. Furthermore, small-scale CCN activation of mineral dust particles into liquid droplets (~10 µm) was observed in the middle part of the cloud, with activation diameters as small as 0.13–0.23 µm, consistent with laboratory findings. DWL observations revealed vertical lifting as the driver of increased water supersaturation, enabling CCN activation. These findings provide new insights into the microphysical processes of dust-embedded clouds and their interactions with the atmosphere.