Remote sensing of aerosols and clouds

Overview

We use observations made at the ground and aboard research aircraft. Physically realistic forward models connect the measured radiances to aerosol and cloud properties.

ACTRIS – ground-based remote sensing

ACTRIS is a pan-European research infrastructure for long-term, quality-assured observations of aerosols, clouds, and trace gases. LMU operates a fully equipped Cloud Remote Sensing Facility and a fully equipped Aerosol Remote Sensing Facility. Cloud radars, lidar and ceilometer systems, a microwave radiometer, and radiation measurements are combined to monitor cloud and aerosol properties continuously.

Ground-based atmospheric remote-sensing instruments in front of a large radar antenna — Ground-based remote sensing instruments at the LMU ACTRIS observational platform.

Polarimetric cloud observation from aircraft

Polarization provides information that is not apparent from radiance alone. Move the divider to compare the true-colour view with the degree of linear polarization (DoLP) for the same cloud scene.

Degree of linear polarization view of a cloudbow — Polarimetric cloud observation, 31 January 2020. Drag the divider, tap a position, or use the arrow keys.

Polarimetric cloud observation, 31 January 2020. Drag the divider, tap a position, or use the arrow keys.

Aircraft and observation geometry

The specMACS instrument is operated in a nadir-looking configuration aboard the German High Altitude and LOng range research aircraft (HALO). Its two wide-field RGB polarization cameras complement the hyperspectral imagers. As the aircraft passes over a cloud scene, the same targets are observed from different viewing directions. These multi-angle measurements support both stereographic reconstruction of cloud geometry and retrievals of cloud microphysical properties.

HALO research aircraft on the ground at night — HALO provides the airborne platform for specMACS observations.

specMACS polarization camera and hyperspectral imager installed behind an aircraft window — The specMACS polarization cameras and hyperspectral imagers view clouds below the aircraft.

Diagram of repeated aircraft observations of a cloud element and comparison of the aggregated polarized measurement with a model fit — Observation geometry and retrieval principle: measurements of the same cloud element from successive aircraft positions are aggregated over scattering angle. The observed polarized signal (dashed) is then compared with the corresponding model result (green).

Related article An LMU feature presents the people and ideas behind this research. Die Wolkenvermesser — LMU München ↗

specMACS-related publications

2016 Ewald, F., Kölling, T., Baumgartner, A., Zinner, T., & Mayer, B. Design and characterization of specMACS, a multipurpose hyperspectral cloud and sky imager ↗. Atmospheric Measurement Techniques, 9, 2015–2042.
2019 Kölling, T., Zinner, T., & Mayer, B. Aircraft-based stereographic reconstruction of 3-D cloud geometry ↗. Atmospheric Measurement Techniques, 12, 1155–1166.
2019 Zinner, T., Schwarz, U., Kölling, T., Ewald, F., Jäkel, E., Mayer, B., & Wendisch, M. Cloud geometry from oxygen-A-band observations through an aircraft side window ↗. Atmospheric Measurement Techniques, 12, 1167–1181.
2019 Ewald, F., Zinner, T., Kölling, T., & Mayer, B. Remote sensing of cloud droplet radius profiles using solar reflectance from cloud sides – Part 1: Retrieval development and characterization ↗. Atmospheric Measurement Techniques, 12, 1183–1206.
2023 Pörtge, V., Kölling, T., Weber, A., Volkmer, L., Emde, C., Zinner, T., Forster, L., & Mayer, B. High-spatial-resolution retrieval of cloud droplet size distribution from polarized observations of the cloudbow ↗. Atmospheric Measurement Techniques, 16, 645–667.
2024 Weber, A., Kölling, T., Pörtge, V., Baumgartner, A., Rammeloo, C., Zinner, T., & Mayer, B. Polarization upgrade of specMACS: calibration and characterization of the 2D RGB polarization-resolving cameras ↗. Atmospheric Measurement Techniques, 17, 1419–1439.
2024 Volkmer, L., Pörtge, V., Jakub, F., & Mayer, B. Model-based evaluation of cloud geometry and droplet size retrievals from two-dimensional polarized measurements of specMACS ↗. Atmospheric Measurement Techniques, 17, 1703–1719.
2024 Volkmer, L., Kölling, T., Zinner, T., & Mayer, B. Consideration of the cloud motion for aircraft-based stereographically derived cloud geometry and cloud top heights ↗. Atmospheric Measurement Techniques, 17, 6807–6817.
2025 Weber, A., Pörtge, V., Emde, C., & Mayer, B. Retrieval of cloud thermodynamic phase partitioning from multi-angle polarimetric imaging of Arctic mixed-phase clouds ↗. Atmospheric Measurement Techniques, 18, 7581–7601.
2026 Volkmer, L., Dörfer, L., & Mayer, B. A multimodal approach to derive cloud microphysics in deep convective clouds from polarized measurements of the cloudbow ↗. EGUsphere [preprint].