Radar Remote Sensing Department

Modern digital radars operating in the frequency band between 40 MHz and 55 MHz can be used for the investigation of various dynamic processes in the middle and lower atmosphere. Their capability to detect coherent back-scattered signals from altitudes starting at 1 km up to greater than 100 km leads to the name MST radar, standing for mesosphere/stratosphere/troposphere radar. MST radars typically operate with peak output powers of several tens of kilowatts to close to 1 MW and allow unattended and continuous operation in the height range of approximately 1 km up to 20 km all year round. 3-D wind vectors, radar reflectivity, and turbulence can be derived from the received back-scatter signals using the Doppler Beam Swinging (DBS) method as well as interferometry. Radar signatures can also be detected by MST radars in the mesosphere region during summer and winter months, but under special conditions. The study of these (polar) mesospheric echoes (PME) is one of the main applications of the MST radars of IAP, the OSWIN radar in Kühlungsborn (54.12°N; 11.77°E), and MAARSY on the North-Norwegian island Andøya (69.30°N; 16.04°E). PME can be used as a tracer of the neutral dynamics occurring in the region due to the strong coupling between the charged and neutral atmospheric species. IAP is currently expanding operations of the MAARSY radar to include 2 remote receiver locations. This expansion will provide full 3-dimensional velocity vectors of PMSE, creating a 7-dimensional dataset for studies of mesospheric winds and turbulence in high spatio-temporal resolution (3 spatial coordinates, 3 line-of-sight velocity vectors, and time).  In addition to the volumetric atmospheric targets, MST radars can also be used to detect meteor head echoes (the dense plasma immediately surrounding ablating meteoroids), providing details about the incoming extra-terrestrial flux of material to the Earth.

Radar Remote Sensing Department

A multi-static meteor radar is a group of meteor radars operating together, each from a different location, but all synchronized in time. By combining their detections, it is then possible to observe the same atmospheric volume from different viewing angles, allowing for more thorough and precise investigations of the mesosphere and lower thermosphere (MLT) winds.

This idea took shape as MMARIA (Multi-static Multi-frequency Agile Radar for Investigations of the Atmosphere), developed at the Leibniz Institute of Atmospheric Physics. An even better approach is SIMONe (Spread-spectrum Interferometric multistatic Meteor radar Observing Network), which avoids range ambiguity issues thanks to the implementation of coded-continuous wave radar technologies. In addition, SIMONe systems are more cost-effective and easier to deploy (and expand) than traditional meteor radar systems.

Thanks to the large number of detections and the multi-static configuration, SIMONe systems allow observing wind divergence and vorticity, determining energy cascades across planetary- and mesoscales, and even estimating mesoscale turbulence dissipation rates.

First tested in Germany in 2018 through a collaboration between IAP, MIT Haystack (USA), and UiT The Arctic University of Norway, SIMONe has since expanded to South America, Norway, and the United States. These networks operate in SIMO, MISO, or MIMO configurations, with SIMONe Germany and SIMONe Norway being the first full MIMO meteor radar networks worldwide.

Now, with rapidly growing datasets, Physics-Informed Machine Learning is helping us to go one step further and provide high-resolution 3D wind fields, offering an unprecedented view of how our upper atmosphere moves and evolves. Hourly mean winds from these systems are freely available through the Madrigal databases.

Radar Remote Sensing Department

The IAP has conducted experiments with Partial Reflection Radars (PRR) for more than 30 years to probe the lowermost part of the Ionosphere. With these radars, typically operated between 2 and 3 MHz, echoes from the Mesosphere-Lower-Thermosphere can be observed continuously due to partial reflection from the relatively sharp boundary between media of different refractive indices. The most common use of these radars is to measure mesospheric winds in the altitude region of about 60 km to 100 km. Two rather large and flexible PRR systems are operated in Northern Norway (Saura) and Northern Germany (Juliusruh).

Wind measurement techniques vary from spaced antenna methods, analyzing the radar echoes received at individual antennas, to Doppler Beam Swinging (DBS), in which the entire symmetric antenna array is also used for reception. In this technique, the line-of-sight velocities are measured for predefined beam pointing directions. Assuming homogeneity within the probed volume, the vertical and horizontal winds are calculated.

Alternatively, the dominant locations of the echoing structures are derived by interferometry for each Doppler-shifted signal. For this technique, typically three or four antennas are used to estimate the locations. The mapping of the radial velocities may then be inverted to vertical and horizontal velocities, and is typically called Imaging Doppler Interferometry.

Both PRRs are typically conducting experiments probing both magneto-ionic components (left- and right-handed circular polarization), allowing the measurement of differential absorption and differential Faraday rotation. From these measurements, the electron density of the ionospheric D region is inferred.

Besides case studies of specific events, these systems proved to be very valuable for long-term monitoring of the Mesosphere / Lower Thermosphere region for already more than two solar cycles.

Radar Remote Sensing Department

The LoLa (Low Latitude) project , coordinated by the Leibniz Institute of Atmospheric Physics (IAP) in Germany, focuses on the installation and promotion of MLT (mesosphere and lower thermosphere) radars, including specular meteor radars (SMRs) and partial reflection radars (PPRs), at strategically selected longitudes, primarily within ±17° of the geographic equator.

The main goal of LoLa is to investigate the short-term variability of planetary waves and atmospheric tides in the MLT region at low latitudes. These waves play a crucial role in linking meteorological processes with space weather, particularly in equatorial regions. Furthermore, MLT radar wind measurements are essential for refining global circulation models that extend above 80 km altitude. Improved models can, in turn, enhance weather forecasts, potentially extending their accuracy from a few days to several weeks.

Additionally, understanding MLT dynamics and their influence on ionospheric electrodynamics is vital for predicting ionospheric weather at low latitudes, which directly affects navigation and communication systems.

The LoLa network comprises IAP-operated radars as well as systems managed by collaborating partners, some of whom are already operating—or have previously operated—radars at low latitudes. IAP actively engages with these partners to expand the network and foster collaboration.

Finally, LoLa research will be supported by satellite wind data (e.g., from MIGHTI and TIDI instruments), Hough function analyses, and general circulation model simulations to provide a comprehensive understanding of MLT dynamics.

Radar Remote Sensing Department

The Ionosonde Juliusruh, located on the island of Rügen, is a long-standing research facility dedicated to continuous ionospheric observation. An ionosonde operates as a vertical radar, transmitting radio pulses into the upper atmosphere and recording their reflections from ionospheric layers. These measurements produce ionograms, which reveal the electron density profile and structural characteristics of the ionosphere. Data from Juliusruh are integrated into international monitoring networks, providing long-term records essential for understanding solar-terrestrial interactions, space weather phenomena, and their impact on global communication systems. The station’s measurements support the development of models for radio propagation, satellite navigation reliability, and the assessment of geomagnetic storm effects. With decades of operation, the Juliusruh Ionosonde contributes to both fundamental geophysical research and applied technologies, serving as an important resource for scientists and engineers worldwide.

The ionosonde Juliusruh was/is part of several scientific and applicational projects:

• 1994-Now: Radio Weather / HF propagation predictions
• 2023-2024: T-FORS Travelling Ionospheric Disturbances Forecasting System (EU)
• 2017-2020: TechTIDE Warning and Mitigation Technologies for Travelling Ionospheric Disturbances Effects (EU-H2020, TechTIDE)
• 2014-2017: Net-TIDE Pilot network for identification of travelling ionospheric disturbances https://sites.google.com/site/spsionosphere/about-the-project

Technical Specification

Optical and Rocket Soundings Department and Radar Remote Sensing Department

All-sky airglow imager is a passive optical remote sensing instrument with suitable filters that provides an opportunity to monitor the spatial variability of the faint (intense) natural atmospheric emissions called airglow (aurora). These emissions occur in the mesosphere and thermosphere/ionosphere through various chemiluminescence processes.

Aurora occurs at high latitudes (~65°–75° magnetic) when charged particles such as protons and electrons interact with atmospheric species like O, O₂, and N₂. It is irregular and localized. In contrast, airglow is a regular phenomenon at low and mid latitudes, produced by atoms and molecules excited through chemical reactions in the upper atmosphere. When these excited species return to their ground state (de-excitation), they release excess energy as photons. The lifetimes of these processes vary among species, making the emissions altitude dependent.

Typical peak altitudes are about 85 km for hydroxyl (OH), 92 km for N₂, 94 km for O₂, 97 km for atomic oxygen green line (O(¹S)), and 250 km for the red line (O(¹D)).

Since December 2016, at the IAP Kühlungsborn, an optical airglow imager has operated with a broadband filter (695–1050 nm) for OH emissions and narrowband filters at 589.3 nm (Na), 866.0 nm (O₂), 557.7 nm (O(¹S)), and 630.0 nm (O(¹D)). A 605.0 nm filter is also used for background OH observations. Due to its location, during the strong geomagnetic activities, this imager also captures the auroral emissions. Continuous monitoring helps investigate atmospheric waves and coupling between atmospheric layers.

Radar Remote Sensing Department

The Magnetometer JRU, located at Juliusruh, in the island of Rügen, is a geophysical instrument designed to continuously record variations of the Earth’s magnetic field. Operating as part of international observatories and data networks, it provides high-resolution measurements that are crucial for monitoring geomagnetic activity. Magnetometers detect fluctuations caused by interactions between the solar wind and the Earth’s magnetosphere. These variations are key indicators of space weather phenomena such as geomagnetic storms, which can disturb satellite operations, navigation systems, and power grids. The Juliusruh magnetometer contributes to both regional and global studies of geomagnetic activity. Its long-term data series support research into solar-terrestrial interactions, secular changes of the geomagnetic field, and real-time space weather services. Integrated into international databases, the station’s measurements are freely available to the scientific community and are used to validate models of geomagnetic disturbances. With its continuous operation and high reliability, the JRU magnetometer provides valuable insights for geophysics, space weather monitoring, and applied technologies that depend on a stable and predictable magnetic environment.

With its magnetometer, the IAP is a contributor to SuperMAG https://supermag.jhuapl.edu/