The following descriptions provide a brief overview of the KITcube and the operation and utility of the various KITcube measurement devices. More in-depth scientific details, technical specifications, and a review of the use of the KITcube in previous campaigns can be found on the KITcube homepage.

KITcube is the advanced integrated atmospheric observation system of the Institute for Meteorology and Climate Research, Tropospheric Research Division (IMK-TRO).

The mobile KITcube combines high-resolution measurements from scanning remote sensing systems (e.g. wind lidar, X-band precipitation radar, humidity and temperature profilers, sun photometers, water vapor and cloud camera systems, and many more) with classical in situ instruments on measurement towers and on weather balloons (local measurements). Fully coordinated scans of the systems make the KITcube a very well suited observation system for studies of thunderstorms, atmospheric convection, clouds, and precipitation. The mobile KITcube main site during the Swabian MOSES measurement campaign is located in Villingen-Schwenningen, the X-band precipitation radar is installed in Bonndorf in the Black Forest.

The stationary KITcube at KIT Campus North in Eggenstein-Leopoldshafen, north of Karlsruhe, consists, among other things, of the 200-meter-high meteorological mast, which has been measuring air temperature, humidity, wind, and turbulence in continuous operation since 1972, and a modern C-band precipitation radar. The stationary KITcube also functions as a permanent AERONET station "Karlsruhe", the mobile KITcube as an additional temporary station during measurement campaigns such as Swabian MOSES ("KITcube_Villingen-Schwenningen"). Thus, both contribute to a worldwide database for aerosol and radiation measurements.

Balloon soundings in the atmosphere

The higher atmospheric layers can be measured preferably with helium-filled weather balloons. Various measuring instruments are attached to these balloons, which then measure various parameters as the balloon rises (and also as it sinks later). Depending on their size, the balloons rise to an altitude of 20 to 35 kilometers and thus fly much higher than airplanes. After the balloon bursts, the descent begins, during which a parachute is usually used to slow the descent. On the one hand, this prevents damage, and on the other hand, it allows measurements to be made under controlled conditions even during descent.

In the simplest case, a so-called radiosonde is attached to a weather balloon. This device measures temperature, humidity, air pressure and position information (GPS) and sends the information by radio to the ground station. In addition, it is possible to hang other instruments on the weather balloon besides the radiosonde. These are then, for example, an ozone instrument, with which the ozone layer, particularly in the stratosphere can be measured, or a precise hygrometer, with which the low water vapor concentration at the transition from the troposphere to the stratosphere (tropopause) at an altitude of about 12 kilometers can be precisely determined. Depending on the situation, a particle measuring instrument is also used to precisely locate cloud droplets, ice crystals or dust particles in the atmosphere.

As part of the Swabian MOSES 2023 measurement campaign, balloon soundings will be carried out at two locations: at the main site in Villingen-Schwenningen and in Alsace, France. In Villingen-Schwenningen, the weather balloons are filled manually and allowed to rise; in Alsace, there is an autolauncher. This autolauncher (Vaisala Autosonde AS41) performs balloon soundings fully automatically controlled remotely.

Fluctuations of the atmospheric ground pressure are an expression of the weather pattern and are also recorded by many amateur meteorologists. In addition to the slow fluctuations recorded by a barometer, thunderstorm cells, for example, can also generate sudden pressure fluctuations. These pressure fluctuations are sources of infrasound waves that can propagate in the atmosphere over long distances. The infrasound range adjoins the audible range at lower frequencies; the transition between the infrasound range and the acoustic sound range is about 20 hertz (audible range spans about 20 to 20,000 hertz, depending on age and volume).

The operated campaign sensor detects pressure fluctuations in the frequency range from about 0.02 to 100 Hertz, and can therefore detect infrasonic waves and acoustic waves in the lower audible range. A sensitive differential pressure sensor is used for detection (Sensirion SPD816-125Pa), which detects the pressure difference between a sealed reference vessel (a glass vessel with a volume of 5 liters) and the environment. To detect the pressure difference, the sensor allows a small flow of air driven by the pressure difference between the reference volume and the outside air through a narrow channel. A heat source is located in the duct, and the air temperature is measured on both sides of the source. The flow velocity can be derived from the temperature difference and from this, finally, the sought pressure difference.

The figure on the right shows the sensor: the reference vessel is wrapped in thermal insulation to prevent rapid temperature fluctuations of the reference - which would also simulate pressure fluctuations. The actual sensor element is located in the metal housing above the reference vessel. The data is automatically recorded with the help of a notebook and transferred to the campaign's data server via an LTE connection.

Only a few measurements have been performed so far to investigate the infrasound signals of convective events. In the Swabian MOSES campaign, infrasound measurements will be combined with the long-range diagnostics of the KITcube instruments to gain additional information on the flow events in a thunderstorm cell.

Author: Dr. Frank Hase, IMK-ASF

A network of soil moisture sensors enables the continuous determination of soil moisture and soil temperature at different depths. The mobile devices used in the campaign consist of individual sensor nodes, to each of which six soil moisture sensors are connected. The sensors are installed in pairs, so the soil moisture and soil temperature can be determined at each location at three different depths. The measured data is transferred to a database via mobile radio and visualized.

The soil moisture sensors work according to the TDT principle (Time Domain Transmission). The principle is based on the influence of the dielectric properties of the soil on the propagation speed of an electromagnetic signal that is transmitted as a pulse to the sensors. Water is characterized by high dielectricity compared to dry soil. A high water content in the soil and thus a high dielectricity slows down the propagation speed of the electromagnetic signal. With the inclusion of other parameters such as soil temperature, the soil moisture can be determined from the propagation velocity.

Why are these measurements important? Soil moisture is an important state variable of natural soils, which is not only of great importance for agriculture (see research objectives). Due to the pronounced heterogeneity and complexity of soils, soil moisture is also characterized by high temporal and spatial variability. Single measurements often cannot adequately represent such changes due to their principle. Wireless sensor networks make it possible to investigate the temporal and spatial dynamics of soil moisture.

More infomation about the activity within Swabian MOSES as well as live data can be found here

Authors: Matteo Bauckholt, Prof. Dr. Peter Dietrich, UFZ

Precipitation measurements with radars such as the KITcube X-band radar provide very high spatial and temporal resolution information that cannot be achieved with a ground network of precipitation gauges. However, they also suffer from typical measurement errors. These are attempted to be minimized by taking advantage of the (relatively few) measurements on the ground to enrich the radar measurement.

For Swabian MOSES, a network of 23 optical distrometers (parsivels) is being set up for the first time. While conventional rain gauges only provide information on the amount of precipitation that has fallen, the use of distrometers also provides information on the composition of the precipitation according to size and precipitation type. Exactly this information can also be estimated from the measurements of the polarimetric KITcube X-band radar. By comparison with the distrometers distributed throughout the measurement area, the radar-based information can be verified and improved by calibration (also of the polarimetric measured quantities).

Author: Dr. Jan Handwerker, IMK-TRO

Despite the massive damage caused by severe hail events, especially in the Swabian MOSES study area, hail is not measured directly at the many weather stations in Germany. However, the size distributions of the hailstones, the so-called spectra, are relevant for several applications. Precipitation radars, for example, also measure hail in principle, but they only provide a total signal (or several signals in the case of modern dual-pole instruments) in the atmosphere at an altitude of about 1 kilometer.

Observed spectra can be used to improve conversion methods of the radar signal to hail on the ground. The hail spectra are also critical for damage to buildings, vehicles, and agricultural crops. Therefore, they are needed for the most accurate calculation of hail damage and hail risk. Finally, long-term measurements of the hailstones can be used to determine possible trends caused by climate change.

The newly developed measuring device HailSens is capable of measuring hail spectra with high temporal resolution. When a hailstone strikes the receiving surface, the surface is set into vibration, which is then detected by a piezoelectric microphone mounted below the receiving surface. From this, it can then be determined how many hailstones hit and how large they are. Each impact of a hailstone is registered and automatically sent to a server. There, the data is then available in almost real time.

As part of the Swabian MOSES field measurement campaign, a total of 10 hail measuring devices have been installed - precisely at the locations where, according to the IMK 's radar analyses, hail occurs most frequently.

Author: Prof. Dr. Michael Kunz, IMK-TRO

The measurement of wind as a vectorial quantity (wind speed and direction) with strong spatial and temporal variability poses great challenges to the measurement concept and measurement technology, but is of fundamental importance for understanding the energy and material balance of the atmosphere.

Doppler lidar instruments determine the velocity of scatterers (aerosol particles) moving with the wind based on the Doppler effect along a laser beam up to distances of 10 kilometers. To determine the wind vector as well as vertical and horizontal sections, the laser beam is directed in different directions into the half-space above the instrument via a controllable mirror system (scanner). A special added value arises from the combined and synchronized use of the instruments, whereby either small-scale (e.g. in valleys) high-resolution flow patterns can be measured or, as in the case of the Swabian MOSES measurement campaign, larger-scale flow characteristics can be measured in more extensive study areas, which means that, for example, the advection and flow convergence important for thunderstorm formation can be determined (see research objectives).

Within the framework of Swabian MOSES, the IMK-TRO operates Doppler lidar devices with data transmission in near real time to determine the wind profile up to heights of 3 kilometers at a total of 7 sites in the study area between the eastern Black Forest, Neckar Valley and western Swabian Alb. These will be complemented by airborne scanning Doppler lidar in June and July (see research aircraft). Instruments of the project partners IMK-IFU and University of Hohenheim complement the network with two additional sites.

Author: Dr. Andreas Wieser, IMK-TRO

The vertical temperature and humidity profile of the atmosphere is crucial for the formation and intensity of thunderstorm events. In addition, the three-dimensional (3D) wind field, especially in the upwind region of a thundercloud, determines the strength of precipitation in the form of rain or hail (see research objectives).

Using the small (size of a yogurt cup) and lightweight (12 gram) swarm probes of Sparv vertical profiles of air temperature, humidity, pressure and the 3D wind field can be measured directly in a thundercloud during mobile deployment. They transmit the measured parameters every 4 seconds via radio to the mobile ground station. A real-time map continuously displays the position of all probes. The swarm probe is a new type of measuring instrument that provides several series of measurements in a defined air volume for up to one hour. Up to 17 balloon-borne probes can be launched simultaneously or in close proximity, for example directly in front of a thundercloud. The probes ascend to a user-defined altitude and then follow the flow in the thundercloud on so-called Lagrangian orbits.

The individual probes can be separated from the balloons in the further course either by remote command or from a further, previously defined height and thus fall to the ground. Due to their low weight, the fall velocity and thus the momentum when hitting the ground is low, so that the probes can be used several times (if they are recovered).

Author: Prof. Dr. Michael Kunz, IMK-TRO

Cosmic-Ray Neutron Sensing (CRNS) is a mobile, non-contact technology for determining mean soil moisture in the vicinity of about 15 hectares. The method is based on the detection of neutrons "reflected" in the soil. Since these are particularly sensitive to hydrogen atoms, a direct dependence of neutron intensity on the prevailing water in the root zone around the sensor can be deduced. Since the neutrons are derived from cosmic events, such as stellar explosions, this measurement method is called Cosmic-Ray Neutron Sensing.

Inside the sensor are usually detector gases (e.g., helium) that react to neutrons passing through and generate a pulse of current. These pulses are counted and stored in the data logger along with information such as GPS coordinates, temperature, air pressure and humidity. The information collected can be used to estimate soil moisture from the signal.

The stationary sensors are already being used successfully in research and agriculture to measure hourly changes in soil moisture over several years. To obtain information about an entire field or a specific catchment area, the detector can be used in mobile mode, called roving. In this mode, the sensor is installed in a vehicle and simply counts neutrons while the vehicle is moving. Measurement data and coordinates are collected every 10 seconds so that an average soil moisture can be calculated for the distance traveled.

As part of the Swabian MOSES 2023 measurement campaign, a stationary cosmic-ray sensor will be installed at the main site in Villingen-Schwenningen. Thus, the mean soil moisture within a radius of about 200m around the sensor and the change over the entire measurement period can be determined.

In the catchment area of the Lindach river, event-related runs are carried out with a mobile Cosmic-Ray-Rover. Before and after heavy rain events, a fixed route is driven so that changes in soil moisture due to precipitation can be determined at the landscape scale. In order to validate the measurement results of the mobile sensor, the locations of the soil moisture networks in the Lindach catchment area are approached. At the respective stations, the vehicle is parked next to the soil moisture network for five to ten minutes, since the measurement uncertainty is lower the longer the rover stays at a location. This allows the results of both measurement methods to be compared at specific points.

A solid estimate of soil moisture at the landscape scale is relevant for hydrological modeling. This can be used to predict future weather developments, for example to estimate the risk from droughts, heat waves or floods (see research objectives).

Authors: Mandy Kasner, Prof. Dr. Peter Dietrich, UFZ

Additional information on Cosmic Ray Neutron Sensing & Roving and its use in other projects: Homepage