Wednesday, 31 January 2024
Hall E (The Baltimore Convention Center)
We present the newly developed holographic particle tracking velocimetry (HPTV) instrument designed for use on the Max Planck CloudKite Helikites.
In-line holography is a simple and powerful optical measurement technique as the objects in a large three-dimensional sample volume can be reconstructed from a single image.
For in-situ cloud measurements, this means individual cloud particles can be resolved and both their cross-section and 3D position in space can be reconstructed.
However, typical airborne holographic measurements on aircrafts are limited by the high true airspeed and therefore have a low spatial sample rate.
To overcome this issue, we deploy our measurement systems using a Helikite, a tethered lighter-than-air aerostat.
The CloudKite Helikite's low true airspeed, combined with a high sample volume of 0.1 L per frame and a high sampling rate in our newest holographic imaging system HPTV, provides more data from each cloud we fly through and resolves it better.
Most importantly, the low true airspeed allowed us to develop a holographic particle tracking instrument:
The HPTV can record up to 35 image pairs per second. We yield a short enough inter-frame time between the images of each pair so that we can track particles from frame to frame.
Thus, with only one imaging system, we can measure not only the position and cross-sectional size but also the velocity of the cloud particles. The resolution limit is 6µm.
By capturing each particle in two consecutive images, we can also improve the accuracy of particle detection and sizing compared to previous holographic systems.
The HPTV instrument is additionally equipped with a 3D pitot tube, a Cloud Droplet Probe, and temperature and humidity sensors for simultaneous measurements. It is designed to work fully automatic in flight.
With this instrument, we will gain more insight into the spatial-temporal properties of cloud droplets on small scales and deepen our understanding of clustering, inhomogeneities, and the mixing processes in clouds.
HPTV can also be used to study the shape and orientation of non-spherical objects such as ice crystals in clouds, volcanic and wildfire ash, and the dispersion of microplastics in the atmosphere.
In-line holography is a simple and powerful optical measurement technique as the objects in a large three-dimensional sample volume can be reconstructed from a single image.
For in-situ cloud measurements, this means individual cloud particles can be resolved and both their cross-section and 3D position in space can be reconstructed.
However, typical airborne holographic measurements on aircrafts are limited by the high true airspeed and therefore have a low spatial sample rate.
To overcome this issue, we deploy our measurement systems using a Helikite, a tethered lighter-than-air aerostat.
The CloudKite Helikite's low true airspeed, combined with a high sample volume of 0.1 L per frame and a high sampling rate in our newest holographic imaging system HPTV, provides more data from each cloud we fly through and resolves it better.
Most importantly, the low true airspeed allowed us to develop a holographic particle tracking instrument:
The HPTV can record up to 35 image pairs per second. We yield a short enough inter-frame time between the images of each pair so that we can track particles from frame to frame.
Thus, with only one imaging system, we can measure not only the position and cross-sectional size but also the velocity of the cloud particles. The resolution limit is 6µm.
By capturing each particle in two consecutive images, we can also improve the accuracy of particle detection and sizing compared to previous holographic systems.
The HPTV instrument is additionally equipped with a 3D pitot tube, a Cloud Droplet Probe, and temperature and humidity sensors for simultaneous measurements. It is designed to work fully automatic in flight.
With this instrument, we will gain more insight into the spatial-temporal properties of cloud droplets on small scales and deepen our understanding of clustering, inhomogeneities, and the mixing processes in clouds.
HPTV can also be used to study the shape and orientation of non-spherical objects such as ice crystals in clouds, volcanic and wildfire ash, and the dispersion of microplastics in the atmosphere.
- Indicates paper has been withdrawn from meeting
- Indicates an Award Winner