Measuring Doppler shifted and backscattered light 100km away: Page 2 of 2

December 16, 2018 //By Julien Happich
Measuring Doppler shifted and backscattered light 100km away
Atmospheric research uses pulsed laser beams to measure temperature and wind speed along the beams by measuring the Doppler shifted and backscattered light at 100km height in the atmosphere.

“The aim of the project is to create compact mobile measurement systems that we can take around the world. Such systems require automatic operation under extreme environment conditions like Antarctica without access to them for long periods of times. We therefore need components that are very robust and reliable as well being able to provide the levels of sensitivity, speed and flexibility required under these challenging conditions. Spectrum’s five-year warranty gives us peace of mind that these critical items can be relied on”, explained Dr. Josef Höffner, who is leading the project.     


Unloading of the mobile LIDAR onto the fast ice in
front of the Australian Antarctic station Davis (69° S)
from the ice breaker “Aurora Australis”

There are several aspects to improving the measurements in this project. The first is to suppress the background noise by having an extremely small field of view for high resolution, optical filtering and small field of views. This means that the laser has to be stabilized in the field of view as well as all filters. The laser itself require a complex and fast real-time stabilization system with nanosecond timing. This is controlled by the Spectrum M2i.6012 20 MS/s AWG and fires at 500 pulses a second for 24 hours a day. The signals from the backscattered light are processed by the Spectrum M4i.4421 250 MS/s 16 bit digitizer. The conditions within the laser are measured with a M4i.2221 2.5 GS/s 8 bit digitizer card. The system handles more than 1GByte/s for 24 hours a day with a response time of about 1ms after processing the measured data in real-time. In total, 21 signals are managed by a software package developed at the IAP.

“We have achieved a compact, highly integrated solution by combining fast, flexible electronics with real-time capability, which is an impressive improvement compared to the previous, large and difficult-to-handle solutions that were many times bigger,” said Dr. Höffner. “Our old system needed a 10 ton, 6m container and this has been shrunk to a 1500kg system using the Spectrum cards and a novel laser. We have nearly finished shrinking this even further to fit into a one-meter cubed box of only 250 Kg, which will use the same electronics and a more compact and advanced laser.”

The sensitivity and portability of this new, highly compact device is enabling new temperature data to be obtained with unprecedented resolution and accuracy in remote places. “Our measurements have already had a big impact on our understanding of the atmosphere and, what’s really exciting, is that we have proven that we can design a system that is reliable, lightweight, compact and efficient enough for future space missions,” concluded Dr. Höffner.

Dr. Höffner presented the latest results from this project at the International Conference on Space Optics that was held on the 9-12 October in Chania, Greece. His paper will be uploaded to the conference website in early 2019 at https://atpi.eventsair.com/QuickEventWebsitePortal/icso-2018/icso


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