Doppler Wind Lidar in Space

Introduction
Wind measurements throughout the atmosphere are crucial for both Numerical Weather Prediction (NWP) and an increasing range of studies related to the global climate, e.g. the El Nino phenomenon. The present network of global wind measurements still shows significant data void areas especially over the tropics, the Southern Hemisphere and the Northern Hemisphere oceans. Surface-based observations from balloon tracking by radar do provide wind profile information but mainly over the continents in the Northern Hemisphere. Single-level sources such as scatterometer (sea level wind measurements) at the ERS-1 satellite, aircraft reports and cloud tracked winds observed by geostationary satellites are not adequate to describe the atmospheric circulation in sufficient detail.

To improve on NWP and climate objectives a supplementary system is needed that provides three-dimensional winds over a large part of the globe. A space-based Doppler Wind Lidar (DWL) has the potential to provide this information in clear air. To assess its feasibility, an Atmospheric Dynamics Earth Explorer Mission has been defined and awarded by ESA for further study.

Doppler Wind Lidar principle
Lidar is an acronym for Light Detection And Ranging. The principle used is to observe the Doppler shift of laser light scattered from atmopsheric aerosols. A laser emits powerful pulses of monochromatic light to the atmosphere. As the pulse propagates through the atmosphere, part of its energy is backscattered to the instrument by particles (typically aerosols generated by anthropogenic, vulcanic and wind erosion activities) moving at the same velocity as the ambient wind. The particle velocity relative to the instrument induces a frequency shift into the backscattered radiation (Doppler effect) which is directly proportional to the speed of the aerosols and inversely proportional to the emitted wavelength of the light.

Current activities
Currently, world-wide industrial and scientific studies of potential space-based lidar systems are carried out. These studies include atmospheric backscatter properties, coherent and incoherent detection techniques, theoretical studies of the impact of DWL for NWP and climate and assimilation of DWL data. For demonstration purposes, the possibility of mounting the lidar on the International Space Station, ISS , is under investigation.

At KNMI we build a framework simulator for trade-off purposes of lidar configurations mounted on the ISS. This work is in cooperation with NLR

Related links
In paving the way for DWL satellite implementations, airborne lidar experiments by aircrafts have been performed in the past and experiments at the Space Shuttle are in preparation.

Contact Information
For more detailed information on Doppler Wind Lidar, please contact Dr. Ir. G.J. Marseille or Dr. A.C.M Stoffelen.

Dr. Ir. G.J. Marseille