Active Remote Sensing
The Integrated Path Differential Absorption Lidar (IPDA) technique using
hard target reflection in the near IR has the potential to deliver
GHG column measurements from aircraft or space with unprecedented
accuracy. IPDA largely eliminates the contribution of atmospheric scattering
by particles and clouds which greatly affects the achievable accuracy of
passive remote sensing instruments. Moreover, this technique can be applied
during daylight or nighttime and at all latitudes since it does not depend
on solar radiation.
The IPDA technique will be employed by the German-French climate mission
MERLIN (Methane Remote Sensing LIDAR Mission) planned for launch around 2021
to measure methane on a global scale. At the Institute of Atmospheric
Physics of DLR, an airborne demonstrator dubbed CHARM-F has
been devised that is capable of measuring both important greenhouse gases,
CO2 and CH4, at the same time. CHARM-F is one of the key instruments to be
flown on the HALO aircraft.
The figure shows the IPDA principle applied from either aircraft or
satellite and a photo of CHARM-F as installed on the German
research aircraft HALO.
The IPDA technique uses laser radiation at two different wavelengths which
are differently absorbed by the target species that are reflected from a
"hard target" which is either the Earth's surface or cloud tops.
In the framework of a BMBF-funded project CHARM-F has been designed, built, and
certified for airborne operation. First airborne measurements (see
references) have shown the capabilities of this
system which is an asset in the context of the AIRSPACE goals.