On the 18th of March 2013, Alexis Merlaud successfully defended his doctoral thesis at UCL in Louvain-La-Neuve. The title of this doctoral thesis is: "Development and use of compact instruments for tropospheric investigations based on optical spectroscopy from mobile platforms". The Phd promotors were Xavier Urbain and Alain Cornet from UCL, and Michel Van Roozendael from BIRA-IASB.

This thesis presents the development of four different remote-sensing instruments dedicated to atmospheric research and their use in field campaigns between 2008 and 2012. The instruments are based on uv-visible spectrometers and installed respectively on a scientific aircraft, ultralight aircraft, and cars. One of the instruments is targeted to operate from an Unmanned Aerial Vehicle (UAV). The Differential Optical Absorption Spectroscopy (DOAS) technique is used to quantify the molecular absorption in the spectra of scattered sky light. These absorptions are then interpreted by modeling the transfer of radiation in the atmosphere.
Airborne platforms enable new measurement geometries, leading for instance to a high sensitivity in the free troposphere. On the other hand, a miniaturization effort is required, especially for the instruments onboard ultralight aircraft and UAV. Reaching the limited size, weight, and power consumption is possible through the use of compact spectrometers and computers, together with custom built electronics circuits and housings.
A common target of the different experiments is to quantify tropospheric nitrogen dioxide (NO2). Regarding this trace gas, the developed instruments provide complementary findings, such as the vertical distribution in the pristine Arctic or the levels in the exhaust plumes of large cities like Riyadh. Car-borne measurements in North-West Europe reveal the horizontal gradients of surface NO2 at various scales. The UAV payload is intended to produce high spatial resolution maps of tropospheric NO2 columns. More...