Development of a laser heterodyne radiometer for ground-based measurements of vertical concentration profiles of trace gas and aerosol precursor gases in the atmosphere
PhD student: Fengjiao SHEN
Developing new instruments to fill the gaps between ground-based surface measurements and satellite observations is highly required for the scientific community in order to bring a better understanding on the vertical distribution of the pollutants and thus to validate the satellite data with the goal of fighting against the global warming.
The proposal is aimed at the development of an innovative infrared laser heterodyne radiometer (LHR) for ground-based in situ continuous measurement of trace gas (Greenhouse gas, CH2O, …. ) and aerosol precursor gases (isoprene, SO2, ….) in the atmospheric column. Trace gas concentrations in the atmosphere are assessed by measuring their absorption of sunlight in the infrared. Each absorption signal is mixed with laser light (the local oscillator) at a near-by frequency in a fast photoreceiver. Scanning the laser wavelength through an absorption feature, results in a scanned beat signal in the radio frequency (RF). Deconvolution of this signal through a retrieval algorithm allows for the extraction of altitude contributions to the column signal (Ref. E. L. Wilson, M. L. McLinden, et al, « Miniaturized laser heterodyne radiometer for measurements of CO2 in the atmospheric column », Appl. Phys. B 114 (2014) 385-393).
This work will be performed in close collaboration with the Laboratoire d’Etudes du Rayonnement et de la Matière en Astrophysique et Atmosphères (LERMA) de l’observatoire de Paris et de l’Université Pierre et Marie Curie (UPMC). The work can be divided into four parts: (1) instrumental development of a mini-LHR including : « optical heterodyne set-up » and « electronic receiver »; (2) measurement of molecular pollutant absorption in the atmospheric column; (3) development of a data inversion algorithm to obtain the vertical profile of the target molecule concentration; (4) measurements validation via the FTS-Paris instrument of the LERMA in the TCCON (http://www.tccon.caltech.edu/) international observation network.
This work will be conducted in the framework of the LABEX CaPPA project: optical metrology of isoprene (WP1).
Key words: Optical instrumentation – Optoelectronics – Spectroscopy – Laser – Trace gas
Director: Prof. Weidong Chen (LPCA)
Financing: ULCO / Labex CaPPA