Measurement and Analysis of Atmospheric Species Using a Low Power Supercontinuum Laser
Document ID: 93
Master's Thesis
The Pennsylvania State University
The Graduate School
Department of Electrical Engineering
Abstract
Optical remote sensing systems operating on the principle of differential absorption have been employed since the mid-1970s for measuring airborne species. Multiwavelength sensing approaches, such as differential absorption lidar (DIAL) and differential absorption and scattering (DAS), are used for single (or a few) species detection boasting high sensitivity and long path detection capability. Broadband techniques, such as differential optical absorption spectroscopy (DOAS), are capable of detecting several species simultaneously over shorter path lengths and employ inversion algorithms to determine individual concentrations of the detected species.
This thesis presents an extension of earlier research using supercontinuum absorption spectroscopy (SAS) to measure atmospheric species. SAS is a broadband differential absorption approach that combines several of the best aspects of traditional multiwavelength, broadband, and hyperspectral techniques for atmospheric sensing. The key component of the SAS approach is a supercontinuum laser, which provides broadband capability while maintaining the qualities of a typical discrete wavelength laser source. This work presents measurements of atmospheric species acquired from a modified transceiver configured to operate on paths of 1 km range. Near-infrared spectra obtained using a high-resolution CCD grating spectrometer as a SAS detector compare well with MODTRANTM simulations, and measurements of oxygen and water vapor absorption are used to demonstrate the capability and illustrate the potential for the SAS technique. A previously developed multiwavelength inversion algorithm is applied to the measurements to accurately determine the concentrations of oxygen and water vapor while in the presence of other interfering species. The results presented validate the usefulness of SAS over long paths, and serve as a demonstration of SAS for near-infrared sensing of atmospheric trace species.
| Citation: | P. S. Edwards, "Measurement and Analysis of Atmospheric Species Using a Low Power Supercontinuum Laser", The Pennsylvania State University, Master's Thesis, August 2009, 80 pages |