Remote sensing of the stratospheric ozone profile using a tunable sideband CO$\sb2$ laser heterodyne spectroscopy

Date of Completion

January 1997


Engineering, Electronics and Electrical|Physics, Atmospheric Science|Physics, Optics|Engineering, Environmental|Remote Sensing




In this work, a systematic approach for remote sensing of stratospheric ozone was developed. Preliminary studies of the line shape, Doppler width, number density, and its theoretical location from Hitran data base using direct detection were made. Seven absorption lines were studied and recorded. These lines were only a few wavenumbers away from various CO$\sb2$ vibrational rotational lines. This extracted information allowed us to choose a few particular lines in our stratospheric measurements. The sweeping of these lines was done by an electro-optic phase modulator capable of tuning from 8-18 GHz with input electrical power of about 10 Watts, and optical power of 300 mW. The uniqueness of this experiment is its sweeping capability with resolution limited by the laser line width ($\approx$100 KHz) and synthesizer tuning. The resolution of our measurements was 5 MHz (0.000016 cm$\sp{-1}$) with signal to noise ratio of 100.^ By using the heterodyne technique in the laboratory, an absorption line of ozone was obtained. The measured ozone line was at 14.65 GHz away from CO$\sb2$ carrier at 9p22 transition line with signal to noise ratio of 100:1 and with resolution of about 5 MHz.^ The next objective was to obtain field data on stratospheric ozone. The field measurements were obtained on February 12 and February 23 1997 between 9:00 A.M and 11:30 A.M. The angle of the sun from the horizon was about 40-45 degrees. With a modified sun tracking system, a window of about 3-5 minutes per scan was obtained.^ A total of three lines were observed and recorded using this heterodyne technique. Information regarding temperature and number density from these lines were estimated. The calculated number density from the Beer-Lambert Law was approximated to be about ${\sim}10\sp{11}$ molecules/cm$\sp3$. The temperature was approximately to 240 to 260K with signal to noise ratio of about 100:1. The importance of this measurement technique was its capability to map individual absorption line for further studies. ^