Remote photometry of the atmosphere using microwave breakdown

Abstract

A novel method for remote optical diagnostics of the atmosphere at heights 30-60 km is proposed. TI• method relies on exciting atoms and molecules of minority species by electron impact during and following an ionizing microwave pulse injected from a focused ground-based transmitter. Free electrons produced in the breakdown region are the exciting agents for the atmospheric target molecules. The mixing ratio of the minority species can then be measured by either detecting the direct emission from allowed transitions or by utilizing lidar techniques to measure the excitation level of metastable states. Computer simulations of the intensity of the expectexl emission, based on kinetic theory of air breakdown, are presented. It is shown that mixing ratios below particle per trillion can be detecte• using microwave heaters with state of the art effective radiation power and modern detection technology. 1. Introduction Accurate, simultaneous, and continuous measurements of the atmospheric mixing ratios of active species are critical in determining quantitative links of increased greenhouse gases and climate change. Despite significant effort the database on which predictions and assessments of climate change are based is still insufficient. There are, in general, two types of data acquisition techniques: in situ and remote. The in situ measurements rely on rockets and stratospheric balloons. These are single-shot measurements that c0nnot be applied to study systematically the temporal dynamics of the concentration of the relevant species. Furthermore, they are hindered by altitude limitations and local contamination problems. The remote techniques rely on ground-or space-based lidars. Despite significant progress, propagation issues, signal to noise ratio limitations, and the high cost and calibration problems of space-based systems limit the extent of passive spectroscopy and lidar-based techniques. The objective of this paper is to propose a novel concept that allows for continuous monitoring of the strato-1Also at ARCO Power Technologies, Incorporated,

Active photometry of atmospheric compositions by microwave breakdown plasma spectroscopy

“…For nitrogen atomic system, two line spectra of 3p 4 S 0 3/2 ‐3s 4 P 5/2 (746.9 nm) and 3p 4 P 0 5/2 ‐3s 4 P 5/2 (821.6 nm) were clearly observed. Both of these lines were not yet predicted in the MBS concept [ Papadopoulos et al , 1994]. Also, we could find two strong lines of oxygen atom, 3p 5 P 1,2,3 ‐3s 5 S 0 2 (777.4 nm) and 3p 3 P 0,1,2 ‐3s 3 S 0 1 (844.6 nm).…”

“…Our main objective of the present research is to identify and assign more than 50 atomic/molecular emission spectra detected under the model stratospheric conditions (at pressure of 10 Torr, ∼30 km in altitude). At this altitude, Papadopoulos et al [1994] predicted 15 major emission lines to be measurable. We have tabulated 50 typical measured emission lines along with the predicted lines in this paper.…”

“…Accurate, in situ, remote sensing, simultaneous, and continuous measurements of the trance amounts of air compositions are essentially important for the clear grasp and the proper countermeasures against these environmental problems. Recently, Papadopoulos et al [1994] proposed an intriguing concept of remote photometry of the atmosphere using microwave breakdown spectroscopy (MBS). This concept utilizes ground‐based assets of pulsed‐microwave system generating breakdown plasmas that allows for continuous monitoring of the stratosphere at altitudes of 25–60 km.…”

“… A laboratory technique of pulsed microwave breakdown plasma spectroscopy (MBS) has been developed for simultaneous, quantitative, in situ, and remote diagnostics of atmospheric compositions. This technique, based upon a concept proposed by Papadopoulos et al [1994], enables for remote photometry of the atomic/molecular spectra emitted from the microwave breakdown plasma of the atmosphere mixed with various kinds of trace gases and air pollutants at relevant breakdown spots in open space. Two different breakdown methods, the single beam method and the dual beam intersection method, have been tested using a small test chamber, a pulsed 9.4 GHz/100 kW magnetron tube, and a high‐resolution wavelength/time resolution spectroscopy system.…”

Development of a dual‐beam intersection technique for microwave breakdown plasma spectroscopy and detection of air compositions

“…The well‐known breakdown theory adequately explains the present threshold field intensity [ MacDonald , 1966; Papadopoulos et al , 1994; Gurevich et al , 1997]. Following to the breakdown theory, we can approximately estimate the magnitude of optimum electric field for pulsed MBS in air, E opt , as where E thr is the critical electric field for breakdown in air, C 0 and C 1 are the constants as functions of ω/ν; ω is the angular frequency of the microwave, and ν is the characteristic electron collision frequency.…”