A ground-based technique for millimeter wave spectroscopic observations of stratospheric trace constituents

Recent concern over possible long term stratospheric changes caused by the introduction of man-made compounds has increased the need for instrumentation that can accurately measure stratospheric minor constituents. The technique of radio spectroscopy at millimeter wavelengths was first used to observe rotational transitions of stratospheric ozone nearly two decades ago, but has not been highly developed until recently. A ground-based observing technique is reported which employs a millimeter-wave superheterodyne receiver and multichannel filter spectrometer for measurements of stratospheric constituents that have peak volume mixing ratios that are less than 10 to the -9th, more than 3 orders of magnitude less than that for ozone. The technique is used for an extensive program of observations of stratospheric chlorine monoxide and also for observations of other stratospheric trace gases such as (O-16)3, vibrationally excited (O-16)3, (O-18)2(O-16), N2O, HO2, and HCN. In the present paper, analysis of the observing technique is given, including the method of calibration and analysis of sources of error. The technique is found to be a reliable means of observing and monitoring important stratospheric trace constituents.