NOAA HIGH RESOLUTION VACUUM IR SPECTROMETER

Abstract

This 3.5 meter vacuum grating spectrometer is of a classical double passed Czerny-Turner configuration and is equipped with a $16^{\prime\prime} \times 8^{\prime\prime} (40 cm \times 20 cm)$ 31.6 grooves/mm Harrison-ruled Bausch and Lomb replica echelle. The entire optical path, except for a 2 cm purged path in front of the detector may be evacuated. A 4 meter stainless steel White-type multipath cell is provided for gas absorption measurements. Data can be simultaneously acquired in analog and digital form. The digital system is controlled by PDP-8/E minicomputer. Outputs go to magnetic tape and digital plotter. At present, rudimentary computations may be done on-line, but final processing is accomplished at the NOAA computer facility. Grating position is measured by an optical 10 bit shaft encoder coupled directly to the precision to the precision lead screw which moves the grating arm. Interesting technical features such as vibration isolation, source operation to eliminate CO absorption lines, rolling mount for the multipath cell, etc., which facilitate the day to day operation have been incorporated. Computer programs for deconvolution and line center location are either available or being put into operational form. The main interest of NOAA is the determination of line and band strengths, and line widths and shapes for molecular spectra of atmospheric interest. In the adjacent laboratory, a newly acquired tunable diode laser is being used to study the 15 $\mu_{m} ~CO_{2}$ band in support of NOAA activities in atmospheric temperature sounding from satellites.