George A. Vanasse

Spectral measurements of high temperature 13 C 16 O 2 and 13 C 16 O 18 O in the 4.3-μm region

High resolution (0.007-cm(-1)) spectral measurements of a hot (800 K) CO(2) sample consisting of 88% (13)C(16)O(2), 11% (13)C(16)O(18)O, and 1% various other isotopes were made in the 4.3-microm region using the Air Force Geophysics Laboratory Fourier transform spectrometer. Vibration-rotation constants which predict line positions to better than 0.001 cm(-1) are presented for several bands of these two isotopes.

Real-Time Spectral Synthesis in Fourier Spectroscopy

A real-time technique to synthesize the spectral distribution from the corresponding interferogram is described. A portable real-time synthesizer has been constructed and test results are presented. Functions with known spectra and an actual interferogram have been used for purposes of evaluation.

High resolution fourier spectroscopy of nitrous oxide at elevated temperatures

The Air Force Geophysics Laboratory high resolution interferometer has been used to measure the infrared absorption spectrum in the 8-μm region of a nitrous oxide sample heated to temperatures up to 800 K. A least-squares-fit was then used to obtain effective molecular constants for 18 rotation-vibration bands. These constants predict the position of spectral lines originating from excited rotational states with an accuracy considerably greater than previously available constants.

Spectral measurements of stack effluents using a double-beam interferometer with background suppression

The emission spectra of the effluents from four selected stacks were measured using a double-beam interferometer to provide real-time background suppression. The double-beam interferometer system, installed in a mobile van, provided the capability for field site measurements and near real-time graphical data display. The advantages of double-beam interferometric background suppression are discussed. Selected spectra were analyzed, and one, from a municipal incinerator, was compared with a FASCODE generated synthetic spectrum.

Selective Modulation Interferometric Spectrometer (SIMS) Technique Applied To Background Suppression

A method of using the SIMS (the Selective Modulation Interferometric Spectrometer) to measure the difference between the spectral content of two optical beams is given. The differencing is done optically; that is, the modulated detector signal is directly proportional to the difference between the two spectra being compared. This optical differencing minimizes the dynamic-range requirements of the electronics and requires only a simple modification of the basic cyclic SIMS spectrometer. This technique can be used to suppress background radiation for the enhancement of target detection and tracking. Laboratory measurements demonstrating the application of this technique are reported.

Tunable Optical Filter Using An Interferometer For Selective Modulation

Using the selective modulation interferometric spectrometer (SIMS) as a tunable filter is proposed. This tunable filter can have a large optical throughput and a resolving power on the order of a few thousand. A basic explanation of the operation of this filter is given with an emphasis on the similarities and differences between it and a Fourier spectrometer. Several equations that have been found to be particularly useful in designing, operating, and calibrating this filter are presented. The construction and operation of a tunable filter prototype are reported.

Atmospheric Infrared Emission Observed At Altitude Of 27000 To 28000m

The molecules in the lower part of atmosphere are in thermal equilibrium with the local surrounding. The infrared emission resulted by their thermal excitation can be studied to determine their temperature and concentration profile in the atmosphere. We used a cryogenically cooled Fourier spectrometer mounted on a balloon-borne platform to study the infrared emission spectrum of atmosphere for this purpose. The experiment, which took place on October 7, 1981, at Holloman AFB, produced the analyzable data for more than two hours at altitude of 27000 ~ 28000 m along the horizontal and the vertical line of sight. The spectral data extended from 550 cm-1 to 1000 cm-1 covering the CO2 15μ bands (Δv2 = 1) with a resolution of 0.2 cm-1. The data were found interesting on two accounts: (1) a continuum background feature was superimposed with the molecular emission feature; (2) the radiance level of the CO2 15μ bands observed along the horizontal line of sight varied by a much greater degree than expected.

Spectral measurements of high temperature 13C16O2 and 13C16O18O

High resolution (0.007 cm-1) spectral measurements of 13C16O2 and 13C16O18O at 600°K and 300°K taken with the Air Force Geophysics Laboratory (AFGL) Fourier Transform Spectrometer are reported. Vibration-rotation constants which predict line positions to within 0.001 cm-1 are presented for several bands of these two isotopes. The CO2 sample contained in the high temperature absorption cell consisted of 88% 13C1602, 11% 13C16O18O, and 1% various other isotopes.

The Sims Technique Applied To Background Suppression

A method of using the SIMS (the selective modulation interferometric spectrometer) to measure the difference between the spectral content of two optical beams is given. The differencing is done optically; that is, the modulated detector signal is directly proportional to the difference between the two spectra being compared. This optical differencing minimizes the dynamic-range requirements of the electronics and requires only a simple modification of the basic cyclic SIMS spectrometer. This technique can be used to suppress background radiation for the enhancement of target detection and tracking. Laboratory measurements demonstrating the application of this technique are reported.