Frank Allario

High resolution spectral measurement of the HNO 3 11.3-μm band using tunable diode lasers

High resolution spectra in the region of the 2nu(9) band of nitric acid have been obtained for selected portions of the HNO(3) spectrum using tunable diode laser techniques. Continuous spectra are presented from 891.25 cm(-1) to 898.77 cm(-1), with a spectral resolution </=0.001 cm(-1) (30 MHz). Absolute line intensities and line positions are presented. Absolute wavelength calibration was obtained by frequency mixing the diode laser with a C(13)O(2)(16) isotope laser. Self and foreign gas (N(2)) broadening coefficients were iteratively calculated from the experimental data and were determined to be alpha(a) = 0.8 cm(-1)/atm and alpha(f) = 0.13 cm(-1)/atm, respectively.

Measurements of NH 3 absorption coefficients with a C 13 O 2 16 laser

Measurements of NH(3) absorption coefficients are presented for several transitions of a C(13)O(2)(16) laser for small concentrations of NH(3) (p </= 1 Torr) for absorption lines broadened to 1 atm with N(2). NH(3) absorption coefficients were determined for laser transitions R(8) (920.2194 cm(-1)) to R(28) (933.8808 cm(-1)) of the 00 degrees 1 - [10 degrees 0,02 degrees 0](I) band. The strongest absorption coefficient [K = 36.09 +/- 1.43 (atm-cm)(-1)] was measured for the R(18) transition for the NH(3) line, aQ(6,6), and is larger than has been found in any previous measurements with a CO(2) laser. The dependence of K on total pressure was also obtained for select transitions, and the frequency separation between the R(18) laser transition and the neighboring NH(3) line [aQ(6,6)] was determined to be 550 +/- 50 MHz. These results are significant for long path absorption monitoring of NH(3) with CO(2) lasers since the path length can be reduced by approximately 40% and for heterodyne mdetection of NH(3) since the relative position of the laser transition to the NH(3) absorption line is well within the bandpass of Hg-Cd-Te photomixers (B >/= 1.5 GHz).

An experiment concept to measure stratospheric trace constituents by laser heterodyne spectroscopy

Laser heterodyne spectroscopy (LHS) techniques with semiconductor laser local oscillators (LO) in the 3–30 μm range have the potential to measure radical gas species in the stratosphere. The goal of this experiment is to measure radical gases from Spacelab, including ClO, ClONO2, HO2, H2O2, N2O5, and HOCl in solar occulation with vertical resolution ≦2km and vertical range from 10 to 70 km. Sensitivity analyses have been performed on ClO and O3 to determine design criteria for the LHS instrument. Results show that O3 and ClO vertical profiles can be measured with an accuracy ≧95% and ≧80%, respectively, over the total profile. These accuracies require the LO to maintain the following characteristics: frequency stability (Δfw≦20 MHz), single-mode power (PLO≧500 μW), and minimum frequency drift (≦5 MHz). Laboratory heterodyne measurements performed with semiconductor lasers generated the same shot-noise photocurrent as CO2 lasers, for comparable single-mode power. “Excess-noise” regions were identified, but could be wavelength controlled by fine control of operating temperature and injection current. Doppler-shift effects and limited solar occultation measurement times due to Spacelab orbits should pose minimum mission constraints on the experiment.

The global troposphere: Biogeochemical cycles, chemistry, and remote sensing

The chemical composition of the troposphere is controlled by various biogeochemical cycles that couple the atmosphere with the oceans, the solid Earth and the biosphere, and by atmospheric photochemical/chemical reactions. These cycles and reactions are discussed and a number of key questions concerning tropospheric composition and chemistry for the carbon, nitrogen, oxygen and sulfur species are identified. Next, we review various remote sensing techniques and instruments capable of measuring and monitoring tropospheric species from the ground, aircraft and space to address some of these key questions. We also consider future thrusts in remote sensing of the troposphere.

Measurement of HCl absorption coefficients with a DF laser

Absorption coefficients in the fundamental P-branch of HCl at several DF laser transitions from 2439.02 cm(-1) to 2862.87 cm(-1) have been measured experimentally. The 2-1 P(3) DF laser transition has been shown to overlap the P(6) HCl(37) absorption line within the halfwidth of an atmospherically broadened line. The absorption coefficient k was measured to be 5.64 +/- 0.28 (atm-cm)cm(-1) for a 0.27% mixture of HCl in N(2) at a total pressure of 760 Torr. A theoretical and experimental comparison of the pressure dependence of k showed that the 2-1 P(3) DF transition lies 1.32 +/- 0.15 GHz from the center of the P(6) HCl absorption line. This line separation is in good agreement with published positions for this DF laser transition and the HCl absorption line. At least four other DF laser transitions in the spectral interval measured are reported showing measurable absorption (>/=10%) for a 10.2% mixture of HCl in N(2) across a 1-m pathlength. Applications of these results to differential absorption lidar (DIAL) and to heterodyne detection are also discussed.

Tunable Laser Heterodyne Spectrometer Measurements of Atmospheric Species

Spectroscopic measurements using tunable laser heterodyne spectrometers in the 3–30 micron range of the spectrum have the potential to measure the vertical profiles of tenuous gas molecules in the atmosphere with ultra high spectral resolution (∆υ ≤ 0.001 cm-1) and high sensitivity [1]. At the NASA Langley Research Center (LaRC), the technology and system level development for demonstrating the “technology readiness” of this technique has been pursued for some time, and a major activity has included technology development of reliable tunable semiconductor lasers [2], laboratory research in the fundamental noise sources of the heterodyne system [3], laboratory measurements of spectroscopic parameters with ultra high spectral resolution [4, 5], sensitivity analyses for potential applications [6] from space and balloon platforms, and development of a Laser Heterodyne Spectrometer (LHS) experiment to measure trace species in the atmosphere from the NASA CV-990 Airborne Laboratory [7]. The experimental flight demonstration is currently scheduled for implementation in the first quarter of fisical year 1983.

Simple technique for sequential q-switching of molecular lasers.

A simple technique for sequentially Q-switching molecular lasers (e.g., CO(2), CO, HF) is discussed in which an optical scanner is used as an optical folding element in a laser cavity consisting of a stationary diffraction grating and partially reflecting mirror. Sequential Q-swtiching of a conventional CO(2) laser is demonstrated in which over sixty-two transitions between 9.2 micro and 10.8 micro are observed. Rapid repetition rates (200 Hz) and narrow laser pulses (<5 microsec) allow conventional signal processing techniques to be used with this multi-wavelength laser source which is a versatile tool for laser propagation studies, absorption spectroscopy, and gain measurements. Results of a preliminary experiment demonstrating the utility of measuring selective absorption of CO(2) laser wavelengths by C(2)H(4) is shown, but selective absorption by atmospheric CO(2), NH(3), and O(3) can also be studied. With appropriate optical sca ners and diffraction gratings, sequential Q-switching of CO and HF lasers is possible.

NASA laser remote-sensing program

Some of the major NASA programs using laser remote sensing techniques are summarized, with emphasis on the development of the Lidar In-space Technology Experiment and the Lidar Atmospheric Sensing Experiment. Insight is provided into the technology being developed for future experiments, primarily wavelength extension into the middle IR range of the spectrum, 3 to 5 microns, and for wind sensing and DIAL measurements. New metrology technology which will lead to improvement measurements for both earth sciences and space physics is discussed. Some of the developments in systems and technology for applications in aviation safety, microburst detection, clear air turbulence, and wave vortex detection are highlighted.

Tunable solid-state lasers - An emerging technology for remote sensing of planetary atmospheres

Tunable solid-state laser technology is rapidly expanding coverage of the electro-magnetic spectrum between 0.20 and 14.0 μm, while dramatically increasing efficiency, lifetime and reliability. The status of several laser technologies will be presented which will be available in the decade of the 1990s to conduct scientific measurements of planetary atmospheres and features of planetary surfaces from orbiting spacecraft.

Overview Of The NASA Tropospheric Environmental Quality Remote Sensing Program

This paper will summarize the current NASA Tropospheric Environmental Quality Remote Sensing Program for studying the global and regional troposphere from space, airborne and ground-based platforms. As part of the program to develop remote sensors for utilization from space, NASA has developed a series of passive and active remote sensors which have undergone field test measurements from airborne and ground platforms. Recent measurements with active lidar and passive gas filter correlation and infrared heterodyne techniques will be summarized for measurements of atmospheric aerosols, CO, SO2, 03, and NH3. These measurements provide the data base required to assess the sensitivity of remote sensors for applications to urban and regional field measurement programs. Studies of Earth Observa-tion Satellite Systems are currently being performed by the scientific community to assess the capability of satellite imagery to detect regions of elevated pollution in the troposphere. The status of NASA sponsored research efforts in interpreting satellite imagery for determining aerosol loadings over land and inland bodies of water will be presented, and comments on the potential of these measurements to supplement in situ and airborne remote sensors in detecting regional haze will be made.