Digital Signal Processing of Fourier Transform Spectra on IBM PC-Compatible Computers
High Resolution Fourier Transform Spectroscopy, 1989
Detector nonlinearity in Fourier transform spectroscopy
High Resolution Fourier Transform Spectroscopy, 1992
Intercomparison of Airborne Measurements of Stratospheric Hydrogen Chloride and Hydrogen Fluoride
Optical Remote Sensing of the Atmosphere
Two sets of stratospheric trace gas columns obtained during the Airborne Arctic Stratospheric Exp... more Two sets of stratospheric trace gas columns obtained during the Airborne Arctic Stratospheric Experiment by Fourier transform infrared absorption spectroscopy differed sufficiently to warrant a reexamination and intercomparison. The intercomparison had three goals: the determination of the source(s) of the discrepancies, the remeasurement of the raw data using a variety of trace gas retrieval methods, and the determination of the errors involved in such measurements. New measurements of the data suggest that the spectra are remarkably consistent, and provide similar vertical columns when analyzed with one set of assumptions and a particular spectrum analysis method. The intercomparison suggests that the absolute value of vertical columns can be altered by changing the model assumptions and the fitting method. Conclusions regarding data intercomparison and methods of data analysis are discussed in the context of future AASE and AAOE missions and the NDSC.
Validation of Stratospheric Ozone Observed by the Atmospheric Trace Molecule Spectroscopy (ATMOS) Experiment During 1992
Optical Remote Sensing of the Atmosphere
Measurements of stratospheric ozone were made by the Atmospheric Trace Molecule Spectroscopy (ATM... more Measurements of stratospheric ozone were made by the Atmospheric Trace Molecule Spectroscopy (ATMOS) experiment from onboard the Space Shuttle during the period 8-16 April 1992. The precision and accuracy of the measurements are discussed in the context of establishing the accuracy and compatibility of the measurements relative to other space-based measurements of ozone. Coincident measurements were obtained from the Stratospheric Aerosol and Gas Experiment (SAGE) II instrument onboard the Earth Radiation Budget Satellite (ERBS) and three instruments, the Microwave Limb Sounder (MLS), the Cryogenic Limb Array Etalon Spectrometer (CLAES), the Halogen Occultation Experiment (HALOE) onboard the Upper Atmospheric Research Satellite (UARS). Three of the instruments, ATMOS, SAGE-II and MLS are demonstrated to be consistent to within ±10% over the altitude range between 100 hPa and 0.5 hPa (approximately 20 to 60 km), with ATMOS and MLS displaying a zero mean bias and a root mean square de...
High-resolution spectroscopy of the Meinel bands of OH and OD
Annual Meeting Optical Society of America
The IR spectrum of the Meinel bands of the OH and OD free radicals was observed in a cold ozone-h... more The IR spectrum of the Meinel bands of the OH and OD free radicals was observed in a cold ozone-hydrogen diffusion flame using the Fourier transform spectrometer at the National Solar Observatory (Kitt Peak). Eighteen bands have been observed in the spectral region between 1900 and 9000 cm-1. Wavenumbers, intensities, line shapes, and isotope shifts have been obtained. The spectrum has been synthesized and optimal molecular parameters obtained using molecular Hamiltonians and nonlinear least-squares fitting techniques. The same spectrum has been observed in two other sources, the inductively coupled plasma and the oxyacetylene flame. Comparisons of the three spectra are being made.
Interactive Fourier analysis on IBM PC-compatible computers
Annual Meeting Optical Society of America
While the techniques of Fourier analysis and signal processing lend themselves to the development... more While the techniques of Fourier analysis and signal processing lend themselves to the development of computer programs for data reduction, relatively few programs offer a full complement of algorithms specialized to spectroscopy. Programs for interactive Fourier analysis should provide an environment in which various techniques can be compared and in which data can be displayed and manipulated in both Fourier domains. The decomp spectral decomposition program is designed for the reduction of Fourier transform spectra and focuses on interactive graphic display and Fourier analysis of data. For experiments that require the maximum achievable accuracy or must coax a modicum of signal from noise the DECOMP package offers something more than black-box spectrum analysis. Techniques of Fourier analysis and signal processing are demonstrated, and an IBM PC-compatible computer is available for hands-on demonstrations.
High resolution spectroscopy of the OH and OD free radicals produced in an inductively coupled plasma discharge
Annual Meeting Optical Society of America
The infrared spectrum of the Meinel bands of the OH and OD free radicals was observed in an induc... more The infrared spectrum of the Meinel bands of the OH and OD free radicals was observed in an inductively coupled plasma (ICP) using the McMath Fourier transform spectrometer at the National Solar Observatory (Kitt Peak). Wavenumbers, intensities, line shapes, and isotope shifts have been determined. The spectrum has been synthesized and optimum molecular parameters obtained using molecular Hamiltonians and nonlinear least-squares fitting techniques. Rotational temperature determinations provide plasma diagnostics in the outer sheath of the plasma.
Resolution enhancement in high resolution Fourier transform spectroscopy
Annual Meeting Optical Society of America
Fourier transform spectroscopy dominates the field of infrared high resolution spectroscopy; howe... more Fourier transform spectroscopy dominates the field of infrared high resolution spectroscopy; however, in many low temperature sources the line profile can be smaller than the instrumental profile producing heavily distorted spectra. The instrumental profile of FT IR instruments is a modified sine function and can greatly complicate the reduction of data taken with Fourier transform spectrometers. A technique for achieving modest resolution enhancement has been developed by modifying a nonlinear line profile fitting algorithm to fit only the spectral components present in the spectrum.
DECOMP: A Fourier Transfom Spectra Decomposition Program
High Resolution Fourier Transform Spectroscopy
Current techniques for processing high resolution Fourier transform spectra revolve around intera... more Current techniques for processing high resolution Fourier transform spectra revolve around interactive graphical display of the spectrum on a computer. The DECOMP spectrum decomposition program is designed explicitly for the reduction of Fourier transform spectra and focuses on reducing a spectrum into a list of line parameters. Basic methods of spectrum manipulation will be demonstrated and a IBM PC - compatible computer will be available for hands-on demonstrations of the process of spectrum analysis. Figures 1 and 2 illustrate the process of background subtraction: in Figure 1 a low resolution spectrum is generated by binning the high resolution spectrum and beneath the spectrum is a background correction function generated by creating a low resolution "minima" spectrum and smoothing the spectrum. The results of the background correction are given in Figure 2. Figure 3 illustrates a common problem in Fourier transform spectroscopy: the finite length of the interferogram...
An Overview of the ATMOS Observations and Preliminary Results From the ATLAS-2 Shuttle Mission
Optimization of spaceborne laser absorption spectroscopy sensor using parameter design
SPIE Proceedings, 2002
ABSTRACT A number of gases present in the atmosphere play roles of interest to various parties. T... more ABSTRACT A number of gases present in the atmosphere play roles of interest to various parties. These are CO2 for its impact on understanding of global sources and sinks of Carbon, CH4 and H2O and their importance for global climate change, HCl and its importance in chemical processes. A space-borne sensor using multiple-wavelength Laser Absorption Spectroscopy (LAS) and mature CW fiber telecom lasers can address the critical questions concerning present and future patterns in these gases. The sensor identified above was designed from the outset using Taguchi Robust design techniques because of the need to adjust to varying science measurement requirements and technology capability as well as achieving optimum performance for optimum cost. The results describe a sensor with a SNR of 150 with a power aperture product of 3.92 watts-m2 on the absorption line is sufficient to meet the science requirements of 0.5% accuracy for determining the column density of CO2.
<title>Satellite-based measurements of CO<formula><inf><roman>2</roman></inf></formula> for carbon flux estimation</title>
Remote Sensing of Clouds and the Atmosphere VI, 2002
Why chose a fourier transform spectrometer?
Fourier Transform Spectrometry, 2001
The magnitude of information flow through a spectrometer may be thought of as the product of two ... more The magnitude of information flow through a spectrometer may be thought of as the product of two quantities, one determined by the spectrometer optics and the other by the detector. Because of its axis of symmetry, the Fourier transform spectrometer (FTS) interferometer has a large entrance aperture and, consequently, a large AΩ product. Another aspect of the quantity of data obtained is the fact that the FTS records data at all frequencies simultaneously, a process called multiplexing. There is a great saving in observation time when one wants to look at many frequencies. Many problems do not require the full resolution of instruments. For these problems, it is useful to have variable resolution, because excess resolution reduces the signal-to-noise ratio. The FTS is especially flexible in this regard and has no equal in the ease of setting the instrumental resolution to the required value. If 1% line shape distortion is necessary, then an FTS with an optimum aperture will require five resolution elements across a line width. In contrast, the grating with an optimum slit width will require 30 elements across a line width. The factor of 6 in required resolving power is a large part of the practical advantage of an FTS. The FTS is the system of choice in the infrared under almost any conditions (with or without a multiplex advantage), and in the visible and UV when high accuracy is required in intensity, line shape, or wave number.
Effects of noise in its various forms
Fourier Transform Spectrometry, 2001
There are always various kinds of noise in the spectrum, generated either in the source or by ele... more There are always various kinds of noise in the spectrum, generated either in the source or by electrical and mechanical variations in the environment or in the Fourier transform spectrometer (FTS) itself. Most often the noise is not discernable in the interferogram, but appears clearly and looks like sharp spikes in the spectrum with random positions, widths, and intensities. It is helpful to note how various sources of noise and artifacts enter into the data. Source variations in frequency and intensity during the observation multiply the envelope of the interferogram in an undesirable way. Photon statistics and thermal processes in the detector and electronics add noise to the ideal interferogram. Fortunately, the errors do not usually interact, and one can consider each of them separately. For both historical and practical reasons, it is convenient to treat the noise in terms of where in the system it arises. A two-output interferometer simplifies the analysis of noise effects. There is an FTS multiplex advantage in noise reduction because all spectral elements are recorded simultaneously. Digitizing noise is negligible for simple spectra, but the dynamic range of observable intensities for emission spectra varies inversely as the number of very strong lines.
Progress in laser sources for lidar applications: Laser sources for 3D-imaging remote sensing
Proceedings of SPIE, 2005
ABSTRACT
Highly excited rotational states of the Meinel system of OH
The Astrophysical Journal, 1990
ABSTRACT The OH infrared spectrum, produced in an inductively coupled plasma discharge, has been ... more ABSTRACT The OH infrared spectrum, produced in an inductively coupled plasma discharge, has been measured with a Fourier transform spectrometer between 1850 and 5768/cm. This source was chosen in order to study the high-rotational quantum number levels of the OH Meinel bands. Two bands in the Delta-v = 1 sequence were observed, and extended to high J values: the P branch of the 1-0 band was observed up to J - 27.5 and the R branch to 13.5. The P branch of the 2-1 band was observed up to J = 25.5 and the R branch to 12. 5. Nonperturbative rotational crossings were observed in both the 1-0 and 2-1 bands. A global nonlinear least-squares fit of the 1-0 and 2-1 bands yielded equilibrium molecular parameters with a standard deviation of 0.0024/cm.
The inductively coupled plasma spectrum of OD in the infrared
Pramana, 1992
ABSTRACT To gain more information about the highly excited rotational states of the Δv = 1 sequen... more ABSTRACT To gain more information about the highly excited rotational states of the Δv = 1 sequence of OD vibration-rotation bands, the spectrum has been produced in an inductively coupled plasma discharge and measured with a Fourier transform spectrometer between 1670 and 5768 cm−1. Along with the extension of 1–0 band, we have been successful in recording the 2–1 band for the first time. A nonlinear least square fit of these bands yielded equilibrium molecular parameters forv = 0, 1 and 2 levels with a standard deviation of 0·0032 cm−1. The centrifugal distortion parameters show a systematic vibrational dependence.
Improved molecular parameters for the Ballik-Ramsay system of diatomic carbon (b^3Σg^− → a^3Πu)
Journal of the Optical Society of America B, 1988
The infrared spectrum of the C2 (b3Σg− → a3Πu) Ballik–Ramsay system was observed in a hollow-cath... more The infrared spectrum of the C2 (b3Σg− → a3Πu) Ballik–Ramsay system was observed in a hollow-cathode discharge source by using a high-resolution Fourier-transform spectrometer. Ten bands with (υ′–υ″) equal to (0–1), (1–2), (2–3), (3–4), (0–0), (1–1), (1–0), (2–1), (3–2), and (4–3) were observed in the spectral region between 3300 and 6500 cm−1. The (3–4) and (4–3) bands were observed for the first reported time. In addition, 360 lines belonging to satellite branches were observed. A global fit of the present data combined with previous high-resolution data in an iterative nonlinear least-square algorithm yields equilibrium molecular parameters with a variance of 0.0051 cm−1. The inclusion of the satellite lines facilitates the direct improvement of the fine-structure parameters. Rotational perturbations were observed in the upper b3Σg− state and were analyzed by using deperturbation methods.
First Observations with the LLNL Optical Imaging Fourier Transform Spectrometer
We present the results of the first observing run with an optical imaging Fourier transform spect... more We present the results of the first observing run with an optical imaging Fourier transform spectrometer (FTS). We have designed and fabricated this FTS for low-background astronomical use as a testbed for a proposed imaging FTS for the Next Generation Space Telescope (NGST). The relatively low background in the optical allows us to mimic the long dwell, step-scan operation of the proposed infrared NGST FTS. In this first data set, we have demonstrated the operation of the system as a multi-band camera and as a medium-resolution 3D spectrometer. Our testbed FTS reflects our current design for the NGST FTS (IFIRS). It is a four-port (two input, two output) Michelson interferometer with two 45 degree, self-compensating beamsplitters and cube-corner retro-reflectors. This system was taken to the 1.5-m McMath-Pierce Solar Observatory (MPSO) in March 1999. MPSO provides a good facility for prototyping astronomical instruments with a horizontal focal plane projected onto a (de)rotating table. We collected data from one output port with an off-the-shelf PixelVision CCD camera with a 1024x1024, thinned SITe chip thermoelectrically cooled to 235K. Our final platescale was about 0.5 arcsec/pixel with an unvignetted field of about 4x4 arcmin. We collected imaging spectroscopy with resolutions of a few to 500 of well-known objects including globular clusters, open clusters, spiral galaxies, elliptical galaxies, and nebular regions. We describe our data reduction procedures with emphasis on the unique aspects of imaging FTS data. We present color-magnitude diagrams of star clusters to demonstrate the utility of the imaging FTS as a camera and compare the signal-to-noise performance with theoretical models and filter-based camera performance. Finally, we present datacubes demonstrating the ability of the imaging FTS to yield ``a spectrum for every pixel''.
Uploads
Papers by Mark C Abrams