Grantee Research Project Results
1997 Progress Report: Orthogonal Background Suppression Technique for EPA's Field Infrared Data Processing
EPA Grant Number: R825366Title: Orthogonal Background Suppression Technique for EPA's Field Infrared Data Processing
Investigators: Blatherwick, R. D.
Institution: University of Denver
EPA Project Officer: Hahn, Intaek
Project Period: October 1, 1996 through September 30, 1999 (Extended to September 30, 2000)
Project Period Covered by this Report: October 1, 1996 through September 30, 1997
Project Amount: $248,743
RFA: Analytical and Monitoring Methods (1996) RFA Text | Recipients Lists
Research Category: Water , Land and Waste Management , Air , Ecological Indicators/Assessment/Restoration , Environmental Statistics
Objective:
The research project, specifically entitled Spectral Background Suppression (SBS), is being developed to provide a user-friendly FTIR spectral data processing and analytical tool that can be used to extract pollutant gas data from backgrounds within point and area source field data, having highly variable water vapor concentrations.Progress Summary:
1. Atmospheric Water Vapor ModelA PC-hosted model has been developed that relates standard atmospheric water vapor mixing ratio in the lower few thousand feet of the troposphere, to standard air temperature and atmospheric pressure. The purpose of this model is to provide the capability of extending discrete laboratory and field FTIR data to the whole space spanned in the physical parameters: water vapor mixing ratio, specific humidity for moist air, air temperature, and atmospheric pressure.
2. Long-Path IR Laboratory Test Setup
The long-path IR (LPIR) absorption
instrumentation had been designed, built, and is being tested at the University
of Denver's Physics Building. The sample compartment consists of a variable path
White Cell. The associated input and output optics have been designed,
fabricated and performance tested with the cell. The cell is cylindrical and has
a volume of about 18 liters, with a maximum folded optical pathlength of 107
meters. Alignment of the cell and the desired pathlength through the cell is
accomplished using a diode laser. A gas dryer ignitor is used as the IR source,
which has a color temperature of about 1800 Kelvin. The IR energy is coupled
from the ignitor position into the cell's input aperture by IR reflective
optics. The output IR beam from the White Cell is shaped and then directed into
DU's Bomem Model DA-2 FTIR Spectrometer. This instrument consists of a Michelson
interferometer with one scanning mirror producing a maximum resolution of 0.01
cm-1. The output of the spectrometer is directed toward an IR beamsplitter which
equally divides the intensity into two separate paths leading to two IR
detectors: InSb detector and HgCdTe. Each detector produces an interferogram
characteristic of its respective bandpass. Through a Fourier Transform
technique, the two interferograms are converted to IR spectra, to be used in the
following: empty White Cell characterization analysis and variable water vapor
analyses.
The temperature of the water vapor generated by boiling distilled water is actively controlled. The actual temperature of the water vapor-air mixture is measured directly within the White Cell. The gas pressure within the cell is controlled by a vacuum pump and measured directly. Performance testing has been conducted for the entire laboratory setup. Some difficulty has been uncovered in the spectrometer's electronics that controls the tachometric function for the interferometer's scanning mirror. (This spectrometer has been used in many balloon flights up into the stratosphere for the high resolution measurement of trace atmospheric gases.) This portion of the electronics has been redesigned, built and is being performance tested.
3. Atmospheric Water Vapor FTIR Spectra
Background absorption spectra from
EPA-RTP Outdoor Site were requested, having been obtained with a closed-path
FTIR system recorded during early summer and autumn 1994 at RTP. These spectra
were recorded as background along a 100 m one-way horizontal background path
near ground level at various times throughout the day, which contain varied
ambient water vapor concentrations. The IR source was artificial positioned
about 100 m from the FTIR receiver. EPA also provided the in-situ measurement
data of water vapor data recorded during the FTIR runs, presented in water vapor
partial pressure as a function of time. The resolution of these spectra is 1
cm-1. The spectral range is from 449.815 cm-1 to 4500.08 cm-1 (22.2 to 2.2 mm).
These spectra, which represent water vapor partial pressure values recorded near
sea level, will be used during the program analysis phase during the 1998
reporting period.
4. Laboratory OBS Analyses
The existing DU software which performs the
principal component analyses (PCA) on FTIR absorption spectra through singular
value decomposition (SVD) has been extensively updated, rewritten to meet the
requirements defined for this grant. The software has been debugged and
successfully performance tested. The PCA analysis process is currently being
performed on the EPA/ORD/RTP closed path FTIR absorption spectra (430 Fall 1994
spectra) recorded for varying values of relative humidity and air temperature.
This effort is being used to characterize the non-linear water vapor
absorptions.
Accomplishments and Research Results:
DU has obtained and analyzed radiometrically calibrated hundreds of FTIR absorption spectra with ASTI, Absolute Solar Transmittance Interferometer (resolution is 2 cm-1) at four locations within the continental US: (1) DOE Southern Great Plains Atmospheric Radiation Measurement Site, Oklahoma, 1,065 feet MSL, June 24-28, 1997 and September 15-October 03, 1997; (2) DU Womble IR Observatory, Mt. Evans, Colorado, 14,150 feet MSL, July 15-17, 1997; (3) University of Denver, Denver, Colorado, 5,400 feet MSL, September 12, 1997. The sun was used as the IR source for these tests recorded in the SWIR band from 1,950 cm-1 to 10,300 cm-1 (0.97 to 5.13 mm).
Future Activities:
The new electronics will be installed into the Bomem spectrometer within the LPIR instrumentation and system tests performed. Then the characterization tests of the White Cell will again be performed and recorded. With this accomplished, the variable water vapor mixing ratio testing will then be concluded, producing hundreds of high resolution IR spectra. The hundreds of field spectra, which represent water vapor partial pressure values recorded over an altitude range of 13,000 feet, will be used during the analysis phase to test for affects of atmospheric water vapor non-linearities as a function of atmospheric pressure changes. This is geared for the end-point user at industrial sites for various elevations around the country. The Mt. Evans spectra are to be used to employ the high altitude affect upon water vapor concentrations for subsequent OBS suppression over a broad range of vapor partial pressures. The Fall 1994 results will be used within the next few weeks to effectively suppress the water vapor backgrounds from the EPA Early Summer 1994 background water vapor spectra. Also, in the next two to three months, the PCA/SVD process will be employed to directly characterize the Long-Path IR Laboratory absorption spectra for controlled amounts of water vapor at controlled cell temperatures and pressures. These will be the input spectra for the construction of the principal component eigen-matrix for water vapor suppression.Journal Articles:
No journal articles submitted with this report: View all 1 publications for this projectSupplemental Keywords:
Principal component factor analysis, target transformation factor analysis, data kernel, , Line-By-Line Radiative Transfer Model., RFA, Scientific Discipline, Toxics, Air, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Chemistry, HAPS, Monitoring/Modeling, tropospheric ozone, Engineering, environmental monitoring, orthogonal background suppression, remote sensing, ambient particle properties, field portable monitoring, ambient air, spectroscopic studies, air quality data, analytical chemistry, FTIR, carbon dioxide, spectroscopic, atmospheric monitoring, water vapor, measurement methods , aerosol analyzers, atmospheric chemistry, Fourier transform infraredProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.