Norton Allen - Academia.edu (original) (raw)
Papers by Norton Allen
Review of Scientific Instruments, Jun 1, 2008
We present a new instrument, Hoxotope, for the in situ measurement of H 2 O and its heavy deuteri... more We present a new instrument, Hoxotope, for the in situ measurement of H 2 O and its heavy deuterium isotopologue ͑HDO͒ in the upper troposphere and lower stratosphere aboard the NASA WB-57. Sensitive measurements of ␦D are accomplished through the vacuum UV photolysis of water followed by laser-induced fluorescence detection of the resultant OH and OD photofragments. The photolysis laser-induced fluorescence technique can obtain S / N Ͼ 20 for 1 ppbv HDO and S / N Ͼ 30 for 5 ppmv H 2 O for 10 s data, providing the sensitivity required for ␦D measurements in the tropopause region. The technique responds rapidly to changing water concentrations due to its inherently small sampling volume, augmented by steps taken to minimize water uptake on instrument plumbing. Data from the summer 2005 Aura Validation Experiment Water Isotope Intercomparison Flights ͑AVE-WIIF͒ out of Houston, TX show agreement for H 2 O between Hoxotope and the Harvard water vapor instrument and for HDO between Hoxotope and the Harvard ICOS water isotope instrument, to within stated instrument uncertainties. The successful intercomparison validates Hoxotope as a credible source of ␦D data in the upper troposphere and lower stratosphere.
Review of Scientific Instruments, Jul 1, 2013
We present a new instrument for the measurement of water vapor in the upper troposphere and lower... more We present a new instrument for the measurement of water vapor in the upper troposphere and lower stratosphere (UT/LS), the Harvard Herriott Hygrometer (HHH). HHH employs a tunable diode near-IR laser to measure water vapor via direct absorption in a Herriott cell. The direct absorption technique provides a direct link between the depth of the observed absorption line and the measured water vapor concentration, which is calculated based on spectroscopic parameters in the HITRAN database. While several other tunable diode laser (TDL) instruments have been used to measure water vapor in the UT/LS, HHH is set apart by its use of an optical cell an order of magnitude smaller than those of other direct absorption TDLs in operation, allowing for a more compact, lightweight instrument. HHH is also unique in its integration into a common duct with the Harvard Lyman-α hygrometer, an independent photo-fragment fluorescence instrument which has been thoroughly validated over 19 years of flight measurements. The instrument was flown for the first time in the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) on NASA's WB-57 aircraft in spring, 2011, during which it demonstrated in-flight precision of 0.1 ppmv (1 s) with 1-sigma uncertainty of 5% ± 0.7 ppmv. Since the campaign, changes to the instrument have lead to improved accuracy of 5% ± 0.2 ppmv as demonstrated in the laboratory. During MACPEX, HHH successfully measured water vapor at concentrations from 3.5 to 600 ppmv in the upper troposphere and lower stratosphere. HHH and Lyman-α, measuring independently but under the same sampling conditions, agreed on average to within 1% at water vapor mixing ratios above 20 ppmv and to within 0.3 ppmv at lower mixing ratios. HHH also agreed with a number of other in situ water vapor instruments on the WB-57 to within their stated uncertainties, and to within 0.7 ppmv at low water. This agreement constitutes a significant improvement over past in situ comparisons, in which differences of 1.5–2 ppmv were routinely observed, and demonstrates that the accuracy of HHH is consistent with other instruments which use a range of detection methods and sampling techniques.
AGUFM, Dec 1, 2005
We report here on new in-situ data on the isotopic composition of atmospheric water vapor that al... more We report here on new in-situ data on the isotopic composition of atmospheric water vapor that allow an unprecedented view into processes affecting the water content of the troposphere and lower stratosphere. Isotopic data from the Harvard ICOS and Hoxotope instruments were obtained on three flights of the WB-57 during the AVE_WIIF campaign of July 2005, over altitudes from 5-19
2015 AGU Fall Meeting, Jan 25, 2016
![Research paper thumbnail of A new photolysis laser-induced fluorescence instrument for the detection of H[sub 2]O and HDO in the lower stratosphere](https://attachments.academia-assets.com/99491181/thumbnails/1.jpg)
](Review of Scientific Instruments, 2008
We present a new instrument, Hoxotope, for the in situ measurement of H 2 O and its heavy deuteri... more We present a new instrument, Hoxotope, for the in situ measurement of H 2 O and its heavy deuterium isotopologue ͑HDO͒ in the upper troposphere and lower stratosphere aboard the NASA WB-57. Sensitive measurements of ␦D are accomplished through the vacuum UV photolysis of water followed by laser-induced fluorescence detection of the resultant OH and OD photofragments. The photolysis laser-induced fluorescence technique can obtain S / N Ͼ 20 for 1 ppbv HDO and S / N Ͼ 30 for 5 ppmv H 2 O for 10 s data, providing the sensitivity required for ␦D measurements in the tropopause region. The technique responds rapidly to changing water concentrations due to its inherently small sampling volume, augmented by steps taken to minimize water uptake on instrument plumbing. Data from the summer 2005 Aura Validation Experiment Water Isotope Intercomparison Flights ͑AVE-WIIF͒ out of Houston, TX show agreement for H 2 O between Hoxotope and the Harvard water vapor instrument and for HDO between Hoxotope and the Harvard ICOS water isotope instrument, to within stated instrument uncertainties. The successful intercomparison validates Hoxotope as a credible source of ␦D data in the upper troposphere and lower stratosphere.
AGU Fall Meeting Abstracts, Dec 1, 2017
AGUFM, Dec 1, 2004
ABSTRACT In recent years the atmospheric science community has placed high priority on obtaining ... more ABSTRACT In recent years the atmospheric science community has placed high priority on obtaining measurements of the isotopic composition of water vapor at near-tropopause altitudes. Because water isotopic composition is altered by all processes involving condensation or evaporation, it can serve as a tracer of the processes governing the water content of air ascending to the stratosphere. Obtaining scientifically useful measurements is made difficult, however, by the scarcity of HDO, the most useful water isotopologue; by the precision and accuracy required to differentiate between dehydration scenarios; and by the potential for contamination. We report here on the first flights of a new instrument designed to meet these needs and to provide high-sensitivity in situ measurements of HDO, H218O, and H2O in the near-tropopause region. The Harvard ICOS Isotope Instrument uses the relatively new technique of Integrated Cavity Output Spectroscopy (ICOS) to provide mid-infrared absorption spectra with a pathlength of 4 km, as opposed to the < 100 m of traditional multipass cells. The instrument offers more than an order of magnitude improvement in sensitivity over traditional in situ mid-infrared spectroscopic instruments. Integration times are 1-3 s, short enough to capture the small spatial scales of tropical deep convection plumes and cirrus layers. Instrument design also focuses on minimizing measurement hysteresis due to contamination, using pharmaceutical-grade fittings and welds to eliminate trapped volumes. We discuss the specific measurement needs for studying near-tropopause dehydration and show validation of the performance of this instrument on a series of test flights in autumn 2004 on NASA's WB-57 high-altitude aircraft. The aircraft payload includes for comparison a second instrument measuring HDO and H2O by a fully independent method (the Harvard Hoxotope Instrument, using photofragment laser-induced fluorescence) as well as two well-established and validated instruments measuring water vapor and total water. The Harvard ICOS Isotope Instrument is proposed for use on upcoming science missions studying water vapor in the near-tropopause region.
ICOSfit is a non-linear least-squares fitting tool originally developed for processing<br> ... more ICOSfit is a non-linear least-squares fitting tool originally developed for processing<br> data from the Anderson Group's ICOS instruments. It has<br> since been extended to support other optical configurations, such as Herriott Cells. See the README for information on installation and building.
In recent years the atmospheric science community has placed high priority on obtaining measureme... more In recent years the atmospheric science community has placed high priority on obtaining measurements of the isotopic composition of water vapor at near-tropopause altitudes. Because water isotopic composition is altered by all processes involving condensation or evaporation, it can serve as a tracer of the processes governing the water content of air ascending to the stratosphere. Obtaining scientifically useful measurements is made difficult, however, by the scarcity of HDO, the most useful water isotopologue; by the precision and accuracy required to differentiate between dehydration scenarios; and by the potential for contamination. We report here on the first flights of a new instrument designed to meet these needs and to provide high-sensitivity in situ measurements of HDO, H218O, and H2O in the near-tropopause region. The Harvard ICOS Isotope Instrument uses the relatively new technique of Integrated Cavity Output Spectroscopy (ICOS) to provide mid-infrared absorption spectra ...
ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from... more ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from the Anderson Group's ICOS instruments. It has since been extended to support other optical configurations, such as Herriott Cells. This release includes: Added etln_fine_tune to address some types of laser feedback Matchline: Optionally group lines by isotopologue See the README for information on installation and building.
ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from... more ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from the Anderson Group's ICOS instruments. It has since been extended to support other optical configurations, such as Herriott Cells. This release includes: Bug fix for parameter scaling of line number density Cleanup of optimization tools See the README for information on installation and building.
ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from... more ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from the Anderson Group's ICOS instruments. It has since been extended to support other optical configurations, such as Herriott Cells. This release includes: Added parameter MaxEnsembleDriftPerScan Renamed parameter TolerableDrift to MaxFinePositionOffset Fixed improper handling of PTEfile options See the README for information on installation and building.
ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from... more ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from the Anderson Group's ICOS instruments. It has since been extended to support other optical configurations, such as Herriott Cells. This release includes: Fixed minor bugs in optimizer utilities Added support for non-pc platforms See the README for information on installation and building.
The Total Carbon Column Observing Network (TCCON) is a network of ground-based Fourier Transform ... more The Total Carbon Column Observing Network (TCCON) is a network of ground-based Fourier Transform Spectrometers that record direct solar absorption spectra of the atmosphere in the near-infrared. From these spectra, accurate and precise column-averaged abundances of atmospheric constituents including CO2, CH4, N2O, HF, CO, H2O, and HDO, are retrieved. This data set contains observations from the TCCON station at Lamont, U.S.A..
Retaining Immigrants in Rural Communities Employee Retention Strategies Slide 2 About this presen... more Retaining Immigrants in Rural Communities Employee Retention Strategies Slide 2 About this presentation • Review of employee retention strategies (ERS) for employers in SME sector in rural Manitoba. • ERS also attract new employees. • Retaining migrant recruits and other multi-cultural employees. • Cross-sector model carrying four categories: job, culture, personal and external.
Review of Scientific Instruments, Jun 1, 2008
We present a new instrument, Hoxotope, for the in situ measurement of H 2 O and its heavy deuteri... more We present a new instrument, Hoxotope, for the in situ measurement of H 2 O and its heavy deuterium isotopologue ͑HDO͒ in the upper troposphere and lower stratosphere aboard the NASA WB-57. Sensitive measurements of ␦D are accomplished through the vacuum UV photolysis of water followed by laser-induced fluorescence detection of the resultant OH and OD photofragments. The photolysis laser-induced fluorescence technique can obtain S / N Ͼ 20 for 1 ppbv HDO and S / N Ͼ 30 for 5 ppmv H 2 O for 10 s data, providing the sensitivity required for ␦D measurements in the tropopause region. The technique responds rapidly to changing water concentrations due to its inherently small sampling volume, augmented by steps taken to minimize water uptake on instrument plumbing. Data from the summer 2005 Aura Validation Experiment Water Isotope Intercomparison Flights ͑AVE-WIIF͒ out of Houston, TX show agreement for H 2 O between Hoxotope and the Harvard water vapor instrument and for HDO between Hoxotope and the Harvard ICOS water isotope instrument, to within stated instrument uncertainties. The successful intercomparison validates Hoxotope as a credible source of ␦D data in the upper troposphere and lower stratosphere.
Review of Scientific Instruments, Jul 1, 2013
We present a new instrument for the measurement of water vapor in the upper troposphere and lower... more We present a new instrument for the measurement of water vapor in the upper troposphere and lower stratosphere (UT/LS), the Harvard Herriott Hygrometer (HHH). HHH employs a tunable diode near-IR laser to measure water vapor via direct absorption in a Herriott cell. The direct absorption technique provides a direct link between the depth of the observed absorption line and the measured water vapor concentration, which is calculated based on spectroscopic parameters in the HITRAN database. While several other tunable diode laser (TDL) instruments have been used to measure water vapor in the UT/LS, HHH is set apart by its use of an optical cell an order of magnitude smaller than those of other direct absorption TDLs in operation, allowing for a more compact, lightweight instrument. HHH is also unique in its integration into a common duct with the Harvard Lyman-α hygrometer, an independent photo-fragment fluorescence instrument which has been thoroughly validated over 19 years of flight measurements. The instrument was flown for the first time in the Mid-latitude Airborne Cirrus Properties Experiment (MACPEX) on NASA's WB-57 aircraft in spring, 2011, during which it demonstrated in-flight precision of 0.1 ppmv (1 s) with 1-sigma uncertainty of 5% ± 0.7 ppmv. Since the campaign, changes to the instrument have lead to improved accuracy of 5% ± 0.2 ppmv as demonstrated in the laboratory. During MACPEX, HHH successfully measured water vapor at concentrations from 3.5 to 600 ppmv in the upper troposphere and lower stratosphere. HHH and Lyman-α, measuring independently but under the same sampling conditions, agreed on average to within 1% at water vapor mixing ratios above 20 ppmv and to within 0.3 ppmv at lower mixing ratios. HHH also agreed with a number of other in situ water vapor instruments on the WB-57 to within their stated uncertainties, and to within 0.7 ppmv at low water. This agreement constitutes a significant improvement over past in situ comparisons, in which differences of 1.5–2 ppmv were routinely observed, and demonstrates that the accuracy of HHH is consistent with other instruments which use a range of detection methods and sampling techniques.
AGUFM, Dec 1, 2005
We report here on new in-situ data on the isotopic composition of atmospheric water vapor that al... more We report here on new in-situ data on the isotopic composition of atmospheric water vapor that allow an unprecedented view into processes affecting the water content of the troposphere and lower stratosphere. Isotopic data from the Harvard ICOS and Hoxotope instruments were obtained on three flights of the WB-57 during the AVE_WIIF campaign of July 2005, over altitudes from 5-19
2015 AGU Fall Meeting, Jan 25, 2016
Review of Scientific Instruments, 2008
We present a new instrument, Hoxotope, for the in situ measurement of H 2 O and its heavy deuteri... more We present a new instrument, Hoxotope, for the in situ measurement of H 2 O and its heavy deuterium isotopologue ͑HDO͒ in the upper troposphere and lower stratosphere aboard the NASA WB-57. Sensitive measurements of ␦D are accomplished through the vacuum UV photolysis of water followed by laser-induced fluorescence detection of the resultant OH and OD photofragments. The photolysis laser-induced fluorescence technique can obtain S / N Ͼ 20 for 1 ppbv HDO and S / N Ͼ 30 for 5 ppmv H 2 O for 10 s data, providing the sensitivity required for ␦D measurements in the tropopause region. The technique responds rapidly to changing water concentrations due to its inherently small sampling volume, augmented by steps taken to minimize water uptake on instrument plumbing. Data from the summer 2005 Aura Validation Experiment Water Isotope Intercomparison Flights ͑AVE-WIIF͒ out of Houston, TX show agreement for H 2 O between Hoxotope and the Harvard water vapor instrument and for HDO between Hoxotope and the Harvard ICOS water isotope instrument, to within stated instrument uncertainties. The successful intercomparison validates Hoxotope as a credible source of ␦D data in the upper troposphere and lower stratosphere.
AGU Fall Meeting Abstracts, Dec 1, 2017
AGUFM, Dec 1, 2004
ABSTRACT In recent years the atmospheric science community has placed high priority on obtaining ... more ABSTRACT In recent years the atmospheric science community has placed high priority on obtaining measurements of the isotopic composition of water vapor at near-tropopause altitudes. Because water isotopic composition is altered by all processes involving condensation or evaporation, it can serve as a tracer of the processes governing the water content of air ascending to the stratosphere. Obtaining scientifically useful measurements is made difficult, however, by the scarcity of HDO, the most useful water isotopologue; by the precision and accuracy required to differentiate between dehydration scenarios; and by the potential for contamination. We report here on the first flights of a new instrument designed to meet these needs and to provide high-sensitivity in situ measurements of HDO, H218O, and H2O in the near-tropopause region. The Harvard ICOS Isotope Instrument uses the relatively new technique of Integrated Cavity Output Spectroscopy (ICOS) to provide mid-infrared absorption spectra with a pathlength of 4 km, as opposed to the < 100 m of traditional multipass cells. The instrument offers more than an order of magnitude improvement in sensitivity over traditional in situ mid-infrared spectroscopic instruments. Integration times are 1-3 s, short enough to capture the small spatial scales of tropical deep convection plumes and cirrus layers. Instrument design also focuses on minimizing measurement hysteresis due to contamination, using pharmaceutical-grade fittings and welds to eliminate trapped volumes. We discuss the specific measurement needs for studying near-tropopause dehydration and show validation of the performance of this instrument on a series of test flights in autumn 2004 on NASA's WB-57 high-altitude aircraft. The aircraft payload includes for comparison a second instrument measuring HDO and H2O by a fully independent method (the Harvard Hoxotope Instrument, using photofragment laser-induced fluorescence) as well as two well-established and validated instruments measuring water vapor and total water. The Harvard ICOS Isotope Instrument is proposed for use on upcoming science missions studying water vapor in the near-tropopause region.
ICOSfit is a non-linear least-squares fitting tool originally developed for processing<br> ... more ICOSfit is a non-linear least-squares fitting tool originally developed for processing<br> data from the Anderson Group's ICOS instruments. It has<br> since been extended to support other optical configurations, such as Herriott Cells. See the README for information on installation and building.
In recent years the atmospheric science community has placed high priority on obtaining measureme... more In recent years the atmospheric science community has placed high priority on obtaining measurements of the isotopic composition of water vapor at near-tropopause altitudes. Because water isotopic composition is altered by all processes involving condensation or evaporation, it can serve as a tracer of the processes governing the water content of air ascending to the stratosphere. Obtaining scientifically useful measurements is made difficult, however, by the scarcity of HDO, the most useful water isotopologue; by the precision and accuracy required to differentiate between dehydration scenarios; and by the potential for contamination. We report here on the first flights of a new instrument designed to meet these needs and to provide high-sensitivity in situ measurements of HDO, H218O, and H2O in the near-tropopause region. The Harvard ICOS Isotope Instrument uses the relatively new technique of Integrated Cavity Output Spectroscopy (ICOS) to provide mid-infrared absorption spectra ...
ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from... more ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from the Anderson Group's ICOS instruments. It has since been extended to support other optical configurations, such as Herriott Cells. This release includes: Added etln_fine_tune to address some types of laser feedback Matchline: Optionally group lines by isotopologue See the README for information on installation and building.
ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from... more ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from the Anderson Group's ICOS instruments. It has since been extended to support other optical configurations, such as Herriott Cells. This release includes: Bug fix for parameter scaling of line number density Cleanup of optimization tools See the README for information on installation and building.
ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from... more ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from the Anderson Group's ICOS instruments. It has since been extended to support other optical configurations, such as Herriott Cells. This release includes: Added parameter MaxEnsembleDriftPerScan Renamed parameter TolerableDrift to MaxFinePositionOffset Fixed improper handling of PTEfile options See the README for information on installation and building.
ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from... more ICOSfit is a non-linear least-squares fit algorithm originally developed for processing data from the Anderson Group's ICOS instruments. It has since been extended to support other optical configurations, such as Herriott Cells. This release includes: Fixed minor bugs in optimizer utilities Added support for non-pc platforms See the README for information on installation and building.
The Total Carbon Column Observing Network (TCCON) is a network of ground-based Fourier Transform ... more The Total Carbon Column Observing Network (TCCON) is a network of ground-based Fourier Transform Spectrometers that record direct solar absorption spectra of the atmosphere in the near-infrared. From these spectra, accurate and precise column-averaged abundances of atmospheric constituents including CO2, CH4, N2O, HF, CO, H2O, and HDO, are retrieved. This data set contains observations from the TCCON station at Lamont, U.S.A..
Retaining Immigrants in Rural Communities Employee Retention Strategies Slide 2 About this presen... more Retaining Immigrants in Rural Communities Employee Retention Strategies Slide 2 About this presentation • Review of employee retention strategies (ERS) for employers in SME sector in rural Manitoba. • ERS also attract new employees. • Retaining migrant recruits and other multi-cultural employees. • Cross-sector model carrying four categories: job, culture, personal and external.