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High-sensitivity detection of trace gases using dynamic photoacoustic spectroscopy

February 1, 2014
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Journal Article
Author:
Charles M. Wynn
…
Published in:
Opt. Eng., Vol. 53 No. 2, February 2014, 021103.
Topic:
detection systems
R&D area:
R&D group:

Summary

Lincoln Laboratory of Massachusetts Institute of Technology has developed a technique known as dynamic photoacoustic spectroscopy (DPAS) that could enable remote detection of trace gases via a field-portable laser-based system. A fielded DPAS system has the potential to enable rapid, early warning of airborne chemical threats. DPAS is a new form of photoacoustic spectroscopy that relies on a laser beam swept at the speed of sound to amplify an otherwise weak photoacoustic signal. We experimentally determine the sensitivity of this technique using trace quantities of SF6 gas. A clutter-limited sensitivity of ~100 ppt is estimated for an integration path of 0.43 m. Additionally, detection at ranges over 5 m using two different detection modalities is demonstrated: a parabolic microphone and a laser vibrometer. Its utility in detecting ammonia emanating from solid samples in an ambient environment is also demonstrated.
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Summary

Lincoln Laboratory of Massachusetts Institute of Technology has developed a technique known as dynamic photoacoustic spectroscopy (DPAS) that could enable remote detection of trace gases via a field-portable laser-based system. A fielded DPAS system has the potential to enable rapid, early warning of airborne chemical threats. DPAS is a new...

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High-sensitivity detection of trace gases using dynamic photoacoustic spectroscopy

Reagent assessment for detection of ammonium ion-molecule complexes

December 1, 2013
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Journal Article
Author:
Kerin E. Gregory
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Published in:
Rapid Commun. Mass Spectrom., Vol. 27, 2013, pp. 2797-2806.
Topic:
detection systems
R&D area:
R&D group:

Summary

An MS-based framework was developed to quantitatively assess API ion-molecule reagent chemistries based on ammonium selectivity versus competing ions, and intrinsic ammonium binding strength and complex survivability for detection. Methyl acetoacetate is an attractive ammonium reagent for vapor-phase API techniques given its high vapor pressure, preferential selectivity, and high critical energy for dissociation.
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Summary

An MS-based framework was developed to quantitatively assess API ion-molecule reagent chemistries based on ammonium selectivity versus competing ions, and intrinsic ammonium binding strength and complex survivability for detection. Methyl acetoacetate is an attractive ammonium reagent for vapor-phase API techniques given its high vapor pressure, preferential selectivity, and high critical...

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Reagent assessment for detection of ammonium ion-molecule complexes

Wind-shear detection performance analysis for MPAR risk reduction

September 16, 2013
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Conference Paper
Author:
John Y. Cho
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Published in:
36th Conf. on Radar Meteorology, 16 September 2013.
Topic:
detection systems
R&D area:
R&D group:

Summary

Multifunction phased array radars (MPARs) of the future that may replace the current terminal wind-shear detection systems will need to meet the Federal Aviation Administration's (FAA) detection requirements. Detection performance issues related to on-airport siting of MPAR, its broader antenna beamwidth relative to the Terminal Doppler Weather Radar (TDWR), and the change in operational frequency from C band to S band are analyzed. Results from the 2012 MPAR Wind-Shear Experiment are presented, with microburst and gust-front detection statistics for the Oklahoma City TDWR and the National Weather Radar Testbed (NWRT) phased array radar, which are located 6 km apart. The NWRT has sensitivity and beamwidth similar to a conceptual terminal MPAR (TMPAR), which is a scaled-down version of a full-size MPAR. The micro-burst results show both the TDWR probability of detec-tion (POD) and the estimated NWRT POD exceeding the 90% requirement. For gust fronts, however, the overall estimated NWRT POD was more than 10% lower than the TDWR POD. NWRT data are also used to demonstrate that rapid-scan phased array radar has the potential to enhance microburst prediction capability.
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Summary

Multifunction phased array radars (MPARs) of the future that may replace the current terminal wind-shear detection systems will need to meet the Federal Aviation Administration's (FAA) detection requirements. Detection performance issues related to on-airport siting of MPAR, its broader antenna beamwidth relative to the Terminal Doppler Weather Radar (TDWR), and...

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Wind-shear detection performance analysis for MPAR risk reduction

Gadolinium oxide coated fully depleted silicon-on-insulator transistors for thermal neutron dosimetry

April 29, 2013
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Journal Article
Author:
Steven A. Vitale
…
Published in:
Nucl. Instrum. Methods Phys. Res. A, Accel., Vol. 721, 2013, pp. 45-9.
Topic:
detection systems
R&D area:
R&D group:

Summary

Fully depleted silicon-on-insulator transistors coated with gadolinium oxide are shown to be effective thermal neutron dosimeters. The theoretical neutron detection efficiency is calculated to be higher for Gd2O3 than for other practical converter materials. Proof-of-concept dosimeter devices were fabricated and tested during thermal neutron irradiation. The transistor current changes linearly with neutron dose, consistent with increasing positive charge in the SOI buried oxide layer generated by ionization from high energy 157Gd(n,γ)158Gd conversion electrons. The measured neutron sensitivity is approximately 1/6 the maximum theoretical value, possibly due to electron-hole recombination or conversion electron loss in interconnect wiring above the transistors.
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Summary

Fully depleted silicon-on-insulator transistors coated with gadolinium oxide are shown to be effective thermal neutron dosimeters. The theoretical neutron detection efficiency is calculated to be higher for Gd2O3 than for other practical converter materials. Proof-of-concept dosimeter devices were fabricated and tested during thermal neutron irradiation. The transistor current changes linearly...

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Gadolinium oxide coated fully depleted silicon-on-insulator transistors for thermal neutron dosimetry

Multifunction Phased Array Radar wind shear experiment

November 5, 2012
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Conference Paper
Author:
Pamela L. Heinselman
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Published in:
26th Conf. on Sever Local Storms, 5-8 November 2012.
Topic:
algorithms
R&D area:
R&D group:

Summary

Terminal Doppler Weather Radars (TDWRs) provide near-ground wind shear detection that is critical for aircraft safety at 46 airports across the United States. These systems are part of the larger network of 510 weather and aircraft surveillance radars owned and operated by government agencies in the continental United States. As the TDWR and other radar systems approach their engineering design life cycles, the Federal Aviation Administration (FAA), National Weather Service (NWS), and Department of Defense (DoD) are considering potential replacement systems (OFCM 2006; Weber et al. 2007). One option under consideration that would maintain the current airspace coverage is a replacement network of 334 Multifunction Phased Array Radars (MPARs) (Weber et al. 2007). The MPAR network described by Weber et al. (2007) would include two classes of systems: A high-resolution, full-scale version with an 8-m diameter antenna, and a lower-resolution terminal version with a 4-m diameter antenna, termed Terminal MPAR, or TMPAR. As the proposed TMPAR design has lower azimuthal beam resolution and less sensitivity than TDWRs, it is crucial to determine the impacts of that design on the detection of low-altitude wind shear. The design of the SPY-1A PAR, a research radar at the National Weather Radar Test Bed in Norman, Oklahoma (Zrnić et al. 2007), makes it a good proxy for examining the potential wind shear detection performance of the TMPAR. Therefore, in spring 2012, the National Oceanic and Atmospheric Administration (NOAA) National Severe Storms Laboratory organized and executed the MPAR Wind Shear Experiment (WSE) in collaboration with the FAA, NOAA's NWS Radar Operations Center, the University of Oklahoma Advanced Radar Research Center (OU ARRC), and the Massachusetts Institute of Technology Lincoln Laboratory (MIT LL). The primary objective of the MPAR WSE was to collect low-altitude observations with the SPY-1A PAR (hereafter, PAR) for comparison with observations from the nearby Oklahoma City (OKC) TDWR. Of particular interest is comparison of MIT LL wind shear detection algorithm performance using data from these two radars; this analysis is reported in Cho et al. (2013). Data were also collected from other radars in central Oklahoma to facilitate basic research on microbursts and other wind-producing storms. This paper provides an overview of the MPAR WSE and observed wind shear events.
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Summary

Terminal Doppler Weather Radars (TDWRs) provide near-ground wind shear detection that is critical for aircraft safety at 46 airports across the United States. These systems are part of the larger network of 510 weather and aircraft surveillance radars owned and operated by government agencies in the continental United States. As...

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Multifunction Phased Array Radar wind shear experiment

Dynamic photoacoustic spectroscopy for trace gas detection

October 29, 2012
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Journal Article
Author:
Charles M. Wynn
…
Published in:
Appl. Phys. Lett., Vol. 101, No. 18, 29 October 2012, 184103.
Topic:
detection systems
R&D area:
R&D group:

Summary

We present a method of photoacoustic spectroscopy in which a laser beam tuned to an absorption feature of a gas is swept through its plume at the speed of sound. The resulting coherent addition of acoustic waves leads to an amplification of the signal without the need for a resonant chamber, thus enhancing the ability to remotely sense the gas. We demonstrate the concept using a tunable CO2 laser and SF6 gas in conjunction with a microphone. Sound pressure levels of 83 dB (relative to 20 uPa) are generated from a 15-ppm plume.
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Summary

We present a method of photoacoustic spectroscopy in which a laser beam tuned to an absorption feature of a gas is swept through its plume at the speed of sound. The resulting coherent addition of acoustic waves leads to an amplification of the signal without the need for a resonant...

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Dynamic photoacoustic spectroscopy for trace gas detection

Towards the detection of aircraft icing conditions using operational dual-polarimetric radar

June 25, 2012
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Conference Paper
Author:
Scott Ellis
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Published in:
7th European Conf. on Radar in Meteorology and Hydrology, ERAD, 25-29 June 2012.
Topic:
algorithms
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R&D group:

Summary

In anticipation of the dual-polarimetric upgrade to the National Weather Service operational radar network (WSR-88D) research is being conducted to utilize this extensive new data source for remote aircraft icing detection. The first challenge is to accurately locate the melting layer. A new image-processing-based algorithm is proposed and demonstrated. The next challenge is to use the dual-polarimetric data above the melting level to distinguish regions containing super-cooled liquid water, which constitutes an aviation icing hazard, from regions of pure ice and snow. It has been well documented that the S-band dual-polarimetric radar signatures at individual range gates of super-cooled liquid water and ice crystals overlap significantly, complicating the identification of icing conditions using individual radar measurements. Recently several investigators have found that the aggregate characteristics of dual-polarimetric radar measurements over regions on the order of several kilometers show distinguishing features between regions containing super-cooled liquid and those with ice only. In this study, the features found in the literature are evaluated, extended and combined using a fuzzy-logic framework to provide an icing threat likelihood. The results of this new algorithm are computed using data collected in Colorado from the Colorado State University CHILL radar and the National Center for Atmospheric Research S-Pol radar (collectively called FRONT – The Front Range Observational Testbed) collected in the winter of 2010/2011 in coordination with the NASA Icing Remote Sensing System (NIRSS) and compared to pilot reports on approach or departure from nearby airports. The preliminary results look encouraging and will be presented. The ultimate goal is to produce an end-to-end algorithm to produce a reliable icing threat product that can then be combined with existing icing detection systems to improve their performance.
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Summary

In anticipation of the dual-polarimetric upgrade to the National Weather Service operational radar network (WSR-88D) research is being conducted to utilize this extensive new data source for remote aircraft icing detection. The first challenge is to accurately locate the melting layer. A new image-processing-based algorithm is proposed and demonstrated. The...

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Towards the detection of aircraft icing conditions using operational dual-polarimetric radar

Exploring the variable sky with LINEAR : photometric recalibration with the Sloan Digital Sky Survey

December 1, 2011
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Journal Article
Author:
Branimir Sesar
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Published in:
Astronomical J., Vol. 142, No. 6, December 2011.
Topic:
LINEAR
R&D area:
R&D group:

Summary

We describe photometric recalibration of data obtained by the asteroid survey LINEAR. Although LINEAR was designed for astrometric discovery of moving objects, the data set described here contains over 5 billion photometric measurements for about 25 million objects, mostly stars. We use Sloan Digital Sky Survey (SDSS) data from the overlapping ~10,000 deg2 of sky to recalibrate LINEAR photometry and achieve errors of 0.03 mag for sources not limited by photon statistics with errors of 0.2 mag at r ~ 18. With its 200 observations per object on average, LINEAR data provide time domain information for the brightest four magnitudes of the SDSS survey. At the same time, LINEAR extends the deepest similar wide-area variability survey, the Northern Sky Variability Survey, by 3 mag.We briefly discuss the properties of about 7000 visually confirmed periodic variables, dominated by roughly equal fractions of RR Lyrae stars and eclipsing binary stars, and analyze their distribution in optical and infrared color?color diagrams. The LINEAR data set is publicly available from the SkyDOT Web site.
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Summary

We describe photometric recalibration of data obtained by the asteroid survey LINEAR. Although LINEAR was designed for astrometric discovery of moving objects, the data set described here contains over 5 billion photometric measurements for about 25 million objects, mostly stars. We use Sloan Digital Sky Survey (SDSS) data from the...

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Exploring the variable sky with LINEAR : photometric recalibration with the Sloan Digital Sky Survey

Noncontact optical detection of explosive particles via photodissociation followed by laser-induced fluorescence

September 12, 2011
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Journal Article
Author:
Charles M. Wynn
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Published in:
Opt. Express, Vol. 19, No. 19, 12 September 2011, pp. 18671-18677.
Topic:
detection systems
R&D area:
R&D group:

Summary

High-sensitivity (ng/cm2) optical detection of the explosive 2,4,6- trinitrotoluene (TNT) is demonstrated using photodissociation followed by laser-induced fluorescence (PD-LIF). Detection occurs rapidly, within 6 laser pulses (~7 ns each) at a range of 15 cm. Dropcasting is used to create calibrated samples covering a wide range of TNT concentrations; and a correspondence between fractional area covered by TNT and PD-LIF signal strength is observed. Dropcast data are compared to that of an actual fingerprint. These results demonstrate that PD-LIF could be a viable means of rapidly and remotely scanning surfaces for trace explosive residues.
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Summary

High-sensitivity (ng/cm2) optical detection of the explosive 2,4,6- trinitrotoluene (TNT) is demonstrated using photodissociation followed by laser-induced fluorescence (PD-LIF). Detection occurs rapidly, within 6 laser pulses (~7 ns each) at a range of 15 cm. Dropcasting is used to create calibrated samples covering a wide range of TNT concentrations; and...

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Noncontact optical detection of explosive particles via photodissociation followed by laser-induced fluorescence

Measurement of the absolute Raman scattering cross sections of sulfur and the standoff Raman detection of a 6-mm-thick sulfur specimen at 1500m

March 1, 2011
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Journal Article
Author:
Roshan L. Aggarwal
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Published in:
J. Raman Spectr., Vol. 42, No. 3, March 2011, pp. 461-464.
Topic:
detection systems
R&D area:
R&D group:

Summary

The absolute Raman scattering cross sections (σRS) for the 471, 217, and 153 cm−1 modes of sulfur were measured as 6.0 ± 1.2 × 10−27, 7.7 ± 1.6 × 10−27, and 1.2 ± 0.24 × 10−26 cm2 at 815, 799, and 794 nm, respectively, using a 785-nm pump laser. The corresponding values of σRS at 1120, 1089, and 1081 nm were determined to be 1.5 ± 0.3 × 10−27, 1.2 ± 0.24 × 10−27, and 1.2 ± 0.24 × 10−27 cm2 using a 1064-nm laser. A temperature-controlled, small-cavity (2.125 mm diameter) blackbody source was used to calibrate the signal output of the Raman spectrometers for these measurements. Standoff Raman detection of a 6-mm-thick sulfur specimen located at 1500 m from the pump laser and the Raman spectrometer was made using a 1.4-W, CW, 785-nm pump laser.
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Summary

The absolute Raman scattering cross sections (σRS) for the 471, 217, and 153 cm−1 modes of sulfur were measured as 6.0 ± 1.2 × 10−27, 7.7 ± 1.6 × 10−27, and 1.2 ± 0.24 × 10−26 cm2 at 815, 799, and 794 nm, respectively, using a 785-nm pump laser. The...

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Measurement of the absolute Raman scattering cross sections of sulfur and the standoff Raman detection of a 6-mm-thick sulfur specimen at 1500m
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