Sensor Systems and Technology

The Center for Sensor Systems and Technology (CSST) designs and develops innovative sensors utilizing proprietary technology for its own use and for delivery to private, academic and government customers.  CSST- developed monitors permit turn-key operation and include easy-to-use data acquisition software which allows integration of the sensor into larger systems.

Recent customers include: the German Aerospace Center (DLR), University of Massachusetts, Massachusetts Institute of Technology, FZ Julich, Pacific Northwest National Laboratory, University of Washington, the Department of Energy, the National Institutes of Health and NASA Ames and Glenn Research Centers.

Commercialization Opportunities

Aerodyne Research has developed a number of successful partnerships with private industry with the goal of producing commercially available instrumentation and sensor systems. Generally involving Aerodyne-proprietary technology, these partnerships typically entail close technical and business working relationships. Prospective partners and collaborators should contact Dr. Freedman, CSST Director or Dr. Charles E. Kolb, President of Aerodyne Research, Inc.

Sensor System Examples

CAPS Nitrogen Dioxide (NO2) Monitor

CSST has developed, built and marketed a state-of-the-art monitor for the detection of ambient levels of nitrogen dioxide, a criteria pollutant. The monitor employs cavity attenuated phase shift (CAPS) techniques to measure the presence of nitrogen dioxide using absorption at 450 nm.  The rack-mounted instrument is capable of detecting 0.1 ppb levels of NO2 with 10 s sampling and requires less than 1 liter per minute of sample flow.  A fast reponse version (1 s) with lower sensitivity (1 ppb) is also available.

CAPS PMex Particle Extinction Monitor

Similar in nature to the CAPS NO2 monitor, the CAPS PMex monitor measures optical extinction (the sum of scattering and absorption) caused by the presence of particles in the environment.  The rack-mounted instrument operates at one of five prechosen wavelengths - near infrared [760 nm], far red [660 nm], red [630 nm], green [530 nm] or blue [450 nm] - with completely autonomous operation, requiring no expendables.  The instrument has a time response of ~ 1 s with a detection limit (3σ) of 2.5 Mm-1; with1 s sampling, the detection level improves to <0.3 Mm-1 at 1 minute sampling.  This monitor is also available for purchase.

CAPS PMssa Particle Single Scattering Albedo Monitor

The CAPS particle single scattering albedo monitor, PMssa, provides separate measurements of both particle-induced light extinction and scattering within the same sample volume, enabling accurate and precise measurement of the single scattering albedo for particles with mobility diameters less than 2 microns.  In order to enable this, it incorporates an integrating nephelometer within the extinction measurement cell.  The response in both channels is highly linear from 0-1000 Mm-1; the noise level in both channels is < 1 Mm-1 with 1 s integration time.  The scattering channel is calibrated versus the extinction using purely scattering particles (i.e., single scattering albedo of 1.0).

Environmental Monitor for Historical Documents

CSST developed, built and delivered a non-intrusive, optical monitor capable of both monitoring the level of humidity and and detecting air leaks by measuring trace amounts of oxygen within the argon-filled, hermetically sealed enclosures which house the nation's Charters of Freedom (Declaration of Independence, Constitution and Bill of Rights). Coupled to the encasements using optical fibers, the sensor system utilizes proprietary spectroscopic sensor technology developed by Aerodyne for the measurement of both water vapor and oxygen. It is currently being used by National Archives and Records Administration personnel to ascertain the environmental integrity of the newly-dedicated encasements.

Fast Response Airborne Humidity Sensor

The high speed (5 Hz frequency response), autonomously-operated, humidity sensor is designed to provide highly accurate atmospheric water vapor (humidity) measurements on board research aircraft. Deployed on board a Twin Otter aircraft operated by the Navy's Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) located at the Naval Postgraduate School, this sensor has successfully provided accurate water vapor measurements in both clear air and within cloud boundaries without any hysteresis. It has been shown to provide far more accurate humidity profiles than competing technologies.

Plant Health Monitor

CSST has developed two versions of a plant health monitor which is sensitive to the photosynthetic activity of green plants and thus to their "health". One system relies on the passive detection of sunlight-induced chlorophyll fluorescence, utilizing a patented technology which allows the sensor to operate in the presence of ambient sunlight which would otherwise provide an insurmountable interference.   A second system incorporates its own light source in order to induce the chlorophyll fluorescence.

Insulated Glass (IG) Window Seal Integrity Sensor

Argon-filled insulated glass (IG) windows are currently filled and shipped without testing for window seal integrity. CSST personnel, using patented technology for the detection of gaseous oxygen, built and demonstrated a non-intrusive, non-contact sensor system to detect the unwanted inflow of air into the window unit. This sensor system was designed with input from the IG window manufacturing industry to ensure compatibility with its testing procedures.


Dr. Andrew Freedman
Andrew Freedman
Ph.D., Physical Chemistry, University of California, Berkeley

Dr. Freedman serves as Director of the Center for Sensor Systems and Technology. His work has focused on a broad range of studies which encompass interfacial phenomena relevant to environmental chemistry, semiconductor processing, and biothreat detection. He has also been responsible for developing many of the technologies discussed above, including the CAPS-based monitors, trace oxygen and humidity sensing systems, plant health monitor and IG window seal integrity monitor.

Joda C. Wormhoudt
Ph.D, Physical Chemistry, Massachusetts Institute of Technology

Dr. Wormhoudt's work has focused on the use of spectroscopically-based diagnostics to determine species concentrations in applications as diverse as the monitoring of combustion flows, semiconductor processing environments and space-based life support systems. Dr. Wormhoudt has utilized spectroscopic techniques to quantify the concentrations of pollutants from aircraft engines, automobiles and refinery flares, to study techniques for sampling explosives from surfaces and soil, and to characterize propellant strand burning using embedded optical fibers. Other recent work includes a program of literature reviews and laboratory measurements in support of an explosives vapor pressure database, performance calculations in support of advanced laser techniques for explosive detection, and the development of software for automated data acquisition and analysis of Raman spectra for gas temperatures.

Paul Kebabian
Ph.D., Electrical Engineering, Massachusetts Institute of Technology

Dr. Kebabian has pioneered the development of novel systems for measuring methane, carbon monoxide and nitrous oxide using novel rare gas discharge lasers. His optical engineering expertise has lead to innovative sensors for chlorophyll fluorescence, nitrogen dioxide, molecular oxygen and water vapor. He holds manl ARI patents encompass the technologies for the CAPS –based monitors, Astigmatic Multipass Absorption Cell, Water Vapor and Oxygen Monitors, Plant Fluorescence Sensor, and Hyperspectral Polarimeter.

Dr. Paola Massoli, Center for Aerosol and Cloud Chemistry
Paola Massoli
Ph.D., Environmental Sciences, Institute for Atmospheric Sciences and Climate (ISAC), Rome, Italy

Dr. Massoli’s research expertise and interests are in the areas of chemical and optical property characterization of tropospheric aerosols and their impact on air quality and climate change. Her research activities have focused on the microphysics of polar stratospheric clouds (PSCs) via custom-built LiDAR (LIght Detection And Ranging) systems, characterizing optical properties of troposphere aerosols via custom-built cavity ring down-based aerosol optical extinction monitors, nephelometers and photo acoustic-based absorption monitors.

Affiliated Personnel

  • Steve Jones, Aerodyne Research, Inc.
  • Timothy Onasch, Aerodyne Research, Inc.


Single Scattering Albedo Monitor for Airborne Particulates, T. B. Onasch, P. Massoli, P. L. Kebabian, F. B. Hills, F. W. Bacon, A. Freedman, Aerosol Sci. Technol., 49, 267-279, 2015.

Intercomparison of a Cavity Attenuated Phase Shift-based extinction monitor (CAPS PMex) with an integrating nephelometer and a filter-based absorption monitor, A. Petzold, T. Onasch, P. Kebabian, A. Freedman, Atmos. Meas. Tech., 6, 1141-1151, 2013.

Doppler spectrum-based polar nephelometer, P. L. Kebabian, T. B. Onasch, J. C. Wormhoudt, A. Freedman, Opt. Lett., 37, 3654-3656, 2012.

Direct Measurement of Aircraft Engine Soot Emissions Using a Cavity-Attenuated Phase Shift (CAPS)-Based Extinction Monitor, Z.. Yu, L. D. Ziemba, T. B. Onasch, S. C. Herndon, S. E. Albo, R. Miake-Lye, B. E. Anderson, P. L. Kebabian, A. Freedman, Aerosol Sci. Tech., 45, 1319-1325, 2011.

Knudsen Effusion Measurement of Organic Peroxide Vapor Pressures, P. L. Damour, A. Freedman, J. Wormhoudt, Propellants, Explosives, Pyrotechnics, n/a. doi: 10.1002/prep.200900083.

Aerosol light extinction measurements by cavity attenuated phase shift (CAPS) spectroscopy: Laboratory validation and field deployment of a compact aerosol particle extinction monitor, P. Massoli, P. L. Kebabian, T. B. Onasch, F. B. Hills, A. Freedman, Aerosol Sci. Tech. 44, 428-435, 2010.

A practical alternative to chemiluminescence-based detection of nitrogen dioxide: cavity attenuated phase shift spectroscopy, P. L. Kebabian, E. C. Wood, S. C. Herndon, A. Freedman, Environ. Sci. Technol., 42, 6040-6045, 2008.

Apparatus for determination of vapor pressures at ambient temperatures employing a Knudsen effusion cell and quartz crystal microbalance, A. Freedman, P. L. Kebabian, Z. Li, W. A. Robinson, J. C. Wormhoudt, Meas. Sci. Technol., 19, 125102 (8 p.), 2008.

Focusing particles with diameters of 1 to 10 microns into beams at atmospheric pressure, R. Deng, X. Zhang,  K. A. Smith, J. Wormhoudt, D. K. Lewis, A. Freedman, Aerosol Sci. Tech., 42, 899-915, 2008. DOI: 10.1080/02786820802360674

Optical extinction monitor using cw cavity enhanced detection, P.L. Kebabian, W.A. Robinson, and A. Freedman, Rev. Sci. Instru. 78, 063102, 2007.

Fluoropolymer-based capacitive carbon dioxide sensor, P.L. Kebabian, A. Freedman, Meas. Sci. Technol., 17:703-710, (2006).

Determination of carbon in steel by laser-induced breakdown spectroscopy using a microchip laser and miniature spectrometer, J. Wormhoudt, F.J. Iannarilli, S. Jones, K.D. Annen, A. Freedman, Appl. Spectrosc. 59, 1098-1102, (2005).

Aluminum alloy analysis using microchip-laser induced breakdown spectroscopy, A. Freedman, F.J. Iannarilli Jr., J.C. Wormhoudt, Spectrochim. Acta B 60, 1076-1082 (2005).

Detection of Nitrogen Dioxide by Cavity Attenuated Phase Shift Spectroscopy, P.L. Kebabian, S.C. Herndon, A. Freedman, Anal. Chem. 77, 724-728 (2005)

Measurement of Trace Water Vapor in a Carbon Dioxide Removal Assembly Product Stream, J. Wormhoudt, J.H. Shorter, J.B. McManus, D.D. Nelson, M.S. Zahniser, A. Freedman, International Conference on Environmental Systems (ICES) July 19-22, 2004, Colorado Springs, CO,  Paper No. 2004-01-2444.

Use of a Prototype Instrument to Detect Short-Term Changes in Solar-Excited Leaf Fluorescence, G.A. Carter, A. Freedman, P.L. Kebabian, H.E. Scott,  Int. J. Remote Sensing, 25,1779-1784 (2004)

Determination of Argon-Filled Insulated Glass Window Seal Failure by Spectroscopic Detection of Oxygen, P.L. Kebabian, R.R. Romano and A. Freedman, Meas. Sci. Technol. 14, 983–988  (2003)

Analysis of Humidity Halos Around Trade Wind Cumulus Clouds, M.L. Lu, J. Wang, A. Freedman, H. H. Jonsson, R. C. Flagan, R. A. McClatchey, and J. H. Seinfeld, J. Atmos. Sciences 60, 1041-1059 (2003)

Remote Sensing of Solar-Illuminated Plant Fluorescence as a Measure Of Photosynthesis Rate, A.Freedman, J. Cavender-Bares, P.L. Kebabian, R. Bhaskar, H. Scott, and F.A. Bazzaz, Photosynthetica, 40, 127-132 (2002).

Spectroscopic Water Vapor Sensor For Rapid Response Measurements of Humidity In The Troposphere, P.L. Kebabian, C.E. Kolb, and A. Freedman, J. Geophys. Res., 107, 4670, doi:10.1029/2001JD002003 (2002).

Fluorescence sensor watches over plants, R. Gaughan, Biophotonics Technology Solutions, January/February, 18 (2001).

A Novel Gas Correlation Sensor for the Detection of Nitrogen Dioxide, P.L. Kebabian, K. Annen, T. Berkoff, and A. Freedman, Meas. Sci. Technol. 11, 499-503 (2000)

Spectroscopic Humidity Sensor for the Space Station, P.L. Kebabian and A. Freedman, SAE Technical Paper Series, 2000-01-2306, 30th International Conference on Environmental Systems (ICES), Toulouse, France, July 2000

Polarimetric Spectral Intensity Modulation (P-SIM): Enabling simultaneous hyperspectral and polarimetric imaging, F.J. Iannarilli, S.H. Jones, H.E. Scott, and P. Kebabian, Proc. SPIE 3698 (1999).

A Passive Two-Band Sensor of Sunlight-Excited Plant Fluorescence, P. Kebabian, A. Theisen, S. Kallelis, and A. Freedman, Rev. Sci. Instrumen. 70, 4386-4393 (1999) Copyright 1999 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. Article available from AIP.

Passive Two-Band Plant Fluorescence Sensor With Applications In Precision Agriculture, P.L. Kebabian, A.F. Theisen, S. Kallelis, H.E. Scott, and A. Freedman, SPIE Proc. 3542,  238 (1999)

Water Vapor Sensing Using Polarization Selection of a Zeeman-Split Argon Discharge Lamp Emission Line, P.L. Kebabian, T.A. Berkoff, and A. Freedman, J. Meas. Sci. Technol., 9, 1793 (1998)

Explosives Detection: A Challenge for Physical Chemistry, J.I. Steinfeld and J. Wormhoudt, Annu. Rev. Phys. Chem. 49, 203-232 (1998).

Embedded Infrared Fiber Optic Absorption Studies of Nitramine Propellant Strand Burning, J. Wormhoudt, P.L. Kebabian, and C.E. Kolb, Combustion and Flame, 111, 73 (1997).

Tunable Infrared Laser Detection of Pyrolysis Products of Explosives in Soils, J. Wormhoudt, et al., Applied Optics, 35, 3992 (1996).