Program SAFEGUARD:

Active FT-IR Ground-Truth Measurements 

AeroSurvey's primary expertise has always been high quality measurements of airborne chemicals using active FT-IR techniques.  We were brought into Program SAFEGUARD in 1996 to make such measurements over test plumes during SAFEGUARD experiments.  Even as our role has expanded to include other tasks within SAFEGUARD, active FT-IR measurements of test plumes have continued to be a large part of AeroSurvey's involvement.

Most of our active FT-IR monitoring of plumes for SAFEGUARD has been done during controlled release experiments.   In the SAFEGUARD controlled releases experiments, we produce test plumes with our own plume generating devices.  The plume generator is set up in a large open area and we position our active FT-IR system 50' - 100' away.  A boom lift is used to hoist a retroreflector up behind the plume just above the top of the stack, as viewed from the active FT-IR instrument.  

There is a tremendous amount of turbulence as the high velocity hot air leaves the stack and enters the relatively cooler and stiller ambient air.  In Kansas, where we conduct many of these controlled release experiments, it seems there is also a stiff breeze blowing most of the time.  All of these factors contribute to the variance in the FT-IR data.  Fortunately, we are able to collect enough spectra that the data can be statistically investigated for the information desired.  

Below, we show some active data collected using the plume generator during a 1999 field experiment.  We released ethanol at 200 degrees Celsius in various concentrations over a forty-five minute period during which the sensor suite was flown over the test stack approximately 20 times.

On multiple occasions SAFEGUARD has teamed with industrial entities, using actual process outputs from various legitimate industrial activities as test plumes.  Though the controlled releases offer greater experimental flexibility, these industrial collections offer more realistic release scenarios.  It is usually sufficient ( and a lot more convenient) in these industrial collections to produce the ground-truth FT-IR data passively but, on occasion,  we have also hoisted a retroreflector up and monitored an industrial stack with the active technique.