The SAFEGUARD sensor suite

For many years, the Holy Grail of atmospheric researchers has been the development of a single sensor capable of simultaneously imaging and measuring chemicals in the atmosphere.  Many developmental efforts have been based on infrared detector arrays or single-detector systems coupled to a scanning device.  SAFEGUARD has taken a different route, opting to simply couple one imaging sensor and one chemical analysis sensor into a sensor suite.  The SAFEGUARD technology, then is essentially a single package comprised of two co-aligned infrared sensors.

The advantage of the SAFEGUARD approach is that it is based on commercial off-the-shelf (COTS) technology.  Imaging is performed by a linescanner, a device in use by the DOD to perform visual and infrared ground mapping for over twenty years.  Chemical analysis is handled by an FT-IR, also representing mature technology.  Although both instruments are modified for use in the SAFEGUARD package, basing the instruments on COTS technology has allowed SAFEGUARD to produce a working system capable of chemical mapping at a fraction of the cost and in a fraction of the time that it would take to develop entirely new sensor technology.

In the SAFEGUARD sensor suite, the linescanner and FT-IR are co-aligned in a downward-looking configuration and mounted in an airborne platform.  The linescanner simultaneously produces multiple images of the scene that passes below the aircraft, with each image capturing the view in a different spectral region.  Manipulation of the linescanner images from the various infrared spectral domains can produce composite images of clouds and plumes that exist between the aircraft and the ground.  The FT-IR's field of view (FOV) sweeps through the scene recorded by the linescanner and records infrared spectra of the intervening atmosphere.  The chemical composition of any clouds or plumes can be deduced with high reliability from the FT-IR spectra produced.

The data shown below were produced during a single pass of the sensor suite over a test field during an outdoor collection experiment in 1997. On the test field, a plume generator was producing a plume of air at 200 degrees Celsius into which a small amount of ethanol was being introduced. The linescanner data was used to produce the image in the top left, in which the ethanol plume has been made to appear in sharp contrast to the surrounding scene. The plot of ethanol concentration vs time in the top right was produced by AeroSurvey, using open-path FT-IR monitoring of the plume from a ground-based location on the test field. The infrared spectrum in the bottom right was produced by the airborne passive FT-IR instrument at the moment that the instrument's field-of-view passed over the plume, clearly revealing the presence of ethanol in the plume.