Design of a Laser Heterodyne Radiometer (LHR) Sensor for Wildfire Detection and Characterization

Fire detection has traditionally been done optically using tools, ranging from human eyes to modern, advanced hyperspectral cameras.  Both the intensity as well as the spectral signature of the light emitting from fires are important parameters to quantify and characterize. Our laboratory is developing and constructing two sensor platforms to demonstrate a novel technology in Fire Optical Measurements (FOM) for both laboratory and simple “field-scale” demonstrations. The first system, to be described in this presentation, operates in the near-infrared region and will focus on potassium light emissions (K-FOM). Radiative emissions from hot potassium are characteristic of intense fires involving biological materials, distinguishing them from fossil fuel combustion.

The system design for K-FOM is framed by our prior experience in developing Laser Heterodyne Radiometry (LHR) sensors used in solar occultation measurements of greenhouse gases, employing a similar optical design.  In K-FOM, light from a flame containing potassium is collected onto a single-mode optical fiber. The collected radiation is mixed with light from a tunable diode laser (Eblana Photonics),  operating near 770 nm, using a 2x2 combiner. The two output fibers from the combiner arerouted to a a balanced detector (Thorlabs), and the resulting radio frequency (rf) power is measured using a Digikey power sensor.

In this presentation, the design and characterization of the K-FOM sensor will be described, along with tests using laboratory flame burners.  Simple field demonstrations are planned for calendar year 2025.