Multi-Spectral Imaging Pyrometer

Langley Research Center, Hampton, VA

Representation of the algorithm used to create a high dynamic range infrared (HDRi) image. (Image: NASA)

Innovators at NASA Langley Research Center have developed a multi-spectral imaging pyrometer utilizing tunable optics. The system uses a conventional infrared imaging camera as the basis and then incorporates an ultrafast, all solid-state, tunable optical filter combined with unique data processing algorithms to function as a multi-color ratio pyrometer but with true imaging capabilities.

Currently, there is no way to provide automatic, independent, emissivity-based temperature corrections at the pixel level for infrared cameras that operate with broadband detectors. Multiwavelength pyrometric systems can make emissivity-corrected temperature measurements but are not imaging devices and lack the ability to view surface gradients and other subtle variations. Optical systems that measure at several discrete wavelengths require the use of multiple optical filters and are slow, bulky, and require high power.

This NASA technology transforms a conventional infrared (IR) imaging system into a multi-wavelength imaging pyrometer using a tunable optical filter. The actively tunable optical filter is based on an exotic phase-change material (PCM), which exhibits a large reversible refractive index shift through an applied energetic stimulus. This change is non-volatile, and no additional energy is required to maintain its state once set.

The filter is placed between the scene and the imaging sensor and switched between user-selected center-wavelengths to create a series of single-wavelength, monochromatic, two-dimensional images. At the pixel level, the intensity values of these monochromatic images represent the wavelength-dependent, black-body energy emitted by the object due to its temperature. Ratioing the measured spectral irradiance for each wavelength yields emissivity-independent temperature data at each pixel.

The filters Center Wavelength (CWL) and Full Width Half Maximum (FWHM), which are related to the quality factor (Q) of the filter, are actively tunable on the order of nanoseconds-microseconds (GHzMHz). This behavior is electronically controlled and can be operated time-sequentially (on a nanosecond time scale) in the control electronics, a capability not possible with conventional optical filtering technologies.

The technology has applications in aerospace: imaging and analysis of rocket plumes, combusting flows, and heat shields; metals manufacturing: process monitoring the melting of metallic ores in mixed states or the formation of surface slag; welding: accurate imaging of weld pool temperatures; and kiln processing: process monitoring in cement kilns.

NASA is actively seeking licensees to commercialize this technology. Please contact Licensing Concierge at This email address is being protected from spambots. You need JavaScript enabled to view it. or call at 202-358-7432 to initiate licensing discussions. For more information, visit here .