Multi-Spectral Imaging Pyrometer

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, blackbody 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 filter’s 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 (GHz-MHz). 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. 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.