Near-infrared multispectral light-field thermography with ambient radiation correction for wide-range temperature measurement

Near-infrared multispectral light-field (NIR-MSLF) thermography was developed for wide-range temperature measurement. By integrating an optical-filter-array with a near-infrared light-field camera, the system enables single-shot acquisition of two-dimensional (2D) temperature distributions of high-temperature objects. Blackbody calibration experiments demonstrated the lower temperature threshold successfully extended to 573 K compared with that of visible multispectral light-field thermography, and errors were maintained below ±10 K over 573-1873 K. Furthermore, to address the effect of intense ambient radiation on accurate temperature calculation, a three-dimensional view-factor mapping (3D-VFM) method was proposed to quantify ambient radiation. By projecting three-dimensional geometric elements onto the pixel plane, the method derives a 2D view-factor distribution, enabling pixel-level correction of ambient radiation. The reliability of the proposed NIR-MSLF thermography and 3D-VFM method was validated through turbine blade film cooling experiments. Under various coolant flow rates, in conditions where ambient radiation may exceed the radiation from turbine blade itself, the NIR-MSLF thermography measured blade surface temperatures with deviations consistently within ±15 K when compared to the buried thermocouples.