Development of a Multi-band Plenoptic Camera for High Temperature Measurements

Abstract

In this thesis, the development of a novel multi-band plenoptic pyrometer is discussed and applied to several applications of interest in the engineering field. The multi-band plenoptic camera is a non-contact measurement technique used to determine the temperature of a surface or flame using the emitted radiation from a body, which can also be referred to as an optical pyrometer. Traditional two-dimensional (2D) pyrometers are limited by the number of wavelengths available, requiring assumptions to be made about surface emissivity. Errors in emissivity can lead to large errors in temperature measurements. The multi-band plenoptic camera is a combination of a plenoptic camera and a linearly variable wavelength filter, which can be used to instantaneously and robustly measure 2D temperatures. The present experiments evaluate the multi-band camera’s ability to determine temperatures from the captured spectral content using a pyrometric technique called spectral pyrometry. Discussion of the design concept and process are presented. Microlens, wavelength, and temperature calibration are data processing steps required for temperature calculations. Three experiments to test the camera’s efficacy in measuring temperature are discussed including a graphite plate at constant and varying temperatures, solid rocket strand burner plumes, and solidifying copper. The multi-band plenoptic camera captured temperatures within the range of thermocouple accuracy for both constant and varying graphite temperatures. The solid rocket plume measurements were of two fuels with a known temperature difference caused by aluminum (Al) particles added to one. Preliminary results showed a temperature increase of 400 C when Al was added to the fuel. Captured temperatures had a range of 800 C. Finally, the copper experiment was designed to test the ability to calculate temperatures with challenging material properties. The multi-band camera was able to distinguish between temperatures of the liquid and solid copper. Several challenges, including low emissivity, high background temperature, and boundary artifacts need to be resolved to reduce errors in temperature measurements. Future work will investigate simultaneously using spectral and angular information to obtain 3D temperatures.