RECENT ADVANCES IN THE DEVELOPMENT OF A MULTIWAVELENGTH IMAGING PYROMETER

A multiwavelength imaging pyrometer (MWIP) is described that permits r eal-time remote sensing of temperature profiles of targets with unknow n emissivity by measuring the spectral radiance of a target at several distinct wavelengths using a 320 x 122-element PtSi ir CCD imager wit h an assembly of seven narrowband ir filters in the range from 1790 to 4536 nm. Based on these measurements, the temperature and model param eters of the target emissivity are determined simultaneously from the least-squares fit of the theoretical model of the ir camera output sig nal to the experimental data. The real-time least-squares minimization is accomplished by combination of Levenberg-Marquardt and simulated-a nnealing algorithms. The experimental MWIP system also includes a leas t-squares-based calibration algorithm for evaluation of effective valu es of peak filter transmissions and center wavelengths based on the de tection of radiation emitted by the precalibrated blackbody source ove r a wide range of temperatures. To achieve high radiometric accuracy, the ir CCD camera was operated with black-level and background subtrac tion and with compensation for dark-current charge as a function of th e detected signal level. To minimize the effect of the response nonlin earity on the accuracy of real-time MWIP temperature estimation, we ha ve developed an algorithm that provides for imager operation at fixed preselected signal level for each spectral channel by adaptively chang ing the duration of the optical integration time of the imager. Initia l testing demonstrated an accuracy of +/- 1.0 degrees C for real-time temperature measurements of the center of the blackbody aperture in th e range from 500 to 1000 degrees C, Temperature resolution of +/- 3 de grees C was demonstrated for the blackbody source viewed through a dou ble-side polished silicon wafer with unknown spectral transmissivity i n the temperature range from 500 to 900 degrees C. (C) 1997 Society of Photo-Optical Instrumentation Engineers.