Nathaniel J. McCaffrey

Multi-wavelength imaging pyrometer

Multi-wavelength imaging pyrometer (M-WIP) is presented for remote sensing of temperature profiles of targets with unknown emissivity. Fast algorithm and software package were developed for calibration and real-time M-WIP measurements. Experimental 7- filter line-sensing M-WIP system was implemented with 320 X 122-element PtSi IR-CCD imager. The M-WIP system was calibrated against a commercial blackbody source over temperature range from 450 degree(s)C to 900 degree(s)C. Signal processing included background subtraction and compensation for variation of dark current with detected signal and signal off-set sue to apparent BCCD trapping effect. Initial M-WIP measurement demonstrated temperature resolution (Delta) T of +/- 1 degree(s)C for blackbody target over temperature range from 600 degree(s)C to 900 degree(s)C.

Recent advances in the development of a multiwavelength imaging pyrometer

A multiwavelength imaging pyrometer (MWIP) is described that permits real-time remote sensing of temperature profiles of targets with unknown emissivity by measuring the spectral radiance of a target at several distinct wavelengths using a 3203122-element PtSi ir CCD imager with an assembly of seven narrowband ir filters in the range from 1790 to 4536 nm. Based on these measurements, the temperature and model parameters of the target emissivity are determined simultaneously from the least-squares fit of the theoretical model of the ir camera output signal to the experimental data. The real-time least-squares minimization is accomplished by combination of Levenberg-Marquardt and simulatedannealing algorithms. The experimental MWIP system also includes a least-squares-based calibration algorithm for evaluation of effective values of peak filter transmissions and center wavelengths based on the detection of radiation emitted by the precalibrated blackbody source over a wide range of temperatures. To achieve high radiometric accuracy, the ir CCD camera was operated with black-level and background subtraction and with compensation for dark-current charge as a function of the detected signal level. To minimize the effect of the response nonlinearity on the accuracy of real-time MWIP temperature estimation, we have developed an algorithm that provides for imager operation at fixed preselected signal level for each spectral channel by adaptively changing the duration of the optical integration time of the imager. Initial testing demonstrated an accuracy of ± 1.0°C for real-time temperature measurements of the center of the blackbody aperture in the range from 500 to 1000°C. Temperature resolution of ± 3°C was demonstrated for the blackbody source viewed through a double-side polished silicon wafer with unknown spectral transmissivity in the temperature range from 500 to 900°C.

Development of emissivity models and induced transmission filters for multiwavelength imaging pyrometry

The results of our work on the development of emissivity models and IR filters for applications in multi-wavelength imaging pyrometry are presented. Techniques such as Fourier transform IR spectroscopy have been deployed to determine the emissivity of Si and SiO2/Si in the temperature range of 331 to 1235 K. These measurements have been obtained for n-Si, p-Si and SiO2/Si in the oxide thickness range of 60 to 500 nm. These results coupled with calculations of emissivity from first principles lead us to model the wavelength dependence of emissivity. Preliminary measurements of emissivity of HgCdTe are reported.

High-frame-rate infrared and visible cameras for test range instrumentation

Field deployable, high frame rate camera systems have been developed to support the test and evaluation activities at the White Sands Missile Range. The infrared cameras employ a 640 by 480 format PtSi focal plane array (FPA). The visible cameras employ a 1024 by 1024 format backside illuminated CCD. The monolithic, MOS architecture of the PtSi FPA supports commandable frame rate, frame size, and integration time. The infrared cameras provide 3 - 5 micron thermal imaging in selectable modes from 30 Hz frame rate, 640 by 480 frame size, 33 ms integration time to 300 Hz frame rate, 133 by 142 frame size, 1 ms integration time. The infrared cameras employ a 500 mm, f/1.7 lens. Video outputs are 12-bit digital video and RS170 analog video with histogram-based contrast enhancement. The 1024 by 1024 format CCD has a 32-port, split-frame transfer architecture. The visible cameras exploit this architecture to provide selectable modes from 30 Hz frame rate, 1024 by 1024 frame size, 32 ms integration time to 300 Hz frame rate, 1024 by 1024 frame size (with 2:1 vertical binning), 0.5 ms integration time. The visible cameras employ a 500 mm, f/4 lens, with integration time controlled by an electro-optical shutter. Video outputs are RS170 analog video (512 by 480 pixels), and 12-bit digital video.

Radiometric performance of 640x480 and 320x244 PtSi IR cameras

Camera designs and radiometric performance evaluation results are presented for two PtSi IR imagers fabricated by the David Sarnoff Research Center. Measurements on the 640 X 480 IR-MOS imaging radiometer with 25 to 150 degree(s)C background temperatures indicated response non-linearity less than +/- 0.3% over 80% of the full signal range. By operation with variable integration time from 240 microsecond(s) ec to 33 msec a scanned image with a NE(Delta) T of less than 0.1 degree(s)C can be maintained over the full temperature range. The 320 X 122 IR-CCD imaging radiometer was designed for operation with integration times ranging from 0.12 to 133 msec to provide for 12 snapshot image settings. The signals from various integration times were effectively matched and scaled to increase the effective maximum measured signal from 1 X 106 to 50 X 106 electrons/pixel. Correction procedures were developed for achieving radiometric accuracy for achieving radiometric accuracy for operation of the imagers over multiple integration times and taking into account the effects of non- linear response of dark current and charge trapping in the readout BCCD registers. The camera stability was shown to be limited by the stability of the calibration source over a three- hour period.

1024 X 1024 pixel high-frame-rate digital CCD cameras

Field deployable, high frame rate visible CCD camera systems have been developed to support the Test and Evaluation activities at the White Sands Missile Range. These visible cameras are designed around a Sarnoff 1024 X 1024 pixel, backside illuminated CCD with a 32-port, split-frame transfer architecture. The cameras exploit this architecture to provide selectable modes from a 30 Hz frame rate at 1024 X 1024 pixels to a 300 Hz frame rate with 1024 X 512 pixels (2:1 vertical binning). The cameras are configured with a 500 mm, f/4 lens, and a Ferro-electric liquid crystal electro-optic shutter, to provide variable integration times from 0.5 to 32 msec. Video outputs provided are RS170 analog video in a reduced 512 X 480 pixel format, and 12-bit full resolution digital video data stream provided through a high speed serial/parallel digital coaxial interface. At a frame rate of 300 frames per second, these cameras deliver video data at an average rate of 1.9 Gbits/sec, and a burst rate of 2.8 Gbits/sec, with the capability of reaching an average 12 bit digital data rate of 3.8 Gbits/sec when higher frame rate imagers become available.

Progress on the development of multiwavelength imaging pyrometer

Experimental Multi-wavelength Imaging Pyrometer (M-WIP) is presented for remote sensing of temperature profiles of targets with unknown spectrally varying emissivity. A software package was developed for calibration and real-time M-WIP measurements. An experimental 7-filter line-sensing M- WIP system was implemented with a 320 X 122-element PtSi IR-CCD imager and an assembly of narrow-band striped IR filters in the spectral range from 1797 nm through 4512 nm. The M-WIP system was calibrated against a commercial blackbody source over temperature range from 450 degree(s)C to 950 degree(s)C. The signal processing included background subtraction, compensation for variation of dark current with detected signal and correction for non-linearities of IR imager response. Initial M-WIP measurements demonstrated real-time temperature resolution (Delta) T of +/- 1 degree(s)C for blackbody target over temperature range from 600 degree(s)C to 900 degree(s)C. Temperature resolution of +/- 4 degree(s)C was demonstrated for the blackbody source viewed through the double polished silicon wafer with unknown spectral transmissivity in the temperature range from 500 degree(s)C to 950 degree(s)C.