Mr. Christopher L. Dobbins Profile

Christopher L. Dobbins

EO/IR Engineer

SPIE Involvement:

Author

Area of Expertise:

Infrared imaging , Signature , NVTherm , UCIR , Infrared detectors , target acquistion

Publications (7)

Proceedings Article | 14 May 2018 Paper

Visualization and analysis of boundary layer transitions using infrared thermography

Caleb Waddle, Jeffrey Bolan, Christopher Dobbins, Zachary Hall, Melissa McDaniel

Proceedings Volume 10661, 106610L (2018) https://doi.org/10.1117/12.2304426

KEYWORDS: Cameras, Thermography, Infrared cameras, Infrared imaging, Visualization, Sensors, Thermal modeling, Image processing, Forward looking infrared, Passive sensors, Testing and analysis

Read Abstract +

The United States Army Aviation and Missile Research, Development and Engineering Center (AMRDEC) has utilized Infrared (IR) cameras to analyze boundary layer transition on additively-manufactured and aluminum wings in half-scale wind tunnel testing. The primary goal of the testing was to collect transition data for validation of Computational Fluid Dynamic (CFD) models with traditional oil flow visualization methods. A secondary goal was to collect transition data using IR thermographic imagery. Using non-contact IR cameras allow for more measurements to be collected in a given time. This work focuses on the IR cameras, the testing (setup, results, and lessons learned), and post analysis of the data. Brief descriptions of the test assets and the cameras are given, followed by a description and discussion of strengths and weaknesses of different methods used to accentuate the thermal signature of the transitions. Lining the wing with a selfadhesive liner can increase the contrast of the transition signature passively, but active heating with a central heating element was shown not to be as effective. General lessons learned for test setup, camera selection, and techniques to increase thermal transition signature are provided within each section. By examining several runs, general observations about the airflow transitions are made. Image processing techniques were utilized to analyze the transition. These techniques and resulting toolsets for data analysis are described. Some of the initial results were analyzed to make some comparisons between the traditional oil flow visualization methods and the thermal imaging methods. The report shows that the oil does not affect the repeatability of the thermal signature, but that the transitions determined by the oil flow analysis and the thermal image do differ slightly. Also, the oil flow is able to visualize a region known as the laminar boundary layer separation, whereas, at this time, this phenomenon is still not apparent in the thermal imagery. Further analysis is ongoing to determine if that separation can actually be seen with this specific test configuration.

Proceedings Article | 19 September 2016 Presentation + Paper

Fast cool-down coaxial pulse tube microcooler

T. Nast, J. Olson, P. Champagne, E. Roth, G. Kaldas, E. Saito, V. Loung, B. McCay, A. Kenton, C. Dobbins

Proceedings Volume 9978, 99780L (2016) https://doi.org/10.1117/12.2238285

KEYWORDS: Cryocoolers, Infrared cameras, Cameras, Head, Mid-IR, Infrared sensors, Sensors, Copper, Staring arrays, Prototyping

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Proceedings Article | 26 May 2016 Paper

Fast cooldown coaxial pulse tube microcooler

T. Nast, J. Olson, P. Champagne, E. Roth, G. Kaldas, E. Saito, V. Loung, B. McCay, A. Kenton, C. Dobbins

Proceedings Volume 9854, 98540E (2016) https://doi.org/10.1117/12.2225327

KEYWORDS: Infrared cameras, Infrared sensors, Infrared imaging, Imaging systems, Cryocoolers, Cameras, Head, Mid-IR, Sensors, Staring arrays

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Proceedings Article | 15 May 2015 Paper

Comparative performance of large-format MWIR and LWIR systems in NV-IPM

Edward Burdette, James Teague, Christopher Dobbins, Samuel Wood

Proceedings Volume 9452, 94520O (2015) https://doi.org/10.1117/12.2190158

KEYWORDS: Mid-IR, Long wavelength infrared, Sensors, NVThermIP, Atmospheric modeling, Medium wave, Fiber optic gyroscopes, Systems modeling, Infrared sensors, Infrared imaging

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Proceedings Article | 9 June 2014 Paper

Reporting NETD: why measurement techniques matter

Ryan Rogers, W. Derrik Edwards, Caleb Waddle, Christopher Dobbins, Sam Wood

Proceedings Volume 9071, 90710T (2014) https://doi.org/10.1117/12.2050559

KEYWORDS: Cameras, Imaging systems, Collimation, Black bodies, Sensors, Collimators, Long wavelength infrared, Infrared imaging, Staring arrays, Infrared sensors

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Proceedings Article | 5 June 2013 Paper

Data analysis tools for imaging infrared technology within the ImageJ environment

Ryan Rogers, W. Derrik Edwards, Caleb Waddle, Christopher Dobbins, Sam Wood

Proceedings Volume 8706, 870608 (2013) https://doi.org/10.1117/12.2016043

KEYWORDS: Modulation transfer functions, Image processing, 3D image processing, Infrared imaging, Sensors, Excel, Image quality, Signal to noise ratio, Imaging systems, Infrared sensors

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Proceedings Article | 5 June 2013 Paper

Compensation for instrument anomalies in imaging infrared measurements

Christopher Dobbins, James Dawson, Jay Lightfoot, William Edwards, Ryan Cobb, Amanda Heckwolf

Proceedings Volume 8706, 870606 (2013) https://doi.org/10.1117/12.2015473

KEYWORDS: Sensors, Thermography, Black bodies, Temperature metrology, Staring arrays, Calibration, Quantum efficiency, Infrared imaging, Nonuniformity corrections, Infrared radiation

Read Abstract +

Infrared imaging is commonly used for performing thermography based on field calibration that simply relates image levels to apparent temperature levels using field blackbodies. Under normal conditions, the correlation between the image levels and blackbody temperature is strong, allowing conversion of the raw data into units of blackbody-equivalent temperature without consideration of other factors. However, if certain instrument anomalies are present, a compensation procedure that involves more in-depth sensor characterization may be required. The procedure, which uses an analysis of temperature-dependent dark current, optical emissions, and detector response, is described along with results for a specific case. The procedure involves first cold soaking a thermal camera and then observing the cooldown behavior of the sensor under non-stressing conditions. Variations in environmental temperature levels are then used to observe cooler performance and dark current levels. A multi-variate linear regression is performed that allows temperature-dependent dark current, lens emission, lens transmission, and detector quantum efficiency to be fully characterized. The resulting data describe for each image pixel a relationship between the scene temperature and the observed values of image signal, detector temperature, and camera temperature. The procedure has been applied successfully to a thermal imager used to collect field data while suffering from instrument anomalies due to a faulty cooler. Using the resulting characterization data for the pixel-dependent dark current, image data collected with the thermal imager was compensated. The compensation involved using spatial filtering to determine temperature shifts caused by the faulty cooler based on the predictable pattern of pixel-to-pixel variations in dark current. The estimated temperature shift was used to compute a compensation offset for each pixel based on its known dark current coefficient. The compensated image data, while still degraded, was sufficiently corrected for the predictable effects of dark current variations to allow valid thermography to be performed.

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