NASA Langley Research Center, Hampton, Virginia
The National Aeronautics and Space Administration, other government agencies, and private industry have requirements to map and analyze 3-dimensional surfaces of varying regularity and material composition. The 3-D inspection system fuses intensity and depth information to provide a topographic description of such surfaces .
Depth measurement is provided by a scanning Coherent Laser Radar (CLR) developed under the Small Business Innovative Research program. The CLR computes distance based on the Frequency Modulated Continuous Wave (FMCW) radar technique using a semiconductor laser operating in a single longitudinal mode as the energy source. The laser is frequency modulated by thermally tuning its wavelength via the injection current. This signal is divided and used both as a local oscillator and the transmitted signal. The local oscillator and reflected energies mix coherently to generate a radio frequency (RF) signal whose frequency is proportional to the range. The measurement rate for sub millimeter accuracy is 10 range measurements per second. This is often an unacceptably slow rate for inspection tasks. To increase the effective measurement rate, intensity-based image analysis is used to identify and locate areas of interest, and subsequently direct the CLR to map only those areas.
The intensity-based analysis is accomplished using a modified Golden Template technique where the pre-event image of a surface serves as a template against which a post-event image of the surface is compared. Candidate anomalies are selected as a result of the comparison and processed to identify true anomalies using gray level image correlation techniques. The range and intensity images are coordinated by defining all image entities with respect to a task space independent of the CLR and camera image frames.
The system has been successfully demonstrated for several applications. For Shuttle tile inspection it measured the gap and height differential between adjacent tiles with an accuracy of 0.075 millimeters (3 sigma), determined the existence or nonexistence of gap fillers and identified them as to type, and detected gouge defects and measured their area, volume, and depth. For bridge inspection it measured the deflection profile of a bridge girder with sub millimeter accuracy. Its ability to map hazardous waste sites was demonstrated to the Department of Energy.
The CLR was developed by Coleman Research Center for NASA's Langley Research Center. The Intensity based analysis and image coordination was developed by Eric G. Cooper and Sixto L. Vazquez of Langley Research Center.
Point of Contact:
Eric G. Cooper,
Mail Stop 152D
1 South Wright Street
NASA Langley Research Center
Hampton, VA 23681-0001
804-864-6674
e.g.cooper@larc.nasa.gov
Sixto L. Vazquez
Mail Stop 152D
1 South Wright Street
NASA Langley Research Center
Hampton, VA 23681-0001
804-864-6684
s.l.vazquez@larc.nasa.gov
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