When a bright light source is viewed through Night Vision Goggles (NVG), the image of the source can appear enveloped in a “halo” that is much larger than the “weak-signal” point spread function of the NVG. The halo phenomenon was investigated in order to produce an accurate model of NVG performance for use in psychophysical experiments. Halos were created and measured under controlled laboratory conditions using representative Generation III NVGs. To quantitatively measure halo characteristics, the NVG eyepiece was replaced by a CMOS imager. Halo size and intensity were determined from camera images as functions of point-source intensity and ambient scene illumination. Halo images were captured over a wide range of source radiances (7 orders of magnitude) and then processed with standard analysis tools to yield spot characteristics. The spot characteristics were analyzed to verify our proposed parametric model of NVG halo event formation. The model considered the potential effects of many subsystems of the NVG in the generation of halo: objective lens, photocathode, image intensifier, fluorescent screen and image guide. A description of the halo effects and the model parameters are contained in this work, along with a qualitative rationale for some of the parameter choices.
An optical beam combined with an array detector in a suitable geometrical arrangement is well-known to provide a range measurement based on the image position. Such a 'triangulation' rangefinder can measure range with short-term repeatability below the 10-5 level, with the aid of spatial and temporal image processing. This level of precision is achieved by a centroid measurement precision of ±0.02 pixel. In order to quantify its precision, accuracy and linearity, a prototype triangulation rangefinder was constructed and evaluated in the laboratory using a CMOS imager and a collimated optical source. Various instrument, target and environmental conditions were used. The range-determination performance of the prototype instrument is described, based on laboratory measurements and augmented by a comprehensive parametric model. Temperature drift was the dominant source of systematic error. The temperature and vibration environments and target orientation and motion were controlled to allow their contributions to be independently assessed. Laser, detector and other effects were determined both experimentally and through modeling. Implementation concepts are presented for a custom CMOS imager that can enhance the performance of the rangefinder, especially with regards to update rate.