Camera motion is a potential problem when a video camera is used to perform dynamic displacement measurements. If
the scene camera moves at the wrong time, the apparent motion of the object under study can easily be confused with
the real motion of the object. In some cases, it is practically impossible to prevent camera motion, as for instance, when
a camera is used outdoors in windy conditions. A method to address this challenge is described that provides an
objective means to measure the displacement of an object of interest in the scene, even when the camera itself is moving
in an unpredictable fashion at the same time. The main idea is to synchronously measure the motion of the camera and
to use those data ex post facto to subtract out the apparent motion in the scene that is caused by the camera motion. The
motion of the scene camera is measured by using a reference camera that is rigidly attached to the scene camera and
oriented towards a stationary reference object. For instance, this reference object may be on the ground, which is
known to be stationary. It is necessary to calibrate the reference camera by simultaneously measuring the scene images
and the reference images at times when it is known that the scene object is stationary and the camera is moving. These
data are used to map camera movement data to apparent scene movement data in pixel space and subsequently used to
remove the camera movement from the scene measurements.
There are numerous ways to use video cameras to measure 3D dynamic spatial displacements. When the scene
geometry is unknown and the motion is unconstrained, two calibrated cameras are required. The data from both scenes
are combined to perform the measurements using well known stereoscopic techniques. There are occasions where the
measurement system can be simplified considerably while still providing a calibrated spatial measurement of a complex
dynamic scene. For instance, if the sizes of objects in the scene are known a priori, these data may be used to provide
scene specific spatial metrics to compute calibration coefficients. With this information, it is not necessary to calibrate
the camera before use, nor is it necessary to precisely know the geometry between the camera and the scene. Field-ofview
coverage and sufficient spatial and temporal resolution are the main camera requirements. Further simplification
may be made if the 3D displacements of interest are small or constrained enough to allow for an accurate 2D projection
of the spatial variables of interest. With proper camera orientation and scene marking, the apparent pixel movements
can be expressed as a linear combination of the underlying spatial variables of interest. In many cases, a single camera
may be used to perform complex 3D dynamic scene measurements. This paper will explain and illustrate a technique
for using a single uncalibrated video camera to measure the 3D displacement of the end of a constrained rigid body
subject to a perturbation.
Triboluminescent phosphors provide a method for converting kinetic signals to optical signals for particle detection. Several methods, including vapor deposition, electron beam, and spray-on were evaluated for depositing a thin translucent coating of ZnS:Mn phosphor material onto transparent substrates. The objective was to be able to optically detect impact events on the back side of the substrate while still retaining some capacity to view distant optical events. During the experiments, optical detectors within a light-tight test chamber were used to measure the optical signals generated by the coatings. The measurements resulted from optical signals that were generated by particle impacts and sample phosphorescence, along with electrical interferences between the particle sources, the ambient background, and the detectors. Signal levels and translucency measurements from various coatings are described, along with lessons learned about the coating processes, the detectors, and the limitations of the measurements.
Fiber optic sensors offer many advantages over electrical sensors for use in harsh environments. One advantage over
distributed electrical sensors is the elimination of the need to route electrical power and wiring to the sensors, which, in
general, improves safety and reduces power consumption. Another advantage is that the optical sensors are immune to
electromagnetic interference that may be caused by radio frequency signals used for communications. Another benefit
of using an optical approach for impact detectors is the implicit immunity from false detections that may otherwise be
caused by unrelated mechanical shock or vibration events. Previous studies have documented the characteristics of the
Optical Debris Impact Sensor (ODIS). With the ODIS, the impacts are inferred by detecting the brief triboluminescent
optical pulses generated by the abrupt charge separation within a phosphor that is caused by the particle impacts. The
main limitations of the ODIS are the small detection area and the limited sensitivity. This paper describes a method for
extending the ODIS to accomplish broad area detection on a surface with potentially higher sensitivity. The sensing
element is comprised of a stack of planar optical waveguides with phosphor-coated strips. The geometry of the design
ensures optical pulses are automatically captured by the waveguides and routed to a fiber optic cable that transports the
signal to a remote high-speed photodetector. Background light levels in the vicinity of the detector are filtered out by
the tailored frequency response of the photodetector.
Fiber optic imaging systems are used in many applications, including medical imaging, machinery diagnostics, and
remote sensing. Most commonly, coherent bundles of optical fibers are used that maintain the spatial positioning of
each fiber throughout the length of the bundle, resulting in a recognizable proximal (camera side) image that is almost
identical to the distal image projected into the bundle by the lens. Although coherent fiber bundles provide excellent
solutions for many imaging applications, their limited flexibility and thermal stress intolerance may prohibit them from
being used in harsh or complex environments. The flexibility and thermal tolerance of a fiber imaging system can be
significantly improved by using an incoherent bundle of fibers wherein the spatial positioning of each fiber is not
preserved throughout the length of the bundle. Incoherent bundles need to be calibrated to provide the means to
reconstruct distal imagery. In reported calibration schemes, the calibration time is strongly dependent on the ratio
between the bundle size and the fiber size. The calibration time can thus become prohibitive for highly resolved images
using many fibers. A novel calibration scheme is described for incoherent bundles where the calibration time is
proportional to the bundle-to-fiber size ratio, resulting in significantly reduced processing time and enabling more
highly resolved images. As an added benefit for medical and remote sensing applications, incoherent light guides
scramble the scene images, which may provide a desirable level of data privacy.
Cameras provide excellent in situ coverage of many events of interest in current state-of-the-art aerospace systems.
From departing earth footage to booster separation events, cameras provide the eyes in the skies for real-time situational
awareness on the ground. One of the principal challenges of using cameras on high-speed aerospace vehicles is
designing the necessary environmental protection systems to isolate the cameras from the harsh aerothermal
environment. An established approach uses an external fairing or aeropod to provide the requisite isolation. The
camera is located within the aeropod, and the image data are sent electrically from the aeropod to the telemetry system.
While this approach has been successfully demonstrated on numerous platforms, there are advantages to moving the
camera into the interior of the vehicle and reducing the size of the imaging hardware within the aeropod. If the size of
the pod hardware can be reduced, multiple imaging sensors can be fit within the same aeropod. Alternatively, a smaller
sensor can allow for a reduced aeropod size with commensurate reduced drag and aerothermal heating. A prototype
fiber optic imaging system was developed for aerospace applications by combining a modified medical endoscope with
a ruggedized camera. With this new configuration, a significantly smaller aeropod can be used to protect only the distal
tip of the endoscope in lieu of the entire camera assembly. The data are acquired through a small lens at the distal tip
and transmitted optically through a coherent imaging fiber bundle to a camera located within the vehicle. Data from
the prototype fiber optic imaging system are compared with data acquired by a standard ruggedized camera. Results of
these tests are reported in this paper.
Emerging dual-camera dual-band (DCDB) infrared camera systems are playing an increasing role in temperature
estimation and range measurement. This paper discusses the optimal design of a DCDB imaging system that makes use
of contemporary filter fabrication technologies and improving detector performance. A two-color stereographic system
allows for the temperatures of the objects to be measured without assuming a priori knowledge of emissivities, as well as
providing a basis for estimating the distances to the objects. Multiple system design approaches are compared and key
elements of the design trade space are described, including the selection of camera separation distance and specific
infrared passbands. Analytical support for the methodology is provided by analyzing data from simulated infrared
scenes. Finally, data from a laboratory-based DCDB system are analyzed and compared with model predictions.
KEYWORDS: Radiometry, Sensors, Radio optics, Solids, Signal detection, Data modeling, Electromagnetism, Optical spheres, 3D scanning, Temperature metrology
Most radiometers are directionally sensitive. Measuring optical radiation in a given environment is typically done using
a collection aperture pointing in the direction of the optical source. The collection aperture has a limited field of view,
and the collection efficiency decreases as the angle from direct line of sight increases. Thus, radiometers typically have
a limited solid angle for viewing sources. This paper describes a model of an omnidirectional, multi-channel, rotating
radiometer that provides a framework for acquiring spatially comprehensive radiometric data from an environment. By
exploiting the spatial diversity of multiple collection apertures in multiple directions, sources from all directions are
measured via three-dimensional scanning. As the radiometer rotates, data are collected that denote the radiant flux seen
by each collection aperture as a function of time. These waveforms are used to determine the directions and magnitudes
of electromagnetic sources in the environment without requiring a priori knowledge about the directions of specific
sources.
KEYWORDS: Particles, Sensors, Signal detection, Fiber optics sensors, Data acquisition, Optical sensors, Waveguides, Active optics, Optical spheres, Signal attenuation
Common sub-millimeter particle impact phenomena range from zero to thousands of joules of impact energy. The
physics of impacts are associated with a wide variety of physical phenomena, including the generation of heat, light, and
sound. Although higher energy impact events may result in vaporization of the impacted material and other easily
detectable effects, lower energy level impacts of interest may occur with little obvious physical effect. Preliminary
research with capacitative sensors provided encouraging results for detecting low-energy impacts. However, vibration
within the sensor mounting structure interfered with the detection of impact events. Research on triboluminescent
phosphors indicated that a thin layer of material could be used to form the basis of an optical sensor to detect small
particle impacts without interference from structural vibrations. A ZnS:Mn phosphor was used as the basis for
developing a triboluminescent fiber optic sensor to detect small particle impact events. Detection of impacts is
accomplished by detecting the optical pulse that is generated by the abrupt charge separation caused by the particle
impact within the phosphor. Laboratory-based experiments were performed to capture the operational characteristics of
the sensor. The data are used to study the characteristic response, sensor repeatability, and spatial homogeneity of the
detection surface. Tests were also performed to identify the energy detection boundary and to assess environmental
survivability. Results of these tests are reported in this paper.
The widespread use of cameras based on uncooled infrared focal plane arrays (IRFPAs) is largely because of rapid commercialization, impressive miniaturization, and low per-unit cost. As performance improves, long-wave IR cameras using uncooled IRFPAs have replaced more expensive cooled units in many applications. The uncooled units generally have a much higher noise floor. However, if the signal is robust, the uncooled units can make the measurements at lower cost. New cameras with smaller pixels continue to reduce the pixel response time, enabling higher frame rates and more applications. Uncooled IRFPAs are thermal detectors, not charge-based devices, and the implicit pixel response time can greatly affect radiometric accuracy. In addition to the pixel response time, the fidelity of radiometric measurements is affected by target size, pixel fill factor, spectral response, stray light, self-heating, and other variables. If radiometric accuracy is required, it is necessary to quantify the effects of these variables. Calibration methods and measurement compensation techniques are described with emphasis on dynamic scene processing applications.
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