Polaris Sensor Technologies (United States)

Direct solar illumination disappears in the umbra when the Moon’s shadow creates a total solar eclipse. However, the sky above an observer in the umbra is not completely dark because of light that scatters into the umbra from the penumbra (partial eclipse region) and beyond. We show that a simple 2nd -order scattering model reproduces the brightness and color within a factor of 2 relative to measurements made with a radiometrically calibrated all-sky imaging system at the total solar eclipse of 21 August 2017 observed in Rexburg, Idaho USA. The model includes a first scattering point outside the umbra and a 2nd scattering point at the center of the umbra that redirects the light downward to the observer. The simulations show that the primary zenith skylight at the center of the umbra arises from light whose first scattering point is near an altitude of 10 km, the first scattering creates an orangish ring of light symmetrically around the horizon up to approximately 10° elevation, and the second scattering creates zenith skylight that is reduced by approximately four orders of magnitude from daylight and that has a slightly higher blue-red ratio than the daylight before and after the eclipse.

Manmade objects typically exhibit polarized signatures that can be utilized for target detection more effectively than thermal signatures alone. IR polarimetric imaging can also suppress clutter to highlight manmade objects in thermal equilibrium. However, quantifying the contrast improvement of polarimetric signatures over that of thermal signatures of the same scene has proved problematic due to the nature and dynamic range of the data. The Pyxis camera, a microbolometer-based imaging polarimeter that produces live polarimetric video of conventional, polarimetric, and fused image products and is small enough to be mounted on commercial drones, has collected datasets that demonstrate the improvement. In this paper, we describe the Pyxis camera, show representative data, and present the metrics used to characterize the improvement of polarimetric imaging over that of conventional thermal imaging.

Detection of targets can be difficult using thermal camera during thermal cross-over periods. Under these conditions, the target takes on the apparent temperature of objects in the foreground or background and becomes undetectable. It is commonly said that the thermal imagery is “washed-out”. When the thermal contrast of an object against its background is zero, many times a polarization contrast of the same object is non-zero. In this paper, we introduce a camera that measures thermal and polarization images in both the mid-wave infrared (MWIR) and long-wave infrared (LWIR). We also show example images and derive a simple equation that explains the conditions under which a polarization signature of an object can be expected.

Polarization spatial heterodyne interferometry (PSHI) allows for the development of compact, vibration insensitive, high spectral resolution sensors. Introducing the imaging qualities of a lenslet array extends the advantages of PSHI to imaging interferometers. The use of Savart plates enables a birefringent interferometer that obtains higher spectral resolution with fewer optical aberrations when compared to alternative designs. In this paper, we describe the design, construction, calibration and validation of a narrowband emission line imaging spectrometer (NELIS), based on Savart plates and liquid crystal polarization gratings, along with its associated theoretical model. This sensor is advantageous for spectral imaging in the areas of remote sensing, biomedical imaging and machine vision.

We have evaluated wire grid polarizers for the thermal infrared in the 3 to 12μm wavelength range. Wire grid structures are an effective means of producing infrared polarizers with short optical path and having large acceptance angles. Performance of two sets of polarizers manufactured by Moxtek, for the 3-5μm and 8-12μm wavelength ranges, were tested in a Mueller matrix spectropolarimeter and found to have transmission ratios on the order of 1000.

Polarimetric remote sensing has demonstrated utility for improving contrast between man-made targets and complex backgrounds. More specifically, polarimetric signatures of man-made targets can be useful for cueing analysts in widearea search applications. However, taking the target cueing to the next level of identification and tracking may require tasking of other sensing modalities. We present research that aims to understand what pose information might be extracted from the polarimetric signatures of under-resolved targets. Through experimentally collected and simulated imagery, we examine the variation in target signatures with respect pose and the relative sensor position aiming to extend the intelligence value of polarimetric imagery.

In September 2009 the Fort Leonard Wood Field Element of the US Army Research Laboratory - Human Research and Engineering Directorate, in conjunction with Polaris Sensor Technologies and Concurrent Technologies Corporation, evaluated the objective performance benefits of Polaris' 3D vision upgrade kit for the TALON small unmanned ground vehicle (SUGV). This upgrade kit is a field-upgradable set of two stereo-cameras and a flat panel display, using only standard hardware, data and electrical connections existing on the TALON robot. Using both the 3D vision system and a standard 2D camera and display, ten active-duty Army Soldiers completed seven scenarios designed to be representative of missions performed by military SUGV operators. Mission time savings (6.5% to 32%) were found for six of the seven scenarios when using the 3D vision system. Operators were not only able to complete tasks quicker but, for six of seven scenarios, made fewer mistakes in their task execution. Subjective Soldier feedback was overwhelmingly in support of pursuing 3D vision systems, such as the one evaluated, for fielding to combat units.

A 2-Cam micro-bolometer imaging polarimeter operating in the LWIR is presented. The system is capable of snapshot imaging Stokes polarimetry in any one channel (S1, S2, or S3) by taking two simultaneous measurements of a scene. For measurements of S1 or S2, the instrument relies on a specially optimized wire-grid beam-splitter. For measurements of S3, a form birefringent quarter-wave retarder is inserted into the optical path. Specifics associated with the design of the wire-grid beam-splitter and the form birefringent quarter-wave retarder will be overviewed, with inclusion of RCWA simulations. Calibration and simulation procedures, as well as calibration targets, will be highlighted, and initial data from the instrument are presented.

Data from a recent "first-look" at using Long Wave InfraRed Imaging Polarimetry (LWIR-IP) to detect surface swimmers is presented and discussed. A significant increase in detection SNR over conventional IR imaging techniques was discovered. The physical phenomena that produces the increased SNR is discussed along with data that shows range effects and their degradation on the SNR. Most significantly, a method to classify the detected object using the same dataset is discussed. Augmenting current swimmer detection systems using this technique will likely significantly decrease the false alarm rates of the system, thus saving manpower resources and preserving force readiness.

The proliferation of remotely operated vehicles (ROVs) has resulted in a need for the capability to see the operational environment in stereo. In a previous paper the theoretical underpinnings for new types of stereoscopic and autostereoscopic flat-panel displays with full-time, full-resolution images (i.e., no temporal multiplexing and no spatial multiplexing) were presented. Recently, a stereoscopic prototype has been constructed at the U.S. Army Aviation & Missile RDEC and testing is underway. The research presented here describes the application of two liquid crystal displays (LCD) sandwiched together to form a compact, rugged stereoscopic display. Polarized glasses are used to view the image in stereo. The prototype provides a full-time, full-resolution stereoscopic 3D display in a package slightly thicker, but no larger, than the standard liquid crystal display used in laptop computers. The LCDs have been characterized using a Stokes vector polarimeter. The characterization results were very interesting and led to some changes in the encoding algorithms. Significant improvements in the display quality were achieved through these adaptations.