Roberta Dixon

Night vision imaging spectrometer (NVIS) performance parameters and their impact on various detection algorithms

In the past 3 years, US Army’s Night Vision and Electronic Sensors Directorate has worked in conjunction with Navy SPAWAR on DARPAs Adaptive Spectral Reconnaissance Program (ASRP). The Night Vision Imaging Spectrometer (NVIS), which is a solar reflective (0.4-2.35um) hyperspectral imaging device, has played a major role in the ASR Program. As with all spectral imaging devices, there exist a certain number of imperfections in the NVIS device. If not handled properly, these imperfections can have an impact upon the performance of certain detection algorithms. This paper will describe the overall measured sensor performance parameters of the NVIS, its imperfections and the effect they may have on algorithm performance. There will also be a discussion concerning the processing tools and methods that have been developed in the past year, and have allowed the imperfections to be removed to some level.

Calibration procedures and measurements for the COMPASS hyperspectral imager

The COMPact Airborne Spectral Sensor (COMPASS) hyperspectral imager (HSI) developed at the Army Night Vision and Electronic Sensors Directorate (NVESD) operates in the solar reflective region. The fundamental advance of the COMPASS instrument is the ability to capture 400nm to 2350nm on a single focal plane, eliminating boresighting and co-registration issues characteristic of dual FPA instruments for visible and SWIR regions. This paper presents a calibration procedure for COMPASS including spectral band profiles and radiometric calibration. These procedures expand on successful calibration procedures used for the Night Vision Infrared Spectrometer (NVIS) system. A high-resolution monochromator was used to map the band center and bandwidth profiles across the FPA with an accuracy goal of ±0.5nm using several different illumination configurations. Although optical distortions are below previous measurement capabilities, accurate band profiles provide additional data to map potential distortions within the system. Radiometric calibration was performed with a NIST-traceable flood source. Test results are presented showing a well-behaved system with an average spectral bandwidth of 8.0nm ±0.5nm over the instrument spectral range.

Enhanced oil spill detection sensors in low-light environments

Although advances have been made in oil spill remote detection, many electro-optic sensors do not provide real-time images, do not work well under degraded visual environments, nor provide a measure of extreme oil thickness in marine environments. A joint program now exists between BSEE and NVESD that addresses these capability gaps in remote sensing of oil spills. Laboratory experiments, calibration techniques, and field tests were performed at Fort Belvoir, Virginia; Santa Barbara, California; and the Ohmsett Test Facility in Leonardo, New Jersey. Weathered crude oils were studied spectroscopically and characterized with LWIR, and low-light-level visible/NIR, and SWIR cameras. We designed and fabricated an oil emulsion thickness calibration cell for spectroscopic analysis and ground truth, field measurements. Digital night vision cameras provided real-time, wide-dynamic-range imagery, and were able to detect and recognize oil from full sun to partial moon light. The LWIR camera provided quantitative oil analysis (identification) for >1 mm thick crude oils both day and night. Two filtered, co-registered, SWIR cameras were used to determine whether oil thickness could be measured in real time. Spectroscopic results revealed that oil emulsions vary with location and weathered state and some oils (e.g., ANS and Santa Barbara seeps) do not show the spectral rich features from archived Deep Water Horizon hyperspectral data. Multi-sensor imagery collected during the 2015 USCG Airborne Oil Spill Remote Sensing and Reporting Exercise and the design of a compact, multiband imager are discussed.

New procedures for the calibration of COMPASS

The Compact Airborne Spectral Sensor (COMPASS) has been flying for over a year and has gathered data in support of a variety of missions. While COMPASS is an array imaging spectrometer, the quality of the spectrometer optics and the alignment of the instrument during assembly have removed many of the sources of error often present in array imaging spectrometers, such as spectral band mis-registration, smile and keystone. Since COMPASS has begun flying, we have been studying new procedures for improving the calibration of the COMPASS sensor and array imaging spectrometers, in general. The use of the on-board calibration sources was compared to using a combination of on-board sources and a scene average, and also compared to using laboratory calibration sources. In addition, different methods for finding and removing bad detectors were investigated. The coupling of the bad detector replacement procedure with the flatfielding was also studied. We have found that bracketing the light levels in the scene is the key to reducing the effect of bad detectors. An effective method of bracketing the scene is to use the scene average for each detector as the white and the on-board dark. Alternative methods using multiple white sources are also attractive. Several examples from collected scene data will be presented and evaluated in terms of image quality in particular bands and Principal Components.

Night vision imaging spectrometer (NVIS) processing and viewing tools

The US Armys Night Vision and Electronic Sensors Directorate (NVESD) has developed software tools for processing, viewing, and analyzing hyperspectral data. The tools were specifically developed for use with the U.S. Armys NVESD Night Vision Imaging Spectrometer (NVIS), but they can also be used to process hyperspectral data in a variety of other formats. The first of these tools is the NVESD Hyperspectral Data Processor, which is used to create a calibrated datacube from raw hyperspectral data files. It can calibrate raw NVIS data to spectral radiance units, perform spectral re-alignment, and can co-register imagery from NVISs VNIR and SWIR subsystems. The second tool is the NVESD Hyperspectral Viewer, which can display focal plane data, generate images, and compute spatial and temporal statistics, produce data histograms, estimate spectral correlation, compute signal-to-clutter ratios, etc. Additionally, this software tool has recently been modified to utilize the INS/GPS data that is currently embedded into NVIS data as well as the high-resolution imagery (HRI) that is collected simultaneously. Furthering its capabilities, Technical Research Associates (TRA) has added the following detection algorithms to the Viewer: N-FINDR, PC and MNF Transformations, Spectral Angle Mapper, and R-X. The purpose of these software developments is to provide the DoD and other Government agencies with a variety of tools, which are not only applicable to NVIS data but also can be applied to other hyperspectral data.

Shortwave (1 to 2.8 um) imagery applications for fun and profit

SWIR (short-wave infrared) imaging technology, phenomena, and applications are described. Commercial SWIR (staring InSb, PtSi, HgCdTe, InGaAs) camera specifications and optimization procedures are discussed. SWIR physics including blackbody distribution, atmospheric MODTRAN predictions, and selected material reflectance measurements are reviewed to illustrate basic guidelines to successful SWIR imaging. SWIR imaging examples of military applications, medical imaging, astronomy, long range observations, plume measurement, and art preservation are included to illustrate the unique properties of SWIR imaging.

Real-time processing of multispectral second-generation thermal imaging systems

Two separate technical developments are described: a long wave (7.5 to 11.2 micron) multi-spectral (5 bands) second generation thermal imager (HgCdTe, 288 by 4) and real time algorithm implementation using a datacube maxvideo image processing system. When combined these two technologies provide an enhanced imaging sensor with several unique features for improved multi-spectral performance; including scene based histogram correction, spatial filtering, and frame averaging. Image processing options are adjusted by the operator to adapt and optimize imagery for different scene conditions via real time feedback. The paper describes system hardware, software development, and laboratory measurements and field observations which demonstrate the impact of different processing strategies against dynamic scene backgrounds. Advantages of real time processing include an NETD/MRTD performance improvement by a factor of 3. The TAS 4X FW/datacube system provides the ability to observe the migration of small quantities of gas (SF6) from stand-off ranges of several kilometers. Filtered imagery when combined with real time processing can provide a new level of imaging performance that can observe scene details unresolvable by other techniques.

Remote measurement of thick oil spill depth using thermal imagery

Visual inspection of crude oil on water can determine the depth of thin layers of oil. However, catastrophic spills with millimeter (mm) thick oil will just be black, with no visual variation as the oil gets thicker. A day/night heat transfer model was developed to determine crude oil slick thickness. The model uses LWIR thermographic imagery, weather station outputs of air and water temperature, relative humidity, solar radiation, wind speed, other weather input such as cloud cover percent and altitudes, and measured thermal conductivity of Alaskan North Slope (ANS) crude oil. Outdoor field-testing was performed with fresh, weathered, and emulsified ANS crude oils that were placed on water at depths of 2-10 mm. A FLIR T640SC camera viewed the scene from a three-story roof-top to simulate small unmanned aerial vehicle (sUAV) altitudes. A low-cost, portable weather station was set up next to the pool and temperature calibrated LWIR imagery was collected every 15-minutes for 24-hours. The average oil surface temperature was measured for each target. The day/night model predicts oil slick thickness within one or two standard deviations. The fidelity of the thickness measurements is dependent on the accurate measurement of the atmospheric and weather parameters, sea state, heat transfer constants, and calibration and stability of the thermal camera.

Mapping and reconnaissance imager, night-enhanced, for sensing of contaminants, oil, and unseen threats (MARINE SCOUT)

MARINE SCOUT is a compact, lightweight, Puma and other small UAS (SUAS) compatible, multi-spectral airborne sensor payload designed to sense and discriminate oil on water (e.g., maritime oil spills), and enable via post-processing the measurement of oil thickness in marine environments. The payload includes near-infrared (NIR), short-wavelength infrared (SWIR), and long-wavelength infrared (LWIR) sensor channels that enable the detection of oil and its byproducts, the rejection of vegetative clutter, and the discrimination of thick crude oils. The stabilized airborne payload hosting the sensors compensates aircraft roll, yaw, and forward motion – the latter using a novel, enabling forward motion compensation (FMC) technology. The airborne payload’s capabilities, combined with a ground station exploitation and human interface computer, support ocean mapping and scene interrogation, producing high-fidelity, mosaiced, geo-rectified, multi-spectral image stacks along with full motion video for use by oil spill responders.

Beam uniformity analysis of infrared laser illuminators

Abstract. Uniform near-infrared (NIR) and short-wave infrared (SWIR) illuminators are desired in low ambient light detection, recognition, and identification of military applications. Factors that contribute to laser illumination image degradation are high frequency, coherent laser speckle and low frequency nonuniformities created by the laser or external laser cavity optics. Laser speckle analysis and beam uniformity improvements have been independently studied by numerous authors, but analysis to separate these two effects from a single measurement technique has not been published. In this study, profiles of compact, diode laser NIR and SWIR illuminators were measured and evaluated. Digital 12-bit images were recorded with a flat-field calibrated InGaAs camera with measurements at F/1.4 and F/16. Separating beam uniformity components from laser speckle was approximated by filtering the original image. The goal of this paper is to identify and quantify the beam quality variation of illumination prototypes, draw awareness to its impact on range performance modeling, and develop measurement techniques and methodologies for military, industry, and vendors of active sources.