Christopher G. Simi

COMPACT airborne spectral sensor (COMPASS)

The COMPACT Airborne Spectral Sensor (COMPASS) design is intended to demonstrate a new design concept for solar reflective hyper spectral systems for the Government. Capitalizing from recent focal plane developments, the COMPASS system utilizes a single FPA to cover the 0.4-2.35micrometers spectral region. This system also utilizes an Offner spectrometer design as well as an electron etched lithography curved grating technology pioneered by NASA/JPL. This paper also discusses the technical trades, which drove the design selection of COMPASS. When completed, the core COMPASS spectrometer design could be used in a large variety of configurations on a variety of aircraft.

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.

Advances in optical parametric oscillators with application to remote chemical sensing

In this paper, we review some recent advances in optical parametric oscillator (OPO) technology, discuss major coherent source issues and then propose possible solutions that have relevance to remote chemical sensing. The authors discuss their latest result on two OPO schemes. 1) Energies up to 1.2 mJ/pulse and continuously tunable OPO output from 6.7 to 9.8 micrometers was obtained using a 5 X 5 X 25 mm3 type II AgGaS2 crystal, pumped a second OPO using NCPM ZnGeP2 to generate output near 8 micrometers . The tandem OPO produced pulse energies of > 1.5 mJ at 7.8 micrometers with an energy conversion efficiency of 6.8 percent. Finally, we describe schemes for generating multiple photons in the 8-12 micrometers band from one initial 1 micrometers pump photon, and thereby increase the quantum efficiency when OPOs are pumped by Nd:YAG lasers.

The mapping reflected-energy sensor-MaRS:a new level of hyperspectral technology

The need to provide high-quality large-area hyperspectral data for land use, geological, environmental, and mapping applications is critical to the US Government in the 21st Century. Technological advances with regard to larger focal plane arrays (FPA) along with maturing spectrometer designs have made it possible for the development of a next generation system beyond AVIRIS. This paper will introduce the MaRS system along with some data examples from Cuprite, NV and the National Arboretum.

Mine detection experiments using hyperspectral sensors

Hyperspectral imaging is an important technology for the detection of surface and buried land mines from an airborne platform. For this reason, hyperspectral was included with SAR sensors in the two deployments that were executed by the CECOM RDEC Night Vision and Electronic Systems Directorate (NVESD) in Fall 2002 and in Spring 2003. The purpose of these deployments was to bring together a wide variety of airborne sensors for the detection of mines, with well ground-truthed targets. The hyperspectral sensors included the Airborne Hyperspectral Imager (AHI), a University of Hawaii LWIR HSI sensor and the Compact Airborne Spectral Sensor (COMPASS), an NVESD VNIR/SWIR sensor. Both a high frequency SAR and a ground penetrating radar were also flown. These experiments were carried out at sites where an extensive array of buried and surface mines were deployed. At the first location, on the east coast, the mines were deployed against several different backgrounds ranging from bare dirt to long grass. At the second location in the desert southwest, the mines were placed on backgrounds ranging from loose sand to mixed sand and vegetation. The COMPASS and AHI sensors were both placed on the Twin Otter aircraft, and data was collected with the airplane as low as 700 ft and as high as 4000 ft. In this paper, the data collected on surface mines will be reviewed, and specific examples from each background type presented. Spectral detection algorithms will be applied to the data and the results of the algorithm processing will be presented.

Tradeoffs for real-time hyperspectral analysis

There has been considerable interest in the application of real-time processing techniques to the problem of hyperspectral scene analysis. Recent satellite and aircraft systems can produce data at a rate far faster than the data can be analyzed by interactive computer procedures. Automated and fast procedures for preparing the data for analyst inspection are required for even laboratory use of the large quantities of data. In addition, there are several real-time applications where the data must be processed as it is being acquired. A typical application is a computing system on-board an airplane for operator analysis of the scene as the hyperspectral sensor collects data. In this paper the possible tradeoffs fore rapid analysis are discussed, including choice of algorithm, possible dimensionality reduction, and reduced display level. A real time anomaly detection processing system based on the N- FINDR algorithm has been designed and implemented for the Night Vision Imaging Spectrometer (NVIS). The N-FINDR algorithm is a linear unmixing based algorithm that automatically finds spectral endmembers. The algorithm works by inflating a simplex inside the data, beginning with a random set of pixels. Once these endmember spectra have been found, the image cube can be unmixed using a least-squares approach into a map of fractional abundances of each endmember material in each pixel. In addition to the N-FINDR algorithm, the real-time processing system performs calibration, bad pixel removal, and display of selected fraction planes. The real-time processor is implemented in a commercial Pentium IV computer.

Night Vision Imaging Spectrometer (NVIS) calibration and configuration: Recent developments

The Night Vision Imaging Spectrometer (NVIS) system has participated in a large variety of hyperspectral data collections for the Department of Defense. A large number of improvements to this system have been undertaken. They include the implementation of a calibration process that utilizes in-flight calibration units (IFCU). Other improvements include the completion and implementation of an updated laboratory wavelength assignments map which provide precise bandwidth profiles of every NVIS pixel. NVESD has recently incorporated a Boeing C-MIGITS II INS/DGPS system, which allows geo-rectification of every frame of NVIS data. A PC-based Dual Real Time Recorder DRTR was developed to extend the collection capability of the sensor and allow the concurrent collection of data from other devices. The DRTR collects data from the NVIS, a Dalsa imager, and data from the CMIGITS-II (C/A code Miniature Integrated GPS/INS Tactical System) which provides navigation information. The integration of the CIMGITS-II allows every data frame of both the NVIS and the DALSA to be stamped with INS/GPS information. The DRTR software can also provide real-time waterfall displays of the data being collected. This paper will review the recent improvements to the NVIS system.

On-board processing for the COMPASS

The Compact Airborne Spectral Sensor (COMPASS) is a hyperspectral sensor covering the 400 to 2350 nm spectral region using a single focal plane and a very compact optical system. In addition, COMPASS will include a high-resolution panchromatic imager. With its compact design and its full spectral coverage throughout the visible, near infrared and SWIR, COMPASS represents a major step forward in the practical utilization of hyperspectral sensors for military operations. COMPASS will be deployed on a variety of airborne platforms for the detection of military objects of interest. There was considerable interest in the development of an on-board processor for COMPASS. The purpose of this processor is to calibrate the data and detect military targets in complex background clutter. Because of their ability to operate on truly hyperspectral data consisting of a hundred or more bands, linear unmixing algorithms were selected for the detection processor. The N-FINDR algorithm that automatically finds endmembers and then unmixes the scene was selected for real-time implementation. In addition, a recently developed detection algorithm, Stochastic Target Detection (STD), which was specifically designed for compatibility with linear unmixing algorithms, was chosen for the detection step. The N-FINDR/STD algorithm pair was first tested on a variety of hyperspectral data sets to determine its performance level relative to existing hyperspectral algorithms (such as RX) using Receiver Operator Curves (ROC) as the basis. Following completion of the testing, a hardware implementation of a real time processor for COMPASS using commercial off-the-shelf computer technology was designed. The COMPASS on-board processor will consist of the following elements: preprocessing, N-FINDR endmember determination and linear unmixing, the STD target detection step, and the selection of a High Resolution Image Chip covering the target area. Computer resource projections have shown that these functions, along with supporting interactive display functions, can operate in real-time on COMPASS data using multi-processor Pentium III class processors.

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.