John A. Antoniades

Use of filter vectors in hyperspectral data analysis

We report recent progress using a filter vector technique to analyze the data from a hyperspectral image. The filter vector technique finds the optimal filter vectors for demixing the complex patterns found in the hyperspectral image. The method has the potential to be implemented in real time since it is fully parallel. Computation of the filter vectors for a given family of known species vectors is fast and direct and improved algorithms for developing of the algorithm which may be updated as conditions change is possible. Advantages of using the filter vector techniques over the technique of pattern matching will be discussed. The portable hyperspectral images for low light spectroscopy (PHILLS) instrument has been used on a number of depolyments in the last year. Typically, the instrument files on the Naval Research Laboratorys P-3 Orion aircraft. Currently, the PHILLS instrument records over 1000 wavelength bands between UV and near IR. Results from a number of deployment and test situations is shown.

Velocity‐shear‐driven ion‐cyclotron waves and associated transverse ion heating

Recent sounding rocket experiments, such as SCIFER, AMICIST, and ARCS-4, and satellite data from FAST, Freja, DE-2, and HILAT, provide compelling evidence of a correlation between small-scale spatial plasma inhomogeneities, broadband low-frequency waves, and transversely heated ions. These naturally arising, localized inhomogeneities can lead to sheared cross-magnetic-field plasma flows, a situation that has been shown to have potential for instability growth. Experiments performed in the Naval Research Laboratorys Space Physics Simulation Chamber demonstrate that broadband waves in the ion-cyclotron frequency range can be driven solely by a transverse, localized electric field, without the dissipation of a field-aligned current. Significant perpendicular ion energization resulting from these waves has been measured. Detailed comparisons with both theoretical predictions and space observations of electrostatic waves found in the presence of sheared cross-magnetic-field plasma flow are made.

Perpendicular ion heating by velocity‐shear‐driven waves

Perpendicular ion heating resulting from velocity-shear-driven ion-cyclotron waves has been measured for the first time. The experiment was performed in the Naval Research Laboratorys Space Physics Simulation Chamber (SPSC) under plasma conditions approaching those in the natural space environment. Sheared cross-field flow is induced by a controllable, inhomogeneous, transverse, DC electric field (LE ∼ (1–2)ρi) created without drawing significant levels of magnetic-field aligned current. Mode frequency data suggest that the most efficient heating occurs when the Doppler shifted frequency in the ion frame is located near a harmonic of the ion-cyclotron frequency.

Comparison of low-cost hyperspectral sensors

Recent advances in large format detector arrays and holographic diffraction gratings have made possible the development of imaging spectrographs with high sensitivity and resolution, at relatively low component cost. Several airborne instruments have been built for the visible and near IR spectral band with 10-nm resolution, and SNR of 200:1. Three instruments are compared, an all-reflective spectrography using a convex grating in an Offner configuration, and two off-the-shelf transmission grating spectrographs using volume holograms. The camera is a 1024 X 1024 frame transfer, back-thinned CCD, with four taps for obtaining high frame rates. Performance and scan data is presented and compared to the design for image quality, distortion, and throughput.

Hyperspectral analysis and target detection system for the Adaptive Spectral Reconnaissance Program (ASRP)

A multiprocessor version of the ORASIS hyperspectral analysis program has been implemented in support of the ASRP. In brief, the long-term technical objectives of the ASRP are to demonstrate the feasibility and military utility of real-time target detection from uncrewed air vehicles using hyperspectral data. This paper presents a preliminary assessment of ORASIS performance and describes the ORASIS development effort designed to meet the ASRP goals. Real-time performance of the analysis program and its potential effectiveness as a target detection method are demonstrated.

A large volume microwave plasma source

We report on the design, construction, and use of a large cavity microwave plasma source. The source is designed to provide a range of space‐plasma‐like conditions in the Naval Research Laboratory Space Physics Simulation Chamber. A new feature of the source design incorporates hard anodized aluminum as the internal cavity area surface and does not use the conventional quartz cavity liner which is prone to overheating and cracking with extended use. By placing a number of small plasma outlet holes around the surface of a 36.8 cm output plate, we are able to provide a fairly radially uniform plasma; by further surrounding the production region and exit with an axial pinch magnetic field we are able to extend this region of plasma uniformity further toward the chamber walls and cover a significant portion of the experimental area. The source provides plasmas with selectable densities between 104 and 108 cm−3 and electron temperatures vary from about 0.5 to 2.0 eV.

Comparison of output from ORASIS and pixel purity calculations

We compare the results produced by the NRL ORASIS algorithm with those produced by ENVIs Pixel Purity Index. Both procedures attempt to find appropriate estimations of the constituent endmembers.

Hyperspectral imaging sensor for the coastal environment

Recent advances in large format detector arrays and holographic diffraction gratings have made possible the development of imaging spectrographs with high sensitivity and resolution, ideally suited for space-based remote sensing of earth resources. An optical system composed of dual spectrographs and a common fore-optic has been designed for the visible-near infrared (VNIR) and shortwave bands with 10-nm spectral resolution, providing 30-meter ground resolution from an altitude of 605 km. The spectrograph designs are based on a modified Offner 1-X relay with spherical mirrors and a convex spherical holographic grating for the secondary mirror. The fore-optic is a three-mirror anastigmatic telescope with a 360-mm focal length to match the pixel pitch of the respective 1024 X 1024 visible silicon CCD and SWIR HgCdTe FPAs. The primary advantages of this design are the relatively low f-number (f/3), large flat field (18 mm), and low distortion. Preliminary performance results of a VNIR testbed grating and spectrograph are presented and compared to the design predictions.

Real-time analysis of hyperspectral data sets using NRL's ORASIS algorithm

The covered lantern project was initiated by the central MASINT Technology Coordination Office to demonstrate the tactical use of hyperspectral imagery with real time processing capability. We report on the design and use of the HYCORDER system developed for Covered Lantern that was tested in June 1995. The HYCORDER system consisted of an imaging spectrometer flying in a Pioneer Uncrewed Aeronautical Vehicle and a ground based real time analysis and visualization system. The camera was intensified allowing dawn to dusk operation. The spectral information was downlinked to the analysis system as standard analog video. The analysis system was constructed from 17 Texas Instrument C44 DSPs controlled by a 200 MHz Pentium Pro PC. A real time, parallel version of NRLs optical real-time adaptive spectral identification system algorithm was developed for this system. The system was capable of running continuously, allowing for broad area coverage. The algorithm was adaptive, accommodating changing lighting conditions and terrain. The general architecture of the algorithm will be discussed as well as results from the test.

Effect of spectral resolution and number of wavelength bands in analysis of a hyperspectral data set using NRL's ORASIS algorithm

We report the results of a tradeoff study for the selection of the number of wavelength bands and resolution needed in a hyperspectral data set in order to separate a scene into its constituent features. This separation is accomplished by finding approximate endmembers using convex mixing and shrink-wrapping techniques. This and related techniques are referred to as NRLs Optical Real-time Adaptive Spectral Identification System (ORASIS). ORASISs algorithms will be briefly described. Once endmembers are found, matched filters are calculated which can then be used to separate (or demix) the scene. We have analyzed synthetic cubes, cubes acquired by NRLs Portable Hyperspectral Imager for Low Light Spectroscopy (PHILLS) sensor, and cubes from other sensors. PHILLS consists of multiple hyperspectral sensors that operate in pushbroom mode. PHILLS has been deployed from aircraft and on the ground in a variety of terrains from the polar icecap to the Florida Keys. The majority of the data were recorded with a 16-bit thermo-electrically cooled camera which records 1024 wavelengths over the range of 200 to 1100 nm. Major features of the scene can be successfully demixed using fewer than 1024 wavelength bands. However, preliminary evidence suggests that finer features require the full wavelength range and resolution.