Barham W. Smith

Improved matched-filter detection techniques

Numerous statistical approaches have been developed for small target detection in cluttered environments. Examples include orthogonal background suppression (OBS) where the initial principal components are suppressed, and the clutter matched filter (CMF) where the principal components are weighted by the inverse of the eigenvalues and the latter principal components are discarded. Our research has shown that improved target detection performance can be obtained by combining certain aspects of both OBS and CMF approaches. This is especially true in the presence of limited scene data (finite number of pixels) or an imperfect reference target spectrum. The basis of this idea is to use weighting by the inverse of the eigenvalues (from CMF) for the initial PCs and the uniform weighting for the later PCs (from OBS). Examples of this new technique and comparisons with OBS and CMF will be shown with model data with realistic clutter containing a chemical plume.

Multispectral Thermal Imager mission overview

The Multispectral Thermal Imager (MTI) is a research and development project sponsored by the Department of Energy and executed by Sandia and Los Alamos National Laboratories and the Savannah River Technology Center. Other participants include the U.S. Air Force, universities, and many industrial partners. The MTI mission is to demonstrate the efficacy of highly accurate multispectral imaging for passive characterization of industrial facilities and related environmental impacts from space. MTI provides simultaneous data for atmospheric characterization at high spatial resolution. Additionally, MTI has applications to environmental monitoring and other civilian applications. The mission is based in end-to-end modeling of targets, signatures, atmospheric effects, the space sensor, and analysis techniques to form a balanced, self-consistent mission. The MTI satellite nears completion, and is scheduled for launch in late 1999. This paper describes the MTI mission, development of desired system attributes, some trade studies, schedule, and overall plans for data acquisition and analysis. This effort drives the sophisticated payload and advanced calibration systems, which are the overall subject of the first session at this conference, as well as the data processing and some of the analysis tools that will be described in the second segment.

Multispectral Thermal Imager (MTI) Payload Overview

MTI is a comprehensive research and development project that includes up-front modeling and analysis, satellite system design, fabrication, assembly and testing, on-orbit operations, and experimentation and data analysis. The satellite is designed to collect radiometrically calibrated, medium resolution imagery in 15 spectral bands ranging from 0.45 to 10.70 micrometer. The payload portion of the satellite includes the imaging system components, associated electronics boxes, and payload support structure. The imaging system includes a three-mirror anastigmatic off-axis telescope, a single cryogenically cooled focal plane assembly, a mechanical cooler, and an onboard calibration system. Payload electronic subsystems include image digitizers, real-time image compressors, a solid state recorder, calibration source drivers, and cooler temperature and vibration controllers. The payload support structure mechanically integrates all payload components and provides a simple four point interface to the spacecraft bus. All payload components have been fabricated and tested, and integrated.

ALEXIS: An Ultrasoft X-Ray Monitor Experiment Using Miniature Satellite Technology

Los Alamos and Sandia National Laboratories are, building an ultrasoft X-ray monitor experiment. This experiment, called ALEXIS (Array of Low-Energy X-Ray Imaging Sensors), consists of six compact normal-incidence telescopes. ALEXIS will operate in the 70 - 110 eV band. The ultrasoft X-ray/EUV band is nearly uncharted territory for astrophysics. ALEXIS, with its wide fields-of-view and well-defined wavelength bands, will complement the upcoming NASA Extreme Ultraviolet Explorer and ROSAT EUV Wide Field Camera, which are sensitive broadzband survey experiments. The program objectives of ALEXIS are to 1) demonstrate the feasibility of a wide field-of-view, normal incidence ultrasoft X-ray telescope system and 2) to determine ultrasoft X-ray backgrounds in the space environment. As a dividend, ALEXIS will pursue the following scientific objectives: 1) to map the diffuse background, with unprecedented angular resolution, in several emission line bands, 2) to perform a 3-color survey of point sources, 3) to search for transient phenomena in the ultrasoft X-ray band, and 4) to provide synoptic monitoring of variable ultrasoft X-ray sources such as cataclysmic variables and flare stars. The six ALEXIS telescopes are arranged in pairs to cover three 40° fields-of-view. During each spin of the satellite, ALEXIS will monitor more than half the sky. Each telescope consists of a layered synthetic microstructure (LSM) mirror, a curved microchannel plate detector, background-rejecting filters and magnets, and readout electronics. The mirrors will be tuned to 72 eV, 85 eV, and 95 or 107 eV bands, chosen to select and deselect interesting line features in the diffuse background. The geometric area of each ALEXIS telescope will be about 15 cm2. The telescopes employ spherical mirrors with the curved detector at prime focus and are limited by spherical aberration to a resolution of about 1°. Assuming nominal reflectivities, quantum efficiency, and filter transmission, the 5a survey sensitivity will be about 2 x 10-3 photons cm-2 s-1 for line emission at the center of the bandpass. ALEXIS is designed to be flown on a small autonomous payload carrier (a minisat) that could be launched from either a Shuttle Get-Away-Special Can or from an expendable launch vehicle. The experiment weighs 100 pounds, draws 40 watts, and produces 10 kbps of data. It can be flown in any low Earth orbit. Onboard data storage allows operation and tracking from a single ground station at Los Alamos.

Modeling the MTI electro-optic system sensitivity and resolution

We present an analysis methodology that offers efficient characterization of the Multispectral Thermal Imager (MTI) electro-optic system response to a wide range of user-specified system parameters and spectral scenarios. This methodology combines physics-based modeling of the MTI hardware with MTI prelaunch characterization data. The resulting models enable the user to generate application-specific sensitivity and resolution studies of the MTI image capture process, and aid in the development of calibration procedures and retrieval algorithms for MTI. In addition to quantifying the MTI response, the methodology developed in this paper is sufficiently general to permit the prototyping and evaluation of a variety of multispectral electro-optic systems. Finally, an example utilizing nominal orbital parameters and targeted MODTRAN scenarios that exercise the various spectral band functions is provided.

Imagers for the magnetosphere, aurora, and plasmasphere

We present a small Explorer mission, Imagers for the Magnetosphere, Aurora, and Plasmasphere (IMAP), to provide the first global magnetospheric images that will allow a systematic study of major regions of the magnetosphere, their dynamics, and their interactions. The mission objective is to obtain simultaneous images of the inner magnetosphere (ring current and trapped particles), the plasmasphere, the aurora, and auroral upflowing ions. The instruments are (1) a Low Energy Neutral Particle Imager for imaging H and O atoms, separately, in the energy range of ~1 to 30 keV, in several energy passbands; (2) an Energetic Neutral Particle Imager for imaging H atoms in the energy range ~15 to 200 keV and, separately, O atoms in the energy range ~60 to 200 keV, each in several energy passbands; (3) an Extreme-Ultraviolet Imager to obtain images of the plasmasphere (the distribution of cold He + ) by means of He + (30.4 nm) emissions; and (4) a Far-Ultraviolet Imaging Monochromator to provide images of the aurora and the geocorona. All images will be obtained with time and spatial resolutions appropriate to the global and macroscale structures to be observed. IMAP promises new quantitative analyses that will provide great advances in insight and knowledge of global and macroscale magnetospheric parameters. The results expected from IMAP will provide the first large-scale visualization of the ring current, the trapped ion populations, the plasmasphere, and the upflowing auroral ion population. Such images, coupled with simultaneously obtained auroral images, will also provide the initial opportunity to globally interconnect these major magnetospheric regions. The time sequencing of IMAP images will also provide the initial large-scale visualization of magnetospheric dynamics, both in space and time.

Multi-spectral band selection for satellite-based systems

The design of satellite based multispectral imaging systems requires the consideration of a number of tradeoffs between cost and performance. The authors have recently been involved in the design and evaluation of a satellite based multispectral sensor operating from the visible through the long wavelength IR. The criteria that led to some of the proposed designs and the modeling used to evaluate and fine tune the designs will both be discussed. These criteria emphasized the use of bands for surface temperature retrieval and the correction of atmospheric effects. The impact of cost estimate changes on the final design will also be discussed.

Expected extreme ultraviolet spectrum of the lunar surface

The moon was recently observed to be a source of very soft x-ray emission. The emission was most intense at wavelengths longer than 62 {angstrom} and was attributed to Thomson scattering of solar x-rays. This observation prompted the authors to study the emissions expected from the lunar surface in the wavelength range between 90 and 500 {angstrom}. Photons in this wavelength range scatter inefficiently. Instead, the solar x-rays are absorbed in the first several microns of lunar regolith. The absorbed x-rays can excite the surface elements and result in fluorescent emission. The authors find that much of the L- and M-shell extreme ultraviolet fluorescence, in the wavelength range between 90 and 500 {angstrom}, have higher peak intensities than the scattered solar spectrum. The total integrated fluorescent emission is also higher than the total scattered solar radiation. The L-shell fluorescent radiation can be an indicator of the surface abundances of Si, Al, Mg and other major lunar elements.

MTI science, data products and ground data processing overview

The mission of the Multispectral Thermal Imager (MTI) satellite is to demonstrate the efficacy of highly accurate multispectral imaging for passive characterization of urban and industrial areas, as well as sites of environmental interest. The satellite makes top-of-atmosphere radiance measurements that are subsequently processed into estimates of surface properties such as vegetation health, temperatures, material composition and others. The MTI satellite also provides simultaneous data for atmospheric characterization at high spatial resolution. To utilize these data the MTI science program has several coordinated components, including modeling, comprehensive ground-truth measurements, image acquisition planning, data processing and data interpretation and analysis. Algorithms have been developed to retrieve a multitude of physical quantities and these algorithms are integrated in a processing pipeline architecture that emphasizes automation, flexibility and programmability. In addition, the MTI science team has produced detailed site, system and atmospheric models to aid in system design and data analysis. This paper provides an overview of the MTI research objectives, data products and ground data processing.

MTI on-orbit calibration

The Multi-spectral Thermal Imager (MTI) will be a satellite- based imaging system that will provide images in fifteen spectral bands covering large portions of the spectrum from 0.45 through 10.7 microns. An important goal of the mission is to provide data with state-of-the-art radiometric calibration. The on-orbit calibration will rely on the pre-launch ground calibration and will be maintained by vicarious calibration campaigns. System drifts before and between the vicarious calibration campaigns will be monitored by several on-board sources that serve as transfer sources in the calibration of external images. These sources can be divided into two groups: a set of sources at an internal aperture, primarily intended to monitor short term drifts in the detectors and associated electronics; and two sources at the external aperture, intended to monitor longer term drifts in the optical train before the internal aperture. The steps needed to transfer calibrations to image products, additional radiometric data quality estimates performed as part of this transfer, and the data products associated with this transfer will all be examined.