R. Rex Kay

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.

The impact of multiplexing on the dynamic requirements of analog-to-digital converters

In data acquisition applications where the signals being digitized are produced in a time-division multiplexed system, the required dynamic performance of the analog-to-digital converter (ADC) is no longer bound by the conditions set forth in the sampling theorem. This results from the introduction of very high-frequency information by the multiplexing process which, while not necessarily containing information of interest, must be processed by the input circuitry of the ADC. In this situation, signal bandwidths and slew rates can greatly exceed those produced in a Nyquist limited system and can surpass the capability of the ADC, thus degrading overall system performance. This paper examines two common multiplexing schemes and their impact on ADC dynamic requirements. First, the authors examine a simple voltage multiplexing scheme typically found in state-of-health or data-logging applications and develop the necessary equations to show how the ADC dynamic requirements are affected. Then, the analysis is extended to a multiplexed photodiode array readout to see how this application further challenges the dynamic performance of the ADC. Finally, the issues associated with developing dynamic test methodologies for assessing ADC performance in multiplexed systems are discussed.

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.

Multispectral thermal imager (MTI) satellite hardware status, tasking and operations

MTI is a comprehensive R&D project, featuring a single satellite in a sun-synchronous orbit designed to collect radiometrically accurate images of instrumented ground sites in 15 spectral bands ranging from visible to long-wave infrared. The satellite was launched from Vandenberg AFB on March 12, 2000 aboard an Orbital Sciences Corporation Taurus rocket. After launch, the operations team completed a 3- month turn-on, check out and alignment procedure, and declared the satellite ready for its R&D mission on June 12, 2000. The satellite is currently healthy, having collected over 1,100 images during its first nine months of operation. This paper presents a brief satellite overview and documents on-orbit status and operational experience, including anomalies and their resolution.

Initial MTI on-orbit calibration performance

The Multispectral Thermal Imager (MTI) is a satellite-based imaging system that provides images in fifteen spectral bands covering large portions of the spectrum from 0.45 through 10.7 microns. This article describes the current MTI radiometric image calibration, and will provide contrast with pre-launch plans discussed in an earlier article. The MTI system is intended to provide data with state-of-the-art radiometric calibration. The on-orbit calibration relies on the pre-launch ground calibration and is maintained by vicarious calibration campaigns. System drifts before and between the vicarious calibration campaigns are monitored by several on-board sources that serve as transfer sources in the calibration of external images. The steps used 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.

Multispectral thermal imaging

Many remote sensing applications rely on imaging spectrometry. Here we use imaging spectrometry for thermal and multispectral signatures measured from a satellite platform enhanced with a combination of accurate calibrations and on-board data for correcting atmospheric distortions. Our approach is supported by physics-based end- to-end modeling and analysis, which permits a cost-effective balance between various hardware and software aspects.