Donald E. Lencioni

The effect of dust on 10.6‐μm laser‐induced air breakdown

Laser‐induced breakdown in very clean air at 10.6 μm is shown to have a threshold of 3 × 109 W/cm2 for large beams and is described well by microwave breakdown theory. Dust particles are shown to lower the threshold by an amount which is greater for larger particles and higher vapor temperatures. There is a minimum in threshold for large particles, which for 200‐nsec pulse length is ≤ 108 W/cm2, corresponding to an energy fluence of 10–20 J/cm2. These results are explained qualitatively by the increase in inverse bremsstrahlung rate caused by exploding particles.

EO-1 Advanced Land Imager

The ALI, which will be flown on the NASA New Millennium Programs EO-1 mission, has been completed and is being integrated with the spacecraft. The motivation for the EO-1 mission is to flight-validate advanced technologies that are relevant to next generation satellites. The ALI telescope is a reflective triplet design having a 15-degree cross-track field-of-view that employs silicon carbide mirrors. It incorporates a multispectral detector and filter array with 10 spectral bands that cover a wavelength range from the visible to the short-wave IR. The paper will describe the instrument and its operation, review test result, and suggest application to a future Landsat instrument.

Design and Performance of the EO-1 Advanced Land Imager

An Advanced Land Imager (ALI) will be flown on the first Earth Observing mission (EO-1) under NASAs New Millennium Program (NMP). The ALI contains a number of key NMP technologies. These include a 15 degree wide field-of-view, push-broom instrument architecture with a 12.5 cm aperture diameter, compact multispectral detector arrays, non-cryogenic HgCdTe for the short wave infrared bands, silicon carbide optics, and a multi-level solar calibration technique. The focal plane contains multispectral and panchromatic (MS/Pan) detector arrays with a total of 10 spectral bands spanning the 0.4 to 2.5 micrometer wavelength region. Seven of these correspond to the heritage Landsat bands. The instantaneous fields of view of the detectors are 14.2 (mu) rad for the Pan band and 42.6 (mu) rad for the MS bands. The partially populated focal plane provides a 3 degree cross-track coverage corresponding to 37 km on the ground. The focal plane temperature is maintained at 220 K by means of a passive radiator. The instrument environmental and performance testing has been completed. Preliminary data analysis indicates excellent performance. This paper presents an overview of the instrument design, the calibration strategy, and results of the pre-flight performance measurements. It also discusses the potential impact of ALI technologies to future Landsat-like instruments.

Radiometric calibration of the EO-1 Advanced Land Imager

The radiometric calibration of the Earth Observation 1 Advanced Land Imager (EO-1 ALI) was completed in the Spring of 1999 at Lincoln Laboratory. This calibration was conducted with the ALI as a fully assembled instrument in a thermal vacuum chamber at operation temperatures. The ALI was calibrated radiometrically at the system level from 0 to > 100 percent Earth-equivalent albedo using a combination of internal and external halogen and Xenon lamps attached to a large integrating sphere. Absolute radiometric calibration was achieved by measuring the output of the integrating sphere at each radiance level prior to ALI illumination using a NIST-traceable spectroradiometer. Additional radiometric characterization of this instrument was obtained from data collected using a collimator designed for the spectral calibration of the ALI. In this paper we review the techniques employed during radiometric calibration and present the measured gain, linearity, offset, signal-to- noise ratio and polarization sensitivity of each pixel. The testing result of a novel, in-flight solar calibration technique are also discussed. Finally, the results from a Lincoln Laboratory/Goddard Space Flight Center Landsat transfer radiometric study are presented.

New Millennium EO-1 Advanced Land Imager

The primary instrument of the first Earth Orbiter satellite (EO-1) under NASAs New Millennium Program will be an Advanced Land Imager (ALI), with multispectral and imaging spectrometer capabilities. The principal motivation for this mission is to flight-validate advanced technologies which are relevant to the next-generation of Earth Science Systems Program Office science needs. The ALI telescope is a reflective triplet design employing silicon carbide mirrors with a 15 degree cross-track field of view. There are three imaging technologies in the ALI. The first is a multispectral panchromatic array with 10 spectral bands in the visible and near IR and short wave IR. The two additional imaging technologies are the Wedge Imaging Spectrometer (WIS) and the Grating Imaging Spectrometer (GIS) that each provides a continuous range of wavelength selections from 0.4 to 2.5 micrometers . Elements of the WIS and GIS were developed but due to budgetary and schedule constraints, and some performance issues, were not included in the flight assembly. The paper will present details of the ALI design and status.

EO-1 Advanced Land Imager in-flight calibration

The EO-1 Advanced Land Imager (ALI) is the first earth- orbiting instrument to be flown under NASAs New Millennium program. The ALI employs novel wide-angle optics and a multispectral and panchromatic spectrometer. EO-1 is a technology verification project designed to demonstrate comparable or improved Landsat spatial and spectral resolution with substantial mass, volume, and cost savings. This paper provides as overview of in-flight calibration and performance assessment of the Advanced Land Imager. Include dare techniques for calibrating and assessing focus and MTF using long, straight man-made objects and monitoring of radiometric linearity and offsets using an internal calibration source, standard Earth references scenes, and solar and lunar observations.

Radiometric calibration stability of the EO-1 advanced land imager: 5 years on-orbit

The Advanced Land Imager (ALI) was developed as a prototype sensor for follow on missions to Landsat-7. It was launched in November 2000 on the Earth Observing One (EO-1) satellite as a nominal one-year technology demonstration mission. As of this writing, the sensor has continued to operate in excess of 5 years. Six of the ALIs nine multi-spectral (MS) bands and the panchromatic band have similar spectral coverage as those on the Landsat-7 ETM+. In addition to on-board lamps, which have been significantly more stable than the lamps on ETM+, the ALI has a solar diffuser and has imaged the moon monthly since launch. This combined calibration dataset allows understanding of the radiometric stability of the ALI system, its calibrators and some differentiation of the sources of the changes with time. The solar dataset is limited as the mechanism controlling the aperture to the solar diffuser failed approximately 18 months after launch. Results over 5 years indicate that: the shortest wavelength band (443 nm) has degraded in response about 2%; the 482 nm and 565 nm bands decreased in response about 1%; the 660 nm, 790 nm and 868 nm bands each degraded about 5%; the 1250 nm and 1650 nm bands did not change significantly and the 2215 nm band increased in response about 2%.

EO-1 Advanced Land Imager calibration and performance overview

The pre-launch measurements and test required for calibration and characterization of the advanced land imager (ALI), which will be flown on NASAs EO-1 mission, have been completed. The instrument level performance testing was conducted at MIT Lincoln Laboratory with the ALI in an operational environment. The overall calibration strategy, which includes both pre-launch and post-launch components, will be described in this paper. The fundamental sensor calibration data comprise five measurement categories: angular position in object space for each pixel; normalized spectral response functions; response coefficients; zero signal offsets; and modulation transfer functions. Performance and characterization test include measurements of noise, SNR, linearity, repeatability, image artifacts, stray light rejection, and cross-talk. An overview of the facilities, equipment, tests and results is presented here.

Summary of the EO-1 ALI performance during the first 2.5 years on-orbit

The Advanced Land Imager (ALI) is a VNIR/SWIR, pushbroom instrument that is flying aboard the Earth Observing-1 (EO-1) spacecraft. Launched on November 21, 2000, the objective of the ALI is to flight validate emerging technologies that can be infused into future land imaging sensors. During the first two and one-half years on-orbit, the performance of the ALI has been evaluated using on-board calibrators and vicarious observations. The results of this evaluation are presented here. The spatial performance of the instrument, derived using stellar, lunar, and bridge observations, is summarized. The radiometric stability of the focal plane and telescope, established using solar, lunar, ground truth, and on-board sources, is also provided.

Flight Test Results of the Earth Observing-1 Advanced Land ImagerAdvanced Land Imager

The Advanced Land Imager (ALI) is the primary instrument on the Earth Observing-1 spacecraft (EO-1) and was developed under NASAs New Millennium Program (NMP). The NMP mission objective is to flight-validate advanced technologies that will enable dramatic improvements in performance, cost, mass, and schedule for future, Landsat-like, Earth Science Enterprise instruments. ALI contains a number of innovative features designed to achieve this objective. These include the basic instrument architecture, which employs a push-broom data collection mode, a wide field-of-view optical design, compact multi-spectral detector arrays, non-cryogenic HgCdTe for the short wave infrared bands, silicon carbide optics, and a multi-level solar calibration technique. The sensor includes detector arrays that operate in ten bands, one panchromatic, six VNIR and three SWIR, spanning the range from 0.433 to 2.35 μm. Launched on November 21, 2000, ALI instrument performance was monitored during its first year on orbit using data collected during solar, lunar, stellar, and earth observations. This paper will provide an overview of EO-1 mission activities during this period. Additionally, the on-orbit spatial and radiometric performance of the instrument will be compared to pre-flight measurements and the temporal stability of ALI will be presented.