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 ALI's 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%.
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.
The Robotic Lunar Observatory (ROLO) project has developed a spectral irradiance model of the Moon that accounts for variations with lunar phase through the bright half of a month, lunar librations, and the location of an Earth-orbiting spacecraft. The methodology of comparing spacecraft observations of the Moon with this model has
been developed to a set of standardized procedures so that comparisons can be readily made. In the cases where observations extend over several years (e.g., SeaWiFS), instrument response degradation has been determined with precision of about 0.1% per
year. Because of the strong dependence of lunar irradiance on geometric angles, observations by two spacecraft cannot be directly compared unless acquired at the same time and location. Rather, the lunar irradiance based on each spacecraft instrument calibration can be compared with the lunar irradiance model. Even single observations by an instrument allow inter-comparison of its radiometric scale with
other instruments participating in the lunar calibration program. Observations by SeaWiFS, ALI, Hyperion and MTI are compared here.
The Advanced Land Imager (ALI) is the primary instrument on the Earth Observing-1 spacecraft (EO-1) and was developed under NASA's 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.
The Advanced Land Imager (ALI) is the primary instrument flown on the first Earth Observing mission (EO-1), launched on November 21, 2000. It was developed under NASA's 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. During the first ninety days on orbit, the instrument performance was evaluated by collecting several Earth scenes and comparing them to identical scenes obtained by Landsat7. In addition, various on-orbit calibration techniques were exercised. This paper will present an overview of the EO-1 mission activities during the first ninety days on-orbit, details of the ALI instrument performance and a comparison with the ground calibration measurements.
An Advanced Land Imager (ALI) will be flown on the first Earth Observing mission (EO-1) under NASA's 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.
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.
The pre-launch measurements and test required for calibration and characterization of the advanced land imager (ALI), which will be flown on NASA's 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.
The spectral response of the Earth Observing 1 Advanced Land Imager (ALI) has been characterized at Lincoln Laboratory as a fully assembled instrument in a thermal vacuum chamber at operational temperatures. The focal pane for this instrument is partially populated over a 3 degree cross-track segment with 9 multispectral bands having a 30-meter ground sample distance (GSD) and a single panchromatic band having a 10- meter GSD. These bands were selected to mimic the six Landsat-7 VNIR/SWIR bands with three additional bands covering 0.433-0.453, 0.845-0.890, 1.20-1.30 micrometers . The instrument system level response was characterized spectrally form 400-900 nm in 2 nm increments and from 900- 2500 nm in 4 nm increments using a collimated monochromatic beam. Spectral artifacts introduced by the monochromatic and the collimator were accounted for using spectrally calibrated silicon and lead-sulfide detector which sampled the beam at each measurement interval. In this paper we describe the techniques employed during spectral calibration, present the measured in band and out of band spectral response for all VNIR bands, and compare the results to those obtained at the component level.
The performance assessment of the EO-1 Advanced Land Imager (ALI) requires software for processing data collected during sensor integration and test, ground calibration, and on- orbit operations. This paper describes the software developed for performance assessment processing and analysis of data collected on the ground during ALI and ground calibration. This involves various characterizations and calibrations of the ALI, including functional test, focus, MTF, radiometric response, spectral response, functional image reconstruction, and internal calibration lamp data processing. Processing examples are given, including results. Also, each section describes the use of this software to support the analysis of data collected on-orbit during mission operations, as well as the types of data to be collected and processed. The interface between MIT Lincoln Laboratory and the EO-1 Mission Operations Center at NASA Goddard Space Flight Center is also described.
Spatial calibrations have been performed on the Advanced Land Imager (ALI) of the EO-1 satellite. Topics discussed in this paper include end-to-end imaging test, measurements of system modulation transfer function (MTF), and pixel lines of sight. The MTF measurements were made by recording scans of a knife-edge past the pixels. The techniques used to place the focal plane at the correct focal position are described, since they make use of MTF measurements. Line-of- sight measurements combine theodolite measurements of the telescope distortions and the photolithographic patterns of the detector arrays with images of a stationary Ronchi ruling recorded with the instrument at its normal operating conditions in a thermal vacuum chamber.
The calibration and performance assessment of the Earth Observing-1 (EO-1) Advanced Land Imager (ALI) required a ground data system for acquiring and processing ALI data. In order to meet tight schedule and budget requirements, an automated system was developed that could be run by a single operator. This paper describes the overall system and the individual Electrical Ground Support Equipment (EGSE) and computer components used. The ALI Calibration Control Node (ACCN) serves as a test executive with a single graphical user interface to the system, controlling calibration equipment and issuing data acquisition and processing requests to the other EGSE and computers. EGSE1, a custom data acquisition syste, collects ALI science data and also passes ALI commanding and housekeeping telemetry collection requests to EGSE2 and EGSE3 which are implemented on an ASIST workstation. The performance assessment machine, stores and processes collected ALI data, automatically displaying quick-look processing results. The custom communications protocol developed to interface these various machines and to automate their interactions is described, including the various modes of operation needed to support spatial, radiometric, spectral, and functional calibration and performance assessment of the ALI.
The EO-1 Advanced Land Imager (ALI) is the first earth- orbiting instrument to be flown under NASA's 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.
The EO-1 Advanced Land Imager (ALI) is the first earth- orbiting instrument to be flown under NASA's 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 at a substantial cost saving. This paper provides an overview of ground calibration and performance assessment of the ALI. Included are techniques for calibrating and assessing spatial, spectral, and radiometric parameters for this instrument. Additionally, the pre-flight technique used to verify in-flight solar calibration is discussed.
Results of the first CCD observations of the x-ray background between 0.2 and 10 keV are presented. Data were obtained from individual sounding rocket flights on May 22, 1995 from White Sands, New Mexico and on October 25, 1995 from Woomera, Australia. The target for the second flight was a bright region of the 3/4 keV x-ray background centered at 0 degree longitude and minus 15 degrees latitude in galactic coordinates. Covering approximately 1800 square degrees, this feature dominates all-sky surveys below the galactic plane from 0.5 to 1.5 keV. This data is compared with data from a dim region of the 3/4 keV x-ray background in the constellation Draco, obtained on the first flight. The detector for these flights was a thin gate CCD built by EEV and designed to maximize x-ray response below 0.75 keV without adopting a backside illumination scheme. Improved quantum efficiency over conventional x-ray CCDs above 1 keV was also achieved due to the high resistivity (1500 ohm-cm) of this device. This type of CCD was flown on the CUBIC experiment in November 1996. Similar devices are also scheduled to be launched on Leicester University's spectrum X/JET-X and XMM/EPIC instruments.
The cosmic unresolved background instrument using CCDs (CUBIC) was scheduled for launch on the Argentine/U.S. SAC-B satellite in October 1996. This instrument is designed to perform moderate resolution nondispersive x-ray spectroscopy of the diffuse x-ray background over the band 0.2 - 10.0 keV using state-of-the-art photon-counting CCDs. The instrument is optimized for spectroscopy of diffuse emission with a field of view approximately 5 degrees multiplied by 5 degrees below 1 keV and 10 degrees multiplied by 10 degrees above 3 keV. Here we discuss the present state of analysis of our preflight calibration data and present preliminary operational plans.
The cosmic unresolved background instrument using CCDs (CUBIC) is currently scheduled for launch on the Argentine/US SAC-B satellite late this year. This instrument is designed to perform moderate resolution nondispersive x-ray spectroscopy of the diffuse x-ray background over the band 0.2 - 10.0 keV using state-of-the-art photon-counting CCDs. The instrument is optimized for spectroscopy of diffuse emission with a field of view of 5 degrees by 5 degrees below 1 keV and 10 degrees by 10 degrees above 3 keV. Observations will typically last 1 - 3 days, and will obtain high quality CCD spectra of the diffuse background, nearby superbubbles and supernova remnants, and the brightest x-ray point sources. This paper gives an overview of the instrument design and CCD detectors.
CUBIC, the cosmic unresolved x ray background instrument using CCDs, is instrumented to make moderate resolution x-ray spectral measurements of diffuse targets at spatial scales of a few degrees. While the energy range is nominally 200 eV - 10 keV, the CCDs have been designed to maximize the soft x ray performance by using novel structures. A two part aperture increases the area-solid angle product above 1 keV to maximize sensitivity to the cosmic component of the diffuse x ray background. Here we report preliminary results of our preflight laboratory calibrations performed at Penn State of the dark current, readnoise, nonlinearity, charge transfer efficiency, energy resolution, and quantum efficiency of the two flight CCDs. We also discuss calibration of the detector field of view and the preliminary area-solid angle product of the instrument.
The Cosmic Unresolved X-ray Background InsLrumenl using CCDs (CUBIC ) is designed to obtain spectral observations of the Diffuse X-ray Background (DXRB) with moderate spectral resolution (E/E 10—60) over the energy range 0.2 — 10 keV using mechanically collimated CCDs. It will be launched on the NASA/Argentine minisat SA C-B in December 1994. At this time, it is the only planned satellite payload devoted to the study of the spectrum of the DXRB. Observations will consist of 1—2 day pointed exposures of each target direction, resulting in a series of high quality spectra. Over the anticipated 3 year lifetime of the satellite, CUBIC will be able to study up to 50% of the sky with 5° x 5° spatial resolution for the subkilovolt Galactic diffuse background, and with 1O x 1O spatial resolution for the extragalactic diffuse background above 2 keV. CUBIC will obtain high quality non-dispersive spectra of soft X-ray emission from the interstellar medium, supernova remnants, and some bright sources, and will make a sensitive search for line emission or other features in the extragalactic cosmic X-ray background from 2 — 10 keY