Publications

The Advanced Land Imager (ALI) is one of three instruments flown on the first Earth Observing mission (EO-1) under NASA's New Millennium Program (NMP). The primary 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 remote sensing instruments. ALI contains a number of innovative features, including all the Category 1 technology demonstrations of the EO-1 mission. These include the basic instrument architecture which employs a push-broom data collection mode, a wide field of view optical design, compact multispectral detector arrays, non-cryogenic HgCdTe for the short wave infrared bands, silicon carbide optics and a multi-level solar calibration technique. The Earth Observing-1 spacecraft was successfully launched on November 21, 2000. During the first sixty days on orbit, several Earth scenes were collected and on-orbit calibration techniques were exercised by the Advanced Land Imager. This paper presents the status of ALI radiometric performance characterization obtained from the data collected during that period.

The process of formulating a remote sensing instrument design from a set of observational requirements involves a series of trade studies during which judgments are made between available design options. The outcome of this process is a system architecture which drives the size, weight, power consumption, cost, and technological risk of the instrument. In this paper, a set of trade studies are described which guided the development of a baseline sensor design to provide vertical profiles (soundings) of atmospheric temperature and humidity from future Geostationary Operational Environmental Satellite (GOES) platforms. Detailed trade studies presented include the choice between an interferometric versus a dispersive spectrometer, the optical design of the IR interferometer and visible imaging channel, the optimization of the instrument spatial response, the selection of detector array materials, operating temperatures, and array size, the thermal design for detector and optics cooling, and the electronics required to process detected interferograms into spectral radiance. The trade study process was validated through simulations of the radiometric performance of the instrument, and through simulated retrievals of vertical profiles of atmospheric temperature and humidity. The flexibility of these system trades is emphasized, highlighting the differing outcomes that occur from this process as system requirements evolve. Observations are made with respect to the reliability and readiness of key technologies. The results of this study were disseminated to industry to assist their interpretation of, and responses to, system requirements provided by the U.S. Government.

The EO-1 Advanced Land Imager (ALI) is the first earth-orbiting instrument to be flown under NASA's New Millenium 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 an overview of in-flight calibration and performance assessment of the Advanced Land Imager. Included are 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 reference scenes, and solar and lunar observations.

Optimal Doppler velocity estimation is explored for a standard Gaussian signal measurement model and thematic maximum likelihood (ML) and Bayes estimation. Because the model considered depends on a vector parameter (velocity, spectrum width (SW), and signal-to-noise ratio (SNR), the exact formulation of an ML or Bayes solution involves a system of coupled equations which cannot be made explicit for any of the parameters. In the past, iterative methods have been suggested for solving the required equations. In addition to being computationally intensive, it is unclear whether an iterative method can be constructed to converge well under general conditions. Simple computational forms are shown to exist when SW and SNR are assumed known. An information theoretic concept is used to propose an adaptive extension of these equations to the general case of SW and SNR unknown. This new idea is developed to the poise of operational application. A Monte Carlo simulations experiment is used to verify that the method can work; the example presented considers the particularly difficult situation of no a priori information for either SW or SNR under the additional constraint of a very small (20 pulse samples) sample size. The improved performance of this new Doppler velocity estimator is documented by comparison with derived optimal bounds and with the performance of the well-known pulse pair (PP) method. Small-sample estimator statistics are presented; and Bayes estimator results, assuming known SW and SNR, are used to provide true performance bounds for comparison. Cramer-Rao (CR) bounds are also derived and shown to be inferior to the Bayes bounds in the small sample case considered.