The CLARREO mission addresses the need to provide accurate, broadly acknowledged climate records that can be used
to validate long-term climate projections that become the foundation for informed decisions on mitigation and adaptation
policies. The CLARREO mission accomplishes this critical objective through rigorous SI traceable decadal change
observations that will reduce the key uncertainties in current climate model projections. These same uncertainties also
lead to uncertainty in attribution of climate change to anthropogenic forcing. CLARREO will make highly accurate and
SI-traceable global, decadal change observations sensitive to the most critical, but least understood climate forcing,
responses, and feedbacks. The CLARREO breakthrough is to achieve the required levels of accuracy and traceability to
SI standards for a set of observations sensitive to a wide range of key decadal change variables. The required accuracy
levels are determined so that climate trend signals can be detected against a background of naturally occurring
variability. The accuracy for decadal change traceability to SI standards includes uncertainties associated with
instrument calibration, satellite orbit sampling, and analysis methods. Unlike most space missions, the CLARREO
requirements are driven not by the instantaneous accuracy of the measurements, but by accuracy in the large time/space
scale averages that are necessary to understand global, decadal climate changes.
The ultimate remote sensing benefits of the high resolution Infrared radiance spectrometers will be realized with
their geostationary satellite implementation in the form of imaging spectrometers. This will enable dynamic
features of the atmosphere's thermodynamic fields and pollutant and greenhouse gas constituents to be observed
for revolutionary improvements in weather forecasts and more accurate air quality and climate predictions. As
an important step toward realizing this application objective, the Geostationary Imaging Fourier Transform
Spectrometer (GIFTS) Engineering Demonstration Unit (EDU) was successfully developed under the NASA
New Millennium Program, 2000-2006. The GIFTS-EDU instrument employs three focal plane arrays (FPAs),
which gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral
bands. The GIFTS calibration is achieved using internal blackbody calibration references at ambient (260
K) and hot (286 K) temperatures. In this paper, we introduce a refined calibration technique that utilizes
Principle Component (PC) analysis to compensate for instrument distortions and artifacts, therefore, enhancing
the absolute calibration accuracy. This method is applied to data collected during the GIFTS Ground Based
Measurement (GBM) experiment, together with simultaneous observations by the accurately calibrated AERI
(Atmospheric Emitted Radiance Interferometer), both simultaneously zenith viewing the sky through the same
external scene mirror at ten-minute intervals throughout a cloudless day at Logan Utah on September 13, 2006.
The accurately calibrated GIFTS radiances are produced using the first four PC scores in the GIFTS-AERI
regression model. Temperature and moisture profiles retrieved from the PC-calibrated GIFTS radiances are
verified against radiosonde measurements collected throughout the GIFTS sky measurement period. Using the
GIFTS GBM calibration model, we compute the calibrated radiances from data collected during the moon
tracking and viewing experiment events. From which, we derive the lunar surface temperature and emissivity
associated with the moon viewing measurements.
The ultimate remote sensing benefits of the high resolution Infrared radiance spectrometers will be realized with
their geostationary satellite implementation in the form of imaging spectrometers. This will enable dynamic
features of the atmosphere's thermodynamic fields and pollutant and greenhouse gas constituents to be observed
for revolutionary improvements in weather forecasts and more accurate air quality and climate predictions.
As an important step toward realizing this application objective, the Geostationary Imaging Fourier Transform
Spectrometer (GIFTS) Engineering Demonstration Unit (EDU) was successfully developed under the NASA New
Millennium Program, 2000-2006. The GIFTS-EDU instrument employs three focal plane arrays (FPAs), which
gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral bands.
The raw GIFTS interferogram measurements are radiometrically and spectrally calibrated to produce radiance
spectra, which are further processed to obtain atmospheric profiles via retrieval algorithms. The radiometric
calibration is achieved using internal blackbody calibration references at ambient (260 K) and hot (286 K)
temperatures. The absolute radiometric performance of the instrument is affected by several factors including
the FPA off-axis effect, detector/readout electronics induced nonlinearity distortions, and fore-optics offsets.
The GIFTS-EDU, being the very first imaging spectrometer to use ultra-high speed electronics to readout
its large area format focal plane array detectors, operating at wavelengths as large as 15 microns, possessed
non-linearity's not easily removable in the initial calibration process. In this paper, we introduce a refined
calibration technique that utilizes Principle Component (PC) analysis to compensate for instrument distortions
and artifacts remaining after the initial radiometric calibration process, thus, further enhance the absolute
calibration accuracy. This method is applied to data collected during an atmospheric measurement experiment
with the GIFTS, together with simultaneous observations by the accurately calibrated AERI (Atmospheric
Emitted Radiance Interferometer), both simultaneously zenith viewing the sky through the same external scene
mirror at ten-minute intervals throughout a cloudless day at Logan Utah on September 13, 2006. The PC vectors
of the calibrated radiance spectra are defined from the AERI observations and regression matrices relating the
initial GIFTS radiance PC scores to the AERI radiance PC scores are calculated using the least squares inverse
method. A new set of accurately calibrated GIFTS radiances are produced using the first four PC scores in
the regression model. Temperature and moisture profiles retrieved from the PC-calibrated GIFTS radiances are
verified against radiosonde measurements collected throughout the GIFTS sky measurement period.
The Geosynchronous Imaging Fourier Transform Spectrometer (GIFTS) Sensor Module (SM) Engineering Demonstration
Unit (EDU) is a high resolution spectral imager designed to measure infrared (IR) radiances using a
Fourier transform spectrometer (FTS). The GIFTS instrument employs three focal plane arrays (FPAs), which
gather measurements across the long-wave IR (LWIR), short/mid-wave IR (SMWIR), and visible spectral bands.
The raw interferogram measurements are radiometrically and spectrally calibrated to produce radiance spectra,
which are further processed to obtain atmospheric profiles via retrieval algorithms. This paper describes the
GIFTS SM EDU Level 1B algorithms involved in the calibration. The GIFTS Level 1B calibration procedures
can be subdivided into four blocks. In the first block, the measured raw interferograms are first corrected for
the detector nonlinearity distortion, followed by the complex filtering and decimation procedure. In the second
block, a phase correction algorithm is applied to the filtered and decimated complex interferograms. The resulting
imaginary part of the spectrum contains only the noise component of the uncorrected spectrum. Additional
random noise reduction can be accomplished by applying a spectral smoothing routine to the phase-corrected
spectrum. The phase correction and spectral smoothing operations are performed on a set of interferogram
scans for both ambient and hot blackbody references. To continue with the calibration, we compute the spectral
responsivity based on the previous results, from which, the calibrated ambient blackbody (ABB), hot blackbody
(HBB), and scene spectra can be obtained. We now can estimate the noise equivalent spectral radiance (NESR)
from the calibrated ABB and HBB spectra. The correction schemes that compensate for the fore-optics offsets
and off-axis effects are also implemented. In the third block, we developed an efficient method of generating
pixel performance assessments. In addition, a random pixel selection scheme is designed based on the pixel
performance evaluation. Finally, in the fourth block, the single pixel algorithms are applied to the entire FPA.
Designed to fulfill a critical inspection need for the Space Shuttle Program, the EVA IR Camera System can detect crack and subsurface defects in the Reinforced Carbon-Carbon (RCC) sections of the Space Shuttle's Thermal Protection System (TPS). The EVA IR Camera performs this detection by taking advantage of the natural thermal gradients induced in the RCC by solar flux and thermal emission from the Earth.
This instrument is a compact, low-mass, low-power solution (1.2cm3, 1.5kg, 5.0W) for TPS inspection that exceeds existing requirements for feature detection. Taking advantage of ground-based IR thermography techniques, the EVA IR Camera System provides the Space Shuttle program with a solution that can be accommodated by the existing inspection system. The EVA IR Camera System augments the visible and laser inspection systems and finds cracks and subsurface damage that is not measurable by the other sensors, and thus fills a critical gap in the Space Shuttle's inspection needs. This paper discusses the on-orbit RCC inspection measurement concept and requirements, and then presents a detailed description of the EVA IR Camera System design.
Designed to fulfill a critical inspection need for the Space Shuttle Program, the Infrared On-orbit RCC Inspection System (IORIS) can detect crack and surface defects in the Reinforced Carbon-Carbon (RCC) sections of the Space Shuttle’s Thermal Protection System (TPS). IORIS performs this detection by taking advantage of the natural thermal gradients induced in the RCC by solar flux and thermal emission from the Earth. IORIS is a compact, low-mass, low-power solution (1.2cm3, 1.5kg, 5.0W) for TPS inspection that exceeds existing requirements for feature detection. Taking advantage of ground-based IR thermography techniques, IORIS provides the Space Shuttle program with a solution that can be accommodated by the existing inspection system. IORIS augments the visible and laser inspection systems and finds cracks that are not easily measurable by the other sensors, and thus fills a critical gap in the Space Shuttle’s inspection needs. Based on crack IR signature predictions and on-orbit gradient expectations, IORIS can achieve crack detection over approximately 96% of the wing-leading edge RCC (using multiple inspections in an orbit period). This paper discusses the on-orbit RCC inspection measurement concept and requirements, and then presents a detailed description of the IORIS design.
A new high spectral resolution (0.25 cm-1) and high spatial resolution (2.6 km) scanning (46 km swath width) Fourier Transform Spectrometer (FTS) has been built for flight on NASA high altitude (approximately 20 km) aircraft. The instrument, called the NPOESS Aircraft Sounding Testbed- Interferometer (NAST-I), has been flown during several field campaigns to provide experimental observations needed to finalize specifications and to test proposed designs for future satellite instruments; specifically, the Cross-track Infrared Sounder (CrIS) to fly on the National Polar-orbiting Operational Environmental Satellite System (NPOESS). NAST-I provides new and exciting observations of mesoscale structure of the atmosphere, including the fine scale thermodynamic characteristics of hurricanes. The NAST-I instrument is described, its excellent spectral and radiometric performance is demonstrated, and surface and atmospheric remote sensing results obtained during airborne measurement campaigns are presented.
NAST-1 is a Fourier transform interferometric sounder that provides very high spectral and spatial resolution measurements of the Earth's atmosphere. The interferometer provides two dimensional, low noise data from the NASA ER-2 aircraft suitable for synthesizing data products of future satellite-borne sounding instrument candidates. It is the first such high altitude aircraft or satellite borne instrument. The instrument provides a 2.6 km nadir footprint and a cross-track field of regard of +/- 48.2 degrees. The instrument has a continuous spectral range of 3.6-16.1 micrometers , spectral resolution of 0.25 cm-1, and radiometric noise on the order of 0.25 K. NAST-1 has proven to be an extremely reliable instrument generating over 100 hours of high-quality flight data, and was delivered to the sponsor on a very tight schedule. Using a first principles model, the noise performance of the instrument was modeled and found to be in close agreement with noise measured in- flight. Alignment jitter has been identified as the major contributor to the system NEdN. This paper describes the mode used to predict the instrument noise performance and discusses the comparison to actual flight data.
KEYWORDS: Interferometers, Optical filters, Calibration, Signal processing, Mirrors, Digital signal processing, Black bodies, Filtering (signal processing), Satellites, Data acquisition
As a testbed to evaluate instrument specifications and data reduction techniques for future satellite atmospheric sounders, an airborne Fourier transform interferometer sounder has been developed for the National Polar-orbiting Operational Environmental Satellite System (NPOESS). The NPOESS Airborne Sounder Testbed Interferometer (NAST-I) collects atmospheric sounding from NASA's high-altitude ER-2 aircraft. Flown at a nominal 20km altitude, collected data is meant to simulate spaceborne atmospheric sounding. The NAST interferometer generates high quality interferograms over the 3.7-16.1 micrometers IR range with a resolution of 0.25cm-1. Interferograms are collected in real-time by an embedded TI TMS320C32 digital signal processing chip housed in an industrial grade 133MHz Pentium PC. Three channels of analog interferogram data and one channel of telemetry data are acquired by four, 16-bit analog to digital converters. Oversampling and decimation are then used to produce high-fidelity samples at a reduced rate and to relax analog filter design requirements. This paper focuses on the signal processing aspects of the instrument and discuss test flight data collected during the instrument's initial flight test.
KEYWORDS: Systems modeling, Time metrology, Model-based design, Manufacturing, Statistical analysis, Matrices, Error analysis, Automotive electronic systems, Electronic circuits, Process control
Fault detection or condition monitoring is critical to the safe and reliable operation of today's complex automatic production systems. This paper describes an approach which performs condition monitoring of production lines based on a max-plus model of the event-time dynamics. In particular, this work pertains to discrete part manufacturing systems such as automotive assembly lines or electronic circuit board lines where the dynamics are governed by the action of certain events, e.g., the processing of a part by a machine or the departure of a part from a buffer. A state model of the event-time dynamics, based in the max-plus algebra, is used to emulate the nominal operation of a production line. The machine completion times are taken as the states of the model. Since only output measurements of the production line are available, an observer is needed to provide estimates of the machine completion times. Because of the nature of the max-plus algebra, a recursive state observer is not obtainable; instead, a block-form state observer is used to update the model state on a periodic basis. A timing residual is formed using the outputs of the model and the output measurements of the plant. The residual is then analyzed using standard statistical process control techniques to detect failures. Simulation results for a simple production line illustrate the approach. The novelties of this approach are the introduction of an event- time observer and the application of the observer to the problem of condition monitoring.
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