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Elliott, Denis

Publications and source records attributed to Elliott, Denis.

10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Comparison of the AIRS, IASI, and CrIS 900 cm-1 Channel for Dome Concordia

We compare AIRS, IASI-A and CrIS under the cold conditions encountered in the daily overpasses of Dome Concordia, which is located on a high plateau in Antarctica, between May 2012 and March 2016. The brightness temperatures at DomeC for the 900 cm-1 atmospheric window channel is 218K on average, but varies seasonally from 185K to 255K. Averaged over all simultaneous overpass data AIRS is 26±13 mK warmer than IASI-A, AIRS is 116±7 mK colder than CrIS. However, we find that differences for both AIRS/IASI-A and AIRS/CrIS are temperature dependent, with AIRS being 250mK colder than IASI-A at 200K. These effects have been independently verified by other investigators. AIRS and CrIS bt900 results for simultaneous overpasses and daily mean values agree within 100 mK. AIRS and IASI simultaneous overpasses agree within 100 mK, but AIRS is 2K warmer than IASI for daily mean values. We attribute this effect to an overactive IASI QC which is sensitive to scene temperature above about 240K. The DomeC data do not reveal if this QC effect is present at temperatures warmer than 255K. These effects need to be taken into account when comparing results from AIRS, IASI and CrIS, and even more so when analyzing data from vintage instruments with respect to climate change.

Aumann, H.H.↗
NASA NTRS2016

Comparison of the AIRS, IASI, and CrIS 900 cm-1 channel for Dome Concordia

We compare AIRS, IASI-A and CrIS under the cold conditions encountered in the daily overpasses of Dome Concordia, which is located on a high plateau in Antarctica, between May 2012 and March 2016. The brightness temperatures at DomeC for the 900 cm-1 atmospheric window channel is 218K on average, but varies seasonally from 185K to 255K. Averaged over all simultaneous overpass data AIRS is 26±13 mK warmer than IASI-A, AIRS is 116±7 mK colder than CrIS. However, we find that differences for both AIRS/IASI-A and AIRS/CrIS are temperature dependent, with AIRS being 250mK colder than IASI-A at 200K. These effects have been independently verified by other investigators. AIRS and CrIS bt900 results for simultaneous overpasses and daily mean values agree within 100 mK. AIRS and IASI simultaneous overpasses agree within 100 mK, but AIRS is 2K warmer than IASI for daily mean values. We attribute this effect to an overactive IASI QC which is sensitive to scene temperature above about 240K. The DomeC data do not reveal if this QC effect is present at temperatures warmer than 255K. These effects need to be taken into account when comparing results from AIRS, IASI and CrIS, and even more so when analyzing data from vintage instruments with respect to climate change.

Elliott, Denis↗
NASA NTRS2012

Performance status of the Atmospheric Infrared Sounder ten years after launch

The Atmospheric Infrared Sounder (AIRS) is a hyperspectral infrared instrument on the EOS Aqua Spacecraft, launched on May 4, 2002. AIRS has 2378 infrared channels ranging from 3.7 μm to 15.4 μm and a 13.5 km footprint at nadir. The AIRS is a “facility” instrument developed by NASA as an experimental demonstration of advanced technology for remote sensing and the benefits of high resolution infrared spectra to science investigations. AIRS, in conjunction with the Advanced Microwave Sounding Unit (AMSU), produces temperature profiles with 1K/km accuracy on a global scale, as well as water vapor profiles and trace gas amounts for CO2, CO, SO2, O3 and CH4. AIRS data are used for weather forecasting, climate process studies and validating climate models. The AIRS instrument has far exceeded its required design life of 5 years, with over 10 years of operations as of September 2012. While the instrument has performed exceptionally well, with little signs of wear, the AIRS Project continues to monitor and maintain the health of AIRS, characterize its behavior and improve performance where possible. Radiometric stability has been monitored and trending shows better than 16 mK/year stability. Spectral calibration stability is better than 1 ppm/year, and a new gain table was recently uploaded to recover 100 significantly degraded or dead channels by switching to their redundant counterpart. At this time we expect the AIRS to continue to perform well for the next decade.

Strow, Larrabee↗
NASA NTRS2008

Cross Calibration and Validation Using CLARREO

The presentation focuses on study questions, effort, and result. Study questions include a focus on MW/LW, error sources and what can be expected, how validation will be performed and what resolution is required, and spatial resolution required for cross-calibration. Study effort includes empirical approach by examining AIRS ,IASI and MODIS cross-calibration methods already in place and estimate the number of clear and Dome C observations possible versus spatial resolution. Study results include 5000 sampler per cross-calibration recommended, insufficient cloud free and Dome C AWS observations for cross calibration and validation at 100km, and less than 20 km IFOV at 100 km swath needed to achieve sufficient samples for cross-calibration of CLARREO.

calibration↗
NASA NTRS2006

Three Years of Atmospheric Infrared Sounder Radiometric Calibration Validation using Sea Surface Temperatures

This paper evaluates the absolute accuracy and stability of the radiometric calibration of the Atmospheric Infrared Sounder (AIRS) by analyzing the difference between the brightness temperatures measured at 2616 cm(exp -1) and those calculated at the top of the atmosphere (TOA), using the Real-Time Global Sea Surface Temperature (RTGSST) for cloud-free night tropical oceans between +/- 30 degrees latitude. The TOA correction is based on radiative transfer. The analysis of the first 3 years of AIRS radiances verifies the absolute calibration at 2616 cm(exp -1) to better than 200 mK, with better than 16 mK/yr stability. The AIRS radiometric calibration uses an internal full aperture wedge blackbody with the National Institute of Standards and Technology (NIST) traceable prelaunch calibration coefficients. The calibration coefficients have been unchanged since launch. The analysis uses very tight cloud filtering, which selects about 7000 cloud-free tropical ocean spectra per day, about 0.5% of the data. The absolute accuracy and stability of the radiometry demonstrated at 2616 cm(sup -1) are direct consequences of the implementation of AIRS as a thermally controlled, cooled grating-array spectrometer and meticulous attention to details. Comparable radiometric performance is inferred from the AIRS design for all 2378 channels. AIRS performance sets the benchmark for what can be achieved with a state-of-the-art hyperspectral radiometer from polar orbit and what is expected from future hyperspectral sounders. AIRS was launched into a 705 km altitude polar orbit on NASA's Earth Observation System (EOS) Aqua spacecraft on 4 May 2002. AIRS covers the 3.7-15.4 micron region of the thermal infrared spectrum with a spectral resolution of nu/Delta nu = 1200 and has returned 3.7 million spectra of the upwelling radiance each day since the start of routine data gathering in September 2002.

climate↗
NASA NTRS2006

Four Years of Absolutely Calibrated Hyperspectral Data from the Atmospheric Infrared Sounder (AIRS) on the Eos Aqua

This viewgraph presentation reviews four years of absolute calibration of hyperspectral data from the AIRS instrument located on the EOS AQUA spacecraft. The following topics are discussed: 1) A quick overview of AIRS; 2) What absolute calibration accuracy and stability are required for climate applications?; 3) Validating of radiance accuracy and stability: Results from four years of AIRS data; and 4) Conclusions.

infrared↗
NASA NTRS2006

AIRS Science Accomplishments Version 4.0/Plans for Version 5

This talk is about accomplishments with AIRS data and what we have learned from almost three years of data what part of this is emerging in Version 4.0 what part we would like to see filtering into Version 5.0 and what part constitute limitations in the AIRS requirements, such as spectral and spatial resolution, which have to be deferred to the wish list for the next generation hyperspectral sounder. The AIRS calibration accuracy at the 1OOmK and stability at the 6 mK/year level are amazing. It establishes the unique capability of a cooled grating array spectrometer in Earth orbit for climate research. Data which are sufficiently clear to match the radiometric accuracy of the instrument, have a yield of less than 1%. This is OK for calibration. The 2616/cm window channel combined with the RTG.SST for tropical ocean allow excellent assessment radiometric calibration accuracy and stability. For absolute calibration verification 100mK is the limit due to cloud contamination. The 10 micron window channels can be used for stability assessment, but accuracy is limited at 300mK due to water continuum absorption uncertainties.

lessons learned↗
NASA NTRS2005

AIRS radiometric calibration validation for climate research

Climate research using data from satellite based radiometers makes extreme demands on the traceability and stability of the radiometric calibration. The selection of a cooled grating array spectrometer for the Atmospheric Infrared Sounder, AIRS, is key, but does not ensured that AIRS data will be of climate quality. Additional design features, plus additional pre-launch testing, and extensive on-orbit calibration subsystem monitoring beyond what would suffice for application of the data to weather forecasting were required to ensure the radiometric data quality required for climate research. Validation that climate data quality are being generated makes use of the sea surface skin temperatures (SST and (obs-calc).

calibration↗
NASA NTRS2005

AIRS Infrared Polarization Sensitivity and In-Flight Observations

The Atmospheric Infrared Sounder (AIRS) is a space-based instrument that measures the upwelling atmospheric spectrum in the infrared. AIRS is one of several instruments on the EOS-Aqua spacecraft launched on May 4, 2002: Typically, instrument polarization is not a concern in the infrared because the scene is usually not significantly polarized. A small amount of polarization is expected over ocean, which can be seen in the AIRS 3.7 (micro)m window channels. The polarization is seen as a signal difference between two channels with the same center frequency but different polarizations. The observations are compared to a model that relies on measurements of instrument polarization made pre-flight. A first look at a comparison of the observations of sea surface polarization to expectations is presented.

infrared↗