A ground-based Fourier transform spectrometer has been developed to measure the atmospheric downwelling infrared radiance spectrum at the earth's surface with high absolute accuracy. The Atmospheric ...Emitted Radiance Interferometer (AERI) instrument was designed and fabricated by the University of Wisconsin Space Science and Engineering Center (UW-SSEC) for the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program. This paper emphasizes the key features of the UW-SSEC instrument design that contribute to meeting the AERI instrument requirements for the ARM Program. These features include a highly accurate radiometric calibration system, an instrument controller that provides continuous and autonomous operation, an extensive data acquisition system for monitoring calibration temperatures and instrument health, and a real-time data processing system. In particular, focus is placed on design issues crucial to meeting the ARM requirements for radiometric calibration, spectral calibration, noise performance, and operational reliability. The detailed performance characteristics of the AERI instruments built for the ARM Program are described in a companion paper. PUBLICATION ABSTRACT
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Abstract
The Atmospheric Emitted Radiance Interferometer (AERI) instrument was developed for the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program by the University of ...Wisconsin Space Science and Engineering Center (UW-SSEC). The infrared emission spectra measured by the instrument have the sensitivity and absolute accuracy needed for atmospheric remote sensing and climate studies. The instrument design is described in a companion paper. This paper describes in detail the measured performance characteristics of the AERI instruments built for the ARM Program. In particular, the AERI systems achieve an absolute radiometric calibration of better than 1% (3σ) of ambient radiance, with a reproducibility of better than 0.2%. The knowledge of the AERI spectral calibration is better than 1.5 ppm (1σ) in the wavenumber range 400– 3000 cm−1.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A global database of infrared (IR) land surface emissivity is introduced to support more accurate retrievals of atmospheric properties such as temperature and moisture profiles from multispectral ...satellite radiance measurements. Emissivity is derived using input from the Moderate Resolution Imaging Spectroradiometer (MODIS) operational land surface emissivity product (MOD11). The baseline fit method, based on a conceptual model developed from laboratory measurements of surface emissivity, is applied to fill in the spectral gaps between the six emissivity wavelengths available in MOD11. The six available MOD11 wavelengths span only three spectral regions (3.8–4, 8.6, and 11–12μm), while the retrievals of atmospheric temperature and moisture from satellite IR sounder radiances require surface emissivity at higher spectral resolution. Emissivity in the database presented here is available globally at 10 wavelengths (3.6, 4.3, 5.0, 5.8, 7.6, 8.3, 9.3, 10.8, 12.1, and 14.3μm) with 0.05° spatial resolution. The wavelengths in the database were chosen as hinge points to capture as much of the shape of the higher-resolution emissivity spectra as possible between 3.6 and 14.3μm. The surface emissivity from this database is applied to the IR regression retrieval of atmospheric moisture profiles using radiances from MODIS, and improvement is shown over retrievals made with the typical assumption of constant emissivity.
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BFBNIB, DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
A field experiment was conducted in northern Chile at an altitude of 5.3 km to evaluate the accuracy of line‐by‐line radiative transfer models in regions of the spectrum that are typically opaque at ...sea level due to strong water vapor absorption. A suite of spectrally resolved radiance instruments collected simultaneous observations that, for the first time ever, spanned the entire terrestrial thermal spectrum (i.e., from 10 to 3000 cm−1, or 1000 to 3.3 μm). These radiance observations, together with collocated water vapor and temperature profiles, are used to provide an initial evaluation of the accuracy of water vapor absorption in the far‐infrared of two line‐by‐line radiative transfer models. These initial results suggest that the more recent of the two models is more accurate in the strongly absorbing water vapor pure rotation band. This result supports the validity of the Turner et al. (2012) study that demonstrated that the use of the more recent water vapor absorption model in climate simulations resulted in significant radiative and dynamical changes in the simulation relative to the older water vapor model.
Key PointsFirst ground‐based spectrally‐resolved observations of entire infrared spectrumExtremely dry conditions result in semi‐transparent regions in far‐infraredObservations used to evaluate line‐by‐line radiative transfer models
The Japanese Greenhouse gases Observing SATellite-2
(GOSAT-2), in orbit since 29 October 2018, follows up the GOSAT mission,
itself in orbit since 23 January 2009. GOSAT-2 monitors carbon dioxide and
...methane in order to increase our understanding of the global carbon cycle.
It simultaneously measures carbon monoxide emitted from fossil fuel
combustion and biomass burning and permits identification of the amount of
combustion-related carbon. To do this, the satellite utilizes the Thermal
and Near Infrared Sensor for Carbon Observation Fourier-Transform
Spectrometer-2 (TANSO-FTS-2). This spectrometer detects gas absorption spectra
of solar radiation reflected from the Earth's surface in the
shortwave-infrared (SWIR) region as well as the emitted thermal infrared
radiation (TIR) from the ground and the atmosphere. TANSO-FTS-2 can measure
the oxygen A band (0.76 µm), weak and strong CO2 bands (1.6 and 2.0 µm), weak and strong CH4 bands (1.6 and 2.3 µm), a weak CO band (2.3 µm), a mid-wave TIR band (5.5–8.4 µm), and a long-wave TIR band (8.4–14.3 µm) with 0.2 cm−1 spectral
sampling intervals. TANSO-FTS-2 is equipped with a solar diffuser target, a
monochromatic light source, and a blackbody for spectral radiance
calibration. These calibration sources permit characterization of
time-dependent instrument changes in orbit. The onboard-recalibrated
instrumental parameters are considered in operational level-1 processing and
released as TANSO-FTS-2 level-1 version 102102 products, which were
officially released on 25 May 2020. This paper provides an overview of the
TANSO-FTS-2 instrument, the level-1 processing, and the first-year in-orbit
performance. To validate the spectral radiance calibration during the first
year of operation, the spectral radiance of the version 102102 product is
compared at temporally coincident and spatially collocated points from
February 2019 to March 2020 with TANSO-FTS on GOSAT for SWIR and with AIRS
on Aqua and IASI on METOP-B for TIR. The spectral radiances measured by
TANSO-FTS and TANSO-FTS-2 agree within 2 % of the averaged bias and 0.5 % standard deviation for SWIR bands. The agreement of brightness
temperature between TANSO-FTS-2 and AIRS–IASI is better than 1 K in the
range from 220 to 320 K. GOSAT-2 not only provides seamless global
CO2 and CH4 observation but also observes local emissions and
uptake with an additional CO channel, fully customized sampling patterns,
higher signal-to-noise ratios, and wider pointing angles than GOSAT.
Research funded by the U.S. Department of Energy's Atmospheric Radiation Measurement (ARM) program has led to significant improvements in longwave radiative transfer modeling over the last decade. ...These improvements, which have generally come in small incremental changes, were made primarily in the water vapor self- and foreign-broadened continuum and the water vapor absorption line parameters. These changes, when taken as a whole, result in up to a 6 W m-2 improvement in the modeled clear-sky downwelling longwave radiative flux at the surface and significantly better agreement with spectral observations. This paper provides an overview of the history of ARM with regard to clear-sky longwave radiative transfer, and analyzes remaining related uncertainties in the ARM state-of-the-art Line-by-Line Radiative Transfer Model (LBLRTM). A quality measurement experiment (QME) for the downwelling infrared radiance at the ARM Southern Great Plains site has been ongoing since 1994. This experiment has three objectives: 1) to validate and improve the absorption models and spectral line parameters used in line-by-line radiative transfer models, 2) to assess the ability to define the atmospheric state, and 3) to assess the quality of the radiance observations that serve as ground truth for the model. Analysis of data from 1994 to 1997 made significant contributions to optimizing the QME, but is limited by small but significant uncertainties and deficiencies in the atmospheric state and radiance observations. This paper concentrates on the analysis of QME data from 1998 to 2001, wherein the data have been carefully selected to address the uncertainties in the 1994-97 dataset. Analysis of this newer dataset suggests that the representation of self-broadened water vapor continuum absorption is 3%-8% too strong in the 750-1000 cm-1 region. The dataset also provides information on the accuracy of the self- and foreign-broadened continuum absorption in the 1100-1300 cm-1 region. After accounting for these changes, remaining differences in modeled and observed downwelling clear-sky fluxes are less than 1.5 W m-2 over a wide range of atmospheric states.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The Atmospheric Infrared Sounder (AIRS) is the first of a new generation of advanced satellite‐based atmospheric sounders with the capability of obtaining high–vertical resolution profiles of ...temperature and water vapor. The high‐accuracy retrieval goals of AIRS (e.g., 1 K RMS in 1 km layers below 100 mbar for air temperature, 10% RMS in 2 km layers below 100 mbar for water vapor concentration), combined with the large temporal and spatial variability of the atmosphere and difficulties in making accurate measurements of the atmospheric state, necessitate careful and detailed validation using well‐characterized ground‐based sites. As part of ongoing AIRS Science Team efforts and a collaborative effort between the NASA Earth Observing System (EOS) project and the Department of Energy Atmospheric Radiation Measurement (ARM) program, data from various ARM and other observations are used to create best estimates of the atmospheric state at the Aqua overpass times. The resulting validation data set is an ensemble of temperature and water vapor profiles created from radiosondes launched at the approximate Aqua overpass times, interpolated to the exact overpass time using time continuous ground‐based profiles, adjusted to account for spatial gradients within the Advanced Microwave Sounding Unit (AMSU) footprints, and supplemented with limited cloud observations. Estimates of the spectral surface infrared emissivity and local skin temperatures are also constructed. Relying on the developed ARM infrastructure and previous and ongoing characterization studies of the ARM measurements, the data set provides a good combination of statistics and accuracy which is essential for assessment of the advanced sounder products. Combined with the collocated AIRS observations, the products are being used to study observed minus calculated AIRS spectra, aimed at evaluation of the AIRS forward radiative transfer model, AIRS observed radiances, and temperature and water vapor profile retrievals. This paper provides an introduction to the ARM site best estimate validation products and characterizes the accuracy of the AIRS team version 4 atmospheric temperature and water vapor retrievals using the ARM products. The AIRS retrievals over tropical ocean are found to have very good accuracy for both temperature and water vapor, with RMS errors approaching the theoretical expectation for clear sky conditions, while retrievals over a midlatitude land site have poorer performance. The results demonstrate the importance of using specialized “truth” sites for accurate assessment of the advanced sounder performance and motivate the continued refinement of the AIRS science team retrieval algorithm, particularly for retrievals over land.
A principal component noise filter has been applied to ground-based high-spectral-resolution infrared radiance observations collected by the Atmospheric Emitted Radiance Interferometers (AERIs) ...deployed by the Atmospheric Radiation Measurement (ARM) program. The technique decomposes the radiance observations into their principal components, selects the ones that describe the most variance in the data, and reconstructs the data from these components. An empirical function developed for chemical analysis is utilized to determine the number of principal components to be used in the reconstruction of the data. Statistical analysis of the noise-filtered minus original radiance data, as well as side-by-side analysis of data from two AERI systems utilizing different temporal sampling, demonstrates the ability of the noise filter using this empirical function to retain most of the atmospheric signal above the AERI noise level in the filtered data. The noise filter is applied to data collected at ARM's tropical, midlatitude, and Arctic sites, demonstrating that the random variability in the data is reduced by 5% to over 450%, depending on the spectral element and location of the instrument. A seasonal analysis of the number of principal components required by the noise filter for each site shows a strong seasonal dependence in the atmospheric variability at the Arctic and midlatitude sites but not at the tropical site. PUBLICATION ABSTRACT
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Clear‐sky outgoing longwave radiation (OLR) is computed using the Atmospheric and Environmental Research (AER), Inc., Rapid Radiative Transfer Model (RRTM) for comparison with the observations of the ...Clouds and the Earth's Radiant Energy System (CERES) for both ocean and land scenes. CERES clear‐sky OLR is in agreement with RRTM model calculations to 0.2% accuracy using best estimate radiosondes (BE) launched coincident with NASA Aqua overpasses at the Atmospheric Radiation Measurement Southern Great Plains (SGP) site and 0.8% using retrieved profiles of temperature, water vapor, ozone, and surface parameters from the Atmospheric Infrared Sounder (AIRS) on the Aqua platform. A partial flux analysis using AIRS radiances implies an accuracy for the RRTM model in the far infrared of 0.4% (about 0.5 W/m2) for wave numbers less than 650 cm−1 (wavelengths greater than 15.4 μm). CERES minus model biases over clear‐sky ocean are similar to previously published results. Ordering the results according to the magnitude of the measured minus model mean bias for nighttime, tropical, ocean gives: +0.57 ± 1.9 W/m2 (Dessler/Fu‐Liou), +0.83 ± 1.5 W/m2 (Huang/MODTRAN5), +1.6 ± 1.6 W/m2 (Moy/RRTM), +3.7 ± 2.1 W/m2 (Dessler/Chou). Comparison of observed minus modeled OLR over land are included in this study. Excluding nonfrozen ocean, a mean difference over land of +2.0 W/m2 for nighttime cases and +1.0 W/m2 for daytime cases is found where the land classes are weighted inversely by their standard error. The nighttime bias is quite consistent across all the land classes. The daytime bias shows less consistency with a tendency toward larger CERES minus AIRS RRTM OLR bias for the land classes with smaller vegetation fraction. Comparison of clear‐sky CERES and AIRS RRTM OLR over cold snow‐/ice‐covered surfaces (mainly in the polar regions) is complicated by the use of the MODIS cloud mask in the identification of the clear CERES footprints used in the comparison. Clear scenes over cold surfaces can be identified more reliably in the daytime, for which the comparison between CERES and AIRS RRTM is better than 1.2 W/m2 indicating good agreement.
The Thermal and Near-Infrared Sensor for Carbon Observation Fourier-Transform Spectrometer-2 (TANSO-FTS-2) onboard the
Japanese Greenhouse Gases Observing SATellite-2 (GOSAT-2) observes a wide
...spectral region of the atmosphere, from the ShortWave-InfraRed (SWIR) to the
longwave Thermal InfraRed radiation (TIR) with 0.2 cm−1 spectral
sampling, and the corresponding spectral resolution (full width at half
maximum, FWHM) of TIR region is less than 0.27 cm−1. TANSO-FTS-2 has
operated nominally since February 2019, and the atmospheric radiance spectra it
has acquired have been released to the public. This paper describes an
updated model for spectral radiance calibration and its validation. The
model applies to the version v210210 TIR products of TANSO-FTS-2 and
integrates polarization sensitivity correction for the internal optics and
the pointing mirror thermal emission. These correction parameters are
characterized by an optimization that depends on the difference between the
spectral radiance of TANSO-FTS-2 and coincident nadir observation data from
the Infrared Atmospheric Sounding Interferometer (IASI) on METOP-B. To
validate the updated spectral radiance product against other satellite
products, temporally and spatially coincident observation points were
considered for the simultaneous nadir overpass (SNO) from February 2019 to March 2021 from the Atmospheric Infrared Sounder (AIRS) on Aqua, IASI on METOP-B, and TANSO-FTS on GOSAT. The agreement of brightness temperatures between TANSO-FTS-2 and AIRS and IASI was better than 0.3 K (1σ) from 180 to 330 K for the 680 cm−1 CO2 spectral range. The brightness temperatures between TANSO-FTS-2 and TANSO-FTS of version v230231, which implemented a new polarization reflectivity of the pointing mirror and was released in June 2021, generally agree from 220 to 320 K. However, there is a discrepancy at lower brightness temperatures, pronounced for CO2 spectral ranges at high latitudes. To characterize the spectral radiance bias for along-track and cross-track angles, a 2-orthogonal simultaneous off-nadir overpass (2O-SONO) is now done for TANSO-FTS-2 and IASI, TANSO-FTS-2 and AIRS, and TANSO-FTS-2 and TANSO-FTS. The 2O-SONO comparison results indicate that the TIR product for TANSO-FTS-2 has a bias that exceeds 0.5 K in the CO2 spectral range for scenes with forward and backward viewing angles greater than 20∘. These multi-satellite sensor and multi-angle comparison results suggest that the calibration of spectral radiance for TANSO-FTS-2 TIR, version v210210, is superior to that of the previous version in its consistency of multi-satellite sensor data. In addition, the paper identifies the remaining challenging issues in current TIR products.
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