The HITRAN database is a compilation of molecular spectroscopic parameters. It was established in the early 1970s and is used by various computer codes to predict and simulate the transmission and emission of light in gaseous media (with an emphasis on terrestrial and planetary atmospheres). The HITRAN compilation is composed of five major components: the line-by-line spectroscopic parameters required for high-resolution radiative-transfer codes, experimental infrared absorption cross-sections (for molecules where it is not yet feasible for representation in a line-by-line form), collision-induced absorption data, aerosol indices of refraction, and general tables (including partition sums) that apply globally to the data. This paper describes the contents of the 2020 quadrennial edition of HITRAN. The HITRAN2020 edition takes advantage of recent experimental and theoretical data that were meticulously validated, in particular, against laboratory and atmospheric spectra. The new edition replaces the previous HITRAN edition of 2016 (including its updates during the intervening years). All five components of HITRAN have undergone major updates. In particular, the extent of the updates in the HITRAN2020 edition range from updating a few lines of specific molecules to complete replacements of the lists, and also the introduction of additional isotopologues and new (to HITRAN) molecules: SO, CH3F, GeH4, CS2, CH3I and NF3. Many new vibrational bands were added, extending the spectral coverage and completeness of the line lists. Also, the accuracy of the parameters for major atmospheric absorbers has been increased substantially, often featuring sub-percent uncertainties. Broadening parameters associated with the ambient pressure of water vapor were introduced to HITRAN for the first time and are now available for several molecules. The HITRAN2020 edition continues to take advantage of the relational structure and efficient interface available at www.hitran.org and the HITRAN Application Programming Interface (HAPI). The functionality of both tools has been extended for the new edition. 

The HITRAN2020 molecular spectroscopic database

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission will provide a calibration laboratory in orbit for the purpose of accurately measuring and attributing climate change. CLARREO measurements establish new climate change benchmarks with high absolute radiometric accuracy and high statistical confidence across a wide range of essential climate variables. CLARREO's inherently high absolute accuracy will be verified and traceable on orbit to Systeme Internationale (SI) units. The benchmarks established by CLARREO will be critical for assessing changes in the Earth system and climate model predictive capabilities for decades into the future as society works to meet the challenge of optimizing strategies for mitigating and adapting to climate change. The CLARREO benchmarks are derived from measurements of the Earth's thermal infrared spectrum (5–50 μm), the spectrum of solar radiation reflected by the Earth and its atmosphere (320–2300 nm), and radio occultation refractivity from which...

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Achieving Climate Change Absolute Accuracy in Orbit

[1] This paper presents the project Earth Cooling by Water Vapor Radiation, an observational programme, which aims at developing a database of spectrally resolved far infrared observations, in atmospheric dry conditions, in order to validate radiative transfer models and test the quality of water vapor continuum and line parameters. The project provides the very first set of far-infrared spectral downwelling radiance measurements, in dry atmospheric conditions, which are complemented with Raman Lidar-derived temperature and water vapor profiles.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2007GL032207

Spectrally resolved observations of atmospheric emitted radiance in the H2O rotation band

The paper presents a review of the far infrared (FIR) properties of the Earth's atmosphere, and the role of these properties in climate. These properties have been relatively poorly understood, and it is one of the purposes of this review to demonstrate that, in recent years, we have made great strides in improving this understanding. Seen from space, the Earth is a cool object, with an effective emitting temperature of about 255 K. This contrasts with a global mean surface temperature of ~288 K, and is due primarily to strong absorption of outgoing longwave energy by water vapour, carbon dioxide and clouds (especially ice). A large fraction of this absorption occurs in the FIR, and so the Earth is effectively a FIR planet. The FIR is important in a number of key climate processes, for example the water vapour and cloud feedbacks (especially ice clouds). The FIR is also a spectral region which can be used to remotely sense and retrieve atmospheric composition in the presence of ice clouds. Recent developments in instrumentation have allowed progress in each of these areas, which are described, and proposals for a spaceborne FIR instrument are being formulated. It is timely to review the FIR properties of the clear and cloudy atmosphere, the role of FIR processes in climate, and its use in observing our planet from space.

The Far-infrared Earth

For the most part, satellite observations of climate are not presently sufficiently accurate to establish a climate record that is indisputable and hence capable of determining whether and at what rate the climate is changing. Furthermore, they are insufficient for establishing a baseline for testing long-term trend predictions of climate models. Satellite observations do provide a clear picture of the relatively large signals associated with interannual climate variations such as El Nino-Southern Oscillation (ENSO), and they have also been used to diagnose gross inadequacies of climate models, such as their cloud generation schemes. However, satellite contributions to measuring long-term change have been limited and, at times, controversial, as in the case of differing atmospheric temperature trends derived from the U.S. National Oceanic and Atmospheric Administration's (NOAA) microwave radiometers.

http://www.star.nesdis.noaa.gov/star/documents/ASIC3-071218-webversfinal.pdf

Achieving satellite instrument calibration for climate change

We present first light spectra from the new Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument. FIRST is a Fourier Transform Spectrometer developed to measure accurately the far-infrared (15 to 100 micrometers; 650 to 100 wavenumbers) emission spectrum of the Earth and its atmosphere. The observations presented here were obtained during a high altitude balloon flight from Ft. Sumner, New Mexico on 7 June 2005. The flight data demonstrate the instrument's ability to observe the entire energetically significant infrared emission spectrum (50 to 2000 wavenumbers) at high spectral and spatial resolution on a single focal plane in an instrument with one broad spectral bandpass beamsplitter. Comparisons with radiative transfer calculations demonstrate that FIRST accurately observes the very fine spectral structure in the far-infrared. Comparisons of the atmospheric window radiances measured by FIRST and by instruments on the NASA Aqua satellite that overflew FIRST are in excellent agreement. FIRST opens a new window on the spectrum that can be used for studying atmospheric radiation and climate, cirrus clouds, and water vapor in the upper troposphere.

https://ntrs.nasa.gov/api/citations/20080014859/downloads/20080014859.pdf

First light from the Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument

Orbital sensors to monitor global climate change during the next decade require low-drift rates for onboard thermometry, which is currently unattainable without on-orbit recalibration. Phase-change materials (PCMs), such as those that make up the ITS-90 standard, are seen as the most reliable references on the ground and could be good candidates for orbital recalibration. Space Dynamics Lab (SDL) has been developing miniaturized phase-change references capable of deployment on an orbital blackbody for nearly a decade. Improvement of orbital temperature measurements for long duration earth observing and remote sensing. To determine whether and how microgravity will affect the phase transitions, SDL conducted experiments with ITS-90 standard material (gallium, Ga) on the International Space Station (ISS) and compared the phase-change temperature with earth-based measurements. The miniature on-orbit thermal reference (MOTR) experiment launched to the ISS in November 2013 on Soyuz TMA-11M with the Expedition 38 crew and returned to Kazakhstan in March 2014 on the Soyuz TMA-10 spacecraft. MOTR tested melts and freezes of Ga using repeated 6-h cycles. Melt cycles obtained on the ground before and after launch were compared with those obtained on the ISS. To within a few mK uncertainty, no significant difference between the melt temperature of Ga at 1 g and in microgravity was observed. Recent International Space Station (ISS) chemistry experiments may improve the reliability of satellites recording Earth's climate data. Orbital monitoring of infrared radiance requires probes with extraordinarily low drift rates of less than 0.1 kelvin per decade. To achieve such precision, materials such as gallium (Ga) that undergo liquid/solid phase changes at precise temperatures are included onboard the satellite and then calibrated against ground-based standards. Shane Topham from the Space Dynamics Laboratory in Utah and co-workers have now resolved uncertainty surrounding the effects of microgravity on the temperature of Ga phase transitions. Experiments on the ISS tested how hermetically sealed Ga samples melted and froze during repeated 6 hour cycles. Only single millikelvin differences were detected between orbiting samples and those on Earth — an accuracy well-suited for remote sensing thermal reference standards.

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Observational study: microgravity testing of a phase-change reference on the International Space Station.

The Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument measured downwelling far-infrared (far-IR) and mid-infrared (mid-IR) atmospheric spectra from 200 to 800 cm−1 at Table Mountain, California (elevation 2285 m). Spectra were recorded during a field campaign conducted in early autumn 2012, subsequent to a detailed laboratory calibration of the instrument. Radiosondes launched coincident with the FIRST observations provide temperature and water vapor profiles for model simulation of the measured spectra. Results from the driest day of the campaign (October 19, with less than 3 mm precipitable water) are presented here. Considerable spectral development is observed between 400 and 600 cm−1. Over 90% of the measured radiance in this interval originates within 2.8 km of the surface. The existence of temperature inversions close to the surface necessitates atmospheric layer thicknesses as fine as 10 m in the radiative transfer model calculations. A detailed assessment of the uncertainties in the FIRST measurements and in the model calculations shows that the measured radiances agree with the model radiance calculations to within their combined uncertainties. The uncertainties in modeled radiance are shown to be larger than the measurement uncertainties. Overall, the largest source of uncertainty is in the water vapor concentration used in the radiative transfer calculations. Proposed new instruments with markedly higher measurement accuracy than FIRST will be able to measure the far-IR spectrum to much greater accuracy than it can be computed. As such, accurate direct measurements of the far-IR, and not solely calculations, are essential to the assessment of climate change.

Observations of downwelling far-infrared emission at Table Mountain California made by the FIRST instrument

The Wide Field Infrared Survey Explorer is a NASA Medium Class Explorer mission to perform an all-sky survey in four infrared wavelength bands. The science payload is a cryogenically cooled infrared telescope with four 1024 2 infrared focal plane arrays covering from 2.8 to 26 μm. Advances in focal plane technology and a large aperture cryogenic telescope allow an all-sky survey to be performed with high sensitivity and resolution. An efficient survey is obtained using a cryogenic scan mirror to freeze the field of view on the sky over the 9.9-second frame integration time. Mercury cadmium telluride (MCT) detectors, cooled to 32 K, are used for the two midwave channels (3.3 μm and 4.6 μm), and Si:As detectors, cooled to < 8.3 K, are used for the two long wavelength channels (12 μm and 23 μm). Cooling is provided by a two-stage solid hydrogen cryostat which provides temperatures < 17 K and < 8.3 K at the telescope and Si:As focal planes, respectively. The science payload supports operations on orbit for the seven-month baseline mission with a goal to support a 13-month extended mission, if possible. The payload recently passed CDR and is being fabricated. This paper provides a payload overview and discusses instrument requirements and performance.

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Wide-field infrared survey explorer science payload update

The NASA climate science mission Climate Absolute Radiance and Refractivity Observatory (CLARREO), which is to
measure Earth's emitted spectral radiance from orbit for 5 years, has an absolute accuracy requirement of 0.1 K (3σ) at
220 K over most of the thermal infrared. To meet this requirement, CLARREO needs highly accurate on-board
blackbodies which remain accurate over the life of the mission. Space Dynamics Laboratory is developing a prototype
blackbody that demonstrates the ability to meet the needs of CLARREO. This prototype is based on a blackbody design
currently in use, which is relatively simple to build, was developed for use on the ground or on-orbit, and is readily
scalable for aperture size and required performance. We expect the CLARREO prototype to have emissivity of ~0.9999
from 1.5 to 50 μm, temperature uncertainties of ~25 mK (3σ), and radiance uncertainties of ~10 mK due to temperature
gradients. The high emissivity and low thermal gradient uncertainties are achieved through cavity design, while the SItraceable
temperature uncertainty is attained through the use of phase change materials (mercury, gallium, and water) in
the blackbody. Blackbody temperature sensor calibration is maintained over time by comparing sensor readings to the
known melt temperatures of these materials, which are observed by heating through their melt points. Since blackbody
emissivity can potentially change over time due to changes in surface emissivity (especially for an on-orbit blackbody)
an on-board means of detecting emissivity change is desired. The prototype blackbody will include an emissivity
monitor based on a quantum cascade laser to demonstrate the concept.

/pdf/a-high-accuracy-blackbody-for-clarreo-4nodjhf8xk.pdf

Harri Latvakoski

Papers

First light from the Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument

Observational study: microgravity testing of a phase-change reference on the International Space Station.

Observations of downwelling far-infrared emission at Table Mountain California made by the FIRST instrument

Wide-field infrared survey explorer science payload update

A high-accuracy blackbody for CLARREO