This article describes the latest stable release (version 2.2) of the Atmospheric Radiative Transfer Simulator (ARTS), a public domain software for radiative transfer simulations in the thermal ...spectral range (microwave to infrared). The main feature of this release is a planetary toolbox that allows simulations for the planets Venus, Mars, and Jupiter, in addition to Earth. This required considerable model adaptations, most notably in the area of gaseous absorption calculations. Other new features are also described, notably radio link budgets (including the effect of Faraday rotation that changes the polarization state) and the treatment of Zeeman splitting for oxygen spectral lines. The latter is relevant, for example, for the various operational microwave satellite temperature sensors of the Advanced Microwave Sounding Unit (AMSU) family.
A suite of programs for high resolution infrared-microwave atmospheric radiative transfer modeling has been developed with emphasis on efficient and reliable numerical algorithms and a modular ...approach appropriate for simulation and/or retrieval in a variety of applications. The Generic Atmospheric Radiation Line-by-line Infrared Code — GARLIC — is suitable for arbitrary observation geometry, instrumental field-of-view, and line shape. The core of GARLIC's subroutines constitutes the basis of forward models used to implement inversion codes to retrieve atmospheric state parameters from limb and nadir sounding instruments.
This paper briefly introduces the physical and mathematical basics of GARLIC and its descendants and continues with an in-depth presentation of various implementation aspects: An optimized Voigt function algorithm combined with a two-grid approach is used to accelerate the line-by-line modeling of molecular cross sections; various quadrature methods are implemented to evaluate the Schwarzschild and Beer integrals; and Jacobians, i.e. derivatives with respect to the unknowns of the atmospheric inverse problem, are implemented by means of automatic differentiation. For an assessment of GARLIC's performance, a comparison of the quadrature methods for solution of the path integral is provided. Verification and validation are demonstrated using intercomparisons with other line-by-line codes and comparisons of synthetic spectra with spectra observed on Earth and from Venus.
•High resolution infrared-microwave radiative transfer model.•Discussion of algorithmic and computational aspects.•Jacobians by automatic/algorithmic differentiation.•Performance evaluation by intercomparisons, verification, validation.
The National Institute of Information and Communications Technology (NICT, Japan) started the Terahertz Project in April 2006. Its fundamental purpose in the next five years is to enable a nationwide ...technical infrastructure to be created for diverse applications of terahertz technology. The technical infrastructure includes the development of semiconductor devices such as terahertz quantum cascade lasers, terahertz-range quantum well photodetectors, and high-precision tunable continuous wave sources. It also includes pulsed terahertz measurement systems, modeling and measurement of atmospheric propagation, and the establishment of a framework to construct a materials database in the terahertz range including standardization of the measurement protocol. These are common technical infrastructure even in any terahertz systems. In this article, we report the current status of developments in these fields such as terahertz quantum cascade lasers (THz-QCLs) (with peak power of 30 mW, 3.1 THz), terahertz-range quantum well photodetectors (THz-QWPs) (tuned at 3 THz) an ultrawideband terahertz time domain spectroscopy (THz-TDS) system (with measurement range of from 0.1 to 15 THz), an example of a database for materials of fine art, and results obtained from measuring atmospheric propagation.
This paper presents the practical theory that was used to implement the Zeeman effect using Stokes formalism in the Atmospheric Radiative Transfer Simulator (ARTS). ARTS now treats the Zeeman effect ...in a general manner for several gas species for all polarizations and takes into account variations in both magnetic and atmospheric fields along a full 3D geometry. We present how Zeeman splitting affects polarization in radiative transfer simulations and find that the effect may be large in Earth settings for polarized receivers in limb observing geometry. We find that not taking a spatially varying magnetic field into account can result in absolute errors in the measurement vector of at least 10K in Earth magnetic field settings. The paper also presents qualitative tests for O2 lines against previous models (61.15GHz line) and satellite data from Odin-SMR (487.25GHz line), and the overall consistency between previous models, satellite data, and the new ARTS Zeeman module seems encouraging.
•We implement the Zeeman effect with Stokes formalism in ARTS.•We give a practical theory for the implementation.•Examples of how the Zeeman effect change RT are presented.•Qualitative Odin-SMR O2 limb sounding model indicates the Zeeman effect is necessary.
Stratospheric Inferred Winds (SIW) is a Swedish mini sub-millimeter limb sounder selected for the 2nd InnoSat platform, with launch planned for around 2022. It is intended to fill the altitude gap ...between 30 and 70 km in atmospheric wind measurements and also aims at pursuing the limb observations of temperature and key atmospheric constituents between 10 and 90 km when current satellite missions will probably come to an end. Line-of-sight winds are retrieved from the Doppler shift of molecular emission lines introduced by the wind field. Observations will be performed with two antennas pointing toward the limb in perpendicular directions in order to reconstruct the 2-D horizontal wind vector. Each antenna has a vertical field of view (FOV) of 5 km. The chosen spectral band, near 655 GHz, contains a dense group of strong O3 lines suitable for exploiting the small amount of wind information in stratospheric spectra. Using both sidebands of the heterodyne receiver, a large number of chemical species will be measured, including O3 isotopologues, H2O, HDO, HCl, ClO, N2O, HNO3, NO, NO2, HCN, CH3CN and HO2. This paper presents a simulation study that assesses measurement performance. The line-of-sight winds are retrieved between 30 and 90 km with the best sensitivity between 35 and 70 km, where the precision (1σ) is 5–10 m s−1 for a single scan. Similar performance can be obtained during day and night conditions except in the lower mesosphere, where the photo-dissociation of O3 in daytime reduces the sensitivity by 50 % near 70 km. Profiles of O3, H2O and temperature are retrieved with high precision up to 50 km ( < 1 %, < 2 %, 1 K, respectively). Systematic errors due to uncertainties in spectroscopic parameters, in the radiometer sideband ratio and in the radiance calibration process are investigated. A large wind retrieval bias of 10–30 m s−1 between 30 and 40 km could be induced by the air-broadening parameter uncertainties of O3 lines. This highlights the need for good knowledge of these parameters and for studying methods to mitigate the retrieval bias.
We present a method for characterizing the magnetic anomalies from the crustal fields in the lower atmosphere of Mars that requires two perpendicular linear polarization measurements of the Zeeman ...effect. The maximum effect of the magnetic field on the signal is found at the Doppler broadening width at low pressures rather than at the magnetically induced line frequency shift, and the effect strongly increases with increasing magnetic field strength. Based on simulations of the Zeeman‐affected spectral cross section of the 119 GHz O2 line in a model Martian atmosphere at various magnetic field strengths, we conclude that it should be possible to probe the strength of the magnetic anomalies remotely with presently available technology. We discuss limitations of the method, how these results could be relevant to the interpretation of residuals in Herschel/HIFI observations of Mars, as well as the application to detection of exoplanetary magnetic fields.
Key Points
Introduction of a new polarimetry method for detection of weak magnetic fields
Model of Mars crustal magnetic fields' influence on oxygen spectra
Discussion on using the Zeeman effect for detection of exoplanetary magnetism
The Terrestrial Systems Modeling Platform (TSMP) was extended with a chemical transport model and polarimetric radar forward operator to enable detailed studies of aerosol-cloud-precipitation ...interactions. The model was used at kilometer-scale (convection-permitting) resolution to simulate a deep convective storm event over Germany which produced large hail, high precipitation, and severe damaging winds. The ensemble model simulation was, in general, able to capture the storm structure, its evolution, and the spatial pattern of accumulated precipitation. However, the model was found to underestimate regions of high accumulated precipitation ( 35 mm) and convective area fraction in the early period of the storm. While the model tends to simulate too high reflectivity in the downdraft region of the storm above the melting layer (mostly contributed by graupel), the model also simulates very weak polarimetric signatures in this region, when compared to the radar observations. The above findings remained almost unchanged when using a narrower cloud drop size distribution (CDSD) acknowledging the missing feedback between aerosol physical and chemical properties and CDSD shape parameters.
We propose a submillimetre-wave atmospheric emission sounding instrument, called Far-InfraRed Experiment (FIRE), for the Japanese Martian exploration programme “Mars Exploration with Lander-Orbiter ...Synergy” (MELOS). The scientific target of FIRE/MELOS is to understand the dust suspended meteorology of the Mars. FIRE will provide key meteorological parameters, such as atmospheric temperature profiles for outside and inside dust storms, the abundance profile of the atmospheric compositions and their isotopes, and wind velocity profiles. FIRE will also provide the local time dependency of these parameters. The observational sensitivity of FIRE/MELOS is discussed in this paper. FIRE will explore the meteorological system of the Martian atmosphere including the interaction between its surface and atmosphere.
► We propose a submillimetre-wave sounding instrument onboard a Mars orbiter. ► The instrument can observe the Martian atmosphere independently from airborne dust. ► We target to observe the temperature, chemical compositions and wind velocity. ► The observations can be done contiguously during day and night. ► Meteorology, climate system and surface–atmosphere interaction will be investigated.
A main limitation today in simulations and inversions of microwave observations of ice hydrometeors (cloud ice, snow, hail, etc.) is the lack of data describing the interaction between ...electromagnetic waves and the particles. To improve the situation, the development of a comprehensive dataset of such scattering properties has been started. The database aims at giving a broad coverage in both frequency (1 to 886 GHz) and temperature (190 to 270 K), to support both passive and active current and planned measurements, and to provide data corresponding to the full Stokes vector. This first version of the database is restricted to totally random particle orientation. Data for 34 particle sets, i.e. habits, have been generated. About 17 of the habits can be classified as single crystals, three habits can be seen as heavily rimed particles, and the remaining habits are aggregates of different types, e.g. snow and hail. The particle sizes considered vary between the habits, but maximum diameters of 10 and 20 mm are typical values for the largest single crystal and aggregate particles, respectively, and the number of sizes per habit is at least 30. Particles containing liquid water are also inside the scope of the database, but this phase of water is so far only represented by a liquid sphere habit. The database is built upon the netCDF4 file format. Interfaces to browse, extract and convert data for selected radiative transfer models are provided in MATLAB and Python. The database and associated tools are publicly available from Zenodo (https://doi.org/10.5281/zenodo.1175572, Ekelund et al., 2018b), and https://doi.org/10.5281/zenodo.1175588, Mendrok et al., 2018, respectively). Planned extensions include non-spherical raindrops, melting particles and a second orientation case that can be denoted as azimuthally random.
This article presents SPARE‐ICE, the Synergistic Passive Atmospheric Retrieval Experiment‐ICE. SPARE‐ICE is the first Ice Water Path (IWP) product combining infrared and microwave radiances. By using ...only passive operational sensors, the SPARE‐ICE retrieval can be used to process data from at least the NOAA 15 to 19 and MetOp satellites, obtaining time series from 1998 onward. The retrieval is developed using collocations between passive operational sensors (solar, terrestrial infrared, microwave), the CloudSat radar, and the CALIPSO lidar. The collocations form a retrieval database matching measurements from passive sensors against the existing active combined radar‐lidar product 2C‐ICE. With this retrieval database, we train a pair of artificial neural networks to detect clouds and retrieve IWP. When considering solar, terrestrial infrared, and microwave‐based measurements, we show that any combination of two techniques performs better than either single‐technique retrieval. We choose not to include solar reflectances in SPARE‐ICE, because the improvement is small, and so that SPARE‐ICE can be retrieved both daytime and nighttime. The median fractional error between SPARE‐ICE and 2C‐ICE is around a factor 2, a figure similar to the random error between 2C‐ICE ice water content (IWC) and in situ measurements. A comparison of SPARE‐ICE with Moderate Resolution Imaging Spectroradiometer (MODIS), Pathfinder Atmospheric Extended (PATMOS‐X), and Microwave Surface and Precipitation Products System (MSPPS) indicates that SPARE‐ICE appears to perform well even in difficult conditions. SPARE‐ICE is available for public use.
Key Points
Combine IR and MW to retrieve IWP from passive operational sensors
We use collocations to train with CloudSat CPR 2C-ICE as a reference data set
Compares well to MODIS and seems to do well even in difficult conditions
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