| 1. |
- Baron, P., et al.
(author)
-
Simulation study for the Stratospheric Inferred Winds (SIW) sub-millimeter limb sounder
- 2018
-
In: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 11:7, s. 4545-4566
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Journal article (peer-reviewed)abstract
- 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 (1 σ ) is 5-10 mĝ€†sĝ'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 mĝ€†sĝ'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..
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| 2. |
- Baron, P., et al.
(author)
-
The level 2 research product algorithms for the superconducting submillimeter-wave limb-emission sounder (SMILES)
- 2011
-
In: Atmospheric Measurement Techniques Discussions. - : Copernicus GmbH. - 1867-8610. ; 4:3, s. 3593-3645
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Journal article (peer-reviewed)abstract
- This paper describes the algorithms of the level-2 research (L2r) processingchain developed for the Superconducting Submillimeter-Wave Limb-EmissionSounder (SMILES). The chain has been developed in parallel to the operationalchain for conducting researches on calibration and retrieval algorithms. L2rchain products are available to the scientific community. The objective ofversion 2 is the retrieval of the vertical distribution of trace gases in thealtitude range of 18-90 km. An theoretical error analysis is conducted toestimate the retrieval feasibility of key parameters of the processing:line-of-sight elevation tangent altitudes (or angles), temperature and O3 profiles. The line-of-sight tangent altitudes are retrievedbetween 20 and 50 km from the strong ozone (O3) line at 625.371 GHz,with low correlation with the O3 volume-mixing ratio and temperatureretrieved profiles. Neglecting the non-linearity of the radiometric gain inthe calibration procedure is the main systematic error. It is large for theretrieved temperature (between 5-10 K). Therefore, atmospheric pressure cannot be derived from the retrieved temperature, and, then, in the altituderange where the line-of-sight tangent altitudes are retrieved, the retrievedtrace gases profiles are found to be better represented on pressure levelsthan on altitude levels. The error analysis for the retrieved HOCl profiledemonstrates that best results for inverting weak lines can be obtained byusing narrow spectral windows. Future versions of the L2r algorithms willimprove the temperature/pressure retrievals and also provide information inthe upper tropospheric/lower stratospheric region (e.g., water vapor, icecontent, O3) and on stratospheric and mesospheric line-of-sight winds.
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| 3. |
- Baron, P., et al.
(author)
-
The Level 2 research product algorithms for the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES)
- 2011
-
In: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 4, s. 2105-2124
-
Journal article (peer-reviewed)abstract
- This paper describes the algorithms of the level-2 research (L2r) processing chain developed for the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES). The chain has been developed in parallel to the operational chain for conducting researches on calibration and retrieval algorithms. L2r chain products are available to the scientific community. The objective of version 2 is the retrieval of the vertical distribution of trace gases in the altitude range of 18–90 km. A theoretical error analysis is conducted to estimate the retrieval feasibility of key parameters of the processing: line-of-sight elevation tangent altitudes (or angles), temperature and ozone profiles. While pointing information is often retrieved from molecular oxygen lines, there is no oxygen line in the SMILES spectra, so the strong ozone line at 625.371 GHz has been chosen. The pointing parameters and the ozone profiles are retrieved from the line wings which are measured with high signal to noise ratio, whereas the temperature profile is retrieved from the optically thick line center. The main systematic component of the retrieval error was found to be the neglect of the non-linearity of the radiometric gain in the calibration procedure. This causes a temperature retrieval error of 5–10 K. Because of these large temperature errors, it is not possible to construct a reliable hydrostatic pressure profile. However, as a consequence of the retrieval of pointing parameters, pressure induced errors are significantly reduced if the retrieved trace gas profiles are represented on pressure levels instead of geometric altitude levels. Further, various setups of trace gas retrievals have been tested. The error analysis for the retrieved HOCl profile demonstrates that best results for inverting weak lines can be obtained by using narrow spectral windows.
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| 4. |
- Birman, Camille, et al.
(author)
-
Information content on hydrometeors from millimeter and sub-millimeter wavelengths
- 2017
-
In: Tellus. Series A, Dynamic meteorology and oceanography. - : Taylor & Francis. - 0280-6495 .- 1600-0870. ; 69:1
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Journal article (peer-reviewed)abstract
- This study examines the information content on hydrometeors that could be provided by a future HYperspectralMicrowave Sensor (HYMS) with frequencies ranging from 6.9 to 874 GHz (millimeter and sub-millimeter regions). Through optimal estimation theory the information content is expressed quantitatively in terms of degrees of freedom for signal (DFS). For that purpose the Atmospheric Radiative Transfer Simulator (ARTS) and its Jacobians are used with a set of 25 cloudy and precipitating profiles and their associated errors from the European Centre for Medium-range Weather Forecasting (ECMWF) global numerical weather prediction model.In agreement with previous studies it is shown that frequencies between 10 and 40 GHz are the most informative ones for liquid and rain water contents. Similarly, the absorption band at 118 GHz contains significant information on liquid precipitation. A set of new window channels (15.37-, 40.25-, 101-GHz) could provide additional information on the liquid phase. The most informative channels on cloud icewater are the window channels at 664 and 874GHz and thewater vapour absorption bands at 325 and 448 GHz. Regarding snow water contents, the channels having the largest DFS values are located inwindow regions (150-, 251-, 157-, 101-GHz). However it is necessary to consider 90 channels in order to represent 90% of the DFS. The added value of HYMS has been assessed against current Special Sensor Microwave Imager/Sounder (SSMI/S) onboard the Defense Meteorological Satellite Program (DMSP) and future (Microwave Imager/Ice Cloud Imager (MWI/ICI) onboard European Polar orbiting Satellite – Second Generation (EPS-SG)) microwave sensors. It appears that with a set of 276 channels the information content on hydrometeors would be significantly enhanced: the DFS increases by 1.7 against MWI/ICI and by 3 against SSMI/S. A number of tests have been performed to examine the robustness of the above results. The most informative channels on solid hydrometeors remain the same over land and over ocean surfaces. On the other hand, the database is not large enough to produce robust results over land surfaces for liquid hydrometeors. The sensitivity of the results to the microphysical properties of frozen hydrometeors has been investigated. It appears that a change in size distribution and scattering properties can move the large information content of the channels at 664 and 874 GHz from cloud ice to solid precipitation.
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| 5. |
- Buehler, S.A., et al.
(author)
-
ARTS, the Atmospheric Radiative Transfer Simulator - Version 2.2, the planetary toolbox edition
- 2018
-
In: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 11:4, s. 1537-1556
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Journal article (peer-reviewed)abstract
- 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.
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| 6. |
- Buehler, Stefan, et al.
(author)
-
A multi-instrument comparison of integrated water vapour measurements at a high latitude site
- 2012
-
In: Atmospheric Chemistry And Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 12:22, s. 10925-10943
-
Journal article (peer-reviewed)abstract
- We compare measurements of integrated water vapour (IWV) over a subarctic site (Kiruna, Northern Sweden) from five different sensors and retrieval methods: Radiosondes, Global Positioning System (GPS), ground-based Fourier-transform infrared (FTIR) spectrometer, ground-based microwave radiometer, and satellite-based microwave radiometer (AMSU-B). Additionally, we compare also to ERA-Interim model reanalysis data. GPS-based IWV data have the highest temporal coverage and resolution and are chosen as reference data set. All datasets agree reasonably well, but the ground-based microwave instrument only if the data are cloud-filtered. We also address two issues that are general for such intercomparison studies, the impact of different lower altitude limits for the IWV integration, and the impact of representativeness error. We develop methods for correcting for the former, and estimating the random error contribution of the latter. A literature survey reveals that reported systematic differences between different techniques are study-dependent and show no overall consistent pattern. Further improving the absolute accuracy of IWV measurements and providing climate-quality time series therefore remain challenging problems.
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| 7. |
- Buehler, Stefan, et al.
(author)
-
Observing ice clouds in the submillimeter spectral range: the CloudIce mission proposal for ESA's Earth Explorer 8
- 2012
-
In: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 5:7, s. 1529-1549
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Journal article (peer-reviewed)abstract
- Passive submillimeter-wave sensors are a way to obtain urgently needed global data on ice clouds, particularly on the so far poorly characterized 'essential climate variable' ice water path (IWP) and on ice particle size. CloudIce was a mission proposal to the European Space Agency ESA in response to the call for Earth Explorer 8 (EE8), which ran in 2009/2010. It proposed a passive submillimeter-wave sensor with channels ranging from 183 GHz to 664 GHz. The article describes the CloudIce mission proposal, with particular emphasis on describing the algorithms for the data-analysis of submillimeter-wave cloud ice data (retrieval algorithms) and demonstrating their maturity. It is shown that we have a robust understanding of the radiative properties of cloud ice in the millimeter/submillimeter spectral range, and that we have a proven toolbox of retrieval algorithms to work with these data. Although the mission was not selected for EE8, the concept will be useful as a reference for other future mission proposals.
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| 8. |
- Eliasson, Salomon, et al.
(author)
-
Systematic and random errors between collocated satellite ice water path observations
- 2013
-
Conference paper (other academic/artistic)abstract
- There remains large disagreement between ice-water path (IWP) in observational data sets, largely because the sensors observe different parts of the ice particle size distribution. A detailed comparison of retrieved IWP from satellite observations in the Tropics (±30° latitude) in 2007 was made using collocated measurements. The radio detection and ranging(radar)/light detection and ranging (lidar) (DARDAR) IWP data set, based on combined radar/lidar measurements, is used as a reference because it provides arguably the best estimate of the total column IWP. For each data set, usable IWP dynamic ranges are inferred from this comparison. IWP retrievals based on solar reflectance measurements, in the moderate resolution imaging spectroradiometer (MODIS), advanced very high resolution radiometer–based Climate Monitoring Satellite Applications Facility (CMSAF), and Pathfinder Atmospheres-Extended (PATMOS-x) datasets, were found to be correlated with DARDAR over a large IWP range (~20–7000 g m-2). The random errors of the collocated data sets have a close to lognormal distribution, and the combined random error of MODIS and DARDAR is less than a factor of 2, which also sets the upper limit for MODIS alone. In the same way, the upper limit for the random error of all considered data sets is determined. Data sets based on passive microwave measurements, microwave surface and precipitation products system (MSPPS), microwave integrated retrieval system (MiRS), and collocated microwave only (CMO), are largely correlated with DARDAR for IWP values larger than approximately 700 g m-2. The combined uncertainty between these data sets and DARDAR in this range is slightly less MODIS-DARDAR, but the systematic bias is nearly an order of magnitude.
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| 9. |
- Eriksson, Patrick, 1964, et al.
(author)
-
A general database of hydrometeor single scattering properties at microwave and sub-millimetre wavelengths
- 2018
-
In: Earth System Science Data. - : Copernicus GmbH. - 1866-3516 .- 1866-3508. ; 10:3, s. 1301-1326
-
Journal article (peer-reviewed)abstract
- 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.
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| 10. |
- Eriksson, Patrick, 1964, et al.
(author)
-
On the microwave optical properties of randomly oriented ice hydrometeors
- 2015
-
In: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 8:5, s. 1913-1933
-
Journal article (peer-reviewed)abstract
- Microwave remote sensing is important for observing the mass of ice hydrometeors. One of the main error sources of microwave ice mass retrievals is that approximations around the shape of the particles are unavoidable. One common approach to represent particles of irregular shape is the soft particle approximation (SPA). We show that it is possible to define a SPA that mimics mean optical particles of available reference data over narrow frequency ranges, considering a single observation technique at the time, but that SPA does not work in a broader context. Most critically, the required air fraction varies with frequency and application, as well as with particle size. In addition, the air fraction matching established density parameterisations results in far too soft particles, at least for frequencies above 90 GHz. That is, alternatives to SPA must be found. One alternative was recently presented by Geer and Baordo (2014). They used a subset of the same reference data and simply selected as "shape model" the particle type giving the best overall agreement with observations. We present a way to perform the same selection of a representative particle shape but without involving assumptions on particle size distribution and actual ice mass contents. Only an assumption on the occurrence frequency of different particle shapes is still required. Our analysis leads to the same selection of representative shape as found by Geer and Baordo (2014). In addition, we show that the selected particle shape has the desired properties at higher frequencies as well as for radar applications. Finally, we demonstrate that in this context the assumption on particle shape is likely less critical when using mass equivalent diameter to characterise particle size compared to using maximum dimension, but a better understanding of the variability of size distributions is required to fully characterise the advantage. Further advancements on these subjects are presently difficult to achieve due to a lack of reference data. One main problem is that most available databases of precalculated optical properties assume completely random particle orientation, while for certain conditions a horizontal alignment is expected. In addition, the only database covering frequencies above 340 GHz has a poor representation of absorption as it is based on outdated refractive index data as well as only covering particles having a maximum dimension below 2 mm and a single temperature
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| 11. |
- Fox, Stuart, et al.
(author)
-
Airborne validation of radiative transfer modelling of ice clouds at millimetre and sub-millimetre wavelengths
- 2019
-
In: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 12:3, s. 1599-1617
-
Journal article (peer-reviewed)abstract
- The next generation of European polar orbiting weather satellites will carry a novel instrument, the Ice Cloud Imager (ICI), which uses passive observations between 183 and 664 GHz to make daily global observations of cloud ice. Successful use of these observations requires accurate modelling of cloud ice scattering, and this study uses airborne observations from two flights of the Facility for Airborne Atmospheric Measurements (FAAM) BAe 146 research aircraft to validate radiative transfer simulations of cirrus clouds at frequencies between 325 and 664 GHz using the Atmospheric Radiative Transfer Simulator (ARTS) and a state-of-the-art database of cloud ice optical properties. Particular care is taken to ensure that the inputs to the radiative transfer model are representative of the true atmospheric state by combining both remote-sensing and in situ observations of the same clouds to create realistic vertical profiles of cloud properties that are consistent with both observed particle size distributions and bulk ice mass. The simulations are compared to measurements from the International Submillimetre Airborne Radiometer (ISMAR), which is an airborne demonstrator for ICI. It is shown that whilst they are generally able to reproduce the observed cloud signals, for a given ice water path (IWP) there is considerable sensitivity to the cloud microphysics, including the distribution of ice mass within the cloud and the ice particle habit. Accurate retrievals from ICI will therefore require realistic representations of cloud microphysical properties.
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| 12. |
- Geer, Alan J., et al.
(author)
-
Bulk hydrometeor optical properties for microwave and sub-millimetre radiative transfer in RTTOV-SCATT v13.0
- 2021
-
In: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 14:12, s. 7497-7526
-
Journal article (peer-reviewed)abstract
- Satellite observations of radiation in the microwave and sub-millimetre spectral regions (broadly from 1 to 1000 GHz) can have strong sensitivity to cloud and precipitation particles in the atmosphere. These particles (known as hydrometeors) scatter, absorb, and emit radiation according to their mass, composition, shape, internal structure, and orientation. Hence, microwave and sub-millimetre observations have applications including weather forecasting, geophysical retrievals and model validation. To simulate these observations requires a scattering-capable radiative transfer model and an estimate of the bulk optical properties of the hydrometeors. This article describes the module used to integrate single-particle optical properties over a particle size distribution (PSD) to provide bulk optical properties for the Radiative Transfer for TOVS microwave and sub-millimetre scattering code, RTTOV-SCATT, a widely used fast model. Bulk optical properties can be derived from a range of particle models including Mie spheres (liquid and frozen) and non-spherical ice habits from the Liu and Atmospheric Radiative Transfer Simulator (ARTS) databases, which include pristine crystals, aggregates, and hail. The effects of different PSD and particle options on simulated brightness temperatures are explored, based on an analytical two-stream solution for a homogeneous cloud slab. The hydrometeor scattering "spectrum" below 1000 GHz is described, along with its sensitivities to particle composition (liquid or ice), size and shape. The optical behaviour of frozen particles changes in the frequencies above 200 GHz, moving towards an optically thick and emission-dominated regime more familiar from the infrared. This region is little explored but will soon be covered by the Ice Cloud Imager (ICI).
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| 13. |
- Gruetzun, Verena, et al.
(author)
-
All-sky information content analysis for novel passive microwave instruments in the range from 23.8 to 874.4 GHz
- 2018
-
In: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 11:7, s. 4217-4237
-
Journal article (peer-reviewed)abstract
- We perform an all-sky information content analysis for channels in the millimetre and sub-millimetre wavelength with 24 channels in the region from 23.8 to 874.4 GHz. The employed set of channels corresponds to the instruments ISMAR and MARSS, which are available on the British FAAM research aircraft, and it is complemented by two precipitation channels at low frequencies from Deimos. The channels also cover ICI, which will be part of the MetOp-SG mission. We use simulated atmospheres from the ICON model as basis for the study and quantify the information content with the reduction of degrees of freedom (Delta DOF). The required Jacobians are calculated with the radiative transfer model ARTS. Specifically we focus on the dependence of the information content on the atmospheric composition. In general we find a high information content for the frozen hydrometeors, which mainly comes from the higher frequency channels beyond 183.31 GHz (on average 3.10 for cloud ice and 2.57 for snow). Considerable information about the microphysical properties, especially for cloud ice, can be gained. The information content about the liquid hydrometeors comes from the lower frequency channels. It is 1.69 for liquid cloud water and 1.08 for rain using the full set of channels. The Jacobians for a specific cloud hydrometeor strongly depend on the atmospheric composition. Especially for the liquid hydrometeors the Jacobians even change sign in some cases. However, the information content is robust across different atmospheric compositions. For liquid hydrometeors the information content decreases in the presence of any frozen hydrometeor, for the frozen hydrometeors it decreases slightly in the presence of the respective other frozen hydrometeor. Due to the lack of channels below 183 GHz liquid hydrometeors are hardly seen by ICI. However, the overall results with regard to the frozen hydrometeors also hold for the ICI sensor. This points to ICI's great ability to observe ice clouds from space on a global scale with a good spatial coverage in unprecedented detail.
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| 14. |
- Holl, Gerrit, et al.
(author)
-
Optimised frequency grids for infrared radiative transfer simulations in cloudy conditions
- 2012
-
In: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 113:16, s. 2124-2134
-
Journal article (peer-reviewed)abstract
- This paper shows that radiometer channel radiances for cloudy atmospheric conditions can be simulated with an optimised frequency grid derived under clear-sky conditions. A new clear-sky optimised grid is derived for AVHRR channel . For HIRS channel 11 and AVHRR channel 5, radiative transfer simulations using an optimised frequency grid are compared with simulations using a reference grid, where the optimised grid has roughly 100–1000 times less frequencies than the full grid. The root mean square error between the optimised and the reference simulation is found to be less than 0.3 K for both comparisons, with the magnitude of the bias less than 0.03 K. The simulations have been carried out with the radiative transfer model Atmospheric Radiative Transfer Simulator (ARTS), version 2, using a backward Monte Carlo module for the treatment of clouds. With this module, the optimised simulations are more than 10 times faster than the reference simulations. Although the number of photons is the same, the smaller number of frequencies reduces the overhead for preparing the optical properties for each frequency. With deterministic scattering solvers, the relative decrease in runtime would be even more. The results allow for new radiative transfer applications, such as the development of new retrievals, because it becomes much quicker to carry out a large number of simulations. The conclusions are applicable to any downlooking infrared radiometer.
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| 15. |
- Holl, Gerrit, et al.
(author)
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SPARE-ICE : Synergistic ice water path from passive operational sensors
- 2014
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In: Journal of Geophysical Research: Atmospheres. - 2169-8996. ; 119:3, s. 1504-1523
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Journal article (peer-reviewed)abstract
- 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.
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| 16. |
- Kasai, Y., et al.
(author)
-
Overview of the Martian atmospheric submillimetre sounder FIRE
- 2012
-
In: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 63-64:SI, s. 62-82
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Journal article (peer-reviewed)abstract
- 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.
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| 17. |
- Kasai, Y., et al.
(author)
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Validation of stratospheric and mesospheric ozone observed by SMILES from International Space Station
- 2013
-
In: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 6:9, s. 2311-2338
-
Journal article (peer-reviewed)abstract
- We observed ozone (O3) in the vertical region between 250 and 0.0005 hPa (~ 12–96 km) using the Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on the Japanese Experiment Module (JEM) of the International Space Station (ISS) between 12 October 2009 and 21 April 2010. The new 4 K superconducting heterodyne receiver technology of SMILES allowed us to obtain a one order of magnitude better signal-to-noise ratio for the O3 line observation compared to past spaceborne microwave instruments. The non-sun-synchronous orbit of the ISS allowed us to observe O3 at various local times. We assessed the quality of the vertical profiles of O3 in the 100–0.001 hPa (~ 16–90 km) region for the SMILES NICT Level 2 product version 2.1.5. The evaluation is based on four components: error analysis; internal comparisons of observations targeting three different instrumental setups for the same O3 625.371 GHz transition; internal comparisons of two different retrieval algorithms; and external comparisons for various local times with ozonesonde, satellite and balloon observations (ENVISAT/MIPAS, SCISAT/ACE-FTS, Odin/OSIRIS, Odin/SMR, Aura/MLS, TELIS). SMILES O3 data have an estimated absolute accuracy of better than 0.3 ppmv (3%) with a vertical resolution of 3–4 km over the 60 to 8 hPa range. The random error for a single measurement is better than the estimated systematic error, being less than 1, 2, and 7%, in the 40–1, 80–0.1, and 100–0.004 hPa pressure regions, respectively. SMILES O3 abundance was 10–20% lower than all other satellite measurements at 8–0.1 hPa due to an error arising from uncertainties of the tangent point information and the gain calibration for the intensity of the spectrum. SMILES O3 from observation frequency Band-B had better accuracy than that from Band-A. A two month period is required to accumulate measurements covering 24 h in local time of O3 profile. However such a dataset can also contain variation due to dynamical, seasonal, and latitudinal effects
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| 18. |
- Larsson, Richard, et al.
(author)
-
A method for remote sensing of weak planetary magnetic fields : Simulated application to Mars
- 2013
-
In: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:19, s. 5014-5018
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Journal article (peer-reviewed)abstract
- 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.
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| 19. |
- Larsson, Richard, et al.
(author)
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A treatment of the Zeeman effect using Stokes formalism and its implementation in the Atmospheric Radiative Transfer Simulator (ARTS)
- 2014
-
In: Journal of Quantitative Spectroscopy and Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 133, s. 445-453
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Journal article (peer-reviewed)abstract
- 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.
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| 20. |
- Larsson, Richard, et al.
(author)
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Martian magnetism with orbiting sub-millimeter sensor: simulated retrieval system
- 2017
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In: Geoscientific Instrumentation, Methods and Data Systems. - : Copernicus Publications. - 2193-0856 .- 2193-0864. ; 6:1, s. 27-37
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Journal article (peer-reviewed)abstract
- A Mars-orbiting sub-millimeter sensor can be used to retrieve the magnetic field at low altitudes over large areas of significant planetary crustal magnetism of the sur- face of Mars from measurements of circularly polarized radi- ation emitted by the 368 GHz ground-state molecular oxygen absorption line. We design a full retrieval system for one ex- ample orbit to show the expected accuracies on the magnetic field components that one realization of such a Mars satellite mission could achieve. For one set of measurements around a tangent profile, we find that the two horizontal components of the magnetic field can be measured at about 200 nT error with a vertical resolution of around 4 km from 6 up to 70 km in tangent altitude. The error is similar regardless of the true strength of the magnetic field, and it can be reduced by re- peated measurements over the same area. The method and some of its potential pitfalls are described and discussed.
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| 21. |
- Mendrok, Jana, et al.
(author)
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ARTS+ - A toolbox for microwave atmospheric radiative transfer in solar system planets
- 2013
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Conference paper (other academic/artistic)abstract
- Microwave and (sub)millimetre-wave frequencies have long been of interest for remote sensing of the Earth and space objects. They suffer less from interference by small particles (dust, clouds), hence penetrate deeper into atmospheres revealing their deeper structures hidden to shorter wavelengths, and possess characteristic line absorption features of many gaseous species, which are of interest for the understanding of atmospheric chemistry and dynamics.Models simulating radiative transfer and wave propagation (RT/WP) have been developed by many institutions. Most of them are designed for a particular, narrow region of the electromagnetic spectrum, certain instrument types or missions, and specific atmospheric conditions. In particular, they are usually set up for a specific planetary body. This high level of specialisation allows for accurate modelling results. However, it also limits the flexibility of those models and comparability between them.For various applications there is a demand on easy and quick calculations of propagation characteristics, like feasibility estimates of missions proposed to space agencies and performance estimates of radiocommunication links between satellites or orbiter and lander.Within an ESA study we have developed a toolbox for microwave RT/WP in planetary atmospheres. The toolbox consists of the RT/WP model and a data package. The RT/WP model is a largely revised and extended version of ARTS, a sophisticated, flexible RT model for Earth atmosphere (3D spherical geometry, diverse absorption models, scattering, polarization, Jacobians). Focus has been on creating a consistent, physics-based model. Several features have been added (radio link and cloud radar modes, zeeman splitting, doppler shifts). A new spectroscopic approach has been implemented considering effects of a range of broadening/pressure-shifting/refracting species, a corresponding spectroscopic line catalogue designed and prepared. At the current state, the data package contains atmospheric and surface data for Earth and the planets Venus, Mars, and Jupiter, but is easily extendable.We will illustrate the capabilities of the toolbox introducing several example cases and presenting results from the toolbox validation.
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| 22. |
- Mendrok, Jana, et al.
(author)
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Sub-millimeter wave radiometer for observation of cloud ice: a proposal for Japanese mission
- 2009
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In: Sensors, Systems, and Next-Generation Satellites XIII. - Bellingham, Wash : SPIE - The International Society for Optics and Photonics. - 9780819477798
-
Conference paper (peer-reviewed)abstract
- Ice clouds play an important role in the energy budget of the atmosphere as well as in the hydrological cycle. Currently cloud ice is one of the largest remaining uncertainties in climate models. Large discrepancies arise from different assumptions on ice cloud properties, in particular on microphysics, which are not sufficiently constrained by measurements. Passive sub-millimeter wave (SMM) techniques have the potential of providing direct information on ice content and particle sizes with daily global coverage. Here we introduce a concept for a compact 2-receiver SMM sensor and demonstrate its capabilities on measurements of ice content, mean particle size, and cloud altitude.
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| 23. |
- Millán, L., et al.
(author)
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SMILES ice cloud products
- 2013
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In: Journal of Geophysical Research: Atmospheres. - : American Geophysical Union (AGU). - 2169-8996 .- 2169-897X. ; 118:12, s. 6468-6477
-
Journal article (peer-reviewed)abstract
- Upper tropospheric water vapor and clouds play an important role in Earth's climate, but knowledge of them, in particular diurnal variation in deep convective clouds, is limited. An essential variable to understand them is cloud ice water content. The Japanese Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES) on board the International Space Station (ISS) samples the atmosphere at different local times allowing the study of diurnal variability of atmospheric parameters. We describe a new ice cloud data set consisting of partial Ice Water Path and Ice Water Content. Preliminary comparisons with EOS-MLS, CloudSat-CPR and CALIOP-CALIPSO are presented. Then, the diurnal variation over land and over open ocean for partial ice water path is reported. Over land, a pronounced diurnal variation peaking strongly in the afternoon/early evening was found. Over the open ocean, little temporal dependence was encountered. This data set is publicly available for download in HDF5 format.
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| 24. |
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| 25. |
- Nukala, Madhuri, et al.
(author)
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Analysis of Light Scattering by two-dimensional Inhomogeneities in Paper using General Radiative Transfer Theory
- 2014
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In: 10TH INTERNATIONAL CONFERENCE ON MATHEMATICAL PROBLEMS IN ENGINEERING, AEROSPACE AND SCIENCES (ICNPAA 2014). - : AIP Publishing LLC. - 9780735412767 ; 1637, s. 750-758
-
Conference paper (peer-reviewed)abstract
- Lateral light scattering simulations of printed dots are analyzed using general radiative transfer theory. We investigated the appearance of a printed paper in relation to the medium parameters like thickness of the paper sample, its optical properties, and the asymmetry factor. It was found that the appearance of a print greatly depends on these factors making it either brighter or darker. A thicker substrate with higher single scattering albedo backed with an absorbing surface makes the dots brighter due to increased number of scattering events. Additionally, it is shown that the optical effects of print also depend on illuminating and viewing angles along with the depth of ink penetration. A larger single scattering angle implies less intensity and the dots appear much blurred due to the shadowing effect prominent when viewed from sides. A fully penetrated dot of the same extinction coefficient as a partial penetrated one is darker due to increased absorption. These results can be used in applications dealing with lateral light scattering.
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