| 1. |
- Hagen, Jonas, et al.
(författare)
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First measurements of tides in the stratosphere and lower mesosphere by ground-based Doppler microwave wind radiometry
- 2020
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Ingår i: Atmospheric Chemistry and Physics. - : Copernicus GmbH. - 1680-7316 .- 1680-7324. ; 20:4, s. 2367-2386
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric tides are important for vertical coupling in the atmosphere, from the stratosphere down to the troposphere and up to the thermosphere. They are planetary-scale gravity waves with well-known periods that are integer fractions of a day and can be observed in the temperature or wind fields in the atmosphere. Most lidar techniques and satellites measure atmospheric tides only in the temperature field and continuous measurements of the tides in the wind field of the stratosphere and lower mesosphere are rare, even though, with modern lidars, they would be feasible. In this study, we present measurements of the diurnal tide in the wind field in the stratosphere and lower mesosphere by ground-based microwave wind radiometry for two different campaigns in tropical and polar regions. Further, we compare our measurements to MERRA-2 reanalysis data. In the tri-monthly mean, we find a good correspondence in the amplitude and phase of the diurnal tide between measurements and reanalysis with the most important features of the diurnal tides represented in both data sets. When looking at shorter timescales, we find significant differences in the data sets. We make an attempt to examine these differences and discriminate between atmospheric variability and noise, and we present some hints for intermittent diurnal tides. We conclude that continuous ground-based observations of tides in the middle atmospheric wind field are feasible, and they deliver consistent results for the mean amplitude and phase of the diurnal tide in the tri-monthly mean. We further discuss the limitations in regards to short timescale observations of tides and the possibility to provide additional insight into middle atmospheric dynamics that is complementary to temperature observations and reanalysis data.
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| 2. |
- Hammar, Arvid, 1986, et al.
(författare)
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Optical Tolerance Analysis for the STEAMR Instrument
- 2013
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Ingår i: TWENTY-FOURTH INTERNATIONAL SYMPOSIUM ON SPACE TERAHERTZ TECHNOLOGY (ISSTT2013).
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Konferensbidrag (refereegranskat)abstract
- The optics of the STEAMR instrument is a complex system involving off-axis mirrors designed to achieve precise imaging of the 14 receiver channel beams from the far field to the corresponding feed horns. An initial optical design was generated by Swedish Space Corporation, which laid the framework for the subsequent IAP design that further developed the optical system to meet the mission performance requirements. Omnisys Instruments is now the prime contractor for the complete STEAMR instrument.Although simulations of the optics presently show good results, little is known about the sensitivity to mechanical errors, i.e. surface deviations and misalignments of the reflectors. This work encompasses a tolerance analysis for the complete optics chain consisting of a 28 reflector focal plane array (FPA) and 6 reflector relay optics. With six degrees of freedom for each reflector, the scale of the required mechanical tolerancing analysis is significant. The goal of this work is therefore to identify critical locations within the optics architecture that have the largest influence on performance.Being a multi-beam instrument, the optics requirements for STEAMR can be divided into two parts: pointing and beam quality. Pointing errors were analysed using the commercial software package ZEMAX, which offers built-in routines for performing Monte-Carlo simulations specifically for tolerancing problems. Beam quality, i.e. sidelobe levels, beam efficiency and polarization plane, were analysed using physical optics routines in GRASP. Simulations in both programs have been carried out using single element perturbation and Monte-Carlo simulations on the complete optics chain.In the first iteration of the analysis, all reflector surfaces were assumed to be perfect. In later analyses, surface errors were also added. Special attention was given to the 1.6 m x 0.8 m carbon fiber main reflector, which is the most sensitive in terms of errors in shape. By running the optical analysis in parallel and in close cooperation with the mechanical design, it has been possible to assume realistic errors for the different parts of the optics. Measurements of the feed horns done by IAP show excellent agreement with simulations, where sidelobe levels around -40 dB was predicted. Therefore, the beams of all feeds have been modelled as perfect Gaussians.
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| 3. |
- Hammar, Arvid, 1986, et al.
(författare)
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Optical Tolerance Analysis of the Multi-Beam Limb Viewing Instrument STEAMR
- 2014
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 4:6, s. 714-721
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Tidskriftsartikel (refereegranskat)abstract
- We report on an optical tolerance analysis of the submillimeter atmospheric multi-beam limb sounder STEAMR. Physical optics and ray-tracing methods were used to quantify and separate errors in beam pointing and distortion due to reflector misalignment and primary reflector surface deforma-tions. Simulations were performed concurrently with the man-ufacturing of a multi-beam demonstrator of the relay optical system which shapes and images the beams to their corresponding receiver feed horns. Results from Monte-Carlo simulations show that the inserts used for reflector mounting should be positioned with an overall accuracy better than 100 µm (~1/10 wavelength). Analyses of primary reflector surface deformations show that a deviation of magnitude 100 µm can be tolerable before deployment, whereas the corresponding variations should be less than 30 µm during operation. The most sensitive optical elements in terms of misalignments are found near the focal plane. This localized sensitivity is attributed to the off-axis nature of the beams at this location. Post-assembly mechanical measurements of the reflectors in the demonstrator show that alignment better than 50 µm could be obtained.
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| 4. |
- Jacob, Karl, et al.
(författare)
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Characterization of the 530-625 GHz receiver unit for the Jupiter mission JUICE/SWI
- 2015
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Ingår i: Proceedings of the 36th ESA Antenna Workshop on Antennas and RF Systems for Space Science.
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Konferensbidrag (refereegranskat)abstract
- The Submillimetre Wave Instrument (SWI) is being developed for the Jupiter Icy moons Explorer (JUICE) missionof the European Space Agency (ESA). In this paper we give an overview of the 530 GHz to 625 GHz receiver unit of SWI and present the first noise temperature measurements covering the complete receiver bandwidth at room temperature operation. In this context we will point out the difficulties with the highly variable local oscillator power within the bandwith, which needs a careful tuning of the multiplier bias voltages in order to optimize the noise temperature and to avoid damage of the mixers. In addition we show initial results at cold temperature operation. Furthermore we will present a first stability measurement showing the temperature dependence of the receiver gain at room temperature operation.
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| 5. |
- Jacob, Karl, et al.
(författare)
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Radiometric performance of the 530 to 625 GHz receiver unit of the submillimetre wave instrument on juice
- 2019
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Ingår i: ISSTT 2019 - 30th International Symposium on Space Terahertz Technology, Proceedings Book. ; , s. 28-31
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Konferensbidrag (refereegranskat)abstract
- The upcoming Submillimeter Wave Instrument on the JUICE spacecraft is a passive radiometer/spectrometer instrument with two heterodyne receivers which are independently tunable in the frequency bands 530 to 625 GHz and 1080 to 1275 GHz. It will study Jupiter’s atmosphere as well as the atmospheres and surface properties of the Galilean moons. This work presents the results of first radiometric tests with a prototype of the 600 GHz receiver. In this context, the baseline ripples caused by the internal calibration target have been characterized using two conical prototypes with a linear and an exponential absorber coating profile. A significant reduction of the baseline ripple amplitude has been measured with the target having the exponential cone profile. The spectroscopic baseline has been characterized for various frequency steps when applying frequency switching as an alternative calibration mode. At some operating frequencies a very flat switching baseline has been measured for frequency throws up to 90 MHz, while at other frequencies significant spectral distortions are measured even with a step size of 22.5 MHz. The first radiometric tests of the sideband gain ratio with a passive Fourier Transform Spectroscopy method demonstrate the general applicability in the 530 to 625 GHz band.
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| 6. |
- Kotiranta, M., et al.
(författare)
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Versatile Radiometric Testbed for the Submillimeter Wave Instrument
- 2022
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Ingår i: 32nd International Symposium of Space Terahertz Technology, ISSTT 2022.
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Konferensbidrag (refereegranskat)abstract
- This paper presents a radiometric testbed for the characterization of the 600-GHz and 1200-GHz double side band heterodyne receivers of the Submillimeter Wave Instrument on the Juice mission of ESA. The testbed enables measurements of receiver noise temperature, gain stability, side band ratio, and beam coalignment in a thermal-vacuum chamber. Receiver spectral response and spurious signal investigations are possible with an optional transmitter. Measurement results obtained for engineering and protoflight models of the instrument are presented.
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| 7. |
- Navas-Guzmán, Francisco, et al.
(författare)
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Zeeman effect in atmospheric O2 measured by ground-based microwave radiometry
- 2015
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 8:4, s. 1863-1874
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Tidskriftsartikel (refereegranskat)abstract
- In this work we study the Zeeman effect on stratospheric O2 using ground-based microwave radiometer measurements. The interaction of the Earth magnetic field with the oxygen dipole leads to a splitting of O2 energy states, which polarizes the emission spectra. A special campaign was carried out in order to measure this effect in the oxygen emission line centered at 53.07 GHz. Both a fixed and a rotating mirror were incorporated into the TEMPERA (TEMPERature RAdiometer) in order to be able to measure under different observational angles. This new configuration allowed us to change the angle between the observational path and the Earth magnetic field direction. Moreover, a high-resolution spectrometer (1 kHz) was used in order to measure for the first time the polarization state of the radiation due to the Zeeman effect in the main isotopologue of oxygen from ground-based microwave measurements. The measured spectra showed a clear polarized signature when the observational angles were changed, evidencing the Zeeman effect in the oxygen molecule. In addition, simulations carried out with the Atmospheric Radiative Transfer Simulator (ARTS) allowed us to verify the microwave measurements showing a very good agreement between model and measurements. The results suggest some interesting new aspects for research of the upper atmosphere
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| 8. |
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| 9. |
- Stähli, O., et al.
(författare)
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Microwave radiometer to retrieve temperature profiles from the surface to the stratopause
- 2013
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Ingår i: Atmospheric Measurement Techniques. - : Copernicus GmbH. - 1867-1381 .- 1867-8548. ; 6:9, s. 2477-2494
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Tidskriftsartikel (refereegranskat)abstract
- TEMPERA (TEMPERature RAdiometer) is a new ground-based radiometer which measures in a frequency range from 51-57 GHz radiation emitted by the atmosphere. With this instrument it is possible to measure temperature profiles from ground to about 50 km. This is the first ground-based instrument with the capability to retrieve temperature profiles simultaneously for the troposphere and stratosphere. The measurement is done with a filterbank in combination with a digital fast Fourier transform spectrometer. A hot load and a noise diode are used as stable calibration sources. The optics consist of an off-axis parabolic mirror to collect the sky radiation. Due to the Zeeman effect on the emission lines used, the maximum height for the temperature retrieval is about 50 km. The effect is apparent in the measured spectra. The performance of TEMPERA is validated by comparison with nearby radiosonde and satellite data from the Microwave Limb Sounder on the Aura satellite. In this paper we present the design and measurement method of the instrument followed by a description of the retrieval method, together with a validation of TEMPERA data over its first year, 2012.
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