Satellite missions for measuring winds in the troposphere and thermosphere will be launched in a near future. There is no plan to observe winds in the altitude range between 30-90 km, though middle atmospheric winds are recognized as an essential parameter in various atmospheric research areas. Sub-millimetre limb sounders have the capability to fill this altitude gap. In this paper, we summarize the wind retrievals obtained from the Japanese Superconducting Submillimeter Wave Limb Emission Sounder (SMILES) which operated from the International Space Station between September 2009 and April 2010. The results illustrate the potential of such instruments to measure winds. They also show the need of improving the wind representation in the models in the Tropics, and globally in the mesosphere. A wind measurement sensitivity study has been conducted for its successor, SMILES-2, which is being studied in Japan. If it is realized, sub-millimeter and terahertz molecular lines suitable to determine line-of-sight winds will be measured. It is shown that with the current instrument definition, line-of-sight winds can be observed from 20 km up to more than 160 km. Winds can be retrieved with a precision better than 5 ms-1 and a vertical resolution of 2-3 km between 35-90 km. Above 90 km, the precision is better than 10 ms-1 with a vertical resolution of 3-5 km. Measurements can be performed day and night with a similar sensitivity. Requirements on observation parameters such as the antenna size, the satellite altitude are discussed. An alternative setting for the spectral bands is examined. The new setting is compatible with the general scientific objectives of the mission and the instrument design. It allows to improve the wind measurement sensitivity between 35 to 90 km by a factor 2. It is also shown that retrievals can be performed with a vertical resolution of 1 km and a precision of 5-10 ms-1 between 50 and 90 km.
A submillimeter wave limb emission sounder, that is to be aboard the Japanese Experiment Module (JEM, dubbed as 'KIBO') at the International Space Station, has been designed. This payload, Superconducting Submillimeter-wave Limb Emission Sounder (SMILES), is aimed at global mappings of stratospheric trace gasses by means of the most sensitive submillimeter receiver ever operated in space. Such sensitivity is ascribed to a Superconductor-Insulator- Superconductor (SIS) mixer, which is operated at 4.5 K in a dedicated cryostat combined with a mechanical cooler. SMILES will observe ozone-depletion-related molecules such as ClO, HCl, HO2, HNO3, BrO and O3 in the frequency bands at 624.32 - 626.32 GHz, and 649.12 - 650.32 GHz. A scanning antenna will cover tangent altitudes from 10 to 60 km in every 53 seconds, while tracing latitudes from 38S to 65N along its orbit. This global coverage makes SMILES a useful tool of observing the low- and mid-latitudinal areas as well as the Arctic peripheral region. The molecular emissions will be detected by two units of acousto-optic spectrometers (AOS), each of which has coverage of 1.2 GHz with a resolution of 1.8 MHz. This high-resolution spectroscopy will allow us to detect weal emission lines attributing to less-abundant species.
A ground-based millimeter-wave radiometer was developed in Communications Research laboratory, and will be operated to observe stratospheric chlorine monoxide, ozone, and nitrous oxide at Eureka, the Arctic stratospheric observatory at 80 degree(s)N and 86 degree(s)W from December 2000. The radiometer is designed to detect weak emission and for long-term observation in a remote site. The most remarkable feature is that all optical components are integrated in the cryo- dewar and cooled down to less than 60 K. This makes the optical length short and is a great advantage to spectroscopic observation of atmosphere because the rapid ripple of spectral baseline due to standing waves never occurs in the input optics and the optics is thermally stable. This new radiometer was installed in Eureka in the spring of 2000. The radiometer system is fully remote- controllable, and will be operated without frequent local operation. We are expecting quasi-simultaneous observation of three molecules with the radiometer from this winter. The detail of the radiometer instruments is presented in this paper.
A submillimeter limb-emission sounder, that is to be aboard the Japanese Experiment Module (JEM, dubbed as KIBO) at the International Space Station, has been designed. This payload, Superconducting Submillimeter-wave Limb-emission Sounder (SMILES), is aimed at global mappings of stratospheric trace gases by means of the most sensitive submillimeter receiver ever operated in space. Such sensitivity is ascribed to a Superconductor-Insulator- Superconductor (SIS) mixer, which is operated at 4.5 K in a dedicated cryostat combined with a mechanical cooler. SMILES will observe ozone-depletion-related molecules such as ClO, Hcl, HO2, HNO3, BrO and O3 in the frequency bands at 624.32-626.32 GHz and 649.12-650.32 GHz. A scanning antenna will cover tangent altitudes from 10 to 60 km in every 53 seconds, while tracing the latitudes form 38 S to 65 N along its orbit. This global coverage makes SMILES a useful tool of observing the low- and mid- latitudinal areas as well as the Arctic peripheral region. The molecular emissions will be detected by two units of acousto-optic spectrometers (AOS), each of which has coverage of 1.2 GHz with a resolution of 1.8 MHz. This high-resolution spectroscopy will allow us to detect weak emission lines attributing to less-abundant species.
An engineering model has been built for a space-borne 640- GHz SIS receiver. It is the key component of Superconducting Submillimeter-Wave Limb-Emission Sounder, which is to be operated aboard the Japanese Experiment Module of the International Space Station in 2005. The receiver includes two Superconductor-Insulator-Superconductor (SIS) mixers cooled at 4.5 K, as well as four High-Electron-Mobility- Transistor (HEMT) amplifiers, two of which cooled at 20 K and the other two at 100 K. These components are integrated in a compact cryostat with two-stage Stirling and Joule- Thomson refrigerators. The receiver components has been successfully cooled and the cryostat has survived random vibration tests. The 640-GHz SIS mixer, which uses a pair of Nb/AlOx/Nb junctions connected in parallel, is built so that a broad RF matching be achieved without mechanical tuners. It is followed by cooled low noise HEMT amplifiers with a noise temperature of less than 17 K. The total receiver noise temperature has been measured around 180 - 220 K over the bandwidth of 5.5 GHz.
NASDA and CRL are planning to develop a spaceborne SMILES, which is to be installed in the Exposed Facility (EF) on the JEM of the ISS. By observing gases such as ClO, HCl, NO, N2O, HO2 and BrO in the stratosphere, JEM/SMILES can trace the chemical reactions concerning the ozone depletion and climate change. Global distribution of those gases will be mapped with a height resolution of about 2 km. JEM/SMILES receives low-intensity signals from those gases with highly sensitive SIS (Superconductor-Insulator-Superconductor) mixers at 640 GHz, which are cooled to 4.2 K by a space-qualified mechanical cooler. The mission target is to demonstrate the effectiveness of the submillimeter-wave limb emission sounding and to establish space applicability of the low-noise SIS mixers and a mechanical 4-K cooler. JEM/SMILES is expected to be launched in 2003, and the experiments will last a year or more.
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