L. Mazuray, J.-C. Barthès, F. Bayle, D. Castel, P. Claviere, F. Delbru, P.-O. Doittau, L. Gladin, P. Guilleux, S. Halbout, D. Lavielle, J.-L. Varin, S. de Zotti, C. Rosolen, H. Ozeki
An acousto-optical spectrometer (AOS) is employed in order to meet scientific mission objectives of submillimeter-wave limb-emission sounder (SMILES) to be aboard the Japanese Experiment Module (JEM) of International space station (ISS). AOS is developed by ASTRIUM for the Japanese space agency (NASDA). The capability of multi channel detection with AOS is suitable for observing multi-chemical species in a wide frequency region. Low noise of the AOS enables us to obtain the spectra with a very high sensitivity. Several technical concerns relating to important instrumental characteristics of AOS are discussed and expected performance of the design are overviewed.
Sensitivity studies of temperature and chemical species (Observed by ISS/JEM/SMILES: O3, HCl, ClO, HO2, BrO, HNO3, CH3CN, and Not observed by SMILES: Temperature, H2O, N2O, NO2, NO, CH3Cl, CO, H2CO, OH and O-atom) was carried out for the SMILES-2 proposal, a sub-mm and THz observation of limb emission from space over the spectral region from 400 GHz to 2.5 THz. Tentative but optimal candidate of frequency bands to cover these species was selected with 3 SIS (Superconductor-Insulator-Superconductor) mixers; SIS-1 (485-489 GHz + 523-527 GHz), SIS-2 (623-627 GHz + 648-652 GHz), SIS-3 (557 GHz + 576.3 GHz) and 2 HEB (Hot Electron Bolometer); HEB-1 (1.8 THz OH) and HEB-2 (2.06 THz O-atom). Temperature can be retrieved with 1 K precision and 1 km vertical resolution from 15 to 120 km. Other chemical species also showed very high single scan precision (random error) comparable to statistical standard error of previous satellite measurements.
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.
On-orbit performance of the radio spectrometer of SMILES is discussed. We focused on the telemetry data of
photodiode current, laser diode current, and laser diode operating temperature. The data showed degradation trend as the
mission went on. This is due to a wear-out phenomenon of commercially available laser diode, which is used as the light
source of the radio spectrometer. Since the laser diodes have a certain lifetime, both screening procedure and operating
condition for them must be properly defined and implemented for ensuring a good performance of the spectrometer
throughout designed mission life. For these purposes, we conducted several kinds of qualification tests including an
accelerated life time test during design phase, and expected life time of the laser diode was derived on the basis of these
test results. In this paper, the results from the qualification tests at ground and the actual performance on orbit with the
telemetry and mission data will be presented.
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.
Laurent Mazuray, F. Bayle, P. Clavieres, F. Delbru, L. Gladin, P. Guilleux, S. Halbout, C. Raballand, M. Reynaud, Marc Trier, Jean-Luc Varin, S. de Zotti, Carlo Rosolen, Hiroyuki Ozeki
An Acousto-Optical Spectrometer (AOS) features the submillimeter-wave limb-emission sounder (SMILES) to be aboard the Japanese Experiment Module (JEM) of International space station (ISS). The Japanese space agency (NASDA) has contracted ASTRIUM for the development of the AOS. Acousto- Optical Spectrometers are well adapted for analyzing in real time with high resolution a wide band and faint signal embedded in radiometric noise. Their usefulness for instantaneous detection and mapping of multi-species emission was first demonstrated in the field of radio astronomy in 1970s and thanks to their compactness and low power consumption, they are highly well adapted to space application. Several technical concerns related to important instrumental characteristics of AOS are discussed and performances are overviewed.
KEYWORDS: Spectroscopy, Adaptive optics, Acousto-optics, Interference (communication), Charge-coupled devices, Analog electronics, Signal to noise ratio, Spectroscopes, Quantization, Data modeling
An acousto-optical spectrometer (AOS) is employed in order to meet scientific mission objectives of submillimeter-wave limb-emission sounder (SMILES) to be aboard the Japanese Experiment Module (JEM) of the International space station (ISS). The capability of multi channel detection with AOS is suitable for observing multi chemical species in a wide frequency region. Wide noise dynamic range enables us to obtain the spectra without unnecessary increase of system noise, suggesting a good combination of AOS with low noise front end system of SMILES> Several technical concerns relating to important instrumental characteristics of AOS are discussed and expected performance of the spectrometers to be used in the JEM/SMILES mission are over viewed.
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.
In order to estimate measurement capability of the Superconducting Submillimter-Wave Limb-Emission Sounder (SMILES) on the Japanese Experiment Module (JEM) of the International Space Station (ISS) and to clarify the scientific impacts of the JEM/SMILES, we are developing the JEM/SMILES simulator. The simulator consists of the forward model and the inversion model. The forward model calculates a brightness temperature by applying the radiative transfer formula to a limb sounding geometry and simulates the effects of the JEM/SMILES sensor characteristics including optics superconductor-insulator-superconductor (SIS) mixers, Acousto-Optical Spectrometer (AOS), and so on, to it. Because it is important to estimate the effects of the sensor for the retrieval, we develop carefully simulated sensor model. The forward model also calculates weighting functions of molecular, the temperature, the pressure and so on. This paper describes how the brightness temperature and weighting functions are calculated in the forward model and how the effects of the sensor are taken into account in the simulator, and finally shows how the optical estimation method (OEM) is applied to our retrieval model.
JEM/SMILES (superconducting SubMIllimeter-wave Limb-Emission Sounder) is currently under development to demonstrate a submillimeter-wave sounder with extremely high sensitivity on the platform of the Japanese Experiment Module (JEM). In the submillimeter region, this is the first mission in space using a low-noise 4K cooled receiver, which is expected to give new observations for radicals in the stratosphere such as BrO. One of the most unique characteristics of the JEM/SMILES observation is its high sensitivity in detecting atmospheric limb emissions in the submillimeter wave range. The purpose of SMILES is global monitoring of the radicals which play important roles in the stratospheric system. We are now using the newly developed JEM/SMILES simulator to model observed spectra (including the characteristics of the SMILES sensor) and simulate the retrieval performance. Some preliminary results of the simulation are obtained in view of the scientific targets of JEM/SMILES.
The Mt. Fuji submillimeter-wave telescope has been operated since November 1998 to survey neutral atomic carbon (CI) toward the Milky Way. It has a 1.2 m main reflector with a surface accuracy of 10 micrometer in rms. A dual polarization superconductor-insulator-superconductor (SIS) mixer receiver mounted on the Nasmyth focus receives 810/492/345 GHz bands in DSB simultaneously. An acousto-optical spectrometer (AOS) has 1024 channels for 0.8 GHz bandwidth. The telescope was installed with a helicopter and bulldozers at the summit of Mt. Fuji (alt. 3725 m) in July 1998 after a test operation at Nobeyama for a year. It has been remotely operated via a satellite communication from Tokyo or Nobeyama. Atmospheric opacity at Mt. Fuji was 0.4 - 1.0 at 492 GHz in 30% of time and 0.07 - 0.5 at 345 GHz in 60% of time during winter five months. The system noise temperature was typically 1200 K (SSB) at 492 GHz and 500 K (DSB) at 345 GHz. The beam size was measured to be 2.'2 and 3.'1 at 492 and 345 GHz, respectively. We have conducted a large-scale survey of the CI (492 GHz) and CO (3 - 2: 345 GHz) emission from nearby molecular clouds with total area of 10 square degrees. We describe the telescope system and report the performance obtained in the 1998 winter.
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