International Space Station Benefits for Humanity

Superconducting Submillimeter-wave Limb-emission Sounder (SMILES)

The superconducting submillimeter-wave limb-emission sounder (SMILES) is the first on board experimental instrument for mechanically-cooled superconducting mixer, as well as high resolution measurement system for atmospheric minor constituents related with stratospheric and mesospheric chemistry. SMILES collected high-quality observation data for six months until the instrument encountered trouble. These data indicate the high performance of SMILES instrument as the data analysis progressed, and the data are expected to be produce a mine of new scientific information. The main scientific objective of the SMILES mission is to study the recovery and stability of the stratospheric ozone also known as the ozone layer Some numeric atmospheric model calculations have suggested that global ozone levels will recover to pre-1980 levels around the middle of the 21st Century. However, there are still considerable uncertainties affecting ozone levels, especially in the bromine budget and chemical processes of inorganic chlorine. In addition, stratospheric cooling due to increases in greenhouse gases in troposphere may affect the trend and stability of the ozone layer. The SMILES mission contributes to these issues by focusing on the detailed halogen chemistry related to ozone destruction processes.

SMILES was launched with Konotori1 by the H-IIB launch vehicle on Sept. 11, 2009 from Tanegashima Space Center in Japan. After being attached to the a port of the Exposed Facility of Kibo (Japan Experiment Module) on the ISS on Sept. 25 , the instrument passed several critical on-board tests. The nominal continuous observation of the earth's atmosphere started on Oct. 12. SMILES performed observation for about six months, until a component of the instrument broke down on Apr. 21, 2010.

SMILES detected weak radiation from atmospheric constituents in the submillimeter wavelength region (0.46-0.48millimeters of wavelength, which corresponds with 624-650 gigahertz of frequency). By calculating the strength of spectral lines coming from various molecular species, the abundance of the species can be retrieved.

One sample (snapshot) of global distribution of atmospheric constituents retrieved from SMILES observation is the ozone depletion and related change in the amount of chlorine compounds around the North Pole . In winter 2010, planetary waves in the stratosphere became vigorous, resulting in a stratospheric sudden warming event at high latitudes (about 40 degrees centigrade increase of temperature within several days). Heterogeneous chemistry process has been underway during this term, and gaseous Hydrochloric acid or HCL decreased within the polar vortex. At the same time chlorine chemistry was activated by the solar radiation outside the polar night region, and it resulted in the high Chlorine Monoxide or ClO region. In this region, ozone destruction has occurred. SMILES can figure out such phenomena with high resolution simultaneously.

In the brightness temperature spectra obtained from SMILES observation data, strong ozone and Hydrochloric acid lines with other minor peaks of Hypochlorous acid or HOCl, Nitric acid or HNO3, Bromine Oxide or BrO, and ozone isotopes can be seen. The noise level of the brightness temperature is around 0.4 Kelvin, which is at least one digit smaller than other space-borne limb sounders.

During the first stage of SMILES instrument development, the current literature-based spectroscopic values were used to set the parameters for the spectrometer. The extremely high performance of the spectroscopy with SMILES has led researchers to reevaluate known atmospheric science data and to develop additional atmospheric investigations to test new parameters.

SMILES was successfully launched and performed atmospheric observation with its high spectral resolution. Unfortunately, its operation was terminated after six-months of observation, but the observation data indicated the outstanding performance of SMILES instrument. In addition, its preliminary scientific results are reasonable and consistent with the results of other space-borne measurements. It is expected that undiscovered information will be found in the data collected over the six months of operation. Further studies related to data processing and analysis will be necessary to determine the real performance of SMILES instrument.

example of observed spectrum with SMILES

An example of observed spectrum with SMILES. For comparison of spectra on different tangent height, the baseline e of each spectrum is vertically displaced. Random noise of . the spectra is about 0.4-0.6 6Kelvin among all tangent height. (Image: courtesy of Fujitsu FIP)

Destruction de l'ozone activée par ClO et HCl

Ozone destruction which was activated with ClO and HCl on Jan. 23, 2010. It is shown as the high ClO region (see “ClO” panel). In the high ClO region, O3 destruction has occurred. (see “Ozone” panel) The area where HCl concentration is low suggests the region of polar vortex (s see “HCl” panel.) (Image: courtesy of Kyoto University)

Takuki SANO
ISS Science Project Office Institute of Space and Astronautical Science, JAXA