The objective of SMILES (Superconducting Submillimeter-Wave Limb-Emission Sounder) is to demonstrate a sensitive submillimeter-wave sounder and to monitor global distributions of the stratospheric trace gases.
SMILES, which is developed in a joint project between JAXA and NICT (National Institute of Information and Communications Technology), is the first to use a superconductive low-noise receiver with a mechanical 4-K refrigerator in space.
Background
Atmospheric changes such as ozone depletion and global warming, which are attributed to human activities, are becoming a serious environmental issue. A major cause of the ozone depletion in the stratosphere is due to trace gases such as chlorine and bromine compounds originated from human-made chlorofluorocarbons (CFCs), halogen containing substances, and others. After the Montreal Protocol [United Nations Environmental Programme, 1987] and its amendments, the total combined abundance of ozone-depleting compounds in the lower atmosphere peaked around 1994, and its exhaust is now slowly declining. The WMO report [2006] says, the recovery of the ozone abundance is estimated around 2060-2075, however the results calculated from chemistry-climate models for the future ozone amount vary considerably with each other. The ozone depletion has been observed not only in the polar latitudes, but also in the mid- and lower latitudes. Furthermore, stratospheric trace gases such as ozone, carbon dioxide and water vapor have serious effects on climate change including global warming.
To perform quantitative assessment for the future we need three-dimensional and simultaneous measurements of ozone and trace gases in the stratosphere. Also important is global accurate data with high resolutions in space and time. A space-bone submillimeter-wave limb-emission sounding has major advantages for measuring these trace gases during day and night in the stratosphere globally.
The objective of the SMILES (Superconducting Submillimeter-Wave Limb-Emission Sounder) mission is to demonstrate highly sensitive submillimeter-wave soundings and to monitor global distributions of the stratospheric trace gases. For these requirements, a superconductive low-noise receiver with a mechanical 4K-class cryocooler is used in space for the first time.
Scientific Objectives
One of the most unique characteristics of the SMILES observation is its high sensitivity in detecting atmospheric limb emission of the submillimeter wave range. This figure shows an example of the limb-emission spectra to be observed by SMILES. Molecular species to be observed by SMILES are:
O3, O3 isotopes (3 types), BrO, CH3CN, ClO, HCl, HNO3, HOCl, and HO2
Thus, the SMILES mission is distinguished as that focusing on the detailed halogen chemistry related to ozone destruction in order to clarify variation and its impact of radical species. Several radical species which is detected by SMILES have never been observed by any other satellite measurements with high accuracy, and the SMILES mission is the first to detect them such as BrO.
Instrumental Capabilities
The atmospheric limb emission collected by the ANT is directed to Submillimeter Receiver (SRX), where the received submillimeter-wave signal is combined with a reference signal (637.32 GHz) from a submillimeter-wave local oscillator (SLO), and is directed to SIS mixers through quasioptics consisting of focusing mirrors, wire-grids, and a sideband filter. Two SIS mixers, one of which for upper sideband (USB: 649.12 GHz - 650.32 GHz) and the other for lower sideband (LSB: 624.32 GHz - 626.32 GHz), are operated for simultaneously down-converting both sidebands into the intermediate frequency (IF) band ranging between 11 GHz and 13 GHz. The IF signals are further down-converted and amplified in the Intermediate Frequency Amplification Section (IFA), and then analyzed by two acousto-optical spectrometers in the Radio Spectrometer (AOS).
Data Processing System
The SMILES ground data processing system consists of an Experiment Operating System (EOS) and Data Processing System (DPS). The EOS receives telemetry signals and sends commands. The DPS is divided into two main units; a data processing system for level 0 and level 1 (DPS-L0/L1) and the DPS-L2. Downlinked raw data from the SMILES is received by the DPS-L0/ L1 at the User Operation Area (UOA) in the Tsukuba Space Center (TKSC). The DPS-L0/L1 processes the raw data consisting of house keeping (HK) data and science data into level 1B data immediately. The level 1B data are periodically transferred with off-line media to the L1B data server connected to the internet. The DPS-L2 located in the Institute of Space and Astronautical Science (ISAS) automatically receives the level 1B data from the data server through the internet and processes the level 1B data into level 2 data. The level 2 data are converted into the HDF-EOS format and are distributed to users accompanied with the ancillary data on the SMILES status through a L2 data server.
After the abortion of atmospheric observation in April of 2010, Both L1B and L2 data are under reprocessing including improvement of each data processing softwares and algorithms.
Validation Plan
As a method of validation of satellite-borne observation data, the comparison with ground-based and other spaceborne observation data is a main way. SMILES observation data were also compared with those subjects, and it is concluded that SMILES data are equally or possibly more precise than them.
In principle, SMILES instrument can have high sensitivity than past spaceborne sensors, so it is necessary to validate with other information than previous observation data and to encourage scientific acceptability of SMILES data for indicate their advantage.
As a result of comparison with SMILES observation data and calculations from multiple numerical models of global distribution of atmospheric constituents, it is found out that both show good agreement. Noticing that SMILES observation and model calculations are implement independently, it is possible that the agreement declares model calculations capture the same feature as that of distribution of atmospheric constituents observed with SMILES.
