Chikako Takahashi

Stratospheric ozone isotope enrichment studied by submillimeter wave heterodyne radiometry: the observation capabilities of SMILES

The isotopic ratio of molecules often provides valuable information about past or presently occurring processes in the atmosphere because chemical and physical processes may give rise to isotope fractionation of molecular species. However, there are so far no published satellite measurements on the spatial and temporal variations of ozone isotopes in the stratosphere. Spectroscopic remote sensing methods can theoretically be used to observe ozone isotope fractionation on a global scale, but sufficient accuracy has not yet been achieved. A new generation of submillimeter-wave receivers employing sensitive superconductor-insulator-superconductor (SIS) detector technology will provide new opportunities for precise remote sensing measurements of ozone isotopes on a global scale. We have estimated the observation capabilities of two different SIS instruments, namely the space-station-borne Japanese Experimental Module/Sub-Millimeter-wave Limb Emission Sounder (JEM/SMILES) instrument, currently planned for launch in 2008, as well as the airborne Submillimeter wave Atmospheric Sounder/Airborne Submillimeter SIS Radiometer (SUMAS/ASUR) sensor. Measurements of the airborne sensor, conducted in 1996, are presented in order to demonstrate the detection of normal-O/sub 3/ and asymmetric-18-O/sub 3/ in the SMILES frequency bands. In the ideal case, JEM/SMILES has the capability to measure the ozone isotope enrichment (/spl delta//sup M/O/sub 3/) in the middle stratosphere with a precision of /spl sim/12/sup 0///sub 00/, /spl sim/11/sup 0///sub 00/, and /spl sim/9/sup 0///sub 00/, for asymmetric-18-O/sub 3/, symmetric-17-O/sub 3/, asymmetric-17-O/sub 3/, respectively, for a daily zonal mean product with resolution of 10/spl deg/ in latitude. The systematic error, including contributions of all instrumental and spectroscopic uncertainties, is estimated to be of the order of 100/sup 0///sub 00/ to 200/sup 0///sub 00/ and should be reduced by prelaunch laboratory measurements and in-flight calibrations. A remaining bias in the SMILES measurements will have to be quantified by dedicated validation campaigns. JEM/SMILES should then be capable to provide valuable information on the global distribution and seasonal variation of ozone isotope fractionation in the stratosphere. This new technology will allow us to shed new light on this still open issue in atmospheric sciences.

Current status of level 2 product of Superconducting Submillimeter-Wave Limb-Emission Sounder (SMILES)

New level 2 products v2.0 of JEM/SMILES are scheduled to be released in Sep., 2011. This will be the first publicreleased version. In pre-released product v1.3, positive bias of retrieved temperature in the stratosphere was the largest issue since temperature is basic parameter which characterizes the atmospheric structure. The new product use latest L1B 007 which includes gain nonlinearity effect of receivers, bias of temperature in upper stratosphere is suppressed. In addition, we stopped temperature retrieval above 40km and refer MLS temperature product with applying migrating tidal model. HCl profiles in mesosphere become constant, which supports this temperature processing.

Submillimeter-wave spectroscopic performance of JEM/SMILES

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.

JEM/SMILES limb-sounding of stratospheric trace species II: simulation results for JEM/SMILES observations

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.

JEM/SMILES limb-sounding of stratospheric trace species I: retrieval algorithm and simulator

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.

Sub-MM limb observation of stratosphere and mesosphere using ISS/JEM/SMILES

Performance of Superconducting Submillimeter-Wave Limb Emission Sounder (SMILES) onboard International Space Station was discussed from the analysis of random errors of Chlorine monoxide (ClO) in the stratosphere and mesosphere. Some lessons learned from the SMILES operation in space are discussed.