The Improved Limb Atmospheric Spectrometer (ILAS), a sensor for stratospheric ozone layer observation using a solar occultation technique, was mounted on the Advanced Earth Observing Satellite (ADEOS), which was put into a Sun‐synchronous polar orbit in August 1996. Operational measurements were recorded over high‐latitude regions from November 1996 to June 1997. This paper describes the data processing algorithm of Version 5.20 used to retrieve vertical profiles of gases such as ozone, nitric acid, nitrogen dioxide, nitrous oxide, methane, and water vapor from the infrared spectral measurements of ILAS. To simultaneously derive mixing ratios of individual gas species as a function of altitude, the nonlinear least squares method was utilized for spectral fitting, and the onion peeling method was applied to perform vertical profiling. This paper also discusses in detail estimation of errors (internal and external errors) associated with the derived gas profiles and compares the errors with repeatability. The internal error estimated from residuals in spectral fitting was generally larger than the repeatability, which suggests either that some unknown factors have not been incorporated into the forward model for simulating observed transmittance data or that some parameters in the model are inaccurate. The external error was almost comparable in magnitude to the repeatability. Numerical simulations were carried out to investigate performance of the nongaseous correction technique. The results showed that the background level of sulfuric acid aerosols has little effect on the retrieved profiles, while polar stratospheric clouds (PSCs) with extinction coefficients of the order of 10−3 km−1 at a wavelength of 780 nm have nonnegligible effects on the profiles of some gas species. Despite the problems that require further investigations, it is shown that the ILAS Version 5.20 algorithm generates scientifically useful products.

[1] The Improved Limb Atmospheric Spectrometer (ILAS) was a solar occultation satellite sensor that was developed by the Environment Agency of Japan to monitor the stratospheric ozone layer. This paper describes methods of registering tangent heights for ILAS vertical profiles of gas mixing ratio and aerosol extinction coefficient. Accurate tangent height registration is crucial for the retrieval of accurate gas mixing ratios from atmospheric absorption spectra. Three methods for tangent height registration have been applied to retrieved ILAS data. The first method is the transmittance spectrum method (TS-M), which uses absorption spectra of oxygen molecules at around 760 nm (O 2 A band) measured by the ILAS visible channel and compares the average transmittance with that calculated theoretically from temperature and pressure using meteorological data. A tangent height is derived from these data. Version 3.10 ILAS data products use the TS-M. A second method is the Sun-edge sensor method (SES-M). This method for registering tangent heights was in mind when ILAS was originally designed. The SES-M geometrically determines the direction of the instantaneous field-of-view (IFOV) of the spectrometer from the angular difference between the top edge of the Sun determined with the SES and the spectrometer's IFOV. Information on the satellite's orbital position and solar position relative to the center of the Earth is used to register the tangent height. Version 4.20 ILAS data products use SES-M. The third method is a hybrid method (Hybrid-M) that was developed to correct for seasonal differences in tangent heights computed by the SES-M. The Hybrid-M assumes that the TS-M can correctly determine the tangent height at 30 km. Version 5.20 ILAS data products (the latest version) use Hybrid-M. Random and systematic errors in the Hybrid-M tangent height registration were estimated. The root-sum-square (RSS) total random error is 30 m, while the total systematic error is +300 ± 360 m in tangent height. Actual errors in tangent height registration in Version 5.20 algorithm are considered to be small judging from the results of comparisons with independent validation data sets. The Hybrid-M gives good estimates of tangent heights in Version 5.20 of the ILAS data processing algorithms.

The inversion method for simultaneous gas (O3, NO2, HNO3, N2O, CH4, H2O, CFC-11, CFC-12, N2O5, and ClONO2) and aerosol retrievals from broadband continuous IR spectra of occultation measurements is described. Both gas and aerosol physical modeling with consideration of the multicomponent character of aerosol and polar stratospheric clouds (PSCs) are used to minimize the difference between measured and modeled transmittance spectra under smoothness constraints imposed on particle-size distributions for each PSC component and positive constraints on all gas and aerosol parameters. The method is tested by numerical simulations in which synthetic occultation measurements inherent to the improved limb atmospheric spectrometer are used. The study reveals that the method has significant advantages over other approaches based on offset or gas-window-channel aerosol correction for accurate gas retrievals and provides additional information on the particle-size composition, volume density, and chemical component character of PSCs.

We studied a thermally assisted magnetic recording on flux-detectable RE-TM media. This recording scheme has a close affinity with near-field optics such as solid immersion lens (SIL) optics and scanning near-field optical microscope (SNOM)-type optics. The requirements for high-density thermo-magnetic recording and a novel near-field optical head were discussed.Index Terms-Magneto-optical disk, near field, RE-TM, thermo-magnetic recording.

A visible grating spectrometer of the Improved Limb Atmospheric Spectrometer (ILAS) aboard the Advanced Earth Observing Satellite (ADEOS) measured atmospheric absorption spectra at a wavelength region from 753 nm to 784 nm, including the molecular oxygen (O 2 ) A-band centered at 762 nm, with a spectral resolution of 0.17 nm. Temperature and pressure profiles throughout the stratosphere were retrieved from the satellite solar occultation measurements of the O 2 Aband absorption spectra. Based on simulation studies, root-sum-square errors associated with several systematic uncertainties in spectroscopic databases and instrument functions were estimated to be 4 K for temperature and 4% for pressure in the stratosphere. Current problems in this retrieval are also presented through comparisons with correlative temperature measurements.