The Global Ozone Monitoring Experiment (GOME) was launched on the European Space Agency's ERS-2 satellite in April 20, 1995. GOME measures the Earth's atmosphere in the nadir geometry, using a set of spectrometers that cover the UV and visible (240 - 790 nm) at moderate resolution (0.2 nm in the UV, 0.4 nm in the visible), employing silicon diode array detectors. GOME takes some 30,000 spectra per day, obtaining full global coverage in three days. We directly fit GOME radiance spectra using nonlinear least-squares analysis to obtain column amounts of several trace species with significant tropospheric concentrations, including ozone (O₃), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), and formaldehyde (HCHO). Measurements of HCHO due to biogenic activity in the troposphere are presented here.

The CRISTA system is highly flexible as regards the location where the measurements are taken. High data densities can be obtained by controlling the view directions of the three IR telescopes. This is used for detailed validation of CRISTA H₂O measurements at 12 km by means of an airplane experiment (FISH). The data are also used to determine water vapor variability at this altitude at midlatitudes. High data density allows detailed analysis of trace gas and temperature fields in the Indonesian region ('Hawk Eye' measurement mode). Pronounced small and medium-scale structures are found here at various altitudes (12 - 45 km). Considerable coupling of these structures is indicated and deserves further analysis.

Temporal variation of chemical species in the stratosphere was investigated based on observations by the Improved Limb Atmospheric Spectrometer onboard the Advanced Earth Observing Satellite. The zonal mean mixing ratio of nitrous oxide at high latitudes in the Southern Hemisphere increased rapidly during November 1996. During the period the circulation pattern changed from the winter polar vortex to the summer pattern and was influenced by the periodic fluctuation of the planetary wave activities. The altitude on which the polar vortex broke down gradually changed from the upper stratosphere to the lower stratosphere. The vertical gradient of the zonal mean mixing ratio of nitrous oxide showed positive value at the level of the rapid temporal increase. The level of the positive vertical gradient is closely associated with that of the polar vortex breakdown. The variation of the tracer mixing ratio was investigated with respect to the boundary of the polar vortex. The mixing ratios inside and outside of the polar vortex evolved with distinctive patterns with time. The evolution of the polar vortex and the shape of it have significant influences on the zonal mean mixing ratio of tracers.

Reanalysis was made for quantitative chemical ozone loss rates in the Arctic stratospheric vortex by using ozone profile data (Version 5.10) obtained with the Improved Limb Atmospheric Spectrometer (ILAS) for the spring of 1997. The analysis method is based on the Match technique. In this study we calculated additional trajectories and set very strict criteria to identify a double-sounded air mass more reliably. The result shows that the integrated ozone loss during February and Match was 1.9 ppmv at 492 - 450 K levels (about 60% losses) and the column ozone loss during two months was 94 DU. The ozone loss rate of the present study was larger than that of the sonde-Match analysis.

In the early 1990s a series of surface-based direct sun and zenith sky measurements of total column ozone were made with SBUV/2 flight models and the SSBUV Space Shuttle instrument in Boulder, Colorado which were compared with NOAA Dobson Instrument direct sun observations and TOMS instrument overpass observations of column ozone. These early measurements led to the investigation of the accuracy of derived total column ozone amounts and aerosol optical depths from zenith sky observations. Following the development and availability of radiometrically stable IAD narrow band interference filter and nitrided silicon photodiodes a simple compact multifilter spectroradiometer was developed which can be used as a calibration transfer standard spectroradiometer (CTSS) or as a surface based instrument remote sensing instruments for measurements of total column ozone and aerosol optical depths. The total column ozone derived from zenith sky observations agrees with Dobson direct sun AD double wavelength pair measurements and with TOMS overpass ozone amounts within uncertainties of about 1%. When used as a calibration transfer standard spectroradiometer the multifilter spectroradiometer appears to be capable of establishing instrument radiometric calibration uncertainties of the order of 1% or less relative to national standards laboratory radiometric standards.

The possibility to derive microphysical properties of polar stratospheric clouds from future MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) -- ENVISAT measurements was investigated. Available refractive index data for PSC candidates were intercompared in order to estimate their reliability. Especially for NAT the laboratory measurements differ significantly and for ternary H₂SO₄/HNO₃/H₂O solutions only one source of data exists. For simulating limb-spectra, a Mie model was implemented in the forward code KOPRA (Karlsruhe Optimized and Precise Radiative transfer Algorithm) in such a way that in parallel to the radiance spectra the derivatives with respect to a variety of microphysical aerosol parameters can be generated. Broadband forward calculations for small and large aerosols were made for various refractive indices. For large particles the PSC signal in the spectrum was up to forty times larger than the noise level. The signal for small particles was around the spectral noise. By minimizing the total retrieval error an automatic microwindow selection was performed for different PSC scenarios. Under the assumption of known radius and width of the aerosol size distribution resulting errors for number density retrieval were less than 3% (9 X 10^-4 cm^-3) for large and around 50% (7 cm^-3) for small particles. For large particles it is possible to perform a two-parameter fit of number density and mode radius with errors less than 10%. Due to the Rayleigh- limit a distinction between radius and number density is not possible for small particles. However, the volume density can be derived with 12% (0.4 micrometer³/cm^-3) uncertainty for large and 20% (2.2 X 10^-2 micrometer³/cm^-3) for small aerosols. These conclusions are valid as long as the aerosol layer is not optically thick which in our examples was the case for water ice (type II) PSCs of number density 0.2 cm^-3 and radius 2.6 micrometer.

Extinction coefficients for stratospheric aerosols at 8 HALOE wavelengths are determined by comparing transmittances data for two adjacent solar occultation measurements, where one limb path is loaded with aerosols but the other path is free of aerosols. These extinction coefficients are used to infer the aerosol properties such as composition and size distribution parameters. Mie theory has been used to calculate the extinction coefficients, and a nonlinear least square method is applied to determine the aerosol properties. Sixteen cases are selected for the retrieval in southern hemisphere at latitudes from 21 to 48 degrees S for the period of 29 Mar - 31 May 1992. Retrieved size width ranges from 1.1 to 1.5 and radius ranges from 0.25 to 0.45 micrometer. These size parameters are within the ranges of in situ measurements at Laramie, Wyoming. Retrieved weight % of H₂SO₄ is larger than the equilibrium value by about 5 to approximately 10 weight %, similar to the results for northern hemisphere at latitudes 20 to 55 degree N for the period from Nov 1991 to Feb 1992.

We present detection methods for polar stratospheric clouds (PSCs) from the Environment Agency of Japan's Improved Limb Atmospheric Spectrometer (ILAS) instrument during the arctic winter of 1996/1997. The PSC detection methods are based on ILAS visible channel measurements in and around the oxygen A absorption band. They involve either full nonlinear or simple linear fitting of the spectra to obtain aerosol optical thickness as a function of tangent height. PSC optical thickness is determined from a subsequent linear fit to aerosol optical thickness as a function of altitude. Results for PSC optical thickness from the two methods agree reasonably well for all cases considered in this study, but only the nonlinear fitting approach allows the definitive identification of PSC events. Comparisons with operational ILAS data products show denitrification, removal of water vapor, and generally low temperatures over the vertical region of the PSC. Finally, we present a fast and simple method for the identification of possible PSC candidates from ILAS measurements.

The Improved Limb Atmospheric Spectrometer (ILAS) on board the Advanced Earth Observing Satellite (ADEOS) successfully observed atmospheric profiles over the Arctic and Antarctic from November 1996 through June 1997. It revealed the frequent occurrence of Polar Stratospheric Clouds (PSCs) over the Arctic between January and mid-March 1997. The ILAS provides a unique data set, including aerosol extinction at 780 nm, nitric acid, water vapor, and nitrous oxide, simultaneously. This paper demonstrates the validity of the ILAS aerosol data and presents an approach to estimate the chemical composition of PSCs. Comparisons are made with data from the Stratospheric Aerosol and Gas Experiment (SAGE) II.

The accuracy of the scalar and vector versions of the STAR code is tested for the Rayleigh atmosphere. The scalar STAR is compared with MODTRAN4.0, however, the comparison revealed major discrepancies between the original STAR and MODTRAN4.0. After the solar irradiance data in STAR was modified and the wavenumber was used for solar irradiance calculation, the relative differences that appear like spikes in the spectral domain were greatly reduced. However, relative differences in the UV-B band are still a bit large (up to +/- 6%) and spikes remain. Examining these two codes, we found that the ozone cross section data used in STAR differs from that in MODTRAN4.0 due to a 15 cm^-1 shift toward higher wavenumbers. Then relative differences between STAR and MODTRAN4.0 were reduced to 2% for wavelengths exceeding 310 nm. For wavelengths shorter than 310 nm, however, the differences increased as wavelengths decreased and reached 5.5% at 300 nm. This resulted from dividing by small radiances because of strong ozone absorption. Increasing the number of atmospheric layers from 36 to 50 in MODTRAN4.0 resulted in differences of less than 2% for wavelengths exceeding 306 nm and 4.5% at 300 nm. The vector STAR is compared with the tables from Coulson et al. (1960) and they are in very good agreement.

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 (O₂) 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 O₂ A-band 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.

The Improved Limb Atmospheric Spectrometer-II (ILAS-II) is a satellite-borne solar occultation sensor developed by the Environment Agency of Japan for measuring ozone, other gas species, and aerosols/PSCs that are related to the ozone chemistry in the stratosphere. The ILAS-II instrument will be installed on board the ADEOS-II satellite that will be put into a sun-synchronous polar orbit by the National Space Development Agency of Japan (NASDA) in November 2001. The ILAS-II measurement is a continuation of that of ILAS on board ADEOS, which obtained data from November 1996 to June 1997. The main components of ILAS-II are four spectrometers and a sun-edge sensor. The spectrometers include an infrared spectrometer to cover about 6 to 12 micrometer in wavelength, a mid-infrared spectrometer 3 to 5.7 micrometer, a narrow band spectrometer around 12.8 micrometer, and a visible spectrometer 753 to 784 nm. The first two spectrometers are used for measuring gas and aerosol/PSC profiles, while the third is for ClONO₂ measurements. The visible spectrometer is used for pressure/temperature measurements as well as aerosol/PSC extinction coefficients. The ILAS_II instrument has already completed its development and environment tests, and now is undergoing satellite system environment tests at NASDA. This paper outlines the characteristics and performance results from laboratory tests along with the present status of development of its data processing algorithm and operational software.

This paper presents NASA's recent direction to invest in the critical science instrument and platform technologies in order to realize more reliable, frequent and versatile missions for future Earth Science measurements. Historically, NASA's Earth Science Enterprise has developed and flown science missions that have been large in size, mass and volume. These missions have taken much longer to implement due to technology development time, and have carried a large suite of instruments on a large spacecraft. NASA is now facing an era where the budget for the future years is more or less flat and the possibility for any major new start does not vividly appear on the horizon. Unfortunately, the scientific measurement needs for remote sensing have not shrunk to commensurate with the budget constraints. In fact, the challenges and scientific appetite in search of answers to a score of outstanding questions have been gradually expanding. With these factors in mind, for the last three years NASA has been changing its focus to concentrate on how to take advantage of smaller missions by relying on industry, and minimizing the overall mission life cycle by developing technologies that are independent of the mission implementation cycle. The major redirection of early investment in the critical technologies should eventually have its rewards and significantly reduce the mission development period. Needless to say, in the long run this approach should save money, minimize risk, promote or encourage partnering, allow for a rapid response to measurement needs, and enable frequent missions making a wider variety of earth science measurements. This paper gives an overview of some of the identified crucial technologies and their intended applications for meeting the future Earth Science challenges.

A system of satellite borne sensor is proposed for measuring the column amount of green house gases in the troposphere from observations of near infrared solar radiation in the sun glint region reflected from water surface of ocean and lakes. A high accuracy determination of the column amount of gases is achieved by measuring the difference of absorption line of greenhouse gas from that of oxygen with using tunable etalons of high resolving power. It is demonstrated by the ground- based measurements of the absorption line of carbon dioxide in the direct solar radiation that the column amount is obtainable with the standard deviation of about 0.4%. The satellite sensor system presented in this paper is compared with other methods from the viewpoint of retrieval error.

Global Change Observation Mission (GCOM) is a new generation of earth observation program by NASDA. GCOM aims to derive trends in climate system by long term and systematic measurements of atmosphere, ocean, and land. GCOM-A1 is one of the first generation of GCOM satellites to be launched in 2006, which was formerly called ADEOS-3A. GCOM-A1 will carry atmospheric instruments; two Japanese, Ozone Dynamics Ultraviolet Spectrometer (ODUS), and Solar Occultation Fourier transform spectrometer from Inclined Satellite (SOFIS), and one foreign atmospheric instrument and a GPS occultation instrument.

The Ozone Dynamics Ultraviolet Spectrometer (ODUS) is one of core sensors onboard Global Change Observation Mission (GCOM)- Al satellite. The ODUS is a Fastie-Ebert type polychromator which measures the solar ultraviolet radiation of 306 nm to 420 nm wavelength region scattered from the Earth's atmosphere and surface. The measuring spectral region contains many absorption features by atmospheric minor constituents such as ozone (O₃), sulfur dioxide (SO₂), nitrogen dioxide (NO₂), and so on. The primary objective of ODUS is to monitor the global total ozone field with an accuracy of 5% before calibration and 2% after calibration. It will map the global total ozone field, except of the latitudinal zone larger than 80 degrees, in one day with better spatial resolution of 20 km by 20 km at nadir than TOMS of 40 km by 40 km. The better spatial resolution will help studying the dynamically related phenomena, such as development of biomass burnings, spreading of urban pollution and of volcanic aerosols, in more detail. In this paper scientific objectives of GCOM A1/ODUS will be discussed and presented.

The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar-occultation Fourier-transform spectrometer developed by the Environment Agency of Japan (EA). SOFIS onboard the Global Change Observation Mission-Al (GCOM-Al) satellite will be put into a 650 km non-sun-synchronous orbit with an inclination angle of 69 deg. GCOM-Al is scheduled to be launched in spring 2006. SOFIS is the successor of the Improved Limb Atmospheric Spectrometer-II (ILAS-II), which with travel onboard the Advanced Earth Observing Satellite-II (ADEOS-II). SOFIS will measure vertical profiles of atmospheric constituents with 0.2 cm^-1 spectral resolution at 3 - 13 micrometer with 1 km vertical resolution. The scientific objective of SOFIS is to measure global vertical distributions of O₃, N₂O, CH₄, CO₂, H₂O, HNO₃, NO₂, aerosols, CFC-11, CFC-12, and ClONO₂. SOFIS uses a double-pass dual-pendulum type Fourier transform spectrometer (FTS) and a diode laser sampling system to reduce the size and weight of the apparatus. Two photovoltaic (PV) HgCdTe (MCT) detectors and a pulse-tube cooler will provide high linearity and low-noise performance. SOFIS also has a visible (O₂ A band) grating spectrometer for pressure and temperature retrieval and a sun- edge sensor for detecting the tangent height position. This paper describes the characteristics of SOFIS and test results of laboratory models of the FTS and the detector.

The Solar-Occultation FTS for Inclined-orbit Satellite (SOFIS) is an instrument for the next atmospheric remote sensing project proposed by the Environment Agency of Japan. The grating infrared spectrometer used by its predecessors (ILAS/ILAS-II) will be replaced with a Fourier-transform spectrometer (FTS) for higher spectral resolution. The three- dimensional distributions of greenhouse gases as well as those of atmospheric species related to stratospheric ozone depletion will be measured by solar occultation from an inclined-orbit satellite. A preliminary study was carried out to clarify the underlying problems in satellite-borne FTS measurement and to seek a proper method for processing the FTS data recorded by SOFIS.

Clear sky longwave radiances and fluxes are compared with the sea surface temperatures for three oceanic regions: Atlantic, Indian, and Pacific. The Clouds and the Earth's Radiant Energy System (CERES) measurements were obtained by the three thermistor bolometers: total channel which measures the radiation arising from the earth-atmosphere system between 0.3 - > 100 micrometer; the window channel which measures the radiation from 8 - 12 micrometer; and the shortwave channel which measures the reflected energy from 0.3 - < 5.0 micrometer. These instruments have demonstrated measurement precisions of approximately 0.3% on the International Temperature Scale of 1990 (ITS-90) between ground and on-orbit sensor calibrations. In this work we have used eight months of clear sky earth-nadir-view radiance data starting from January 1998 through August 1998. We have found a very strong correlation of 0.97 between the CERES window channel's weekly averaged unfiltered spectral radiance values at satellite altitude (350 km) and the corresponding weekly averaged sea surface temperature (SST) data covering all the oceanic regions. Such correlation can be used in predicting the sea surface temperatures using the present CERES Terra's window channel radiances at satellite altitude very easily.

Clouds are recognized as an important factor in the earth's climate system. In particular, the optical and microphysical properties such as the optical thickness and droplet size are needed for understanding cloud processes. Therefore Kawamoto et al. (2000) developed a retrieval algorithm for the cloud optical thickness and effective particle radius on a global scale. In this work, we retrieve the cloud liquid water path and columnar cloud droplet number density as by-products, in addition to the cloud optical thickness and effective particle radius. The annual mean characteristics of these quantities on a global scale are described.

We have investigated effects of the temperature dependence of water absorption indexes and of absorbing aerosols on the retrieval of cloud microphysical properties from the multi- spectral solar reflectance measurement by the airborne Multi- channel Cloud Pyranometer (MCP) system through collocated two- aircraft validation flights. For the clean liquid-water clouds, the reasonable cloud parameters were successfully retrieved by taking into account the temperature dependence of the complex refractive index of water by Kou et al. For the water cloud contaminated by absorbing aerosols, the present MCP-retrieval, under the assumption of pure liquid-water clouds, underestimated the visible optical thickness and overestimated the effective particle radius. The result suggests that new remote sensing techniques should be developed to discriminate and evaluate the effects of cloud particles and aerosols.

The Moderate Resolution Imaging Spectroradiometer (MODIS), a major facility instrument on board the Terra Spacecraft, was successfully launched into space in December of 1999. MODIS has several near-IR channels within and around the 0.94- micrometer water vapor bands for remote sensing of integrated atmospheric water vapor over land and above clouds. MODIS also has a special near-IR channel centered at 1.375-micron with a width of 30 nm for remote sensing of cirrus clouds. In this paper, we describe briefly the physical principles on remote sensing of water vapor and cirrus clouds using these channels. We also present sample water vapor images and cirrus cloud images obtained from MODIS data.

It is of great interest to investigate the properties on the cloud optical, microphysical, and geometrical parameters, in particular, of low-level marine clouds which play crucial influence on the global climate system. Top height, base height, and geometrical thickness of cloud layer are considered here as cloud geometrical parameters. These parameters are very important to retrieve, because top and base heights are the factors which govern the strength of greenhouse effect through the thermal radiation from/to cloud layer, whereas the geometrical thickness is the key parameter for the estimation of gaseous absorption in cloud layer where multiple scattering process dominates. In this study, an algorithm was developed to retrieve simultaneously cloud optical thickness, effective particle radius, top height, and geometrical thickness of cloud layer from the spectral information of visible, near infrared, thermal infrared, and oxygen A band channels. This algorithm was applied to FIRE (First ISCCP Regional Experiment, 1987) airborne data which included the above four channels and targeted at the low-level marine clouds off the coast of California in summer. The retrieved results seems to be comparable to the in situ microphysical observation although further validation studies are required for the cloud geometrical parameters in particular.

Cloud microphysical parameters such as optical thickness, effective particle radius, and liquid water path are obtained by measuring reflected or emitted radiation at various wavelengths from visible to microwave spectral region. Individual methods have both advantage and disadvantage since the cloud radiative properties are dependent on the relationship between particle size distribution and wavelength of radiation. Therefore comparison of retrieved parameters between different remote sensing measurements is important. On the other hand, the combination of various types of sensor is quite effective to the retrieval of cloud properties. In this study, some issues on the comparison between satellite remote sensing and groundbased or aircraft observations are discussed and some ideas such as statistical method are presented.

Preliminary to the launch of the first Meteosat Second Generation (MSG) satellite and within support of the Geostationary Earth Radiation Budget experiment onboard of MSG, algorithms are tested to retrieve aerosol optical parameters and their possible signature on the Earth Radiation Budget (ERB). For this existing data from instruments on satellites in low earth orbit is used like NOAA/AVHRR and ScaRaB. In particular AVHRR data are used for retrieving aerosol optical parameters which then will be related to ERB measurements from ScaRaB.

A global three-dimensional transport model that can simultaneously treat main tropospheric aerosols, i.e., carbonaceous (organic and black carbons), sulfate, soil dust, and sea salt, is developed. It is coupled with a Center for Climate System Research (CCSR)/National Institute for Enviormental Studies (NIES) atmospheric general circulation model (AGCM), and the meteorological field of wind, temperature, and specific humidity can be nudged by reanalysis data. Simulated results are compared with not only observations for aerosol concentrations but also the optical thickness and Angstrom exponent retrieved from remote sensing data such as National Oceanic and Atmospheric Administration (NOAA)/Advanced Very High Resolution Radiometer (AVHRR) and Aerosol Robotic Network (AERONET). A general agreement is found between simulated results and observations spatially seasonally, and quantitatively. The present model is also coupled with the radiative process over both the solar and thermal regions. The annual and global mean radiative forcing by anthropogenic aerosols from fossil fuel sources is estimated to be -0.5 W m^-2 over the clear sky for the direct effect and -2.0 W m^-2 for the indirect effect.

For better understanding the distribution of atmospheric aerosol over China and its impact on climate, remote sensing aerosol optical depth (AOD) from satellite over 25 lakes has been done in China. The distribution of aerosol over the whole country is interpolated from these data. Four Sun-photometers also have been used to measure the data of AOD nearby four of these lakes for validating the remote sensing algorithm of satellite. The result shows that the southeast region of China has the biggest AOD over four seasons of the year and the value of AOD has slight variety between different seasons; the northwest area of China has a maximum in spring, but in other seasons, the value of AOD is low. This result fit to the fact that spring is the dry season in northwest of China and dust storm often occurs in this area, other season seldom has dust storm. The high value of AOD in the southeast China is coincident with the intensive industry, agriculture and other human activities in this region.

Digital Earth raises the requirement of dynamic monitoring of global land surface with extremely high resolution. Therefore, high-resolution surface reflectance is the basic parameter for earth observation which should be retrieved for further research and application purposes. To meet the above requirement, atmospheric correction is the necessary step for any space-borne and air-borne sensors in solar radiation waveband. There have been a lot of discussion and methods for atmospheric correction. In this paper, we shortly review the situation and then suggest a strategy of atmospheric correction for high surface resolution. An approximate expression of atmospheric spread function is derived. Numerical simulation reveals the significant features of atmospheric correction. Case study is made showing the procedure of the correction.

Due to the complexity of atmospheric aerosol, validation efforts are required to test satellite retrievals. Here we give an overview of our aircraft and ship validation measurements near Hawaii. Some examples of the measurements are shown which illustrate some of the variability we have encountered. This effort is ongoing and can provide important background measurements for satellite validation as well as radiation studies.

The determination of the aerosol size distribution and of important microphysical parameters, e.g. effective radius, surface-area and volume concentration of tropospheric aerosol, from a small number of extinction and backscatter lidar data is an inverse ill-posed problem. In this paper we examine the influence of different spheroids on the retrieval process.

We report on the utility of a spectrograph flown on the Space Shuttle that measured ionospheric constituents including metal atoms and ions. The distribution of ions is shown for an organized pillar of magnesium ions extending more than 140 km of altitude.

Spatial resolution of CCD imaging spectrometer is deteriorated by cross talk between the elements. Some examples of such a cross talk of CCD elements is shown, and the deteriorated spatial resolution is analyzed. Eye system of some biological things utilizes such a cross talk positively to improve the performance. How to improve the performance? The function is called lateral inhibition. The concept and function of the lateral inhibition is applied to improve the deteriorated performance of CCD imaging sensor. The results of analysis and simulations of the improvement by lateral inhibition are shown. Furthermore, it was clarified that this technology can be applied to synthesize high quality CCD imaging system.

The resolution limit attainable by large ground-based telescopes is limited by the refraction index fluctuations of the turbulent atmosphere. To overcome this limitation Adaptive Optics systems measure and compensate atmospheric-induced distortions. When working in the visible, only a partial compensation is possible. We analyze the image formation process in these conditions. We provide a model for the wave front statistics, which allows a simple estimate of the instantaneous PSF. New deconvolution techniques could be developed by using this approximation.

A Frequency-Shifted Feedback (FSF) laser has an intracavity acousto-optic modulator (AOM) and the spectral output consists of a chirped frequency comb evenly spaced at the cavity free spectral range (FSR). An FSF laser is a useful source for optical frequency domain reflectometry (OFDR). We present a new average atmospheric temperature sensor by OFDR using an FSF laser for the first time. The beat signal, which is detected through the self-delayed heterodyne detection of an FSF laser, is proportional to the path difference, and measurements can be done within the frequency bandwidth of a cavity FSR. Furthermore, the beat frequency characteristics are unrelated to the beat order. Therefore, the path measurement resolution is consist and unrelated to the path difference. Changes in atmospheric refractive index primarily depend on variation of temperature and pressure. Observing variation in path difference with an FSF laser should allow calculation of the average atmospheric temperature along the path if the change in pressure is known. As the path difference increases, the temperature resolution improves. This paper outlines the principle of the average atmospheric temperature measurement using an FSF laser and presents preliminary experimental result.

Effects of cloud horizontal inhomogeneity on the shortwave reflection are investigated from the viewpoint of cloud optical thickness retrieval for overcast boundary layer clouds. Monte Carlo radiative transfer model is employed to simulate bidirectional reflection functions in 1-km spatial resolution, for inhomogeneous cloud field that is generated by two-dimensional bounded cascade model. The independent pixel approximation (IPA) biases in mean (M) and standard deviation (S) of logarithm of retrieved optical thickness are defined, where S denotes cloud inhomogeneity parameter. The biases describe modification of the frequency distribution of optical thickness from true one due to effects of horizontal radiation transport. It is ascertained that observation in off-nadir view with oblique sun is inappropriate for optical remote sensing of clouds since the horizontal inhomogeneity produces large uncertainty. It is found that the radiation field substantially looks smoother than IPA with overhead sun, while it looks rough with oblique sun, especially in forward scattering view. The regression formulae of the IPA biases are presented for geometrically rough cloud field, and the parameterizations are easily applicable to first order correction of the optical thickness retrieval.

Observation of stellar speckle-patterns is a useful optical remote-sensing technique of terrestrial atmospheric turbulence. The wind velocity (magnitude and direction) at the turbulence layer is determined by movement of the speckle patterns. The altitude and refractive index structure constant of the turbulence layer are also deduced from the peak height and width of speckle-pattern correlation-peak. A new simple system, which consists of an image intensified CCD and a photomultiplier tube attached on a 50 cm telescope, has been developed for observing the speckle-patterns. The system is utilized to continuously monitor the parameters of atmospheric turbulence ranging from 2 km to 20 km. Results of the monitoring measurement over a year are presented.

Numerical experiment was performed using a general circulation model (GCM) including aerosol indirect effect into water cloud and the simulated global distribution of cloud droplet radii was compared with the global distribution of cloud effective radii retrieved from Advanced Very High Resolution Radiometer (AVHRR). Comparisons of GCM calculation with AVHRR retrieval showed that our GCM generally can simulate the global characteristics of cloud droplet radii such as a land-sea contrast associated with difference of aerosol abundance and coastal region features due to aerosol injection from adjacent continental area. AVHRR retrieval and GCM simulation, however, are turned out to show disagreement over tropical region. AVHRR retrieval may tend to overestimate droplet radii due to the contamination of signal by drizzles and ice particles, whereas our GCM does not treat aerosol indirect effect in deep convective clouds predominant over tropics. Over equatorial central Pacific, where satellite retrieval may suffer from statistical biases, satellite retrieval and GCM simulation are also found to be different.

This paper presents the measurements of maritime aerosols over Seto Inland Sea (Japan), East China Sea and Western Australia. The photopolarimetric data of skylight have been collected by a portable multi-spectral polarimeter named PSR-1000, which has six observing wavelength bands corresponding to the ADEOS/POLDER sensor. The PSR-1000 measures the direct sunlight, which provides Angstrom exponent as well as optical thickness of aerosols. It also measures polarization of atmospheric light, which is available to retrieve the aerosol characteristics. Observations with PSR-1000 have been undertaken since 1996. The obtained results show the spatial change of aerosol properties and exhibit each intrinsic feature for each region.

This paper defines scientific requirements for the Ozone Dynamics Ultraviolet Spectrometer (ODUS). ODUS is a cross- track scanning spectrometer like Total Ozone Mapping Spectrometer (TOMS) developed by NASA. This instrument is planned to be flown on the Global Change Observation Mission (GCOM)-A1 satellite. ODUS measures solar ultraviolet radiation backscattered from the Earth's atmosphere. This study examines the necessity and feasibility of retrieval algorithms for total ozone, volcanic sulphur dioxide (SO₂), nitrogen dioxide (NO₂) and several other constituents related to ozone chemistry and summarizes requirement definitions for specifications of the ODUS instrument. Finally, we review the conformance of the development policy for retrieval algorithms with the current specifications of the ODUS instrument.

UV spectrometers onboard satellites have provided trend data of total O₃ for more than two decades. These data have shown the validity of satellite measurements. However, for next-generation observation and to monitor the recent O₃ depletion accurately, a high-fidelity spectrometer with high signal to noise ratio (SNR) is essential. For this purpose, the Ozone Dynamics UV Spectrometer (ODUS) has been designed to have higher spectral and spatial resolutions and wide spectral range. It will be launched on the Global Change Observation Mission (GCOM)-A1 satellite in 2006. ODUS covers back- scattered light from 306 to 420 nm with 0.5 nm spectral and 20 km spatial resolutions using a Fastie-Ebert type polychromator and a one-dimensional UV Si-CMOS array detector. The array detector is designed and manufactured specially for ODUS. It has different size pixels and 234 on-chip CMOS amplifiers, which are tuned for each spectral radiance level. ODUS is a nadir-look mapping spectrometer with a mechanical scatter, which can acquire global data in one day. It is expected to provide information about total O₃, SO₂, NO₂, BrO, OClO, H₂CO, surface albedo, and aerosol.

The seasonal variation of aerosol optical depth have been studied using solar radiation data from the multi-filter rotating shadow-band radiometer (MFRSR) from July 1998 to July 2000 in Kwangju, Korea. The MFRSR is a ground-based instrument that measures the global and diffuse components of solar irradiance at seven wavelengths, 415, 500, 610, 665, 862, 940 and total band. The channels were used to measure aerosol optical depth (AOD) except 940 nm. Langley plot of the natural log of the direct irradiance versus air mass was used to determine optical depth from the slope and the solar irradiance at the top of the atmosphere at each wavelength. The variation of total atmospheric optical depth (TOD) shows seasonal characteristics with maxima in spring and winter and minima in summer. Aerosol optical depth (AOD) was determined by subtracting the effects of molecular scattering and absorption by ozone and water vapor from the TOD. Angstrom coefficient was also determined from the slope of aerosol optical depth spectra. The annual value of aerosol optical depth varied from 0.02 to 0.87 at a wavelength 672 nm during the measurement period. In spring the AOD values were affected by long range transport aerosol from China. Increased local anthropogenic aerosols in the region have also significantly affected the AOD value in fall.

This paper focuses on detection of the cloud coverage and its thermodynamic phase using the combined data derived from POLDER and OCTS on board the satellite ADEOS. The POLDER has provided polarization information with multi-angle viewing. This directional information is closely related to the scattering behavior of cloud particles in light scattering simulations. Thermal data given by OCTS infrared channels is available to determine the cloud top temperature. Our basic idea to detect the cloud thermodynamic phase is based on the combination of polarization from POLDER and brightness temperature from OCTS. It is shown that our algorithm has improved the distinction of water/ice cloud.

ODUS (Ozone Dynamics Ultraviolet Spectrometer) on the GCOM (Global Change Observation Mission)-A1 mission will measure the ozone, SO₂, NO₂ and other trace constituents both in the stratosphere and in the troposphere through the backscatter ultraviolet (BUV) technique from 306 nm to 420 nm. In the present paper, the design concepts of the ODUS were clarified and a trade-off study among various spectrometer types was done. Since GCOM-A1 will have a non-sun-synchronous orbit, the thermal condition during a recurrent cycle will be more variable than that of a sun-synchronous orbit. Therefore, misalignment caused by thermal stress distortion was expected to be the most critical matter. As a result, a simple conventional Ebert type spectrometer was employed. However astigmatism is a matter of serious concern for the Ebert type spectrometer, because it leads to a significant loss of the input photon flux caused by the image extension of the entrance slit in the direction of detector height. The optimal slit height was determined by the trade-off study between high throughput and the image distortion due to astigmatism. As a detector, a linear photodiode array was employed for ODUS. As the detector is custom made, the shape and the arrangement of each photodiode pixel can be modified by changing the mask design. We optimized the detector height for each photodiode pixel to maximize the SN ratio by calculating the instrument function. According to the above process, the detector was newly fabricated with a dramatic change of the mask design. The new detector was combined with the previously fabricated laboratory model spectrometer. We successfully obtained atmospheric scatter data on the ground with a signal to noise ratio of 350 at the wavelength of around 400 nm.

Lidar observations of stratospheric aerosols have been performed at Ny-Aalesund (79 degrees N, 12 degrees East), Svalbard every winter since January 1994. We detected many PSC events in the stratosphere under low temperature condition, especially in 1994/95, 1995/96, 1996/97 winter campaigns. Meanwhile in the Antarctic, lidar observations were made from April, 1997 to January, 1998 at Dome Fuji (78 degrees South, 40 degrees East), and many PSCs were detected almost every day from the end of May to mid October. In the Arctic, PSC layers at the initial stage of appearance were composed mainly of solid particles in each winter season and the layers at sufficiently low temperatures were composed of spherical particles. In the Antarctic, PSCs similar to those over Ny- Aalesund were also detected frequently while the polar vortex was developing or the vortex was unstable. But after a remarkable decrease in the temperature by the invasion of blocking high into the polar vortex, PSCs detected were mainly composed of solid particles.

Ground-based, optical monitoring of the NO₂ column density and aerosol optical thickness is described. The instrument consists of a solar radiation spectrometer (SRS) and a conventional sunphotometer, both mounted on the same sun- tracker and operated automatically. From daytime measurements in Chiba, Japan during 1998 - 2000, variations of NO₂ and aerosol are analyzed. A correlation coefficient between NO₂ and aerosol is larger than 0.90 in winters. Because of the capability of simultaneous, real time measurement, this method is particularly suitable for air pollution studies in city areas.

We present the retrieval algorithm of aerosol optical thickness over the land area. The algorithm is based on the dark-target approach combined with the texture analysis. In the first part of the algorithm, we employ the 6S code to calculate the relevant radiance components. The aerosol optical thickness is retrieved over the sea surface assuming a surface reflectance of 0.02. Two-dimensional linear interpolation is applied to tentatively determine the optical thickness over the land area that is surrounded by the sea area. In the second part, a difference image is calculated between an actual satellite image (turbid image, NOAA AVHRR channel 1 on December 1, 1997) and a clear image that is obtained by applying the atmospheric correction to a satellite image (December 15, 1997). The atmospheric feature included in the difference image is then analyzed by the texture analysis. For each area that includes both land and sea surfaces, and is categorized into a texel (i.e. its atmospheric feature is considered to be uniform), the optical thickness of the land area is assumed to be the same with that over the sea area. In addition, we present a Taerosol model on the basis of the ground measurements conducted at 11 sites on the Kanto plain during December 22 to approximately 24, 1997. In this model, chemical composition data are used to derive the single scattering albedo and the asymmetry parameter. These optical parameters are useful to improve the accuracy of the radiation calculation with the 6S code.

SWIFT is a small (< 85 kg, approximately 0.5 m³, < 100 W) satellite instrument which is designed to accurately measure global horizontal winds and ozone concentrations in the stratosphere. SWIFT is similar to the highly successful WINDII instrument currently operating on the UARS satellite. Both use a field-widened Michelson interferometer set at high path difference to image the Doppler shift of atmospheric emission. The data set provided by SWIFT will provide essential input to the next generation of Numerical Weather Prediction (NWP) models which are currently being developed by meteorological organizations worldwide. SWIFT is currently a leading candidate to fill the foreign instrument opening for the NASDA GCOM-A1 mission, providing highly complimentary data to the ODUS and SOFIS instruments. SWIFT allows direct measurement of stratospheric dynamics and high vertical resolution ozone profiling to maximize the scientific return for this mission.