齋藤 尚子

The Greenhouse gases Observing SATellite (GOSAT) monitors carbon dioxide (CO2) and methane (CH4) globally from space. The Thermal and Near infrared Sensor for Carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) installed on GOSAT measures spectra absorbed by atmospheric minor components including greenhouse gases in infrared wavelength regions. This paper describes the characterization and validation of the CO2 and CH4 profiles retrieved from the thermal infrared (TIR) spectra observed by GOSAT. The retrieved CO2 and CH4 profiles were compared with the corresponding aircraft data provided by the National Oceanic and Atmospheric Administration (NOAA)/Earth System Research Laboratory (ESRL)/Global Monitoring Division (GMD)/Carbon Cycle Greenhouse Gases (CCGG) group. This group has been conducted an aircraft program since 1992 to collect air samples mainly in North America. Each in situ aircraft profile was compared with those retrieved from TIR spectra without considering the effect of its averaging kernel. The root mean square (RMS) and bias errors of the retrieved CO2 and CH4 profiles were evaluated seasonally and with respect to atmospheric pressure. This comparison with aircraft data provides significant information for further improvement of the TIR retrieval algorithm.

The thermal infrared band of the main sensor of the greenhouse gas observing satellite (GOSAT), the TANSO-FTS, must be calibrated with accuracy higher than 0.3 K in the brightness temperature T-bb for retrieving CO2 concentration with accuracy of 1% in the upper atmosphere. However, that accuracy has not been achieved because of some error sources. One is the systematic bias in the radiance spectrum resulting from effects of radiation emitted from internal optics and multiple scattering of target signals. Another is the polarization effect of the pointing mirror. Both effects can be merged into two parameters, gain and offset, in the two point calibration procedure. They can be tuned by comparing the spectrum with well-calibrated spectra such as those from the AIRS sensor. Based on the corrected radiance spectra, global CO2 concentrations were processed. However, they show peculiar latitudinal distribution implying the existence of temporally variant parameters that can affect the calibration. This bias can be reduced by referring to housekeeping data of the satellite in the calibration procedure. The stratospheric ozone distribution is also analyzed. The sensor demonstrated the difference in the ozone hole feature between spring 2009 and 2010 over the South Pole.

Radiometric calibration accuracy of 0.3 K in Tbb is necessary to retrieve CO2 concentration profile with accuracy of 1 % in the upper atmosphere. In case of the thermal infrared (TIR) band (band 4) of GOSAT-TANSO-FTS, interferometric phase correction procedure is very important because the total transmittance of the optics at the band is about 70 % because of opacity of dichroic mirrors of band 1-3 placed obstructing the field of view of band 4, and the mirrors reflect the radiation emitted from inside of the optics. Based on the results from the thermal vacuum tests (TVTs) of the sensor, it is found that interferometric signal is almost zero when the sensor view a target of which temperature is about 280-300K because the radiation emitted from inside of the spectrometer controlled at about 296 K has completely opposite phase to that of the target. It is also found that the interferometric final phase of the calibrated signal varies when the total signal is almost zero because of weak signals that have phases differ from both of those of targets and calibrators. A candidate phase correction procedure is proposed based on that adopted for a previous space FTS sensor, IMG/ADEOS. Non-linearity correction for the detector and polarization efficiency correction are also desccussed. © 2008 SPIE.

The Improved Limb Atmospheric Spectrometer-II (ILAS-II) monitored components associated with Polar ozone depletion. ILAS-II was on board the Advanced Earth Observing Satellite-II (ADEOS-II, "Midori-II"), which was successfully launched on 14 December 2002 from the Tanegashima Space Center of the Japan Aerospace Exploration Agency (JAXA). ILAS-II used a solar occultation technique to measure vertical profiles of ozone (O&lt inf&gt 3&lt /inf&gt ), nitric acid (HNO&lt inf&gt 3&lt /inf&gt ), nitrogen dioxide (NO&lt inf&gt 2&lt /inf&gt ), nitrous oxide (N&lt inf&gt 2&lt /inf&gt O), methane (CH&lt inf&gt 4&lt /inf&gt ), water vapor (H&lt inf&gt 2&lt /inf&gt O), chlorine nitrate (ClONO&lt inf&gt 2&lt /inf&gt ), dinitrogen pentoxide (N&lt inf&gt 2&lt /inf&gt O&lt inf&gt 5&lt /inf&gt ), CFC-11, CFC-12 and aerosol extinction coefficients at high latitudes in both the Northern and Southern hemispheres. ILAS-II included Sun-tracking optics and four spectrometers, a Sun-edge sensor, and electronics. The four spectrometers measured in the infrared (channel 1) between 6.21 and 11.76 μm, in the midinfrared (channel 2) between 3.0 and 5.7 μm, at high resolution in the infrared (channel 3) between 12.78 and 12.85 μm, and in the visible (channel 4) between 753 and 784 nm. The vertical height of the entrance slit was 1 km at the tangent point. A Sun-edge sensor accurately registered tangent height. After an initial check of the instruments, ILAS-II recorded routine measurements for about 7 months, from 2 April 2003 to 24 October 2003, a period that included the formation and collapse of an Antarctic ozone hole in 2003 that was one of the largest in history. All of the ILAS-II data were processed using the version 1.4 data-processing algorithm. Validation analyses show promising results for some ILAS-II measurement species, which can be used to elucidate mechanisms of Polar ozone depletion. Studies are ongoing on ozone depletion, on the formation mechanisms of Polar stratospheric clouds, on denitrification, and on air mass descent. A state-of-the-art data retrieval algorithm that is currently being developed will yield more sophisticated data sets from the ILAS-II data in the near future. Copyright 2006 by the American Geophysical Union.

The Greenhouse Gases Observing Satellite (GOSAT) will be launched in 2008 for global observations of greenhouse gases such as CO2 and methane. This study examines the feasibility of retrieving CO2 concentrations from the infrared spectra of the GOSAT/Therimal and near infrared Sensor for Carbon Observation (TANSO)-FTS. Retrieval simulations in which the maximum a posteriori (MAP) method was applied to pseudo-spectra at 700-800 cm(-1) from TANSO-FTS ("CO2 15-mu m band") showed that retrieved CO2 profiles agreed with true CO2 profiles to within the total errors throughout the troposphere above 700-800 hPa when atmospheric conditions such as temperature used in the computation of the spectra were known. In contrast, discrepancies between retrieved CO2 and true CO2 concentrations increased if temperatures used in the retrieval included random errors; a random scatter of +/- 0.5 K caused a discrepancy that was 12 times larger at similar to 750 hPa. However, appropriate channel selection based on CO2 and temperature information could reduce the effect of temperature uncertainty on CO2 retrievals in this spectral region: the discrepancy between retrieved and true concentrations at similar to 750 hPa in the case with channel selection was about one-third of the discrepancy without any channel selection.

The Greenhouse gases Observing Satellite (GOSAT) is a Japanese satellite that is intended to observe CO2 concentration from space and to contribute to advancement of research of the source/sink estimation of CO2. The GOSAT main sensor is a Fourier Transform Spectrometer (FTS) named "TANSO-FTS", which covers a wide terrestrial radiation spectrum including CO2 absorption bands at 1.6 mu dm, 2.0 mu m, and 15 mu m. The former two bands are used to estimate columnar concentration of CO2; the latter is used to retrieve the vertical profile of CO2 in the upper atmosphere above about 700 hPa pressure level. In addition, another installed on the satellite is an imaging sensor that will be used to detect clouds and aerosols: Cloud and Aerosol Imager (CAI). The Center for Climate System Research (CCSR) has contracted with the Japan Aerospace Exploration Agency (JAXA) to develop an algorithm to retrieve CO2 concentration profiles from data measured by the thermal infrared (TIR) band of the TANSO-FTS sensor. We adopt the maximum a posteriori method (MAP) to retrieve the vertical profile of atmospheric parameters from thermal infrared spectra. Key techniques for retrieving CO2 concentrations are 1) reduction of temperature estimation error through channel selection, 2) optimization of the initial guess for CO2 profile based on the output from a chemical transport model (CTM), and 3) usage of data from the 1.6 mu m band of TANSO-FTS as an additional constraint in retrieval of vertical profiles Of CO2. Although thermal infrared spectrum data have poor vertical resolving power for CO2 concentration in the lower atmosphere, particularly in the boundary layer, we expect that CO2 amount in the lower atmosphere can be deduced by substituting the upper level concentration from the columnar concentration estimated from the 1.6 mu m band data.

The successor of the Improved Limb Atmospheric Spectrometer (ILAS), ILAS-II, aboard the Advanced Earth Observing Satellite-II (ADEOS-II) measured atmospheric absorption spectra at a wavelength region from 753 rim to 784 nm, including the molecular oxygen (O(2)) A-band centered at 762 nm, with a FWHM spectral resolution of 0.06 nm. Temperature and pressure profiles between similar to10 km and 80 km were retrieved from the solar occultation measurements of the 02 A-band spectra during the operational period of ADEOS-II in 2003. Based on the actual measured data during the smallest atmospheric variability, the repeatability of the measurement, which is a measure of the measurement precision, for temperature and pressure was estimated to be 1-2 K and 0.5-2%, respectively. Comparisons between ILAS-II and the U.K. Met. Office (UKMO) stratospheric analyses or the NASA's UARS/HALOE and TIMED/SABER temperature data are performed. Regardless of the good precision, it is found that the ILAS-II temperatures are systematically lower in the stratosphere and significantly higher in the lower mesosphere.

Considering global increase in greenhouse-gases, observation and monitoring of the earth's atmosphere with space-borne instruments are essential. Satellite measurement offers the advantage of global and long-term monitoring. In the short wave infrared (SWIR) region of 1.6-1.9 μm, major greenhouse gases (carbon dioxide (CO2)), water vapor (H2O), and methane (CH4) have absorption spectra of moderate strength without interference by other molecule absorption. In addition, we can use the un-cooled detector for this wavelength region. Two different types of observation geometry will be discussed; one is nadir-looking with sun glint light source for the column amount retrieval and the other is limb-looking with scattered light source for the vertical profile retrieval. We propose the four-ports Fourier transform spectrometer (FTS) for this application. One input port is for nadir-looking measurements and the other input port is for limb-looking measurements. One output port is used for greenhouse gases measurements and the other port is used for the oxygen (O2) absorption spectra measurement for the optical path length calibration. The instrumentation of the FTS, retrieval algorithm and expected performance are discussed, and ground test results are also presented.

The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar occultation Fourier transform spectrometer (FTS), developed by the Ministry of the Environment (MOE) of Japan, that will be onboard the Global Change Observation Mission-A1 (GCOM-A1) satellite. GCOM-A1 will be placed in a 650 km non-sun-synchronous orbit, with an inclination angle of 69 deg. SOFIS is the successor of ILAS-II, which will be onboard the Advanced Earth Observing Satellite-II (ADEOS-II). SOFIS measures atmospheric constituent vertical profiles with 0.24 cm(-1) spectral resolution in 3-13 mum and 1 km vertical resolution. SOFIS will measure the global distribution of O-3, HNO3, NO2, N2O, CH4, H2O, CO2, CFC-11, CFC-12, CIONO2, aerosol extinction, atmospheric pressure, and temperature. SOFIS uses a double-pass dual-pendulum type FTS with diode laser sampling system to reduce the size and weight. Two photo-voltaic (PV) MCT (HgCdTe) detectors and a pulse-tube cooler will achieve high linearity and low-noise performance. In addition, it has a visible (O-2 A band) grating spectrometer for pressure and temperature retrieval and a sun-edge sensor for the tangent height position detection. We describe the performance test results of the laboratory model and present the instrumentation and engineering model test results.

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 though 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.