Global Greenhouse Gas Observation by Satellite

Transcription

1 Global Greenhouse Gas Observation by Satellite

2 Greenhouse gases Observing SATellite Figure 1. Overview of GOSAT ( JAXA) The Greenhouse Gases Observing Satellite (GOSAT) will be the world s first satellite to observe the concentrations Studies (NIES), and the Japan Aerospace Exploration Agency (JAXA) (Fig. ). of carbon dioxide and methane, two major greenhouse gases, from space. (Fig. 1) MOE: Ministry of the Environment Analyses of GOSAT observation data will make it possible to ascertain the global distributions of carbon dioxide (CO ) and methane (CH 4 ) and the geographical distribution of and seasonal and inter-annual variations Developing sensors (in collaboration with JAXA) Validating processed products Contributing to international efforts to reduce carbon emissions through scientific application of GOSAT observation data. in the flux (i.e., emission and absorption) of greenhouse gases. The results of the analysis will not only contribute to a deeper scientific understanding of the behaviors MOE Responsibilities Shared of the causative agents Managing the Science Team and promoting of global warming, but NIES: National data utilization will also provide fundamental Institute for information Environmental for refining climate Studies Developing and improving NIES JAXA change prediction and JAXA: Japan methods to derive greenhouse gas concentrations Aerospace formulating global warming countermeasures. from satellite and auxiliary Exploration The GOSAT Agency data Higher-level processing, Developing sensors (in collaboration with MOE) Project is a joint effort validation, and distribution of data products to external parties Developing, launching and operating the satellite of the Ministry of the Estimating carbon fl ux using models Environment (MOE), Acquiring satellite observation data, including Cooperating with JAXA activities data reception and recording the National Institute Level 1 processing of data and its calibration for Environmental Cooperating with MOE and NIES activities Figure. Role Sharing in the GOSAT Project 1 Greenhouse gases Observing SATellite Project

3 Goals of the GOSAT Project 1 Goals of the GOSAT Project Emissions of CO have increased drastically over the past century as a result of the mass consumption of fossil fuels due to the expansion of industrial activities resulting in dramatic increases in atmospheric concentrations of CO (Fig. 3). CO, which is a greenhouse gas, leads to an increase in atmospheric temperatures. In addition to CO, species such as CH 4, nitrous oxide (N O), and halocarbons were designated as greenhouse gases subject to restrictions by the Kyoto Protocol; however, CO account for 81% of the total greenhouse effect caused by these gases (Fig. 4). The growing concentration of greenhouse gases in the atmosphere not only raises the temperature but can also cause droughts where rainfall is already scarce and floods in places where precipitation is already abundant, so there are concerns that, without intervention, significant damage will occur. That being the case, the global community is moving toward reducing greenhouse gas emissions. Under the United Nations Framework Convention on Climate Change, the Kyoto Protocol, which defines targets for emission reductions by developed nations, was agreed upon in 1997 and came into force in February. In order for every nation on the globe to adopt measures for reducing greenhouse gas emissions, it is essential to set rational goals based on accurate predictions of climate change and its impact. At the same time, it is important to determine emission levels per country, and to evaluate various reduction measures based on that knowledge. The foremost purpose of the GOSAT Project is to produce more accurate estimates of the flux of greenhouse gases on a subcontinental basis (several thousand kilometers square). This is expected to help contribute to environmental administration efforts such as ascertaining the amount of CO absorbed or released per region and evaluating the carbon balance in forests. Furthermore, by engaging in research using the GOSAT data, we will accumulate new scientific knowledge on the global distribution of greenhouse gases and its temporal variations, and the mechanism of the global carbon cycle and its effect on climate, which will prove useful in predicting future climate change and assessing its impact. Additionally, the Project will expand upon existing earthobserving satellite technologies, develop new methodologies to measure greenhouse gases, and promote the technological development necessary for future earth-observing satellites. CO concentration (ppm) N O concentration (ppb) Carbon dioxide (CO ) Methane (CH 4 ) Nitrous oxide (N O) Year Figure 3. Changes in concentrations of primary greenhouse gases in the atmosphere (Modified from the IPCC Fourth Assessment Report) Halocarbons 13% Nitrous oxide (N O) 6% Methane (CH 4 ) 18% Carbon dioxide (CO ) 63% Figure 4. Contributions of the primary greenhouse gases to the increase in air temperature (The above figures are based on the bestestimates of radiative forcing gases from 175 to 5, modified from the IPCC Fourth Assessment Report) (a) February (b) August Absorption Figure 5. The data obtained through GOSAT is expected to allow for this kind of computation of the global distribution of CO flux (Simulation, (a) February, (b) August, carbon conversion [gc/m /day]) CH 4 concentration (ppb) Emissions

4 GOSAT Sensors and Observation Methods GOSAT Sensors and Observation Methods GOSAT will observe infrared light reaching its sensors from the earth s surface and the atmosphere and give spectra which can be used to calculate the column abundances of CO. The column abundances are expressed as the total number of molecules of target gases over the unit surface area or as the ratio of target gas molecules to the total number of molecules in dry air per unit surface area. GOSAT will orbit the earth in roughly 1 minutes at an altitude of approximately 666 km and return to the same orbit in three days (Fig. 6). The observation instrument onboard the satellite is called the Thermal And Near-infrared Sensor for carbon Observation (TANSO). TANSO is composed of two sensors: a Fourier Transform Spectrometer (FTS) and a Cloud Aerosol Imager (CAI). Tables 1 and summarize the target species, bands, and other specifications of the two sensors. TANSO-FTS utilizes optical interference, which is induced by splitting the incoming light into two optical paths to create an optical path difference between the two, and then recombining them. A light intensity distribution as a function of wavelength (spectrum) can be obtained by conducting a mathematical conversion called the Fourier transform on the signals observed while changing the optical path difference little by little. Bands 1 to 3 of FTS will provide the spectra of sunlight reflected from the earth s surface in the daytime and band 4 will observe light emitted from the atmosphere and the earth s surface throughout the day and night. The characteristics of sunlight reflection differ greatly between land and water surfaces. Seawater and freshwater absorb light which makes detection of the reflection difficult. However, in certain directions, sunlight is reflected as specular reflection and glitters brightly, so the sensor will target such points for observation over large water surfaces. GOSAT TANSO-CAI will observe the state of the atmosphere and the ground surface during the daytime in image form. The imagery data from TANSO-CAI will be used to determine the existence of clouds over a wide area including the field of view of FTS. When aerosols or clouds are detected, the characteristics of the clouds and the aerosol amounts are identified. This information is used to correct for the effects of clouds and aerosols on the spectra obtained by FTS. Over a three-day period, TANSO-FTS will take spectra from several tens of thousands points distributed uniformly over the surface of the earth. Since analysis can only be done on cloud-free areas, only approximately 1 percent of the total number of observation points can be used for calculating the column abundances of CO. Even so, the number of data points significantly surpasses the current number of ground measuring points (currently under ), and will serve to fill in areas where measurement has not been conducted to date. Table 1. Specifications of the Fourier Transform Spectrometer (FTS) sensor Band 1 Band Band 3 Band 4 Spectral coverage [μm].758~ ~ ~ ~14.3 Spectral resolution [cm -1 ] Target species O CO CH 4 CO H O CO CH 4 Instantaneous field of view/ Field of observation view at nadir Single-scan data acquisition time * 1 μm = 1/1 mm Instantaneous fi eld of view: 15.8 mrad Field of view for observation (footprint): diameter of app. 1.5 km 1.1,., 4. seconds Table. Specifications of the Cloud and Aerosol Imager (CAI) sensor Band 1 Band Band 3 Band 4 Spectral coverage [μm].37~.39 (.38).668~.688 (.678).86~.88 (.87) Target substances Cloud, Aerosol Swath [km] Spatial resolution at nadir [km] 1.56~1.68 (1.6) Sunlight Descending 666 km 1km diameter Ascending Figure 6. Conceptual diagram of GOSAT observation and the satellite orbits (three days, 44 orbits) 5km(on the Equator) 3 Greenhouse gases Observing SATellite Project

5 Longitude(deg.E) Copyright (c) 7 NIES Analysis Methods of GOSAT data 3 Analysis Methods of GOSAT data The data taken by the FTS and CAI sensors will be processed as shown in Figure 7. FTS-observed values provide spectra while CAI-based data will be used to generate cloud and aerosol information. These data will be combined together to calculate the CO column abundances at observation points with no or only thin clouds and aerosol layer present. Furthermore, an atmospheric transport model will be used with the obtained distribution of column abundance of CO to estimate the global distribution of CO fl ux as well as the three-dimensional distribution of CO concentrations. Sensors terly basis, and mapped out globally. The next step in data processing is the estimation of the flux of CO using the acquired column abundances of CO. We effectively reverse the atmospheric transport model to trace the origins of the CO detected by GOSAT, and estimate the flux of CO on a sub-continental scale (Fig. 5). The current method of estimating flux of CO depends solely on ground-based observation data, which results in significant errors in estimations for regions such as Africa and South America, where observation points are scarce. GOSAT is Observation data Processed products CO absorb light with particular wavelengths. Therefore, by measuring how much light was absorbed by these molecules, the amounts of CO existing through the optical paths can be calculated. Fig. 8 provides an example of spectra that are expected to be obtained from observation by FTS. The spectra structures like teeth of a comb indicate the absorption by gases, such as CO, and the depths correlate with their column abundances. TANSO-FTS sensor (provided by JAXA) TANSO-CAI sensor (provided by JAXA) April August Interferogram Cloud/aerosol distribution Radiance(W/m /micron/str) Latitude(deg.N) Wavelength(μm) Spectrum FTS SWIR Pseudo Data Sun Zenith Angle = 8 deg. Count = 6346 Column abundances of CO? Low density High density? (ppm) Among spectra obtained with FTS, only those spectra with no clouds in the field of view of the 3D distribution of CO CO flux FTS will be identified with the use of images Figure 7. Outline of GOSAT data processing from CAI. This is possible because the spatial resolution of CAI is high enough to detect cloud contamination in the field of view of FTS. The spectra with no clouds will then be analyzed using a numeric calculation capable of acquiring observation data almost uniformly around the globe and hence is expected to reduce errors in estimated CO flux. Furthermore, using the distribution of method called the retrieval method based on Wavenumber (cm -1 ) the characteristics of absorption by gas, and CO flux obtained in this manner and Absorption band of water vapor(ho) 15 Absorption band of carbon dioxide(co) the column abundances of CO will be the atmospheric Absorption band of methane(ch4) 1 Absorption band of oxygen(o) derived. The CO absorption bands near 1.6μm transport model, it Absorption band of ozone(o3) 5 and. μm are quite important because they will be possible to provide us with a large amount of information Wavelength (μm)..5 simulate the global 13cm near the earth s surface where the changes in 19cm -1 64cm-1 58cm -1 5cm 3 48cm -1 O HO CO CO CO distribution of CO 1 1 HO CO concentrations are most apparent. The absorption band near 14 μm is used for obtainsions. 1 in three dimen- CO CH Wavelength (μm) Wavelength (μm) Wavelength (μm) Band 1 Band Band 3 ing information mainly at altitudes of km and Wavenumber (cm -1 ) above. HO 8 CH4 O3 CO CO Figure 8. Examples of 6 spectra obtainable through 4 Once enough points of data are accumulated, GOSAT observation and the acquired column abundances of CO and the absorption Wavelength (μm) CH 4 can be averaged on a monthly and quar- bands of CO Band 4 Radiance (W/m /micron/str) Radiance(W/m /micron/str) Radiance (W/m /micron/str) 4

6 Evaluation of Data Analysis Methods and Validation of Products 4 Evaluation of Data Analysis Methods and Validation of Products The GOSAT Project conducts research (Fig. 1). The column abundances of CO will on analytical methods for decreasing uncertainty in be compared to observation data taken by high-resolution Fourier transform spectrometer or by direct obser- the calculation of column abundances and evaluates the validity of the methods by conducting simulations. Furthermore, we are planning to validate in aircraft, while cloud and aerosol data will be validated vation using the instruments installed on the ground or the analytical methods and the products processed using ground-based remote sensing instruments such as from GOSAT data after the satellite is launched. lidar or a sky radiometer. The amounts of CO flux and Based on the results of the validation, we will conduct further research into improving our 3D distribution of CO will also be evaluated. methods. We have already performed a number of experiments to simulate satellite observation. One example of these simulations involved retrieving CO concentration by installing a Fourier transform spectrometer, which functions on the same principles as TANSO-FTS, near the top of Mt. Tsukuba at an altitude of approximately 8 m and observing the sunlight reflected on the farmland at the foot of the mountain (Fig. 9). At the same time, a small aircraft with CO in-situ instruments took aerial measurements between the nearground level of the farmland and an altitude of 3, m. The results of these two observations were compared and found to be basically in agreement, proving the reliability of our method of evaluating the CO column abundance. Further simulation tests are planned on an ongoing basis so as to assess and improve the analysis methods. After the launch, the GOSAT data will be processed into products which will provide Farmland CO in-situ instrument CH 4 in-situ instrument FTS Mt.Tsukuba Max.3,m Figure 9. Outline of simulation tests conducted at Mt. Tsukuba in 5 Aerosols GOSAT FTS onboard the airplane Scattered light In-situ instrument onboard the airplane Concentration measurement at various altitudes information on CO columns, CO flux, and the 3D distribution of CO (Fig. 7). These products will be verified and evaluated using highly accurate data independently obtained by ground platforms or aircraft Ground-based high-resolution FTS Laser beam Lidar Sky radiometer In-situ instrument installed at the terrestrial station Figure 1. Schematic illustration of post-launch product validation experiments 5 Greenhouse gases Observing SATellite Project

7 Data Distribution 5 Data Distribution NIES has been developing the GOSAT Data Handling Facility (DHF), which will process GOSAT data (Fig. 11). After data reception and Level 1 processing by JAXA, GOSAT observation data will be transferred to the GOSAT DHF via Tsukuba WAN, a high-speed network in Tsukuba. At the GOSAT DHF, the GOSAT data and reference data from other sources will be used to generate the column abundances of CO, CO flux, and the 3D distribution of CO with the cooperation of external computing centers. Table 3 shows the standard products that the GOSAT DHF will provide. Level 1 data to be provided by JAXA (L1B of FTS observation) and higher-level products to be generated by NIES (L1B and L1B+ of CAI and L, L3, L4A and L4B of FTS) will be available for use and searching by the general public by accessing the GOSAT DHF via networks. The provision of GOSAT products to the general public is scheduled for after the validation phase following the launch of the satellite. In addition, the GOSAT DHF will compile observation requests from users and forward them to JAXA. Table 3. Standard products to be provided by the GOSAT DHF. See Figure 7 for how each product type will be generated Product Level Sensor Description L1B FTS Spectrum data obtained by the Fourier transform of interferogram data CAI Radiance data including parameters for band-to-band registration and geometric correction (before map projection) L1B+ CAI Radiance data including parameters for band-to-band registration, geometric correction and map projection L FTS CO column abundances (TBD) CH 4 column abundances (TBD) L3 FTS CO column concentrations projected on a map (Monthly and quarterly averages) CH 4 column concentrations projected on a map (Monthly and quarterly averages) L4A - Amount of CO fl ux per region, for each of 64 regions (Monthly averages) L4B - CO global distribution data (3D, Monthly averages) L1data NIES/DHF GOSAT Data Handling Facility Data at each level JAXA L,L3,L4 data (From JAXA Website) Data users Reference data Input data, parameters Computation results Input data, parameters Computation results Validation and experiment data Entities providing reference data Computing center Computing center Entities providing validation and experiment data Figure 11. Workfl ow of GOSAT data processing 6

8 Organization and Schedule 6 Organization and Schedule GOSAT is scheduled to be launched in early 9, with full-fledged data acquisition to start three to six months after the launch. NIES has formed a project unit (Fig. 1) for carrying out the GOSAT Project. This unit will develop methods for calculating the CO column abundances from the GOSAT data, develop models for estimating CO flux, validate and evaluate the results. At the same time, it will develop and operate the GOSAT DHF which will process the data, and provide information to users. Center for Global Environmental Research Yasuhiro Sasano, Director (Climate Change Research Project) Core Research Project Tatsuya Yokota, Leader Shamil Maksyutov, Sub-leader Development of data processing techniques Ground- and aircraft-based experiments for validation Development of carbon balance models NIES GOSAT Project Tatsuya Yokota, Leader Cooperation Hiroshi Watanabe, Office Manager Development and operation of DHF (Project promotion) NIES GOSAT Project Office Validation Osamu Uchino, Manager Public relations, other activities Figure 1. GOSAT Project at NIES (as of March 8) Cooperative sections in NIES Validation, research on data utilization, etc. Cooperative organizations outside NIES Computing centers, method development, validation, research on data utilization, etc. Ministry of the Environment National Institute for Environmental Studies GOSAT Project Japan Aerospace Exploration Agency For more information, please contact: GOSAT Project Office Center for Global Environmental Research National Institute for Environmental Studies 16- Onogawa, Tsukuba-shi, Ibaraki Japan TEL: FAX: gosat-prj1@nies.go.jp URL: Published by the Center for Global Environmental Research, National Institute for Environmental Studies 8.5.