Hiroshi Suto

Japan Aerospace Exploration Agency, Chōfu, Tōkyō, Japan

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Publications (73)46.15 Total impact

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    ABSTRACT: This work describes the radiometric calibration of the short-wave infrared (SWIR) bands of two instruments aboard the Greenhouse gases Observing SATellite (GOSAT), the Thermal And Near infrared Sensor for carbon Observations Fourier Transform Spectrometer (TANSO-FTS) and the Cloud and Aerosol Imager (TANSO-CAI). Four vicarious calibration campaigns (VCCs) have been performed annually since June 2009 at Railroad Valley, NV, USA, to estimate changes in the radiometric response of both sensors. While the 2009 campaign $( hbox{VCC}^{2009})$ indicated significant initial degradation in the sensors compared to the prelaunch values, the results presented here show that the stability of the sensors has improved with time. The largest changes were seen in the 0.76 $muhbox{m}$ oxygen A-band for TANSO-FTS and in the 0.380 and 0.674 $muhbox{m}$ bands for TANSO-CAI. This paper describes techniques used to optimize the vicarious calibration of the GOSAT SWIR sensors. We discuss error reductions, relative to previous work, achieved by using higher quality and more comprehensive in situ measurements and proper selection of reference remote sensing products from the Moderate Resolution Imaging Spectroradiometer used in radiative transfer calculations to model top-of-the-atmosphere radiances. In addition, we present new estimates of TANSO-FTS radiometric degradation factors derived by combining the new vicarious calibration results with the time-dependent model provided by Yoshida (2012), which is based on analysis of on-board solar diffuser data. We conclude that this combined model provides a robust correction for TANSO-FTS Level 1B spectra. A detailed error budget for TANSO-FTS vicarious calibration is also provided.
    IEEE Transactions on Geoscience and Remote Sensing 01/2014; 52(7):3991-4004. · 3.47 Impact Factor
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    ABSTRACT: The thermal infrared (TIR) band of Thermal and Near-Infrared Sensor for carbon Observations Fourier Transform Spectrometer (TANSO-FTS) on the Greenhouse gases Observing SATellite (GOSAT) measures a wide range of scene temperatures using a single detector band with broad spectral coverage. This work describes the vicarious radiometric calibration over a large footprint (10.5 km) and high temperature surface using well-calibrated ground-based and airborne FTS sensors. The vicarious calibration campaign of GOSAT was conducted at Railroad Valley, NV in June 2011. During the campaign, the Scanning High-resolution Interferometer Sounder (S-HIS) mounted on the high-altitude NASA ER-2 aircraft observed upwelling radiation and the ground-based Surface-Atmospheric Emitted Radiance Interferometer (S-AERI) observed infrared thermal emission from the atmosphere and the surface at the same location and time as the GOSAT TANSO-FTS. We validated TANSO-FTS TIR radiance with S-HIS radiance using double difference method, which reduces the effect of differences in the observation geometry. In this paper, we estimated the TANSO-FTS Instantaneous Field of View average temperature and emissivity by the coincident S-AERI and S-HIS observed radiance. The double difference between TANSO-FTS and S-HIS result in a difference of 0.5 K at atmospheric window channels (800 ~ 900 cm-1) and CO2 warm brightness temperature channels (700 ~ 750 cm-1), 0.1 K at ozone channels (980 ~ 1080 cm-1), and more than 2 K at CO2 cool brightness temperature channels (650 ~ 700 cm-1). The main reason of remaining errors is attributed to a calibration error in the TANSO-FTS Level 1B product version under evaluation.
    IEEE Transactions on Geoscience and Remote Sensing 01/2014; 52(1):89-105. · 3.47 Impact Factor
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    ABSTRACT: The Fourier-transform spectrometer on board the Japanese GOSAT satellite offers an excellent opportunity to study the impact of instrument resolution on retrieval accuracy of CO2 and CH4. This is relevant to further improve retrieval accuracy and to optimize the cost-benefit ratio of future satellite missions for the remote sensing of greenhouse gases. To address this question, we degrade GOSAT measurements with a spectral resolution of ≈ 0.24 cm-1 step-by-step to a resolution of 1.5 cm-1. We examine the results by comparing relative differences at various resolutions, by referring the results to reference values from the Total Carbon Column Observing Network (TCCON), and by calculating and inverting synthetic spectra for which the true CO2 and CH4 columns are known. The main impacts of degrading the spectral resolution turn out to be consistent for the first two approaches; pure forward model errors identified with simulated measurements are much smaller. For GOSAT spectra, the most notable effect on CO2 retrieval accuracy is the increase of the standard deviation of retrieval errors from 0.7% to 1.0% when the spectral resolution is reduced by a factor of six. The retrieval biases against atmospheric water abundance and airmass become stronger with decreasing resolution. The error scatter increase for CH4 columns is less pronounced. The selective degradation of single spectral windows demonstrates that the retrieval accuracy of CO2 and CH4 is dominated by the spectral range where the absorption lines of the target molecule are located. For both GOSAT and synthetic measurements, retrieval accuracy decreases with lower spectral resolution, suggesting increasing interference errors.
    Atmospheric Measurement Techniques Discussions. 12/2013; 6(6):10399-10441.
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    ABSTRACT: Fourier transform spectrometer (FTS) has many advantages, especially for greenhouse gases and air pollution detection in the atmosphere, because a single instrument can provide wide spectral coverage and high spectral resolution with highly stabilized instrumental line function for all wavenumbers. Several channels are usually required to derive the column amount or vertical profile of a target species. Near infrared (NIR) and shortwave infrared (SWIR) spectral regions are very attractive for remote sensing applications. The GHG and CO of precursors of air pollution have absorption lines in the SWIR region, and the sensitivity against change in the amounts in the boundary layer is high enough to measure mole fractions near the Earth surface. One disadvantage of conventional space-based FTS is the spatial density of effective observation. To improve the effective numbers of observations, an imaging FTS coupled with a two-dimensional (2D)-camera was considered. At first, a mercury cadmium telluride (MCT)-based imaging FTS was considered. However, an MCT-based system requires a calibration source (black body and deep-space view) and a highly accurate and super-low temperature control system for the MCT detector. As a result, size, weight, and power consumption are increased and the cost of the instrument becomes too high. To reduce the size, weight, power consumption, and cost, a commercial 2D indium gallium arsenide (InGaAs) camera can be used to detect SWIR light. To demonstrate a small imaging SWIR-FTS (IS-FTS), an imaging FTS coupled with a commercial 2D InGaAs camera was developed. In the demonstration, the CH4 gas cell was equipped with an IS-FTS for the absorber to make the spectra in the SWIR region. The spectra of CH4 of the IS-FTS demonstration model were then compared with those of traditional FTS. The spectral agreement between the traditional and IS-FTS instruments was very good.
    Proc SPIE 10/2013;
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    ABSTRACT: Microvibrations onboard greenhouse gases observing satellite (GOSAT) cause scan speed variations in the TANSO Fourier transform spectrometer. The associated periodic sampling errors generate ghost features in O<sub>2</sub> A-band spectra, where surface pressure and aerosol properties are retrieved to determine the optical path through the atmosphere. A correction algorithm has been developed to re-compute the interferograms at equally spaced sampling intervals. The key is to determine iteratively the amplitude and phase of sinusoidal perturbations with predetermined frequencies to minimize the magnitude of the out-of-band ghosts artifacts after correction of the sampling grid. This correction algorithm drastically reduces errors in retrieved surface pressure and improves agreement with ground-based observations.
    Applied Optics 07/2013; 52(20):4969-4980. · 1.69 Impact Factor
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    ABSTRACT: Spectroscopic measurements of sunlight backscattered by the Earth's surface is a technique widely used for remote sensing of atmospheric constituent concentrations from space. Thereby, remote sensing of greenhouse gases poses particularly challenging accuracy requirements for instrumentation and retrieval algorithms which, in general, suffer from various error sources. Here, we investigate a method that helps disentangle sources of error for observations of sunlight backscattered from the glint spot on the ocean surface. The method exploits the backscattering characteristics of the ocean surface which is bright for glint geometry but dark for off-glint angles. This property allows for identifying a set of clean scenes where light scattering due to particles in the atmosphere is negligible such that uncertain knowledge of the lightpath can be excluded as a source of error. We apply the method to more than 3 yr of ocean-glint measurements by the Thermal And Near infrared Sensor for carbon Observation (TANSO) - Fourier Transform Spectrometer (FTS) onboard the Greenhouse Gases Observing Satellite (GOSAT) which aims at measuring carbon dioxide (CO2) and methane (CH4) concentrations. The proposed method is able to clearly monitor recent improvements in the instrument calibration of the oxygen (O2) A-band channel and suggests some residual uncertainty in our knowledge about the instrument. We further assess the consistency of CO2 retrievals from several absorption bands between 6400 cm-1 (1565 nm) and 4800 cm-1 (2100 nm) and find that the absorption bands commonly used for monitoring of CO2 dry air mole fractions from GOSAT allow for consistency better than 1.5 ppm. Usage of other bands reveals significant inconsistency among retrieved CO2 concentrations pointing at inconsistency of spectroscopic parameters.
    Atmospheric Measurement Techniques Discussions. 05/2013; 6(3):4371-4400.
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    ABSTRACT: The Carbon Monitoring Satellite (CarbonSat) is one of two candidate Earth Explorer Opportunity Missions, scheduled for launch in 2018. Its goal is to monitor tropospheric CO2 and CH4 by measuring reflected Sun light in the infrared (four separate observation windows between 0.7 and 2.0 μm). Since the Fourier-transform spectrometer on board the Japanese GOSAT satellite observes at a very similar range as the planned CarbonSat spectrometer, GOSAT spectra offer an excellent opportunity to study the impact of instrument settings on retrieval accuracy. The main topic of this study is the impact of spectral resolution on retrieval accuracy of CO2 and CH4, i.e., does a lowered resolution make spectroscopic errors more obvious? This question is relevant for the CarbonSat mission because the instrument line shape will probably be about five times broader than for GOSAT, but it is also of general interest for the remote sensing of CO2 and CH4. Two different approaches are used to reduce the spectral resolution of the native GOSAT spectra. The columns of CO2 and CH4 that are retrieved from the spectra are then compared to collocated observations from six different observation sites of the Total Carbon Column Observing Network (TCCON). The two instrument settings with a similar spectral resolution but different degradation approach give a similar increase in scatter and decrease of correlation. For the CO2 retrieval accuracy, the only notable effect of lowering the spectral resolution from GOSAT to CarbonSat resolution is the increase of the standard deviation of retrieval errors from 0.7% to 1.0%. Other quality criteria (convergence, inter-stational bias) do not change. For CH4 columns, the standard deviation hardly increases (from 0.9% to 1.0%). Reducing the spectral resolution does not further increase the strength nor the significance of retrieval biases with respect to water abundance, albedo, or solar zenith angle. The selective degradation of single windows demonstrates that the retrieval accuracy of CO2 and CH4 is dominated by the spectral range where the absorption bands of the target molecule are situated.
    04/2013;
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    ABSTRACT: GOSAT which was launched on 23rd of January, 2009 has been operated over four years and an area for improvements such as the observation specifications and hardware methods as well as the measurement accuracy. Therefore we have studied the mission of the GOSAT follow-on, that is GOSAT-2 to leverage greenhouse gases observation from space for the science as well as the practical use such as the effort against global warming by the improvements of the observation performances. At first, we defined the requirements for the concentration measurement accuracies, the estimation error of the net flux and so on which should be accomplished in the next generation based on the GOSAT observation results. Secondly, the specifications of the mission instruments have been studied to satisfy the mission requirements and were defined. To confirm the possibilities of the defined specifications, we have carried out trial manufacture and considerations and redefined the specifications of the mission instruments. The principal improvement point is the increase of the number of the useful data. A large part of GOSAT data have been contaminated with the clouds and only a few percent of the measured data are used. To increase the useful data, we considered the following some kinds of methods. 1. Reduction of the IFOV size; It is possible to reduce the influence of the clouds if the IFOV size becomes small. But it is hard to compensate the reduction of the SNR, so we will give up the reduction of the IFOV size. 2. Adoption of multi FOV;GOSAT has only one FOV and we have considered to increase the number of the FOV to increase the number of the data by the adoption of the multi photo diodes detector. But the optical cross talk which is generated by the multipath reflection between cover glass and photo diodes is too large and exceeded our requirement. So we gave up the adoption of the multi FOVs. 3. Adoption of an intelligent pointing; We are considering to detect the clouds in the FOV of the FTS on orbit and to drive the line of sight to the area where there is no clouds. We are now studying the method to detect the clouds and drive the pointing mirror. 4. Increase of the SNR; In the high-latitude region, the luminance of the solar ray reflection is low, so the SNR is low and it's difficult to observe the high-latitude region of the northern hemisphere in winter. It is possible to extend the observation area to the high-latitude region if the SNR is increased. The increase of the SNR will be realized by the expansion of the aperture size and the adoption of the over sampling. We are now conducting the trial manufacture of the large size corner cube which is used in the Fourier Transform Spectrometer mechanism. In the presentation, I will introduce the mission requirement to GOSAT-2 and the results of the trial manufacture as well as the specifications of the mission instruments which are redefined.
    04/2013;
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    ABSTRACT: To monitor the global column concentration of carbon dioxide (CO2) and methane (CH4) from space, the Greenhouse gases Observing SATellite (GOSAT) was launched on January 23, 2009, and has started the operational observation. During four years operational periods, the radiometric, geometric and spectroscopic characterizations of TANSO have been continuously conducted with updating the Level-1 processing algorithm. The latest version of v150 was applied the analog circuit non-linear response correction of band-1 and the correction procedure for improper scan-interval. Newly applied correction methods were supported to derive the accurate XCO2 and XCH4 from Level-2 processing. In parallel, the re-processed products of Level-1 by v150 were conducted for the last 3 years observation data. The evaluated Level-2 data based on v150 suggested us that these products still have following features; the bias offset on M-gain products against H-gain products, the bias difference between land and ocean products, the higher Chi2 for band-2 data caused by scan-interval correction and the biases on brightness temperature at 15-um region against AIRS or IASI products. The main cause of these features is imperfect calibration of TANSO-FTS instruments. In addition, the non-linear mechanism on analog circuit for band1 was identified through the ground-based experiment. The second source of non-linear response excites the artificial signals on absorption lines. Also, the polarization parameters, emissivity of black body and obscuration ratio for TIR will be updated. To improve the spectral quality, we will plan to apply the correction procedure and updated calibration parameters on upcoming Level-1 products. In this presentation, the detail of processing algorithm and parameters derived four years operation will be presented.
    04/2013;
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    ABSTRACT: Pressing open questions about the carbon cycle can be addressed with precise measurements of the three most abundant CO2 isotopologues 16O12C16O, 16O13C16O, and O16C12O18. Such measurements can, e.g., help to further constrain oceanic and biospheric net fluxes or to differentiate between the gross biospheric fluxes photosynthesis and respiration. The 2041-2047nm (about 4885-4900cm-1) spectral region contains separated absorption lines of the three most abundant CO2 isotopologues. Their spectral properties make this spectral region well suited for the use of a light path proxy method for the retrieval of δC13 and δO18 (the ratio of heavier to lighter isotopologues relative to a standard). An optimal estimation based light path proxy retrieval for δC13 and δO18 has been set up, applicable to GOSAT (Greenhouse gases Observing Satellite) and ground-based FTS (Fourier transform spectrometer) measurements. Initial results show that it is possible to retrieve δC13 and δO18 from ground-based FTS instruments with a precision of 0.6-1.6‰ and from GOSAT with a precision of about 30‰. Comparison of the achievable precision with the expected atmospheric signals shows that ground-based FTS remote sensing measurements have the potential to gain valuable information on δC13 and δO18 if averaging a sufficient number of measurements. It seems unlikely that this applies also to GOSAT because of the lower precision and a conceptual larger sensitivity to scattering related errors in satellite viewing geometry.
    Journal of Quantitative Spectroscopy and Radiative Transfer 11/2012; 113(16):2009–2017. · 2.38 Impact Factor
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    ABSTRACT: To observe the global column concentration of carbon dioxide (CO2) and methane (CH4) from space, the Greenhouse gases Observing SATellite (GOSAT) was launched on January 23, 2009, and has started the operational observation. Thermal and Near Infrared Sensor for Carbon Observation- Fourier Transform Spectrometer (TANSO-FTS) has been continuously measuring CO2 and CH4 distributions globally, and the retrieved column CO2 and CH4 data have been distributed to the public. Over three-years operational periods, the useful scientific data sets and interesting articles for carbon source/sink evaluation were produced and published, and these results have been supporting to well understanding of carbon cycle. Currently, the importance of space-based carbon observation has been approved and desired the continuous observation in toward. Through the TANSO-FTS operation with the radiometric, geometric and spectroscopic characterizations, we learned how to improve the accuracy of XCO2 and XCH4 based on short-wavelength FTS. The correction procedures for micro-vibration from companion components, non-linear response of analogue and digitizing circuit are key role on the current on-board operating TANSO-FTS. On instrumental aspects, the robustness and improvements will be required on the future mission. To elucidate the carbon cycle more precisely, our experiences have to be summarized and applied in the future missions. In this presentation, the detail of lessons and learned from TANSO-FTS operation will be presented.
    Proc SPIE 10/2012;
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    ABSTRACT: The Thermal And Near infrared Sensor for carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) onboard the Greenhouse gases Observing SATellite (GOSAT) (nicknamed "Ibuki") has been providing global space-borne observations of carbon dioxide (CO2) and methane (CH4) since 2009. In this paper, we first describe the version V150.151 operational Level 1 algorithms that produce radiance spectra from the acquired interferograms. Second, we will describe the on-orbit characteristics and calibration of TANSO-FTS. Overall function and performance such as signal to noise ratio and spectral resolution are within design objectives. Correction methods of small on-orbit degradations and anomalies, which have been found since launch, are described. Lastly, calibration of TANSO Cloud and Aerosol Imager (TANSO-CAI) are summarized.
    Atmospheric Measurement Techniques 10/2012; 5(10):2447-2467. · 3.21 Impact Factor
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    ABSTRACT: GOSAT which is dedicated to monitor the column concentration of carbon dioxide and methane was launched almost 3 and half years ago, and the data processing algorithm have been improved a few times based on the calibration and validation, and the precision of the concentration data have been increased. These data gave us a realization of the availability of the GHG observation from space. And it has been required to expand this mission to make it useful for mankind. So we have investigated the requirements for the next generation greenhouse gases observations from space and have defined the mission requirements for GOSAT-2. The measurement accuracy target of Carbon Dioxide concentration defined in this mission requirement is 0.5 ppm at 500km and 2,000km mesh spatial resolution over the land and ocean, respectively and 1 month average. To achieve this target, GOSAT-2 will adopt the Fourier Transform Spectrometer (FTS) and the imager along with GOSAT, but the functions and performances will be improved. For example, the CO observation band will be added and the grating spectrometer for UV band of CAI will be adopted to measure NO2 and to improve the aerosol retrievals. Following the presentation of the GOSAT observation results, the concept of GOSAT-2 will be shown.
    Proc SPIE 09/2012;
  • 07/2012;
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    ABSTRACT: The Thermal And Near infrared Sensor for carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) onboard the Greenhouse gases Observing SATellite (GOSAT)(nicknamed "Ibuki") has been providing global space-borne observations of carbon dioxide (CO2) and methane (CH4) since 2009. In this paper, first, the most recent operational Level 1 algorithms to produce the spectral radiance from the acquired interferogram are described. Second, we will describe the on-orbit characteristics and calibrations of TANSO-FTS. Overall functions and performances such as signal to noise ratio and spectral resolution are within design objectives. Correction methods of small on-orbit degradations and anomalies, which have been found since the launch are described. Lastly, calibrations of TANSO Cloud and Aerosol Imager (TANSO-CAI) are summarized. However, the Level 1B algorithms of TANSO-CAI are not mentioned, here in this paper.
    Atmospheric Measurement Techniques Discussions. 04/2012; 5(2):2959-3018.
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    ABSTRACT: To monitor the global column concentration of carbon dioxide (CO2) and methane (CH4) from space, the Greenhouse gases Observing SATellite (GOSAT) was launched on January 23, 2009, and has started the operational observation. Thermal and Near Infrared Sensor for Carbon Observation- Fourier Transform Spectrometer (TANSO-FTS) has been continuously measuring CO2 and CH4 distributions globally every three days, and data distribution to the public started from Feb. 16, 2010. During three years operational periods, the radiometric, geometric and spectroscopic characterizations of TANSO have been continuously conducted with updating the Level-1 processing algorithm. To make a precise spectroscopic observation, correction algorithms were newly developed, demonstrated and installed on operational processing. Two major corrections are discussed. One is a correction of the scan-speed instability caused by micro-vibration from satellite. Through the on-orbit data analysis, degrading spectroscopic accuracy caused by periodically micro-vibrations was found, and these distortion effects were compensated with applying the re-sampling technique for interferogram. The other is non-linearity correction in the electronics. The main course of non-linearity is electronic filters on band 1 signal chain. The zero-level offset is slightly changed with input signal levels. To compensate the non-linear effect, the additional correction schemes are approved from recent version of Level-1 processing. In this presentation, the detail of on-orbit characteristics, processing algorithm of Level-1 and the current status of TANSO will be discussed.
    04/2012;
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    ABSTRACT: Greenhouse gases Observing SATellite (GOSAT) was launched on January 23, 2009, to monitor the global column concentration of carbon dioxide (CO2) and methane (CH4) from space. Thermal and Near Infrared Sensor for Carbon Observation- Fourier Transform Spectrometer (TANSO-FTS), which is the main instrument of GOSAT, has been continuously measuring CO2 and CH4 distributions globally every three days, and data distribution to the public started from Feb. 16, 2010. Over three years operational periods, the useful scientific data sets and interesting articles for carbon source/sink evaluation were produced and published, and these results have been supporting to well understanding of carbon cycle. Currently, the importance of space-based carbon observation has been approved and desired the continuous observation in toward. OCO-2, TanSat, MicroCarb and CarbonSat will be planned to launch in up-coming years and follow to observe the global carbon distribution. Through the GOSAT operation, we learned a lot of things on the instrument, software, processing algorithm and operation; what should be improved in the following mission. To elucidate the carbon cycle more precisely, our experiences were summarized and have to be approved on the mission design of GOSAT-2. In parallel, the feasibility studies such as sampling strategy, band expansion, mapping capability were carried out to answer; what should be emphasis and encouragement for a good understanding of CO2 and CH4 sources and sinks and the underlying carbon cycle. The detail of lessons learned form GOSAT and the mission design of GOSAT-2 will be presented.
    04/2012;
  • Source
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    ABSTRACT: The recent advent of very high spectral resolution measurements by the Fourier Transform Spectrometer (FTS) on board the Greenhouse gases Observing SATellite (GOSAT) platform has made possible the retrieval of sun-induced terrestrial chlorophyll fluorescence (Fs) on a global scale. The basis for this retrieval is the modeling of the in-filling of solar Fraunhofer lines by fluorescence. This contribution to the field of space- based carbon cycle science presents an alternative method for the retrieval of Fs from the Fraunhofer lines re- solved by GOSAT-FTS measurements. The method is based on a linear forward model derived by a singular vector decomposition technique, which enables a fast and robust inversion of top-of-atmosphere radiance spectra. Retrievals are performed in two spectral micro-windows (∼2–3 nm width) containing several strong Fraunhofer lines. The statistical nature of this approach allows to avoid potential retrieval errors associated with the modeling of the instrument line shape or with a given extraterrestrial solar irradiance data set. The method has been tested on 22 consecutive months of global GOSAT-FTS measurements. The fundamental basis of this Fs retrieval approach and the results from the analysis of the global Fs data set produced with it are described in this work. Among other findings, the data analysis has shown (i) a very good comparison of Fs intensity levels and spatial patterns with the state-of-the-art physically-based Fs retrieval approach described in Frankenberg et al. (2011a), (ii) the overall good agreement between Fs annual and seasonal pat- terns and other space-based vegetation parameters, (iii) the need for a biome-dependent scaling from Fs to gross primary production, and (iv) the apparent existence of strong directional effects in the Fs emission from forest canopies. These results reinforce the confidence in the feasibility of Fs retrievals with GOSAT- FTS and open several points for future research in this emerging field.
    Remote Sensing of Environment 01/2012; 121:-251. · 5.10 Impact Factor
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    ABSTRACT: Here, we report preliminary estimates of the column averaged carbon
    Atmospheric Measurement Techniques 01/2012; 5(4):-707. · 3.21 Impact Factor
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    ABSTRACT: The Thermal and Near Infrared Sensor for carbon Observations Fourier Transform Spectrometer (TANSO-FTS) onboard the Greenhouse gases Observing SATellite (GOSAT) collects high spectral resolution spectra of reflected sunlight in the molecular oxygen (O2) A-band near 760 nm, the carbon dioxide (CO2) bands near 1600 and 2060 nm, and the methane (CH4) band near 1660 nm. The O2 measurements are used to estimate the surface pressure and the dry air column, which are used to define the column-averaged CO2 and CH4 dry air mole fractions, XCO2 and XCH4. O2 measurements are ideal for this application because the O2 dry air mole fraction is almost constant and well known. However, systematic errors in the O2 measurements can introduce biases in the XCO2 and XCH4 retrievals from TANSO-FTS. For example, 1% overestimate of the O2 column retrievals introduced a 10 hPa high bias in surface pressure and a 4 hPa low bias in XCO2 in early retrievals. This near-global bias has been traced to uncertainties in the O2 A-band absorption cross sections. Other spatially-varying O2 errors have been traced to uncertainties in the calibration of the TANSO-FTS A-band channel. For example, non-linearity in the A-band channel response introduces errors in the depths of both O2 lines and solar Fraunhofer lines. There are three possible sources of non-linearity: detector, analogue circuit (amplifier and electric filters), and analogue to digital converter (ADC). Observations acquired with the flight instrument and laboratory experiments with TANSO-FTS engineering model (EM) is being used to discriminate and correct these errors. The EM tests have largely vindicated the silicon photo-diode detector, but show that the non-linearity of the analogue circuit and ADC is almost identical to that seen in data acquired by the on-orbit flight model. We have developed and applied a correction to the measured interferograms from the flight instrument and confirmed it validity by showing that the Fraunhofer line depth anomaly and systematic residuals are removed. We will demonstrate how well we can improve the accuracy of the surface pressure and XCO2 retrievals by correcting the non-linearity of O2 A-band measurement.
    AGU Fall Meeting Abstracts. 12/2011;

Publication Stats

151 Citations
46.15 Total Impact Points

Institutions

  • 2006–2012
    • Japan Aerospace Exploration Agency
      Chōfu, Tōkyō, Japan
    • Kyoto University
      • Department of Molecular Engineering
      Kioto, Kyōto, Japan
  • 2010–2011
    • National Institute for Environmental Studies
      • Center for Global Environmental Research
      Tsukuba, Ibaraki, Japan