The Greenhouse gases Observing SATellite (GOSAT) was developed to contribute to monitoring of carbon dioxide and methane from space [1]. The mission objectives are global greenhouse gas measurements from space with precision of 1 % for CO2 and 2 % for CH4 in seasonal mean. The GOSAT carries Thermal And Near infrared Sensor for carbon Observation (TANSO) for precise measurement of greenhouse gases. Main instrument is Fourier Transfer Spectrometer (TANSO-FTS) to observe atmospheric absorption spectra of CO2 and CH4 with high spectral resolution of 0.2 cm-1, broad wavelength coverage of 0.76 − 14.3 microns, wide swath of 790 km and frequent revisit of 3 days. Cloud and Aerosol Imager (TANSO-CAI) is simultaneously on board for cloud detection and correction of optical thin cirrus and aerosol interference within the FTS instantaneous field of view. The GOSAT satellite was launched by H2A-15 rocket on January 23, 2009. The Level 1B products of calibrated spectra were released from September 2009 in public. The Level 2 products of CO2 and CH4 column densities were released from February 2010 [2]. The normal observation data is acquired over one year regularly from April 2009. The mission lifetime is 5 years.
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 supporting the global carbon cycle elucidation. It is important to monitor the greenhouse gases in long-term period with same data quality. During 7.5 years operational periods, GOSAT passed the designed lifetime, which is 5 years, and some components report the change of characteristic in-orbit. The pointing mechanism, which has a capability of change a line of scene both of along track and cross track, is equipped on GOSAT. To keep the quality of spectra from TANSO-FTS and try to ambitious observation plan, the pointing mechanism is switched to the backup one in January 2015. In addition, the spectral resolution is degraded due to the bias of ZPD position science 2014. The compensation algorithm is developed and implemented on the operational system and completed the reprocessing for all passed observation data. The pointing mechanism, observation pattern, and processing algorithm were renovated, and GOSAT can provide the long-term and consistent quality spectra.
The GOSAT thermal infrared (TIR) band calibration is reviewed for the five-year time period from April 2009 through
March 2014. Pre-launch characterization has been augmented by post-launch analysis of on-orbit data and comparison
with coincident measurements from other satellite, airborne, and ground-based sensors. Successive refinements of the
TIR band ground-processing software have incorporated corrections for detector non-linearity and polarization.
Estimates of radiometric uncertainty have also been made. The comparison of GOSAT TIR band nadir and off-nadir
comparisons (SNOs and SONOs) provide a quantitative spectral assessment of the radiometric bias relative to the NASA
AIRS and EUMETSAT IASI sensors.
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.
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.
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.
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. The Thermal And Near infrared Sensor for
carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) and Cloud and Aerosol Imager (TANSO-CAI) are
onboard GOSAT to derive the precise amount of CO2 and CH4 in the earth's atmosphere. The first high spectral
resolution SWIR spectra by TANSO-FTS and the image by TANSO-CAI were acquired on Feb. 7, 2009. TANSO has
been continuously measuring CO2 and CH4 distributions globally every three days, and data distribution to the public has
started from Feb. 16, 2010. Over two year operation periods, the radiometric, geometric and spectroscopic
characterizations of TANSO have been continuously conducted with updating the Level-1 processing algorithm. Timeseries
of radiometric, geometric and spectroscopic response were determined and performed with on-orbit and vicarious
calibrations. In the updated Level-1 processing, the newly developed correction algorithm for micro-vibration effects is
operationally installed and improved the accuracy of medium gain condition. In this presentation, the detail of on-orbit
characterization and the current status of TANSO will be described..
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 two 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 correction of the scan-speed instability caused by microvibration
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. In this presentation, the detail of on-orbit
characteristics and the current status of Level-1procesing for TANSO will be presented.
To map the global column dry mole fractions of carbon dioxide (CO2) and methane (CH4), the Green house gases
Observing SATellite (GOSAT) was launched on January 23, 2009. The Thermal And Near infrared Sensor for carbon
Observation Fourier-Transform Spectrometer (TANSO-FTS) and Cloud and Aerosol Imager (TANSO-CAI) are onboard
on GOSAT to derive the precise amount of CO2 and CH4 in atmosphere measuring the solar light intensity reflected and
scattered on the earth's surface and the thermal radiation. The first high spectral resolution Short Wave Infrared (SWIR)
spectra by TANSO-FTS and the image by TANSO-CAI were acquired on February 7, 2009. TANSO has been
continuously measuring CO2 and CH4 distributions in global every three days periods, and data distribution for public
users was started from February 16, 2010. After the launch, the on-orbit characterization of performance, calibration, and
health monitoring of TANSO has been continuously conducted with updating the Level-1 and -2 processing algorithm.
During the over one-year operation period, a few anomalies such as instability of pointing mechanism, varying offset of
pointing position, small wave-number shift and Zero Path Difference position change, were observed. The radiometric
responses for FTS and CAI are also slightly changing. To minimize these effects in data using, quality flags were
additionally included in product, response functions are updated and the regular operation procedure was slightly
changed. In this presentation, the detail of on-orbit status of TANSO will be reported.
The greenhouse gas observing satellite (GOSAT) was launched on 23 January 2009. Its main sensor, the "thermal and
near infrared sensor for carbon observation Fourier transform spectrometer (TANSO-FTS)", is functioning normally. It
can measure a wide spectrum including three CO2 absorption bands at 1.6 μm and 2.0 μm (Short Wavelength InfraRed,
SWIR band), and 15 μm (Thermal InfraRed, TIR band). The former two bands are used to estimate columnar
concentrations of CO2. The latter is used to retrieve the vertical profile of CO2 concentration in the upper troposphere.
Simulation studies show that high radiometric calibration accuracy of 0.3 K in brightness temperature Tbb is necessary to
retrieve a CO2 concentration profile with accuracy of 1% in the upper atmosphere. The sensor's fundamental
performance was evaluated during the initial checkout period, which continued for six months. Results show that most of
the radiometric performance is achieved as designed. However, results also show that some systematic biases exist in the
TIR spectrum because of the opacity of the dichroic mirrors of SWIR bands obstructing the field of view of the TIR
band. These biases can be mostly removed by explicitly considering radiation--that emitted from inside of the optics and
multiple scattering of target signals--in the calibration procedure. Using a three-day global composite of the clear sky
spectrum, CO2 concentrations in the upper atmosphere were retrieved preliminarily. Results show a convincing
hemispheric concentration gradient, which agrees well with the climatologic distribution of CO2.
The Greenhouse gases Observing SATellite (GOSAT) monitors carbon dioxide (CO2) and methane (CH4) globally from
space. It is a joint project of Japan Aerospace Exploration Agency (JAXA), Ministry of the Environment (MOE) and
National Institute for Environmental Studies (NIES). GOSAT is placed in a sun-synchronous orbit of 666km and 12:48
local time, with an inclination angle of 98 deg. It was launched on January 23, 2009 from Tanegashima Space Center.
There are two instruments on GOSAT. The Thermal And Near infrared Sensor for carbon Observation Fourier-
Transform Spectrometer (TANSO-FTS) detects the Short wave infrared (SWIR) reflected on the earth's surface as well
as the thermal infrared (TIR) radiated from the ground and the atmosphere. TANSO-FTS is capable of detecting wide
spectral coverage; three narrow bands (0.76, 1.6, and 2 μm) and a wide band (5.5-14.3 μm) with 0.27 cm-1 spectral
resolution. The TANSO Cloud and Aerosol Imager (TANSO-CAI) is a radiometer of ultraviolet (UV), visible, and
SWIR to correct cloud and aerosol interference. For three months after the launch, the on-orbit function and
performance have been checked out. Now level 1A (raw interferogram) and level 2B (spectra) are now being processed
and provided regularly with calibration data.
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.
In order to validate and calibrate TANSO-FTS data of the GOSAT satellite, and also to develop the retrieval algorism
for deriving the column density of CO2 and CH4 from spectra, the airborne SWIR (Short Wave Infrared Region) FTS
(Fourier transform spectrometer) has been developed, characterized and demonstrated. This instrument is named as
TSUKUBA model. The basically performance test of TSUKUBA model was carried out in our laboratory, and the
measured modulation efficiencies are 70% (Band1), 85% (Band2) and 88% (Band3), respectively. The measured values
of SNR with the equivalent black body temperature for 30% surface albedo are 190 (13050cm-1), 148 (6200cm-1), and
165 (5000cm-1) without polarization measurement. The measured values of full width at half maximum (FWHM) of
instrumental line shape functions are 0.38cm-1, 0.26cm-1, 0.25 cm-1 of band 1, 2, and 3, respectively. This instrument is
also able to measure the scene flux with P and S polarization, simultaneously, as TANSO-FTS SWIR measures. In 2007,
the first and second flight campaigns were arranged and the sunlight reflected spectra over the earth's surface was
obtained. This instrument was mounted on high-altitude airplane with image motion compensator and damping platform,
and flied over southern Australia and Siberia. The instrumental design and the results of performance tests as well as the
flight campaign are presented.
In order to characterize the pre-launch performance of
Thermal And Near infrared Sensor for carbon Observation
Fourier-Transform Spectrometer (TANSO-FTS) and Cloud and Aerosol Imager (TANSO-CAI) on the Green house
gases Observing SATellite (GOSAT) under the environmental condition on orbit as well as in the laboratory, the Proto
Flight Model (PFM) for TANSO-FTS and CAI have been developed. TANSO-FTS has three narrow bands of 0.76, 1.6
and 2.0 micron (Band 1, 2 and 3) with +/-2.5cm maximum optical path difference, and a wide band of 5.5 - 14.3 micron
(band 4) in thermal near infrared region. TANSO-CAI is a radiometer for detection and correction of clouds and aerosol
effects which might degrade the column concentration retrieval of CO2 and CH4. It has four spectral band regions;
ultraviolet (UV), visible, near IR and SWIR.
The basic character of TANSO-FTS and CAI, such as the Signal to Noise Ratio (SNR), the polarization sensitivity
(PS), Instantaneous Field Of View (IFOV), spectral response, and also Instrumental Line Shape Function (ILSF)
have been characterized by introducing the light emitted from the black body, halogen lamp and the tunable diode laser.
In addition to these characterizations, micro vibration effect on orbit has been investigated on TANSO-FTS. There prelaunch
test results demonstrated that TANSO will provide data for high accuracy CO2 and CH4 retrieval on orbit.
KEYWORDS: Calibration, Fourier transforms, Signal to noise ratio, Sensors, Polarization, Short wave infrared radiation, Black bodies, Clouds, Satellites, Pulmonary function tests
TANSO-FTS (Thermal And Near infrared Sensor for carbon Observation Fourier Transform Spectrometer) and
TANSO-CAI (Cloud and Aerosol Imager) are a space-born optical sensor system mainly oriented for observation of
greenhouse gases (GHGs). TANSO will be installed on the Greenhouse gases Observing SATellite "GOSAT" and
launched in early 2009. The TANSO-FTS is a Fourier transform spectrometer which has 3 SWIR bands (0.76, 1.6 and
2.0 μm) and 1 TIR band (5.5 - 14.3 μm) for observation of scattering light and thermal radiation from the earth, mainly
focused on CO2 absorption spectra. The TANSO-CAI is an imager for detection and correction of clouds and aerosol
effects to determine GHGs quantities. The instrument characteristics of TANSO-FTS are high SNR (~300), quick
interferogram scan (1.1 ~ 4.0 s) with moderate wave-number resolution (~0.2 cm-1), and polarization measurement. Now,
integration and test of proto-flight model of TANSO have been completed. In this paper, the results of performance test
such as SNR, ILS, polarization sensitivity, etc. are described.
Greenhouse gases Observing SATellite (GOSAT) is designed to monitor the carbon dioxide (CO2) and the methane
(CH4) globally from orbit and is scheduled to be launched in 2008. Two instruments are accommodated on GOSAT.
Thermal And Near infrared Sensor for carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) detects the
Short wave infrared (SWIR) reflected on the earth's surface as well as the thermal infrared (TIR) radiated from the
ground and the atmosphere. TANSO-FTS is capable of detecting wide spectral coverage, specifically, three narrow
bands (0.76, 1.6, and 2 micron) and a wide band (5.5-14.3 micron) with 0.2 cm-1 spectral resolution. As the second
sensor, TANSO Cloud and Aerosol Imager (TANSO-CAI) is a radiometer of ultraviolet (UV), visible, and SWIR to
correct cloud and aerosol interference.
Since the contaminant deposition onto these optical sensors significantly affects the sensing capability, the spectroscopic
contamination control over wide spectral range is exercised from the initial phase of GOSAT development to on-orbit
operation.
This paper presents overview of GOSAT contamination control plan and test results from contamination environment
monitoring during thermal vacuum test using satellite system Structure and Thermal Model "STM". The result from
on-going contamination environment monitoring of clean room at the spacecraft test and assembly building is also
presented in launch site.
KEYWORDS: Fourier transforms, Sensors, Signal to noise ratio, Atmospheric modeling, Stray light, Near infrared, Infrared sensors, Polarization, Black bodies, Satellites
In order to estimate and demonstrate the performance of Thermal And Near infrared Sensor for carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) and Cloud and Aerosol Imager (TANSO-CAI) under the environmental
condition on orbit, the Engineering Model (EM) for TANSO-FTS and CAI have been developed and demonstrated. The
TANSO-FTS has three narrow bands detectable regions; 0.76, 1.6 and 2micrion (Band1, 2 and 3) with +/⊥2.5cm
maximum optical path difference, and a wide band (5.5 − 14.3micron in thermal near infrared region. The TANSO-CAI
is a radiometer of ultraviolet (UV), visible, and SWIR, which has 4 spectral band regions with 1 dimensional array CCDs.
The initial performance tests have been carried out in the laboratory and the thermal vacuum chamber. The Signal to Noise Ratio (SNR), the polarization sensitivity (PS), Instantaneous Field Of View (IFOV) and response for FTS and CAI,
and also the Instrumental Line Shape Function (ILSF) for FTS have been characterized in this test by introducing the
light emitted from the black body, halogen lamp and the tunable diode laser. As a results of these experiments, it is
appeared that the some modification of system for manufacturing the proto flight model (PFM) is required, and now in
progressing.
In addition to these characterizations, the newly developed tests, such as the stray light measurement and micro
vibration test, are applied on TANSO-FTS to estimate the effect on orbit. These tests methods and results are presented in
this paper.
In order to validate and calibrate the GOSAT satellite data, and also to develop the retrieval algorism for deriving the
column density of CO2 and CH4 from spectra, the airborne SWIR (Short Wave Infrared Region) FTS (Fourier transform
spectrometer) has been developed and characterized. This instrument is called as TSUKUBA model. The initial
performance test of TSUKUBA model was carried out in our laboratory, and the measured modulation efficiencies are
70% (Band1), 85% (Band2) and 88% (Band3), respectively. The measured values of SNR with the equivalent black
body temperature for 30% surface albedo are 190 (13050cm-1), 148 (6200cm-1), and 165 (5000cm-1). The measured
values of full width at half maximum (FWHM) of instrumental line shape functions are 0.38cm-1, 0.26cm-1, 0.25 cm-1 for
band 1, 2, and 3, respectively. The instrumental design and the results of performance tests are presented.
The Greenhouse gases Observing SATellite (GOSAT) is a satellite to monitor the carbon dioxide (CO2) and the
methane (CH4) globally from orbit. GOSAT will be placed in a 666 km sun-synchronous orbit of 13:00 local time, with
an inclination angle of 98 deg. Two instruments are accommodated on GOSAT. Thermal And Near infrared Sensor for
carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) detects the Short wave infrared (SWIR) reflected
on the earth's surface as well as the thermal infrared (TIR) radiated from the ground and the atmosphere. TANSO-FTS
is capable of detecting wide spectral coverage, specifically, three narrow bands (0.76, 1.6, and 2 micron) and a wide
band (5.5-14.3 micron) with 0.2 cm-1 spectral resolution. TANSO Cloud and Aerosol Imager (TANSO-CAI)
is a radiometer of ultraviolet (UV), visible, and SWIR to correct cloud and aerosol interference. The paper
presents the instrument design of TANSO-FTS/CAI, and test results using Bread Board Model (BBM) are presented.
The Greenhouse Gases Observing SATellite (GOSAT) is a satellite to monitor the carbon dioxide (CO2) and the
methane (CH4) globally from orbit. Two instruments are accommodated on GOSAT. Thermal And Near infrared Sensor
for carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) detects the Short wave infrared (SWIR)
reflected on the earth's surface as well as the thermal infrared (TIR) radiated from the ground and the atmosphere.
TANSO-FTS is capable of detecting wide spectral coverage, specifically, three narrow bands (0.76, 1.6, and 2 micron)
and a wide band (5.5-14.3 micron) with 0.24 wavenumber spectral resolution. TANSO Cloud and Aerosol Imager
(TANSO-CAI) is a radiometer of ultraviolet (UV), visible, and SWIR to correct cloud and aerosol interference.
The contaminant deposition on the sensors significantly affects the sensing capability. So the spectroscopic
contamination control over wide spectral range is required from the process of GOSAT development to on-orbit
operation.
The paper presents the instrument design of TANSO-FTS and TANSO-CAI, overview of GOSAT contamination control
plan, results from spectral analysis of deposited outgas, test result of hydrazine (rocket and satellite thruster propellant)
injection to an optical surface, as well as test result from contamination environment monitoring using a vacuum
chamber and contamination witness plates.
Global warming has become a very serious issue for human beings. In 1997, the Kyoto Protocol was adopted at the Third Session of the Conference of the Parties to the United Nations Framework Convention on Climate Change (COP3), making it mandatory for developed nations to reduce carbon dioxide emissions by six (6) to eight (8) per cent of their total emissions in 1990, and to meet this goal sometime between 2008 and 2012.
The Greenhouse gases Observing SATellite (GOSAT) is designed to monitor the global distribution of carbon dioxide (CO2) from the space. GOSAT is a joint project of Japan Aerospace Exploration Agency (JAXA), the Ministry of Environment (MOE), and the National Institute for Environmental Studies (NIES). JAXA is responsible for the satellite and instrument development, MOE is involved in the instrument development, and NIES is responsible for the satellite data retrieval. The satellite is scheduled to be launched in 2008. In order to detect the CO2 variation of boundary layers, both the technique to measure the column density and the retrieval algorithm to remove cloud and aerosol contamination are investigated. Main mission sensor of the GOSAT is a Fourier Transform Spectrometer with high optical throughput, spectral resolution and wide spectral coverage, and a cloud-aerosol detecting imager attached to the satellite. The paper presents the mission sensor system of the GOSAT together with the results of performance demonstration with proto-type instrument aboard an aircraft.
Global warming has become a very serious issue for human beings. In 1997, the Kyoto Protocol was adopted at the Third Session of the Conference of the Parties to the United Nations Framework Convention on Climate Change (COP3), making it mandatory for developed nations to reduce carbon dioxide emissions by six (6) to eight (8) per cent of their total emissions in 1990, and to meet this goal sometime between 2008 and 2012.
The Greenhouse gases Observing SATellite (GOSAT) is design to monitor the global distribution of carbon dioxide (CO2) from orbit. GOSAT is a joint project of Japan Aerospace Exploration Agency (JAXA), the Ministry of Environment (MOE), and the National Institute for Environmental Studies (NIES). JAXA is responsible for the satellite and instrument development, MOE is involved in the instrument development, and NIES is responsible for the satellite data retrieval. The satellite is scheduled to be launched in 2008. In order to detect the CO2 variation of boundary layers, both the technique to measure the column density and the retrieval algorithm to remove cloud and aerosol contamination are investigated. Main mission sensor of the GOSAT is a Fourier Transform Spectrometer with high optical throughput, spectral resolution and wide spectral coverage, and a cloud-aerosol detecting imager attached to the satellite. The paper presents the mission sensor system of the GOSAT together with the results of performance demonstration with proto-type instrument aboard an aircraft.
Fourier transform spectrometer (FTS) has fast optics, and it can realize high resolution within the range from visible light to thermal infrared radiation. FTS intrinsically has the problem that it takes long time to obtain spectrum, because it needs mechanical scanning. But we developed spaceborne FTS system which has the ability of high speed scanning and data handling. By high speed scanning, FTS makes it possible to have high altitude resolution in occultation, and imaging in nadir observation.
EarthCARE (Earth Clouds, Aerosol and Radiation Explorer) project is a candidate of the ESA (European Space Agency) Earth Explorer Core Missions. There are many uncertainties mainly caused by aerosols, clouds and their interaction with radiation in predictions of climate change using numerical models. EarthCARE will provide vertical and horizontal distributions and physical characteristics of clouds and aerosols, and also provide the Earth radiation budget. EarthCARE is the joint proposal between ESA, National Space Development Agency of JAPAN (NASDA) and Communications Research Laboratory (CRL). The Phase-A study is going on. The EarthCARE satellite has five sensors, Cloud Profiling Radar (CPR), ATmospheric LIDar (ATLID), Multi-Spectral Imager (MSI), Broad Band Radiometer (BBR) and Fourier Transform Spectrometer (FTS). NASDA is studying FTS design. Main objective of EarthCARE FTS is to provide spectrally resolved outgoing radiance. This spectrum has many useful signatures from the surface/cloud/aerosol/water which can not get from spectrally integrated measurement. Another objective of EarthCARE FTS is a compact Michelson interferometer, which covers from 5.6 µm to 25 µm with 0.5 cm-1 spectral resolution. The FOV (Field Of View) is 10km so that the data can be used in conjunction with BBR.
IPCC third report says that we have still a lot of uncertainties to predict global warming even using latest GCMs. Regarding atmospheric radiation, uncertainty of the radiative forcing is still large, which is mainly caused by aerosols, clouds, and water vapor interacting among them. National Space Development Agency of JAPAN (NASDA) and Communications Research Laboratory (CRL) started Phase-A study with European Space Agency (ESA) in the EarthCARE project. The objectives of EarthCARE project are to observe vertical and horizontal distributions and physical characteristics of aerosols and clouds from a satellite, and also to measure the precise Earth radiation budget simultaneously. Finally we will be able to evaluate physical processes of clouds and aerosols regarding the radiative budget and forcing. The EarthCARE satellite carries 5 sensors, namely Cloud Profiling RADAR (CPR), Atmospheric LIDAR (ATLID), Multi-Spectral Imager (MSI), Broad Band Radiometer (BBR) and Fourier Transform Spectrometer (FTS). The result of the pre-Phase A study shows the synergy observation benefits using some compensative combinations of sensors, such as CPR/ATLID for clouds, ATLID/MSI for aerosols, BBR/FTS for the radiation budget. NASDA and CRL are studying FTS and CPR, respectively. CPR is a 94GHz RADAR using 2.5m diameter reflector with Doppler measurement mode. The sensitivity is -38dBZ. The vertical and horizontal resolution is 100 m, 1 km, respectively. FTS is a Michelson interferometer of which spectral measurement range is from 5.7 μm to 25 μm with 0.5 cm-1 unapodized spectral resolution. FOV is 10 km by 10 km. EarthCARE is planned to be launched in 2008 for 2 years mission. Phase-A study will continue until the end of 2003.
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 650km non-sun-synchronous orbit, with an inclination angle of 68 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 μm and 1 km vertical resolution. SOFIS will measure the global distribution of O3, 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 (O2, A band) grating spectrometer for pressure and temperature retrieval and a sun-edge sensor for the tangent height position detection. We present the test results of FTS and detector assembly engineering model and describe the SOFIS/FTS calibration system.
The Ozone and Pollution measuring Ultraviolet Spectrometer (OPUS) is scheduled to launch on board the GCOM A1 satellite, to measure ozone, sulfur dioxide (SO2), nitrogen dioxide (NO2) and other chemical species including aerosols. OPUS measures the backscattered ultraviolet radiance with the wavelength step of 0.5 nm in ultraviolet-near infrared regions. This wavelength step is coarse compared with that of GOME, but it was found that this difference do not substantially affect the uncertainty in SO2 estimation. Simulation study using the radiative transfer code of MODTRAN reveals that the wavelength range of 310 - 320 nm was found to be sensitive for SO2 detection in case of solar backscattered radiation measurements from space. We will present the estimation method of total column SO2 amount from the backscattered radiance observed with OPUS, using the fine structure of SO2 absorption spectrum.
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 satellite. We describe the performance test results of the laboratory model and present the instrument and engineering model test results.
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 1.5-1.9 micrometers , 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 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.
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.
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.
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.
The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar occultation Fourier transform spectrometer developed by the Environmental Agency of Japan, and onboard the Global Change Observation Mission-AI (GCOM- A1) satellite. GCOM-AI will be placed in a 650 km non-sun- synchronous orbit in 2006, with an inclination angle of 69 deg. SOFIS is the successor of the Improved Limb Atmospheric Spectrometer-II, which is onboard the Advanced Earth Observing Satellite-II (ADEOS-II). SOFIS measures the vertical profile of the atmospheric constituents with 0.2 cm-1 spectral resolution at 3 - 13 micrometers and 1 km vertical-resolutions. The target of SOFIS measurements is a global distribution of O3, HNO3, NO2, N2O, CH4, H2O, CO2, CFC-11, CFC-12, ClONO2, aerosol extinction, atmospheric pressure and temperature. SOFIS uses a double-pass flexible blade Fourier transform spectrometer (FTS) and a diode laser sampling system to reduce the size and weight of the apparatus. Two photovoltaic HgCdTe 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 conceptual design of the instrument and examines the test results of laboratory models of the FTS and the detector.
Atmospheric composition measurements from satellites are essential for monitoring the earth’s environment. The Ozone Dynamics UV Spectrometer (ODUS) will be launched on the Global Change Observation Mission (GCOM) -A1 satellite in 2006. ODUS covers from 306 to 420 nm back scattered light with 0.5 nm spectral and 20 km spatial resolution using a Fastie-Ebert type polychromator and a one-dimensional UV Si-CMOS array detector. It is a nadir-looking mapping spectrometer with a mechanical scanner, which can acquire global data in one day. It is expected to provide information about total O3, SO2, NO2, BrO, OCIO, HCHO, surface albedo, and aerosol type. Total 03 is inferred from look-up tables calculated with the radiative transfer on multiple solar back scattering. Other constituents are derived in such a way that the deviation of the measured and calculated radiance is minimized. We use the STAR (System for Transfer of Atmospheric Radiation) code for radiative transfer calculation. In recent years, tropospheric O3 measurement has become important for biomass burning and urban air pollution monitoring. The sensitivity of various O3 vertical profiles on the ODUS spectra is studied and tropospheric O3 retrieval algorithm will be presented.
The Ozone Dynamics Ultraviolet Spectrometer (ODUS) is a satellite-borne, nadir-looking ultraviolet spectrometer for measuring total ozone amount. It will be launched in 2006 onboard Japanese earth observation satellite GCOM-A1 (GCOM : Global Change Observation Mission). The ODUS instrument measures continuous spectrum from 306 to 420nm with 0.5nm spectral step and 20km spatial resolution, using an Ebert-type polychromator and an one-dimensional silicon CMOS array detector, which will improve the accuracy of the retrieved total ozone amount. This paper presents an overview of the ODUS instrument and performance.
A laboratory model of the space borne compact FTS was manufactured and tested. This type of compact FTS with medium spectral resolution (approximately 0.8 cm-1) and high spectral scan rate (approximately 10 Hz) is suitable for the observation of the vertical distribution of atmospheric constituents, especially for the observation of solar occultation. The rapid vertical velocity of tangent points requires a high spectral scan rate of the instrument. One of the candidates of platforms is the International Space Station (ISS). The results of a sensitivity study show that a moderate spectral resolution of approximately 1 cm-1 is sufficient for measuring vertical distributions of the trace gases with a measurement error less than 10%. The laboratory model is based on the Bomem/MR series with balanced rotary scan action and a frictionless flex blade at the center of rotation. For data sampling, a diode laser is utilized instead of a He-Ne gas laser. This technique provides the compactness and longevity in FTS needed for the satellite borne system. For this instrument, a vibrational environment test was conducted and it was proved to be well-balanced and to be a stable structure with a high resonance frequency. This paper also proposes a space borne interferometer.
The Ozone Dynamics Ultraviolet Spectrometer (ODUS) is a satellite-borne, nadir-looking ultraviolet spectrometer for measuring total ozone amount. It will be launched in 2005 onboard Japanese earth observation satellite GCOM-A1. The ODUS instrument measures continuous spectrum from 306 to 420 nm with 0.5 nm spectral resolution and 20 km spatial resolution, using an Ebert-type polychromator and a one-dimensional silicon CMOS array detector, which will improve the accuracy of the retrieved total ozone amount. We have completed the conceptual design of system, and manufactured and tested the laboratory model of the detector and the optical assembly. We have succeeded in developing a detector with sufficient sensitivity and a polychromator with little stray light. We have also confirmed the optical performance and evaluated the detailed wavelength structure of the instrument function. This paper presents an overview of the ODUS instrument, the summary of the evaluation results of the laboratory models.
ClONO2 is one of the most important species governing the chemistry of stratosphere, especially ozone depletion, particularly in the polar regions. A compact echelle grating spectrometer (f equals 200 mm) with 0.2 cm-1 spectral resolution around the 780.2 cm-1 chlorine nitrate (ClONO2) absorption band has been designed and tested. This is a part of the flight model of the Improved Limb Atmospheric Spectrometer-II (ILAS-II) mission onboard Advanced Earth Observing Satellite II (ADEOS-II). Using an off axis parabolic collimator and two cylindrical off axis parabolic collecting mirrors, this spectrometer is a compact space-borne instrument optimized for solar occultation measurements. The solar absorption spectra measured with the array detector on the ground are consistent with the designed spectral resolution and the resolution simulated with the Code V optical performance simulator. Radiometric and spectrometric pre-launch calibration results of the spectrometer are discussed. The instrument slit function measurement with a tunable diode laser and integrating sphere is also discussed.
A feasibility study for the solar occultation observation from space has been carried out. An ordinary Michelson type Fourier transform spectrometer with 1 cm-1 resolution and 10 Hz rapid sampling showed best feasibility by the trade offs among the sensitivity and resource consideration. For the low- cost and quick development, it is assumed to use design similar to a commercial laboratory model. By using 200 K TE cooled PC-MCT detector, it showed least resource requirement and the SNR greater than 150 over 800 to 3300 cm-1. By using 80 K MCT, it is possible to achieve the SNR greater than 500 can be achieved with more resources for weight and power.
Results of conceptual design study of a solar occultation infrared sensor, improved limb atmospheric spectrometer-II (ILAS-II) which will be onboard ADEOS-II spacecraft, is discussed. The ILAS-II will have four grating spectrometers for solar occultation measurement: two are identical to the spectrometers of the ILAS onboard ADEOS to be launched in 1996. To observe ClONO2, which is a key species that controls catalytic destruction of ozone, an echelle grating spectrometer with 0.14 cm-1 resolution for the 780.2 +/- 1 cm-1 region will be added to the ILAS-II. Another new spectrometer will cover the 3 to 5.7 micrometers region to characterize the aerosols such as sulfuric acid aerosols and PSCs as well as to observe the chemical species.
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