TANSO-CAI-2 onboard GOSAT-2 satellite is a multi-spectral imager for the observation of cloud and aerosol. The CAI- 2 has 10 observation bands with 7 different wavelengths, which cover 340-1630 nm. The wavelength width of each band is less than 13 nm in the UV to NIR band and less than 73 nm in the SWIR band. From Feb. 2019, the evaluation of the initial calibration phase was carried out to calibrate the geometric and radiometric characteristics. Following the initial calibration phase, the evaluation of radiometric performance has been continuously conducted. The evaluation of dark level and dark noise has shown almost stable results, although there is some variation. The radiometric response evaluation using the lunar calibration data and the ROLO model showed a degradation in the UV Bands, especially in Band 1 (340 nm), which showed a degradation of about 8% in the two years relative to Band 4 (865 nm). No obvious response degradation was observed for the other bands. Those results suggest that the radiometric performance of the CAI-2 is almost maintained for two years since the initial calibration phase.
On 29th of October, 2018, GOSAT-2 was launched as the successor to GOSAT which is the first satellite dedicated to the greenhouse gases observation..
After the about 16 hours critical phase, GOSAT-2 moved to the commissioning phase and the functional and performant checkout of the bus system in November was followed by the one of the mission instruments in December.
The first light of the TANSO-CAI-2 was taken in the beginning of November along with the bus system checkout and the checkout of the TANSO-CAI-2 stared in the beginning of December.
The checkout of the TANSO-FTS-2 started in the middle of December. The first light of the FTS-2 was taken in the middle of December as part of the checkout of itself because the about three weeks of outgas to avoid the contamination had been needed. Though a few anomalies had been found in the checkout, it confirmed that FTS-2 and CAI-2 had worked well and all performances and functions met the requirements and the differences from the design were little except the temperature of the band 4 and 5 of FTS-2.
All data acquisition was completed at end of December except the system total operation test which is the test using all relevant systems including the ground system and this test was performed in the beginning of January of 2019.
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.
In January of 2009, GOSAT which is the first satellite dedicated to observing greenhouse gases, that is Carbon Dioxide and Methane was launched. GOSAT stands for Greenhouse Gases Observing Satellite.
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.
The Greenhouse gases Observing SATellite (GOSAT) monitors carbon dioxide (CO2) and methane (CH4) globally from space. The Thermal and Near infrared Sensor for Carbon Observation Fourier-Transform Spectrometer (TANSO-FTS) installed on GOSAT measures spectra absorbed by atmospheric minor components including greenhouse gases in infrared wavelength regions. This paper describes the characterization and validation of the CO2 and CH4 profiles retrieved from the thermal infrared (TIR) spectra observed by GOSAT. The retrieved CO2 and CH4 profiles were compared with the corresponding aircraft data provided by the National Oceanic and Atmospheric Administration (NOAA)/Earth System Research Laboratory (ESRL)/Global Monitoring Division (GMD)/Carbon Cycle Greenhouse Gases(CCGG) group. This group has conducted an aircraft program since 1992 to collect air samples mainly in North America. Each insitu aircraft profile was compared with those retrieved from TIR spectra without considering the effect of its averaging kernel. The root mean square (RMS) and bias errors of the retrieved CO2 and CH4 profiles were evaluated seasonally and with respect to atmospheric pressure. This comparison with aircraft data provides significant information for further improvement of the TIR retrieval algorithm.
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.
The thermal infrared band of the main sensor of the greenhouse gas observing satellite (GOSAT), the TANSO-FTS,
must be calibrated with accuracy higher than 0.3 K in the brightness temperature Tbb for retrieving CO2 concentration
with accuracy of 1% in the upper atmosphere. However, that accuracy has not been achieved because of some error
sources. One is the systematic bias in the radiance spectrum resulting from effects of radiation emitted from internal
optics and multiple scattering of target signals. Another is the polarization effect of the pointing mirror. Both effects can
be merged into two parameters, gain and offset, in the two point calibration procedure. They can be tuned by comparing
the spectrum with well-calibrated spectra such as those from the AIRS sensor. Based on the corrected radiance spectra,
global CO2 concentrations were processed. However, they show peculiar latitudinal distribution implying the existence
of temporally variant parameters that can affect the calibration. This bias can be reduced by referring to housekeeping
data of the satellite in the calibration procedure. The stratospheric ozone distribution is also analyzed. The sensor
demonstrated the difference in the ozone hole feature between spring 2009 and 2010 over the South Pole.
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.
Greenhouse gases Observing SATellite (GOSAT) is a Japanese mission to observe greenhouse gases, such as CO2 and
CH4, from space with a Fourier transform spectrometer and a push broom imager. The GOSAT was launched on January
23, 2009. The GOSAT is operated normally and acquired the observation data over 1.5 year from April 2009 of initial
calibration and validation phase. The Level 1 products were released to public from October 2009, the Level 2 from
February 2010. The Level 1 products are updated and evaluated the calibration accuracies in the operational observation
phase.
Greenhouse gases Observing SATellite (GOSAT) is a Japanese mission to observe greenhouse gases, such as CO2 and
CH4, from space with a Fourier transform spectrometer and a push broom imager. The GOSAT was launched on January
23, 2009. The initial functional check-out phase was completed on April 10 to confirm the on-orbit performance. The
initial calibration and validation phase was completed on July 30 in the following 3 months to acquire observation data at
calibration and validation sites. The initial calibration was evaluated on accuracies of radiometry, geometry and
spectrometry by using acquired data. The results were reflected to the improvement of the Level 1 algorithm and the
products. The initial calibrated Level 1 products have been already released to the GOSAT research PIs in August.
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.
Greenhouse gases Observing SATellite (GOSAT) is a Japanese mission to observe greenhouse gases, such as CO2 and
CH4, from space. The GOSAT carries a Fourier transform spectrometer and a push broom imager. The development of
GOSAT satellite and sensors has almost finished after the characterization of sensor performance in laboratory. In orbit,
the observation data will be evaluated by onboard calibration data and implemented by ground processing system. Level
1 algorithm and processing system are developed by JAXA. The post-launch calibration items are planned and the
methods are developed before launching. We show the Level 1 processing and in-orbit calibration of GOSAT sensors.
KEYWORDS: Calibration, Sensors, Fourier transforms, Reflectivity, Short wave infrared radiation, Black bodies, MODIS, Signal to noise ratio, Lamps, Gases
Greenhouse gases Observing SATellite (GOSAT) is a Japanese mission to observe greenhouse gases, such as CO2 and
CH4, from space. The GOSAT carries a Fourier transform spectrometer and a push broom imager. The GOSAT
development is going on in phase-C/D and characterized the sensor performance in laboratory. In orbit, the observation
data will be evaluated by onboard calibration data and implemented by ground processing system. The post-launch
calibration items are planned and the methods will be developed before the launch. The methods are investigated by
analyzing the current MODIS data, which has similar wavelength bands to GOSAT. In this paper, we show the
calibration plans of pre-flight test, onboard calibration, and post-launch vicarious calibration of GOSAT sensors.
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.
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