Takahiro Kawashima

The pre-launch performance test and calibration results of Thermal And Near-infrared Sensor for carbon Observation (TANSO) on GOSAT

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.

Onboard spectral calibration for the Japanese hyper-spectral sensor

The Japanese hyper-spectral sensor provides data products covering continuous spectral bands in the wavelength range from 400 nm to 2500 nm. It is characterized by a SNR of > 450 in the VNIR and>300 in the SWIR range at a ground resolution of 30 m x30 m. This report is concerned with the onboard wavelength calibration methods for the Japanese hyper-spectral sensor. As a result of trade study, the combination of a transmission type glass filter containing rare earth oxides, a Mylar polyester film and a quartz tungsten-halogen-lamp was selected. This method covers the wavelength range from 400 nm to 2450 nm. For the purpose of wavelength shift estimation, the method employing the mean square deviation as merit-function was found to be stable and precise. The accuracy of the absorption peak wavelength determination will be expected less than 2% (=0.2 nm) for the VNIR spectral resolution and 5% (=0.625 nm) for the SWIR spectral resolution.

Prelaunch performance test results of TANSO-FTS and CAI on GOSAT

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.

The performance test results for engineering model (EM) of thermal and near infrared sensor for carbon observation (TANSO) on GOSAT

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.

Development of onboard fast lossless compressors for multi and hyperspectral sensors

Fast and small-footprint lossless compressors for multi and hyper-spectral sensors have been developed. The compressors are employed for HISUI (Hyper-spectral Imager SUIte: the next Japanese earth observation project that will be on board ALOS-3). By using spectral correlations, the compressor achieved the throughput of 30Mpel/sec for hyper-spectral images and 34Mpel/sec for multi-spectral images, which covers the data acquisition throughput of HISUI, on a radiation tolerant FPGA (field-programmable-gated-array). We also implemented the compressor on the evaluation model device of HISUI, and confirmed its feasibility and compression performance of actual hyper-spectral sensor data.

Sensitivity studies on sulfur dioxide measurements with satellite-borne solar backscattered ultraviolet spectrometer

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.

Effect of temperature on onboard calibration reference material for spectral response function retrieval of the hyperspectral sensor of HISUI-SWIR spectral case

HISUI (Hyperspectral Imager SUIte) is the next Japanese earth observation sensor, which consists of hyperspectral and multispectral sensors. The hyperspectral sensor is an imaging spectrometer with the VNIR (400-970nm) and the SWIR (900-2500nm) spectral channels. Spatial resolution is 30 m with swath width of 30km. The spectral resolution will be better than 10nm in the VNIR and 12.5nm in the SWIR. The multispectral sensor has four VNIR spectral bands with spatial resolution of 5m and swath width of 90km. HISUI will be installed in ALOS-3 that is an earth observing satellite by JAXA. It will be launched in FY 2015. This paper is concerned with the effect of temperature on onboard calibration reference material (NIST SRM2065) for spectral response functions (SRFs) retrieval of the hyperspectral sensor. Since the location and intensity of absorption features are sensitive to material temperature, the estimated center wavelength and bandwidth of the SRFs may include the uncertainty. Therefore, it is necessary to estimate the deviation of the wavelength and the bandwidth broadening of the SRFs when the material temperature changes. In this paper we describe the evaluation of uncertainty of the SRF’s parameters retrieval and show some simulation’s results.

GOSAT/TANSO: Instrument Design and Level 1 Product Processing Algorithms

TANSO-FTS is a space-born Fourier transform spectrometer onboard GOSAT and has acquired mainly CO2 and CH4 absorption spectra globally since 2009. The instrument design of TANSO-FTS and the level 1 product processing algorithms are described.

SOFIS FTS EM test results

The Solar Occultation FTS for Inclined-orbit Satellite (SOFIS) is a solar occultation Fourier transform spectrometer developed by the Ministry of the Environment (MOE) in Japan for the Global Change Observation Mission-A1 (GCOM-A1) satellite. GCOM-A1 will be placed in a 650 km non-sun-synchronous orbit, with an inclination angle of 69 degrees. ABB-Bomem is a sub-contractor of NTSpace (NEC-Toshiba Space) for the design and manufacturing of the FTS Engineering Model of SOFIS. SOFIS measures the vertical profile of the atmospheric constituents with 0.2 cm-1 spectral resolution for the spectral range covering 3-13 μm. The atmospheric vertical resolution of SOFIS is 1 km. 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. NTSpace in Japan is the prime contractor of SOFIS. The spectrometer is an adapted version of the classical Michelson interferometer using an optimized optical layout and moving retro-reflectors. A solid-state laser diode operating at 1550 nm is used as metrology source of the interferometer. Its highly folded optical design results in a high performance instrument with a compact size. SOFIS FTS implements high performance control techniques to achieve outstanding speed stability of the moving mechanism. This paper describes the test activities of the SOFIS-FTS Engineering Model (EM) and preliminary results. The performances of the FTS are presented in terms of key parameters like signal-to-noise ratio, modulation efficiency and stability. Spectra acquired are shown and test methodology and analyses are presented. Lessons learned during assembly, integration and testing are described as well as improvements planned to be implemented in the Flight Model.

Quick-scanning FTS development and application

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.