GCOM-C1 (Global Change Observation Mission- Climate 1) Mission/Shikisai
The GCOM-C1 program was approved by Japanese Space Activity Commission in December, 2009.
• The system design and EM design of GCOM-C1 including SGLI started in July 2009
• The SGLI PDR was over in March, 2010. The manufacturing of SGLI EM has been started.
• The CDR (Critical Design Review) of GCOM-C1 satellite system was held in Feb. 2013, and JAXA has started manufacturing the flight model components of GCOM-C1 satellite. 1)
In July 2017, the GCOM-C project received the nickname Shikisai (meaning colors in Japanese). The nickname was chosen by JAXA in a public contest. 2)
The GCOM-C1 spacecraft is 3-axis stabilized. Power of > 4.25 kW is provided at EOL (End of Life). The spacecraft on-orbit dimensions are (deployed configuration): 4.6 m (X) x 16.3 m (Y) x 2.8 m (Z).
The spacecraft has a mass of about 2093 kg at launch (dry bus mass of 1374 kg, propellant mass of 176 kg, SGLI mass of 400 kg). The satellite generates power of 4 kW. The design life is 5 years.
Figure 1: Illustration of the GCOM-C1 spacecraft (image credit: JAXA) 3)
Launch: A launch of GCOM-C1 is scheduled for 23 December 2017 on an H-IIA vehicle from the Yoshinobu Launch Complex at TNSC (Tanegashima Space Center), Japan. The launch provider is Mitsubishi Heavy Industries, Ltd. 4) 5)
H-IIA launch vehicle No. 37 incorporates JAXA's newly developed technology to insert GCOM-C1/Shikisai and SLATS/Tsubame into different orbital altitudes, respectively. It will expand opportunities of multiple satellite launch and take full advantage of the capability of H-IIA.
Orbit of GCOM-C1: Sun-synchronous orbit, altitude = 798 km, inclination of 98.6º, LTDN (Local Time on Descending Node) at 10:30 hours.
RF communications: The S-band is used for TT&C data transmission: TT&C data rates at 29.4 kbit/s (USB), 1 Mbit/s (QPSK,) and 1.6 kbit/s in SSA (S-band Single Access). Command data rates: 4 kbit/s (USB), 125 kbit/s (SSA). The payload data downlink in X-band (8105 MHz) with a data rate of 138.76 Mbit/s, modulation = OQPSK (Offset Quadrature Phase Shift Keying). Direct real-time downlink of payload data to receiving stations with agreement.
Real-time observation data over Japan are transmitted by X-band to JAXA's ground stations at Katsuura, or EOC (Earth Observation Center at Hatoyama, Saitama). The received data are distributed immediately after Level-1 data processing.
Global observation data observed by SGLI are transmitted in X-band to KSAT (Kongsberg Satellite Services) Station in Svalbard, Norway together with some HK data. KSAT is the commercial Norwegian company. GCOM-C1 transmits telemetry stored in the onboard recorder at relatively fast data rate of 1Mbit/s to KSAT/Svalbard by S-band/QPSK..
• SLATS/Tsubame, a minisatellite of JAXA with a launch mass of 400 kg.
- The launch vehicle will insert the SLATS/Tsubame minisatellite into a lower orbit of ~ 500 km.
Sensor complement: (SGLI, a single instrument is flown)
SGLI (Second-generation Global Imager):
SGLI is an advanced multi-purpose visible/infrared (VNIR, SWIR, TIR) imager of GLI heritage, flown on ADEOS-II. The objective is to measure ocean color, SST (Sea Surface Temperature), land use and vegetation, snow and ice, clouds, aerosols and water vapor, etc. 6) 7)
• The prime goal of SGLI is to retrieve global aerosol distributions. To achieve this target, SGLI will have 2 polarization channels with 3 directions
• SGLI is mainly focused to land and coastal areas. There are 11 channels with an IFOV of 250 m. GLI on ADEOS-II had only 6 channels of 250 m resolution.
The SGLI assembly features two separate sensors (radiometers) labeled VNIR (Visible Near Infrared) and IRS (Infrared Scanner). Note, the VNIR device is also referred to as VNR in the text.
• VNIR is a pushbroom instrument providing 14 channels in the VNIR spectral region (actually also in the UV), 11 channels are termed VNIR-NP (VNIR Non-Polarized), and 2 channels are called VNIR-P (VNIR-Polarized). The VNIR-P channels of the polarimeter provide 3 polarization angles at: 0º, 60º, and 120º.
The VNIR-NP channels are divided into three 24º pushbroom type telescopes configured in the cross-track direction to realize the wide FOV (70º) requirement with wide spectral range (380 nm to 865 nm). Each telescope has refractive telecentric optics and 11 channels CCD on which the '11 channel bandpass filter assembly' is mounted. 8)
To realize the VNIR-P polarization observation, three linear polarization channels (0º, 60º and 120º) are set for two pushbroom telescopes which are dedicated for 670 nm and 865 nm observation. A tilting operation around the Y-axis of ±45º is required for VNIR-P to observe aerosols (scattering angle requirement). The scattering angle observation is calculated using the satellite orbital position, sun and observation target direction. A scattering angle direction between 60º and 120º is required for the aerosol retrieval over the land surface.
• IRS is a whiskbroom type scanning radiometer (mechanical method) covering the SWIR (Shortwave Infrared) and TIR (Thermal Infrared) spectral regions.
SGLI has a capability of simultaneous nadir and slant observations. In addition, the sensor has a capability of along-track multiangle observation. A chance of multi-angle observations on forest areas with less cloud influence will increase comparisons with cross- track observations. In the GCOM –C1 project, global AGB (Above Ground Biomass) data will be provided as a standard product that is estimated by taking advantage of the multiangle observation capability.
Figure 2: Schematic view of the SGLI instruments (image credit: JAXA)
The key VNIR observation channels such as 670 nm and 865 nm are being observed with both low and high dynamic range independently according to the requirements (Table 2). The total spectral channels for SGLI are optimized to 19 channels including tilting polarization observation (there were 36 channels for GLI instrument). On the other hand, the SGLI standard products are increased from 22 products of GLI to 29 products.
The basic IFOV (Instantaneous Field of View) is set to 250 m - compared to GLI's 1 km requirement. Using this higher resolution with a wide FOV (1150 km for VNR and 1400 km for IRS), it is expected that the human activity influence on Earth's environment can be studied.
Table 1: Key parameters of the SGLI instrument
Table 2: Radiometric specification of the VNIR channels of SGLI
Table 3: Specification of the IRS (SWIR and TIR) channels of SGLI
The optical SGLI instrument is being designed and developed at NEC Toshiba Space, Tokyo, Japan. In turn, NEC Toshiba Space selected Sofradir of France to provide the infrared detectors for SGLI. As of 2008, Sofradir is providing concept studies for the cooled infrared MCT (HgCdTe)focal plane array detectors of the SGLI instrument. The two TIR arrays are centered on 10.8 and 12 µm wavelengths respectively, which are hybridized on a single readout circuit for accurate registration. 9) 10) 11)
Figure 3: Illustration of the SGLI VNIR instrument (image credit: NEC Toshiba, JAXA)
The IRS whiskbroom scanner features six channels in the region of 1.05 µm to 12 µm (Table 3). The 45º tilted scan mirror is rotated around the X-axis continuously to realize a scan of 80º for Earth observation; in addition, the onboard calibrator (blackbody, solar diffuser, and inner light source) and deep space are being scanned on each scanner revolution. Compared with the double-sided mirror employed on GLI and MODIS, the constant incident angle to the IRS scan mirror represents an advantage for the calibration function.
Figure 4: Illustration of the SGLI IRS instrument (image credit: NEC Toshiba, JAXA)
The observation light is directly focused onto the focal plane using a Ritchey-Chretien type telescope without any relay optics. The infrared spectral range is divided by the dichroic filter for the SWIR and TIR regions in order to optimize the detection process.
The four SWIR channels employ an InGaAs photodiode detector array cooled to -30ºC using a Peltier thermo electronic cooler. The two TIR channels use a photovoltaic type HgCdTe (PV-MCT) detector array cooled to 55 K by a Stirling-cycle cooler. The bandpass filters corresponding to the spectral channels are mounted on the focal plane in the detector packages.
The solar diffuser (made of Spectralon), the inner light source using LEDs (Light Emitting Diodes) for the SWIR channels and a high-emissivity blackbody for the TIR channels, are used as the onboard calibrator. These calibration sources and a deep space window, arranged around the scan mirror, make it possible to obtain calibration data on every scan.
Table 4: The SGLI level 2 products 12)
Figure 5: Photo of the SGLI instrument (image credit: JAXA)
1) Keizo Nakagawa, Masaaki Mokuno, Kazuhiro Tanaka, Tsuyoshi Maeda, "Development Status of GCOM-C1 Satellite System," Proceedings of the 29th ISTS (International Symposium on Space Technology and Science), Nagoya-Aichi, Japan, June 2-8, 2013, paper: 2012-n-05
3) Keiji Imaoka + many contributors, "JAXA Earth Observation Missions," Mini-Workshop on A-Train Science, Tokyo, Japan, March 8, 2013, URL: http://suzaku.eorc.jaxa.jp/GCOM_W/materials/atrainws_mar2013/3_Imaoka.pdf
4) "Launch of Global Changing Observation Mission - Climate "SHIKISAI" (GCOM-C) and Super Low Altitude Test Satellite "TSUBAME" (SLATS) aboard H-IIA Vehicle No. 37," JAXA Press Release, 27 October, 2017, URL: http://global.jaxa.jp/press/2017/10/20171027_h2af37.html
5) "Shikisai/Tsubame/H-IIA F37 Countdown," JAXA, URL: http://global.jaxa.jp/projects/sat/gcom_c/index.html
6) Yoshiaki Honda, "Overview of GCOM-C1/SGLI Science," Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium) 2010, Honolulu, HI, USA, July 25-30, 2010
7) Hiroshi Murakami, Masahiro Hori, Takashi Nakajima, Mitsuhiro Toratani, Teruo Aoki, Makoto Kuji, Yoshiaki Honda, "Preparation of GCOM-C1 Science Mission," Proceedings of IGARSS (IEEE Geoscience and Remote Sensing Society) 2014, Québec, Canada, July 13-18, 2014
8) Atsuo Kurokawa, Yasuhiro Nakajima, Shinji Kimura, Hiroshi Atake, Yoshihiko Okamura, Kazuhiro Tanaka, Shunji Tsuida, Kenichi Ichida, Takahiro Amano, "High-precision narrow-band optical filters for global observation," Proceedings of the ICSOS (International Conference on Space Optical Systems and Application) 2012, Ajaccio, Corsica, France, October 9-12, 2012, URL: http://icsos2012.nict.go.jp/pdf/1569607351.pdf
9) P. Chorier, A. Dariel, L. Vial, A. Poupinet, M. Vuiliermet, P. Tribolet, "Sofradir advances in Infrared detectors for Space Applications," Proceedings of the 26th ISTS (International Symposium on Space Technology and Science) , Hamamatsu City, Japan, June 1-8, 2008
10) Yoshihiko Okamura, Kazuhiro Tanaka, Takahiro Amano, Masaru Hiramatsu, Koichi Shiratama, "Design and bread-boarding activities of the Second-generation Global Imager (SGLI) on GCOM-C," Proceedings of the 7th ICSO (International Conference on Space Optics) 2008, Toulouse, France, Oct. 14-17, 2008
11) Yoshihiko Okamura, Kazuhiro Tanaka, Takahiro Amano, Masaru Hiramatsu, Koichi Shiratama, "Breadboarding activities of the Second-generation Global Imager (SGLI) on GCOM-C," Proceedings of SPIE, 'Sensors, Systems, and Next-Generation Satellites XII,' edited by Roland Meynart, Steven P. Neeck, Haruhisa Shimoda, Shahid Habib, Vol. 7106, 71060Q-1, Cardiff, UK, Sept. 15, 2008
12) Keizo Nakagawa, "Global Change Observation Mission (GCOM)," Proceedings of ISPRS (International Society for Photogrammetry and Remote Sensing) Technical Commission VIII Symposium, Kyoto, Japan, Aug. 9-12, 2010, URL: http://www.isprs.org/proceedings/XXXVIII/part8/headline/JAXA_Special_Session%20-%201/JTS12_20100306153736.pdf
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (email@example.com).