STATUS OF THE FIRST SATELLITE OF THE GLOBAL CHANGE OBSERVATION MISSION - WATER (GCOM-W1) Misako Kachi 1, Keiji Imaoka 1, Masahiro Hori 1, Kazuhiro Naoki 1, Takashi Maeda 1, Arata Okuyama 1, Marehiro Kasahara 2, Norimasa Ito 2, Keizo Nakagawa 2 Haruhisa Shimoda 1,3, and Taikan Oki 1,4 1 Earth Observation Research Center (EORC), Japan Aerospace Exploration Agency (JAXA), 2-1-1 Sengen, Tsukuba, Japan 2 GCOM Project Team, Japan Aerospace Exploration Agency (JAXA), 2-1-1 Sengen, Tsukuba, Japan 3 Tokai University, Tokyo, Japan 4 The University of Tokyo, Tokyo, Japan Abstract The first generation satellite of the Global Change Observation Mission Water SHIZUKU (GCOM- W1) was launched from JAXA Tanegashima Space Center on May 18, 2012. It joined A-train orbit on June 29. The GCOM-W1 satellite carries the Advanced Microwave Scanning Radiometer 2 (AMSR2), which is a successor instrument of AMSR-E on NASA s Aqua satellite. AMSR2 has started scientific observation at 40 rpm since July 3, 2012. Initial checkout of the satellite and the instrument has completed on August 10 without major problem. Preliminary results of L2 geophysical parameters seems good condition, but validation activities have been conducted from now. During the initial calibration and validation period, JAXA will conduct the activities with PIs and collaborating agencies. AMSR2 standard products will be distributed to public for research and educational purposes though web site (https://gcom-w1.jaxa.jp/) after calibration/validation phase. Current data distribution schedule is to distribute Level 1 products (brightness temperature) to public in January 2013, and Level 2 (geophysical parameters) in May 2013. INTRODUCTION: The Global Change Observation Mission (GCOM) is planned as the comprehensive observation system of the Earth System s essential variables of atmosphere, ocean, land, cryosphere, and ecosystem (Imaoka et al., 2010). Most of these observations are expected to provide data commonly useful to the climate research and the meteorology. Additionally, the mission is designed to find out the traces of human-induced environmental changes, such as deforestations, forest fires, air and water quality changes to distinguish the human-induced changes and the natural cyclic changes. GCOM consists of two medium size of satellites; GCOM-W (water) will carry the Advanced Microwave Scanning Radiometer 2 (AMSR2); and GCOM-C (climate) will carry the Second Generation Global Imager (SGLI). Three consecutive generations of GCOM satellites with one year overlap in orbit enables over 13 years observation in total. Major characteristics of the first generation of those two satellites are described in Table 1. AMSR2 instrument on board the first generation satellite of GCOM-W (GCOM-W1 or SHIZUKU ) satellite is multi-frequency, total-power microwave radiometer system with dual polarization channels for all frequency bands. The instrument is a successor of JAXA s Advanced Microwave Scanning Radiometer for EOS (AMSR-E) on the NASA's Aqua satellite, which was launched in May 2002, and continues AMSR-E observations.
GCOM-W1 GCOM-C1 Instrument Advanced Microwave Scanning Radiometer-2 Second-generation Global Imager Sun Synchronous orbit Sun Synchronous orbit Orbit Altitude:699.6km (on Equator) Altitude:798km (on Equator) Inclination: 98.2 degrees Inclination: 98.6 deg. Local sun time: 13:30+/-15 min Local sun time: 10:30+/- 15min Satellite scale 5.1m (X) * 17.5m (Y) * 3.4m (Z) (on-orbit) 4.6m (X) * 16.3m (Y) * 2.8m (Z) (on-orbit) Satellite mass 1991kg 2093kg Launch JFY 2011 by H-IIA Rocket JFY 2014 by H-IIA Rocket Mission life 5-years 5-years Table 1: Major characteristics of GCOM-W1 and GCOM-C1 satellites. OVEVIEW OF THE GCOM-1 SATELLITE: Status of the mission; The GCOM-W1 satellite was launched from JAXA Tanegashima Space Center on May 18, 2012 (JST). The early orbit checkout of GCOM-W1 satellite and AMSR2 instrument was performed for about three months after the launch. Since it took 45 days to insert the satellite into A-Train orbit, the checkout tasks were carried forward between intervals of orbit control events (Kasahara et al., 2012). The GCOM-W1 satellite has joined A-train orbit since June 29. After GCOM-W1 was inserted into the planned position on the A-Train orbit, AMSR2 was spun up to 40 rpm, and then set to science mode to start observation on July 3. Initial checkout of the satellite and the instrument has completed on August 10 without major problem. The GCOM-W1 satellite was installed in front of the Aqua satellite to keep continuity of AMSR-E observations and provide synergy with the other A-Train instruments for new Earth science researches. AMSR2 instrument: Targets of the GCOM-W1 satellite are water-energy cycle, and will carry the AMSR2. AMSR2 will continue AMSR-E observations of water vapor, cloud liquid water, precipitation, SST, sea surface wind speed, sea ice concentration, snow depth, and soil moisture (Table 2). Basic concept of AMSR2 is almost identical to that of AMSR-E: conical scanning system with large-size offset parabolic antenna, feed horn cluster to realize multi-frequency observation, external calibration with two temperature standards, and total-power radiometer systems. Basic characteristics of the AMSR2 instrument are indicated in Table 3. Figure 1 shows Level 1 products (brightness temperature) of each observation channel which are basis for geophysical parameters. G E O Products Areas Resolution Accuracy Release Standard Goal Range ±1.0K Brightness Global 5-50km ±1.5K ±1.5K (systematic) temperature ±0.3K (random) 2.7-340K Integrated Global, over water vapor ocean 15km ±3.5kg/m 2 ±3.5kg/m 2 ±2.0kg/m 2 0-70kg/m 2 Integrated cloud Global, over liquid water ocean 15km ±0.10kg/m 2 ±0.05kg/m 2 ±0.02kg/m 2 0-1.0kg/m 2 Precipitation Global, Ocean ±50% Ocean ±50% Ocean ±20% except cold 15km Land ±120% Land ±120% Land ±80% latitude 0-20mm/h Sea surface Global, over temperature ocean 50km ±0.5 C ±0.5 C ±0.2 C -2-35 C Sea surface Global, over wind speed ocean 15km ±1.5m/s ±1.0m/s ±1.0m/s 0-30m/s Sea ice Polar region, 15km ±10% ±10% ±5% 0-100% concentration over ocean Snow depth Land 30km ±20cm ±20cm ±10cm 0-100cm Soil moisture Land 50km ±10% ±10% ±5% 0-40% Table 2: List of AMSR2 standard products and its target accuracies.
Center Freq. [GHz] Band Width [MHz] NEΔT[K] Polarization Beam Width [deg.] (Ground resolution [km]) Sampling interval [km] 6.925 / 7.3 350 < 0.34/0.43 1.8 (35 x 62) 10.65 100 < 0.70 1.2 (24 x 42) 18.7 200 < 0.70 0.65 (14 x 22) 10 V and H 23.8 400 < 0.60 0.75 (15 x 26) 36.5 1000 < 0.70 0.35 (7 x 12) 89.0 A/B 3000 < 1.20/1.40 0.15 (3 x 5) 5 Table 3: Frequency channels and resolutions of AMSR2 instrument 6V 6H 7V 7H 10V 10H 18V 18H 22V 22H 37V 37H 89AV 89AH 89BV 89BH Figure 1: AMSR2 brightness temperature of all channels from 6.9 to 89 GHz for one orbit. 5 Following improvements of AMSR2 instrument were conducted based on experience in the AMSR-E mission; a) Deployable main reflector system with 2.0m diameter; b) Frequency channel set is identical to that of AMSR-E except additional 7.3GHz channel for radio frequency interference (RFI) mitigation; and c) Two-point external calibration with the improved a Hot-temperature noise Source (HTS). In addition, deep-space maneuver will be considered to check the consistency between main reflector and Cold Sky Mirror (CSM). Figure 2 is comparison of brightness temperature (without map-projection) between AMSR2 and AMSR-E. Increase of antenna size from 1.6 m (AMSR-E) to 2.0 m (AMSR2) resulted in around 18% improvement in spatial resolution at 6.9 GHz channels in AMSR2 compared to AMSR-E. Figure 3 shows status of RFI in AMSR2. RFI signals at 7.3 GHz channels are more evident and outspread than those at 6.9 GHz channels. Over land, they are evident over Southeast Asia, Eastern Europe, Russia, and so forth. Also, frequency of occurrences of RFI are higher over ocean too. There are still many regions with small difference of brightness temperature between 6.9 and 7.3 GHz channels. Simple RFI identification will be tested by using this difference. In addition to above improvements, observation width of AMSR2 is increased compared to AMSR-E. Figure 4 shows increase of observation swath width of AMSR2. AMSR2 Level 1 (brightness temperature) products retain all scan points from Level 1A (observation counts) product, resulting in the increase of swath width. Nominal swath width (instrument assured) is still 1457.8 km same as that of AMSR-E, but effective swath width is wider than 1600 km after scan-bias correction.
Figure 2: Improvement in spatial resolution. Left: AMSR-E brightness temperature of 6.9 GHz Horizontal polarization channel over Australia (without map-projection). Right: Same as left figure but for AMSR2. Figure 3: Status of radio frequency interference (RFI) in C-bands. Upper left: AMSR2 brightness temperature of 6.9 GHz vertical polarization channel from 11 to 26 July, 2012. Upper right: Same as upper left but for 7.3 GHz. Lowe left: Difference of brightness temperature between 6.9 GHz and 7.3 GHz vertical polarization channels.
Figure 4: Increase of swath width. Left: AMSR-E brightness temperature of 36.5 GHz Vertical polarization channel in swath width of 1457.8 km over northern South America for ascending orbits of 24 September 2011. Right: Same as left but for AMSR2 in swath width of 1617.6 km for ascending orbits of 24 July 2012. EARLY RESULTS FROM AMSR2: Figure 5 shows the first image of AMSR2 observed on July 3, 2012. The figure is one-day color composite image of gobal Earth using brightness temperatures at the dual polarization channels at 89.0 GHz and the vertical polarization channel at 23.8 GHz. Colors of yellowish-white indicate the area where the scattering signature at 89 GHz channels excels because of the strong precipitation or ice sheets. Dark and light coloring of blue reflects the information of the 23.8 GHz water vapor channels and indicates the changes of water vapor and clouds. The status of arctic sea ice extent can be captured by AMSR2. The arctic sea ice extent recorded 4.21 million km 2 on August 24, 2012, and updated the lowest record by the satellite observation in September 2007. It continued decreasing of extent until September 16, and recorded the lowest value of 34.9 million km 2. Figure 6 is sea ice concentration of the Arctic Ocean for September 16, 2012 observed by AMSR2, and average distribution of that in 1980s. Figure 7 is AMSR2 rainfall product when it observed Typhoon No.11 in 2012. AMSR2 rainfall will be added to processing of JAXA Global Rainfall Watch (Kachi et al., 2011), which is a near-real-time version of the Global Satellite Mapping of Precipitation (GSMaP) product (Kubota et al., 2007), after validation. AMSR2 rainfall algorithm will be base algorithm of GSMaP for the Global Precipitation Measurement (GPM) mission, which led by Japan and U.S., in coordination with international partner agencies. The GCOM-W1 satellite will play an important role within the GPM mission. Figure 5: Color composite image of AMSR2 brightness temperatures during July 3-4, 2012.
Figure 8 shows examples of three-day average of AMSR2 sea surface temperature (SST) and total precipitable water. Microwave sea surface temperature (SST) is being recognized as a powerful tool for frequent mapping of global ocean, in combination with infrared observations, since microwave instruments can observe SST under the clouds where infrared instruments cannot. Figure 6: AMSR2 sea ice concentration on September 16, 2012 (left) and average sea ice concentration in September of 1980s (right). Sea ice concentration product is under validation. Algorithm was developed by Dr. J. Comiso, NASA. Figure 7: AMSR2 rainfall of Typhoon No.11 "HAIKUI" at around 2:30 A.M. on August 7, 2012 (JST). Rainfall product is under validation. Algorithm was developed by Dr. K. Aonashi, Meteorological Research Institute, Japan. Figure 8: Three-day average of AMSR2 sea surface temperature (left) and total precipitable water (right) during September 26-28, 2012. Sea surface temperature and total precipitable water products are under validation. SST algorithm was developed by Dr. A. Shibata, Meteorological Research Institute, Japan, and total precipitable water by Mr. M. Kazumori, Japan Meteorological Agency.
TOWARD ARCHIVING CLIMATE RECORDS: Continuous, homogeneous, and accurate observation of geophysical parameters, which construct the Earth environment, is one of key issues for understanding and evaluating signals of climate change and variation. The GCOM mission is JAXA s first mission whose concept emphasizes importance of long-term observation by satellite. Through AMSR-E and AMSR2 on board three generation of GCOM-W, we can make continuous and homogeneous observation of water cycle variables more than 25 years. Furthermore, integration of those data with past microwave imager data will enable us to evaluate trends of water cycle variables for nearly 50-year, such as changes in sea ice extent. It is needless to say that information provides us substantial information to understand long-term climate variation. JAXA has developed and distributed long-term dataset of sea ice concentration and sea ice extent of Arctic and Antarctic oceans from November 1, 1978 to March 31, 2012, using observations from the Scanning Multichannel Microwave Radiometer (SMMR) on board the Nimbus-7 Pathfinder satellite, the Special Sensor Microwave Imager (SSM/I) on U.S. Defense Meteorological Satellite Program (DMSP) satellites, AMSR-E and Windsat data. Algorithm developed for AMSR-E was applied to each data. Data is available at JAXA s web site via internet (http://kuroshio.eorc.jaxa.jp/jasmes/climate/). We have plan to extend this climate record toward future period by using AMSR2 and its follow-on instruments, which will be on board second and third generation of GCOM-W series. Figure 5: Climate record of Arctic (upper) and Antarctic (lower) sea ice extent from 1978 to 2012 by using SMMR, SSM/I and AMSR-E, and Windsat. Record will be expanded to the future by AMSR2 and follow-on instruments. FUTURE SCHEDULE AMSR2 standard products will be distributed through the GCOM-W1 Data Providing Service (https://gcom-w1.jaxa.jp/). Data will be distributed to general users after completion of calibration/validation. Current schedule of data distribution to general users is Level 1 products in January 2013, and Level 2 and 3 products in May 2013. The GCOM-W1 Data Providing Service System has been in operation since August 2011 to distribute AMSR2 standard products along with AMSR and AMSR-E standard products. The system was
designed with user friendly interfaces. After simple registration, users enable to search products by three ways; 1) choose by categories and/or geophysical parameters; 2) choose by looking explanation of products; and 3) choose by name of satellites and/or sensors. AMSR2 original data format will be HDF5, and those of AMSR and AMSR-E are HDF4, but some format transformations are available at the system when users request products; 1) from HDF5 or HDF4 to GeoTIFF or TIFF; 2) from HDF5 or HDF4 to netcdf (netcdf 4 classic model, CF-1.4); and 3) from HDF4 to HDF5. Registered users can also use sftp or http protocols to download data without searching. There are many ongoing works during calibration/validation phase in preparing for public release of AMSR2 products. Further assessment of coefficients such as spillover factors and non-linearity corrections will be conducted during this phase. We also plan detailed investigation and corrections of calibration data, such as detailed analysis of intra-orbit brightness temperature anomaly to assess accurate HTS effective temperature, and removal of various intrusions into CSM counts including likely RFI, lunar emission, and Earth Tb through FEED-CSM spillover. Improvement of geometric calibration is also needed. Currently, preliminary coefficients were already applied, but further improvements will be needed. Regarding RFI identification, simple identification will be tested for C- band by using difference of brightness temperature between 6.9 and 7.3GHz channels. And we plan to conduct systematic survey of RFI in 6.9/7.3, 10.65, and 18.7 GHz channels. REFERENCES Imaoka, K., Kachi, M., Fujii, H., Murakami, H., Hori, M., Ono, A., Igarashi, T., Nakagawa, K., Oki, T., Honda, Y., Shimoda, H. (2010) Global Change Observation Mission (GCOM) for monitoring carbon, water cycles, and climate change. Proc. of the IEEE, 98, pp 717-734. Kachi, M., Kubota, T., Ushio, T., Shige, S., Kida, S., Aonashi, K., Okamoto, K., Oki, R. (2011) Development and Utilization of JAXA Global Rainfall Watch System based o Combined Microwave and Infrared Radiometers Aboard Satellites. IEEJ Transactions on Fundamentals and Materials, 131, pp 729-737. (In Japanese with English abstract) Kasahara, M., Imaoka, K., Kachi, M., Fujii, H., Naoki, K., Maeda, T., Ito, N., Nakagawa, K., Oki, T. (2012) Status of AMSR2 on GCOM-W1. Proc. of the SPIE Europe Remote Sensing, in press. Kubota, T., Shige, S., Hashizume, H., Aonashi, K., Takahashi, N., Seto, S., Hirose, M., Takayabu, Y.N., Ushio, T., Nakagawa, K., Iwanami, K., Kachi, M.. Okamoto. K. (2007) Global precipitation map using satelliteborne microwave radiometers by the GSMaP project: production and validation. IEEE Trans. Geosci. Remote Sensing, 45, pp 2259-2275.