Both of JMA’s Himawari-8/9 geostationary meteorological satellites (the successors to the MTSAT series) are equipped with highly improved Advanced Himawari Imagers (AHIs). JMA aims to establish a stable and continuous satellite observation system with redundancy based on twin satellite operation involving Himawari-8 and -9, which is expected to contribute to disaster risk reduction in Asia and the western Pacific until 2029.
The most valuable function of meteorological satellites is their ability to monitor atmospheric phenomena globally and uniformly over various areas such as seas, deserts and mountains where surface-based observation is difficult. World Weather Watch (WWW; a core World Meteorological Organization (WMO) program) is supported by multiple geostationary and polar-orbiting meteorological satellites that form space-based observation networks, and the satellite missions JMA started in 1978 have long contributed to the program for the East Asia and Western Pacific region. With their new sensors, Himawari-8/9 will further support and lead to the improvement of meteorological services in a variety of fields including weather forecasting, climate monitoring, natural disaster prevention and safe transportation.
Himawari-8 was launched and entered operation at 2:00 UTC on 7 July 2015. This was followed on 2 November 2016 by the launch of Himawari-9 which started backup operation in March 2017. Both satellites are scheduled to operate until 2029. Himawari-8 was chiefly used for observation during the early part of this period, with Himawari-9 in a back-up role. Their operation has been switched on 13 December 2022 to place Himawari-9 in the main observational role with Himawari-8 as back-up.
Himawari-8/9’s AHIs have 16 observation bands (3 for visible, 3 for near-infrared and 10 for infrared). The observation bands of the satellites will facilitate understanding of cloud conditions. Additionally, the time interval of full-disk observations is 10 minutes for Himawari-8/9. Along with such observation, Himawari-8/9 also observe certain areas so frequently that the whole of Japan is covered in with 2.5 minutes intervals. The spatial resolutions of Himawari-8/9 are 0.5 – 1 km for visible bands and 1 – 2 km for near-infrared and infrared bands.
The enhanced observation functions of the satellites are expected to support unprecedented levels of precision in monitoring for the movement of tropical cyclones and clouds bringing heavy local rain. It is also possible to observe the distribution of volcanic ash and aerosols with high accuracy. Data derived from Himawari-8/9 is used for cloud imagery, and utilized in numerical weather prediction and related fields based on calculation to estimate values such as temperature and wind direction/speed in the upper atmosphere.
The imager scans the earth by moving internal scanning mirrors in the east-west direction starting from the north. During the 10 minutes it takes to scan the full disk, the unit also scans a limited target region such as the area around Japan by changing the direction of the mirrors. Light gathered by the mirrors is dispersed into 16 wavebands before being converted into electrical signals by detectors for each band, and the signals are in turn transmitted to ground stations.
Himawari-8/9 and their ground stations are operated by a company established under JMA's Private Finance Initiative (PFI) project. The company receives data from Himawari-8/9 and controls the satellites using antennas and other equipment.
Satellite Program Division, Japan Meteorological Agency
E-mail: metsat AT met.kishou.go.jp