Japan and Earth Observation Systems

Himawari GMS Himawari MTSAT MOS JERS-1 ADEOS TRMM ALOS Strix SAR

Japan has operated three types of Earth observation systems: one for meteorology, one for oceanography, and one for general remote sensing. Earth Observation Satellites continuously observe the earth from space, and the acquired data are provided as satellite images and are used to study environmental problems, to monitor disasters and to explore resources.

JAXA (the former NASDA) already launched seven "Earth Observation Satellites" including MOS-1, MOS-1b, JERS-1, ADEOS, TRMM, ADEOS-II and ALOS.

Most "Earth Observation Satellites" observe particular region periodically from the orbit of 400 - 1,000 km altitude, and observe whole the Earth in some days. Each satellite carries many kinds of instrument as the eye to discriminate the surface of the Earth such as vegetation, sea surface temperature, etc. The weather satellite "Himawari" is one of "Earth Observation Satellites" and keeps watching the Earth from the geo-stationary orbit of about 36,000 km altitude.

Remote Sensing is a technology to observe objects' size, shape and character without direct contact with them. The reason why they can be observed without contact because of the characteristics of electromagnetic waves, such as light reflected or radiated from the objects. These reflected or radiated electromagnetic waves are received by sensors aboard earth observation satellites. In general, the characteristics of reflected or radiated electromagnetic waves depend on the type or condition of the objects. Therefore by understanding the characteristics of electromagnetic waves and by comparing to the observed information, it is possible to know the size, shape and character of the objects.

With visible and near-infrared sensors, it is possible to measure the strength of solar light reflection by some objects on the Earth. By analyzing these data, it is possible to understand land use classification, vegetation coverage, etc. Thermal infrared sensors observe thermal infrared rays radiated by ground, sea surface, clouds, etc., and can understand sea surface temperature, cloud distribution, etc. day and night to utilize them for weather forecasting.

Passive microwave sensors ["microwave radiometer"] can observe microwave radiated by ground surface, sea surface, clouds, etc., to understand sea surface temperature, precipitation distribution, etc. day and night. SAR (Synthetic Aperture Radar) out of active microwave sensor, is used to understand forest distribution, topography, etc, as well as sea surface wind direction and velocity by using scatterometer.

There are several types of orbits, and the orbit is selected depending on purposes of the satellites. Earth observation satellites have a major mission to observe the entire earth, so they circle the most suitable Sun-synchronous sub-recurrent orbit. A sub-recurrent orbit means that after a certain number of days, the satellite repeats its original orbit. This orbit enables the satellite to observe the same area at regular intervals.

With sun-synchronous orbit, positioning between the satellite and the sun is always the same, which means the area the satellite flies over always gets same sunlight angle. With this orbit, the incidence angle of sunlight to the land surface is always the same, and it allows to observe radiation and reflection from the land surface accurately.

The Earth Observation Research Center (EORC) was founded to conduct Earth-observing satellite data acquisition, processing, and research in April 1995. It analyzes observation data acquired by Earth-observing satellites, develop algorithms to derive geophysical parameters and to calibrate and validate satellite data, and try to maintain the quality of the data. It also promotes research and application of satellite data in the fields of meteorology, control of forestry and fisheries resources, disaster prevention and national land use, and global environmental changes.