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1. Introduction
Observation and prediction of global environmental changes brings significant benefit to people, such as precise and detailed weather forecasting. It is also important for acting against environmental changes to understand the global mechanisms of environmental changes that are complicated each other through circulation of atmosphere or water.
An advanced way of measuring changes in the global environment is through spaceborne remote sensing technologies using radars (active microwave sensors). These can be used for observing phenomena or making measurements in cases where the phenomena are large scale or occurring in areas that are far offshore or in remote locations where it is difficult to obtain measurements by other means. Spaceborne radar measurement technologies have the ability to cover wide ranges in a short time as well as to make measurements that are highly accurate. Moreover, they are not affected by cloud cover or sun angle1). There are four kinds of spaceborne radars monitoring the Earth environment changes currently.
These are: Synthetic Aperture Radar (SAR), Ocean Scatterometer (SCAT), Altimeter (ALT) and Precipitation Radar (PR).
Mainly, Elachi contributed to the development of the first to the third ones2), which were developed largely by the Jet Propulsion Laboratory, and Fugono and Okamoto, leading research at the Communications Research Laboratory, developed the last one, the precipitation radar.
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