SAR (Synthetic Aperture Radar) is active microwave sensor with high spatial resolution which can observe the earth all weather condition and during day and night and is used in various fields of applications. NASDA has contributed to various experiments using SAR. In 1983, SAR-580 experiment in Japan was conducted by NASDA in collaboration with CCRS and Japanese research organizations. NASDA and MITI prepared and conducted JERS-1 verification program with selected domestic and foreign principal investigators. NASDA is conducting research on future SAR mounted on ALOS (Advanced Land Observing Satellite) which will be launched around 2000. In this paper, features and applications of SAR data are presented and key technologies of SAR are presented.

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In November 1991 and in October and November 1992, We made experiments to detect artificial slicked areas by the C-band Synthetic Aperture Radar on the European Remote Sensing Satellite-1. Artificial slick areas were produced by spilling oleyl alcohol from a small ship in the Pacific ocean about 100 km off the coast of Japan. Sea truth data were collected by the research vessel and the small ship used to spill oleyl alcohol. The ERS-1 SAR images were processed by NASDA. The artificial polluted areas were clearly detected by ERS-1 SAR under some different conditions of wind speeds less than 11 m/s. The damping of the scattered power was nearly 4-5 dB for the wind speed less than 11 m/s. However, we could not detect artificial slick by ERS-1 SAR when wind speed was about 14 m/s.

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The spaceborne radar to measure rain has not been realized yet. In this paper, the airborne rain radar and the result of the joint experiment between USA and Japan is introduced in the beginning. Then, the plan of the Tropical Rainfall Measuring Mission (TRMM) is introduced with the results of conceptual design study and development of the BBM (Bread Board Model) of the TRMM rain radar. The radar, operating at 13.8 GHz and designed to meet TRMM mission objectives, has the minimum measurable rain rate about 0.5 mm/h with a range resolution of 250 m, a horizontal resolution of about 4 km, and a swath width of 220 km. An active phased array radar system with the 128-element is adopted to achieve a contiguous scanning within the swath. The basic characteristics of BBM were confirmed by experiments.

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Passive microwave radiometers have merits of comparatively light weight and small electric power when loading on satellites, and capabilities of observing many geophysical parameters under all weather conditions. The Special Sensor Microwave / Imager (SSM/I) aboard the U.S. Defense Meteorological Satellite Program is considered to become a level of an operational sensor, after several experimental sensors were developed from early 1970’. The data of the SSM/I are open to the public not only in U.S., but also in other countries. Recent results of earth observations obtained by the SSM/I are presented, focusing on water vapor content over the ocean, precipitation, marine wind speed, and land surface temperature .

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The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) is an imaging sensor with high spatial resolution and extensive spectral coverage from visible to thermal infrared region, which is scheduled to be launched in morning sun-synchronous Earth orbit on the platform of NASA’s Earth Observing System (EOS-AM) in 1998. The instrument will have three bands in the visible and near infrared with 15-m spatial resolution, six bands in the short-wave infrared with 30-m spatial resolution and five bands in the thermal infrared with 90-m spatial resolution. An additional band in the near infrared with 15-m spatial resolution will provide stereo viewing capability combined with the nadir viewing band. The ASTER instrument is being built based on the scientific requirements of the ASTER Science Team. This team is an international team of Japanese and American scientists, who are responsible for the algorithm development of the standard data products and the higher science data products. The algorithm developments and future science potential evaluation are mainly promoted by the ASTER simulation data generated from airborne experiments. Some examples of the airborne experiments in thermal infrared region are shown here to demonstrate the temperature and surface compositional mapping capabilities.

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Spaceborne backscatter lidar (laser radar) can measure aerosols and clouds with a high vertical resolution and improve understanding the role of them in the physical climate system. Spaceborne DIAL (Differential Absorption Lidar) technique can measure the vertical profiles of atmospheric water vapor and improve understanding of the global hydrological cycle. In this paper research activities in Japan for the spaceborne backscatter and water vapor DIAL systems will be reviewed.

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