nel. 
)EOS 
A SAR System on the ALOS 
H. Wakabayashi, Y. Osawa, K. Toda, 
T. Hamazaki, and R. Kuramasu 
Earth Observation Satellite Department 
National Space Development Agency of Japan 
1-29-6, Hamamatsu-cho, Minato-ku, Tokyo, 105 JAPAN 
Commission |, Working Group 4 
KEY WORDS: SAR, Development, Land, ALOS, PALSAR 
ABSTRACT: 
The Advanced Land Observing Satellite (ALOS) is a Japanese high resolution earth observation satellite and will be 
used for cartography, environmental and hazard monitoring. National Space Development Agency of Japan (NASDA) 
has recently investigated users' requirements and conducted a feasibility study on the ALOS. As a result, mission 
requirements were clarified, and then proposed specifications for sensors and a satellite system were defined. The 
ALOS has both optical and microwave imaging sensors to achieve these requirements. Especially, the L-band 
synthetic aperture radar (SAR), which is a follow-on sensor of the JERS-1/SAR, has capabilities of look-angle change 
and the ScanSAR mode.The ALOS is scheduled to be launched in 2002 by Japanese H-Il rocket. This paper introduces 
an outline of mission concepts, a satellite system configuration, and the SAR characteristics of the ALOS. 
1. INTRODUCTION 2. MISSION CONCEPT 
There are many kinds of remote sensing satellites in orbit The main mission of the ALOS are cartography, 
and in planning stage. Some satellites, such as the environmental and hazard monitoring by using both 
NOAA's and the ADEOS-II (Nakajima et a/., 1994) are optical and microwave high resolution sensors. Maps are 
dedicated to global observation by using wide-swath very important information for managing a country's 
sensor and relatively short orbit repeat cycle. On the resources: e.g., cultivated area, forest, and so on. In 
other hand, high resolution satellites, such as the Japan, 1/25,000 maps cover whole Japanese territory, 
Landsat, the SPOT and the JERS-1 are providing useful and are being revised about every five years by the 
data for regional observation. Japanese Geographical Survey Institute. However, 
“paper” maps larger than 1/31,680 scale cover only 31% 
NASDA surveyed future needs on regional observation of the whole world. Especially, in developing countries, 
and clarified the user's requirements. NASDA also more than 9096 are unmapped in this scale. Also, in 
conducted a feasibility study on sensors and a satellite recent years, Geographical Information System (GIS) 
system and defined proposed specifications. As the has been developed eagerly in many countries, however, 
result, the Advanced Land Observing Satellite (ALOS), enough “digital” geographical data has not been collected 
which is focusing on regional observations, was decided. yet. The "digital" data of wide area could be efficiently 
And a high resolution optical sensor (AVNIR-2: Advanced collected by remote sensing, particularly, from space. 
Visible and Near-infrared Radiometer type-2) as well as a The GIS is very efficient way to manage the countries' 
synthetic aperture radar (PALSAR: Phased Array type L- resources, because of its capability and flexibility, that 
band Synthetic Aperture Radar, formerly called 'VSAR") making/revising precise maps on GIS using remotely 
were chosen as the mission instruments of the ALOS. sensing data, are helpful to the "sustainable 
The Japanese government has just authorized the phase development". These maps are also useful to 
B budget of the ALOS. The ALOS project is going to the environmental monitoring. According to our recent 
preliminary design and the BBM phase. The ALOS is investigation, to make/revise 1/25,000 scale maps needs 
currently scheduled to be launched in 2002 by Japanese 2.5 m horizontal resolution for determination of land 
H-II rocket. conditions, and 5 m vertical accuracy for drawing 
elevation contours. Also, multispectral bands of 10 m 
This paper introduces mission concepts and general horizontal resolution as well as L-band SAR data are 
characteristics of the ALOS satellite. In the latter part of required for classification of land cover, such as 
this paper, we will concentrate on the detailed vegetation, forests, urban area, and so on (Osawa et al., 
characteristics of the PALSAR system. 1995). 
193 
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996