ALOS-4 (Advanced Land Observing Satellite-4 )
The Advanced Land Observing Satellite-4 (ALOS-4) is a Japanese Aerospace Exploration Agency (JAXA) mission aimed at observing and monitoring disaster-hit areas, forests, sea-ice, and monitoring infrastructure displacement. Planned for launch by March 2023, ALOS-4 will replace the current ALOS-2 mission and will have an improved sensor.
|31 Mar 2024
|End of life date
|31 Mar 2030
|Atmosphere, Ocean, Land, Gravity and Magnetic Fields, Snow & Ice
|Multi-purpose imagery (ocean), Multi-purpose imagery (land), Vegetation, Albedo and reflectance, Gravity, Magnetic and Geodynamic measurements, Landscape topography, Sea ice cover, edge and thickness, Soil moisture, Snow cover, edge and depth, Ocean surface winds, Atmospheric Winds, Ice sheet topography
|Ocean imagery and water leaving spectral radiance, Land surface imagery, Vegetation type, Fire fractional cover, Earth surface albedo, Land surface topography, Wind vector over sea surface (horizontal), Sea-ice cover, Snow cover, Soil moisture at the surface, Iceberg fractional cover, Sea-ice type, Glacier motion, Sea-ice sheet topography, Oil spill cover, Crustal Motion, Above Ground Biomass (AGB), Snow melting status (wet/dry)
|PALSAR-3, SPAISE3 (AIS)
|Data collection, Imaging microwave radars
|CEOS EO Handbook
|See ALOS-4 (Advanced Land Observing Satellite-4 ) summary
ALOS-4 will carry the Phased Array type L-band Synthetic Aperture Radar-3 (PALSAR-3), an L-band Synthetic Aperture Radar (SAR), which will provide continuity with greater resolution in comparison to ALOS-2 for monitoring infrastructure development, forest management and land deformation and subsistence. ALOS-4 will also carry the SPace based AIS Experiment (SPAISE3), a high performance satellite Automatic Identification System (AIS), to monitor the oceans by receiving AIS signals from vessels.
PALSAR-3 will make microwave measurements at a frequency of 1270 Mhz in the L-band. It will be able to observe in three modes: Stripmap mode, ScanSAR mode and Spotlight mode. Stripmap mode will have a spatial resolution ranging from 3-10m and a swath width between 100-200 km while ScanSAR mode will have a spatial resolution of 25 m and a swath width of 700 km. Spotlight mode will have the greatest spatial resolution of 3m x 1m at a Swath width of 35 km.
ALOS-4 will fly in a Sun-synchronous orbit at an altitude of 628 km. It will have an orbital inclination of 97.9°, an orbital period of 97 minutes and a repeat cycle of 14 days.
Space and Hardware Components
ALOS-4 will have a mass of approximately 2990 kg and dimensions of 10 m x 20 m x 6.4 m. The prime contractor for the construction of ALOS-4 is the Mitsubishi Electric corporation. ALOS-4 will downlink data in the ka-band at a rate of 1.8 or 3.6 Gbps.
The Advanced Land Observing Satellite-4 (ALOS-4) is a Japanese Aerospace Exploration Agency (JAXA) mission aimed at observing and monitoring disaster-hit areas, forests, sea-ice, and monitoring infrastructure displacement. The mission will also be able to monitor vessels in the oceans and heavy marine traffic areas. Planned for launch by March 2023, ALOS–4 will replaced the current ALOS-2 mission and will have an improved sensor, the Phased Array type L-band Synthetic Aperture Radar-3 (PALSAR-3), which, when compared to its predecessor PALSAR-2 onboard ALOS-2, will achieve both higher resolution and a broader observation swath. The ALOS-4 will also be equipped with the SPace based AIS Experiment (SPAISE3), a high performance satellite Automatic Identification System (AIS) to detect signals from ocean vessels.
Monitoring Land Deformation and Subsidence
Radar satellites can measure diastrophism or ground transformation caused by volcanic activity of an earthquake up to a few centimetres by comparing acquired data in the same area at different times. The location of a magma reservoir and its movement from surface displacement can be estimated by continuously monitoring volcanoes, and such an estimation can contribute to understanding volcanic activities which is vital in Japan with high volcanic activity. ALOS-4 will increase the observation frequency to once every two weeks, when compared to ALOS-2 which flies in the same orbit and can observe one volcano just four times a year, so that disaster prevention agencies can find abnormal changes such as volcanic activity, land subsidence, or landslides, and provide early warning for the public. In addition, the swath width will be drastically increased from 50 km to 200 km while keeping a high resolution, enabling observation of a broader area at the same time when a large-scale disaster that damages wide areas occurs.
Forest covers 30% of all land area in the world, and deforestation is responsible for significant greenhouse gases net emissions. Therefore, forest conservation and assessment are important. JAXA and the Japan International Cooperation Agency (JICA) are cooperatively developing the JICA-JAXA Forest Early Warning System in the Tropics (JJ-FAST). Using observation data from ALOS-2, the JJ-FAST can detect areas of deforestation in the order of a few hectares, and is currently operational in 77 countries. However, there are many smaller deforestation areas, and ALOS-4 will conduct observations more frequently with five times more precision to detect smaller deforestation areas that cannot be monitored by ALOS-2.
Monitoring Infrastructure Development
JAXA carries out research to detect the annual displacement of structure due to the deterioration of dams, levees, port facilities and infrastructure by analysing time series of ALOS-2’s data. ALOS-4 will acquire data with more frequency, enabling the detection of annual displacement that grows slowly and gradually, such as structural distortion and subsidence, with precision of a few millimetres. Through such detailed observations, the satellite data is expected to be utilised for more efficient infrastructure maintenance.
ALOS-4 will have a mass of approximately 2990 kg and dimensions of 10 m x 20 m x 6.4 m. It will be in a sun-synchronous orbit at an altitude of 628 km, an orbital inclination of 97.9 deg and have a 14 day revisit time. The prime contractor for the construction of ALOS-4 is the Mitsubishi Electric corporation. ALOS-4 will downlink data in the ka-band at a rate of 1.8 or 3.6 Gbps.
ALOS-4 is on track to be launched by March 2023 on a JAXA H3 rocket from Tanegashima Space Centre. The H3 rocket, manufactured by Mitsubishi Heavy Industries, is an expendable launch system that is in development in Japan.
The Phased Array type L-band Synthetic Aperture Radar-3 (PALSAR-3) is a L-band Synthetic Aperture Radar (SAR). The L-band, which represents microwave measurements in the range 1-2 GHz, has continuously been developed in Japan. The instrument will measure at a frequency of 1270 MHz in the L-band. With the utilisation of digital beamforming techniques, the swath width of PALSAR-3 will improve while maintaining the ground resolution.
PALSAR-3 observes in three modes: Stripmap mode, ScanSAR mode and Spotlight mode. Regular stripmap mode observation is right-side, incidence angle of 30-44°. The other beams and left-side observation are used for quick disaster monitoring. The performance characteristics of the PALSAR instrument are presented in Table 1.
Centre Frequency (MHz)
1236.5 or 1257.5 or 1278.5
Swath Width (Km)
Available Incidence angle range (°)
The images below show a comparison of the coverage of 1 repeat cycle (14 days) between PALSAR-3 and PALSAR-2.
The SPace based AIS Experiment (SPAISE3) enables ALOS-4 to monitor the oceans by receiving AIS signals from vessels as well as by acquiring the PALSAR-3 images. SPAISE3 has eight antennas and adopts ground-based digital beam-forming (DBF) method as one of effective countermeasures against radio wave interference regions. Using this technology the detection success rate of ships in heavy marine traffic areas will be improved compared to SPAISE2. SPAISE3 development is JAXA’s ongoing project in cooperation with the Nippon Electric Corporation (NEC).
1) “JAXA | Advanced Land Observing Satellite-4 (ALOS-4).” Japan Aerospace Exploration Agency, https://global.jaxa.jp/projects/sat/alos4/.
2) “ALOS-4｜ALOS@EORC.” ALOS-4｜ALOS@EORC, https://www.eorc.jaxa.jp/ALOS/en/alos-4/a4_about_e.htm.
3) “ALOS-4｜ALOS@EORC.” ALOS-4｜ALOS@EORC, https://www.eorc.jaxa.jp/ALOS/en/alos-4/a4_sensor_e.htm.
4) “ALOS 4 - Gunter's Space Page.” Gunter's Space Page, 1 December 2021, https://space.skyrocket.de/doc_sdat/alos-4.htm.
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).