APPENDIX 6
OVERVIEW OF
THE ADVANCED LAND OBSERVING SATELLITE-4(ALOS-4) MISSION6-1

1. Introduction
The Advanced Land Observing Satellite-4 (ALOS-4) will observe the Earth's surface using its onboard the Phased
Array type L-band Synthetic Aperture Radar-3 (PALSAR-3). The data will be utilized for monitoring disaster, forest,
sea ice, infrastructure, and many other applications with the advantages of Synthetic Aperture Radar (SAR) such as
all-weather and day-and-night observation capability. With further improved observation performance compared tothe predecessor PALSAR-2 aboard ALOS-2, the satellite aims at achieving both high resolution and a broader
observation swath.
ALOS-4 is equipped with a SAR antenna at the lower part of its body and with two solar array paddles at bothsides, as shown in Figure 1. The observation data is transmitted to a ground station via. Ka-band data downlink withmaximum rate of 3.6 Gbps. ALOS-4 will operate in the same orbit plane as ALOS-2. Table 1 shows system
specifications of ALOS-4.

Fig. 1 ALOS-4 in-orbit configuration.
Table 1 ALOS-4 current specifications (under designed).
Mission Instruments

Orbit

Mission lifetime
Satellite mass
Data downlink

・・・・・・・

PALSAR-3 (Phased Array-type L-band Synthetic Aperture Radar-3)
SPAISE3 (SPace based AIS Experiment 3)
Sun-synchronous sub-recurrent orbit
Altitude: 628 km
Inclination angle: 97.9 degree
Local sun time at descending: 12:00 ± 15 min.
Revisit time: 14 days (15-3/14 rev/day)(Same orbit as ALOS-2)
7 years
Approx. 3 tons
3.6 Gbps/1.8 Gbps (Ka-band)

2. PALSAR-3 Specification
ALOS-4 carries the state-of-the-art L-band SAR called PALSAR-3. For the continuity of ALOS-2 data, PALSAR3 will inherit the major function and performance (NESZ, S/A, etc.) of PALSAR-2 aboard ALOS-2. The observation
swath width of PALSAR-3 will be expanded from PALSAR-2 without spoiling the spatial resolution by using thedigital beam-forming (DBF) technique.
Fig. 2 and Table 2 show geometries and specifications of PALSAR-3, respectively. Spotlight and Stripmap modes
will provide high resolution data. ScanSAR mode will observe wider area with 700 km swath width at the expenseof spatial resolution. The observation repetition frequency of ALOS-4 will also be improved owing to the expanded
swath width.
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Fig. 2 Geometry of PALSAR-3 observation modes.
Table 2 PALSAR-3 observation modes and specifications.
Observation mode

Spotlight

Stripmap 3m

Stripmap 6m

Stripmap 10m

SAR mode

Slidingspotlight

Center frequency(MHz)1257.51257.5

Bandwidth (MHz)8484

422828Resolution (m)3x1(Rg x Az)

361025(1 look)

Swath width (km)35 x 35(Rg x Az)

200100200

100200100700(4 scan)

Polarization(HV basis)

1, 2

1, 2

1, 2, 4

1, 2

1, 2, 4

1, 2

1, 2, 41, 2

Incidence angle
range (degree)

8-70

30-56

8-70

30-56

8-70

29-56

8-70

8-70

Split-band option(for ionosphericcorrection)

N/A

N/A

N/A

N/A

N/A

28+10
MHz

N/A

N/A

Stripmap

ScanSAR
ScanSAR1236.5 or 1257.5 or 1278.5*Items in red color represent improvements or modifications from PALSAR-2

3. Standard Product
PALSAR-3 Standard Data Products (Level 1) are radiometrically and geometrically calibrated data and will beprovided for ALOS-4 users. Table 3 shows the definitions of the Standard Data Products. In addition, higher-level
data products including global mosaic and disaster map are planned to be released.
Table 3 PALSAR-3 standard data procucts.
Level
1.1
1.5
2.1

Definition
Range and azimuth compressed single-look complex (SLC) data on slant range
Geo-coded or geo-referenced amplitude image projected to map coordinate
Ortho-rectified amplitude image projected to map coordinate

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