APPENDIX 5
OVERVIEW OF
THE ADVANCED OPTICAL SATELLITE(ALOS-3) MISSION5-1

1. Introduction
The Advanced Optical Satellite (ALOS-3) is the next high-resolution optical mission as a successor of theAdvanced Land Observing Satellite (ALOS, “Daichi”) in Japan Aerospace Exploration Agency (JAXA). ALOS-3
is now under developing in the Critical Design Review (CDR) phase, and to be launched in JFY 2020 as current
plan. The major mission objectives of ALOS-3 are(1) to contribute safe and secure social including provisions for natural disasters, and(2) to create and update geo-spatial information.
The wide-swath and high-resolution optical imager (WISH, as a tentative name) is designed to be achieved themission objectives and consists of the panchromatic band and multispectral bands by six channels.

2. Specifications of ALOS-3 and Instrument (WISH)
Figure 1 shows in-orbit artificial image of ALOS-3, and Table 1 summarizes the current specifications of thesatellite. The satellite’s orbit is kept as the sun-synchronous and sub-recurrent with 10:30 am of local sun time, but
the repeat cycle is 35 days from 46 days of ALOS’s one. This is enhanced observable frequency at middle and highlatitude areas, however small pointing angle observations are necessary to cover the entire area in low latitudes.
Table 2 summarizes the current specifications of the WISH, which is considered to improve and enhance a fineresolution and global observation capabilities achieved by the Panchromatic Remote Sensing for Stereo Mapping(PRISM) and the Advanced Visible and Near Infrared Radiometer type-2 (AVNIR-2) onboard ALOS. For example,
the ground sampling distance (GSD) is 0.8 m of WISH’s panchromatic band compared with 2.5 m of PRISM, and3.2 m for multi-spectral bands with 10 m of AVNIR-2, even the observation swath widths are same as 70 km atnadir, respectively.
For multi-spectral observation, two channels are added from AVNIR-2 i.e. Coastal and Red Edge that willcontribute to bathymetry and environmental monitoring in coast regions, and to activation level monitoring in forests,
vegetation and agricultural areas. The data quantization is also improved to 11 bits/pixel from 8 bits/pixel of PRISM
and AVNIR-2. This improvement will contribute to obtain better image quality. On the other hand, this accrues ahuge amount of mission data, therefore the Optical Data Relay Satellite (JDRS) that is also under developed, will
be used to downlink them from space to ground.
Unfortunately, along-track stereo observation by multi-sensors like PRISM had not been selected, however thesatellite has the body pointing capability within 60 deg. in cone-shape from nadir that will contribute in an
emergency observation if a natural disaster happens for example. More detail about observation modes is introducedin Section 3.

Fig. 1 ALOS-3 in-orbit image.

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Table 1 ALOS-3 specifications (under designed).
Items

Specifications

Orbit

TypeAltitude
Local Sun Time
Revisit
Instruments
Ground Sampling
Distance (GSD)
Swath width
Mass
Size
Duty
Design life timeSun-synchronous sub-recurrent
669 km at the equator
10:30 am +/- 15 minutes at the descending node
35 days (Sub-cycle 3 days)- Wide-swath and high-resolution optical imager (WISH, as a tentative)- Dual-frequencies Infrared sensor (hosted payload)- Panchromatic band of WISH (Pa): 0.8 m- Multispectral band of WISH (Mu): 3.2 m (6 bands)
70 km at nadir
Approx. 3 tons at launch
5 m×16 m×3.5 m on orbit
10 mins / recurrent
Over 7 years

Table 2 ALOS-3 WISH current specifications (under designed).
Items
Specifications
Panchromatic band (Pa)
GSD, Swath width
0.8 m, 70 km at nadir
Wavelength
0.52-0.76 micrometers
MTF, SNR
0.1, 200
Quantization
11 bits / pixel
Multispectral band (Mu)
GSD, Swath width
3.2 m, 70 km at nadir
WavelengthBand 1: 0.40-0.45 (Coastal)(micrometers)
Band 2: 0.45-0.50 (Blue)
Band 3: 0.52-0.60 (Green)Band 4: 0.61-0.69 (Red)Band 5: 0.69-0.74 (RedEdge)
Band 6: 0.76-0.89 (NIR)
MTF, SNR
0.2, 200Quantization
11 bits / pixel
Mission data rate
Approx. 4 Gbps (after onboard data compression: 1/4 (Pa), 1/3(Mu))- Direct Transmission: Ka and X-band
Mission data downlink- via. the Optical Data Relay Satellite
Pointing< 60 degrees by body pointing

3. ALOS-3 Observation Modes
Based on the satellite agility within 60 deg. pointing capability, five observation modes are prepared to meetvarious user requirements. The details are as follows.
3.1. Stripmap observation mode
ALOS-3 can normally perform observation covering 70 km in width and 4,000 km in along-track direction as thestripmap observation mode. To increase the acquisition frequency, the images will be taken by less than 25 deg.
pointing angle in cross-track direction (GSD < 1m) when the satellite track is in oceans. Fig. 2 (a) shows an exampleof the stripmap observation.
3.2. Point observation mode
If the user has a certain ground point or an area of interest (AOI), ALOS-3 can observe there using pointing
capability within 60 deg. This mode will be used for natural disaster monitoring, for example. Fig. 2 (b) shows anexample of the observable coverages by 60 deg. pointing in cross-track direction.
3.3. Observation direction changing mode
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ALOS-3 can observe any given point by the pointing capability up to 60 deg. in all direction against the satellite
nadir. This will be used when the large natural disaster happens. In the case of Japan, it can be activated within 24hours after receiving the request. This will be used when the large natural disaster happens e.g. the expecting Nankai
Trough large earthquake. Fig. 2 (c) shows an example of the observation direction changing mode to obtain
information if the Nankai Trough large earthquake occurs.
3.4. Wide-area observation modeThis mode can cover in wide-ranging area of 200 km (in along-track direction) x 100 km (in cross-track direction)by satellite’s single orbital passage. This will be also used when the large natural disaster happens.
3.5. Stereoscopic observation mode
To acquire stereo-pair images, two ways have been proposed: 1) in single orbital path, and 2) combining two
stripmap observations by nadir view and backward view in neighboring path after three days that is sub-cycle revisit
orbit. The way 1) will be however not sufficient base-to-height ratio (B/H) to derive terrain information. As theadvantages of the way 2), that is possible to set suitable B/H, and can acquire images over large area. However, thiswill depend on weather conditions i.e. cloud covers, to success acquisition of the stereo images within short period
as a disadvantage.

(a) Stripmap observation mode.

(b) Observable area coverages by point (c) Observation direction changing
observation mode from some nadir mode.
path (“N” in this example).

Fig. 2 Example of ALOS-3 major observation modes.

4. Standard Product
Table 3 summarizes the definition of the standard product of ALOS-3. The image data will be provided in CEOS
format or GeoTIFF format.
Table 3 The definition of ALOS-3 Standard product (under designed).
Level
1ADefinition

Note
Frame subset and uncompressed data

Raw data

1B1

Radiometric system corrected data from level Separate to individual CCD unit.
1A productNo map projection and resampling.

1B2

Radiometric and geometric system corrected
data from level 1A product with Rational
Polynomial Coefficient (RPC) file.
Option
R: Geo-referenced, G: Geo-coded
Simple ortho-rectified image using existing
Digital Elevation/Surface Model (DEM/DSM).
Option
R: Geo-referenced, G: Geo-coded

1C

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Scene-frame unit.
Select: Map projection, Resampling, Pixel
spacing
Scene-frame unit.
Select: Map projection, Resampling, Pixel
spacing