Minimize ALOS-2

ALOS-2 (Advanced Land Observing Satellite-2; SAR mission) / Daichi-2

ALOS-2 is the follow-on JAXA L-SAR satellite mission of ALOS (Daichi) approved by the Japanese government in late 2008. The overall objective is to provide data continuity to be used for cartography, regional observation, disaster monitoring, and environmental monitoring.

The post-ALOS program of JAXA has the goal to continue the ALOS (nicknamed Daichi) data utilization - consisting of ALOS-2 (SAR satellite) and ALOS-3 (optical satellite) in accordance with Japan’s new space program.

In 2010, ALOS has been operated for more than four years since January 2006 to accomplish four mission goals, including: cartography, regional observations, disaster monitoring, and resource surveys. ALOS-2 will continue the L-band SAR observations of the ALOS PALSAR (Phased Array L-band Synthetic Aperture Radar) and will expand data utilization by enhancing its performance. Table 2 shows the major observation advantages of the planned ALOS-2 mission when compared with the ALOS PALSAR. 1) 2) 3) 4) 5) 6) 7) 8)

Note: The ALOS (Daichi) spacecraft was retired on May 12, 2011. The JAXA recovery team had been trying to communicate with ALOS for about three weeks after it developed a power generation anomaly.

Disaster monitoring
(secure the public safety)

- To contribute to the nation’s disaster prevention activities through fast access to damaged areas during serious disasters in Japan, Asia and so on, as well as continuous monitoring of subsequent disasters and/or recovery/reconstruction status over the areas.
- To contribute to improving disaster prediction accuracy, etc. by providing disaster-related organizations with InSAR data necessary for deformation forecast/monitoring.

Land monitoring
(preserve and manage national land)

- To provide national land information in a timely manner and promote its utilization based upon archived data developed by wide range of observation data as well as its continuous acquisitions.

Agricultural monitoring
(facilitate food supply)

- To contribute to sophistication and sustainability of agriculture by providing related organizations with the observation data necessary for evaluation of irrigated rice.

Natural resource Exploration (facilitate natural resources & energy supply)

- To contribute to enhancing the method of natural resource exploration by providing related organizations with the observation data necessary for detecting oil and mineral resources in the ground and seabed.

Global forest monitoring
(resolve global-level environmental issues)

- To contribute to solving global warming issues by providing related organizations with data derived from global monitoring of tropical rain forests to identify carbon sinks.

Table 1: Overview of the ALOS-2 primary mission objectives

Observation parameter

ALOS (launch 2006)

ALOS-2 (launch 2014)



Observation frequency

- Revisit time: 46 days

- Revisit time: 14 days

-Daytime observation is limited by sharing with optical observation

- No conflict

- Incidence angle : 8-60º
- Right-side looking

- Incidence angle: 8-70º
- Right- or left-side looking observation capability

Spatial resolution

- Strip map: 10 m
- ScanSAR: 100 m

- Strip map: 3 m /6 m /10 m
- ScanSAR: 100 m
- Spotlight: 1 m x 3 m

Table 2: SAR instrument comparison between ALOS and ALOS-2

 

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Figure 1: Long-Term Plan of JAXA Earth Observation (image credit: JAXA) 9)

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Figure 2: Artist's rendition of the ALOS-2 spacecraft in orbit (image credit: JAXA)

Spacecraft:

The ALOS-2 system is developed by Mitsubishi Electric Corporation under contract to JAXA (Japan Aerospace and Exploration Agency).

A proper description of the spacecraft will be provided when available.

Precise positioning using GPS: ALOS-2 is equipped with spaceborne dual-frequency GPS receivers using both L1 and L2 bands, and demonstrated precise navigation on orbit. However, to achieve higher resolution observation and more accurate orbit maneuvering for next Earth observation satellites, an advanced GPS receiver was necessary. The JAXA Guidance and Control Group has been conducting a series of studies for a next-generation spaceborne GPS receiver. In this development, an enhancement of navigation accuracy is a major theme, and the new receiver will be reinforced with the ability to receive multiple frequencies and multiple channels to meet with GPS modernization. 10)

Recently, an algorithm of enhancing navigation accuracy especially when using the L1 band only by reducing the error due to ionospheric delay has been developed Based on the algorithm developed in this work, a software installed in the GPS receiver for ALOS-2 is developed (Ref. 4).

Real-time GPS L1 navigation:

- In monitoring disasters, real-time navigation using L1 signal is important

- Algorithm of enhancing navigation accuracy is developed (estimate of ionospheric delay and its change)

- Measurement accuracy < 10 m (95%, 3Drss).

Offline precise positioning:

- Dual (L1 and L2) off-line position determination < 1m

- ALOS-2 SAR frequency is overlapped with L2 signal

- Enhanced low-noise amplifier for GPS receiver with endurance against SAR signal is being developed

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Figure 3: GPS L2 signal and SAR frequency allocation used in ALOS and ALOS-2

Orbit

Sun-synchronous orbit: altitude = 628km, inclination = 97.9º
Local sun time : 12:00 ± 15 min
Revisit time: 14 days; number of cycles/day: 15 3/14
Orbit control: ≤ ± 500 m

Mission design life

5 years ( with a goal of 7 years)

Spacecraft mass

2120 kg

Spacecraft size (deployed)

9.9 m (x) x 16.5 m (y) x 3.7 m (z)

Spacecraft power generation

5.2 kW (EOL)

Downlink communications

X-band: 800 Mbit/s (16 QAM), 400/200 Mbit/s (QPSK)
Ka-band: 278 Mbit/s (QPSK) via the DRTS (Data Relay Technology Satellite) of JAXA

Launch

H-IIA launch vehicle from TNSC

Table 3: Overview of major spacecraft parameters

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Figure 4: Illustration of the deployed ALOS-2 spacecraft (image credit: JAXA) 11) 12)

Agile spacecraft: ALOS-2 has a body pointing function of ±30º in the roll axis. For the purpose of minimizing observation intervals, the requirement for attitude maneuvering is up to 2 minutes from the Earth pointing attitude to right- or left-looking, and the maneuvering from right- to left-looking (or from left- to right-looking) is up to 3 minutes, as shown in Figure 5.

To achieve a high agility of maximum attitude rate, 0.7º/s in roll axis, one Reaction Wheel (RW) is aligned with the roll axis, and the other four RWs are mutually skewed. This RW assembly was developed by the JAXA GCG (Guidance and Control Group), and establishes more than 0.9 Nm output torque and maximum momentum 40 Nms (at 3200 rpm). The numerical simulation results of attitude pointing are summarized in Table 4.

Case

No of RWs

Requirement

Result (seconds)

Nominal to Right- or Left

5
4 (case A)
4 (case B)

Up to 2 minutes
N/A
N/A

109
124
133

Right- to Left (or Left- to Right)

5
4 (case A)
4 (case B)

Up to 3 minutes
N/A
N/A

159
178
197

Table 4: Simulation results of attitude maneuvering. Case-A stands for the RW aligned roll axis failure, and Case-B for one of the skewed RWs failure

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Figure 5: Conceptual image of attitude pointing (image credit: JAXA)

RF communications: The requirement calls for a payload data transmission rate of 800 Mbit/s in X-band. With a traditional modulation scheme of QPSK, the transmission speed peaks at about 400 Mbit/s since the frequency bandwidth allocation is limited to 375 MHz by the ITU (International Telecommunication Union) regulations.

To solve this problem, the project designed and developed XMOD (Multi-mode High Speed Modulator), capable of achieving a (max) data rate of 800 Mbit/s. The XMOD device has the following features, not only to achieve the 800 Mbit/s data rate, but also to target strong international competitiveness as well as high system reliability. 13) 14) 15)

1) Use of a 16QAM 16 (Quadrature Amplitude Modulation) scheme to enable the 800 Mbit/s data rate, regarded as the world’s highest RF data rate, implemented as a single X-band carrier.

2) Adoption of the QPSK (Quadrature Phase Shift Keying) technique to comply with existing ground stations and improve robustness.

3) Implementation of a “Multi-mode/Multi-rate” design capable of supporting various satellite projects.

4) Introduction of some cutting-edge techniques for space and a high reliability design to improve the tolerance to space radiation effects.

5) Reduction of XMOD in size and mass by boosting double-sided mounting techniques and applying small lightweight parts.

• Baseband module: The baseband module consists of the following devices:

- WizardLink family of multi-Gigabit Serializer/Deserializers (Ser/Des)

- SRAM-based FPGA (Virtex-4QV)

- High-speed Digital-to-Analog Converter (DAC5675A-SP)

- antifuse-FPGA

- TCXO (Temperature Compensated Crystal Oscillator).

• RF module: The RF modules performs quadrature modulation on the I-channel and Q-channel signals generated by the baseband module, and then the modulated signals are amplified as desired.

• Load oscillator module: The local oscillator module generates the X-band local carrier frequency for the quadrature modulator

• DC/DC: The DC/DC converter, 30V-53V unregulated bus support, supplies regulated DC power to all the XMOD modules

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Figure 6: Block diagram of XMOD (image credit: JAXA)

Modulation scheme

16QAM without differential coding
QPSK with differential coding

Data rate

800, 400, or 200 Mbit/s

Frequency bandwidth

< 275 MHz: @ 800, or 400 Mbit/s (specification), 238.3 MHz (obtained result)
< 150 MHz: @ 200 Mbit/s (specification), 123.3 MHz @ 200 Mbit/s (obtained result)

Interface

Data: WizardLink
TLM/CMD: EIA-422
RF: Coaxial

Operating temperature

-20 to + 50ºC

Operating voltage

30 to 53 VDC

RF output power

+5 dBm ± 1 dB

Power consumption

≤ 25.5 W (specification), 19.02 W (obtained result)

Mass

≤ 3.36 kg, internal redundancy (specification), 2.64 kg (obtained result)

Size

277 mm x 106 mm x 186 mm (max), internal redundancy

Table 5: Specification of the XMOD device

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Figure 7: Photo of the XMOD EM (Engineering Model), image credit: JAXA

ALOS-2 has an improved data handling function which consists of a high-rate and huge-amount storage system, MDHS (Mission Data Handling System), and two types of high-rate transmission systems, DT (Direct Transmission) and DRC (Dual -Receive Channel), as shown in Figure 8. MDHS has a data storage volume of 130 GB. MDHS collects mission data from PALSAR-2 and health monitoring data from other components, and carries out digital processing such as adding of forward error correction code, file pointer management, and so on. It can be operated in various modes such as simultaneous record and replay, replay follow write, this scheme will contribute to flexible data handling operations.

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Figure 8: Illustration of the MDHS scheme regarding data transmission (top) and the data collection scheme (bottom), image credit: JAXA

The PALSAR-2 Electric Unit (ELU) consists of System Controller (SC), Data Processor (DP), as shown in Figure 12. SC receives command from satellite and sends telemetry to satellite. DP compresses mission data and sends it to MDHS.

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Figure 9: Photo of the ALOS-2 proto flight model at JAXA's Tsukuba Test Facility in April 2012 (image credit: JAXA) 16)

 

Launch: A launch of ALOS-2 is scheduled for 2014 on a H-IIA 202 vehicle from TNSC (Tanegashima Space Center), Japan. The launch provider is Mitsubishi. 17)

The secondary missions manifested on the ALOS-2 mission by JAXA are: 18)

• SPROUT (Space Research on Unique Technology), a nanosatellite of ~7 kg of Nihon University, Tokyo, Japan.

• Rising-2, a cooperative microsatellite (43 kg) project of Tohoku University (Sendai) and Hokkaido University, Sapporo, Japan.

• UNIFORM-1 (University International Formation Mission-1), of Wakahaya University, Wakayama, Japan.

• SOCRATES (Space Optical Communications Research Advanced Technology Satellite), a microsatellite (~ 50 kg) mission of NICT (National Institute of Information and Communications Technology), Koganei, Japan.

Orbit: Sun-synchronous near-circular sub-recurrent orbit, altitude = 628 km, inclination = 97.9º, period = 97.4 minutes, revisit time = 14 days, number of orbits/day = 15 3/14, LSDN (Local Sun time on Descending Node) = 12:00 hours ± 15 min.

To achieve higher coherence of interferometry, autonomous accurate orbit maneuvering (within 500 m orbital tube) and enhanced GPS receiver with endurance against L-band SAR signal were developed. The orbit control requirement to satisfy the geometric restriction which arises from the repeat-pass SAR interferometry, is illustrated in Figure 10. The reference Earth-fixed flight path is defined for a repeat cycle of its orbit. ALOS-2 satellite must fly within a tube-shaped corridor, the center of which is the reference flight path. The radius of the tube-shaped corridor, 500 m, is the tolerance of an orbit error. The orbit prediction, based on a detailed perturbation model, is introduced to generate the reference flight path. Using it as a reference of orbit maintenance, unnecessary orbital maneuvers can be avoided.

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Figure 10: Schematic view of the recurrent error with respect to reference orbit (image credit: JAXA)

As a result of numerical simulations, throughout the mission life, orbit maintenance within the 500 m tube was verified to be accomplished 99.7% of the time, which exceeds the requirement of 95%. An average period between orbit maneuvers was 4.9 days for in-plane maneuver and 176 days for out-of-plane maneuver. The minimum interval of in-plane maneuvers during active solar period was estimated 1.5 days. This means the autonomous orbit maintenance is essential for this mission in terms of operational aspects.

The on-board software of ALOS-2 can handle operations of orbit determination, maneuver prediction and planning, and maneuver executions for both drag-makeup maneuvers and inclination maneuvers. This feature of autonomy is expected to be great help for efficient ground operations of ALOS-2. 19)

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Figure 11: Flow chart of autonomous orbit control algorithm (image credit: JAXA)

 


 

Sensor complement: (PALSAR-2, CIRC, SPAISE2)

PALSAR-2 (Phased Array L-band Synthetic Aperture Radar-2):

PALSAR-2 is an L-band SAR instrument based on APAA (Active Phased Array Antenna) technology. The APAA of ALOS-2 allows not only conventional stripmap and ScanSAR, but also Spotlight mode observations with electronic beam steering in the range and azimuth directions. To cover wide area observations, PALSAR-2 offers the capability of wide incidence angle (8º - 70º) electronic beam steering as well as a means for left-side or right-side looking observations from the satellite ground track; the required spacecraft maneuver for this observation change can be accomplished in about 2 minutes from the nominal nadir look direction. 20) 21) 22) 23) 24) 25) 26) 27)

System design: The PALSAR-2 system is composed of two subsystems: the Antenna subsystem (ANT) and the Electric Unit (ELU).

ELU: The key components of the ELU are Exciter (EX), Transmitter (TX), Receiver (RX), Digital Processor (DP), and System controller (SC).

As for the RF signal, EX generates the pulse, selects two chirp signals (up / down and phase modulation) with selected center frequencies of either 1257.5, 1236.5 or 1278.5 MHz in order to avoid the interference into RNSS (Radio Navigation Satellite Service) using the L-band, and stretches the signal to the selected bandwidth at either 84 MHz, 42 MHz, 28 MHz or 14 MHz. The received radar echo signal is compressed by the BAQ (Block Adaptive Quantization) or the improved BAQ algorithm. The compression mode is selected from 4 bit, 2 bit, and no compression with or without the improved compression mode. Figure 12 shows the system diagram of PALSAR-2.

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Figure 12: System diagram of PALSAR-2 (image credit: JAXA)

Tables 6 and 7 summarize the specification and the PALSAR-2 system parameters.

Radar carrier center frequency

1236.5 / 1257.5 / 1278.5 MHz (selectable)

Band, wavelength

L-band, 22.9 cm

PRF (Pulse Repetition Frequency)

1500 to 3000 Hz

Range of bandwidths

14 / 28 / 42 / 84 MHz

Polarization

Single / dual / full / compact (compact polarization is an experimental mode)

Look direction

Right or left

Beam steering range

Elevation: ±30º; Azimuth: ±3.5º

Antenna width, length

2.9 m, 9.9 m

Incidence angle

8º to 70º

Range resolution, azimuth resolution

3 m / 6 m / 10 m / 100 m, 1 m / 3 m / 6 m / 10 m / 100 m

Peak power radiation

3.3 kW with 3/5 aperture in Spotlight and Ultra-fine mode
6.1 kW with full aperture in High-sensitive, Fine and ScanSAR mode

Mass of the SAR antenna

547.7 kg

Mass of the SAR ELU (Electric Unit)

109.1 kg (ELU controls all SAR signal generations and beam management)

Table 6: PALSAR-2 system parameters

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Figure 13: Schematic diagram of PALSAR-2 elements (image credit: MELCO)

Parameter \ Mode

Spotlight

Stripmap

ScanSAR

Ultra-fine

High-sensitive

Fine

Frequency

1257.5 MHz

1257.5 MHz or 1236.5 / 1278.5 MHz, selectable

Incidence angle

8º to 70º range

Bandwidth

84 MHz

84 MHz

42 MHz

28 MHz

14 MHz

Ground resolution

3 m (rg) x 1 m (az)

3 m

6 m

10 m

100 m

Swath

25 km (rg) x 25 km (az)

50 km

50 km
(FP:30 km)

70 km
(FP:30 km)

350 km
5 looks

Polarization

SP

SP/DP

SP/DP/FP/CP

SP/DP/FP/CP

SP/DP

Data rate

800 Mbit/s

800 Mbit/s

800 Mbit/s

400 Mbit/s

400 Mbit/s

NESZ

-24 dB

-24 dB

-28 dB

-26 dB

-26 dB

S/A: range

25 dB

25 dB

23 dB
FP:Co-pol: 23 dB
FP:X-pol: 15 dB

25 dB
FP:Co-pol: 20 dB
FP:X-pol: 10 dB

25 dB

S/A: azimuth

20 dB

25 dB

20 dB

23 dB

20 dB

Table 7: Summary of the PALSAR-2 specifications

The specification of Table 7 is defined for an incidence angle of 37º above the equator. The polarization acronyms are as follows:

- SP: Single Polarization

- DP: Dual Polarization

- FP: Full Polarization (quad)

- CP: Compact Polarization (experimental mode).

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Figure 14: Illustration of conventional PALSAR-2 polarization modes (same as implemented on PALSAR), image credit: JAXA

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Figure 15: Schematic view of new polarization mode CP of PALSAR-2 (image credit: JAXA)

The enhanced instrument performance of ALOS-2, enabled through the right-and-left looking observation capability, will greatly expand the FOR (Field of Regard) of the satellite, up to about 3 times (from 870 km on Daichi to 2,320 km), for event monitoring services.

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Figure 16: SAR antenna orientation shown in nadir (left) and in right-side looking direction (right), image credit: JAXA

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Figure 17: Schematic view of the spotlight mode configuration (image credit: JAXA)

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Figure 18: Observation modes of PALSAR-2 on ALOS-2 (image credit: JAXA)

L-band SAR antenna (ANT): ANT is an active phased array antenna which steers the beam in both elevation and azimuth direction (±30º in elevation and ±3.5º in azimuth). It has a size of 9.9 m (azimuth) x 2.9 m (elevation) and is composed of 5 electrical panels. The antenna consists of 1,080 radiation elements which are driven by 180 TRMs (Transmit and Receive Modules). The design enables to steer and form the beam in elevation and azimuth direction for several imaging modes: Stripmap, Spotlight and ScanSAR. The antenna nominal pointing is in the nadir direction and it is pointing 30º sideways when observing (either to the left side or to the right side of the ground track). 28)

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Figure 19: PALSAR-2 antenna configuration (image credit: JAXA, MELCO)

The SAR antenna is a DRC (Dual Receive Channel) system (Figure 20):

- The full aperture (5 panels) or partial aperture ( 3 of 5 panels, No 2, 3 and 4) of the antenna aperture may be used for signal transmission (Tx). The peak radiation power is 3,300 W with three panels for Spotlight mode and Ultra-Fine mode, or 5,100 W with full aperture for High sensitive mode, Fine mode and ScanSAR mode.

- In receive, the antenna is divided into two separate partitions in along-track. The signals of both receiving antenna partitions are being detected and recorded separately; this concept permits wide-swath acquisitions.

Wide swath coverage for polarimetric observation: ALOS-2 SAR utilizes a type of polarimetry as single, dual and quad (full-pol.) as a standard mode, and compact (or hybrid) as an experimental mode. Full-pol. mode on ALOS-2 is a system which realizes transmitted polarization by replacing horizontal / vertical by turns with an interval of PRI (Pulse Repetition Interval). Therefore, when selecting full-pol. mode, the PRF of full-pol. is doubled as that of single/dual-pol., which means that the available swath in full-pol. is drastically restricted. In the case of conventional mode (“fine mode”: resolution of 10 m), the range coverage of full-pol. becomes 30 km, which is less than a half of single/dual-pol. (70 km).

The wider coverage of full-pol. is also achieved by using the DRC method. Since the full-pol. mode requires two receive channels for H and V polarization synchronously, utilization of the DRC mode for full-pol. requires double channels compared with the conventional full-pol. Mode, namely quad- receive channel. For the purpose of wide coverage and observation capability in higher incidence angles for full-pol. mode, ALOS-2 can execute the DRC and full-pol. observation simultaneously, in “high sensitive mode” (HS mode). The swath of the full-pol. mode in HS mode is 40-50 km with a resolution of down to 6 m in an off-nadir angle of 18-35º.

Another approach for wider coverage of polarimetric observation is a new technique of “compact (or hybrid) polarimetry”. Since one T/R module of ALOS-2 has two identical amplifiers for H and V polarimetry, RF signals of H/V polarization with an optimum phase offset is generated from each antenna element, and resultantly circular or oriented at 45º is transmitted. Although polarimetric information of compact pol. is not enough compared to that of full-pol., the swath of compact polarimetry is wider than that of full-pol., and is the same as that of single/dual polarimetry mode.

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Figure 20: Single transmit/ antenna system (left) and difference of PRF (right), image credit: JAXA)

Legend to Table 7: Performance values @ incidence angle of 37º; CP: Compact Polarimetry (Linear+circular), FP: Full Polarimetry (HH+HV+VV+VH).

TRMs (Transmit Receive Modules):

The TRMs enable to select the polarization of single (HH/VV/HV), dual (HH + HV=VV + VH), quad (HH + HV + VV + VH), and compact polarimetry (Tx: oriented 45º or circular, Rx: H or V) by transmitting H and V polarization simultaneously. In L-band, the propagation disturbances and especially the ionospheric effects like Faraday rotation and phase delay have to be considered and if possible to be corrected. The quad polarimetry mode uses the alternative pulses of H and V which increase the PRF and result in a narrow swath.

The SAR instrument features a CP (Compact Polarimetry) mode as an experimental mode which can transmit the H and V polarization simultaneously resulting in a linear polarization oriented at 45º or circular (LHCP or RHCP), selectable by command.

Compared to the TRMs used in PALSAR, establishing higher power amplification in the TRMs of PALSAR-2 through a wider operational frequency range is necessary, as summarized in Table 8. An output power of 34 W is generated at the PALSAR-2 TRM output port with a low-loss and high-power solid state power amplifier using a GaN (Gallium Nitride) HEMT (High Electron Mobility Transistor). - The performance of a HPA (High-Power Amplifier) using GaN HEMT is tested by a breadboard model and confirmed to meet the requirement. Figure 21 shows the outside view of the HPA and the inside view of the BBM (Breadboard Model).

Item or parameter

ALOS / PALSAR

ALOS-2 / PALSAR-2

HPA (High Power Amplifier)

Si BJT (Bipolar Junction Transistor)

GaN HEMT

Tx power

25 W

34 W

Operational frequency range

28 MHz

85 MHz

Number of TRMs

80

180

Efficiency

25%

35%

Noise figure

2.9 dB

2.9 dB

TRM size

203 mm x 117 mm x 23.5 mm

200 mm x 110 mm x 14.6 mm

TRM mass

675 g

400 g

Table 8: Performance comparison of the PALSAR and PALSAR-2 instrumentation

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Figure 21: Outside view of the HPA (left) and its inside BBM (image credit: JAXA)

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Figure 22: TRM architecture of the L-band SAR instrument (image credit: JAXA)

The image quality with chirp modulation: To distinguish each pulse, PALSAR-2 implements the chirp modulation.

- Up/down and phase modulation in each pulse

- PALSAR is only Down chirp.

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Figure 23: Schematic view of up/down chirp modulation in PALSAR-2 (image credit: JAXA)

Chirp signal management: In order to reduce range ambiguities, the ALOS-2 PALSAR-2 system has an ability to send up/down chirp signals alternatively.

Data compression algorithm: The maximum data rate (800 Mbit/s) of PALSAR-2 is much higher than that of PALSAR (240 Mbit/s max) due to the improved performances of the SAR instrument providing higher resolution data and a wide swath. To realize the frequent observations and data acquisitions, it is necessary to develop a new data compression technique on board with a highly efficient and a low error rate.

The data compression technique for PALSAR-2 is BAQ (Block Adaptive Quantization) or an improved BAQ version, namely DS-BAQ (Down-Sampling BAQ selectable. The BAQ technique, used for other SAR satellite like TerraSAR-X and COSMO-SkyMed, is the conventional technique. DS-BAQ is the new data compression technique. At conventional radar system, the A/D sampling frequency is wider than the transmitting bandwidth to decrease the ambiguity level. In DS-BAQ, the differential bandwidth between transmitting bandwidth and A/D sampling frequency is cut before BAQ processing (Ref. 20).

Figures 24 and 25 show the simulation results amplitude and phase error analysis, respectively. According to these Figures, DS-BAQ is able to decrease the error more than the BAQ technique in same compression ratio.

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Figure 24: The result of amplitude error analysis between BAQ and DS-BAQ (image credit: JAXA)

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Figure 25: The result of phase error analysis between BAQ and DS-BAQ (image credit: JAXA)

The error analysis result based on a simulation comparing the two compression algorithms under several polarization modes shows that, in the same data compression ratio, down-sampling BAQ satisfies the lower errors of both amplitude and phase better than BAQ. The compression ratio was evaluated on the BBM (Breadboard Model) of the data compression module, confirming also its processing speed.

The implementation of the data compression algorithm is such that a compression mode is onboard selectable between the DS-BAQ, the original BAQ, and direct output without data compression.

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Figure 26: Schematic view of the down-sampling BAC algorithm (image credit: JAXA)

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Figure 27: Overview of ALOS-2 implementation phases (image credit: JAXA, Ref. 4)

 

CIRC (Compact Infrared Camera):

CIRC is an infrared demonstration instrument of JAXA with state-of-the-art COTS (Commercial-off-the-Shelf) technology developed at MELCO (Mitsubishi Electric Corporation). The camera is equipped with an uncooled infrared array detector (microbolometer). The main objective of CIRC is to provide infrared imagery for wildfire detection. CIRC is mounted onto the spacecraft pointing to the right of the flight path at an off-nadir angle of 30º (Figure 28). CIRC is a small size instrument with a mass of ~ 3 kg. 29) 30) 31)

Wildfires are one of the major and chronic disasters affecting many countries in the Asia-Pacific region, and indications are that this will get worse with global warming and climate change. Wildfire detection is one of the main goals in the Sentinel Asia project and to share this information in near real-time across the Asia-Pacific region.

The goal is to realize frequent observations by loading CIRC devices in as many satellites as possible by taking advantage of there small size, low weight, and low power consumption. Other mission targets of the CIRC are volcanoes or heat island phenomena in a city.

JAXA developed two CIRC instruments, one will be launched aboard the ALOS-2 spacecraft; the second one will be launched in 2014 onboard CALET (CALorimetric Electron Telescope), which will be installed in the JEM -EF (Japanese Experiment Module) on the ISS (International Space Station) in 2014.

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Figure 28: Schematic view of ALOS-2 and the mounting location of CIRC (image credit: JAXA)

The baseline specifications of the CIRC instrument are listed in Table 9. The detector has a large format (640 x 480 pixels) to capture a wide field of view. Spatial resolution is an important factor for wildfire detection; it is 200 m from an altitude of 600 km (ALOS-2) and 130 m from an altitude of 400 km (CALET). Eliminating the cooling system reduces the size (110 mm x 180 mm x 230 mm) and the consumption power (<20 W) for CIRC.

Instrument mass, size

3 kg, 180 mm x 110 mm x 230 mm

Spectral range

8-12 µm

Spatial resolution

< 200 m @ 600 km altitude (corresponding to < 0.33 mrad)

Detector, Number of pixels

Uncooled infrared detector, 640 x 480

FOV (Field of View)

12º x 9º (128 km x 96 km)

Exposure time

33 ms

Dynamic range

180 K - 400 K

NEDT (Noise Equivalent Differential Temperature)

0.2 K@300 K

Table 9: Baseline specifications of CIRC

Microbolometer: The project adopted microbolometers as an infrared FPA (Focal Plane Array) of the CIRC device. Microbolometers are based on the principle of detecting infrared energy as minute changes of the IR absorber temperature when infrared radiation id detected. Their advantage is that they do not require a cooling system, such as a mechanical cooler. Sensors without a detector cooling system can be made to have a small size, low mass and low power consumption.

CIRC features a SOI (Silicon-on-Insulator) diode uncooled IR FPA developed by MELCO. Its pixel size is 25 µm square. The SOI diode uncooled IR FPA uses a single-crystal silicon pn-junction diode as a temperature sensor. The single-crystal sensor based on silicon LSI (Large-Scale Integration) technology gives it a low-noise characteristic. The NEDT (Noise Equivalent Differential Temperature) is 40 mK with f/1 optics. The drive and readout circuits are almost the same as those of the commercial IR camera. For the space application, the project performed a radiation damage test, and a screening of commercial devices.

Athermal optics: CIRC employs f/1.2 refractive optics with a focal length of 78 mm. The orbital temperature change of the optics will cause a defocus because the refractive indices of the lens materials are highly dependent on temperature. To compensate for this defocus, the project may employ a focus mechanism or a heater to keep the optics’ temperature constant. However, such mechanisms increase the instrument resources. An athermal optics can compensate for the defocus due to the temperature change without such mechanisms. CIRC can operate in a temperature range from -15º to 50ºC while maintaining its performance. Figure shows the optical design of CIRC. The athermal optics of the CIRC compensates for the defocus by a combination of different lens materials and diffractive lenses. The CIRC optics uses a germanium and a chalcogenide glass (GASIR). The MTF and athermal characteristics of the CIRC device have been verified in laboratory tests.

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Figure 29: Block diagram of the CIRC instrument (image credit: JAXA)

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Figure 30: Optical design of CIRC (image credit: JAXA)

Shutterless system: The project eliminated the mechanical shutter from the CIRC for downsizing reasons. A mechanical shutter is more commonly used as a calibration source. Therefore, a way was devised to achieve temperature calibration and straylight correction from the inside the CIRC device. The project obtained images of various temperature blackbody with different CIRC temperatures in order to perform stray-light correction by temperature of the CIRC device.

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Figure 31: Photo of the CIRC PFM (Proto Flight Model) for the ALOS-2 mission (image credit: JAXA)

Airborne observations with the CIRC GTM (Ground Test Model): The project carried out airborne observations with the GTM) of CIRC. The model was constructed for establishing a way to perform ground calibration and carry out field observations before fabrication of the PFM.

Observational flight were carried out on March, 22 and 28, 2012. The aircraft was a “Cessna172 Sky hawk”. The observation area was Tsukuba City, Tsuchiura City in the south of Ibaraki Prefecture, and Narita City in Chiba Prefecture, all in Japan. The flight altitude ranged from 300 m to 750 m. The GSD (Ground Sample Distance) at these altitudes ranged from 10 cm to 25 cm. The flights confirmed that the performance of the CIRC is as expected and sufficient for launch on ALOS-2.

 

SPAISE2 (SPace based Automatic Identification SystemExperiment 2)

SPAISE2 is a second generation AIS instrument of JAXA featuring: 32)

• A 4 channel AIS signal reception capability (simultaneously 2 channels)

• Digital sampling and ground signal processing archtecture.

Main sensor

Cross dipole antenna

Channel frequencies

AIS #1: 161.975 MHz, AIS #2: 162.025 MHz
AIS #3: 156.775 MHz, AIS #4: 156.825 MHz

Minimum receiver sensitivity:

-112 dBm

Sampling rate

76.8 kHz

Instrument mass, size

7 kg x 2, 1050 mm x 800 mm x 800 mm

Table 10: Parameters of the SPAISE2 instrument

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Figure 32: Schematic view of the AIS system (image credit: JAXA)

 


 

Ground system:

An overview of the CIRC ground system is shown in Figure 33. The ACGS (ALOS-2/CIRC Ground System) consists of three components: a CIRC observation planning system, a data processing system, and a data archive system.

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Figure 33: Overview of ACGS (ALOS-2/CIRC Ground System), image credit: JAXA (Ref. 31)

Generally, observation plans are constructed in response to requests from users by the CIRC observation planning system, utilizing satellite operation information. After observation, the data processing system obtains Level-0 data from the ALOS-2 ground system and performs geometric and radiometric correction to produce Level-1 data. Then, the detection of wildfires, for example, is conducted to produce Level-2 data. Subsequently, the Level-1 and Level-2 data are released online through the data archive system, making them available to the users.


ALOS-2 ground system:

The ALOS-2 ground system is composed of the Satellite Control and Mission Operation System and the Information System, located at the JAXA Tsukuba Space Center. The Information System will have the functions of data processing, archiving, cataloging and user service functions for ALOS and ALOS-2.

For the global observation, the ALOS-2 ground system will utilize data relay communication and very fast X-band direct downlink (Figure 34). The observation data of PALSAR-2 will be once recorded on the solid state recorder onboard ALOS-2 and reproduced at 278 Mbit/s for Ka-band and at 800/400/200 Mbit/s via X-band.

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Figure 34: The ALOS-2 ground system and tracking network (image credit: JAXA, Ref. 27)

When a disaster occurs, command will be ready within 60 minutes for emergency observation. After the Ground station receives the observation data, the emergency product will be ready within 60 minutes. Figure 35 shows the example of quick tasking and processing in natural disaster occurrence.

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Figure 35: Example of quick tasking and processing in a natural disaster event (image credit: JAXA)

 

ALOS-2 science capabilities include global environmental monitoring using the time-series PALSAR-2. The research target also covers biospheric, cryospheric, and coastal ocean research as well as disaster mitigation. Table 11 summarizes these research products. 33)

Category

Product

Contents

Biosphere

25-m spaced annual global mosaics (using orthorectified slope corrected SAR)

Produced using the DEM (DSM). Global browse, 500 m global browse mosaic, global 3 m resolution mosaic, and ScanSAR ortho-slope corrected path for quasi-deforestation monitoring of pantropical regions, i.e., Brazil, Indonesia, are also included.

Forest and wetland monitoring

Generate global forest maps, i.e., forest/non-forest or forest maps with more classes and also wetland change maps.

Biomass estimation

Experimentally creates a biomass map using the gamma-naught-biomass, biomass-lidar, and biomass-classification methods

Land use classification

Creates the LULUCF map at several test sites

Agriculture

Crop monitoring using the SAR

Geosphere

Deformation

DinSAR and time-series analysis, surface deformations caused by earthquakes, volcanic activities, subsidence, and landslides, such as quick deformation patterns of earthquakes and annual monitoring of the Japan islands

Soil moisture

Soil moisture will be generated from PolSAR data.

DEM (Digital Elevation Model)

To be generated by stacking, correction of topographic and ionospheric error is an issue

Cryosphere

Sea ice identification

Creates monthly ScanSAR mosaics for both polar regions and temporal changes for glacier movement.

Marine

Wind speed distribution

LMOD (L-band modulation function) developed for PALSAR will be improved by using the dual-polarized PALSAR-2.

Disaster

Sensitivity research for disasters

Time-series SAR data (amplitude), PolSAR and InSAR (coherence) will be combined to detect the best combination for each disaster. Flooding in urban areas is one target.

Fire scar

Using time-differentiation of the slope-corrected HV, fire risk areas will be detected.

Table 11: List of geophysical products


1) Shinichi Suzuki, Yuji Osawa, Yasushi Hatooka, Tomohiro Watanabe, “The Post-ALOS program,” Proceedings of the 27th ISTS (International Symposium on Space Technology and Science) , Tsukuba, Japan, July 5-12, 2009, paper: 2009-n-02

2) Masanobu Shimada, “Advanced Land Observation Satellite (ALOS) and its follow-on satellite, ALOS-2,” Proceedings of the 4th International POLinSAR 2009 Workshop, Jan. 26-30, 2009, ESA/ESRIN, Frascati, Italy, URL: http://earth.esa.int/workshops/polinsar2009/participants/535/pres_8_Shimada_535.pdf

3) Yukihiro Kankaku, Yuji Osawa, Shinichi Suzuki, Tomohiro Watanabe, “The Overview of the L-band SAR Onboard ALOS-2,” Proceedings of PIERS (Progress In Electromagnetics Research Symposium), Moscow, Russia, August 18-21, 2009, URL: http://piers.org/piersproceedings/download.php?file=cGllcnMyMDA5TW9zY293fDNQMV8wNzM1LnBkZnwwOTAyMTgyMTAzMTU=

4) Yoshihisa Arikawa, Yuji Osawa, Yasushi Hatooka, Shinichi Suzuki, Yukihiro Kankaku, “Development Status of Japanese Advanced Land Observing Satellite-2,” Proceedings of the SPIE Remote Sensing Conference, Toulouse, France, Vol. 7826, Sept. 20-23, 2010, 'Sensors, Systems, and Next-Generation Satellites XIV,' edited by Roland Meynart, Steven P. Neeck, Haruhisa Shimoda, doi: 10.1117/12.866675

5) http://www.jaxa.jp/projects/sat/alos2/index_e.html

6) http://www.jaxa.jp/pr/brochure/pdf/04/sat29.pdf

7) Yukihiro Kankaku, Yuji. Osawa, Yasushi Hatooka, Shinichi Suzuki, “Overview of Advanced Land Observing Satellite-2 (ALOS-2)” Proceedings of ISPRS Technical Commission VIII Symposium, Aug. 9-12, 2010, Kyoto, Japan

8) Masanobu Shimada, “Advanced Land Observation satellite (ALOS) and ALOS-2,” Leiden, The Netherlands, May 17, 2011, URL: http://www.agentschapnl.nl/sites/default/files/bijlagen/2011-05_TWA_NSO%20Seminar_JAXA_Shimada_file_alos12.pdf

9) Takao Akutsu, “JAXA’s Contributions to the Climate Change Monitoring,” June 7, 2011, URL: http://www.oosa.unvienna.org/pdf/pres/copuos2011/tech-20.pdf

10) Yoshihisa Arikawa, Tomoya Niwa, Hideki Saruwatari, Yasushi Hatooka, Yuji Osawa, “ALOS-2 System Design and PFM Current Status,” Proceedings of the 29th ISTS (International Symposium on Space Technology and Science), Nagoya-Aichi, Japan, June 2-8, 2013, paper: 2013-n-41

11) Masanobu Shimada, Yukihiro Kankaku, Manabu Watanabe, and Takeshi Motooka, “Current Status of the ALOS-2 / PALSAR-2 and the CALVAL Program,” CEOS SAR CALVAL Workshop at ASF (Alaska Flight Facility), Fairbanks, AK, Nov. 7-9, 2011, URL: http://www.asf.alaska.edu/sites/all/files/documents/2011-ceos-workshop/Current%20Status%20of%20ALOS-2,%20M.Shimada.pdf

12) Shinichi Suzuki, Yuji Osawa, Yasushi Hatooka, Yukihiro Kankaku, Tomohiro Watanabe, “Overview of Japan’s advanced land observing satellite-2 mission,” Proceedings of SPIE, 'Sensors, Systems, and Next-Generation Satellites XIII,' edited by Roland Meynart, Steven P. Neeck, Haruhisa Shimoda, SPIE Vol. 7474, 2009, 74740Q

13) Kazuya Inaoka, Masashi Shirakura Terumi Sunaga, Masaaki Shimada, Noboru Takata, “Development of an X-band Multi-mode High speed Modulator -Design and Development test Results of Engineering Model,” Proceedings of the 28th ISTS (International Symposium on Space Technology and Science), Okinawa, Japan, June 5-12, 2011, paper: 2011-j-10

14) Shinichi Suzuki , Yukihiro Kankaku,; Hiroko Imai, Yuji Osawa, “Overview of ALOS-2 and ALOS-3", Proceedings of SPIE,' Earth Observing Missions and Sensors: Development, Implementation, and Characterization II,' Vol. 8528, Kyoto, Japan, October 29, 2012, 852811 (November 9, 2012); doi:10.1117/12.979184

15) Awano Johta, Nakadai Mitsuhiro, Yajima Masanobu, “Study of TT&C Communication System for Next Generation JAXA Satellite,”Proceedings of TTC 2013, 6th International Workshop on Tracking Telemetry and Command Systems for Space Applications, Darmstadt, Germany, Sept. 10-13, 2013

16) Shinichi Suzuki, Yukihiro Kankaku, Yuji Osawa, “ALOS-2 development status and draft acquisition strategy,” Proceedings of SPIE Remote Sensing 2012, 'Sensors, Systems, and Next-Generation Satellites,' Edinburgh, Scotland, UK, Vols. 8531-8539, Sept. 24-27, 2012, paper: 8533-9

17) Naoki Okumura, “Launch Schedule in 2014 : ALOS-2,” JAXA, The 20th Session of the APRSAF (Asia-Pacific Regional Space Agency Forum), Hanoi, Vietnam, December 3-6, 2013, URL: http://www.aprsaf.org/annual_meetings/aprsaf20/pdf/program/day3/D3_1120_2_Japan.pdf

18) Toshinori Kuwahara, Kazaya Yoshida, Yuji Sakamoto, Yoshihiro Tomioka, Kazifumi Fukuda, Nobuo Sugimura, Junichi Kurihara, Yukihoro Takahashi, “Space Plug and Play Compatible Earth Observation Payload Instruments,” Proceedings of the 9th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 8-12, 2013, Paper: IAA-B9-1502, URL: http://media.dlr.de:8080/erez4/erez?cmd=get&src=os/IAA/archive9/Presentations/IAA-B9-1502.pdf

19) Toru Yamamoto, Isao Kawano, Takanori Iwata, Yoshihisa Arikawa, Hiroyuki Itoh, Masayuki Yamamoto, Ken Nakajima, “Autonomous Precision Orbit Control of ALOS-2 for Repeat-Pass SAR Interferometry,” Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium), Melbourne, Australia, July 21-26, 2013

20) Yukihiro Kankaku, Yuji Osawa, Shinichi Suzuki, “The current status and brief results of Engineering Model for PALSAR-2 onboard ALOS-2,” Proceedings of the 28th ISTS (International Symposium on Space Technology and Science), Okinawa, Japan, June 5-12, 2011, paper: 2011-n-18

21) Yukihiro Kankaku, Yuji Osawa, Yasushi Hatooka, Shinichi Suzuki, “The overview of the L-band SAR onboard ALOS-2,” ISPRS Technical Commission VIII Symposium in Kyoto, Japan, August 10, 2010

22) Y. Okada, T. Hamasaki , M. Tsuji, M. Iwamoto, K. Hariu, Y. Kankaku, S. Suzuki, Y. Osawa, “Hardware Performance of L-band SAR System Onboard ALOS-2,” Proceedings of IGARSS (International Geoscience and Remote Sensing Symposium), Vancouver, Canada, July 24-29, 2011

23) Hiroyuki Inahata, Hiroshi Koyama, “Evolution of SAR Satellite for Agriculture Applications,” Proceedings of APRSAF-18 (18th Session of the Asia-Pacific Regional Space Agency Forum), Singapore, Dec. 6-9, 2011, URL: http://www.aprsaf.org/data/aprsaf18_data/eo/D2-15_APRSAF18_MELCOforWeb.pdf

24) Osamu Ochiai, Masanobu Shimada, and the JAXA BOS-2 group, “ALOS-2 status and Acquisition Strategy Update,” CEOS SDCG 2, USGS HQ, VA, USA, Sept 13-14, 2012, URL: http://www.ceos.org/attachments/SDCG-2/Day01_008_SDCG2_1_8_JAXA_ALOS-2.pptx

25) Yukihiro Kankaku, Yuji Osawa, Shinichi Suzuki, “The Developmental Status of PALSAR-2 onboard ALOS-2,” Proceedings of the 29th ISTS (International Symposium on Space Technology and Science), Nagoya-Aichi, Japan, June 2-8, 2013, paper: 2013-n-42

26) Yukihiro Kankaku, Shinichi Suzuki, Yuji Osawa, “ALOS-2 Mission and Development Status,” Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium), Melbourne, Australia, July 21-26, 2013

27) Shinichi Suzuki, Yukihiro Kankaku, Masanobu Shimada, “ALOS-2 Acquisition Strategy,” Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium), Melbourne, Australia, July 21-26, 2013

28) Y.Okada, S. Nakamura, K. Iribe, Y. Yokota, M. Tsuji, M.Tsuchida, K.Hariu, Y.Kankaku, S.Suzuki, Y.Osawa, M.Shimada, “System design of wide swath, high resolution, full polarimetric L-band SAR onboard ALOS-2,” Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium), Melbourne, Australia, July 21-26, 2013

29) Masataka Naitoh, Haruyoshi Katayama, Masatomo Harada, Ryoko Nakamura, Eri Kato, Yoshio Tange, Ryota Sato , Koji Nakau, “Development of the Compact Infrared Camera (CIRC) for Earth Observation,” Proceedings of the ICSO (International Conference on Space Optics), Ajaccio, Corse, France, Oct. 9-12, 2012, paper, ICSO-066, URL: http://congrex.nl/icso/2012/papers/FP_ICSO-066.pdf

30) Masatomo Harada, Haruyoshi Katayama, Masataka Naitoh, Masahiro Suganuma, Ryoko Nakamura, Yoshio Tange, Takao Sato, “Development of the Compact Infrared Camera (CIRC) for Earth Observation,” ICSO 2010 (International Conference on Space Optics), Rhodes Island, Greece, Oct. 4-8, 2010, URL: http://congrex.nl/icso/Papers/TPosters/10_Harada.pdf

31) Masataka Naitoh, Haruyoshi Katayama, Masatomo Harada, Ryoko Nakamura, Eri Kato, Yoshio Tange, Ryota Sato, Koji Nakau, “Compact Infrared Camera (CIRC) for Earth Observation,” Proceedings of the 29th ISTS (International Symposium on Space Technology and Science), Nagoya-Aichi, Japan, June 2-8, 2013, paper: 2013-n-29

32) Keizo Nakagawa, “R&D of JAXA Satellite Application Mission,” MEWS26 (26th Microelectronics Workshop), Tsukuba, Japan, Oct. 24-25, 2013, URL: https://eeepitnl.tksc.jaxa.jp/mews/jp/26th/data/1_1.pdf

33) Masanobu Shimada, “ALOS-2 Science Program,” Proceedings of IGARSS (IEEE International Geoscience and Remote Sensing Symposium), Melbourne, Australia, July 21-26, 2013


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.