The Advanced land observing satellite-4 (ALOS-4) is a follow-on mission of ALOS-2 "Daichi-2" and which will be launched in Japanese Fiscal Year (JFY) 2023 by H3 launch vehicle. ALOS-4 carries the-state-of-the-art L-band SAR (PALSAR-3, Phase Array type L-band Synthetic Aperture Radar-3) to respond higher user requirements than that of ALOS-2. The observation swath is 200 km which is four times wider than that of PALSAR-2 onboard ALOS-2, which is achieved by digital beam forming (DBF) and phase spoiling techniques. ALOS-4 also carries the SPace based Automatic Identification System for ships Experiment (SPAISE3), which is successor of SPAISE2 onboard ALOS-2. The features of SPAISE3 are the antenna composed by eight elements, and Automatic Identification System for ships (AIS) signal processing which adopts ground based DBF system as one of methods to eliminate the AIS signal collision in ship crowded area.

This paper describes the current status of Advanced Land Observing Satellite-4 (ALOS-4) and its two instruments: Phased Array-type L-band Synthetic Aperture Radar-3 (PALSAR-3) and SPace based Automatic Identification System for ships Experiment (SPAISE3). PALSAR-3 is the successor of PALSAR-2 which was boarded on ALOS-2(Advanced Land Observing Satellite-2) and has 3m resolution and 200km observation swath by using Digital Beam Forming (DBF) technology. SPAISE3 is a high-performance satellite AIS receiver and the successor of SPAISE2 boarded on ALOS-2. SPAISE3 has eight antennas and adopts ground-based 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 area will be improved compared to SPAISE2.

Phased-Array L-band Synthetic Aperture Radar-3 (PALSAR-3) onboard Advanced Land Observing Satellite-4 (ALOS-4) is a spaceborne L-band Synthetic Aperture Radar (SAR) system, capable of high resolution and wide swath observation. ALOS-4 utilizes digital beamforming (DBF) and multiple transmit channel (MTC) techniques to overcome swath width and azimuth resolution trade-off relationship. In addition, ALOS-4 signal data requires signal processing, such as azimuth multi-beamforming and sub-band phase correction, before conventional SAR image processing can be implemented. In this paper, newly developed signal pro-cessing algorithm for ALOS-4 and results of the validation of the algorithm using flight model data will be discussed.

Japan is a geographically active region which experiences natural disasters such as earthquakes, floods, and volcanic activities. Thus, Japan has developed advanced world leading disaster prevention technology utilizing space applications. Especially, the Japanese ALOS series satellites target for prevention and mitigation of natural disasters. The Advanced Land Observing Satellite-4 (ALOS-4) is a successor of ALOS-2. Key components such as Phased Array type L-band Synthetic Aperture Radar (PALSAR-3) and Space based Automatic Identification System Experiment (SPAISE3) are based on improved designs from PALSAR-2 and SPAISE2 of ALOS-2. The missions of ALOS-2/4 are to observe the change of geographical conditions regarding before and during natural disasters along with monitoring signals sent from ships on the ocean. PALSAR-3 enables observation throughout the day and night by microwave radar technologies. The L-band SAR can observe the ground through leaves and branches by using long wavelengths, therefore it enables close observation of changes on ground surface. SPAISE3 serves an important role to detect AIS signals from ocean vessels specifically to identify congested oceanic traffic areas of ships. These components are introduced in this paper. ALOS-4 is currently in the integration phase for each completed component with testing of the integrated satellite system having commenced.

Phased Array type L-band Synthetic Aperture Ra-dar-3 (PALSAR-3) onboard Advanced Land Observing Satellite-4 (ALOS-4) is a spaceborne L-band Synthetic Aperture Radar (SAR) system. ALOS-4 is capable of achieving high resolution (3m) with 4 times wider swath width compared to ALOS-2. Hardware design and implementation of SAR techniques, namely digital beamforming (DBF) in the elevation direction and multiple transmit channel (MTC), enables high-resolution wide-swath observation. Data acquired by ALOS-4 requires specific signal processing techniques such as azimuth multi-beamforming and sub-band phase correction for high resolution wide swath image production. The flight model of PALSAR-3 system has been integrated and final test evaluation is expected to finish by the middle of 2021.

Japan Aerospace Exploration Agency (JAXA) is currently developing the ALOS-2 follow-on L-band Synthetic Aperture Radar (SAR) mission, namely Advanced Land Observing Satellite-4 (ALOS-4). ALOS-4 aims to enhance the use of ALOS-2, such as improving disaster risk detection capability, by increasing swath width and temporal resolution with new technologies. JAXA is currently developing a flight model and is also considering ALOS-4 observation plan for the launch in JFY2021. In this presentation, we will report the outline of ALOS-4 L-band SAR observation, the observation plan, and the latest development status.

ALOS-4 succeeds the concept of ALOS-2 and hence the system design of ALOS-4 satellite basically follows on that of ALOS-2, except for improvements in mission performance. The swath width is drastically improved in ALOS-4 by applying DBF (Digital Beam Forming) technique. DBFU (DBF Unit) is newly designed for ALOS-4 SAR sensor. In ALOS-4 system, receiving channels are divided into 6 sub-arrays in elevation, and received signals are converted into digital data independently by ADCs for DBF processing. In conventional radar systems, high frequency signals, such as L-band signals, are down-converted by local and COHO (COHerent Oscillator) signals by mixers in RF front-end to make sampling frequency lower. In DBF systems composed of multiple receiving channels, the number of local and COHO signals must be increased to match the number of channels. To overcome this issue, under sampling technique is applied. This technique allows band-pass filtered signals to be sampled at a rate below the Nyquist frequency of the target signal. With under sampling, COHO signals can be eliminated, so downsizing of H/W scale of DBFU can be achieved. This paper describes the under sampling system design result for ALOS-4.

ALOS-4 succeeds the concepts of ALOS-2[1] except for improvements in mission performance. ALOS-4 utilizes digital beam forming on receive to improve observation swathwidth [2]. PALSAR-3 on-board ALOS-4 has an onboard digital beam forming processor in order to increase the swathwidth of the 3m resolution Stripmap mode to 200 km. Transmit signal with a wide beam-width in the elevation direction is generated in order to cover the wider swathwidth. The reflected signal from the ground is received by several independent receive channels, which are processed in order to form several antenna patterns. There is an inverse relationship between the beam-width and the antenna length. It is necessary that the antenna length should be short in order to obtain the wide beam-width.One way of downsizing the antenna length is to turn off the Transmit/Receive Modules (TRMs), which are connected to each antenna element of Active Phased Array Antenna (APAA). However, this will cause the NESZ to get worse due to the reduction of transmit power.The phase spoiling technique is utilized to solve this problem. Even with a long antenna, wide beam-width can be obtained with this technique. In this paper, the principle of the phase spoiling technique with various phase distributions and the simulation results applied to APAA installed on ALOS-4 are presented.

This paper describes the mission of Advanced Land Observing Satellite-4 (ALOS-4) currently under development by JAXA and the characteristics of L-band SAR system, namely Phased Array-type L-band Synthetic Aperture Radar-3 (PALSAR-3). In particular, the observation modes, performance specifications, and standard products of PALSAR-3 are shown focusing on the changes from ALOS-2.

ALOS-4 succeeds the concepts of ALOS-2 and hence system design of ALOS-4 satellite basically follows that of ALOS-2, except for improvements in mission performance. In order to use data sets of both ALOS-2 and ALOS-4 for monitoring long term (more than 10 years) changes, the orbit of ALOS-4 is identical to that of ALOS-2. Even though ALOS-4 and ALOS-2 share the same orbit, revisit time of ALOS-4 can be shortened by increasing the swath width. Therefore ALOS-4 utilizes digital beam forming on receive to improve observation swath width. PALSAR-3, the successor of PALSAR-2 onboard ALOS-2, is now designed as an active phased array antenna with on-board digital beam forming processor in order to increase the swath width of the 3m resolution Stripmap mode to 200 km. Transmit signal with a broad beam-width in the elevation direction is generated in order to cover the wider swath. The reflected signal from the ground is received by several independent receive channels and processed to form several antenna patterns. To achieve approximately equivalent NESZ as ALOS-2, the size of PALSAR-3 antenna is designed to be 1.2 times larger than that of PALSAR-2/ALOS-2.ALOS-4 has successfully passed its Preliminary Design Review and engineering model is currently under development. This paper describes the radar instrument design of ALOS-4.

The Advanced Land Observing Satellite-2 (ALOS-2) was successfully launched on 24th May, 2014, carrying the state-of-the-art L-band synthetic aperture radar, PALSAR-2. The satellite was developed and is stably operated by Japan Aerospace Exploration Agency (JAXA). As of January 2018, the satellite bus system and PALSAR-2 system are working very well. The PALSAR-2 data were acquired based on a systematic observation strategy to achieve consistent data acquisitions in time and space. JAXA also respond to the emergency observation requests for disasters. The observation data are distributed to both scientific and commercial users and utilized for disaster monitoring, environmental monitoring, and many other fields of applications.

This paper introduces the operational status of the Advanced Land Observing Satellite-2 (ALOS-2) and its follow-on L-band SAR mission in Japan. ALOS-2 observes the earth surface with the Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) that is effectively used for many applications such as land deformation mapping and forest change mapping. To keep and enhance the applications using PALSAR-2 data, JAXA plans to launch a successor satellite to the ALOS-2 in Japanese Fiscal Year 2020. The concepts of the ALOS-2 follow-on are expanding swath width and increasing observation frequency while keeping high spatial resolution of the PALSAR-2 for improving the response of disaster monitoring, early detection of anomalies on the earth surface, and enabling time-series interferometric SAR (INSAR) analysis.

The Advanced Land Observing Satellite-2 (ALOS-2) was successfully launched on 24th May, 2014. The mission sensor of ALOS-2 is the Phased Array type L-band Synthetic Aperture Radar-2 called PALSAR-2 which is the state of the art L-band SAR system. At After launch, the initial checkout and the calibration and validation phase had been completed, and the PALSAR-2 standard products were released via web site at the end of November 2015. Until now, ALOS-2 has had contributed to a lot of emergency observations for disasters such as earthquakes flood, land slide which were impacted by typhoons, and volcano eruptions, not only in Japan but also in the world. Furthermore, based on the Basic Observation Scenario (BOS) of ALOS-2, base map data are collected and archived for the interferometry SAR processing in Japan area as well as global world. This document describes the results of ALOS-2 operation in routine operation phase.

The Advanced Land Observing Satellite-2 (ALOS-2) was launched from Tanegashima Space Center by H-IIA rocket successfully on 24th May 2014. The Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) is the state-of-the-art L-band SAR system which succeeds to PALSAR onboard ALOS. PALSAR-2 uses almost whole bandwidth allocated for L-band active sensor of Earth Exploration Satellites Service specified by the Radio Regulation in order to realize the high resolution observation, and also, PALSAR-2 transmits more than 6 kW power using 180 TRMs driven by Gallium Nitride (GaN) amplifier which is the first use for satellite in order to realize the lower Noise Equivalent Sigma Zero. Furthermore, because ALOS-2 carries PALSAR-2 only, PALSAR-2 antenna can be mounted under the satellite body. It enables to observe right-/left-looking observation by satellite maneuvering. And the high accuracy orbit control which maintains within 500 m radius tube for the reference orbit enables high coherence for the InSAR processing. Using these new technologies, ALOS-2 has been operating to fulfill the mission requirements such as disaster monitoring and so on. At this moment, one year has passed since the launch. This document introduces the first year operation result of ALOS-2.

Advanced Land Observing Satellite-2 (ALOS-2) is a spaceborne Synthetic Aperture Radar (SAR) system, developed by Mitsubishi Electric Corporation under contract to Japan Aerospace Exploration Agency (JAXA). The SAR system named Phased Array type L-band Synthetic Aperture Radar-2(PALSAR-2) is installed to ALOS-2. Its unique frequency of L-band is expected continuous investigation such as forest, volcanoes, and earthquake activities. Compact polarimetry mode and Along track interferometry (ATI) mode are available in PALSAR-2 as experimental mode. The evaluation of each experimental mode has been completed and reported in this paper. Compact polarimetry mode is that H and V polarization are transmitted at the same time, therefore the swath can be maintained. Each polarization status of compact polarimetry is calculated from the covariance matrix using some assumption. The full polarimetry-like image can be obtained as first evaluation. Along track interferometry is the technique to detect the moving target. ALOS-2 has two receiver channels. The moving target and its velocity are obtained from the interferometric image of each channel. The velocity can be calculated from the phase difference between two images. This result compared with another method using Doppler shift to validate it.

The Advanced Land Observing Satellite-2 (ALOS-2) is the RADAR satellite which is carrying the state-of-the-art L-band Synthetic Aperture Radar (SAR) called PALSAR-2 (Phased Array type L-band SAR-2) which succeeds to the PALSAR mounted on ALOS “Daichi”. PALSAR had contributed to various applications such as disaster, deformation, deforestation, agriculture and natural resource monitoring by providing enormous observation data from 2006 to 2011. Therefore, ALOS-2 is expected to continue the ALOS PALSAR mission and its contributions. ALOS-2 was successfully launched by H-IIA rocket from Tanegashima Space Center at 24thMay 2014. This paper shows the initial status of PALSAR-2 after launch.

PALSAR-2 (Phased Array type L-band Synthetic Aperture Radar-2) is a spaceborne L-band SAR (Synthetic Aperture Radar) system installed on Japanese Advanced Land Observing Satellite-2 (ALOS-2). PALSAR-2 is expected to provide valuable data for global monitoring and disaster monitoring. To meet the variety of demands, PALSAR-2 provides various operational modes. This paper describes the overview of the calibration plan of PALSAR-2. Since PALSAR-2 have more than 1,000 operational modes, effective and efficient procedure is crucial. The process is divided in three different phases; pre-launch calibration, check-out phase (C/O phase) after the launch, and image calibration phase. The overview of each phase is described.

JAXA is developing the Advanced Land Observing Satellite-2 (ALOS-2) carrying the state of the art L-band SAR named PALSAR-2. ALOS-2 mission is the follow-on of ALOS “Daichi” mission and PALSAR-2 succeeds to PALSAR onboard ALOS. PALSAR contributed to domestic and international disaster management activities by its interferometric application (InSAR). Compared to the PALSAR, higher spatial resolution, better NESZ (Noise Equivalent Sigma Zero) and better S/A (Signal to Ambiguity ratio) are required for PALSAR-2. In order to meet these requirements, JAXA introduced several improvements such as maximum bandwidth observation for PALSAR-2, spotlight mode with Active Phased Array Antenna, high power efficiency device, chirp modulation technique and dual receiving antenna system. In addition, very accurate orbit control and short repeat-pass orbit (14 days) will give higher coherence of interferometry.

This paper describes SAR system design of the Advanced Land Observing Satellite-2 (ALOS-2), which is a next-generation Japanese L-band SAR satellite. Since one of an important mission of ALOS-2 is a global monitoring using its unique frequency of L-band, a capability of wider coverage is required. On the contrary, in the point of disaster monitoring especially for urban area, relatively higher spatial resolution is essential. To comply with such a contradictive requirement of wide swath and high resolution, ALOS-2 utilizes a dual-receive channel (DRC) technique, and achieved a coverage area of up to 50km with a spatial resolution of down to 3m. In the paper, the H/W design of ALOS-2 DRC mode is explained. For a wider coverage of polarimetric observation, ALOS-2 installs the fully redundant and “quad-receive channel” system to full-polarimetric mode, achieving a maximum coverage of 50km at 6m resolution. As an experimental mode, new polarimetric mode called “compact polarimetry” is installed for a wide coverage of polarimetric observation.

This paper describes the performance, calibration method, and observation scenarios for the ALOS-2/PALSAR-2 polarimetry mode. It also describes simulation studies conducted using data from Pi-SAR-L2, JAXA's L-band airborne SAR, for calibration and application studies.

The Advanced Land Observing Satellite-2 (ALOS-2) carries the state-of-the-art L-band Synthetic Aperture Radar (SAR) called PALSAR-2 which succeed to the ALOS / PALSAR. Since more acquisition modes of PALSAR-2 than those of PALSAR may trigger more conflicts among user requests, systematic acquisition strategy is very important to achieve the mission requirements. For example, trade-off studies have been made for INSAR basemap data acquisition through discussion with user groups, and an optimum scenario was proposed to fulfill both requirements for quick response and time-series data acquisition under a same condition (incidence angle, descending/ascending, left/right look). As the ALOS data resulted in a comprehensive and homogeneous global archive, consistent data archives will be requested for ALOS-2 as well. This paper describes a draft acquisition strategy for PALSAR-2.

Advanced Land Observation Satellite-2 (ALOS-2) is a space borne Synthetic Aperture Radar (SAR) system, which is the follow-on L-SAR satellite mission of ALOS. Compared to the previous mission ALOS/PALSAR, the new L-band SAR system is capable of achieving both high resolution (down to 1m) and wide swath (up to 500km), with an improved image quality. The hardware (H/W) of ALOS-2, including L-band SAR sensor, is developed by Mitsubishi Electric Corporation under the contract of Japan Aerospace and Exploration Agency (JAXA). This paper describes the H/W design and performance of the ALOS-2 SAR sensor with a focus on the engineering model (EM) test performance.