This paper summarizes an operational calibration result of the Advanced Land Observing Satellites-2 (ALOS-2, nicknamed "DAICHI-2"). ALOS-2, the successor to the Phased Array-type L-band Synthetic Aperture Radar (PALSAR) onboarded ALOS "DAICHI" from 2006 to 2011, was launched in 2014 and has been operating smoothly beyond its design mission life of 7 years; the PALSAR-2 onboard ALOS-2 has shown its maximum contribution in practical applications by the basic observations of global land areas with time-series high resolution, and in emergency observations during natural disasters. The observation capability of PALSAR-2 has been improved over PALSAR e.g., a finer spatial resolution of 1 x 3m by the Spotlight observing mode, a wider swath width of 490 km by the ScanSAR mode, and a right-and-left looking function. To take full advantage of these capabilities, sensor calibration is extremely important. This paper reports the latest operational calibration result of PALSAR-2 during more than 9 years of its mission operation period.

Ionospheric total electron content (TEC) can significantly affect the range geometric accuracy of spaceborne L-band synthetic aperture radar (SAR) data. This study aims to estimate the ionospheric TEC from single spaceborne L-band SAR data based on the concept of the split-spectrum method. We estimated the SAR-based TEC from the range misregistration between lower- and higher-range spectral split-band amplitude images acquired using the Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) onboard the Advanced Land Observing Satellite-2 (ALOS-2). A comparison of the SAR-based TEC with the TEC observed by the Global Navigation Satellite System showed a linear relationship with a slope of 0.76 after correcting for offsets in the estimated value. This slope seemingly represents the ionospheric TEC ratio below the ALOS-2 orbit. Correcting the ionospheric range delay in PALSAR-2 data with the SAR-based TEC estimates improved the slant range accuracy from 2.67 m to 0.77 m.

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.

The south coast of Java is located in an active subduction zone where the Indo-Australian plate is beneath the Eurasian plate with a velocity of 7,0 cm/year. The phenomena lead to the area front of disaster, especially earthquakes and tsunami. Some areas along the coast of JAVA are being pressed (subsidence) or lifted due to the tectonic activity of the plate. Also, the activity can result in the creation of areas that have the potential to experience ground movement. However, information about it with scientific evidence is still inadequate. Therefore it is necessary to observe the effects of tectonic activity in southern Java on land surface changes along the coastline and estimate the potential epicenter of earthquakes due to this activity. In this study, we observed land deformation along the southern coast of Java to determine which areas experienced significant deformation. Based on the result, we can estimate the future earthquake's potential epicenter and the land movement area. Also, we analyzed the duration required since the last observation of earthquake events or land movement in the area. The land deformation observation uses satellite radar SAR data of ALOS-2 PALSAR-2 provided by JAXA. The type of SAR data is a stripmap with a 3 x 8-meter resolution. The time acquisition varied for each area observed from 2017 to 2020. The covered area of studies is spread from West to East (Pandagelang, Lebak, Sukabumi, Cianjur, Garut, Pangandaran, Banjar, Cilacap, Kebumen, Purworejo, and Bantul).

Ionospheric path delay (IPD) correction methods for creating an ortho-rectification product of L-band SAR were examined using the Phased Array type L-band Synthetic Aperture Rader-2 (PALSAR-2). Slant range correction values for the IPD were estimated using two methods. First one is coregistration between a radar geometry simulated image created using digital surface model (DSM) and a SAR amplitude image. Second one is using a total electron content (TEC) map. The geometric accuracy of the ortho products created using each correction was evaluated. The TEC map correction improved the geometric accuracy, while the coregistration one decreased. The individual slant-range shifts calculated by the co-registration showed a relationship with forest canopy height. The reason why the error increased in the co-registration correction is inferred that a false slant range shift is created due to the height difference between the scattering center point of the L-band SAR and the DSM in the forest, which results in adding an error to the slant-range correction value.

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.

This study investigated the geometric errors in L-band synthetic aperture radar (SAR) caused by the effects of the ionosphere and troposphere based on observational evidence derived from the Phased Array type L-band SAR-2 (PALSAR-2) onboard the Advanced Land Observing Satellite-2 (ALOS-2) data, which were obtained by calibration and validation works, and external numerical data. First, the ionospheric path delay (IPD) and the tropospheric path delay (TPD) on PALSAR-2 data were estimated. The results revealed that the zenith IPD ranges from approximately 1 m to 12 m, according to the observation period, due to the solar activity cycle. In contrast, the zenith TPD ranges from 2.30 m to 2.75 m depending on the seasonal variation. Next, the slant-range error of PALSAR-2 with the slant IPD and the slant TPD were compared to investigate the relationships between them. These relationships indicated a strong correlation between the slant-range error of L-band SAR and the slant IPD, whereas the correlation with the slant TPD was not confirmed. This result suggests that the effect of the ionosphere could be the significant error factor in the L-band SAR geometric accuracy. Finally, the effective geometric accuracy of PALSAR-2 was simulated by removing the IPD and TPD. As a result, the standard deviation of the slant-range error was reduced from 2.709 m to 1.206 m, and a bias of −5.288 m remained.

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.

Future satellite SAR (SAT-SAR) will be required to provide more value-added observations in addition to constellation services. The SAT-SAR and sub-missions will need to be more sophisticated. This paper proposes applying KR product array processing to Digital Beam Forming (DBF) and synthetic aperture processing for the azimuth of the SAT-SAR. This paper presents the initial results of simulations for both high resolution and wide swath with about twice the Rx effective aperture length.

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.

Compact-hybrid SAR (CP) is a dual-polarization (dual-pol) SAR mode that transmits a circular polarization (CirP) and measures the received signal at the horizontal and vertical antenna polarization. It is now admitted that the actual SAR technology does not permit the generation of a perfectly CirP and this may significantly affect CP radiometric and phase information. Since all the existing CP calibration models assume a perfectly transmitted CirP, there is an immediate need for the development of a new model that permits efficient assessment and calibration of CP non-circularity. In this article, a new general polarimetric hybrid SAR model (PolHyb) is introduced for both dual- (CP) and quad-polarization hybrid SAR modes. PolHyb explicitly includes the transmitted polarization non-circularity, in addition to conventional radar transmit and receive distortion matrices, channel imbalances and Faraday rotation contamination. The non-circularity of transmitted polarization is expressed in terms of the axial ratio (AR), which used to be popular in the 1960s for characterization of circularly polarized (transmit and receive) dual- and quad-polarization radar. The new CP model derived from PolHyb is adapted to PALSAR2-CP and used as the basis of an efficient method for an assessment of CP non-circularity using Amazonian rainforests. PALSAR2-CP data collected at four different beams (H2-6 to H2-9), with incidence angle varying between 30° and 45°, allows for the first ever demonstration of non-circularity of PALSAR2 CP transmitted polarization. Although it is lower than 0.5 dB for H2-6 and H2-7, the AR of PALSAR2-CP transmitted polarization increases significantly with incidence angle to reach up to 1 dB at Beam H2-8, and 2.3 dB at the highest incidence angles of Beam H2-9.

We investigated L-band cross-polarized normalized radar cross section (NRCS) dependence on ocean surface wind for wind speed retrieval. Because it has been reported that the L-band HV NRCS significantly changes due to the Faraday rotation (FR), analysis was conducted on observed NRCS with less influence of FR. About 50,000 match-ups, each consisting of the L-band NRCS, incidence angles, wind speeds and wind directions, were collected from the Phased- Array L-band Synthetic Aperture Radar-2 (PALSAR-2) and scatterometer wind vectors. Based on the match-ups, the L- band HH NRCS dependence on incidence angle and wind vector is modeled for 25 to 40° incidence angles. The derived relation indicates that the wind sensitivity of the L-band HV NRCS is almost equivalent to that of the HH one. Wind speeds are then estimated from the match-ups, based on the derived model function. A comparison with the reference scatterometer winds reveals a 0.37m/s bias and 2.9m/s root mean square (RMS) error.

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.

Recent climate warming has been pronounced in the arctic and sub-arctic region with the average annual temperature increasing between 2 - 3° since the 1950 [1] . Accelerated temperature increases have driven declines in sea ice extent, snow cover duration, glacier mass, and increase in permafrost temperatures [1] . Increasing evidence from the permafrost zone suggests the abrupt permafrost thaw may be the norm for many parts of the Artic and sub-arctic landscape 1950 [1] , [2] . Climate warming is causing the initiation and expansion of abrupt permafrost thaw (called thermokarst), which even though it occurs at point locations, often cause much deeper permafrost thaw to occur more rapidly. Repeated mapping and/or monitoring of ongoing permafrost indicator changes in infrastructure corridor and surrounding lands is important for the assessment of transportation and energy infrastructure safety, and predicting eminent collapse.

ALOS2-PALSAR2, which was launched on the 24th of May 2014, is equipped with an experimental Compact mode (CP) ([1], [2]), that can collect CP images at various incidence angles (H2-1 to H2-9, from 18° to 44°). PALSAR2-CP transmits a circular polarization and measures the received signal at the horizontal and vertical antenna polarization. Recently, it was brought out that the actual technology does not permit the generation of a perfectly circular polarization [3]. The transmitted polarization is non circular, and the non circularity varies with incidence angle. Since all the calibration methods developed for CP assume that the transmitted polarization is perfectly circular, there is immediate requirement for the development of a new CP calibration model that includes the transmitted polarization non circularity. In this study, a new CP calibration model, which explicitly includes the transmitted polarization non circularity, in addition to conventional radar transmit and receive distortion matrices, channel imbalances and Faraday rotation contamination, is introduced. The new CP model is adapted to ALOS2-PALSAR2 and used as the basis of a new method for assessment of CP non circularity using Amazonian rainforests, at low Faraday rotation. ALOS2-CP data collected at four different beams (H26 to H29), with incidence angle varying between 30° and 44°, permit the first ever demonstration of non circularity of ALOS2 CP transmitted polarization. It is shown that the transmitted polarization axis ratio of ALOS2-CP increases with incidence angle, and can reach up to 2.5 dB at the most raising incidence angle (44°) of the beam H29.

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 relationship between ocean wind vectors and L-band normalized radar cross sections (NRCS) is examined to modify the L-band geophysical model function (GMF) using the Phased-Array L-band Synthetic Aperture Radar 2 (PALSAR-2) and scatterometer wind data. Since the PALSAR-2 has a function of dual polarized ScanSAR, the sensitivity of L-band HV on wind fields is examined. Though the HV signal shows wind speed and incidence angle dependencies, they are too noisy to be used for wind detection. In order to seek the possible cause, the L-band NRCS is compared with Faraday rotation (FR) angle, indicating a clear positive relationship between the HV NRCSs and with the FR angle. The HH/HV ratio from the PALSAR-2 observation is compared with theoretical ones calculated from FR angle. The observation and theory correspond in terms of the tendency that the HH/HV decreases with increasing the FR angle and its sensitivity decreases with incidence angle. On the other hand, the decreasing ratio of the observation exceeds the theoretical one resulting in increasing discrepancy with the FR angle. Since the HH NRCS is not significantly affected by FR, the L-band HH GMF is modified in order to cover the wider incidence angle ranges from 17° to 50°. Based on the derived GMF, wind speeds are estimated and compared with the buoy-measured winds. The comparison shows the -0.75 m/s bias and 2.07 m/s root mean square (rms) error.

This paper reports the result of over 3 years routine calibration and validation works for the Phased Array type L-band Synthetic Aperture Radar-2 (P ALSAR-2) onboard the Advanced Land Observing Satellite-2 (ALOS-2). The major observation modes and beams were evaluated, and we confirmed that the PALSAR-2 product satisfy its specification over 3 years: absolute radiometric accuracy is less than 0.5 dB, geometric accuracy is less than 10 meters (RMS), and polarimetric calibration was successfully conducted.

ALOS-2-PALSAR is equipped with an experimental Compact mode (CP), which can collect CP images at various incidence angles. PALSAR2-CP transmits a circular polarization and measures the received signal at the horizontal and vertical antenna polarization. Recently, it was brought out that the actual SAR technology does not permit the generation of a perfectly circular polarization and this may significantly affect CP information [1]. Since all the calibration methods assume that the transmitted polarization is perfectly circular, there is an immediate need for a new CP calibration model that is more suitable to actual CP SARs. In this study, a new CP calibration model that takes into account the non circularity of transmitted polarization, in addition to conventional SAR transmitter and receiver distortion matrices, is introduced. The CP calibration model is used as the basis for the development of an efficient method that permits the measurement of transmitted polarization axis ratio, and its variations with incidence angle. The method is validated using PALSAR2-CP data collected at various incidence angles on the Amazonian forests. It is shown that the transmitted polarization axis ratio varies with PALSAR2-CP beam, and can reach up to 1.1 dB for the CP mode (H2-8) (at about 37° incidence angle).

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.

This paper reports the polarimetric characteristics of temporarily coherent radio frequency interference (RFI) observed by ALOS-2 PALSAR-2. The RFI has high interferometric coherence as if it is a backscattered signal from the ground. However, its radio frequency band and the Doppler frequency are different from the backscattered signal. The RFI, namely, intermittently transmitted wideband (ITWB) RFI, effects both interferometric and polarimetric analysis, because it has high temporal interferometric and polarimetric coherency. The detection and removal scheme for the ITWV RFI is also discussed in this paper.

In 2016, the Advanced Land Observing Satellite-2 (ALOS-2, “DAICHI-2”) observed various disaster affected areas. Japan Aerospace Exploration Agency (JAXA) operated the emergency observation more than hundred times in the year. The Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) aboard ALOS-2 contributed for detecting the disaster affected area, ground deformation and flood affected area. Especially for the ground deformation and damaged area detection caused by the devastating earthquakes in 2016, e.g., Kumamoto earthquakes in Japan and Kaikoura earthquake in New Zealand, researchers provided variable analytical results from ALOS-2 observation data. In this paper, some examples of the emergency observation results are presented.

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.

One of the main missions of the Advanced Land Observing Satellite-2 (ALOS-2, “DAICHI-2” ) is the disaster monitoring. Japan Aerospace Exploration Agency (JAXA) has operated the emergency observation more than hundred times in 2015. Not only the most important event in 2015, the Mw 7.8 Gorkha earthquake on April 25, the Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) aboard ALOS-2 observed various floods, volcano eruptions and earthquakes. In this paper, we present some emergency observation results which were impossible to be performed by the previous ALOS. That is, automatically burst aligned ScanSAR to ScanSAR interferometry and, left / right looking for increasing acquisition opportunity.

In this paper, we report a radio frequency interference (RFI) detection method which is exclusively sensitive to the temporally pulsed wide-band signal. We use local autocorrelation in the range-time azimuth-frequency domain instead of typical range-frequency azimuth-time domain. Traditional RFI detectors assume that RFI have time-varying wide-band (TVWB) and / or time-stationary narrow-band (TSNB) features. The proposed method assumes that there is another type of RFI, namely, intermittently transmitted wide-band RFI. This kind of RFI superimposes on the SLC image however, its short pulse duration hinders us to detect it in range-frequency azimuth-time domain. Contrarily, in range-time azimuth-frequency domain, this kind of RFI can be detected easily. Here, we present a basic methodology and experimental results.

ALOS-Next/Tandem-L is a proposal for a highly innovative L-band SAR satellite mission for the global observation of dynamic processes on the Earth's surface with hitherto unparalleled quality and resolution. It is based on a collaboration between DLR and JAXA which started with a pre-phase A study in 2013 and is currently undergoing a phase A study. Thanks to the novel imaging techniques and the vast recording capacity with up to 8 Tbytes/day, it will provide vital information for solving pressing scientific questions in the biosphere, geosphere, cryosphere, and hydrosphere. By this, the new L-band SAR mission will make an essential contribution for a better understanding of the Earth system and its dynamics. ALOS-Next/Tandem-L will, moreover, open new opportunities for risk analysis, disaster management and environmental monitoring by employing especially designed acquisition modes and techniques in combination with a reconfigurable tandem satellite configuration and an L-band SAR instrument with advanced digital beamforming techniques.

Correlations between L-band SAR polarimetric parameters obtained with airborne SAR (Pi-SAR-L2) and metrics obtained with airborne LiDAR were examined to identify the relationship between the full polarimetric parameters and forest parameters obtained for a natural forest in Indonesia. Values of a0HVand a0VVshow good correlations with canopy height and 90thpercentile metrics of LiDAR, with R2values of 0.85-0.89. These correlations show higher R2values than the value of 0.33 for a0HVvs. above-ground biomass. The results indicate that a0shows a robust correlation with tree height weighted to taller trees. Polarimetric parameters estimated from a single tree also support the results. Entropy and anisotropy obtained from a single tree shows almost the same value, and a is about 45°, while the tree height ranges 2 m to 6 m. This indicates that these parameters are preferable for land cover classification.

We tested the performance of the stereo observations of the Panchromatic Remote-sensing Instrument for Stereo Mapping (PRISM) onboard the Advanced Land Observing Satellite (ALOS) in the mapping of forest aboveground biomass (AGB) in Japan. Digital canopy height models (DCHMs), which are differences between PRISM digital surface models and surveying-based digital terrain models (DTMs), were compared to in situ AGB measurements of several forest types (number of stands: 28; average stand size: 0.54 ha; stand size range: 0.25-3.00 ha). DCHM values exhibited a significant correlation with AGB (r = 0.66-0.87; five different DCHMs), and the root-mean-square error and bias of the regression model evaluated by the leave-one-out cross-validation were 37.2-57.8t/ha(22.1%-32.6%) and-0.11-1.89 t/ha, respectively. There was no saturation in the relationship between DCHM and AGB (AGB range: 19-332 t/ha). The correlations between DCHM and mean canopy height (r = 0.17-0.52) and between DCHM and Lorey's height (r = 0.26-0.66) were weaker than the correlation between DCHM and AGB. The PRISM AGB distribution estimated by the regression model was consistent with a tree density map produced from aerial photos. Comparison to Phased Array-type L-band Synthetic Aperture Radar (PALSAR) data showed that the PRISM DCHMs can estimate high AGB over the saturation level of PALSAR backscattering coefficient, i.e., 100-200 t/ha. The results described here demonstrate that the PRISM DCHMs are capable of wall-to-wall AGB estimation at 50-m resolution. This approach will be useful for improving the performance of satellite-based AGB estimation when an accurate DTM is available.

The temporal variations (diurnal and annual) in arboreal (εTree) and bare soil (εSoil) dielectric constants and their correlation with precipitation were examined for several trees in Japan. A significant (1 σ (standard deviation) and 2 σ) εTreeincrease is observed after rainfall at 89.8% and 90.5% probability. However, rainfall does not always induce significant εTreeincreases. Rainfall of more than 5 mm/day can induce 1 σ εTreeTree increase at a 59.6% probability. In order to examine whether the increase in εTree affects the L-band σ0variation in a forest, the four-year temporal variation of the L-band backscattering coefficient (σ0) was estimated from observations by the Advanced Land Observing Satellite Phased Array type L-band Synthetic Aperture Radar. Observed maximum absolute deviations from the mean over the forest area were 1.0 and 1.2 dB for σHH0and σHV0, respectively, and 4.0 and 3.0 dB over open land. σ0and rainfall correlations show that εTreeand σForest0are proportional to precipitation integrated over seven or eight days; εSoiland σOpen land0are proportional to precipitation integrated over three days. This finding indicates that εTreevariations influence σForest areas0. A stronger correlation between σHV0and precipitation is observed in several sites with low σHV0, where less biomass is expected, and several sites with high σHV0, where more biomass is expected. A weaker correlation between σHV0and precipitation is observed for several sites with high σHV0. These differences may be explained by the different contributions of double bounce scattering and potential transpiration, which is a measure of the ability of the atmosphere to remove water from the surface through the processes of transpiration. The two other results were as follows: 1) The functional relation between aboveground biomass and σ0showed dependence on precipitation data, this being an effect connected with seasonal changes of the εTree. This experiment reinforces the fact that the dry season is preferable for retrieval of woody biomass from inversion of the functional dependence of SAR backscatter and for avoiding the influence of rainfall. 2) The complex dielectric constant for a tree trunk, which is measured between 0.2 and 6 GHz, indicates that free water is dominant in the measured tree.

In this study, we examine the applicability of digital surface model (DSM) generated from ALOS PRISM data for mapping forest above ground biomass (AGB). We obtained the digital canopy height model (DCHM) by calculating the differences between the PRISM DSM and surveying-based digital elevation model (DEM), and investigated the relationship between the DCHM values and field measured mean tree height and AGB in Northern Hokkaido, Japan. The results show a strong linear relationship between the field measured AGB and PRISM-DCHM (R = 0.872, n = 25). The RMSE and bias of the regression model, which were evaluated by the leave-one-out cross validation, are 38.1 t/ha (22 %) and -0.2 t/ha, respectively. Saturation at high AGB is not shown. We also demonstrate the wall-to-wall AGB mapping by using the regression model and the PRISM DCHM image. A pan-sharpen image generated from PRISM and AVNIR-2 images is utilized for forest cover mapping. The PRISM-based AGB values are generally reasonable except for high mountain areas. The relationship between the PRISM AGB and backscattering coefficient measured by L-band synthetic aperture radar (PALSAR) is consistent with the regression models discovered by the previous researches.

Aboveground (AG)-biomass was estimated from a field biomass collection and LiDAR observations for a natural forest in Indonesia. The derived AG-biomass data were plotted against full polarimetric parameters calculated from Polarimetric and Interferometric Airborne Synthetic Aperture Radar L2 (Pi-SAR-L2) and PALSAR data. The α°-AG-biomass curve shows saturation by around 100 tons/ha, while for entropy, correlation is observed up to 200 tons/ha. The largest coefficient of determination (R2= 0.2348) was observed for the range with AG-biomass of more than 100 tons/ha for the relation between AG-biomass and entropy. The α°HV-biomass plot derived from PALSAR data shows smaller variance in the dry season than in other seasons, indicating that dry season data is preferable for a more accurate estimate of AG-biomass.

The 2011 off the Pacific coast of Tohoku earthquake was observed using phased array type L-band synthetic aperture radar (PALSAR) and polarimetric and interferometric airborne synthetic aperture radar (PiSAR) full-polarimetric data. Representative polarimetric parameters were calculated from full-polarimetric data for urban areas, where most of the buildings were destroyed by the subsequent tsunami, in order to identify the radar scattering mechanism in these areas. These parameters were compared with the ones observed before the disaster. The full-polarimetric data analysis shows that the affected areas were represented by surface scattering with high entropy, indicating that a complex scattering mechanism with nonreflection symmetry is involved. The coherence between HH and VV and that between RR and LL are the most important factors in distinguishing the disaster areas from the data. Alpha angle and anisotropy are also important factors in this respect; however, anisotropy derived from PiSAR data does not show the difference between areas with collapsed and still-standing buildings. This may be because the azimuth slope angle for the target urban area is different before and after the disaster for both PALSAR and PiSAR data. Owing to the double-bounce scattering from azimuthally rotated targets in the urban areas, the power estimated from the four-component decomposition model is distributed within a wide range not only for double-bounce scattering but also for volume and surface scatterings. Additionally, the model does not show a systematic change between before and after the disaster, and σ0for four polarizations with 30-m resolution does not show a systematic difference.

We investigated the relationship between HH and HV gamma naught values by PALSAR and biomass of Japanese natural forest (44 sites) to develop an effective retrieval algorithm of forest above ground biomass by using PALSAR data. As same as previous studies, our results showed a positive logarithmic relationship between PALSAR gamma naught and in situ forest biomass. HV polarized data showed smaller RMSE and higher saturation level than HH data. The results also showed that slope corrected PALSAR data had much smaller RMSE than the non-corrected data.