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Targeted on accurate and efficient ship detection of Synthetic Aperture Radar imagery, sea-land segmentation is key for the complex port scenes. Despite the importance of this task, current methods are still severely influenced by several limitations, such as high level of image speckle noise, complicated backscattering characteristics. In order to overcome these issues, we propose a sea-land segmentation method of Synthetic Aperture Radar imagery based on multi-source data registration. To be specific, high-resolution optical remote sensing images and high-precision coastline vector data are integrated with Synthetic Aperture Radar images for accurate sea-land segmentation. First, the Pyramid Level-by-level Guided-Histogram of the Orientated Phase Congruency method is developed for the registration of Synthetic Aperture Radar and optical images, making two types of images into the same spatial reference. Following this, the high-precision coastline vector data collected from optical images is transferred to the Synthetic Aperture Radar image, realizing accurate sea-land segmentation. Finally, aiming at ship detection tasks, two quantitative evaluation indicators for sea-land segmentation are proposed: (1) the Absolute Segmentation Accuracy; and (2) the Ship Mis-segmentation Index. The accuracy and efficiency of the proposed method are tested and verified on Gaofen-3 SAR images of Yokosuka Port, Japan. Experimental results show that the proposed method achieves an Absolute Segmentation Accuracy of 3.15 pixels, a Ship Mis-segmentation Index of 9.23% and processing time of 82.92 s on average, which reveals that the proposed method outperforms current popular approaches in terms of accuracy and efficiency. [ABSTRACT FROM AUTHOR]

From June 29 to July 1, 2015, a phreatic eruption occurred in Owakudani, the largest fumarole area in Hakone volcano, Japan. In this study, an interferometric synthetic aperture radar (InSAR) time series analysis of the Advanced Land Observing Satellite‐2 (ALOS‐2)/Phased Array type L‐band Synthetic Aperture Radar‐2 (PALSAR‐2) data was performed to measure deformation after the eruption. The results show that the central cones of the volcano have subsided since the eruption and its deflation source is located beneath the previously estimated bell‐shaped conductor, which is considered as a sealing layer confining a pressurized hydrothermal reservoir. Therefore, the InSAR results demonstrate the deflation of the hydrothermal system beneath the volcano. One possible cause of this deflation is compaction due to a decrease in pore pressure caused by rupture and fluid migration during and after the eruption. Plain Language Summary: From June 29 to July 1, 2015, an eruption occurred in Owakudani, the largest steaming area in Hakone volcano, Japan. Our analysis using satellite radar demonstrates that the central part of Hakone volcano has subsided since the eruption and that the deflation source is located in the reservoir of hot water beneath the volcano. One possible cause of this deflation is compaction due to a pressure drop produced by rupture and fluid migration during and after the eruption. Key Points: Posteruptive deflation beneath the central cones of Hakone volcano was detected by radar interferometry after the 2015 phreatic eruptionOur model inversion suggests that deflation of a hydrothermal system confined by a sealing layer beneath the volcano has been taking placeThe hydrothermal system deflation is likely attributable to rupture of the sealing layer and system depressurization due to the eruption [ABSTRACT FROM AUTHOR]

From June 29 to July 1, 2015, a phreatic eruption occurred in Owakudani, the largest fumarole area in Hakone volcano, Japan. In this study, an interferometric synthetic aperture radar (InSAR) time series analysis of the Advanced Land Observing Satellite‐2 (ALOS‐2)/Phased Array type L‐band Synthetic Aperture Radar‐2 (PALSAR‐2) data was performed to measure deformation after the eruption. The results show that the central cones of the volcano have subsided since the eruption and its deflation source is located beneath the previously estimated bell‐shaped conductor, which is considered as a sealing layer confining a pressurized hydrothermal reservoir. Therefore, the InSAR results demonstrate the deflation of the hydrothermal system beneath the volcano. One possible cause of this deflation is compaction due to a decrease in pore pressure caused by rupture and fluid migration during and after the eruption. Plain Language Summary: From June 29 to July 1, 2015, an eruption occurred in Owakudani, the largest steaming area in Hakone volcano, Japan. Our analysis using satellite radar demonstrates that the central part of Hakone volcano has subsided since the eruption and that the deflation source is located in the reservoir of hot water beneath the volcano. One possible cause of this deflation is compaction due to a pressure drop produced by rupture and fluid migration during and after the eruption. Key Points: Posteruptive deflation beneath the central cones of Hakone volcano was detected by radar interferometry after the 2015 phreatic eruptionOur model inversion suggests that deflation of a hydrothermal system confined by a sealing layer beneath the volcano has been taking placeThe hydrothermal system deflation is likely attributable to rupture of the sealing layer and system depressurization due to the eruption [ABSTRACT FROM AUTHOR]

Coseismic and postseismic crustal deformations caused by earthquake episodes are important in understanding the mechanisms of these episodes as well as the fault rheology near an epicentral area. Specifically, interferometric synthetic aperture radar (InSAR) and synthetic aperture radar (SAR) pixel tracking can depict high‐resolution crustal deformation fields associated with earthquakes and volcanic activities without installing on‐site observation instruments. In this study, we investigate the coseismic and postseismic near‐fault crustal deformations associated with the 2016 Kumamoto earthquake sequence in southwest Japan using ALOS‐2/PALSAR‐2 (Phased Array‐type L‐band SAR‐2) data. Coseismic three‐dimensional (3‐D) displacement fields inferred from PALSAR‐2 pixel tracking data showed 1.6 m of horizontal displacements and 2 m of subsidence at maximum, despite the mainshock focal mechanism that was dominated by strike‐slip components with N‐S extension axes. The locations of large displacement variations along surface ruptures due to the mainshock were almost identical to a region where infrastructure was damaged, thus implying the generation of strong ground seismic waves. By using conventional InSAR stacking, we inferred two independent quasi‐east‐west and quasi‐vertical displacement fields as cumulative postseismic deformations following the mainshock over a period of about 2 years. The near‐fault postseismic deformation represented complicated displacement characteristics that could not be explained by a single physical process. Deformation signals around Aso volcano were interpreted by the effects of postseismic physical processes as well as geological heterogeneous structures. Plain Language Summary: Coseismic and postseismic crustal deformation fields provide information for inferring slip distributions occurring along a fault, and these data are helpful for understanding the geological characteristics around an epicentral area. By using satellite synthetic aperture radar (SAR) images, we can derive crustal deformation maps with high spatial resolutions and high measurement accuracy without installing on‐site observation instruments. In this paper, we offer coseismic and postseismic crustal deformation maps associated with the 2016 Kumamoto earthquake sequence on Kyushu Island, SW Japan, which were derived using the Japanese SAR satellite ALOS‐2/PALSAR‐2 data. Measurements of displacements along with details on Earth surface ruptures due to earthquakes also allow us to understand the variations in rupture processes along seismogenic faults. Furthermore, comparisons of the spatial and temporal variations of coseismic and postseismic deformations can provide information on the geophysical mechanisms of long‐term deformations following a mainshock. Key Points: PALSAR‐2 pixel tracking and InSAR revealed near‐fault coseismic and postseismic deformations due to the 2016 Kumamoto earthquake sequenceSignificant coseismic displacement variations along the surface ruptures imply complicated fault rupture processes during the mainshockPostseismic deformations can be interpreted by multiple physical processes and geological heterogeneous structures [ABSTRACT FROM AUTHOR]

MDT recovery over coastal regions is challenging, as the mean sea surface (MSS) and geoid/quasi-geoid models are of low quality. The altimetry satellites equipped with the synthetic aperture radar (SAR) altimeters provide more accurate sea surface heights than traditional ones close to the coast. We investigate the role of using the SAR-based MSS in coastal MDT recovery, and the effects introduced by the SAR altimetry data are quantified and assessed. We model MDTs based on the multivariate objective analysis, where the MSS and the recently released satellite-only global geopotential model are combined. The numerical experiments over the coast of Japan and southeastern China show that the use of the SAR-based MSS improves the local MDT. The root mean square (RMS) of the misfits between MDT-modeled with SAR altimetry data and the ocean data is lower than that derived from MDT computed without SAR data—by a magnitude of 4–8 mm. Moreover, the geostrophic velocities derived from MDT modeled with the SAR altimetry data have better fits with buoy data than those derived from MDT modeled without SAR data. In total, our studies highlight the use of SAR altimetry data in coastal MDT recovery. [ABSTRACT FROM AUTHOR]

In the buried-object search technique using a pulsed radar, the estimation method for the buried-pipe location and the underground propagation velocity of the electromagnetic wave by means of a synthetic aperture method has been studied. In general, the electromagnetic wave attenuates as it propagates m the underground and the amplitude of the received signal often becomes extremely small. Therefore, it has been difficult in the signal processing using the amplitude value to recognize several buried objects at different depths by an identical discrimination standard. To resolve this difficulty, a new zero-crossed synthetic aperture method is developed. In the underground cross-sectional image, the waves reflected from a buried pipe form a hyperbolic pattern dependent on the underground propagation velocity of the electromagnetic wave. By evaluating only the edge of this hyperbolic pattern, the underground propagation velocity of the electromagnetic wave and the location of the buried object are estimated. First, to extract the edge, the amplitude value at the time when the observed signal has a ‘0’ amplitude is replaced with ‘1’ if the phase of the original waveform changes from minus to plus whereas with ‘-1’ if it changes from plus to minus. The amplitude at other time points is replaced with ‘0.’ Subsequently, a synthetic aperture process (addition process) is carried out. Since the absolute value of the amplitude is 1 or 0, it is not necessary to consider the effect of the attenuation of the amplitude due to propagation of the electromagnetic wave as a discrimination reference in the estimation of the location of the buried pipe after the addition process. The location of the buried pipe can be detected accurately. [ABSTRACT FROM AUTHOR]

Flood detection using a spaceborne synthetic aperture radar (SAR) has become a powerful tool for organizing disaster responses. The detection accuracy is increased by accumulating pre-event observations, whereas applying multiple observation modes results in an inadequate number of observations with the same mode from the same orbit. Recent flood detection studies take advantage of the large number of pre-event observations taken from an identical orbit and observation mode. On the other hand, those studies do not take account of the use of multiple orbits and modes. In this study, we examined how the analysis results suffered when pre-event observations were only taken from a different orbit or mode to that of the post-event observation. Experimental results showed that inundation areas were overlooked under such non-ideal conditions. On the other hand, the detection accuracy could be recovered by combining analysis results from possible alternate datasets and became compatible with ideal cases. [ABSTRACT FROM AUTHOR]