Masayoshi Matsumoto

Continuous Observation of Natural-Disaster-Affected Areas Using Ground-Based SAR Interferometry

Ground-based synthetic aperture radar (GB-SAR) is an effective technique for monitoring over a widespread area. Save for the fact that it is installed on the ground, the GB-SAR operates in the same way as air- and satellite-borne microwave SAR remote sensing systems. By repeated acquisition of data and application of the repeat-pass interferometry principle, this technique can detect very small changes over a scene with a typically high temporal resolution of only a few minutes. In the system used in this study, interferometer error is less than 10% and the temporal resolution is approximately five minutes. Some applications require extensive monitoring capability; for instance, in this study, the GB-SAR technique was used to monitor a post-landslide surface in order to assess slope stability and to ensure the safety of the area. Whereas no major events were observed, the technique proved capable of detecting even small changes caused by snowfalls. The technique was also used to monitor the displacement of the ground surface in a tsunami-affected area in which the stability of the ground had come into question. The results of this assessment indicated that the distribution of displacement tended to be larger in waterfront areas and seemed to correlate to tidal effects. Although both of these measurement campaigns represent preliminary research, the advantages of the GB-SAR technique have been well illustrated. In this paper, the results of these measurements are provided, and the capability and potential of the technique are discussed.

Estimation of biomass of tree roots by GPR with high accuracy positioning system

A new approach for estimation of the tree root biomass is proposed by using GPR system with high accuracy positioning system. The 3D images of subsurface can be obtained clearly with this system, which we refer as “3DGPR”. We try to estimate the biomass of tree roots quantitatively by measuring the volume of the tree roots. We tested this system for tree roots measurement, and the broadening of the tree root with horizontal direction could be detected with 500 MHz and 800 MHz antenna. We excavated this tree every 10 cm from 0 cm to 50 cm to validate the accuracy of the result. Compared with the measurement result and the excavated one, the tree root whose diameter is more than 5 cm could be detected correctly. Some tree roots whose diameter is 3 cm also could be detected. The diameter in most of the tree roots is more than 2cm. In this result, we expect that the volume is supposed to be estimated within 30 percent error by using the excavated result for calibration data.

Landslide observation by ground-based SAR interferometry

A ground-based synthetic aperture radar (GB-SAR) system was installed for the observation and monitoring of post-landslide slope in Kurihara-city, Miyagi, Japan. The system is operated at 17 GHz (Ku-band) with a frequency bandwidth of 150 MHz. Horn antennas scan about 2 m horizontally to cover a large observation area and SAR processing is applied to achieve higher azimuth and range resolutions. In addition, the interferometric technique is used to detect very small changes on the target, resulting in the expected interferometer resolution of 0.1 mm. In 2011, the system operated from November to December to acquire preliminary results and to study the feasibility of the technique for monitoring landslide surface. During the period, major events on the landslide surface did not happen and, thus, no significant changes were detected by the GB-SAR system. However, it detected small movements at some locations approaching to the system that is likely caused by a snowfall. It demonstrates the capability of the GB-SAR technique in detecting very small changes on a target.

Simultaneous observation data of GB-SAR/PiSAR to detect flooding in an urban area

We analyzed simultaneous observation data with ground-based synthetic aperture radar (GB-SAR) and airborne SAR (PiSAR) over a flood test site at which a simple house was constructed in a field. The PiSAR under flood condition was 0.9 to 3.4 dB higher than that under nonflood condition. GB-SAR gives high spatial resolution as we could identify a single scattering component and a double bounce component from the house. GB-SAR showed that the difference between the flooding and nonflooding conditions came from the double bounce scattering. We also confirm that the entropy is a sensitive parameter in the eigenvalue decomposition parameters, if the scattering process is dominated by the double bounce scattering. We conclude that and entropy are a good parameter to be used to detect flooding, not only in agricultural and forest regions, but also in urban areas. We also conclude that GB-SAR is a powerful tool to supplement satellite and airborne observation, which has a relatively low spatial resolution.

GB-SAR/PiSAR simultaneous experiment for a trial of flood area detection

We performed a Ground Based SAR (GB-SAR) and PiSAR simultaneous experiment over a flood test site. In this site, one prefab was constructed in a baseball field of a Nihon University in Chiba, Japan. The PiSAR observations were done for three days with different soil moisture condition of ~25%, ~50%, and 100%. Some GB-SAR experiments have been also done in two of three days and the scattering process are examined. Preliminary experiment with GB-SAR showed that L-band sigma0 from a double scattering of ground-wall is increased for a few dB, when a reflectivity of the ground is assumed to be 1. These increase are also confirmed in the test site for both PiSAR and GB-SAR. Furthermore, high resolution GB-SAR images show double and single bounce scattering from a metal bar behind the wooden board of the prefab. We conclude that L-band SAR has a enough ability to detect a flooding area in urban site.

Coherent scatterer selection based on cherence of interleaved sub-images for atmospheric correction of ground-based synthetic aperture radar interferometry

Ground-based synthetic aperture radar (GB-SAR) interferometry is a technique suitable for monitoring the movement and/or deformation of widespread targets remotely. The technique is capable of detecting a few tenths of millimeters. However, since the measurement is commonly carried out with a long-range distance, the influence of atmospheric condition can be a serious issue. A common and a practical way of correcting the influence on interferometric phase is based on coherent scatteres (CSs). In the present paper, a newly proposed method to detect CSs from measured data is discussed. The method detects CSs by taking the complex coherence of two SAR sub-images, which are formed from a data set. In order to form sub-images, the measured data are interleaved and SAR processing is applied respectively. An experimental demonstration showed that the method can successfully detect deployed corner reflectors as CSs. Furthermore, the movement of a target can accurately be measured when atmospheric correction based on CSs, which are detected by the proposed method. Since the method requires only data sets in the analyzing time period to detect CSs, the proposed method has an advantage in the real-time detection of target movements over a conventional method based on dispersion index, which requires number of data sets.

Analysis of electromagnetic wave scattering from a dielectric dihedral structure by polarimetric GB-SAR

The electromagnetic wave scattering from a dielectric dihedral structure is discussed in this paper. In order to measure the scattering mechanism, we measured a scattering from a brick by using a polarimetric GB-SAR system. And we found three scattering characteristics of the dielectric dihedral structure. Especially, separated scattering at the center of the target in HV component and penetration of electromagnetic wave in VV component may be used to extract information of a target. Then, we validated a scattering from a concrete block at different azimuth angles and detected the dependency of the azimuth angles by evaluating the polarization orientation angle based on circular polarization basis. Therefore, the polarimetric GB-SAR can validate the scattering mechanism of buildings by using dielectric dihedral object like a concrete block.