In the Kanto region of Japan, a large quantity of natural gas is dissolved in brine. The large-scale production of gas and iodine in the region has caused large-scale land subsidence in the past. Therefore, continuous and accurate monitoring for subsidence using satellite remote sensing is essential to prevent extreme subsidence and ensure the safety of residences. This study focused on the small baseline subset (SBAS) method to assess ground deformation trends around the Kanto region. Data for the SBAS method was acquired by the Advanced Land Observing Satellite (ALOS)-2 Phased Array type L-band Synthetic Aperture Radar (PALSAR)-2 from 2015 to 2019. A comparison of our results with reference levelling data shows that the SBAS method underestimates displacement. We corrected our results using linear regression and determined the maximum displacement around the Kujyukuri area to be approximately 20 mm/year; the mean displacement rate for 2015–2019 was −7.9 ± 2.9 mm/year. These values exceed those obtained using past PALSAR observations owing to the horizontal displacement after the Great East Japan Earthquake of 2011. Moreover, fewer points were acquired, and the root mean-squared error of each time-series displacement value was larger in our results. Further analysis is needed to address these bias errors.

High-resolution synthetic aperture radar (SAR) data are widely used for disaster monitoring. To extract damaged areas automatically, it is essential to understand the relationships among the sensor specifications, acquisition conditions, and land cover. Our previous studies developed a method for estimating the phase noise of interferograms using several pairs of TerraSAR-X series (TerraSAR-X and TanDEM-X) datasets. Atmospheric disturbance data are also necessary to interpret the interferograms; therefore, the purpose of this study is to estimate the atmospheric effects by focusing on the difference in digital elevation model (DEM) errors between repeat-pass (two interferometric SAR images acquired at different times) and single-pass (two interferometric SAR images acquired simultaneously) interferometry. Single-pass DEM errors are reduced due to the lack of temporal decorrelation and atmospheric disturbances. At a study site in the city of Tsukuba, a quantitative analysis of DEM errors at fixed ground objects shows that the atmospheric effects are estimated to contribute 75% to 80% of the total phase noise in interferograms.

これまで著者らは，衛星SARデータを用いて，被害が大きい地域において地区レベルで建物の被害状況の把握を目標とし，予め都市域を切り出したコヒーレンス画像を用いた手法の開発を行ってきた．本研究では，熊本地震を取り上げ，LバンドのALOS-2 PALSAR-2による複数の撮影条件（異なる軌道，撮影方向）で取得した画像を用いて，コヒーレンスと建物の被害度の関係を明らかにすることを目的とした．熊本県益城町を解析対象とし，益城町内の200メートルメッシュ内のコヒーレンスの平均値と建物の被害度の関係を評価した．その結果，撮影条件によらず，これらに有意な相関があることとともに，被害度が小さいほど撮影条件によるコヒーレンスのばらつきが大きい傾向があることを示した．さらに本研究による土地被覆を考慮したコヒーレンスと被害度のモデルの構築には，撮影日，撮影間隔，基線長100m程度の違いよりも，軌道や撮影方向による違いの影響が大きいことを明らかにした．

Synthetic aperture radar has a clear advantage over optical satellites in being able to monitor the Earth’s surface under any weather condition. The Phased Array type L-band Synthetic Aperture Radar-2 (PALSAR-2) aboard Advanced Land Observing Satellite 2 (ALOS-2) is a unique and highly useful sensor that can acquire high-resolution data using dual-beam receivers. This study aimed at evaluating, both qualitatively and quantitatively, the backscattering characteristics detected via full polarimetric PALSAR-2 data from the shorelines of various types of coasts, using the administrative zone vector data of the National Land Numerical Information (NLNI) database. The four-component scattering images derived from full polarimetric PALSAR-2 data were used to evaluate the characteristics of scattering models that affect shoreline detection. Canny edge detection was applied to the four decomposed datasets (surface, double-bounce, volume and helix scattering power) and the edges of these four datasets were combined by logical conjunction analysis. The results show that a part of the edge line in the surface scattering power image corresponded with the sandy coast shoreline. The boundary between land and sea indicated by the edge line in the surface, double-bounce, volume and helix scattering power image corresponded with the rocky coast and seawalls shoreline, which were analysed using histograms. The relationship between the four-component scattering model and the edges in these components can be explained by an L-band SAR backscattering mechanism.