城市地面沉降监测技术方法与应用

本文阐述了城市地面沉降监测的技术方法,重点介绍了水准测量和合成孔径雷达干涉(InSAR)监测在城市地面沉降监测中的适用性。以杭州市为例,通过多期水准测量、In SAR监测等技术方法,获取了杭州市2015—2020年地面沉降空间分布特征和发展趋势信息,并针对城市区域内重要基础设施、大型线状工程、跨江桥梁等进行了地面沉降应用分析。将历史及同期开展的城市水准测量成果与In SAR监测结果进行对比,显示两种技术方法测量结果具有较好的一致性,不同技术方法可以相互弥补,将两种技术方法进行融合处理和综合分析的建设思路,可以为新一线城市地面沉降监测和控制提供科学的决策依据。

Advances in space-borne SAR interferometry and its application to ground deformation monitoring

The development of Differential Synthetic Aperture Radar Interferometry （D-InSAR）, in terms of its evolution from classic to advanced forms, such as Least-Squares approach, Permanent Scatterer Interferometry, Small Baseline Subset, and Coherent Pixel Technique, is reviewed, describing concisely the main principles of each method and highlighting the difference and relationship between them. Applications of InSAR technology in China were then introduced, together with the obstacles to overcome and feasible strategies, such as integrating MERIS/MODIS data to compensate for the atmospheric effect and GPS, and multi-platform SAR data to make InSAR technique practical and operational under various conditions. The latest devel- opments were then analyzed along with high-quality SAR data, available thanks to the newly launched high-tech satellites, TerraSAR-X, and Cosmo Sky-med, and conclusions were drawn about the main limitations of the technique.

Unsupervised Change Detection in Multitemporal SAR Images Using MRF Models

An unsupervised change-detection method that considers the spatial contextual information in a log-ratio difference image generated from multitemporal SAR images is proposed. A Markov random filed (MRF) model is particularly employed to exploit statistical spatial correlation of intensity levels among neighboring pixels. Under the assumption of the independency of pixels and mixed Gaussian distribution in the log-ratio difference image, a stochastic and iterative EM-MPM change-detection algorithm based on an MRF model is developed. The EM-MPM algorithm is based on a maximiser of posterior marginals (MPM) algorithm for image segmentation and an expectation-maximum (EM) algorithm for parameter estimation in a completely automatic way. The experiment results obtained on multitemporal ERS-2 SAR images show the effectiveness of the proposed method.

Monitoring cyanobacteria-dominant algal blooms in eutrophicated Taihu Lake in China with synthetic aperture radar images

Monitoring algal blooms by optical remote sensing is limited by cloud cover.In this study,synthetic aperture radar(SAR) was deployed with the aim of monitoring cyanobacteria-dominant algal blooms in Taihu Lake in cloudy weather.The study shows that dark regions in the SAR images caused by cyanobacterial blooms damped the microwave backscatter of the lake surface and were consistent with the regions of algal blooms in quasi-synchronous optical images,confirming the applicability of SAR for detection of surface blooms.Low backscatter may also be associated with other factors such as low wind speeds,resulting in interference when monitoring algal blooms using SAR data alone.After feature extraction and selection,the dark regions were classified by the support vector machine method with an overall accuracy of 67.74%.SAR can provide a reference point for monitoring cyanobacterial blooms in the lake,particularly when weather is not suitable for optical remote sensing.Multi-polarization and multi-band SAR can be considered for use in the future to obtain more accurate information regarding algal blooms from SAR data.

Landslide monitoring with high-resolution SAR data in the Three Gorges region

Employing the well-known D-InSAR technique,we investigated landslide monitoring in the Three Gorges region using TerraSAR-X data.The experiment demonstrates that using both the amplitude and differential phase allows us to identify the precise location,deformation and time range of occurrence of certain landslides.To overcome the atmospheric effect on D-InSAR results,a time-series analysis was also carried out.The observed nonlinear relationship between the deformation and water level suggests that reservoir water level fluctuation is one of the major causes of landslides,which is significant in terms of issuing landslide warnings.In addition,the comparison of TerraSAR-X and C-band ASAR data results indicates that TerraSAR-X data provide far more reasonable deformation measurements because of their high temporal and spatial resolutions.

Chinese Satellite-based Flood Mapping and Damage Assessment in Dongdian Flood Detention Basin,China

Against the background of rapid climate warming,frequent and severe flooding disasters significantly impact socio-economic development and human life.In 2023,due to the northward movement of Typhoon Doksuri,extreme precipitation occurred in northern China,which resulted in a massive flood event in the Haihe River basin.Seven flood detention basins(FDBs)in North China were successfully implemented to effectively alleviate the downstream flood pressure.Leveraging all available Chinese satellite data,we monitored the flooding process daily,focusing on reviewing the flooding in the Dongdian FDB.The results indicate that since the activation of Dongdian FDB on August 1,the flood reached the urban area of Tianjin in just nine days and inundated the entire detention basin.Flooding persisted in the detention basin for about a week before gradually receding.The total maximum inundated area in the whole region was 307.5 km^(2),including 240.5 km^(2)of arable land,7.0 km^(2)of greenhouse land,and 9.7 km^(2)of built-up land,with an average inundation duration of 19 days.The total cumulative inundated arable land area was 240.5 km^(2),with an average inundation time of 21 days.This study shows that multi-source Chinese satellite data can provide comprehensive information and adequate references for post-disaster assessments.