Kailiang Deng

Terrestrial laser scanning (TLS) is an efficient tool to capture the point cloud for facade modeling. However, it is not easy to obtain the position by Global Navigation Satellite System (GNSS) as occluded by high buildings, which would lead to a problem for orienting the TLS data to a target coordinate system. In this paper, we propose a coarse-to-fine registration method for reliably orient the TLS data using digital line graph (DLG). The orientation is completed by horizontal plane registration and elevation registration part. The proposed method is composed of five steps: (1) Using the proposed method to extract the corner points from the building outline of DLG. (2) Using the proposed method based on RANSAC algorithm to extract the corner points and the façade point clouds of the TLS data. (3) Coarse alignment of the two extracted sets of corner points using 4PCS algorithm; (4) Fine registration by 2D-ICP algorithm; and (5) Completing elevation registration using elevation control points. Three data sets are employed to perform the experiments, and the results confirm that the proposed method is reliable and efficient in achieving the registration DLG and TLS data. By comparing to two other typical registration methods, the proposed method performs better.

Distributed scatterers (DSs) are necessary to increase point density in multi-temporal InSAR (MT-InSAR) monitoring. The identification of homogeneous pixels (HPs) is the first and key step for DS processing to overcome the low signal-to-noise ratio condition. Since multi-polarization data are good at describing geometrical structures and dielectric properties of ground objects, they have been applied for HP identification. However, polarimetric information is not enough for identifying areas with similar ground objects but different deformation. We propose a novel DS preprocessing algorithm based on polarimetric interferometric homogeneous pixel (PIHP) identification. Firstly, a novel Polarimetric InSAR (PolInSAR) similarity that combines polarimetric intensity, interferometric coherence, and phase is proposed, which is readily available in multi-baseline and multi-polarization data and flexible by controlling weighting factors. Secondly, based on the binary partition tree (BPT) framework, object-orientated multi-scale PIHP identification is achieved, which is suitable for complex deformation scenes. Tested with simulated quad-polarization data, our method shows improvement in phase quality and point density, especially in the deformed areas, compared with the traditional HP identification method based on the polarimetric homogeneity (PolHom) test and the method with ground object type map. Tested with 30 quad-polarization Radarsat-2 images over Kilauea Volcano, the point density of our method is three times higher than that of the PolHom test in vegetation areas. Our method is proven to be more sensitive and mechanically more advanced to homogeneous pixels identification than the traditional ones, which is helpful for phase optimization, spatial enlargement of monitoring points, and stability of the MT-InSAR algorithm.

Many coastal cities reclaim land from the sea to meet the rapidly growing demand for land caused by population growth and economic development. Settlement in reclaimed land may delay construction and even damage infrastructures, so accurately predicting the settlement over reclaimed areas is important. However, the limited settlement observation and ambiguous final settlement estimation affect accurate settlement prediction in traditional methods. This study proposes a new strategy to solve these problems by using the Multitemporal Interferometric Synthetic Aperture Radar (MT-InSAR) method and takes the Xiamen Xiang’an International Airport, built on reclaimed land, as an example. The MT-InSAR is adopted to process the Sentinel-1 images to obtain the settlement history of the study area. The results show that settlement mainly occurs in the reclaimed areas, with the maximum average settlement rate exceeding 40 mm/y. We use the statistical properties of curve fitting to choose the best curve model from several candidate curve models to predict the settlement time series. The Asaoka method is used to identify the critical state between settlement and stability. We predict the consolidation time of the whole study area and reveal that the deformation rate is positively correlated with the consolidation time. The maximum remaining settlement time is over ten years since 24 December 2019. Therefore, manual compaction operations can be carried out to speed up settlement in the areas that need a long time to consolidate. The proposed method can be used to predict the settlement of similar reclaimed areas, and the predicted results can provide a reference for engineering construction.

Cross-domain polarimetric synthetic aperture radar interpretation is urgently needed, due to the rapid data growth and label scarcity. However, the class distribution shift problems hinder the reuse of labeled samples among cross-domain images. Most of the existing domain adaptations can only handle the cross-domain case of same categories between source and target domains, while the categories of the target domain are usually more abundant than those of the source domain. To improve the usability of labeled samples among cross-domain images, an unsupervised generalized zero-shot domain adaptation (uGZSDA) based on scattering component semantics (SCSs) is proposed. By using SCSs and limited labeled samples (seen categories) in the source domain, more land cover types (seen and unseen categories) in the unlabeled target domain can be inferred. First, a stacked autoencoder (SAE) extracts source/target-domain features, and SCSs of typical land covers are constructed by cross-domain databases and statistical scattering components. Second, combining SAE features and source-domain samples, the most likely seen class samples in the target domain are selected by probability sorting, and the SAE is retrained by obtained selected seen samples. Third, the unseen class samples in the target domain are inferred by the retrained SAE, classification probability, and semantic similarity. Finally, the selected seen and inferred unseen class samples in the target domain are used to further retrain the SAE, and the target domain is classified by the retrained SAE and the classifier. The proposed uGZSDA is verified among 16 cross-domain PolSAR datasets. Using SCS and two to three types of seen samples from the source domain, the accuracies of seven types of land covers in the unlabeled target domain can reach 76–83.96%.

Multi-temporal Interferometric Synthetic Aperture Radar (MT-InSAR) has been widely used for ground motion identification and monitoring over large-scale areas, due to its large spatial coverage and high accuracy. However, automatically locating and assessing the state of the ground motion from the massive Interferometric Synthetic Aperture Radar (InSAR) measurements is not easy. Utilizing the spatial-temporal characteristics of surface deformation on the basis of the Small Baseline Subsets InSAR (SBAS-InSAR) measurements, this study develops an improved method to locate potential unstable or dangerous regions, using the spatial velocity gradation and the temporal evolution trend of surface displacements in large-scale areas. This method is applied to identify the potential geohazard areas in a mountainous region in northwest China (Lajia Town in Qinghai province) using 73 and 71 Sentinel-1 images from the ascending and descending orbits, respectively, and an urban area (Dongguan City in Guangdong province) in south China using 32 Sentinel-1 images from the ascending orbit. In the mountainous area, 23 regions with potential landslide hazards have been identified, most of which have high to very high instability levels. In addition, the instability is the highest at the center and decreases gradually outward. In the urban area, 221 potential hazards have been identified. The moderate to high instability level areas account for the largest proportion, and they are concentrated in the farmland irrigation areas, and construction areas. The experiment results show that the improved method can quickly identify and evaluate geohazards on a large scale. It can be used for disaster prevention and mitigation.

Reclaimed airports usually have fragile geological structures and are susceptible to the uneven ground settlements caused by filling-material consolidation, underground construction, and dynamic loading from takeoff and landing of aircrafts. Therefore, deformation monitoring is of great significance to the safe operation of reclaimed airports. This study adopts an improved permanent-scatterer interferometric synthetic-aperture radar strategy to map the spatiotemporal deformation of Shenzhen Bao'an International Airport in China using ascending and descending Envisat/ASAR data acquired from 2007 to 2010 and Sentinel-1 data from 2015 to 2019. The results show that uneven settlements of the airport concentrate in the new reclaimed land. Then we explore the settlement characteristics of each functional area. Furthermore, we separate out the dynamic-load settlement of runway No. 2 and confirm the settlements caused by dynamic load. This study provides new ideas for studying deformation in similar fields, and technical references for the future construction of Shenzhen Airport.

Airborne vector gravimetric data have become increasingly available. A general band-limited horizontal boundary value problem using horizontal components of these vector gravimetric data is formulated and solved to compute regional geoid. The disturbing potential on the geoid is determined directly using the data in the air. This one-step approach is permitted by exploiting the following: 1) band-limited property of both the disturbing potential and the data; 2) the orthogonality of the horizontal components of the gravity vector; and 3) the additive rule of the spherical functions. Then geoidal undulations can be readily obtained according to the Bruns formula.