Remote sensing data, such as satellite images, and remote sensing derived digital elevation models (DEMs) are credited by simplifying many geological processes that require costly and laborious field ...work, such as lineament extraction. Furthermore, the recent increase in the availability of DEMs from many free open sources as well as their advantages over satellite imagery have promoted their wide application as remote sensing methods for lineament extraction. The quality of a DEM affects the results of its application, and this quality is controlled by its vertical accuracy and spatial resolution. The objectives of this study were to assess and verify the effects of the vertical accuracies of DEMs on lineament extraction. The area around Baoji city, Shaanxi province, China, was selected as a case study and the lineaments were automatically extracted using the LINE algorithm of PCI Geomatica from three DEMs with different vertical accuracies: tri stereo ZY3 imagery derived DEM, SRTM1V3, and ASTGDEMV2. All of these DEMs have 1″ spatial resolution (approx. 30 m). The results showed that the vertical accuracy of the applied DEM affects the number, length, and density of the extracted lineaments, where these quantities increase with increasing vertical accuracy of the DEM.
A good understanding of the quality of digital elevation model (DEM) is a perquisite for various applications. This study investigates the accuracy of three most recently released 1-arcsec global ...DEMs (GDEMs, Copernicus, NASA and AW3D30) in five selected terrains of China, using more than 240,000 high-quality ICESat-2 (Ice, Cloud and land Elevation Satellite) ALT08 points. The results indicate the three GDEMs have similar overall vertical accuracy, with RMSE of 6.73 (Copernicus), 6.59 (NASA) and 6.63 m (AW3D30). While the accuracy varies considerably over study areas and among GDEMs. The results show a clear correlation between the accuracy and terrain slopes, and some relationship between the accuracy and land covers. Our analysis reveals the land cover exerts a greater impact on the accuracy than that of the terrain slope for the study area. Visual inspections of terrain representation indicate Copernicus DEM exhibits the greatest detail of terrain, followed by AW3D30, and then by NASADEM. This study has demonstrated that ICESat-2 altimetry offers an important tool for DEM assessment. The findings provide a timely and comprehensive understanding of the quality of newly released GDEMs, which are informative for the selection of suitable DEMs, and for the improvement of GDEM in future studies.
Gaofen-7 (GF-7) is the world's first Earth observation satellite to integrate optical stereo cameras and laser altimeters, mainly serving global 1:10000 scale stereo mapping. GF-7 can synchronously ...acquire laser altimetry points (LAPs) and stereo images with submeter resolution, aiming to effectively improve the vertical positioning accuracy of stereo images through joint geopositioning of LAPs and stereo images. This study proposed a quantitative evaluation model for theoretical vertical accuracy of GF-7 stereo images, LAPs, and the joint geopositioning of LAPs and stereo images. Without using ground control points (GCPs), the estimated theoretical vertical root mean square errors (RMSEs) of GF-7 stereo images, LAPs, and joint geopositioning of LAPs and stereo images were 2.02-8.49, 0.09, and 0.59-0.75 m, respectively. Subsequently, accuracy verification experiments were conducted using GF-7 data covering Hubei Province, China. The actual vertical RMSE of stereo images and joint geopositioning of LAPs and stereo images were 3.19 and 0.68 m, respectively, and the actual vertical RMSE of LAPs was consistent with the theoretical value. The experimental results confirm that the method proposed in this study is effective. The results of theoretical estimation and experimental verification both indicate that with the assistance of LAPs, the vertical accuracy of GF-7 stereo images without GCPs can meet the requirements of 1:10000 scale mapping. The results of this study have important reference value for improving GF-7 data processing methods and guiding the design of future satellites that integrate optical stereo cameras and laser altimeters.
Digital surface models (DSMs) extracted from very high resolution (VHR) satellite stereo images are becoming more and more important in a wide range of geoscience applications. The number of software ...packages available for generating DSMs has been increasing rapidly. The main goal of this work is to explore the capabilities of VHR satellite stereo pairs for DSMs generation over different land-cover objects such as agricultural plastic greenhouses, bare soil and urban areas by using two software packages: (i) OrthoEngine (PCI), based on a hierarchical subpixel mean normalized cross correlation matching method, and (ii) RPC Stereo Processor (RSP), with a modified hierarchical semi-global matching method. Two VHR satellite stereo pairs from WorldView-2 (WV2) and WorldView-3 (WV3) were used to extract the DSMs. A quality assessment on these DSMs on both vertical accuracy and completeness was carried out by considering the following factors: (i) type of sensor (i.e., WV2 or WV3), (ii) software package (i.e., PCI or RSP) and (iii) type of land-cover objects (plastic greenhouses, bare soil and urban areas). A highly accurate light detection and ranging (LiDAR) derived DSM was used as the ground truth for validation. By comparing both software packages, we concluded that regarding DSM completeness, RSP produced significantly (p < 0.05) better scores than PCI for all the sensors and type of land-cover objects. The percentage improvement in completeness by using RSP instead of PCI was approximately 2%, 18% and 26% for bare soil, greenhouses and urban areas respectively. Concerning the vertical accuracy in root mean square error (RMSE), the only factor clearly significant (p < 0.05) was the land cover. Overall, WV3 DSM showed slightly better (not significant) vertical accuracy values than WV2. Finally, both software packages achieved similar vertical accuracy for the different land-cover objects and tested sensors.
Very high-resolution (VHR) stereo satellite images provide detailed spatial and spectral information for detecting and monitoring artificial or natural objects. This information can also be used for ...object-based change detection. This study aims to reveal the potential of three-dimensional (3D) information generated from VHR stereo satellite images to determine the physical changes that may occur on Gordion tumuli. For this purpose, point cloud data were generated from WorldView-3 and KOMPSAT-3 stereo satellite images. The accuracy of these datasets was tested using 161 check points (CPs). On the other hand, digital surface models (DSMs) generated from VHR stereo satellite images were used for object-based modelling of tumuli. The vertical accuracy of these DSMs was tested by comparing them with reference DSMs extracted from Unmanned Aerial System (UAS) images. As a result of the vertical accuracy assessment of the point cloud data, 0.16 m and 0.53 m root mean square error (RMSE) values were obtained for WorldView-3 and KOMPSAT-3 data, respectively. The average RMSE values obtained as a result of the model-based comparison of DSMs are 0.28 m for WorldView-3 and 0.57 m for KOMPSAT-3. These results demonstrate that the sub-metre level physical changes occurring on tumuli can be determined by VHR stereo satellite images.
Unmanned aerial vehicles (UAVs) are increasingly used in various environmental research projects and other activities that require accurate topography images. The quality of elevation models derived ...from UAV measurements varies depending on many variables (e.g. UAV equipment used, terrain conditions, etc.). In order to improve the quality of digital models based on UAV image data, additional GNSS-RTK measurements are usually made at ground control points. The aim of this article is to evaluate the mathematical accuracy of terrain models created without ground control points. The accuracy of the models is considered in two directions: vertical and horizontal. Vertical (elevation) accuracy is calculated based on airborne laser scanning (ALS) data and horizontal (location) accuracy is calculated through comparison with high-resolution orthophotomaps. The average elevation accuracy of all created UAV-based DEMs is found to be 2.7–2.8 m (MAE), 3.1–3.3 m (RMSE), and the average horizontal accuracy is 2.1 m. Despite the low accuracy of the UAV models, the topography is reflected very well in the spatial images. This may be related to the regular and symmetrical distribution of height errors. To improve the accuracy parameters of UAV-based DEMs, it is proposed that they be rapidly georeferenced based on orthophotomaps.
Abstract
Digital elevation models (DEMs) are the fundamental datasets for coastal ecosystem monitoring, and several global open‐accessed DEMs have recently been reported. In coastal regions, a ...comprehensive vertical accuracy assessment of these DEMs has not yet been carried out. In this study, eight open‐access DEM datasets, including SRTM‐3, SRTM‐1, TanDEM‐X, ASTER GDEM v3, MERIT DEM, AW3D30, NASADEM, and CoastalDEM, were investigated across the coastal region of the Chinese mainland using high accuracy ICESat‐2 data as a reference. Statistical tools including mean absolute error (MAE) and root mean square error (RMSE) were selected to describe the data error/uncertainty and spatial distribution. Moreover, the effects of elevation ranging, slope degree, geomorphogenesis and landuse on vertical accuracy were further analyzed to assess their applicability. The assessment results revealed that the CoastalDEM and NASADEM datasets had the highest accuracy, with MAE values of 1.68 and 1.88 m and RMSE values of 2.55 and 2.61 m, for 3‐arc second and 1‐arc second resolution DEMs, respectively. Other DEMs with close accuracies include AW3D30, SRTM‐1, MERIT, and SRTM‐3 DEM. The results proved that the CoastalDEM outperformed other datasets, indicating its applicability in coastal regions.
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