Topographic Change Analysis Research Articles

Analysis of Corneal Topographic Changes after Upper Lid Surgery in Congenital and Acquired Ptosis

Objective: To assess the corneal topographic and refractive changes after ptosis surgery. Study Design: Prospective longitudinal study. Place and Duration of Study: Armed Forces Institute of Ophthalmology, Rawalpindi Pakistan, from Jan 2020 to Jul 2021. Methodology: A total of 90 individuals were selected by non-probability convenience sampling. Patients with diagnosed Ptosis and planned for surgery were followed up for six months post-surgery. Corneal topography, visual acuity, and physical assessment for Ptosis were done pre and post-surgery and compared for differences. Result: There were more cases of acquired Ptosis than congenital in our sample (p=<0.001). The patients had more poor levator function pre-operatively (p=0.291), which improved to fair post-operatively (p=<0.0001). Post-operatively, a significant decrease in the SimK and Cylinder power was observed in the sample. The visual acuity improved significantly, and the MRD also improved. With no significant change in CCT post-operatively. Conclusion: Our study showed that post-surgery SimK, visual acuity, MRD, and cylindrical power improved. However, the CCT did not show significant alterations.

Dense optic nerve head deformation estimated using CNN as a structural biomarker of glaucoma progression.

To present a new structural biomarker for detecting glaucoma progression based on structural transformation of the optic nerve head (ONH) region over time. Dense ONH deformation was estimated using deep learning methods namely DDCNet-Multires, FlowNet2, and FlowNetCorrelation, and legacy computational methods namely the topographic change analysis (TCA) and proper orthogonal decomposition (POD) methods. A candidate biomarker was estimated as the average magnitude of deformation of the ONH and evaluated using longitudinal confocal scans of 12 laser treated and 12 contralateral normal eyes of 12 primates from the LSU Experimental Glaucoma Study (LEGS); and 36 progressing eyes and 21 longitudinal normal eyes from the UCSD Diagnostic Innovations in Glaucoma Study (DIGS). Area under the ROC curve (AUC) was used to assess the diagnostic accuracy of the biomarker. AUROC (95% CI) for LEGS were: 0.83 (0.79, 0.88) for DDCNet-Multires; 0.83 (0.78, 0.88) for FlowNet2; 0.83 (0.78, 0.88) for FlowNet-Correlation; 0.94 (0.91, 0.97) for POD; and 0.86 (0.82, 0.91) for TCA methods. For DIGS: 0.89 (0.80, 0.97) for DDCNet-Multires; 0.82 (0.71, 0.93) for FlowNet2; 0.93 (0.86, 0.99) for FlowNet-Correlation; 0.86 (0.76, 0.96) for POD; and 0.86 (0.77, 0.95) for TCA methods. Lower diagnostic accuracy of the learning-based methods for LEG study eyes were due to image alignment errors in confocal sequences. Deep learning methods trained to estimate generic deformation were able to estimate ONH deformation from image sequences and provided a higher diagnostic accuracy. Our validation of the biomarker using ONH sequences from controlled experimental conditions confirms the diagnostic accuracy of the biomarkers observed in the clinical population. Performance can be further improved by fine-tuning these networks using ONH sequences.

Analysis of topographic changes after the 2011 Tohoku-oki tsunami around the Gamo Lagoon in Miyagi Prefecture using digital elevation models combining terrestrial and submarine topography

Analysis of topographic changes after the 2011 Tohoku-oki tsunami around the Gamo Lagoon in Miyagi Prefecture using digital elevation models combining terrestrial and submarine topography

Historical Structure from Motion (HSfM): Automated processing of historical aerial photographs for long-term topographic change analysis

Precisely measuring the Earth’s changing surface on decadal to centennial time scales is critical for many science and engineering applications, yet long-term records of quantitative landscape change are often temporally and geographically sparse. Archives of scanned historical aerial photographs provide an opportunity to augment these records with accurate elevation measurements that capture the historical state of the Earth surface. Structure from Motion (SfM) photogrammetry workflows produce high-quality digital elevation models (DEMs) and orthoimage mosaics from these historical images, but time-intensive tasks like manual image preprocessing (e.g., fiducial marker identification) and ground control point (GCP) selection impede processing at scale. We developed an automated method to process historical images and generate self-consistent time series of high-resolution (0.5–2 m) DEMs and orthomosaics, without manual GCP selection. The method relies on SfM to correct camera interior and exterior orientation and a robust multi-stage co-registration approach using modern reference terrain datasets for geolocation refinement. We demonstrate the method using scanned images from the North American Glacier Aerial Photography (NAGAP) archive collected between 1967 and 1997. We present results for two sites with variable photo acquisition geometry and overlap — Mount Baker and South Cascade Glacier in Washington State, USA. The automated method corrects initial camera position errors of several kilometers and produces accurately georeferenced, high-resolution DEMs and orthoimages, regardless of camera configuration, acquisition geometry, terrain characteristics, and reference DEM properties. The average RMS reprojection error following bundle adjustment optimization was 0.67 px (0.15 m) for the 261 images contributing to 10 final DEM mosaics between 1970 and 1992 at Mount Baker, and 0.65 px (0.13 m) for the 243 images contributing to 18 individual DEMs between 1967 and 1997 at South Cascade Glacier. The relative accuracy of elevation values in the historical time series stacks was 0.68 m at Mount Baker and 0.37 m at South Cascade Glacier. Our products have reduced systematic error and improved accuracy compared to DEM products generated using SfM with manual GCP selection. Final elevation change measurement precision was ∼0.7–1.0 m over a 30-year period, enabling the study of processes with rates as low as ∼1-3 cm/yr. Our results demonstrate the potential of this scalable method to rapidly process archives of historical imagery and deliver new quantitative insights on long-term geodetic change and Earth surface processes.

EVALUATION OF UAV-BORNE PHOTOGRAMMETRY AND LASER SCANNING FOR 3D TOPOGRAPHIC CHANGE ANALYSIS AT AN ACTIVE ROCK GLACIER

Abstract. Point clouds derived from UAV-borne laser scanning and UAV-borne photogrammetry provide new opportunities for 3D topographic monitoring in geographic research. The airborne acquisition strategy overcomes common challenges of ground-based techniques, such as limited spatial coverage or heterogeneous measurement distribution, and allows flexible repeated acquisitions at high temporal and spatial resolution. While UAV-borne 3D sensing techniques are expected to thereby enhance geographic monitoring, their specific potential for methods and algorithms of 3D change analysis is yet to be investigated. In our study, we assess point clouds originating from UAV-borne photogrammetry using dense image matching (DIM) and UAV-borne laser scanning (ULS) as input for 3D topographic change analysis at an active rock glacier in the Austrian Alps. We analyse surface change by using ULS and DIM point clouds of 2019 and 2021 as input for two state-of-the-art methods for pairwise surface change analysis: (1) The Multiscale Model to Model Cloud Comparison (M3C2) algorithm and (2) a recent M3C2-based approach (CD-PB M3C2) using plane correspondences to reduce the uncertainty of quantified change. We evaluate ULS-based and DIM-based change analysis regarding their performance in (1) achieving high spatial coverage of derived changes, (2) accurately quantifying magnitudes and uncertainty of change, and (3) detecting significant change (change magnitudes > associated uncertainty). As reference we use change quantified between two terrestrial laser scanning (TLS) surveys undertaken simultaneously with the ULS and DIM data acquisitions. Our study shows the improved spatial coverage of M3C2 achieved with point clouds acquired with UAVs (+ 60% of core points used for change analysis). For CD-PB M3C2, ULS and DIM point clouds enabled a spatially more uniform distribution of plane pairs used for change quantification and a slightly higher spatial coverage (+6% – +7% of core points used for change analysis) compared to the TLS reference. Magnitudes of M3C2 change were closer to the TLS reference for ULS-ULS (mean difference: 0.04 m; std. dev.: 0.05 m) compared to ULS-DIM (mean difference: 0.12 m; std. dev.: 0.08 m). Similar results were obtained for CD-PB M3C2 using ULS-ULS (mean difference: 0.02 m; std. dev.: 0.01 m) and ULS-DIM (mean difference: 0.06 m; std. dev.: 0.01 m). Moreover, magnitudes of change were above the associated uncertainty in 82% – 89% (M3C2) and 89% – 90% (CD-PB M3C2) of the area of change analysis. Our findings demonstrate the potential of ULS and DIM point clouds as input for accurate 3D topographic change analysis for the study at hand and can support the design and setup of 3D/4D Earth observation systems for rock glaciers and natural scenes with complex topography, such as landslides or debris covered glaciers.

Development of a Numerical Model to Analyze the Formation and Development Process of River Mouth Bars

An integrated sediment management approach that includes the recovery of the amount of declined sediment supply is effective as a fundamental solution to coastal erosion. During planning, it is essential to analyze the transfer mechanism of the sediments generated from estuaries (the junction between a river and sea) to assess the amount and rate of sediment discharge (from the river to sea) supplied back to the coast. Although numerical models that interpret the tidal sand bar flushing process during flooding have been studied, thus far, there has been no study focusing on the formation and development processes of tidal sand bars. Therefore, this study aims to construct wave deformation, flow regime calculation, and topographic change analysis models to assess the amount of recovered sediment discharge and reproduce the tidal sand bar formation process through numerical analysis for integrated littoral drift management. The tidal sand bar formation process was simulated, and the wave energy and duration of action concepts were implemented to predict the long-term littoral movement. The river flux and wave conditions during winter when tidal sand bars dominantly develop were considered as the external force conditions required for calculation. The initial condition of the topographic data directly after the Maeupcheon tidal sand bar flushing during flooding was set as the initial topography. Consequently, the tidal sand bar formation and development due to nearshore currents dependent on the incident wave direction were reproduced. Approximately 66 h after the initial topography, a sand bar formation was observed at the Maengbang estuary.

Correspondence-driven plane-based M3C2 for lower uncertainty in 3D topographic change quantification

The analysis and interpretation of 3D topographic change requires methods that achieve low uncertainties in change quantification. Many recent geoscientific studies that perform point cloud-based topographic change analysis have used the Multiscale Model to Model Cloud Comparison (M3C2) algorithm to consider the associated uncertainty. Change measured with the M3C2 approach, however, is difficult to interpret where (1) change occurs in directions different to the direction of change computation or (2) the quantified magnitudes of change are exceeded by the associated uncertainty due to a rough surface morphology. We present a correspondence-driven plane-based M3C2 approach that is tailored to quantifying small-magnitude (< 0.1 m) 3D topographic change of rough surfaces by reducing the uncertainty of quantified change. The approach (1) extracts planar surfaces in point clouds of successive epochs, (2) identifies corresponding planar surfaces between two point clouds using a binary random forest classification, and (3) calculates M3C2 distances and the associated uncertainty between the corresponding planar surfaces. This correspondence-driven plane-based M3C2 does not require recognition or reconstruction of geometrically complex objects but instead quantifies change between less complex, homologous planar surfaces. The approach further allows to relate change directly to a moving object. We apply our approach to a bi-weekly time series of terrestrial laser scanning point clouds acquired at a rock glacier in the Austrian Alps. The approach enables a sevenfold reduction in the uncertainty associated with topographic change compared to standard M3C2. Significant change is therefore detected in 72.62% to 76.41% of the area of change analysis, whereas standard M3C2 detects significant change in only 16.21% (2-week timespan) to 59.96% (10-week timespan) of the same area. The correspondence-driven plane-based M3C2 complements 3D change analysis in applications that aim to quantify small-magnitude topographic change in photogrammetric or laser scanning point clouds with low uncertainties in natural scenes which are characterised by overall rough surface morphology and by individual rigid objects with planar surfaces (e.g., rock glaciers, landslides, debris covered glaciers).

Optical coherence tomography-measured retinal nerve fiber layer thickness values compensated with a multivariate model and discrimination between stable and progressing glaucoma suspects

PurposeOur previously introduced multivariate model, compensating for intersubject variability, was applied to circumpapillary retinal nerve fiber layer (RNFL) values measured with optical coherence tomography in glaucoma suspects with or without prior progressive optic disc (OD) change in a series of confocal scanning laser tomography (CSLT, HRT III) measurements.MethodsIn this prospective study, OD change during CSLT follow-up was determined with strict, moderate, and liberal criteria of the topographic change analysis (TCA). Model compensation (MC) as well as age compensation (AC) was applied to RNFL sectors (RNFLMC vs. RNFLAC). Diagnostic performance of RNFLMC vs. RNFLAC was tested with an area under the receiver operating characteristic (AUROC) and was compared between methods.ResultsForty-two glaucoma suspects were included. Patients without prior progressive OD change during the CSLT follow-up (= stable) had thicker RNFL thickness values in most areas and for all progression criteria. RNFLMC AUROC for the global RNFL (0.719) and the inferior quadrant (0.711) performed significantly better compared with RNFLAC AUROC (0.594 and 0.631) to discriminate between stable and progressive glaucoma suspects as defined by the moderate criteria of CSLT progression analysis (p = 0.028; p = 0.024).ConclusionMC showed a slight but significant improvement in detection of subjects with prior progressive OD change among a group of glaucoma suspects, when compared to AC, which is the compensation method commonly used during OCT data evaluation in daily routine. Further studies are warranted to validate the present results.

Comparative analysis of refractive and topographic changes after eye muscle surgery

HintergrundÜber die Frage, ob nach Augenmuskeloperationen Refraktions- oder Topographieveränderungen zu erwarten sind, besteht weitestgehend Unklarheit.Material und MethodenIn der vorliegenden Studie wurden prä- sowie postoperativ von 229 Augen objektive Refraktion, Pentacam (Fa. Oculus, Menlo Park, CA, USA) und Visus erhoben und analysiert. Die Untersuchung erfolgte präoperativ, am ersten postoperativen Tag sowie nach 3 Monaten.ErgebnisseNach Operationen an einem sowie 2 geraden Augenmuskeln bestehen signifikante Veränderungen des Astigmatismus (p < 0,001), jedoch normalisiert sich dieser nach 3 Monaten wieder auf das präoperative Niveau. Ebenso war dieser Verlauf nach kombinierten Operationen von geraden und schrägen Augenmuskeln zu belegen.SchlussfolgerungEs lässt sich daher postulieren, dass eine umfangreiche Aufklärung von Patienten hinsichtlich passagerer Veränderungen des Zylinders insbesondere bei Beteiligung gerader Augenmuskeln unabdingbar ist und postoperativ eine ergänzende Refraktions- und Topographiekontrolle bei mangelnder Visusrehabilitation sinnvoll sein kann.

Corneal hysteresis as a risk factor for optic nerve head surface depression and retinal nerve fiber layer thinning in glaucoma patients

To evaluate the role of corneal hysteresis (CH) as a risk factor for progressive ONH surface depression and RNFL thinning measured by confocal scanning laser ophthalmoscopy (CSLO) and spectral-domain optical coherence tomography (SD-OCT), respectively in glaucoma patients. Prospective study. A total of 146 eyes of 90 patients with glaucoma were recruited consecutively. The CH measurements were acquired at baseline and 4-months interval using the Ocular Response Analyzer (Reichert Instruments, Depew, NY). Eyes were imaged by CSLO (Heidelberg Retinal Tomograph [HRT]; Heidelberg Engineering, GmbH, Dossenheim, Germany) and SD-OCT (Cirrus HD-OCT; Carl Zeiss Meditec AG, Dublin, CA) at approximately 4-month intervals for measurement of ONH surface topography and RNFL thickness, respectively. Significant ONH surface depression and RNFL thinning were defined with reference to Topographic Change Analysis (TCA) with HRT and Guided Progression Analysis (GPA) with Cirrus HD-OCT, respectively. Multivariate cox proportional hazards models were used to investigate whether CH is a risk factor for ONH surface depression and RNFL progression after adjusting potential confounding factors. All patients with glaucoma were followed for an average of 6.76 years (range, 4.56–7.61 years). Sixty-five glaucomatous eyes (44.5%) of 49 patients showed ONH surface depression, 55 eyes (37.7%) of 43 patients had progressive RNFL thinning and 20 eyes (13.7%) of 17 patients had visual field progression. In the cox proportional hazards model, after adjusting baseline diastolic IOP, CCT, age, baseline disc area and baseline MD, baseline CH was significantly associated with ONH surface depression and visual field progression (HR = 0.71, P = 0.014 and HR = 0.54, P = 0.018, respectively), but not with RNFL thinning (HR = 1.03, P = 0.836). For each 1-mmHg decrease in baseline CH, the hazards for ONH surface depression increase by 29%, and the hazards for visual field progression increase by 46%. The CH measurements were significantly associated with risk of glaucoma progression. Eyes with a lower CH were significantly associated with an increased risk of ONH surface depression and visual field progression in glaucoma patients.

Surface displacement and topographic change analysis of the Changhe landslide on September 14, 2019, China

On September 14, 2019, a reactivated landslide with a volume of 1.3 × 107 m3 occurred in Changhe Town, Tongwei County, Gansu Province, China. As a result, a provincial highway, brickfield, and bridge were destroyed. Based on field investigation, interferometric synthetic aperture radar (InSAR) as well as unmanned aerial vehicle (UAV) photogrammetry, high-resolution remote sensing imagery, and digital elevation model, we addressed the surface displacement, travel distance, topographic changes, and causative factors of the Changhe landslide. The result shows the combination of ascending and descending orbit datasets can not only be used to monitor the landslide surface displacement but also to verify the deformation results. This landslide is a typical retrogressive landslide where large pre-failure deformation exists in the lower part of the landslide body. We detected the surface travel distance of the landslide and found spatial differences exist in the surface travel distance of the landslide. The deposit volume slightly exceeds erosion volume due to decompaction during the landslide. The frequency distribution of the basic topographic factors before and after the landslide is different, which indicates that the landslide event significantly changed the local topography and geomorphology. This study provides an insight into the spatiotemporal evolution of the landslide and has practical importance for early warning of landslides and risk mitigation.

Different Paths for Developing Terrestrial LiDAR Data for Comparative Analyses of Topographic Surface Changes

High resolution terrestrial laser scanning data (TLS; terrestrial LiDAR) provide an excellent background for quantitative resource estimation through the comparative analysis of topographic surface changes. However, unlike airborne LiDAR data, which is usually provided as classified and contains a class of ground points, raw TLS data include all of the points of the scanned space within the specified scanner range. In effect, utilizing the latter data to estimate the volume of the resource by the differential analysis of digital elevation models (DEMs) requires the data to be specially prepared, i.e., separating from the point cloud only the data that represent the relevant class. In the case of natural resources, e.g., mineral resources, the class is represented by ground points. This paper presents the results that were obtained by differential analysis of high resolution DEMs (DEM of difference (DoD) method) using TLS data that were processed both manually (operator noise removal) and with the use of the automatic Cloth Simulation Filter (CSF) algorithm. Three different time pairs of DoD data were analyzed for a potential gravel-cobble deposit area of 45,444 m2, which was located at the bottom of the mouth section of the Scott River in south-east Svalbard. It was found that the applied method of ground point classification had very little influence on the errors in the range of estimating volumetric parameters of the mineral resources and measurement uncertainty. Moreover, it was shown that the point cloud density had an influence on the CSF filtering efficiency and spatial distribution of errors.

Analysis of visual, refractive, topographic and aberrometric changes in different uncommon accelerated cross-linking protocols in keratoconus: A 12 month follow-up

To describe the visual, refractive, topographic and aberrometric outcomes of six different accelerated cross-linking (ACXL) protocols in progressive keratoconus (KC) at 12 months. This observational retrospective study included 62 eyes of 49 patients with progressive KC that received one of the following accelerated cross-linking protocols: Group I (8 patients, 5.4 J/cm 2, 15mWx12min, pulsed), Group II (11 patients, 5.4 J/cm 2 , 6mWx15min, continuous), Group III (16 patients, 5.4 J/cm 2 , 9mWx10min, continuous), Group IV (13 patients, 5.4 J/cm 2 , 30mWx6min, pulsed), Group V (8 patients, 7.2 J/cm 2 , 15mWx16min, pulsed) and Group VI (6 patients, 7.2 J/cm 2 , 30mWx8min, pulsed). Best corrected visual acuity (BCVA), sphere, refractive cylinder, spherical equivalent (SE), maximum keratometry (Kmax), mean keratometry (Km), flat keratometry (K1), steep keratometry (K2), thinnest pachymetry, total aberrations, high order aberrations (RMS-HOA), spherical aberration, coma and trefoil were studied previously and at 12 months. Intragroup and intergroup statistical analysis was performed. Postoperative complications were noted. 11 patients were females(22,45%) and 38 males(77,55%). Improvement in the BCVA was observed in all groups (P > 0.05). Kmax reduced in all patients and was statistically significant in groups II (p = 0.041), III (p = 0.017), IV (p = 0.018) and V (p = 0.018). Flattening of the Km was significant in groups II (p = 0.028), IV (p = 0.008) and V (p = 0.028), as well as the K1 in groups IV(p = 0.01) and V(p = 0.028) and K2 in group IV(p = 0.036). There was no significant difference in the thinnest pachymetry in any of the groups. Total aberrations, RMS-HOA, spherical aberration and coma reduced in all groups with statistical significance in Group V (P = 0.016). Two patients in Group I had anterior stromal scarring and one patient in Group V presented an unexpected overflattening. Progression was noticed in one patient in Group II. Accelerated CXL protocols included in this study can be considered effective and safe procedures in stopping the progression of keratoconus at 12 months. Improvement in BCVA and wavefront analysis is observed, but results are limited by the number of patients. Caution should be taken when applying high radiance and long duration protocols to prevent undesirable events.

Mapping the extent and methods of small-scale emerald mining in the Panjshir Valley, Afghanistan

Emerald mining in the Panjshir Valley, Afghanistan, has occurred for thousands of years, yet few records exist documenting the detailed spatial extent, techniques, or productivity of small-scale miners. This study proposes new methods to map and monitor the extent and changes in small-scale mining in remote and inaccessible terrain by integrating multispectral remote sensing analysis with archival geologic data and three-dimensional topographic change detection to examine emerald deposit zones and mining activity in the Panjshir Valley. Specifically, previously mapped geologic units known to host emeralds were re-analyzed using Landsat multispectral analysis to investigate the potential distribution of mining activity. Interpretation of very fine-resolution satellite imagery showed that mining activity is becoming more concentrated and transitioning from traditional tunneling methods to mechanized surface excavation. Finally, topographic change analysis of mechanized mine sites was combined with archival grade data to estimate production and consider improved recovery methods by small-scale miners.

Geomorphic process signatures reshaping sub‐humid Mediterranean badlands: 2. Application to 5‐year dataset

AbstractBadland landscapes exhibit high erosion rates and represent the main source of fine sediments in some catchments. Advances in high‐resolution topographic methods allow analysis of topographic changes at high temporal and spatial scales. We apply the Mapping Geomorphic Processes in the Environment (MaGPiE) algorithm to infer the main geomorphic process signatures operating in two sub‐humid badlands with contrasting morphometric attributes located in the Southern Pyrenees. By interrogating a 5‐year dataset of seasonal and annual topographic changes, we examine the variability of geomorphic processes at multiple temporal scales. The magnitude of geomorphic processes is linked to landform attributes and meteorological variables. Morphometric differences between both adjacent badlands allow us to analyse the role of landform attributes in the main geomorphic process reshaping landscapes subjected to the same external forcing (i.e. rainfall and temperature).The dominant geomorphic process signatures observed in both badlands are different, despite their close proximity and the same rainfall and temperature regimes. Process signatures determining surface lowering in the gently sloping south‐facing badland, characterized by lower connectivity and more vegetation cover, are driven by surface runoff‐based processes, both diffuse (causing sheet washing) and concentrated (determining cutting and filling, rilling and gullying). The steeper, more connected north‐facing slopes of the other badland are reshaped by means of gravitational processes, with mass wasting dominating topographic changes. In terms of processes determining surface raising, both mass wasting and cutting and filling are most frequently observed in both badlands. There is a clear near‐balanced feedback between both surface‐raising and ‐lowering processes that becomes unbalanced at larger temporal scales due to the thresholds overcome, as the volume associated with surface lowering becomes higher than that associated with raising‐based processes. Rainfall variables control surface flow processes, while those variables associated with low temperature have a significant relation with mass movement‐based processes and other localized processes such as regolith cohesion loss. Finally, our results point out that morphometry (slope and connectivity) together with vegetation cover are key factors determining geomorphic processes and associated topographic changes. © 2020 John Wiley &amp; Sons, Ltd.

Special Issue on “Advances in Remote Sensing and Geoscience Information Systems of the Coastal Environments”

Ryu, J.-H.; Jung, H.-S.; Lee, S., and Cui, T., 2019. Special Issue on “Advances in Remote Sensing and Geoscience Information Systems of the Coastal Environments”. In: Jung, H.S.; Lee, S.; Ryu, J.H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. v–xi. Coconut Creek (Florida), ISSN 0749-0208.Advanced remote sensing (RS) and geoscience information system (GIS) have become more essential to understanding the coastal environmental characteristics of Earth surfaces. In this special issue, a total of 52 papers have been published. These papers studied on a variety seas including the Yellow Sea (YS), East China Sea (ECS), South China Sea, Arctic Ocean, North West Pacific, and the Greenland Sea. Forty of these papers studied on the YS and the ECS. Remotely sensed data from various platforms, including satellite, airborne, unmanned aircraft, Helikite and Unmanned Surface Vehicle (USV) images, were used for analysis, and GIS spatial data, reanalysis data and models were also utilized. Ocean colour images were mainly applied to detect marine environment changes (SST, chlorophyll-a and suspended particle matter) and benthic and floating vegetation. High-resolution images were mainly used in the analysis of topographic changes, sedimentary phases and habitat changes in small study areas. SAR images were mainly used for detection of oil spill and sea ice, and could also be used in studies to estimate the moving speed of the target using dual receive antenna mode of the SAR sensor. Unmanned aerial vehicles were mainly used to analyze geographical features and topographic deformation along the coast. Furthermore, hyperspectral images were used for precise detection of vegetation and oil spill studies.

HIGH-FREQUENCY 3D GEOMORPHIC OBSERVATION USING HOURLY TERRESTRIAL LASER SCANNING DATA OF A SANDY BEACH

Abstract. Geomorphic processes occur spatially variable and at varying magnitudes, frequencies and velocities, which poses a great challenge to current methods of topographic change analysis. For the quantification of surface change, permanent terrestrial laser scanning (TLS) can generate time series of 3D point clouds at high temporal and spatial resolution. We investigate how the temporal interval influences volume change observed on a sandy beach regarding the temporal detail of the change process and the total volume budget, on which accretion and erosion counteract. We use an hourly time series of TLS point clouds acquired over six weeks in Kijkduin, the Netherlands. A raster-based approach of elevation differencing provides the volume change over time per square meter. We compare the hourly analysis to results of a three- and six-week observation period. For the larger period, a volume increase of 0.3 m3/ m2 is missed on a forming sand bar before it disappears, which corresponds to half its volume. Generally, a strong relationship is shown between observation interval and observed volume change. An increase from weekly to daily observations leads to a five times larger volume change quantified in total. Another important finding is a temporally variable measurement uncertainty in the 3D time series, which follows the daily course of air temperature. Further experiments are required to fully understand the effect of atmospheric conditions on high-frequency TLS acquisition in beach environments. Continued research of 4D geospatial analysis methods will enable automatic identification of dynamic change and improve the understanding of geomorphic processes.

A Workflow to Estimate Topographic and Volumetric Changes and Errors in Channel Sedimentation after Disturbance

Light Detection and Ranging (LiDAR) methods, such as ground-based Terrestrial Laser Scanning (TLS), have enabled collection of high-resolution point clouds of elevation data to calculate changes in fluvial systems after disturbance, but are often accompanied by uncertainty and errors. This paper reviews and compares TLS analysis methods and develops a workflow to estimate topographic and volumetric changes in channel sedimentation after disturbance. Four analytic methods to estimate topographic and volumetric changes were compared by quantifying the uncertainty in TLS-derived products: Digital Elevation Model (DEM) of difference (DOD), Cloud to Cloud (C2C), Cloud to Mesh (C2M), and Multiple Model to Model Cloud Comparison (M3C2). Mean errors across surfaces within each dataset contributed to a propagation error of 0.015–0.016 m and 0.017–0.018 m for the point clouds and derived DEMs, respectively. The estimated error of the total volumetric change implied increased errors in the conversion of point clouds into a surface by C2M and DOD; whereas C2C and M3C2 were generally simpler, efficient, and accurate techniques for evaluating topographic changes. The comparison of methods to analyze TLS data will contribute to applications of remote sensing of hydro-geomorphic processes in stream channels after disturbance. The workflow presented also aids in estimating uncertainties inherent in data collection and analytic methods for topographic and volumetric change analysis.

High-resolution monitoring of beach topography and its change using unmanned aerial vehicle imagery

Beaches suffer from considerable degradation due to the dual influences from natural and human-induced factors. Higher resolution topographic data are frequently needed for assessment of the rapid changes and for building the models that can predict the evolution of these natural environments. In this paper, a low-altitude quad-rotor unmanned aerial vehicle (UAV), equipped with a non-metric camera, was used to acquire the two periods of UAV images in a complex beach of Wujiao Bay where the significant geomorphic changes occurred mainly due to the strong scouring of the drainage gullies. A detailed practical technique workflow was presented for deploying the low-altitude UAV for high-resolution monitoring the topography and the changes of the beach. The high resolution orthomosaic with geo-reference accuracy less than 1 pixel and the Digital Surface Model data with high vertical accuracy of approximately 10 cm were achieved by applying the UAV photogrammetry process based on Structure from Motion method to numerous overlapped UAV images. These data were further applied to the topographic change monitoring and analysis of the beach. This study greatly enhanced the applicability of the UAV remote sensing and enriched the existing tools for the high resolution topographic survey and geomorphic change detection in the complex beach.

Diagnostic Precision of the Confocal Scanning Laser Ophthalmoscopy in the Large Optic Disc with Physiological Excavation - a Long-Term Study

17 Subjects with presumed bilateral physiological cupping and large optic discs were included in this long-term follow-up study. All subjects underwent regular detailed ophthalmologic examinations, including intraocular pressure measurement via Goldmann applanation tonometry (GAT), retinal nerve fiber layer imaging via optical coherence tonometry (OCT) and visual field testing and optic disc imaging using the HRT. Glaucomatous progression was identified using the HRT's tools (stereometric trend analysis [STA] and topographic change analysis [TCA]). In the initial examination, all 17 subjects were classified as "pathological", by the HRT's Moorfield's Regression Analysis (MRA). Over the observation period of 9.2 ± 5 years, only 1 of the 17 subjects showed an ensured conversion to normal tension glaucoma with glaucomatous visual field defects. The remaining 16 subjects show no visual field defects to date. STA showed significant changes in 3 subjects alone, in 1 subject TCA showed a significant change alone, and in 1 subject both analyses showed a progressive change. After 9 years of regular examinations, 16 of the 17 subjects that were classified as "pathological" using MRA showed no glaucomatous visual field defects. In 5 out of these 16 subjects, progressive changes of the optic disc could be recorded via HRT. Therefore, the diagnostic precision of the HRT measurements seems to be limited in patients with large discs and physiological cupping.