The development of new methods for estimating precise forest structure parameters is essential fo... more The development of new methods for estimating precise forest structure parameters is essential for the quantitative evaluation of forest resources. Conventional use of satellite image data, increasing use of terrestrial laser scanning (TLS), and emerging trends in the use of unmanned aerial systems (UASs) highlight the importance of modern technologies in the realm of forest observation. Each technology has different advantages, and this work seeks to incorporate multiple satellite, TLS- and UAS-based remote sensing data sets to improve the ability to estimate forest structure parameters. In this paper, two regression analysis approaches are considered for the estimation: random forest regression (RFR) and support vector regression (SVR). To collect the dependent variable, in situ measurements of individual tree parameters (tree height and diameter at breast height (DBH)) were taken in a Japanese cypress forest using the nondestructive TLS method, which scans the forest to obtain de...
Since around 2000, GIS researchers in Japan have collaborated to provide materials for GIS lectur... more Since around 2000, GIS researchers in Japan have collaborated to provide materials for GIS lecture classes for university undergraduates. As a result, a GIS core curriculum, a Japanese version of GIS Body of Knowledge (BoK), and a series of PowerPoint presentation files were developed. These materials are online and available to anybody with free of charge. However, they have not yet published free-access online materials for GIS exercises using software and spatial data. Therefore, we launched a new project in 2015 to produce such materials. The learning topics in the materials were selected based on products from the previous projects. Software packages used for GIS operations are free open-source ones. The materials have been provided as open educational resources with a Creative Commons license on the GitHub platform. The materials were used in a university class of GIS exercises to verify whether they are effective for undergraduate students. In this paper, we introduce the dev...
We conducted topographic measurements using unmanned aerial vehicles and by terrestrial laser sca... more We conducted topographic measurements using unmanned aerial vehicles and by terrestrial laser scanning at inaccessible sea cliffs with an overhanging complex shape in eastern Japan. From the repeated measurements, we constructed multitemporal three-dimensional point clouds of the sea cliffs to quantitatively evaluate the volumetric changes in the cliffs with a high spatial resolution (in centimeter). As potential main triggers of rockfalls and slope failures, high sea waves and strong earthquakes were examined with the time series of eroded volumes. It is suggested that sea waves have a greater impact than earthquakes on sea-cliff erosion. The approaches provided in this study have great potential for a wide range of applications including high spatial monitoring of other inaccessible, complex-shaped sea cliffs with high data accuracy and low acquisition and operational costs.
Natural Hazards and Earth System Sciences Discussions
Debris avalanche caused by the sector collapse of a volcanic mountain often forms characteristic ... more Debris avalanche caused by the sector collapse of a volcanic mountain often forms characteristic depositional landforms including hummocks. Not only sedimentological but also geomorphological analyses of debris avalanche deposits (DAD) are crucial to clarify the size, mechanisms, and processes of the debris avalanche. We investigate the morphology of hummocks newly identified in the DAD at the north-eastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS) and the structure-from-motion multi-view stereo photogrammetry (SfM), we obtained high-definition digital elevation model (DEM) and orthorectified image of the DAD surface with hummocks. Detailed geometric features of the hummocks are investigated using the RPAS-derived high-definition DEM. The source volume of the DAD was also estimated by reconstructing the original shape of the mountain body using a lower-resolution satellite-based DEM. For th...
Following the heavy rainfall caused by the typhoon-12 on 20th August 2014, Hiroshima city in Japa... more Following the heavy rainfall caused by the typhoon-12 on 20th August 2014, Hiroshima city in Japan was struck by a series of landslides including numerous mudslides and debris flows. The landslides affected several suburban residential areas mostly in the Asaminami and Asakita wards causing a great loss of property and the death of 74 residents. This study concerns a bivariate statistical approach to analyse if a landslide susceptibility study would have been able to identify the vulnerable areas beforehand. Firstly, we prepared a landslide susceptibility map (LSM) using a 10 m DEM, geological information and past occurrences of landslides. The landslides after the typhoon event were later used to access the accuracy of the LSM. The inventory of landslides before and after the typhoon event was interpreted from the high-resolution satellite images. The results show that a similar landslide susceptibility study could have identified vulnerable areas and helped in mitigating the disas...
Using 'Structure from Motion' past geomorphic landscapes can be recreated; Analysis of Geomorphic... more Using 'Structure from Motion' past geomorphic landscapes can be recreated; Analysis of Geomorphic changes using aerial photograghs; 'Structure from Motion' has to be used carefully as it can produce a 3D models that aren't accurate;
Devastating tsunami waves induced by The off the Pacific coast of Tohoku Earthquake severely inun... more Devastating tsunami waves induced by The off the Pacific coast of Tohoku Earthquake severely inundated valleys along the ria-type (notched rocky) coast in northeastern Japan, causing erosion of bedrock on valley-side slopes. Using high-resolution topographic data obtained by terrestrial and airborne laser scanning, we investigated detailed morphology of the eroded valley in a typical site at Aneyoshi. We found several characteristic features likely affected by tsunami wave erosion: 1) a series of small cliffs on the valley-side slopes related to the tsunami flow depth, 2) an inverse asymmetry of side slopes at ingrown meander bends, 3) an exceptionally wide valley bottom near the coast, and 4) a knickpoint located around the maximum tsunami run-up point far back from the coast. These topographic features are ascribable to repeated tsunami wave erosion since the mid Holocene.
ABSTRACT Many different models exist for landslide prediction. Possibly the parameter with the hi... more ABSTRACT Many different models exist for landslide prediction. Possibly the parameter with the highest uncertainty in these models is soil depth. While most studies acknowledge its importance, few studies include spatial variability of soil depth in the predictions. In addition, in mountainous areas landslides are one of the main processes shaping the relief and therefore have a significant impact on the spatial distribution of soils. In this study, we model the interaction between long-term soil formation and landsliding. Soil formation from bedrock is modeled by a depth-dependent soil production function. Soil is then redistributed in the landscapes by water erosion processes and landslides. Factor of safety is calculated at each time step by using the dynamic soil thickness and rainfall. First, the model is evaluated by comparison of modeled soil depth with published field measurements (Iida et al., 1999). The relation between soil depth and topographical attributes, such as slope, curvature or compound topographic index show how including landsliding processes generates patterns of soil depth that reflect much better the observations than a simple model that only includes soil formation and water erosion. Finally, the model is applied to a study area in the Akaishi Mountains to model the occurrence of landslides in that area. Landslides were mapped by remote sensing between 1992-2002. It is shown how by taking into account the modeled soil depths, the prediction of landslide occurrence is improved over a model with spatially constant soil depth.
ABSTRACT A coastal rocky terrace with an elevation of ca. 20 m a.s.l. is located around Cape Todo... more ABSTRACT A coastal rocky terrace with an elevation of ca. 20 m a.s.l. is located around Cape Todogasaki at the middle section of the ria-type rocky coast in Sanriku, northeastern Japan. In spite of its 20-m height, the tsunami waves induced by the 2011 Tohoku Earthquake were high enough to spread over the terrace. To clarify the effects of tsunamis on the terrace surface micromorphology, we performed field measurements of structure-from-motion multi-view stereo (SfM-MVS) photogrammetry using a digital camera mounted on a small unmanned aerial vehicle (sUAV). Terrestrial laser scanning was also carried out on the site for data validation. Geographical coordinates of benchmarks for georeferencing the SfM data were measured in the field using a GNSS rover, capable of postprocessing carrier-phase correction with centimeter accuracies. A 10-cm resolution digital elevation model (DEM) was then generated in SfM software, and micromorphology of the terrace surface was analyzed using the DEM. Despite limited basin area draining into the terrace, erosional characteristics likely formed by streamflow were identified. Sedimentological characteristics of thin clasts accumulation likely derived from terrace edge in-situ bedrock were also examined in the field. Based on clast shape and degree of weathering, three layers of deposit were identified: large fresh and angular clasts recently emplaced laying on the top. The spatial pattern of their imbrication for the three layers evidenced a landward flow direction. Furthermore, some angular boulders (2–3 m diameter) showing different degrees of weathering on their faces suggest that they were recently dislodged and displaced landward. These observations indicate that the uplifted terrace surface underwent erosion by not only the 2011 tsunami but also repeated significant tsunamis in the past.
The uplift of the Arabian Shield and the opening of the Red Sea led to the development of steep d... more The uplift of the Arabian Shield and the opening of the Red Sea led to the development of steep drainage systems in the Western Arabian Peninsula. Although the Peninsula has been studied from a geological perspective, in relation to oil production, plate tectonics and eolian systems such as sand dunes, the steep mountainous drainage basins have received much less attention. This paper aims to assess the characteristics and development of 36 drainage basins in the Western Arabian Peninsula, using a digital elevation model (DEM), principal component analysis (PCA), and hierarchical cluster analysis (CA). Three major principal components (PC1 to PC3) are found to explain 73% of total variance. CA divided the basins into two or four groups. The division by CA strongly reflects PC1, showing that the two analyses give comparable results. PC1 strongly reflects basin dimensions and drainage texture, and their positive correlations indicate the significant effect of basin relief and slope on mass wasting and limited stream incision in small basins under an arid climate. PC2 mainly reflects the effect of bedrock geology, suggesting that volcanic rocks tend to produce more elongated and less eroded immature basins than crystalline rocks do. PC3 mainly reflects the basin relief and slope and the length of each stream segment, which may also reflect the effect of mass wasting on stream development.
A waterfall highlights the locus of active fluvial erosion of bedrock, and its mechanism has been... more A waterfall highlights the locus of active fluvial erosion of bedrock, and its mechanism has been the subject of several studies; however, erosional processes remain to be clarified for specific rock structures composing a waterfall. Herein, the detailed morphology of cliffs around a waterfall is examined by a terrestrial laser scanning (TLS) approach to analyze erosional processes occurring in the cliffs. The study site is Kegon Falls in Japan, which has a vertical drop of surface water from the top of its cliff and groundwater outflows from its lower portion. The entire cliff is mostly overhanging and minor rockfalls are often observed. The latest major rockfall occurred in 1986, causing an approximate 8-m upstream shift of the waterfall lip. From the point cloud obtained by TLS measurement, a digital elevation model on a vertical plane was generated, and cross-sectional profiles were extracted. A distinct 5-to 10-m depression was found at the bottom of the upper andesite layer of the waterfall cliff, which appears to have been formed by freeze-thaw and wet-dry weathering following the upstream shift of the surface water drop. Stability analysis of the waterfall cliff with an undercutting notch indicates that the igneous rock composing the cliff is sufficiently strong to maintain its current overhanging shape and that catastrophic collapse of the entire waterfall face rarely occurs. Following the formation of the depression, the upper cliff face appears to have been gradually eroded by gravitational collapses of relatively small blocks bounded by columnar and platy joints.
Projected scenarios of climate change involve general predictions about the likely changes to the... more Projected scenarios of climate change involve general predictions about the likely changes to the magnitude and frequency of landslides, particularly as a consequence of altered precipitation and temperature regimes. Whether such landslide response to contemporary or past climate change may be captured in differing scaling statistics of landslide size distributions and the erosion rates derived thereof remains debated. We test this notion with simple Monte Carlo and bootstrap simulations of statistical models commonly used to characterize empirical landslide size distributions. Our results show that significant changes to total volumes contained in such inventories may be masked by statistically indistinguishable scaling parameters, critically depending on, among others, the size of the largest of landslides recorded. Conversely, comparable model parameter values may obscure significant, i.e. more than twofold, changes to landslide occurrence, and thus inferred rates of hillslope denudation and sediment delivery to drainage networks. A time series of some of Earth's largest mass movements reveals clustering near and partly before the last glacial-interglacial transition and a distinct step-over from white noise to temporal clustering around this period. However, elucidating whether this is a distinct signal of first-order climate-change impact on slope stability or simply coincides with a transition from short-term statistical noise to long-term steady-state conditions remains an important research challenge.
The development of new methods for estimating precise forest structure parameters is essential fo... more The development of new methods for estimating precise forest structure parameters is essential for the quantitative evaluation of forest resources. Conventional use of satellite image data, increasing use of terrestrial laser scanning (TLS), and emerging trends in the use of unmanned aerial systems (UASs) highlight the importance of modern technologies in the realm of forest observation. Each technology has different advantages, and this work seeks to incorporate multiple satellite, TLS- and UAS-based remote sensing data sets to improve the ability to estimate forest structure parameters. In this paper, two regression analysis approaches are considered for the estimation: random forest regression (RFR) and support vector regression (SVR). To collect the dependent variable, in situ measurements of individual tree parameters (tree height and diameter at breast height (DBH)) were taken in a Japanese cypress forest using the nondestructive TLS method, which scans the forest to obtain de...
Since around 2000, GIS researchers in Japan have collaborated to provide materials for GIS lectur... more Since around 2000, GIS researchers in Japan have collaborated to provide materials for GIS lecture classes for university undergraduates. As a result, a GIS core curriculum, a Japanese version of GIS Body of Knowledge (BoK), and a series of PowerPoint presentation files were developed. These materials are online and available to anybody with free of charge. However, they have not yet published free-access online materials for GIS exercises using software and spatial data. Therefore, we launched a new project in 2015 to produce such materials. The learning topics in the materials were selected based on products from the previous projects. Software packages used for GIS operations are free open-source ones. The materials have been provided as open educational resources with a Creative Commons license on the GitHub platform. The materials were used in a university class of GIS exercises to verify whether they are effective for undergraduate students. In this paper, we introduce the dev...
We conducted topographic measurements using unmanned aerial vehicles and by terrestrial laser sca... more We conducted topographic measurements using unmanned aerial vehicles and by terrestrial laser scanning at inaccessible sea cliffs with an overhanging complex shape in eastern Japan. From the repeated measurements, we constructed multitemporal three-dimensional point clouds of the sea cliffs to quantitatively evaluate the volumetric changes in the cliffs with a high spatial resolution (in centimeter). As potential main triggers of rockfalls and slope failures, high sea waves and strong earthquakes were examined with the time series of eroded volumes. It is suggested that sea waves have a greater impact than earthquakes on sea-cliff erosion. The approaches provided in this study have great potential for a wide range of applications including high spatial monitoring of other inaccessible, complex-shaped sea cliffs with high data accuracy and low acquisition and operational costs.
Natural Hazards and Earth System Sciences Discussions
Debris avalanche caused by the sector collapse of a volcanic mountain often forms characteristic ... more Debris avalanche caused by the sector collapse of a volcanic mountain often forms characteristic depositional landforms including hummocks. Not only sedimentological but also geomorphological analyses of debris avalanche deposits (DAD) are crucial to clarify the size, mechanisms, and processes of the debris avalanche. We investigate the morphology of hummocks newly identified in the DAD at the north-eastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS) and the structure-from-motion multi-view stereo photogrammetry (SfM), we obtained high-definition digital elevation model (DEM) and orthorectified image of the DAD surface with hummocks. Detailed geometric features of the hummocks are investigated using the RPAS-derived high-definition DEM. The source volume of the DAD was also estimated by reconstructing the original shape of the mountain body using a lower-resolution satellite-based DEM. For th...
Following the heavy rainfall caused by the typhoon-12 on 20th August 2014, Hiroshima city in Japa... more Following the heavy rainfall caused by the typhoon-12 on 20th August 2014, Hiroshima city in Japan was struck by a series of landslides including numerous mudslides and debris flows. The landslides affected several suburban residential areas mostly in the Asaminami and Asakita wards causing a great loss of property and the death of 74 residents. This study concerns a bivariate statistical approach to analyse if a landslide susceptibility study would have been able to identify the vulnerable areas beforehand. Firstly, we prepared a landslide susceptibility map (LSM) using a 10 m DEM, geological information and past occurrences of landslides. The landslides after the typhoon event were later used to access the accuracy of the LSM. The inventory of landslides before and after the typhoon event was interpreted from the high-resolution satellite images. The results show that a similar landslide susceptibility study could have identified vulnerable areas and helped in mitigating the disas...
Using 'Structure from Motion' past geomorphic landscapes can be recreated; Analysis of Geomorphic... more Using 'Structure from Motion' past geomorphic landscapes can be recreated; Analysis of Geomorphic changes using aerial photograghs; 'Structure from Motion' has to be used carefully as it can produce a 3D models that aren't accurate;
Devastating tsunami waves induced by The off the Pacific coast of Tohoku Earthquake severely inun... more Devastating tsunami waves induced by The off the Pacific coast of Tohoku Earthquake severely inundated valleys along the ria-type (notched rocky) coast in northeastern Japan, causing erosion of bedrock on valley-side slopes. Using high-resolution topographic data obtained by terrestrial and airborne laser scanning, we investigated detailed morphology of the eroded valley in a typical site at Aneyoshi. We found several characteristic features likely affected by tsunami wave erosion: 1) a series of small cliffs on the valley-side slopes related to the tsunami flow depth, 2) an inverse asymmetry of side slopes at ingrown meander bends, 3) an exceptionally wide valley bottom near the coast, and 4) a knickpoint located around the maximum tsunami run-up point far back from the coast. These topographic features are ascribable to repeated tsunami wave erosion since the mid Holocene.
ABSTRACT Many different models exist for landslide prediction. Possibly the parameter with the hi... more ABSTRACT Many different models exist for landslide prediction. Possibly the parameter with the highest uncertainty in these models is soil depth. While most studies acknowledge its importance, few studies include spatial variability of soil depth in the predictions. In addition, in mountainous areas landslides are one of the main processes shaping the relief and therefore have a significant impact on the spatial distribution of soils. In this study, we model the interaction between long-term soil formation and landsliding. Soil formation from bedrock is modeled by a depth-dependent soil production function. Soil is then redistributed in the landscapes by water erosion processes and landslides. Factor of safety is calculated at each time step by using the dynamic soil thickness and rainfall. First, the model is evaluated by comparison of modeled soil depth with published field measurements (Iida et al., 1999). The relation between soil depth and topographical attributes, such as slope, curvature or compound topographic index show how including landsliding processes generates patterns of soil depth that reflect much better the observations than a simple model that only includes soil formation and water erosion. Finally, the model is applied to a study area in the Akaishi Mountains to model the occurrence of landslides in that area. Landslides were mapped by remote sensing between 1992-2002. It is shown how by taking into account the modeled soil depths, the prediction of landslide occurrence is improved over a model with spatially constant soil depth.
ABSTRACT A coastal rocky terrace with an elevation of ca. 20 m a.s.l. is located around Cape Todo... more ABSTRACT A coastal rocky terrace with an elevation of ca. 20 m a.s.l. is located around Cape Todogasaki at the middle section of the ria-type rocky coast in Sanriku, northeastern Japan. In spite of its 20-m height, the tsunami waves induced by the 2011 Tohoku Earthquake were high enough to spread over the terrace. To clarify the effects of tsunamis on the terrace surface micromorphology, we performed field measurements of structure-from-motion multi-view stereo (SfM-MVS) photogrammetry using a digital camera mounted on a small unmanned aerial vehicle (sUAV). Terrestrial laser scanning was also carried out on the site for data validation. Geographical coordinates of benchmarks for georeferencing the SfM data were measured in the field using a GNSS rover, capable of postprocessing carrier-phase correction with centimeter accuracies. A 10-cm resolution digital elevation model (DEM) was then generated in SfM software, and micromorphology of the terrace surface was analyzed using the DEM. Despite limited basin area draining into the terrace, erosional characteristics likely formed by streamflow were identified. Sedimentological characteristics of thin clasts accumulation likely derived from terrace edge in-situ bedrock were also examined in the field. Based on clast shape and degree of weathering, three layers of deposit were identified: large fresh and angular clasts recently emplaced laying on the top. The spatial pattern of their imbrication for the three layers evidenced a landward flow direction. Furthermore, some angular boulders (2–3 m diameter) showing different degrees of weathering on their faces suggest that they were recently dislodged and displaced landward. These observations indicate that the uplifted terrace surface underwent erosion by not only the 2011 tsunami but also repeated significant tsunamis in the past.
The uplift of the Arabian Shield and the opening of the Red Sea led to the development of steep d... more The uplift of the Arabian Shield and the opening of the Red Sea led to the development of steep drainage systems in the Western Arabian Peninsula. Although the Peninsula has been studied from a geological perspective, in relation to oil production, plate tectonics and eolian systems such as sand dunes, the steep mountainous drainage basins have received much less attention. This paper aims to assess the characteristics and development of 36 drainage basins in the Western Arabian Peninsula, using a digital elevation model (DEM), principal component analysis (PCA), and hierarchical cluster analysis (CA). Three major principal components (PC1 to PC3) are found to explain 73% of total variance. CA divided the basins into two or four groups. The division by CA strongly reflects PC1, showing that the two analyses give comparable results. PC1 strongly reflects basin dimensions and drainage texture, and their positive correlations indicate the significant effect of basin relief and slope on mass wasting and limited stream incision in small basins under an arid climate. PC2 mainly reflects the effect of bedrock geology, suggesting that volcanic rocks tend to produce more elongated and less eroded immature basins than crystalline rocks do. PC3 mainly reflects the basin relief and slope and the length of each stream segment, which may also reflect the effect of mass wasting on stream development.
A waterfall highlights the locus of active fluvial erosion of bedrock, and its mechanism has been... more A waterfall highlights the locus of active fluvial erosion of bedrock, and its mechanism has been the subject of several studies; however, erosional processes remain to be clarified for specific rock structures composing a waterfall. Herein, the detailed morphology of cliffs around a waterfall is examined by a terrestrial laser scanning (TLS) approach to analyze erosional processes occurring in the cliffs. The study site is Kegon Falls in Japan, which has a vertical drop of surface water from the top of its cliff and groundwater outflows from its lower portion. The entire cliff is mostly overhanging and minor rockfalls are often observed. The latest major rockfall occurred in 1986, causing an approximate 8-m upstream shift of the waterfall lip. From the point cloud obtained by TLS measurement, a digital elevation model on a vertical plane was generated, and cross-sectional profiles were extracted. A distinct 5-to 10-m depression was found at the bottom of the upper andesite layer of the waterfall cliff, which appears to have been formed by freeze-thaw and wet-dry weathering following the upstream shift of the surface water drop. Stability analysis of the waterfall cliff with an undercutting notch indicates that the igneous rock composing the cliff is sufficiently strong to maintain its current overhanging shape and that catastrophic collapse of the entire waterfall face rarely occurs. Following the formation of the depression, the upper cliff face appears to have been gradually eroded by gravitational collapses of relatively small blocks bounded by columnar and platy joints.
Projected scenarios of climate change involve general predictions about the likely changes to the... more Projected scenarios of climate change involve general predictions about the likely changes to the magnitude and frequency of landslides, particularly as a consequence of altered precipitation and temperature regimes. Whether such landslide response to contemporary or past climate change may be captured in differing scaling statistics of landslide size distributions and the erosion rates derived thereof remains debated. We test this notion with simple Monte Carlo and bootstrap simulations of statistical models commonly used to characterize empirical landslide size distributions. Our results show that significant changes to total volumes contained in such inventories may be masked by statistically indistinguishable scaling parameters, critically depending on, among others, the size of the largest of landslides recorded. Conversely, comparable model parameter values may obscure significant, i.e. more than twofold, changes to landslide occurrence, and thus inferred rates of hillslope denudation and sediment delivery to drainage networks. A time series of some of Earth's largest mass movements reveals clustering near and partly before the last glacial-interglacial transition and a distinct step-over from white noise to temporal clustering around this period. However, elucidating whether this is a distinct signal of first-order climate-change impact on slope stability or simply coincides with a transition from short-term statistical noise to long-term steady-state conditions remains an important research challenge.
Structure-from-Motion Multi-View Stereo (SfM-MVS) photogrammetry has become one of the popular... more Structure-from-Motion Multi-View Stereo (SfM-MVS) photogrammetry has become one of the popular methods widely applied in various geomorphological studies. Unlike the orthodox photogrammetry, the data processing of SfM-MVS photogrammetry is more straightforward allowing instantaneous acquisition of high-resolution, accurate topographic data based on varying platforms including small Unmanned Aerial Vehicle (UAV). Here we review the methodological basics and geomorphological applications of SfM-MVS photogrammetry to discuss the efficiency and possibilities of the innovative approach in geomorphology. Particularly we focus on the slope (mass movements), fluvial, coastal, tectonic, glacial/periglacial and volcanic processes. We also discuss some issues on the SfM-MVS methodology including its coverage area, resolution, frequency, accuracy and quality assessment, as well as the future of the SfM-MVS approach in geomorhpology.
High-resolution data of landforms have become widely available along with the technical revolutio... more High-resolution data of landforms have become widely available along with the technical revolution of topographic measurements, particularly related to laser scanning technology. Aerial laser scanning (ALS) has become popular in basic topographic measurements and frequently applied to related geoscientific studies in the recent decades. Applications of terrestrial laser scanning (TLS) to geosciences are less frequent and mostly limited to Europe and North America, although in places like Japan, they may permit the detection of rapid topographic changes under the humid, tectonically-active environment. The purpose of this review article is to summarize the current situation of TLS applications in geomorphology and related sciences, and to illuminate the future directions of such applications. First, we briefly explain the principles of TLS methodology, including the basics of field measurement and post-processing of TLS data. Then we review some case studies of TLS in geomorphology, mostly those performed in Europe and North America. The examples deal with collapses of sea cliffs, landslides and debris flows, sedimentation of fluvial deposits, soil erosion and tectonic activity of faults. We then point out some issues in acquisition, processing and analysis of TLS-derived point cloud data and digital elevation models (DEMs) with a higher resolution compared to the traditional methods. Issues on accuracy and resolution are particularly crucial, because selection of appropriate scales for the target material is often directly related to the results of analysis, and such appropriate scales should be taken in consideration before the acquisition of TLS data in the field. This means that the higher resolution is not always better in relation to the scale of the target landforms and the accuracy of measurement. Time-series assessment, which is the most typical and fundamental analysis of such high-resolution data, also strictly depends on the accuracy of measurement. Also, robust analyses for TLS-derived high-resolution point clouds and DEMs are further examined. Various analytical methodologies for not only morphology of earth surfaces (such as roughness) but also other elements including the intensity and waveform of laser returns need to be developed. To expand the use of TLS in geomorphology and geosciences, establishment of sharing systems of well-formatted high-resolution datasets, data processing tools and instruments should also be pursued.
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Papers by Yuichi S . Hayakawa