This study presents a new open-access dataset of 18 plots from alpine forests of the Alpine Space... more This study presents a new open-access dataset of 18 plots from alpine forests of the Alpine Space. Eight detection algorithms were tested and evaluated against forest inventory data using a novel, automated matching procedure. Forest structure remains a key issue limiting tree detection, and algorithms would probably benefit from an adaptive tuning in order to achieve a better trade-off between omission and commission errors.
This article gives an overview of the state of the art 3D data acquisition systems (i. e. airborn... more This article gives an overview of the state of the art 3D data acquisition systems (i. e. airborne laser scanning and digital aerial cameras) and the derivation of forestry related information from the derived 3D points clouds. The described examples are focusing on forest area delineation, growing stock and biomass estimation, forest growth assessment, forest road extraction as well as its changes. The shown examples are located in the Alpine space and discuss the possibilities and limitations of integrating these data sources into operational forestry applications.
ISPRS International Journal of Geo-Information, 2019
Structural measures for retaining and distributing water—i.e.; reservoirs, flood retentionand pow... more Structural measures for retaining and distributing water—i.e.; reservoirs, flood retentionand power plants—play a key role to protect and feed a growing world population in a rapidlychanging climate. In this work, we introduce an automated method to detect potential reservoir orretention area locations in digital terrain models. In this context, a potential reservoir is a largerterrain form that can be turned into an actual reservoir by constructing a dam. Based on contourlines derived from terrain models, potential reservoirs are found within a predefined range of damlengths, and the locally optimal ones are then extracted. Our method is to be applied in the veryearly stages of project planning and for area-wide potential analysis. Tests in a 100 km² study areabring promising results, but also show a certain sensitivity regarding terrain model quality andresolution. In total, 250–300 candidate polygons with a total volume of more than 6 million m³ werefound. In order to facilitate ...
Multi-temporal airborne laserscanning data for forestry applications During the last decade airbo... more Multi-temporal airborne laserscanning data for forestry applications During the last decade airborne laserscanning (ALS) data has been established as a suitable data source for three-dimensional description of forests and for deriving forest parameters. For the study area Vorarlberg, Austria, the potential of multi-temporal ALS data (data from 2004 and 2011) was analyzed for deriving the amount of harvests in terms of area and stem volume. The data were used as well to assess the site index with the aid of the changes in top heights. The analyses have shown that harvested areas could be detected with a minimum mapping unit of 20 m2, which corresponds to harvested single trees from the dominant canopy layer. The average amount of harvested stem volume could be estimated with an overall accuracy of 96.4%. The derived changes in top heights clearly reflect the local growth conditions. For the study area Liechtenstein two ALS data sets (leaf-on and leaf-off) were used for the differenti...
Für die Aufnahme von topographischen Informationen wird verstärkt flugzeuggetragenes Laserscannin... more Für die Aufnahme von topographischen Informationen wird verstärkt flugzeuggetragenes Laserscanning (engl. Airborne Laser Scanning, ALS) eingesetzt. Dabei eignet sich ALS als aktive Fernerkundungsmethode besonders für die Abtastung von bewaldeten Gebieten. Speziell in Forstanwendungen ist die aus ALS Daten abgeleitete Höheninformation der Vegetation eine fundamentale Eingangsgröße, die der Berechnung vieler Forstparameter (Baumhöhen, Stammvolumen, Biomasse) zugrunde liegt. Zusätzlich haben sich ALS Daten als Input für eine, auf Objekthöhen basierte, Waldabgrenzung bereits bewährt. Bis dato werden hauptsächlich Orthophotos für eine manuelle bzw. semi-automatisierte Waldabgrenzung verwendet, wobei schattige Bereiche die Detektierung von Waldrändern und vor allem Waldlücken stark beeinträchtigen. Hier zeigt ALS ein großes Potential und bietet in den meisten Fällen gegenüber einer manuellen Bildinterpretation deutliche Vorteile. Im Rahmen dieser Arbeit wird ein vollautomatischer Ansatz p...
The objective of this paper is to present and evaluate a new geometrically unambiguously defined ... more The objective of this paper is to present and evaluate a new geometrically unambiguously defined approach to calculate forest canopy cover, also known as crown coverage (CC) from airborne laser scanning (ALS) data based on national forest inventory (NFI) data. The CC is defined as the proportion of the forest floor covered by the vertical projection of the tree crowns. Most forest definitions lack in precise geometrical definitions for the calculation of CC and therefore, the results of common calculation methods differ and tend to be incomparable. To demonstrate the effect of such an unclear defined, common CC calculation method, CC maps, generated from moving window algorithms using different kernel shapes and sizes, are calculated and analyzed for three study areas in Tyrol, Austria. The new unambiguously approach, the tree triples method, is based on defining CC as a relation between the sum of the crown areas of three neighbouring trees at a time and the area of their convex hu...
The objective of this paper is to evaluate a new approach for the automatic delineation of forest... more The objective of this paper is to evaluate a new approach for the automatic delineation of forested areas based on airborne laser scanning (ALS) and national forest inventory (NFI) data. In the Austrian NFI a forest area is mainly defined with four fundamental criteria. One of these criteria, the so called "crown coverage", is the most complex variable and therefore the main focus of this paper is on defining and implementing this criterion in an automatic process to delineate forested areas. Based on Austrian NFI data functions were determined for two different test sites in Austria, describing the criterion crown coverage as a relation between tree height and the distance between trees. Based on the ALS data an automatic method on the basis of adapting -shapes was developed to link these functions to the ALS data. The approach was tested for two different test sites in Austria. For the first test site a tree species independent function was applied. The results of the d...
Earth Resources and Environmental Remote Sensing/GIS Applications III, 2012
ABSTRACT The monitoring of flood events with synthetic aperture radar (SAR) sensors has attracted... more ABSTRACT The monitoring of flood events with synthetic aperture radar (SAR) sensors has attracted a considerable amount of attention during the last decade, owing to the growing interest in using spaceborne data in near-real time flood management. Most existing methods for classifying flood extent from SAR data rely on pure image processing techniques. In this paper, we propose a method involving a priori knowledge about an area taken from a multitemporal time series and a digital elevation model. A time series consisting of ENVISAT ASAR acquisitions was geocoded and coregistered. Then, a harmonic model was fitted to each pixel time series. The standardised residuals of the model were classified as flooded when exceeding a certain threshold value. Additionally, the classified flood extent was limited to flood-prone areas which were derived from a freely available DEM using the height above nearest drainage (HAND) index. Comparison with two different reference datasets for two different flood events showed that the approach yielded realistic results but underestimated the inundation extent. Among the possible reasons for this are the rather coarse resolution of 150 m and the sparse data coverage for a substantial part of the time series. Nevertheless, the study shows the potential for production of rapid overviews in near-real time in support of early response to flood crises.
International Journal of Applied Earth Observation and Geoinformation, 2015
ABSTRACT Flood mapping from Synthetic Aperture Radar (SAR) data has attracted considerable attent... more ABSTRACT Flood mapping from Synthetic Aperture Radar (SAR) data has attracted considerable attention in recent years. Most available algorithms typically focus on single-image techniques which do not take into account the backscatter signature of a land surface under non-flooded conditions. In this study, harmonic analysis of a multi-temporal time series of >500 ENVISAT Advanced SAR (ASAR) scenes with a spatial resolution of 150 m was used to characterise the seasonality in backscatter under non-flooded conditions. Pixels which were inundated during a large-scale flood event during the summer 2007 floods of the River Severn (United Kingdom) showed strong deviations from normal seasonal behaviour as inferred from the harmonic model. The residuals were classified by means of an automatic threshold optimisation algorithm after masking out areas which are unlikely to be flooded using a topography-derived index. The results were validated against a reference dataset derived from high-resolution airborne imagery. For the water class, accuracies > 80% were found for non-urban land uses. A slight underestimation of the reference flood extent can be seen, mostly due to the lower spatial resolution of the ASAR imagery. Finally, an outlook for the proposed algorithm is given in the light of the Sentinel-1 mission.
This study presents a new open-access dataset of 18 plots from alpine forests of the Alpine Space... more This study presents a new open-access dataset of 18 plots from alpine forests of the Alpine Space. Eight detection algorithms were tested and evaluated against forest inventory data using a novel, automated matching procedure. Forest structure remains a key issue limiting tree detection, and algorithms would probably benefit from an adaptive tuning in order to achieve a better trade-off between omission and commission errors.
This article gives an overview of the state of the art 3D data acquisition systems (i. e. airborn... more This article gives an overview of the state of the art 3D data acquisition systems (i. e. airborne laser scanning and digital aerial cameras) and the derivation of forestry related information from the derived 3D points clouds. The described examples are focusing on forest area delineation, growing stock and biomass estimation, forest growth assessment, forest road extraction as well as its changes. The shown examples are located in the Alpine space and discuss the possibilities and limitations of integrating these data sources into operational forestry applications.
ISPRS International Journal of Geo-Information, 2019
Structural measures for retaining and distributing water—i.e.; reservoirs, flood retentionand pow... more Structural measures for retaining and distributing water—i.e.; reservoirs, flood retentionand power plants—play a key role to protect and feed a growing world population in a rapidlychanging climate. In this work, we introduce an automated method to detect potential reservoir orretention area locations in digital terrain models. In this context, a potential reservoir is a largerterrain form that can be turned into an actual reservoir by constructing a dam. Based on contourlines derived from terrain models, potential reservoirs are found within a predefined range of damlengths, and the locally optimal ones are then extracted. Our method is to be applied in the veryearly stages of project planning and for area-wide potential analysis. Tests in a 100 km² study areabring promising results, but also show a certain sensitivity regarding terrain model quality andresolution. In total, 250–300 candidate polygons with a total volume of more than 6 million m³ werefound. In order to facilitate ...
Multi-temporal airborne laserscanning data for forestry applications During the last decade airbo... more Multi-temporal airborne laserscanning data for forestry applications During the last decade airborne laserscanning (ALS) data has been established as a suitable data source for three-dimensional description of forests and for deriving forest parameters. For the study area Vorarlberg, Austria, the potential of multi-temporal ALS data (data from 2004 and 2011) was analyzed for deriving the amount of harvests in terms of area and stem volume. The data were used as well to assess the site index with the aid of the changes in top heights. The analyses have shown that harvested areas could be detected with a minimum mapping unit of 20 m2, which corresponds to harvested single trees from the dominant canopy layer. The average amount of harvested stem volume could be estimated with an overall accuracy of 96.4%. The derived changes in top heights clearly reflect the local growth conditions. For the study area Liechtenstein two ALS data sets (leaf-on and leaf-off) were used for the differenti...
Für die Aufnahme von topographischen Informationen wird verstärkt flugzeuggetragenes Laserscannin... more Für die Aufnahme von topographischen Informationen wird verstärkt flugzeuggetragenes Laserscanning (engl. Airborne Laser Scanning, ALS) eingesetzt. Dabei eignet sich ALS als aktive Fernerkundungsmethode besonders für die Abtastung von bewaldeten Gebieten. Speziell in Forstanwendungen ist die aus ALS Daten abgeleitete Höheninformation der Vegetation eine fundamentale Eingangsgröße, die der Berechnung vieler Forstparameter (Baumhöhen, Stammvolumen, Biomasse) zugrunde liegt. Zusätzlich haben sich ALS Daten als Input für eine, auf Objekthöhen basierte, Waldabgrenzung bereits bewährt. Bis dato werden hauptsächlich Orthophotos für eine manuelle bzw. semi-automatisierte Waldabgrenzung verwendet, wobei schattige Bereiche die Detektierung von Waldrändern und vor allem Waldlücken stark beeinträchtigen. Hier zeigt ALS ein großes Potential und bietet in den meisten Fällen gegenüber einer manuellen Bildinterpretation deutliche Vorteile. Im Rahmen dieser Arbeit wird ein vollautomatischer Ansatz p...
The objective of this paper is to present and evaluate a new geometrically unambiguously defined ... more The objective of this paper is to present and evaluate a new geometrically unambiguously defined approach to calculate forest canopy cover, also known as crown coverage (CC) from airborne laser scanning (ALS) data based on national forest inventory (NFI) data. The CC is defined as the proportion of the forest floor covered by the vertical projection of the tree crowns. Most forest definitions lack in precise geometrical definitions for the calculation of CC and therefore, the results of common calculation methods differ and tend to be incomparable. To demonstrate the effect of such an unclear defined, common CC calculation method, CC maps, generated from moving window algorithms using different kernel shapes and sizes, are calculated and analyzed for three study areas in Tyrol, Austria. The new unambiguously approach, the tree triples method, is based on defining CC as a relation between the sum of the crown areas of three neighbouring trees at a time and the area of their convex hu...
The objective of this paper is to evaluate a new approach for the automatic delineation of forest... more The objective of this paper is to evaluate a new approach for the automatic delineation of forested areas based on airborne laser scanning (ALS) and national forest inventory (NFI) data. In the Austrian NFI a forest area is mainly defined with four fundamental criteria. One of these criteria, the so called "crown coverage", is the most complex variable and therefore the main focus of this paper is on defining and implementing this criterion in an automatic process to delineate forested areas. Based on Austrian NFI data functions were determined for two different test sites in Austria, describing the criterion crown coverage as a relation between tree height and the distance between trees. Based on the ALS data an automatic method on the basis of adapting -shapes was developed to link these functions to the ALS data. The approach was tested for two different test sites in Austria. For the first test site a tree species independent function was applied. The results of the d...
Earth Resources and Environmental Remote Sensing/GIS Applications III, 2012
ABSTRACT The monitoring of flood events with synthetic aperture radar (SAR) sensors has attracted... more ABSTRACT The monitoring of flood events with synthetic aperture radar (SAR) sensors has attracted a considerable amount of attention during the last decade, owing to the growing interest in using spaceborne data in near-real time flood management. Most existing methods for classifying flood extent from SAR data rely on pure image processing techniques. In this paper, we propose a method involving a priori knowledge about an area taken from a multitemporal time series and a digital elevation model. A time series consisting of ENVISAT ASAR acquisitions was geocoded and coregistered. Then, a harmonic model was fitted to each pixel time series. The standardised residuals of the model were classified as flooded when exceeding a certain threshold value. Additionally, the classified flood extent was limited to flood-prone areas which were derived from a freely available DEM using the height above nearest drainage (HAND) index. Comparison with two different reference datasets for two different flood events showed that the approach yielded realistic results but underestimated the inundation extent. Among the possible reasons for this are the rather coarse resolution of 150 m and the sparse data coverage for a substantial part of the time series. Nevertheless, the study shows the potential for production of rapid overviews in near-real time in support of early response to flood crises.
International Journal of Applied Earth Observation and Geoinformation, 2015
ABSTRACT Flood mapping from Synthetic Aperture Radar (SAR) data has attracted considerable attent... more ABSTRACT Flood mapping from Synthetic Aperture Radar (SAR) data has attracted considerable attention in recent years. Most available algorithms typically focus on single-image techniques which do not take into account the backscatter signature of a land surface under non-flooded conditions. In this study, harmonic analysis of a multi-temporal time series of >500 ENVISAT Advanced SAR (ASAR) scenes with a spatial resolution of 150 m was used to characterise the seasonality in backscatter under non-flooded conditions. Pixels which were inundated during a large-scale flood event during the summer 2007 floods of the River Severn (United Kingdom) showed strong deviations from normal seasonal behaviour as inferred from the harmonic model. The residuals were classified by means of an automatic threshold optimisation algorithm after masking out areas which are unlikely to be flooded using a topography-derived index. The results were validated against a reference dataset derived from high-resolution airborne imagery. For the water class, accuracies > 80% were found for non-urban land uses. A slight underestimation of the reference flood extent can be seen, mostly due to the lower spatial resolution of the ASAR imagery. Finally, an outlook for the proposed algorithm is given in the light of the Sentinel-1 mission.
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Papers by Markus Hollaus