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Papers by Andreas Ullrich

LIDAR technology based on time-of-flight ranging with short laser pulses enables the acquisition ... more LIDAR technology based on time-of-flight ranging with short laser pulses enables the acquisition of accurate and dense 3D data in form of so-called point clouds. The technique is employed from different platforms like stable tripods in terrestrial laser scanning or aircrafts, cars, and ships in airborne and mobile laser scanning. Historically, these instruments used analogue signal detection and processing schemes with the exception of instruments dedicated for scientific research projects or bathymetry. In 2004, a laser scanner device for commercial applications and for mass data production, the RIEGL LMS-Q560, was introduced to the market, making use of a radical alternative approach: digitizing the echo signals received by the instrument for every laser pulse and analysing these echo signals off-line in a so-called full waveform analysis in order to retrieve almost all information contained in the echo signal using transparent algorithms adaptable to specific applications. In the...

Laser Radar Technology and Applications XIX; and Atmospheric Propagation XI, 2014

RIEGL LIDAR instruments are based on echo digitization and provide point cloud data by online wav... more RIEGL LIDAR instruments are based on echo digitization and provide point cloud data by online waveform processing or full waveform data for external full waveform analysis or both. The advantages of online waveform processing of being fast and highly accurate for most typical target situation are made up by full waveform processing for demanding echo signal shapes when employing sophisticated algorithms. It is investigated how online waveform processing performs in turbid media and where the limitations are by analyzing experimental results when measuring in a fog chamber. An algorithm is proposed to determine the visibility range from the echo waveforms return of the medium.

Proceedings of SPIE, 2005

Waveform digitizing laser scanners for surveying and surveillance applications. [Proceedings of S... more Waveform digitizing laser scanners for surveying and surveillance applications. [Proceedings of SPIE 5988, 59880P (2005)]. Andreas Ullrich, Rainer Reichert. Abstract. We discuss the potential of waveform digitizing scanning ...

Direct detection laser radar systems with echo signal digitization and subsequent full waveform a... more Direct detection laser radar systems with echo signal digitization and subsequent full waveform analysis provide additional information on the target's properties compared to conventional discrete echo systems. We focus on the advantages of utilizing the additional information especially in the course of airborne laser scanning, improving for example the mandatory process for classifying the measurement data for generating high-quality digital terrain models. We present field data to demonstrate the superiority of full-waveform data over conventional laser data.

A family of high-performance 3D imaging laser sensor are presented providing rapid acquisition of... more A family of high-performance 3D imaging laser sensor are presented providing rapid acquisition of 3D data of naturally reflecting objects within a wide field-of-view and up to ranges up to 1000 meters. Beside the basic 3D-information the sensors also supply, pixel for pixel, true color information gained by an additional passive channel. This color information allows an instantaneous automatic texturing of 3D models. The sensor are of a rugged and compact design and can thus be used even under adverse environmental conditions. Potential applications include scene acquisition for virtual reality modeling, 3D-imaging of large buildings in the field of architecture, topographic mapping and dimensional measurements of vessels, furnaces, tanks, etc. The sensor makes use of high-speed laser ranging based on the time-of-flight method using a pulsed laser source in combination with precise mechanical scanning of the measuring beam. Data are provided at a standard parallel interface allowing easy integration with any standard PC based system for data visualization and data processing. These data are provided with an average data rate up to 18 000 measurements per second. Examples of data acquired with the sensors are presented, accuracy and ranging capability are discussed.

Classifying vegetation points from 3D airborne laser scanner (ALS) point clouds is a challenge an... more Classifying vegetation points from 3D airborne laser scanner (ALS) point clouds is a challenge and focus of current research. In particular, low vegetation points are very difficult to identify. The basic problem is that so far the majority of ALS systems have provided only the 3D coordinates of scattering objects and most of the criteria used in classifying points had to rely on simple geometric characteristics of a point relative to its neighbourhood. Methods for ALS data processing could be much improved if ALS systems measure, in addition to the range, further physical observables which can be used for vegetation classification. New ALS systems, which record the full echo-waveform, may provide crucial information for the classification of vegetation points. In this paper we show that the additional features derived from the full-waveform data -the amplitude, the pulse width and the number of pulses -can be used to discriminate between vegetation and non-vegetation points without using geometry information. Thus, a truly three dimensional representations of the classified ALS points can be obtained. The classification algorithm is based on a decision tree technique. The applicability of this method is demonstrated on data collected by the RIEGL LMS-Q560 sensor over the Schönbrunn area of Vienna. The performance of the classification algorithm was checked manually on 500 points randomly distributed and on several test zones selected over the study area. We found an overall accuracy of 88.6% with a kappa coefficient of 0.8.

Auf dem Laserscannermarkt erscheinen zunehmend Systeme, welche neben dem eigentlichen Scanner mit... more Auf dem Laserscannermarkt erscheinen zunehmend Systeme, welche neben dem eigentlichen Scanner mit auch Komponenten zur digitalen Bilderfassung ausgestattet sind. Diese zusätzliche Informationsquelle wird dabei zum Einfärben der vom Laserscanner erzeugten Punktwolke oder zur Texturierung modellierter Objekte genutzt. Für diesen Vorgang ist eine geometrische Referenzierung zwischen Punkwolke und Bilddaten unabdingbar. Diese basiert unter anderem auf den Parameterwerten aus einer Kamerakalibrierung. Die Genauigkeit und Zuverlässigkeit der Referenzierung wird umso gewichtiger, wenn eine über die bloße Kolorierung der Punktwolke hinausgehende Integration beider komplementären Datenquellen beabsichtigt ist.

Airborne laser scanning, often referred to as lidar or laser altimetry, is a remote sensing techn... more Airborne laser scanning, often referred to as lidar or laser altimetry, is a remote sensing technique which measures the round-trip time of emitted laser pulses to determine the topography of the Earth's surface. While the first commercially available airborne laser scanners recorded only the time of one backscattered pulse, state-of-the-art systems measure first and last pulse; some are able to measure up to five pulses. This is because there may be several objects within the travel path of the laser pulse that generate multiple echoes. Pulse detection is then used to determine the location of these individual scatterers. In this paper we discuss the physical measurement process and explain the way how distributed targets (such as trees or inclined surfaces) transform the emitted pulse. It is further shown through theoretical experiments that different detectors may yield quite different height information, depending on the type of the target. For example, even in the simple case of a tilted roof (with a tilt angle of 45°) the range values obtained by using different detectors may vary by ~ 0.4 m for a laser footprint size of 1 m. Airborne laser scanner systems that digitise the full waveform of the backscattered pulse would give more control to the user in the interpretation process. It would e.g. be possible to pre-classify the acquired data with respect to the shape of the echoes, to use different detection methods depending on surface cover and the intended application, and to employ more physically-based retrieval methods.

Small-footprint airborne laser scanners with waveform-digitizing capabilities are becoming increa... more Small-footprint airborne laser scanners with waveform-digitizing capabilities are becoming increasingly available. Waveform-digitizing laser scanners seize the physical measurement process in its entire complexity. This leads the way to the possibility of deriving the backscatter cross section which is a measure of the electromagnetic energy intercepted and reradiated by objects. The cross section can be obtained by firstly decomposing the echo waveform in several distinct echoes, whereas for each echo its range, amplitude and width are known. Then the radar equation can be used for calibrating the waveform measurements using external reference targets with known backscatter cross sections. The final outcome is a 3D point cloud where each point represents one scatterer with a given cross section and echo width. Using these physical attributes and various geometric criteria the point cloud can be segmented or classified. In this paper this procedure is demonstrated based on waveform measurements acquired by the RIEGL LMS-Q560 sensor. The cross section of the homogenous reference targets is estimated with a RIEGL reflectometer and Spectralon® targets.

Isprs Journal of Photogrammetry and Remote Sensing, 2006

... Administration (NASA) have demonstrated the value of recording the complete waveform of the b... more ... Administration (NASA) have demonstrated the value of recording the complete waveform of the backscattered echo for vegetation analysis. In this paper we present the RIEGL airborne laser scanner LMS-Q560, which is one of the first commercial full-waveform digitising laser ...

Small-footprint airborne laser scanners with waveform-digitising capabilities are becoming increa... more Small-footprint airborne laser scanners with waveform-digitising capabilities are becoming increasingly available. Waveformdigitising is particularly advantageous when the backscattered echo waveform is complex because it allows selecting processing algorithms adjusted to the task. In addition, waveform-digitising laser scanners depict the physical measurement process in its entire complexity. This opens the possibility to derive the backscatter cross section which is a measure of the electromagnetic energy intercepted and reradiated by objects. In this paper approaches for deriving the cross section along the laser ray path are discussed. For data storage and processing reasons a practical approach is to model the waveform as the sum of a number of echoes backscattered from individual scatterers. This approach involves estimating the number of echoes, finding a match between the modelled echoes and the measured waveform, and estimating the cross section using calibration targets. For estimating the number and position of echoes the Average Square Difference Function (ASDF) method, which is a discrete time delay estimation technique, is tested. The results show that ASDF is a promising approach which appears to be less affected by noise compared to more traditional echo detection methods.

... Full-waveform measurements acquired over urban and rural test areas in Austria using the RIEG... more ... Full-waveform measurements acquired over urban and rural test areas in Austria using the RIEGL LMS-Q560 have already been used in ... et al., 2008) and to improve the quality of terrain models obtained by filtering the ALS derived 3D point cloud (Doneus et al., 2008; Ullrich ...

LIDAR technology based on time-of-flight ranging with short laser pulses enables the acquisition ... more LIDAR technology based on time-of-flight ranging with short laser pulses enables the acquisition of accurate and dense 3D data in form of so-called point clouds. The technique is employed from different platforms like stable tripods in terrestrial laser scanning or aircrafts, cars, and ships in airborne and mobile laser scanning. Historically, these instruments used analogue signal detection and processing schemes with the exception of instruments dedicated for scientific research projects or bathymetry. In 2004, a laser scanner device for commercial applications and for mass data production, the RIEGL LMS-Q560, was introduced to the market, making use of a radical alternative approach: digitizing the echo signals received by the instrument for every laser pulse and analysing these echo signals off-line in a so-called full waveform analysis in order to retrieve almost all information contained in the echo signal using transparent algorithms adaptable to specific applications. In the...

Laser Radar Technology and Applications XIX; and Atmospheric Propagation XI, 2014

RIEGL LIDAR instruments are based on echo digitization and provide point cloud data by online wav... more RIEGL LIDAR instruments are based on echo digitization and provide point cloud data by online waveform processing or full waveform data for external full waveform analysis or both. The advantages of online waveform processing of being fast and highly accurate for most typical target situation are made up by full waveform processing for demanding echo signal shapes when employing sophisticated algorithms. It is investigated how online waveform processing performs in turbid media and where the limitations are by analyzing experimental results when measuring in a fog chamber. An algorithm is proposed to determine the visibility range from the echo waveforms return of the medium.

Proceedings of SPIE, 2005

Waveform digitizing laser scanners for surveying and surveillance applications. [Proceedings of S... more Waveform digitizing laser scanners for surveying and surveillance applications. [Proceedings of SPIE 5988, 59880P (2005)]. Andreas Ullrich, Rainer Reichert. Abstract. We discuss the potential of waveform digitizing scanning ...

Direct detection laser radar systems with echo signal digitization and subsequent full waveform a... more Direct detection laser radar systems with echo signal digitization and subsequent full waveform analysis provide additional information on the target's properties compared to conventional discrete echo systems. We focus on the advantages of utilizing the additional information especially in the course of airborne laser scanning, improving for example the mandatory process for classifying the measurement data for generating high-quality digital terrain models. We present field data to demonstrate the superiority of full-waveform data over conventional laser data.

A family of high-performance 3D imaging laser sensor are presented providing rapid acquisition of... more A family of high-performance 3D imaging laser sensor are presented providing rapid acquisition of 3D data of naturally reflecting objects within a wide field-of-view and up to ranges up to 1000 meters. Beside the basic 3D-information the sensors also supply, pixel for pixel, true color information gained by an additional passive channel. This color information allows an instantaneous automatic texturing of 3D models. The sensor are of a rugged and compact design and can thus be used even under adverse environmental conditions. Potential applications include scene acquisition for virtual reality modeling, 3D-imaging of large buildings in the field of architecture, topographic mapping and dimensional measurements of vessels, furnaces, tanks, etc. The sensor makes use of high-speed laser ranging based on the time-of-flight method using a pulsed laser source in combination with precise mechanical scanning of the measuring beam. Data are provided at a standard parallel interface allowing easy integration with any standard PC based system for data visualization and data processing. These data are provided with an average data rate up to 18 000 measurements per second. Examples of data acquired with the sensors are presented, accuracy and ranging capability are discussed.

Classifying vegetation points from 3D airborne laser scanner (ALS) point clouds is a challenge an... more Classifying vegetation points from 3D airborne laser scanner (ALS) point clouds is a challenge and focus of current research. In particular, low vegetation points are very difficult to identify. The basic problem is that so far the majority of ALS systems have provided only the 3D coordinates of scattering objects and most of the criteria used in classifying points had to rely on simple geometric characteristics of a point relative to its neighbourhood. Methods for ALS data processing could be much improved if ALS systems measure, in addition to the range, further physical observables which can be used for vegetation classification. New ALS systems, which record the full echo-waveform, may provide crucial information for the classification of vegetation points. In this paper we show that the additional features derived from the full-waveform data -the amplitude, the pulse width and the number of pulses -can be used to discriminate between vegetation and non-vegetation points without using geometry information. Thus, a truly three dimensional representations of the classified ALS points can be obtained. The classification algorithm is based on a decision tree technique. The applicability of this method is demonstrated on data collected by the RIEGL LMS-Q560 sensor over the Schönbrunn area of Vienna. The performance of the classification algorithm was checked manually on 500 points randomly distributed and on several test zones selected over the study area. We found an overall accuracy of 88.6% with a kappa coefficient of 0.8.

Auf dem Laserscannermarkt erscheinen zunehmend Systeme, welche neben dem eigentlichen Scanner mit... more Auf dem Laserscannermarkt erscheinen zunehmend Systeme, welche neben dem eigentlichen Scanner mit auch Komponenten zur digitalen Bilderfassung ausgestattet sind. Diese zusätzliche Informationsquelle wird dabei zum Einfärben der vom Laserscanner erzeugten Punktwolke oder zur Texturierung modellierter Objekte genutzt. Für diesen Vorgang ist eine geometrische Referenzierung zwischen Punkwolke und Bilddaten unabdingbar. Diese basiert unter anderem auf den Parameterwerten aus einer Kamerakalibrierung. Die Genauigkeit und Zuverlässigkeit der Referenzierung wird umso gewichtiger, wenn eine über die bloße Kolorierung der Punktwolke hinausgehende Integration beider komplementären Datenquellen beabsichtigt ist.

Airborne laser scanning, often referred to as lidar or laser altimetry, is a remote sensing techn... more Airborne laser scanning, often referred to as lidar or laser altimetry, is a remote sensing technique which measures the round-trip time of emitted laser pulses to determine the topography of the Earth's surface. While the first commercially available airborne laser scanners recorded only the time of one backscattered pulse, state-of-the-art systems measure first and last pulse; some are able to measure up to five pulses. This is because there may be several objects within the travel path of the laser pulse that generate multiple echoes. Pulse detection is then used to determine the location of these individual scatterers. In this paper we discuss the physical measurement process and explain the way how distributed targets (such as trees or inclined surfaces) transform the emitted pulse. It is further shown through theoretical experiments that different detectors may yield quite different height information, depending on the type of the target. For example, even in the simple case of a tilted roof (with a tilt angle of 45°) the range values obtained by using different detectors may vary by ~ 0.4 m for a laser footprint size of 1 m. Airborne laser scanner systems that digitise the full waveform of the backscattered pulse would give more control to the user in the interpretation process. It would e.g. be possible to pre-classify the acquired data with respect to the shape of the echoes, to use different detection methods depending on surface cover and the intended application, and to employ more physically-based retrieval methods.

Small-footprint airborne laser scanners with waveform-digitizing capabilities are becoming increa... more Small-footprint airborne laser scanners with waveform-digitizing capabilities are becoming increasingly available. Waveform-digitizing laser scanners seize the physical measurement process in its entire complexity. This leads the way to the possibility of deriving the backscatter cross section which is a measure of the electromagnetic energy intercepted and reradiated by objects. The cross section can be obtained by firstly decomposing the echo waveform in several distinct echoes, whereas for each echo its range, amplitude and width are known. Then the radar equation can be used for calibrating the waveform measurements using external reference targets with known backscatter cross sections. The final outcome is a 3D point cloud where each point represents one scatterer with a given cross section and echo width. Using these physical attributes and various geometric criteria the point cloud can be segmented or classified. In this paper this procedure is demonstrated based on waveform measurements acquired by the RIEGL LMS-Q560 sensor. The cross section of the homogenous reference targets is estimated with a RIEGL reflectometer and Spectralon® targets.

Isprs Journal of Photogrammetry and Remote Sensing, 2006

... Administration (NASA) have demonstrated the value of recording the complete waveform of the b... more ... Administration (NASA) have demonstrated the value of recording the complete waveform of the backscattered echo for vegetation analysis. In this paper we present the RIEGL airborne laser scanner LMS-Q560, which is one of the first commercial full-waveform digitising laser ...

Small-footprint airborne laser scanners with waveform-digitising capabilities are becoming increa... more Small-footprint airborne laser scanners with waveform-digitising capabilities are becoming increasingly available. Waveformdigitising is particularly advantageous when the backscattered echo waveform is complex because it allows selecting processing algorithms adjusted to the task. In addition, waveform-digitising laser scanners depict the physical measurement process in its entire complexity. This opens the possibility to derive the backscatter cross section which is a measure of the electromagnetic energy intercepted and reradiated by objects. In this paper approaches for deriving the cross section along the laser ray path are discussed. For data storage and processing reasons a practical approach is to model the waveform as the sum of a number of echoes backscattered from individual scatterers. This approach involves estimating the number of echoes, finding a match between the modelled echoes and the measured waveform, and estimating the cross section using calibration targets. For estimating the number and position of echoes the Average Square Difference Function (ASDF) method, which is a discrete time delay estimation technique, is tested. The results show that ASDF is a promising approach which appears to be less affected by noise compared to more traditional echo detection methods.

... Full-waveform measurements acquired over urban and rural test areas in Austria using the RIEG... more ... Full-waveform measurements acquired over urban and rural test areas in Austria using the RIEGL LMS-Q560 have already been used in ... et al., 2008) and to improve the quality of terrain models obtained by filtering the ALS derived 3D point cloud (Doneus et al., 2008; Ullrich ...