1,721,204 research outputs found
Sviluppi della Tecnologia Laser Scanner
No full textLo sviluppo della tecnologia laser scanner negli ultimi cinque anni ha portato a maggiore affidabilità del dato ed alla possibilitàdi caratterizzare l’intero segnale laser riflesso dalla superficie terrestre: suolo e componenti sopra il suolo.
La possibilità di stimare variabili di interesse per la gestione e per la pianificazione forestale è già ben documentata e si avvarrà quindi di dati più accurati e di metodologie testate. La ricerca svolta fino ad oggi ha appurato che la validità delle stime dai dati laser scanner sono molto diverse in funzione del tipo di bosco analizzato, variando, nel caso delle stime del volume, da un errore praticamente non significativo fino ad errori del 30% delle stime nel caso di boschi molto complessi. Questo fattore va ad indicare che, per sfruttare pienamente questa tecnologia, è importante stabilire quali metodologie applicare in funzione del tipo di bosco analizzato. Con queste informazioni si potrà quindi procedere ad applicare in modo “stratificato” metodi diversi in zone diverse, come richiede il nostro territorio notoriamente caratterizzato da un’alta variabilità di condizioni e quindi di copertura forestale. L’apporto futuro dei dati laser scanner da satellite non è da sottovalutare, considerando che potenzialmente si potranno avere, a costi pressoché nulli, migliaia di punti campionati sul territorio italiano, ottenuti da un unico strumento. Non sarà possibile scegliere quando e dove questi punti verranno rilevati, ma potrà risultare comunque interessante utilizzarli come componente informativa aggiuntiva in molti casi. Ad esempio, metodi automatici per verificare le modifiche della copertura e della struttura vegetazionale possono essere applicati per monitoraggi a lungo termine del territorio nazionale. Si potrà anche verificare l’estendibilità di alcune stime eseguite da dati lidar da aeromobile utilizzando i dati da satellite, integrandoli in un disegno campionario stratificato
State of the Art of Ground and Aerial Laser Scanning Technologies for High-Resolution Topography of the Earth Surface
No full textAirborne and terrestrial laser scanning (respectively ALS and TLS) have become, in the past years, well established technologies for measuring spatial characteristics of objects on the earth surface and the geometry of the earth surface itself. Research and development have created the technology for providing a market with a wide choice of instruments.
The distinctive data produced by laser scanners is a 3D point cloud with high-quality positional and return-related information (3D coordinates, reflectance, return echo ordinal number etc...). Partially obstructed impulses give multiple returns, thus important added value to the dataset, by penetrating gaps which are present in certain elements (e.g. vegetation) and reflecting the ground surface as last return. In the last years sensors have been developed which provide the digitization of full return waveform. This capability provides significant data for sophisticated classification and reflectance calibration of the targets and a practically infinite number of return targets per emitted pulse (Briese et al., 2008).
Terrestrial and airborne laser scanning share many features related to scanning mechanisms and processing methods whereas they also differ in terms of accuracy, range, data-capture modes and project size (Vosselman and Maas, 2010). In this presentation a comprehensive overview of airborne and terrestrial laser scanning technology and processing is presented focusing on aspects related to high resolution topography of the earth surface. Accuracies, error budgets, and processing methods to improve and assess quality of the scan are reported to give an outline of the potential of current laser scanner sensors for providing high resolution models of the earth surface
IceSAT/GLAS Waveform Signal Processing for Ground Cover Classification: State of the Art
No full textRemote sensing data from waveform lidar sensors supply the complete profile of the backscattered signal. This characteristic opens interesting new frontiers for the study of land cover because, in addition to range measurements, further physical properties of objects may be derived through analysis of the return impulse. This paper’s intent is to assess the state of the art in waveform signal processing aimed at land cover interpretation. We start with a description of GLAS data structure and follow with a review of specific signal processing techniques that can be applied. Conclusions discuss the state of the art methods from the perspective of practical applications
Assessing a Template Matching Approach for Tree Height and Position Extraction from Lidar-Derived Canopy Height Models of Pinus Pinaster Stands
Full text linkIn this paper, an assessment of a method using a correlation filter over a lidar-derived digital canopy height model (CHM) is presented. The objective of the procedure is to obtain stem density, position, and height values, on a stand with the following characteristics: ellipsoidal canopy shape (Pinus pinaster), even-aged and single-layer structure. The process consists of three steps: extracting a correlation map from CHM by applying a template whose size and shape resembles the canopy to be detected, applying a threshold mask to the correlation map to keep a subset of candidate-pixels, and then applying a local maximum filter to the remaining pixel groups. The method performs satisfactorily considering the experimental conditions. The mean tree extraction percentage is 65% with a coefficient of agreement of 0.4. The mean absolute error of height is ~0.5 m for all plots except one. It can be considered a valid approach for extracting tree density and height in regularly spaced stands (i.e., poplar plantations) which are fundamental for extracting related forest parameters such as volume and biomass
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