Eleonora Maset

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Archivio istituzionale della ricerca - Università degli Studi di Udine

POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREASEleonora Maset, PhDeleonora.maset@uniud.itTopography, Remote Sensing and Mobile Mapping Systems LaboratoryUniversity of  Udine6th World Landslide ForumFlorence – Italy16 November 2023 INTRODUCTION▪ The Interconnected Nord-Est Innovation Ecosystem (iNEST) project aims to extend the advantages of digitalization to the main specialization areas of Northeast Italy.▪ Research focused on improving the resilience of mountain areas to the risks of climate change and geo-hydrological hazards. ▪ Activities employ current and legacy cartographic data to monitor the evolution of torrents and sediment-related phenomena at a regional scale, and high-resolution topographic surveys to locally assess the interaction between sediment dynamics and channel control works.▪ The goal is to define best practices for remote sensing surveys, also applicable by practitioners and local authorities.E. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 2REMOTE SENSING TECHNIQUES: UAV PHOTOGRAMMETRY AND LASER SCANNINGREMOTE SENSING TECHNIQUES▪ Platforms and data sources are proliferating at an unprecedent speed.▪ Unmanned aerial vehicles (UAVs) are the dominant platform among low-altitude airships, allowing extensive, high-detailed and repeated surveys.  ▪ UAVs are mainly equipped with low-cost and easy-access cameras to acquire images, processed via Structure from Motion (SfM) to obtain 3D point clouds.▪ Photogrammetry cannot see beneath the vegetation that often covers the area of interest.  E. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 4Liang et al. (2022). Close-range remote sensing of forests, IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE, 10.1109/mgrs.2022.3168135LASER SCANNING▪ Laser scanning (or LiDAR – Light Detection and Ranging) offers a suitable solution to model the bare terrain surface.▪ Active system that emits infrared signals able to penetrate through gaps in the forest canopy, measuring points on the ground. ▪ LiDAR sensors increasingly used as UAV payload (ULS –UAV-borne Laser Scanning).▪ Need for understanding accuracy and precision provided by ULS and its ability to effectively penetrate vegetation and provide high detailed Digital Terrain Models (DTMs). https://precisioncroptech.com/phoenix-lidar/E. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 5LITERATURE REVIEW▪ Most of the articles are related to forest inventory: ULS point clouds are mainly employed for crown structure metrics assessment.▪ The canopy penetration ability is strongly affected by scanner settings and flight properties:➢ pulse repetition rate➢ number of returns recorded➢ scan angle (field of view)➢ number of flight directions➢ leaf-on/leaf-off conditionsE. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 6Brede et al. (2022). Peering through the thicket: effects of UAV LiDAR scanner settings and flight planning on canopy volume discovery. International Journal of Applied Earth Observation and Geoinformation, 10.1016/j.jag.2022.103056▪ Dense vegetation can negatively influence the accuracy of the DTM.▪ Occlusions at the bottom of the canopy cannot be easily overcome with ULS.CASE STUDIES: ULS FOR 3D TERRAIN MAPPINGULS SYSTEM AND DATA COLLECTIONDJI Matrice 300 RTK ▪ Weight: 6.3 kg▪ Max payload: 2.7 kg▪ Flight time: 55 minutesE. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 8DJI Zenmuse L1▪ System accuracy: 5 – 10 cm @ 50 m▪ Ranging accuracy: 3 cm @ 100 m▪ Number of returns: up to 3▪ Point rate: 480,000 pts/s▪ Real-time point cloud coloringDATASET 1 – THE VEGLIATO TORRENT▪ Number of points: 125,038,120▪ Post-processing time: ~ 4.5 hours▪ Flight altitude: 80 m agl▪ GSD: 1.8 cm/pixel▪ Number of points: 65,940,003▪ Post-processing time: ~10 min▪ Flight altitude: 80 m aglArea of 80,000 m2, river banks and fluvial terraces, medium to high vegetation on the sides.E. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 9250 m 250 m▪ Occlusions caused by vegetation did not allow to reach the bare ground in some areas.DATASET 1 – THE VEGLIATO TORRENTE. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 10250 mSurface density [pts/m2]750 15000250 mSurface density [pts/m2]7500▪ Bare ground completely covered.Point clouds automatically filtered to extract ground points.1500DATASET 1 – THE VEGLIATO TORRENT▪ ULS was able to reconstruct both the upper part of the tree crowns and the bare ground▪ No ground points measuredunder the canopy by photogrammetryE. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 1110 m10 mDATASET 2 – THE MOSCARDO TORRENTArea of 7,500 m2, river banks covered by brushes and low vegetation.▪ Number of points: 2,201,544▪ Flight altitude: 120 m agl▪ Number of points: 49,732,683▪ Flight altitude: 35 m agl▪ GSD: 0.9 cm/pixelE. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 12DATASET 2 – THE MOSCARDO TORRENT▪ ULS detected few points on the ground beneath the low vegetationE. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 1310 m10 m▪ Higher point density and level of detail in the photogrammetric cloudDATASET 3 – THE LAGOON IN LIO MAGGIORE4.5 km of river banks covered by low vegetation. ▪ 202 points measured with high-precision GNSS receiver▪ Mean error on the DTM: +0.179 m (+/- 0.157 m)E. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 14850 mDATASET 3 – THE LAGOON IN LIO MAGGIORE▪ Ground accurately mapped below the treesx x xx xxxxxxxE. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 152 m2 m▪ Brushes and dense riparian vegetation prevents the laser pulse from reaching the bare groundCONCLUSIONS▪ This work is part of an ongoing research that aims at defining best practices for terrain monitoring in vegetated areas. ▪ Although laser scanning guarantees higher canopy penetrability than photogrammetry, several limits still exist in the presence of low vegetation. ▪ Results are affected by flight parameters: best practices must be established to guide the choice of sensor and flight settings.▪ Data fusion and the integration of terrestrial topographic techniques could be useful to obtain a complete and accurate DTM.E. MASET - POINT CLOUDS FOR TERRAIN MONITORING IN VEGETATED AREAS 16THANK YOU FOR THE ATTENTION!This study was carried out within the Interconnected Nord-Est Innovation Ecosystem (iNEST) and received funding from the European Union Next-GenerationEU (PIANO NAZIONALE DI RIPRESA E RESILIENZA (PNRR) – MISSIONE 4 COMPONENTE 2, INVESTIMENTO 1.5 – D.D. 1058 23/06/2022, ECS00000043). This work reflects only the author’s views and opinions, neither the European Union nor the European Commission can be considered responsible for them.Thanks to globaRT – Geomatica & Topografia for providing dataset 3.

Point clouds for terrain monitoring in vegetated areas.

https://air.uniud.it/bitstream/11390/1271006/2/WLF6_2023_presentation.pdf

Point clouds for terrain monitoring in vegetated areas.

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Archivio istituzionale della ricerca - Università degli Studi di Udine