Program Title : PHIL LIDAR 1. Hazard Mapping of the Philippines using LiDAR
Program B. LiDAR Data Processing and Validation by SUCs and HEIs
Project Title : Project 8. LIDAR Data Processing and Validation in the Visayas: Central Visayas (Region 7)
Period Covered : April 2014 – June 2016
Implementing Agency : University of San Carlos
Project Leader : Roland Emerito S. Otadoy, Ph.D.
Source of Fund : DOST-GIA
Amount of Grant for this Period: P 9,135,089.00
Monitoring Agency : Philippine Council for Industry, Energy, and Emerging Technology Research and Development
Table of Contents
1. Introduction 2
1.1 Administration 2
1.2 Airborne Laser Scanning – The LiDAR 6
1.2 Pulsed Laser Ranging 8
1.2.1 Continuous Wave Laser Ranging 10
1.2.2 LiDAR Measurements 12
2. Mananga River Basin 16
2.1 Reconnaissance Survey 17
2.2 Data Processing 20
2.2.1 Editing of DTM and DSM 21
The University of San Carlos (USC) in Cebu City is one of the fourteen partner universities of the PhilLiDAR 1 (Hazard Mapping of the Philippines Using LiDAR) research program funded by the Department of Science and Technology (DOST)with the Philippine Council for Industry, Energy, and Emerging Technology Research and Development (PCIEERD). The research program is spearheaded by the College of Engineering, University of the Philippines-Diliman through the Training Center for Applied Geodesy and Photogrammetry (TCAGP) with Dr.Enrico Paringit as program leader. The program will run for three years from 2014 to 2017. The objectives and the corresponding expected outputs of the program are the following:
|Continue acquiring LiDAR datasets in critical areas not covered by the DREAM program||LiDAR point clouds|
|Obtain digital elevation models (DEM)||Digital surface model (DSM) and digital
terrain model (DTM)
|Extract features essential to flood modeling and hazard assessment||Surface feature heights and laser intensity in digital standard (binary) format|
|Conduct ground validation of the data|
generated by the Data Acquisition
|Conduct topographic and hydrographic|
surveys to obtain river profile and cross-
section data that will be integrated into
|Conduct hydrologic measurements necessary for flood model calibration and validation||Flood hazard maps of 2/3 of the country|
|Generate flood hazard maps|
To carry out the above objectives the Phil LiDAR 1 research program is subdivided into component projects namely:
1. The Data Acquisition Component (DAC) – responsible for the acquisition of LiDAR Data
2. The Data Validation and Bathymetry Component (DVBC) – responsible for the conduct of validation, topographic and hydrographic
3. Data Processing Component (DPC) – responsible for the processing of LiDAR data, and generation of digital elevation models and their
4. Flood Modeling Component – responsible for flood modeling.
5. Data Archiving and Distribution Component (DAD) – responsible for the archiving and distribution of all data sets and products.
To facilitate collaboration between UP-Diliman and the partner universities in each region of the country, Program B under Phil LiDAR 1 was established and is known as ‘LiDAR Data Processing and Validation by SUCs and HEIs’. Under this program a project in each SUC/HEI is identified; for USC it is called Project 8. LIDAR Data Processing and Validation in the Visayas: Central Visayas (Region 7), which is also known as Phil LiDAR 1.B.8. The partner universities are shown in Figure 1.1. They are grouped into clusters, namely the Luzon Cluster, the Visayas Cluster, and the Mindanao Cluster. The schematic flow of data is shown in Figure 1.2.
Figure 1.1. Partner universities and the corresponding project sites of the Phil LiDAR 1 research program. The partner universitiesare grouped into clusters: Luzon Cluster, Visayas Cluster, and Mindanao Cluster. Phil LiDAR 1.B.8 is officially known in the University of San Carlos (USC) as USC Phil LiDAR 1. It is housed at the USC Phil LiDAR Research Center, Josef Baumgartner Learning Resource Center, University of San Carlos-Talamban Campus, Nasipit, Talamban, Cebu City. Our organizational structure is shown in Figure 1.3. The project started in April 2014 and will end in March 2017.
Figure 1.4. The new USC Phil LiDAR 1 team
1.2 Airborne Laser Scanning – The LiDAR
LiDAR is a non-destructive remote sensing technique for the measurement of distances and provides a relatively novel tool for generating a unique and comprehensive mathematical description of the target (e.g. vegetation and infrastructure). LiDAR measures the properties of scattered light to determine the range and other information of a distant target (Wehr and Lohr 1999). The prevalent method is the use of laser pulses, with frequencies in excess of 150 kHz. The distance between the sensor and the target can be measured by either measuring the time that a laser pulse takes to travel between the sensor and the target (time-of-flight LiDAR) or measuring the phase difference between the incident and reflected laser beams (phase-shift measurement LiDAR).
Laser scanning is the use of opto-mechanical assembly to scan a certain area on the ground with laser beam (photons ) as the sensing carrier (Wehr and Lohr 1999). It is an active system in that the assembly emits the sensing photons and collects the reflected photons through a sensor. The intensity of the reflected light depends on the reflecting surface and can therefore be used in sensing the type of topography. Since the laser consists of a narrow beam of light (narrow instantaneous field of view), laser scanning involves deflecting the beam in a pre-defined pattern to cover the region of interest in the lateral direction.
The forward motion of the assembly completes the full sampling coverage of the region with high point density (see lower part of Figure 1.5). A laser scanning assembly not only detects the properties of the illuminated region on the ground but also measures the distance between that region on the ground and the assembly, a process called ranging. This is determined by time of flight measurements, that is, by measuring the time the photons are emitted to the time they arrive in the sensor. If is the distance, called the range, from the ranging unit to the object’s surface, and is the speed of light, the traveling time of the photon can be determined as,
A laser scanner works in the same way as a RADAR (RAdio Detection And Ranging) except that the ranging signal is a laser beam in the near infrared to visible wavelengths. For this reason, laser scanner is also known as LADAR (LAser Detection And Ranging) or LiDAR (Light Detection And Ranging). LiDAR data can be used in conjunction with an onboard GPS and Inertial Navigation System (INS) for precise determination of locations (Lang, et al. 2010).
When the laser was invented, it was called a solution seeking for a problem. Nowadays, lasers are ubiquitous in our technology dependent society. The advantage of using laser in ranging is its susceptibility to be produced in high energy pulses at short time intervals (see Section 1.2.1) and its highly collimated (narrow) beam (due to spatial coherence) requires a narrow aperture. Soon after the invention of the laser, its precise ranging potential was immediately realized. When pulsed lasers with high repetition rates became available, scanning laser systems were soon contemplated. The use of lasers for remote sensing was conceptualized in the 1960s (Ritchie 1996) but rapid growth of the use of commercial airborne LiDAR with fine spatial resolution was realized only in the latter half of the 1990s (Lang, et al. 2010).
The primary components of a laser scanning assembly are shown in Figure 1.5. They can be subdivided into the following:
- laser ranging unit – consists of the emitting laser and the electro-optical receiver
- opto-mechanical scanner – component responsible for the scanning action of the laser
- control and processing unit
The two popular types of lasers, namely the pulsed laser and continuous-wave laser, provide two ways of laser ranging: pulsed ranging and continuous-wave ranging, respectively.