Disaster Geo-Information Management – Maximizing Data Accuracy Speaker : Sr. Mohaizi Mohamad, FISM, FMGA PhD Mgmt, MSc LAD (Mal), MSc GIS (Aust), MSc Cart(Neth), BSc Survey (Mal) Email: mohaizi@geomatika.com.my Hp: +6019-6264421

Outline Presentation Abstract Introduction Methodology LiDAR Work Accurate Data For Flood LiDAR Water Flow LiDAR Drainage Pattern Optimum Data Accuracy Ground Registration Conclusion

Abstract Flood occurrence increased alarmingly in recent years in Northern Peninsular Malaysia. Largely caused by human activities, continued development of the densely populated flood plains, encroachment on flood-prone areas and destruction of forest and hill slopes. Official solutions for flood control - engineering based, ineffective to combat extensive monsoon floods. Readiness of highly accurate topographic heighting data at 10cm is recommended for hydrological spatial analysis. LIDAR technology couple with GPS technology of First Order Geodetic needed to create a highly precise GIS-based topographic layer for automated hydrological systems analyses and automated flood plan delineation.

Flood Kedah, Nov 2010 Source: Google Using LIDAR technology couples with GPS technology of First Order Geodetic and methodologies, an accurate and reliable Flood Risk Map can easily be produced over Northern Peninsular Malaysia for Disaster Geo-Information Management.

Introduction LiDAR stand for Light Detection And Ranging. An optical remote sensing technology that measures properties of scattered light to find range and/or other information of a distant target. The prevalent method to determine distance to an object or surface is to use laser (light) pulses. Like the similar radar technology, which uses radio waves, the range to an object is determined by measuring the time delay between transmission of a pulse and detection of the reflected signal. LIDAR technology has application in Geomatics, archaeology, geography, geology, geomorphology, seismology, remote sensing and atmospheric physics. 5

Methodology LIDAR system consists of several advanced technologies as can be seen in the image. 6

LiDAR Work Infrared Laser scans from side to side Receiver – measure accurately intensity, travel time & compute distance of the first pulse and the last returned pulses. IMU- keep track of the rotation of the aircraft in three axis GPS- keep track of the exact location of the aircraft in space

Accurate Data For Flood MADA, Kedah, Malaysia; Feb. 2010 LIDAR data is very high vertical accuracy which enables it to represent the Earth surface accurately. Laser returns are recorded from no matter what target the laser happens to strike. Red points indicated as the ground points, extracted from the overall LIDAR measurements. White points classified as the trees or non-ground point heights. Classification of these two types of points will represent the different data for bare earth and features with accurate elevation value.

Classification LiDAR Data Points of vegetation Points of soil MADA, Kedah, Malaysia; Feb. 2010 9

LiDAR Water Flow Rapid LiDAR data with the accuracy of 10cm on open area and 1m on heavily vegetated area (theoretically), LIDAR data are capable of creating accurate models for drainage flow pattern modeling to analyze the flood. MADA, Kedah, Malaysia; Feb. 2010 White lines and arrows - directions of waterflow if water falls on every position. The thickness if the line represent the speed of waterflow.

LiDAR Drainage Pattern The sump points are vital for flood risk detection, flood preventing, and area effected by flood analysis. With additional data such as soil information, these sump points can be shown as the precise positions of the risky water sump that may cause landslide after the flood season. MADA, Kedah, Malaysia; Feb. 2010 Green and Red rectangular represent the waterflow directions and the water sump points

Optimum Data Accuracy MADA, Kedah, Malaysia; July 2010 By using RTK GPS, rapid ground data will collect at designated area and will compare with LIDAR data. This technique ensures that all LiDAR data achieve the accuracy which is up to 5cm on the clear ground. By using RTK technique, the LiDAR data will reduce to the exact level of elevation based on the ground survey information. In Malaysia, the RTK GPS technique is being governed by the MyRTKNet and MyGeoid by JUPEM.

Ground Registration MADA, Kedah, Malaysia; July 2010 Rapid GPS ground control will be compared with LiDAR data to identify the different heighting value. The average of different heighting value will be used to reduce all the heighting of LiDAR data. The deliverable is the + 5cm accuracy achievement.

Analysis Data POINT ID X Y Z GCPs (m) Z LiDAR (m) Different Value (m) Average Different (m) 1 251291.5427 706061.3381 4.3868 4.510 0.1232 0.047114 2 251309.2661 706037.8725 4.5067 4.590 0.0833 3 251325.1292 706021.8001 4.4007 4.390 0.0107 4 251297.3525 706002.1293 4.6168 4.600 0.0168 5 251279.2489 706029.9268 4.5253 4.580 0.0547 6 251269.2431 706047.8952 4.4442 4.280 0.1642 7 251243.2594 706024.8210 4.4751 0.0349 8 251263.0533, 706003.7961 4.6441 4.660 0.0159 9 251277.2689 705985.7231 4.5201 4.570 0.0499 10 250865.0077 706105.6406 4.5781 4.540 0.0381 11 250873.7549 706094.7060 4.4868 4.500 0.0132 12 250858.6140 706080.0587 4.4244 4.410 0.0144 13 250849.2627 706091.9289 4.5229 0.0129 14 250839.2160 706102.1302 4.4874 4.460 0.0274 The Average Different heighting value will insert into modeler to reduced all LiDAR data over designated area to achieve the optimum data accuracy.

RTK GPS Real time kinematic (RTK) surveying is the latest dynamic GPS survey technique that utilizes short observations times and enable you to move between stations. RTK GPS can instantly determine the position of a roving unit to centimeter-level accuracy using carrier phase positioning. This technique is ideal for various applications such as engineering, cadastral, topographic and detail surveys. The use of a network of reference stations instead of a single reference station allows to model the systematic errors in the region and thus provides the possibility of an error reduction. This allows a user not only to increase the distance at which the rover receiver is located from the reference, it also increases the reliability of the system and reduces the RTK initialization time.

MyRTKnet Configuration Network of 50 dual frequency GNSS referense stations in Peninsular Malaysia Network of 28 dual frequency GNSS reference stations in East Malaysia Control Centre at JUPEM Headquarter

RTK VRS Networking This latest technique significantly reduces systematic errors and extends the operating range with improved initialization and accuracy. It is an autonomous surveying where users do not need to set up their own base stations. This technique provides integrity monitoring with all users sharing the same common established coordinate frame.  

Conclusion Airborne LIDAR technology together with GPS survey is now a proven method for acquiring accurate digital terrain model data and associated imagery under a wide range of conditions. As an active sensor it can be used when other remote sensing tools will not work, especially in the coastal zone where its flexibility and non invasiveness are extremely relevant features. We believe that access to a technology that enables the acquisition and fusion of baseline cartographic data and digital photos in much shorter time periods when compared to conventional methods can speed up the initiation of projects related to flood analysis, and we believe GPS survey will can optimum the accuracy of LIDAR data to ensure it will be a very promising technique in topographic surveying.