EFFECTS OF DEMs FROM DIFFERENT
RESOLUTIONS IN DERIVING STREAM
NETWORKS THRESHOLD VALUES AND
MORPHOMETRIC ANALYSIS
NOR AZURA BINTI ISHAK
UNIVERSITI SAINS MALAYSIA
2018
EFFECTS OF DEMs FROM DIFFERENT RESOLUTIONS IN DERIVING STREAM NETWORKS THRESHOLD VALUES AND MORPHOMETRIC
ANALYSIS
by
NOR AZURA BINTI ISHAK
Thesis submitted in fulfilment of the requirements for the degree of
Master of Science
ii
ACKNOWLEDGEMENT
First and foremost, Alhamdulillah, all praises to the Almighty Allah for his merciful and giving me the strength and making this possible. I also owe my gratitude to all those people who have made this dissertation possible and because of whom my master research experience has been one that I will cherish forever.
Special thanks to Ministry of Higher Education for the scholarship and providing me with this great opportunity to pursue my Masters. I would like to express my thanks to Department of Drainage Malaysia (DID), Department of Surveying and Mapping Malaysia (JUPEM), providing me some data during my studies.
My deepest gratitude is to my main supervisor, Assc. Prof. Sr. Dr. Mohd Sanusi bin S.Ahamad. I have been amazingly fortunate to have a supervisor who gave me the freedom to explore on my own, and at the same time the guidance to recover when my steps faltered. He has also been commenting on my views and helping me understand and enrich my ideas. His patience and support helped me overcome many crisis situation and finish this dissertation. I would also like to express my special thanks to my co-supervisor, Prof. Dr. Aminuddin bin Ab.Ghani for generously given his time, expertise and useful advises to better my work.
Most importantly, none of this would have been possible without the love and patience of my family. I would like to express my heart-felt gratitude to my mom and dad, Rohana Rahmat and Ishak Yusoff and my mother and father in laws Zakiah Salleh and All Bakry Alias and my brothers and sisters. Finally, gratitude also goes to my beloved husband, Ahmad Munzir All Bakry. He have been a constant source of love, concern, support and strength all these years. Thank you
iii TABLE OF CONTENTS ACKNOWLEDGEMENT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS LIST OF SYMBOLS ABSTRAK ABSTRACT
CHAPTER ONE: INTRODUCTION
1.1 Research Background 1.2 Problem Statement
1.3 Scope of study 1.4 Aim and Objectives 1.5 Area of Study
1.6 Limitations of the Study 1.7 Chapter outline
CHAPTER TWO: LITERATURE REVIEW
2.1 Introduction
2.2 GIS and remote sensing application towards river stream network 2.2.1 Geographic Information System (GIS)
2.2.2 Remote Sensing Page ii iii vii viii x xii xiv xv 1 3 5 7 7 10 11 13 13 14 15
iv 2.3 Digital elevation model (DEM)
2.3.1 DEM from Shuttle Radar Topography Mission (SRTM) 2.3.2 DEM from ASTER Global Digital Elevation Model (GDEM)
2.3.3 DEM from NEXTMap World 30 m 2.3.4 DEM from Topographic Map
2.4 Effect of DEM resolution 2.5 Quality Accuracy Assessment of Digital Elevation Model
2.6 Influence of stream networks parameters 2.6.1 Influence of Threshold number 2.6.2 Influence of Stream Order 2.7 Spatial interpolation method
2.8 Morphometric parameters 2.9 Summary
CHAPTER THREE: METHODOLOGY
3.1 Introduction
3.2 Research Methodology
3.3 Processing of the Geospatial Data 3.3.1 Data Acquisition
3.3.2 Ground Control Points (GCPs) 3.3.3 Comparing reference DEMs to GCP
3.3.4 Comparison of DEMs accuracy assessment 3.4 Preparation of HEC-GeoHMS Watershed Modeling 3.4.1 Terrain pre-processing
3.4.2 Stream network extraction from multiple DEMs
17 19 22 24 25 26 28 31 31 32 35 37 38 39 39 42 42 43 43 44 44 47 53
v 3.4.3 Analysis of stream network influence
3.4.4 Derivation of flow accumulation threshold number 3.4.5 Derivation of stream ordering
3.5 Morphological Analysis
3.5.1 Quantitative morphometric analysis of watershed
CHAPTER FOUR: RESULT AND DISCUSSION
4.1 Introduction
4.2 Resolution Analysis on various DEMs 4.2.1 Root Mean Square Error (RMSE) 4.2.2 Vertical Accuracy Assessment of DEMs 4.2.3 Spatial vertical profiling of elevation 4.3 Sensitivity analysis of stream network
4.3.1 Identifying the river network differences
4.3.2 Flow accumulation threshold number and stream order plot 4.3.3 Total stream length plot
4.4 Morphometric parameters analysis 4.4.1 Linear parameters
4.4.2 Areal parameters 4.4.3 Relief characteristic 4.5 Summary
CHAPTER FIVE: CONCLUSION AND RECOMMENDATIONS
5.1 Introduction 5.2 Recommendations 54 54 55 56 56 59 59 60 63 65 68 68 75 81 82 82 89 92 93 95 97
vi
REFERENCES
LIST OF PUBLICATIONS
98 110
vii
LIST OF TABLES
Page
Table 1.1 Previous method compared with current study 5 Table 3.1
Table 3.2
Specification of dataset
Linear, areal and relief morphometric parameters
42 58 Table 4.1 Summary descriptive statistics comparison of DEMs using
different DEMs against spot height measured elevation.
62 Table 4.2 Linear parameters of Jawi watershed at 1st threshold 84 Table 4.3 Linear parameters of Jawi watershed at 2nd threshold 84 Table 4.4 Table 4.5 Table 4.6 Table 4.7 Table 4.8 Table 4.9 Table 4.10
Linear parameters of Jawi watershed at 3rd threshold Linear parameters of Jawi watershed at 4th threshold Linear parameters of Jawi watershed at 5th threshold Linear parameters of Jawi sub basin for DID river
Linear parameters of Mengkuang sub-basin for DID river Linear parameters of Mengkuang sub-basin at 1st threshold Linear parameters of Mengkuang sub-basin at 2nd threshold 84 85 85 85 87 87 87 Table 4.11 Linear parameters of Mengkuang sub-basin at 3rd threshold 88 Table 4.12 Linear parameters of Mengkuang sub-basin at 4th
threshold
88 Table 4.13 Linear parameters of Mengkuang sub-basin at 5th
threshold
88 Table 4.14 Areal parameters of Jawi sub-watershed 91 Table 4.15 Areal parameters of Mengkuang sub-watershed 91 Table 4.16 Relief characteristics of the Jawi sub-basin 92 Table 4.17 Relief characteristics Mengkuang sub-basin 93
viii
LIST OF FIGURES
Page
Figure 1.1 Study area for objective 1 (SPT & SPS) 9 Figure 1.2 Study area for objective 2 and 3 (SPT & SPS) 10 Figure 2.1 Sample of raw SRTM 30 m image for Pulau Pinang 22 Figure 2.2 Sample of raw ASTER image for Pulau Pinang 23 Figure 2.3 Sample of raw NextMap World 30 m image for Pulau
Pinang
25 Figure 2.4 Sample of topographic map in shape files in study area. 26 Figure 2.5 Example of stream order using the method of (a) Horton’s
(b) Strahler’s Law Source
34
Figure 3.1 Flow of research methodology 41
Figure 3.2 HEC-GeoHMS general processing including terrain preprocessing and watershed processing
46 Figure 3.3 Overview of GIS and watershed modelling using
HEC-GeoHMS
47 Figure 3.4 The DEM data before filling of DEM sinks using
HEC-GeoHMS
48 Figure 3.5 The DEM data after filling of DEM sinks using
HEC-GeoHMS
49 Figure 3.6 Extraction concept of flow direction from DEM. 50 Figure 3.7 Extraction concept of flow accumulation from DEM. 51 Figure 3.8 Location of outlet (lowest point) at Mengkuang River Dam 53 Figure 3.9 Method of ordering system for stream order one
(example).
55 Figure 4.1 Sample distribution of the GCPs through the study area. 61 Figure 4.2 Scatter plot of DEMs vs GCPs elevation (SPT & SPS) 64 Figure 4.3 Elevation profiles between flat and hilly area.(SPT & SPS) 66 Figure 4.4 Elevation profiles for flat area.(SPT & SPS) 67
ix
Figure 4.5 Elevation profiles for a hilly area (SPT & SPS) 67 Figure 4.6 (a) Flow direction, (b) flow accumulation, (c) stream
definition and (d) stream segmentation (SPT & SPS)
69 Figure 4.7 (e) Catchment grid delineation, (f) catchment polygon
processing, (g) drainage line processing and (h) adjoint catchment processing (SPT & SPS)
70
Figure 4.8 The sub-basin of study area at Jawi and Mengkuang River as derived from HEC-GeoHMS tool processing. (SPT & SPS)
71
Figure 4.9 Comparison of accumulated stream network for Jawi River.
73 Figure 4.10 Comparison of accumulated stream network for
Mengkuang River
74 Figure 4.11 Graph analysis stream order for Jawi sub-watershed 77 Figure 4.12 Graph analysis stream order for Mengkuang
sub-watershed
80 Figure 4.13 Graph analysis of variation in the total stream length at
different threshold with various data sources (Jawi sub-watershed)
x
LIST OF ABBREVIATIONS
ASTER Advanced Spaceborne Thermal Emission Reflection Radiometer
AVHRR Advanced Very High Resolution Radiometer (AVHRR) CGIAR-CSI Consultative Group for International Agriculture Research–
Consortium for Spatial Information DEM Digital Elevation Model
DID Department of Irrigation and Drainage Malaysia ERS Earth Resources System
GIS Geographical Information System GCP Ground data control points
GPS Global positioning system IDW Inverse Distance Weighing
IFSAR Interferometric Synthetic Aperture Radar
JUPEM Department of Surveying and Mapping Malaysia LiDAR Light detection data
ME Mean error
NASA National Aeronautics and Space Administration NIMA National Imagery and Mapping Agency
RMSE Root Mean Square Error
SAR Synthetic Aperture Radar (SAR) SRTM Shuttle Radar Topographic Mapping SPOT Satellite Pour I’Observation de Terre SWAT Soil and Water Assessment Tool
xi SWIR Shortwave Infrared
TIR Thermal Infrared
TIN Triangulated irregular network Topo to Raster Topographic DEM
USGS U.S. Geological Survey
USACE United States Army Corps of Engineers VNIR Near Infrared
xii LIST OF SYMBOLS A Area (Rb) Bifurcation ratio (Rb) (Rc) Circularity ratio (R2) Coefficient of determination (Dd) Drainage density (T) Drainage Texture (Re) Elongation ratio
(Ff) Form factor
(Δh) Height differences
z Height of watershed mouth
A Inductance ratio
L Length
Z Maximum height of the watershed (Rbm) Mean bifurcation ratio
n Number of checked elevation points
Zo Observed elevation Zp Predicted elevation (Rr) Relief ratio S Standard deviation Sb Slope U Stream order
(Lu) Stream length
xiii
Nu Total stream no
H Total watershed relief
xiv
PENGARUH KETINGGIAN BERDIGIT DARI RESOLUSI YANG BERBEZA DALAM MENDAPATKAN RANGKAIAN NILAI AMBANG ALIRAN SUNGAI
DAN ANALISIS MORFOMETRI
ABSTRAK
Penggunaan Model Ketinggian Berdigit (DEM) terhadap kajian kawasan tadahan air telah diterima dan digunakan dalam pelbagai aplikasi yang melibatkan kajian hidrologi. Walau bagaimanapun, terdapat cabaran terhadap penentuan ketepatan permukaan topografi sesuatu kawasan dimana penggunaan kajian berasaskan lapangan dalam menentukan permukaan topografi mengambil masa yang agak lama. Oleh itu,kajian ini telah dijalankan untuk mengkaji dan menilai ketepatan ketinggian pelbagai model berdigit terhadap rangkaian aliran sungai. Kajian ini telah mengenalpasti penarafan ketepatan ketinggian model ketinggian berdigit daripada pelbagai sumber dan resolusi yang berbeza. Sumber DEM daripada SRTM, ASTER, NEXTMap World 30 dan peta topografi telah digunakan dalam kajian sebagai penilaian dan perbandingan ketepatan. Ralat Punca Min Kuasa Dua (RMSE) diperolehi dalam penilaian ketepatan tegak. Hasil kajian menunjukkan nilai RMSE untuk SRTM ialah ± 8.15 m, ± 8.68 m untuk ASTER, dan ± 7.98 m untuk NEXTMap World 30, telah berada dalam kebolehtelapan yang dibenarkan oleh USGS. Seterusnya, kajian aliran sungai menggunakan SRTM 30 m menunjukkan hasil yang serupa dengan kajian yang dilakukan oleh Jabatan Pengairan dan Saliran Malaysia. Sementara itu, hasil analisis membuktikan bahawa rangkaian saliran dari SRTM 30 m dengan nilai ambang 40 adalah paling hampir dengan saliran rujukan. Hasil kajian telah memberi petunjuk kepada nilai-nilai ambang yang berkesan dan sesuai untuk analisis rangkaian aliran sub-lembangan sungai masa hadapan.
xv
EFFECTS OF DEMs FROM DIFFERENT RESOLUTIONS IN DERIVING STREAM NETWORKS THRESHOLD VALUES AND MORPHOMETRIC ANALYSIS
ABSTRACT
The use of Digital Elevation Model on the watershed survey has been accepted and applied in various applications involving hydrological studies. However, there is a challenge to determine topographic surface accuracy in the areas where the use of ground-based topographic surface studies takes a long time. Therefore, this research was conducted to study and determine the height accuracy from multiple digital models over network of streams. The study has determined the height accuracy rating of the digital elevation model from various sources and different resolutions. DEM sources from SRTM, ASTER, and NEXTMap World 30 and topographic maps were used to assess and compare the accuracy. The Root Mean Square Error (RMSE) was acquired in the vertical accuracy assessment. The results show that the RMSE value for SRTM is ± 8.15 m, ± 8.68 m for ASTER, and ± 7.98 m for NEXTMap World 30, are within the permissibility allowed by the USGS. Subsequently, the river flow study on the SRTM 30 m establishes a similar result with the study performed by the Malaysian Drainage and Drainage Department. Meanwhile, the analysis reveals that the drainage network from SRTM 30 m with threshold values of 40 was closest to the referenced drainage. The result has signifies the most appropriate values for an effective stream threshold network to be considered suitable for future river sub-basin analysis.
1
CHAPTER ONE
INTRODUCTION
1.1 Research Background
Digital Elevation Model (DEM) has been commonly incorporated in many research involving various forms of surface topography. DEM that is produced from the aerial and satellite imageries are photographic representation of the earth (Korsgaard et al., 2016). The first satellite photograph of earth was taken from the US satellite Explorer 6 in 1959. Based on the report by the USGS, the emphasis on DEM studies started from USGS USA which presented the topography across the United States (Wang and Wade, 2008). DEM study has undergone the evolution and development utilities around the world. It can then be deduced that DEMs have gradually gained the interest of many which encompass digital topographic data.
Subsequently, the development of satellite data showed an enormous growth in the number of mapping topography. Examples are Satellite Pour I’Observation de Terre (SPOT), Earth Resources System (ERS) and RADARSAT. DEM could be freely acquired from Shuttle Radar Topographic Mapping (SRTM), GOTO30, ASTER GDEM, and Cartosat-1 (Patel et al, 2016). DEM is a main topographic product and becomes a crucial demand for many applications (Polat et al., 2015). DEM has positively impact various applications, mainly in land and water resource. Besides, DEM is highly capable in obtaining various forms of data from low to high resolution in order to assist researchers in the development of various applications such as river network delineation, flood modeling, geology, forestry, and hazard mapping.
2
(Hosseinzadeh, 2011). For instance, the blueprints of the drainage system and catchment boundary which include various characteristics such as aspects, slope and contour have mainly utilized DEMs (Rahman et al., 2010).
Studies on accuracy assessment between various data sources have been extensively performed towards DEM in a large scale which is emphasized at a regional scale over rural and urban areas (Pulighe et al., 2015). Therefore, in a crucial application using various DEM, accuracy assessment is implemented mostly to conduct dissimilarity analysis where open-sourced DEMs consist of multiple grid cell size resolution datasets which determine the quality to derive topographic analysis. Realizing that accuracy assessment is an important part in DEM method, an initiative was taken to implement in the river stream network to highlight the importance of accuracy in computing watershed delineation and stream network.
The Department of Irrigation and Drainage Malaysia (DID) was established to monitor and to solve any issues which are related to river catchment management and streamflow data (DID, 2010). Basically, it is relatively dependent on the national agency’s (e.g., DID) data stream network since all dataset are collected through surveying river network in the field yet costing a large amount of money (Li and Wong, 2010). Therefore, instead of relying on the traditional surveying in the field dataset, the objective of this research is to examine the competency by utilizing a diverse set of DEMs data based on the constructive approach in generating river stream network.
Although DEMs can be potentially generated in constructivist-derived river stream network, they also have tremendous advantages which are relevant to the river stream. This will facilitate a deeper understanding and analysis. According to (Vaze et al., 2010), it is perceived that the ability of DEM in generating river network delineation cannot be denied. Moreover, the cost and time requirement are less than
3
the traditional methods. Despite that, contrasting outcomes can be obtained when the utilization of different DEM resolution on the topographic features and hydrology is investigated. Past studies on identifying the effects of topographic and hydrological attributes onto small watershed DEMs towards from northern Idaho have been thoroughly reviewed by (Zhang et al., 2008).
In a specific study, six DEMs were utilized and the different resolutions of DEMs have produced diverse structures and shapes of watershed which provided different channel length and extracted hillslope. Further research is needed to investigate how stream network threshold value should be a component of DEM sensitivity towards river network studies. According to (Ariza-Villaverde et al. 2015), there is a significant and strong relationship between DEM resolution and threshold value in river network studies. Hence, the research objective is to study the different DEM resolution coupled with the geographical information system (GIS) and to examine the potential of this tool in assessing the extraction drainage river stream network.
1.2 Problem statement
The sensitivity of Digital Elevation Model (DEM) has been in the limelight due to the differing spatial resolution which offered different results in river network applications. (Li and Wong, 2010) claimed that some studies using different data sources has experienced problems in analyzing the stream network and failed to provide consistent results due to different spatial resolutions.
Specifically, in the stream network studies, the spatial resolution of DEMs is an essential part in extracting the river network as the resolution and precision have genuine ramifications towards hydrological parameter. (Jana et al., 2007 stated that
4
although DEM has been acknowledged as sensitive towards resolution, the interpolation method has to be taken into account as this will influence the outcome of DEM accuracy. In particular, the report has found weaknesses in the method of interpolation and concluded that the DEM often contains errors in flat areas.
In addition to the weaknesses reported by (Jana et al., 2007), a study by (Sharma et al., 2010) revealed that it is difficult to understand or explain as the interpolation method or cell size of resolution is plausible in affecting DEM accuracy whilst hydrological application passively depends on DEM accuracy. However, extracting drainage network is often strongly dependent on the high quality of DEMs resolution for it to be an effective method to determine the topographic contours, computing elevation slope, and aspect (Liu and Zhang, 2011).
Furthermore, few researchers in Malaysia are interested in exploring the issue of DEM sensitivity towards river watershed. (Tan et al., 2015) conducted a study on the sensitivity of DEM resolution and using different DEM sources and DEM resampling techniques. Nevertheless, the stream networks threshold values are often left out in the discussion. These views are consistent with those of (Bhowmik et al., 2015), when they claimed that stream network threshold generally enhances the effectiveness and benefit analysis when it comes to stream network studies, but frequently misses out when a comparison between the pervasiveness of traditional field survey approach and stream network generate from DEMs is made.
Therefore, in such situations, the stream network threshold parameters should be highlighted beside the DEM resolution which emphasized digital stream network mapping by conducting an assessment in improving accuracy, precision, and efficiency. It is important to quantify these perceived changes in resolution to which these changes could lead to accurate river networks, thus, the watershed stream
5
network delineation can be improved. Table 1.1 shows previous method use to compare with current study.
AUTHORS METHOD NUMBER
OF DEM USED
THRESHOLD USED
Singh et al., 2014
Extract the river network from
DEMs
Extract all river parameters and
using ArcGIS
Compute the morphometric
parameters
2 X
Vaze et al., 2010
Compared DEM data with field
survey elevations point.
Compare the stream network and
watershed with single DEM with multiple resolution.
1 X
Li and Wong, 2010
Nearest neighbour
resampling.
Extract river from
different sources of
DEMs
Compares extracted river
networks with National
Hydrography Dataset
(NHD)
3 X
Li, 2014
Extract watershed boundary and
stream network data from National Hydro Network (NHN)
Using Arc Hydro tools in ArcGIS
1
Current study
Extract the river networks from
multiple DEMs and resolution.
Compute the morphometric
parameters
4
Table 1.1 Previous method compared with current study
1.3 Scope of study
This study attempts to quantify the relative relationship between various open-source Digital Elevation Models (DEMs) and stream network delineation response towards sample of watershed along the Seberang Perai River. An accuracy assessment was conducted in order to achieve the main purpose. DEMs accuracy is tremendously important to calculate the ambiguity of terrain parameters such as slope, aspect and
6
basic information in order to estimates errors in drainage maps (Tobergte and Curtis, 2013). Therefore, spot height from the Department of Surveying and Mapping Malaysia (JUPEM) as an independent ground truth data are required to compare with open-source DEMs.
Attention was given at variances in threshold number resulting from the replacement of DEMs resolution. This research focuses on geomatics perspective and without the involvement of hydrological or flood modelling. The semi-distributed HEC-GeoHMS tool in ArcGIS was employed to create a stream drainage network analysis model for the Seberang Perai River watershed. The model was then conducted to find the differences in the plausible effect on streamflow. The river network data were extracted from the Department of Irrigation and Drainage Malaysia (DID). Further datasets have been compared to extracted river stream network from various open-source DEMs. The effectiveness of stream drainage network extracted from multiple DEMs was evaluated based on stream threshold and morphometric parameter. In order to explore these concerns, the following research questions are outlined:
What is the extent of changes in resolution effects among various DEMs?
How to measure the accuracy assessment?
Which is the best reading for accuracy assessment among the various datasets?
What is the most suitable method to extract the stream network?
What are the factors that may affect the pattern?
Are the morphometric parameters adequate to represent the different resolution of stream network analysis?
7
1.4 Aim and Objectives
This study aims to understand the accuracy assessment of multiples resolution DEMs datasets effects towards river stream network. Based on the postulated research questions, the following research objectives are formulated:
1. To determine the effects of the resolution of various DEMs sources through the vertical accuracy assessment.
2. To measure the influence of stream order and threshold number towards stream network formation extracted from the various DEMs sources.
3. To extricate and quantify the linear, areal, relief parameters derived from DEMs on drainage sub-watershed of study area.
1.5 Area of Study
Pulau Pinang is located at the northern area of Peninsular Malaysia and is bordered by Kedah to the north and east, to the south by Perak and to the west by the Strait of Melaka. The total area of Pulau Pinang is 1,031 km2 or with a total population of 1.70 million (Malaysia Statistics Department, 2015). It consists of five districts such as Northeast and Southwest districts for island besides Seberang Perai. The Seberang Perai district is further subdivided into three districts which are Central Seberang Perai District, South Seberang Perai District, and North Seberang Perai District. The major economic activities in Pulau Pinang State are manufacturing-based, mainly the high-tech electronics plants, automotive industry, and shipping which contributed 13.6% to the Malaysia manufacturing sector (Malaysia Statistics Department, 2013). Agriculture and livestock farming are also important occupations found in this area. This research will focus on the river in South Seberang Perai District and Central Seberang Perai District for DEMs accuracy and stream network analysis.
8
The Jawi river watershed and Mengkuang Dam were chosen to perform the analysis. The Jawi river watershed is situated in South Seberang Perai and is one of the major watersheds and consists of sub-watershed rivers, namely, Bakap River, Duri River, Baung River, Badak Mati River, and Bakar Arang River (DID 2010). The Jawi river system flows through major towns such as Bukit Tambun and finally discharging into the Strait of Melaka. The average of the study area is dominated by both undulating and flat land which is generally covered by agricultural fields.
Mengkuang Dam is located at Central Seberang Perai District and is the only water dam at Seberang Perai. According to (Maznah and Makhlough, 2015), 80% of drinking water have been supplied to the Penang state and received almost 90% of water input from the Kulim river. Since the drought season causes an inadequate supply of raw water, the Sungai Dua water treatment plant is supplied with raw water from the Mengkuang dam (Sallet et al., 2011). The dam catchment is surrounded by Taman Rimba Bukit Mertajam hills and receives heavy precipitation in the form of rainfall, most of which occurs from October to December. The terrain surface of surrounding area is suitable to study on the accuracy assessment in different resolution. Figure 1.1 shows the whole study area for Seberang Perai Tengah and Seberang Perai Selatan. This figure provides detailed for objective 1 which emphasis on vertical accuracy assessment. Meanwhile, Figure 1.2 shows the study area associate with objective 1 and 2. The study area comprise of 2 watershed where Mengkuang watershed located at Seberang Perai Tengah (SPT) and Jawi watershed is located in Seberang Perai Selatan (SPS). Both watersheds are shown in shaded areas.
