INTRODUCTION
Mangroves are developing in Bang La, HaiPhong city
Mangroves are essential to Earth's ecosystems, offering critical services such as protection against natural disasters like tsunamis and tropical cyclones, as well as supporting timber extraction, fisheries, and fodder collection They play a crucial role in preserving regional and global ecological integrity However, mangrove ecosystems are increasingly vulnerable to pollution from mining activities, oil spills, heavy metals from shipbreaking, and industrial developments, including the construction of dams and embankments for water diversion.
Research indicates that the vulnerability of mangrove ecosystems is linked to their biogeochemistry, which adversely affects both aquatic and terrestrial flora and fauna (Bastakoti et al., 2018; Jha and Joshi, 2018; Sari and Rosalina, 2016).
Rising carbon dioxide (CO2) levels in the atmosphere are a significant driver of climate change, leading to increased air and sea temperatures, as well as ocean acidification, which threatens marine ecosystems like coral reefs and mangroves To combat this issue, one of the most effective strategies is to plant and restore mangrove forests while enhancing the protection of existing ones.
A study by Nguyen et al (2013) highlights the critical role of mangroves in coastal ecosystems, emphasizing their ability to protect shorelines from erosion and contribute to climate change mitigation.
Over the past 50 years, mangrove destruction has accelerated significantly and continues to decline, as highlighted by various studies (Donato et al., 2011; Ambsdorf et al., 2017; Estoque et al., 2018; Radabaugh et al., 2018) This degradation is primarily driven by human activities, including the clearing of mangrove forests for agriculture, urban development, tourism, and the extraction of resources such as firewood, construction materials, wood chips, pulp, and charcoal.
Mangroves play a vital role in coastal regions by supporting stable food supplies and fostering economic activities Their unique ecosystems provide significant opportunities for aquaculture, capture fisheries, and port-related industries, leveraging local resources and geographic advantages (Thomas et al., 2017; Refinda, 2017; Souza et al., 2018).
Mangroves play a crucial role in supporting aquatic life by providing essential feeding, nursing, and breeding habitats for various species Additionally, these vital ecosystems are home to diverse fauna, including marine mammals and seabirds, highlighting their ecological significance.
2018) An approximate calculation of the mangroves forests area in Vietnam was about 400,000 ha in the beginning of the 20th century (Pham and Yoshino,
2015) Mangroves forests in Vietnam has been using for various purposes (Tien et al., 2018)
A study by Hien et al (2018) highlights that the biodiversity of mangroves in HaiPhong is under threat due to the expansion of aquaculture and other developmental activities, which also impacts various economic functions of land use In recent years, there has been a notable increase in shrimp farming, driven by the goals of socio-economic development (Amano et al.).
Effective resource management is essential for meeting human needs sustainably, particularly in the context of shrimp farming, which poses a threat to mangrove ecosystems (Quach, 2018) To address this issue, it is crucial to update estimates of shrimp farming areas and assess the frequency of changes affecting mangrove habitats (Pham and Yoshino, 2015) Over the past two decades, remotely sensed data has been extensively utilized for mapping and monitoring mangrove environments, providing valuable insights for research and enhancing our understanding of mangrove ecology (Umroh et al., 2016; Sunwoo et al., 2018; Zulfa and Norizah, 2018) Consequently, Geographic Information Systems (GIS) and remote sensing (RS) have proven instrumental in analyzing vegetation and environmental elements.
Over the past two decades, the coastal zone of Hai Phong has undergone significant changes due to economic and social development, leading to a dramatic decline in mangrove areas and an increase in unproductive land (Evans, 2011; Quang, 2011) Given the vital role of mangroves in environmental health, it is essential to conduct a thorough analysis of land use and land cover changes (LULCC) driven by factors such as tropical storms, inadequate planning, and aquaculture practices Addressing these issues is urgent, alongside the need to develop strategies for the protection and restoration of mangrove ecosystems Therefore, comprehensive spatial analysis, particularly long-term assessments, is crucial for understanding these changes Recent studies at both national and international levels have highlighted the importance of spatial analysis in monitoring LULCC in coastal regions.
This project aims to provide recommendations and solutions by utilizing current remotely sensed data sources to evaluate and monitor climatic and non-climatic factors affecting mangrove ecology The focus of the study is to analyze land use and land cover change (LULCC) through spatio-temporal remotely sensed data to address key questions: What is the current status of mangrove management in Hai Phong, Vietnam? How has mangrove vegetation changed over selected years? What future research directions can be recommended for improved management?
LITERATYRE REVIEW
Overall GIS and Remote sensing
A Geographic Information System (GIS) is a powerful tool for capturing, storing, manipulating, analyzing, managing, and presenting various types of geographical data Essentially, GIS functions like a web or mobile application that allows users to integrate their data with maps, enabling visualization and analysis to uncover patterns and trends.
(Geospatial World, 2018) Fig 2.1 GIS Data Layers, Source:Arizona.edu
A geographic information system (GIS) is a powerful tool that allows users to access and analyze various types of geographic data By integrating multiple data layers, such as street maps, building information, and vegetation data, GIS enables the creation of detailed and informative maps.
Fig 2.2 Various use of GIS, Source:Cbronline.com
Geographic Information Systems (GIS) excel in storing and processing extensive spatial data, integrating information from diverse sources regarding content, format, projection, and scale This capability allows for the creation of a unified database that is easily accessible Understanding GIS highlights its significance in recognizing the importance of location and the reasons behind spatial relationships (Nguyen, 2017).
Geographic Information Systems (GIS) play a crucial role in analyzing geographic data, revealing enduring patterns and providing essential insights for problem-solving They offer practical knowledge on spatial data and facilitate the observation of technical aspects related to GIS programs, while also serving as a standard reference for historical events and trends.
Landsat imagery is an archive OC earth images Landsat-1 began its journey in
1972 Around the world, Landsat receiving stations are a unique resource for global change researches and used in various fields like Agriculture, Cartography, Geology, Forestry, Regional planning, Surveillance & education
Table 2.1 Types of series of Landsat imagery
Moderate resolution Earth-observing satellites, like Landsat, provide essential capabilities for monitoring land use and changes over large areas This invaluable tool offers repetitive and comprehensive observations of the Earth, enabling researchers and managers to effectively analyze and manage land across extensive geographical regions.
Satellite imagery has become a reliable tool for the consistent monitoring and modeling of land use and land cover patterns (Lo and Choi, 2004; Thakur et al., 2017) Additionally, since 2008, Landsat data has been accessible for free, enhancing research opportunities in this field (Salim et al., 2018).
Sentinel-2, an Earth observation mission by the European Space Agency, utilizes a cloud-based platform for effective distribution management and import of imagery for GIS applications, adhering to OGC standard web services.
Multispectral Imager‟s (MSI), Sentinel-2 launched in 2015 The imagery of Sentinel-2 has three distinguished spatial resolution, they are 10 m, 20 m and
60 m (ESA, 2015) Which can define a very small water area or garden (Hedley et al., 2018) Sentinel-2 data have 13 spectral bands and radiometric resolution of the sensor is 12-bit (ESA, 2015; Tominget al., 2016)
The global application of Sentinel-2 multi-spectral imagery enables extensive multi-temporal coverage, as highlighted by Storey et al (2016) and Castillo et al (2017) This technology has proven valuable across various fields, including the assessment of above-ground biomass in mangroves, the analysis of land use changes from non-forest areas, and the monitoring of water quality in lakes (Castillo et al., 2017).
A map serves as a visual representation that conveys geographic information, blending art and science to depict real-world features An effective map should be informative yet easily understandable, incorporating essential elements such as spatial reference, scale, and a summary of specific information, like the locations of villages.
Application of GIS and remote sensing to detect land use and land cover change
Land use and land cover change (LULC) is a significant process influenced by both natural events and human activities, leading to alterations that affect ecosystems (Ruiz-Luna and Berlanga-Robles, 2003) These environmental changes are increasingly concerning due to human impact on the Earth's surface Understanding LULC is crucial for effective planning, management, and utilization of natural resources (Kumar et al., 2013) Human-induced changes to the terrestrial surface underscore the importance of LULC in global ecological planning and decision-making for a sustainable future.
Understanding the status of mangroves relies on distinguishing between plant, land, and water features in remotely sensed data based on their reflectivity The use of GIS and remote sensing technology to analyze changes in mangrove ecosystems is widely adopted globally (Thi et al., 2014; Thomas et al., 2014).
GIS and remote sensing techniques have long been recognized for their effectiveness in monitoring urban growth by detecting changes in land use and land cover These technologies play a crucial role in formulating and executing policies aimed at addressing economic, environmental, and social goals within the framework of sustainable rural development.
Application of GIS and remote sensing to detect mangrove extents
Mangroves, despite their significant benefits, are among the most endangered ecosystems globally Unregulated developments, such as mega-tourism projects, polluting industries, and extensive shrimp farming, pose severe threats to these vital habitats The use of Geographic Information Systems (GIS) and Remote Sensing technology has emerged as a crucial tool for detecting and monitoring mangrove extents, highlighting the need for sustainable management practices to protect these ecosystems.
Vietnam's mangrove ecosystems are facing severe degradation, highlighting the urgent need for locally-led community development initiatives that promote economic growth while safeguarding these vital coastal habitats Although previous studies on this issue have been limited, recent years have seen a growing interest among researchers in the protection of mangroves, emphasizing the importance of sustainable practices for both environmental conservation and community welfare.
Recent studies over the past five years have revealed significant findings in GIS and Remote Sensing, particularly concerning mangroves and land use/land cover change (LULCC) It is essential to enhance the application of these technologies to further advance research in this field.
Mangroves
Mangrove is a type forest found in coastal swamps with fines and salty sediments that flooded by tides and abounded by salt-tolerant trees or shrubs(Sheng and Zou, 2017)
Mangroves thrive in coastal areas and estuaries where freshwater meets seawater, primarily in tropical and subtropical regions (Bochove et al., 2014) There are six distinct types of mangroves categorized by geophysical, geomorphological, and biological factors (Thom et al., 1984).
- Composite river and wave-dominated
The wave height of the mangrove forests decreases according to the exponential law and the depreciation level depends mainly on three indicators: forest structure, density and forest cover
Mangroves cover approximately 137,760 km² across 118 countries, primarily located in tropical and subtropical regions (Alatorre et al., 2016; Giri et al., 2011) These unique ecosystems account for 0.7% of the world's total tropical forest area and are predominantly situated between latitudes 30° N and 30° S, within the inter-tropical zone where seawater temperatures reach around 20°C Notably, Asia hosts the largest share of mangrove coverage, comprising 42%, followed by Africa.
Fig 2.4 Spatial distribution of mangroves in the world,
Over the past 50 years, Asia has witnessed a staggering 50% loss of its mangrove areas, with destruction continuing to escalate in certain regions Globally, 30% of mangrove forests have vanished, highlighting a critical environmental crisis (Godoy and Lacerda, 2015; FAO).
1994, total coverage of mangrove area is about 5.8 million of hectares, therein 35% of the Mangroves are found in the Caribbean and Latin America (Lugo,
2002), which distributed in 32o 20‟ N latitude at Bermuda, and 28o 30‟ S latitude at Santa Clara, Santa Catarina, Brazil
Africa's total mangrove area spans approximately 25,960 km², with significant regions located from Mauritania at 19º 10' N in the northwest to Angola at 10º S in the southwest, and extending to South Africa at 29º S.
Mangrove areas in Africa have significantly declined, with a total loss of 31.5 hectares across 17 estuaries, primarily concentrated in Nigeria This alarming trend highlights the urgent need for conservation efforts to protect these vital ecosystems, which extend from 110°S in the Southeast to 28°N in the Northeast, including regions like Madagascar (Fatoyinbo and Simard, 2013; Hoppe-Speer et al., 2014).
The mangrove forests of Oceania thrive in a tropical climate characterized by high rainfall and an average temperature of 24ºC This region spans from 30° latitude to 73° longitude, covering approximately 17,590 sq km (Donato et al., 2011) In the Pacific islands, the total mangrove area reaches about 343,735 ha, with Indonesia alone accounting for 23% of global mangrove cover Australia follows with 977,975 ha (7.1%), while Papua New Guinea contributes 480,12 ha (3.5%) (Chaudhuri et al., 2015) Australia boasts nearly 12,000 km² of mangroves, Papua New Guinea exceeds 4,000 km², and Fiji and the Solomon Islands have 200 km² and 640 km², respectively (Ellison, 2000).
The Asian continent hosts the largest and most diverse mangrove area globally, with significant regions along the Arabian Sea, Bay of Bengal, and Gulf of Thailand Indonesia accounts for 3,112,989 hectares (22.6%) of this area, followed by Burma with 494,584 hectares (3.6%), Bangladesh at 436,570 hectares (3.1%), Malaysia with 505,386 hectares (3.7%), India at 368,276 hectares (2.7%), the Philippines with 263,137 hectares (1.9%), and Iranian mangrove forests covering 93.37 km² Southeast Asia alone comprises 33.8% of the world's total mangrove ecosystems.
Mangroves in Southeast Asia
Southeast Asia is home to the most diverse and unique mangrove forests, which account for 38% of the world's total mangrove ecosystem Covering approximately 18 million hectares, these rich habitats play a crucial role in supporting biodiversity and maintaining ecological balance.
The region located between 5° N and 5° S latitude, known for its tropical climate, experiences high levels of precipitation and is prone to various natural disasters Recent events, such as storms, tsunamis, and cyclones, have been exacerbated by factors like landslides and deforestation, highlighting the area's vulnerability to environmental challenges.
Mangrove forests in Southeast Asia play a crucial role for coastal communities; however, they face significant threats due to over-harvesting, fuelwood collection, and reduced freshwater availability These activities, driven by the needs of local populations living near mangrove areas, have led to a decline in natural resources and diminished silt deposition, putting the health of these vital ecosystems at risk.
Fig 2.5 Spatial distribution of mangroves in Southeast Asia
In recent years, the rapid expansion of aquaculture, particularly shrimp farming in Southeast Asia, has led to significant environmental concerns Experts indicate that the aquaculture industry is a major contributor to mangrove deforestation, with agricultural practices and excessive salt bed usage exacerbating the issue Over the past three decades, mangrove areas in Southeast Asia have suffered devastating losses, with reductions of 25% in Malaysia and up to 50% in Thailand (Primavera, 2005).
Considering the benefit of palm oil plantation, local communities and companies are getting more interested, which caused major deforestation in the mangrove forests in Malaysia (Richards and Friess, 2016)
Rapid urban and industrial development in coastal areas has intensified pressure on ecosystems, particularly in Vietnam's mangrove regions Recent studies indicate that economic benefits from mining in these areas have significantly reduced freshwater inflow and increased salinity, leading to wastewater accumulation This has severely impacted the biodiversity of mangrove ecosystems.
Table 2.2 Mangrove area in Southeast Asian countries
Rapid urban and industrial development in coastal areas is placing significant pressure on ecosystems Recent studies indicate that economic benefits derived from mining in Vietnam's mangrove regions have led to a substantial decrease in freshwater inflow, resulting in increased salinity and wastewater contamination These changes have severely impacted the biodiversity of mangrove habitats.
The mangroves in Vietnam dived into four main zones among a
2012), where zone-I is distributed from Ngoc Cape to Do Son cape,
Zone-II is distributed from to Do
Son cape to Lach Truong cape,
Zone-III is distributed from Lach
Truong cape to Vung Tau cape and
Zone-IV is distributed from Vung
Tau Cape to Nai Cape- Ha Tien
Fig 2.6 Spatial distribution of mangroves in Vietnam,
Importance of mangroves
Mangrove plays an incredible rule in the ecosystem They provide invaluable ecosystem services with a strong foundation for an immensely productive and biologically complete ecosystem(Bochove et al., 2014; Ecoviva, 2016;Huxham
Mangroves, despite covering less than one percent of global tropical forests, are among the most valuable ecosystems on Earth They offer numerous ecosystem services that benefit humanity, including productive fishing grounds, carbon storage, enhanced tourism and recreation, soil erosion prevention, and protection against destructive tropical storms.
Healthy mangrove forests offer significant opportunities for sustainable revenue through eco-tourism, sports, fishing, and various recreational activities.
Buffer zone between land and see
Mangrove serves as a buffer zone between land and sea (Keller, et al,
The mangrove ecosystem, characterized by its diverse taxonomy, plays a crucial role in providing shelter along tropical shores These vital habitats create a natural buffer zone, maintaining elevation in the upper inter-tidal zone despite rising sea levels Mangroves are essential for numerous species, including salt-tolerant plants, fish, and various terrestrial and aquatic animals.
Mangrove also tends to the first line of defense for coastal communities against tropical storms, cyclone, hurricanes etc (Tanaka, 2009;
Unlimited capacity for absorbing CO2
Mangrove forests play a crucial role in global climate regulation by utilizing sunlight and carbon dioxide during photosynthesis to synthesize organic matter, which also helps prevent evaporation On average, these ecosystems store approximately 10,000 tonnes of carbon per hectare each year in their biomass and soil Additionally, mangroves are integral to the carbon and nitrogen conversion cycles, significantly contributing to carbon dioxide mitigation and helping to alleviate the greenhouse effect.
Mangroves serve as a vital resource, significantly enhancing livelihoods by providing essential goods such as firewood, timber, food, and medicine (Hossain et al., 2016; Lamsal et al., 2017; Dharmawan, 2018) These trees have historically been favored for firewood, while their timber is prized for crafting fine furniture and building boats, making it a crucial income source for many coastal families (Winton et al., 2017; Huxham et al., 2017; Dos-Santos and Lana, 2017) Additionally, mangroves contribute to the local economy through honey production, offering a valuable marketable resource for communities living near these ecosystems (Ecoviva, 2016; Huxham et al., 2017).
Mangroves protect both the saltwater and the freshwater ecosystems
Mangroves play a crucial role in maintaining water quality due to their complex root systems, which effectively filter and trap sediments, heavy materials, and pollutants Their dense roots prevent high concentrations of nitrates and phosphates from entering freshwater zones, thereby protecting aquatic life, including insects and fish.
Sedimentation and Prevention of soil erosion
Mangroves play a crucial role in retaining sediments from upstream, which helps prevent contamination of downstream waterways (Woodroffe et al., 2016; Huxham et al., 2017) Their active growth and organic matter deposition stabilize sediments and contribute significant annual siltation, creating fertile land that supports agricultural and fisheries development This has led local governments to consider encroaching on sea dikes to expand land use (Kathiresan, 2003; Ecoviva, 2016; Huxham et al., 2017) Additionally, mangroves are essential in combating soil erosion and protecting land from damage caused by tropical storms (Othman, 1994; Ecoviva, 2016; Huxham et al., 2017).
The role of microbial communities in forest
Microorganisms, including bacteria, fungi, yeasts, and microbes, found in soil and mangroves, are essential for decomposing complex compounds like starch, cellulose, and chitin They possess the ability to rapidly mineralize these substances due to their production of powerful exo-enzymes such as cellulase, amylase, proteinase, and chitinase These microorganisms play a crucial role in the metabolic cycle and contribute significantly to the health of marine ecosystems.
Case study
Mangrove forests play a crucial role in supporting local communities by providing essential resources for their livelihoods while also exhibiting significant biodiversity influenced by climatic and environmental factors (Huxham et al., 2017; Schild et al., 2018) These ecosystems not only fulfill basic needs and offer protection against natural disasters but also drive economic growth through various resources (Huxham et al., 2017; Wilson et al., 2018) However, while mining activities globally contribute to economic development, they also pose serious environmental risks (Conlin and Jolliffe, 2010).
A study titled "Application of Analytical Hierarchy Process (AHP) Technique to Evaluate the Combined Impact of Coal Mining on Land Use and Environment: A Case Study in Ha Long City, Quang Ninh Province, Vietnam," conducted by Vu et al (2017) and published in the International Journal of Environmental Problems, highlights significant environmental impacts of coal mining The research indicates that land use and land cover (LULC) in the coal mining area correlates directly with annual coal production, affecting all types of land in Ha Long City.
A study by Umroh (2016) utilized Landsat imagery and GIS techniques to analyze the distribution of mangroves on Pongok Island The findings revealed that the mangrove ecosystem is densely populated and actively protected by local communities, who are conscious of the importance of mangrove conservation and prohibit mining activities in the surrounding areas.
In the 2008 paper "Climate Change and Coastal Vulnerability Assessment: Scenarios for Integrated Assessment" by Nicholls, published in the Integrated Research System for Sustainability Science, the study highlights the impact of non-climatic drivers on coastal vulnerability The findings emphasize the critical need for integrated assessments to address these non-climatic factors effectively.
Peter Saenger from the School of Environment, Science, and Engineering explores the interconnectedness of the environment, economy, and society in his work titled "Sustainable Management of Mangroves," published in the Southern Cross University library The author addresses the challenges faced by existing mangrove management systems and presents a framework for integrated coastal zone management.
(iii) Developing mangrove management plans;
(Nguyen, McAlpine et al.) Reassessing the value of mangroves;
(vi) Rehabilitation of degraded mangroves
A study by Nguyen et al (2013) titled "The Relationship of Spatial-Temporal Changes in Fringe Mangrove Extent and Adjacent Land-use: A Case Study of Kien Giang Coast, Vietnam" examines the spatial-temporal changes in fringe mangrove extent and width over 20 years using Landsat TM images The findings reveal a significant correlation between increased deforestation and factors such as shrimp farming, crop production, and urban development This research highlights the primary drivers of mangrove changes, providing valuable insights for the Department of Planning and Information Development to implement effective preservation and management strategies.
A report titled "Observatoire des mangroves dans la zone Indo-Pacifique," published by the University of Nouvelle-Caledonia, highlights significant environmental issues, legal challenges, and economic conditions affecting mangroves While mining has garnered global attention for its role in socio-economic development, it indirectly impacts mangroves through the release of pollutants and sediments that threaten neighboring ecosystems The toxicity of these pollutants poses a serious risk to both mangrove biodiversity and human health.
Mangroves, unique ecosystems found in tropical and subtropical regions, play a crucial role in protecting wildlife and providing valuable commercial products and ecosystem services To enhance the quality of these resources and improve environmental conditions, it is essential to integrate best practices with mining, tourism, and agricultural activities This holistic approach aims to assess and mitigate harmful activities in mangrove areas, ultimately promoting sustainable development and increasing the productivity of mangrove forests.
RESEARCH OBJECTIVES AND METHODOLOGY
Research goal and objectives
This study establishes a scientific basis for the detection and monitoring of coastal mangrove extent changes through the use of remotely-sensed satellite data, supporting sustainable mangrove management in Vietnam amidst a changing climate.
In order to achieve an overall research goal, there are four specific objectives defined as below:
This study aims to assess the current status of mangrove extents and management strategies in Hai Phong City, Vietnam It seeks to answer critical questions regarding the condition of mangroves and the effectiveness of existing management practices in the region.
This study aims to create thematic maps illustrating the extent of coastal mangroves in Hai Phong city for specific years: 1990, 2000, 2005, 2010, 2015, 2016, 2017, and 2018 The objective is to assess the changes in coastal mangrove areas over these selected years.
- To quantify the changes in coastal mangrove extent during the selected periods (1990- 1995, 1995- 2000, 2000- 2005, 2005- 2010 and 2010- 2015):
This proposed to answer the questions of which period has changed the most and how much
To identify key drivers of coastal mangrove changes during This proposed to answer the questions of what are the drivers of coastal mangrove changes in Hai Phong city
This article aims to identify practical solutions for sustainable coastal mangrove management, focusing on potential future research directions that can improve management practices.
Research scope
This study concentrated on the coastal districts of Hai Phong city, specifically targeting the areas within Tien Lang district where mangroves thrive Additionally, it included the Bang La and Dai Hop communes in Kien Thuy district, both of which are known for their existing mangrove ecosystems.
In this study, multi-temporal Landsat and Sentinel images were used to cover study areas from 1990- 2018 In addition, mangrove extents are quantified during the period 1990- 2018.
Methodology
Human activities and climate change are significantly altering land cover, raising serious concerns about the implications of these changes.
Hai Phong is an attractive study destination due to its stunning beauty and significance as a hub for recreation, rich in ecological and socioeconomic resources However, the city faces serious environmental pollution issues that threaten local livelihoods, highlighting the urgent need for immediate action to address these challenges.
I am motivated to pursue studies in GIS and Remote Sensing to enhance my expertise in this field The growing application of Remote Sensing and GIS across academic, social, and business sectors highlights their significance and relevance today.
GIS and Remote Sensing studies are valuable tools for enhancing mangrove management This research focuses on analyzing land use and land cover change (LULCC) by utilizing spatiotemporal remotely sensed data to achieve specific objectives.
- To analyze the status and current mangrove management schemes
- To identify key drivers of coastal mangrove changes during the selected periods
- To find out feasible solutions to enhance coastal mangrove management in a sustainable way
Data collecting, synthesizing and analyzing documents have used in the first steps of scientific research
Diagram 3.1 Flowchart of image classification methods applied in this study
Collected data from the field was analyzed by using MS Word, MS Excel and ArcMap
The study will use historical Landsat Thematic Mapper images and
Sentinel images from 1994, 2001, 2006, 2010, 2015, and 2018, along with data from Landsat 7, Landsat 5, and Sentinel 2A/B, have been utilized to analyze changes in coastal land use and specifically in mangrove extents This analysis demonstrates a significant spatial agreement in mangrove distribution, as highlighted by Rudiastuti et al (2016).
Table 3.1Remotely sensed data used this study
No Image codes Date Spatial
Source:Earthexplorer.usgs.gov, Glovis.usgs.gov
3.3.4 Investigation of the status of spatial mangrove extents and current mangrove management schemes
To assess the current status of coastal mangrove extents, this study reviews secondary data and management activities by central and local governments, utilizing historical maps and remote sensing data for accurate mapping (Table 3.1) The resulting map serves as a crucial tool for evaluating the extent of mangrove areas.
A semi-structured social survey was conducted to collect information on historical records based on the experiences and practices of the local commune
(Dahdouh-Guebas, 2004) It helped us to determine the structure, to review therevious conditions and investigate the environmental factors that have an effect the study area
A comprehensive field survey was conducted to gather data on the socio-economic conditions, natural resources, environmental factors, climate change impacts, and disaster management issues within the study area.
A social survey was conducted among households near mangrove areas, focusing on residents aged 30 years and older who have lived there for over three decades, along with government officials and community leaders The survey aimed to gather insights on their experiences and observations in the study area Based on the collected data, a sustainable mangrove management model will be proposed to minimize risks, incorporating public consultation and strategies for risk assessment.
3.3.5 Construction of coastal mangrove thematic maps in selected years
Effective change detection and vegetation dynamics studies require essential preprocessing tools, such as ArcGIS, to minimize errors This preprocessing involves tasks like rectification, re-projection, registration, and correcting for topographic and atmospheric effects, including cloud interference It is crucial to define the origin of a raster dataset, and the re-project tool is utilized to convert data from one projection to another, with data typically collected in the WGS 1984 geographic coordinate system Prior to re-projecting, the original data's coordinate system is verified, and reflectance values from satellite imagery are computed using the raster calculator in ArcGIS.
Once preprocessing have done, image Interpretationbeen performed in the
After preprocessing, image interpretation was conducted using ArcGIS, allowing for easier visualization of different colors, such as Red, Blue, and Green, which are essential for distinguishing between objects This combination of various information sources enhances the analysis by generating individual spectral reflections By merging the Red (associated with mangroves), Green, Blue, and NIR bands, a colorful composite raster layer was created, facilitating more effective data interpretation (ESRI).
2010), which open nearly true color of the object that we expect in an image (Miller et al., 2017)
ArcTool box => Data Management tools => Raster => Raster processing
RGB (Mangroves, Water, Aquacultures, Others)
Table 3.2 Useful Bands for mapping
As vegetation absorbs nearly all red light this band is useful for distinguishing between vegetation and soil and in monitoring vegetation health
This has similar qualities to band 1 but not as extreme The bandit matches the wavelength for the green we see when looking at vegetation
Open water, generally with greater than 95% cover of water, including streams, rivers, lakes, and reservoirs
Construction, residential, commercial, industrial, transportation and facilities, grass, sod, timber trees, shrubs, other live ground covers
3.3.5.3 Normalized Difference Vegetation Index (NDVI)
Satellite images were enhanced using vegetation indices, specifically NDVI, to accurately identify the extent of mangroves Land Use and Land Cover (LULC) classification was essential for detecting temporal changes in mangrove areas In this classification, mangroves are assigned a value of 1, while water bodies receive a value of 2, and other land types, including residential areas and bare/wet soils, are categorized as 3 Agriculture and aquaculture are classified as 4 Higher NDVI values indicate denser mangrove vegetation, with values close to -1 representing non-vegetation, such as water or bare/wet soils, and values approaching +1 indicating dense vegetation.
1 𝑁𝐷𝑉𝐼 = 𝑁𝐼𝑅 – 𝑅𝐸𝐷/𝑁𝐼𝑅 + 𝑅𝐸𝐷 (Pervin et al., 2016; Nguyen, 2017) Where: NIR is Near Infrared, RED is (visible) Red
The range of NDVI is from -1 to 1
Table 3.3 NDVI values for various cover types
Rock, sand, or snow NDVI