Friday, 16 August 2019

GIS and RS for wetland mapping


Paper review
Objective
The aim of this paper is to map vernal pools in the Northeastern United States using high-resolution LiDAR data and aerial imagery.

Background of the study
In this study the importance of wetlands has been emphasized. Wetland are the natural water resources inundated or perennial. Although a distinct definition of wetland is not available but defined by various authors have some common features such as aquatic habitats, including marshes, swamps, bogs, fens, peatlands, prairie potholes, vernal pools, and aquatic beds, among others. In general, wetlands are transitional habitats situated between wet (e.g., lakes, rivers, streams, estuaries) and dry environments. Thus, the demarcation of a wetland lies along a continuum of water gradient and is somewhat arbitrary. Some wetland definitions include open-water habitats (e.g., lakes, rivers, streams) as wetlands, while others exclude permanent deep water and focus more on shallow water habitats. Wetlands exist in numerous sorts of atmospheres, on each landmass except Antarctica. They vary in size from disconnected prairie potholes to immense salt bogs. They are found along coasts and inland. A few wetlands are forests. Others are like watery fields.

Benefits of wetlands
Wetlands provide abundant ecological and socioeconomic benefits, such as providing habitats for fish, wildlife, and plant, storing floodwater and reducing peak runoff, recharging groundwater, filtering impurities in water, acting as nutrient and sediment sinks, protecting shorelines from erosion, and providing a range of recreational opportunities (e.g., boating, fishing, hunting).

Methodology
In this case study, 1-m resolution light detection and ranging (LiDAR)derived digital elevation modelling (DEM) in conjunction with LiDAR intensity imagery was used to map prairie wetlands and surface hydrologic flow pathways. The LiDAR intensity imagery was used to delineate wetland inundation areas, where as the LiDAR DEM was used to delineate wetland depressions, catchments, and surface hydrologic flow pathways.
Arc GIS is used to streamline the procedures for automated delineation of wetland catchments and flow paths, the proposed framework the toolbox consists of three tools: Wetland Depression Tool, Wetland Catchment Tool, and Flow Path Tool.
The Wetland Catchment Tool uses the digital elevation modelling (DEM) grid and the wetland polygon layers resulted from the Wetland Depression Tool as input, and exports wetland catchment layers in both vector and raster format. Various morphometric properties (e.g., width, length, area, perimeter, maximum depth, mean depth, volume, elongations, and compactness) are computed and included in the attribute table of the wetland vector layers.
The wetlands were identified for prairie pothole region (PPR) in north America
The chart given below is proposed framework for outlining wetland catchments and flow paths.

Results
The results obtained by comparing a small portion of the prairie pothole region of Dakota to the inundation polygons derived from the 2011 LiDAR intensity data and the NWI polygons created in the early 1980s by the U.S. It was observed that the national wetlands inventory (NWI) in this region is significantly out of date. The acquired light detecting and ranging data in October 2011 relatively shows large disjointed NWI wetlands coalesced and formed even larger wetland complexes during the extremely wet period.

Conclusion
According to the author except north America and parts of Europe, comprehensive national-scale wetland inventories are not available foremost countries. The author argues that technologies like GIS and remote sensing has greatly improved the geo-mapping of wetlands.

Reference
GIS and remote sensing applications in Wetland mapping and monitoring. Qiusheng Wu.

Review by,

Ehsan Nazeer




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