Detection of Changes in Surface Water Bodies Urban Area with NDWI and MNDWI Methods

Land surface water bodies, an essential part of the Earth’s water cycle such as rivers, lakes, swamp, and reservoirs, influence the global ecosystem and climate global significantly. Makassar, one of the most populated cities in Indonesia, recently experiences massive development that affects the existence of vegetation area and urban aquatic ecosystem. This study attempts to detect the urban surface water bodies and to monitor the change by using Landsat OLI TIRS. In order to extract the high accuracy of data, the image data utilized in this study was acquired by Landsat 8 OLI TIRS sensor on 14 December 2000, 27 December 2009 and 06 January 2019 from the United States Geological Survey (USGS) portal analyzed by Normalized Difference Water Index (NDWI) and Modified Normalized Difference Water Index (MNDWI). These methods are scientifically used to classify the data into two categories consisted of water and non-water objects. The result shows that in the last nine years, urban surface water bodies increased around 129.8 ha distributed mostly in Manggala area. Due to rapid urban development such as housing, makes the urban runoff concentrating in low land and creates giant swamp as well as an urban wetland. In coastal areas however decline of the water body due to dominantly by massive reclamation, housing and factory settlement. The increase of urban surface water bodies can lower the urban heat while massive development in the built-up area can worsen the urban heat

Application of Satellite Imagery and Water Indices to the Hydrography of the Cetina River Basin (Middle Adriatic)

The paper gives a brief description of the remote sensing method used for the identification and extraction of water surfaces. Landsat 8 and Sentinel 2 satellite imagery was used to separate land from bodies of water in the complex karst area surrounding the Croatian Cetina River, flowing into the Adriatic Sea. Water indexing methods are presented in detail. The most frequently used water indices were selected: NDWI, MNDWI, AWEI_nsh, AWEI_sh, WRI and LSWI, and their results compared. The combination of satellite imagery and calculated water indices is concluded to be very useful for the identification and mapping of the area and banks of lakes, riverine zones, river mouths and the coastline in the coastal zone. Landsat 8 satellite imagery is slightly inferior to Sentinel 2 due to lower image resolution. The best results were obtained with the NDWI water index and the worst with LSWI

Development of Geospatial and Temporal Characteristics for Hispaniola’s Lake Azuei and Enriquillo Using Landsat Imagery

In this paper, we used Landsat imagery for water body identification to create a novel 36-year surface area extent time series for lakes Azuei (Haiti) and Enriquillo (Dominican Republic) aimed at illuminating the dramatic temporal changes of these two lakes not just at yearly but at monthly or even sub-monthly scales. We used the Normalized Difference Water Index (NDWI) to extract water features and we also used spatial differentiation and thresholding techniques to remove clouds and associated shadows from the scene that were then passed through gap filling algorithms to complete and extract the lake extent polygons. We also explored the challenges that arrive from trying to combine RS-based Digital Elevation Model data with locally collected bathymetric data to yield a seamless representation of the topographic features of the rift valley that contains the two lakes. This “bathtub” model was then meshed with the lake extent polygons to compute lake volumes, maximum depths, and geospatially referenced lake levels rating curves. We used this data to examine the lakes and their geospatial characteristics in the context of the lakes’ growth/shrinking patterns. While we did not carry out a full hydrologic analysis we attempted to illuminate how specific lake levels cause what type of flooding and especially answered the questions if (a) Lake Azuei would ever spill into Lake Enriquillo, and (b) what the maximum lake levels need to be before spilling into neighboring watersheds

Remotely sensed mid-channel bar dynamics in downstream of the Three Gorges Dam, China

The downstream reach of the Three Gorges Dam (TGD) along the Yangtze River (1560 km) hosts numerous mid-channel bars (MCBs). MCBs dynamics are crucial to the river’s hydrological processes and local ecological function. However, a systematic understanding of such dynamics and their linkage to TGD remains largely unknown. Using Landsat-image-extracted MCBs and several spatial-temporal analysis methods, this study presents a comprehensive understanding of MCB dynamics in terms of number, area, and shape, over downstream of TGD during the period 1985−2018. On average, a total of 140 MCBs were detected and grouped into four types representing small ( 2 km2), middle (2 km2 − 7 km2), large (7 km2 − 33 km2) and extra-large size (>33 km2) MCBs, respectively. MCBs number decreased after TGD closure but most of these happened in the lower reach. The area of total MCBs experienced an increasing trend (2.77 km2/yr, p-value 0.01) over the last three decades. The extra-large MCBs gained the largest area increasing rate than the other sizes of MCBs. Small MCBs tended to become relatively round, whereas the others became elongate in shape after TGD operation. Impacts of TGD operation generally diminished in the longitudinal direction from TGD to Hankou and from TGD to Jiujiang for shape and area dynamics, respectively. The quantified longitudinal and temporal dynamics of MCBs across the entire Yangtze River downstream of TGD provides a crucial monitoring basis for continuous investigation of the changing mechanisms affecting the morphology of the Yangtze River system

Spatio-Temporal Change of LakeWater Extent in Wuhan Urban Agglomeration Based on Landsat Images from 1987 to 2015

Urban lakes play an important role in urban development and environmental protection for the Wuhan urban agglomeration. Under the impacts of urbanization and climate change, understanding urban lake-water extent dynamics is significant. However, few studies on the lake-water extent changes for the Wuhan urban agglomeration exist. This research employed 1375 seasonally continuous Landsat TM/ETM+/OLI data scenes to evaluate the lake-water extent changes from 1987 to 2015. The random forest model was used to extract water bodies based on eleven feature variables, including six remote-sensing spectral bands and five spectral indices. An accuracy assessment yielded a mean classification accuracy of 93.11%, with a standard deviation of 2.26%. The calculated results revealed the following: (1) The average maximum lake-water area of the Wuhan urban agglomeration was 2262.17 km2 from 1987 to 2002, and it decreased to 2020.78 km2 from 2005 to 2015, with a loss of 241.39 km2 (10.67%). (2) The lake-water areas of loss of Wuhan, Huanggang, Xianning, and Xiaogan cities, were 114.83 km2, 44.40 km2, 45.39 km2, and 31.18 km2, respectively, with percentages of loss of 14.30%, 11.83%, 13.16%, and 23.05%, respectively. (3) The lake-water areas in the Wuhan urban agglomeration were 226.29 km2, 322.71 km2, 460.35 km2, 400.79 km2, 535.51 km2, and 635.42 km2 under water inundation frequencies of 5%–10%, 10%–20%, 20%–40%, 40%–60%, 60%–80%, and 80%–100%, respectively. The Wuhan urban agglomeration was approved as the pilot area for national comprehensive reform, for promoting resource-saving and environmentally friendly developments. This study could be used as guidance for lake protection and water resource management

Characteristics of Supraglacial Channels and Drainage Networks on Antarctic Ice Shelves

Supraglacial channels that flow on ice shelves can store and transport large volumes of meltwater to various locations (e.g., moulins, lakes, crevasses) during the melt season, so they play an important role in glacial hydrology and ice shelf stability. However, the current understanding of supraglacial channels is limited, especially the underlying processes and the controls on their development and variability. This study uses multiple remotely sensed data including satellite imagery and Digital Elevation Models (DEMs) to measure supraglacial channels in Antarctica. Five contrasting ice shelves around the margin of the Antarctic Ice Sheet are chosen as the study sites – Bach, Nansen, Nivlisen, Riiser-Larsen and Roi Baudouin ice shelves. Supraglacial lakes and channels are mapped by automatic delineation method during the melt season in 2020 and 2022, and key fluvial metrics are calculated, e.g., number, length, width, depth, sinuosity, bifurcation ratio, orientation, slopes and drainage density. Extensive supraglacial lakes and channels were observed on all five Antarctic ice shelves during the peak of the melt season and most were interconnected to form a total of 119 channel networks at different scales. The results demonstrate that: (ⅰ) supraglacial channel networks often occurred in areas with low elevations and near grounding lines, (ⅱ) supraglacial channel networks on different ice shelves exhibited different drainage patterns and hydromorphic characteristics, (ⅲ) the surface topography and structural glaciology of ice shelves affected the distribution of the supraglacial channel network. Future work could focus on long-term observation of supraglacial channels and exploring the applicability of terrestrial river-related research methods (e.g., hydrological modelling) to supraglacial channels

Literature review of the remote sensing of natural resources

Abstracts of 596 documents related to remote sensors or the remote sensing of natural resources by satellite, aircraft, or ground-based stations are presented. Topics covered include general theory, geology and hydrology, agriculture and forestry, marine sciences, urban land use, and instrumentation. Recent documents not yet cited in any of the seven information sources used for the compilation are summarized. An author/key word index is provided