scholarly journals Evaluating spectral indices for water bodies extraction in western Tibetan Plateau

2021 ◽  
Author(s):  
Hafiza Wajiha Khalid ◽  
Rao M. Zahid Khalil ◽  
Muhammad Ateeq Qureshi
Keyword(s):  
Tibetan Plateau ◽  
Water Bodies ◽  
Spectral Indices ◽  
Western Tibetan Plateau

Use of water indices in the determination of thermokarst lakes according to remote sensing data

2021 ◽  
pp. 67-74
Author(s):  
Artem Pshenichnikov
Keyword(s):  
Visual Analysis ◽  
Remote Sensing Data ◽  
Water Bodies ◽  
Identical Result ◽  
Spectral Indices ◽  
Quadratic Error ◽  
Thermokarst Lakes ◽  
Ndvi Index ◽  
Water Indices

The results of application of six spectral indices (AWEI, MNDWI, NDVI, NDWI, TCW, WRI) for the isolation of thermokarst lakes in tundra landscapes of northern Yakutia are presented. To assess the accuracy of decryption of lakes, an average quadratic error (MSE) was calculated. The minimum MSE value is 0.11 km2 and corresponds to the NDWI index. An almost identical result (0.12 km2) is found in the WRI index, slightly worse (0.15 km2) one — in the NDVI index. An MNDWI index has the highest mean square error (7.02 km2). Visual analysis also showed better decryption of water bodies using the NDWI, WRI and NDVI indices, which allows the use of these indices for automatical isolatation water bodies.

scholarly journals Association of the pre-monsoon thermal field over north India and the western Tibetan Plateau with summer monsoon rainfall over India

2015 ◽  
Vol 33 (8) ◽  
pp. 1051-1058 ◽  
Author(s):  
S. D. Bansod ◽  
S. Fadnavis ◽  
S. P. Ghanekar
Keyword(s):  
Tibetan Plateau ◽  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Summer Monsoon Rainfall ◽  
North India ◽  
Monsoon Region ◽  
The North ◽  
Western Tibetan Plateau ◽  
Asian Summer ◽  
Summer Monsoon Region

Abstract. In this paper, interannual variability of tropospheric air temperatures over the Asian summer monsoon region during the pre-monsoon months is examined in relation to Indian summer monsoon rainfall (ISMR; June to September total rainfall). For this purpose, monthly grid-point temperatures in the entire troposphere over the Asian summer monsoon region and ISMR data for the period 1949–2012 have been used. Spatial correlation patterns are investigated between the temperature field in the lower tropospheric levels during May over the Asian summer monsoon region and ISMR. The results indicate a strong and significant northwest–southeast dipole structure in the spatial correlations over the Indian region, with highly significant positive (negative) correlations over the regions of north India and the western Tibetan Plateau region – region R1 (north Bay of Bengal: region R2). The observed dipole is seen significantly up to a level of 850 hPa and eventually disappears at 700 hPa. Thermal indices evaluated at 850 hPa level, based on average air temperatures over the north India and western Tibetan Plateau region (TI1) and the north Bay of Bengal region (TI2) during May, show a strong, significant relationship with the ISMR. The results are found to be consistent and robust, especially in the case of TI1 during the period of analysis. A physical mechanism for the relationship between these indices and ISMR is proposed. Finally the composite annual cycle of tropospheric air temperature over R1 during flood/drought years of ISMR is examined. The study brings out the importance of the TI1 in the prediction of flood/drought conditions over the Indian subcontinent.

scholarly journals Diurnal and Seasonal Variations of Surface Energy and CO2 Fluxes over a Site in Western Tibetan Plateau

Atmosphere ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 260 ◽  
Author(s):  
Xingbing Zhao ◽  
Changwei Liu ◽  
Nan Yang ◽  
Yubin Li
Keyword(s):  
Heat Flux ◽  
Energy Balance ◽  
Tibetan Plateau ◽  
Surface Energy ◽  
Seasonal Variations ◽  
Surface Energy Balance ◽  
Diurnal Variations ◽  
Heat Fluxes ◽  
Co2 Fluxes ◽  
Western Tibetan Plateau

Land surface process observations in the western Tibet Plateau (TP) are limited because of the abominable natural conditions. During the field campaign of the Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX III), continuous measurements on the four radiation fluxes (downward/upward short/long-wave radiations), three heat fluxes (turbulent sensible/latent heat fluxes and soil heat flux) and also CO2 flux were collected from June 2015 through January 2017 at Shiquanhe (32.50° N, 80.08° E, 4279.3 m above sea level) in the western Tibetan Plateau. Diurnal and seasonal variation characteristics of these surface energy and CO2 fluxes were presented and analyzed in this study. Results show that (1) diurnal variations of the seven energy fluxes were found with different magnitudes, (2) seasonal variations appeared for the seven energy fluxes with their maxima in summer and minima in winter, (3) diurnal and seasonal variations of respiration caused by the biological and chemical processes within the soil were found, and absorption (release) of CO2 around 0.1 mg m−2 s−1 occurred at afternoon of summer (midnight of winter), but the absorption and release generally canceled out from a yearly perspective; and (4) the surface energy balance ratio went through both diurnal and seasonal cycles, and in summer months the slopes of the fitting curve were above 0.6, but in winter months they were around 0.5. Comparing the results of the Shiquanhe site with the central and eastern TP sites, it was found that (1) they all generally had similar seasonal and diurnal variations of the fluxes, (2) caused by the low rainfall quantity, latent heat flux at Shiquanhe (daily daytime mean always less than 90 W m−2) was distinctively smaller than at the central and eastern TP sites during the wet season (generally larger than 100 W m−2), and (3) affected by various factors, the residual energy was comparatively larger at Shiquanhe, which led to a small surface energy balance ratio.

scholarly journals Stable Isotope Variations in Precipitation and Moisture Trajectories on the Western Tibetan Plateau, China

2007 ◽  
Vol 39 (4) ◽  
pp. 688-693 ◽  
Author(s):  
Wusheng Yu ◽  
Tandong Yao ◽  
Lide Tian ◽  
Yaoming Ma ◽  
Naoyuki Kurita ◽  
...  
Keyword(s):  
Stable Isotope ◽  
Tibetan Plateau ◽  
Western Tibetan Plateau

scholarly journals Decreasing Influence of Summer Snow Cover Over the Western Tibetan Plateau on East Asian Precipitation Under Global Warming

2021 ◽  
Vol 9 ◽  
Author(s):  
Zhibiao Wang ◽  
Renguang Wu ◽  
Zhang Chen ◽  
Lihua Zhu ◽  
Kai Yang ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Snow Cover ◽  
East Asian ◽  
Summer Precipitation ◽  
Northern China ◽  
The Tibetan Plateau ◽  
Western Tibetan Plateau ◽  
Asian Summer ◽  
Tibetan Plateau Snow Cover ◽  
East Asian Summer Precipitation

In recent years, some studies emphasized the influence of western Tibetan Plateau summer snow on the East Asian summer precipitation. With the temperature rise in the past decades, the snow cover over the western Tibetan Plateau in summer has significantly decreased. This raises the question whether the impact of the Tibetan Plateau snow has changed. The present study identifies a prominent change in the influence of the western Tibetan Plateau snow cover on the East Asian summer precipitation. Before the early 2000’s, positive precipitation anomalies extend from the southeastern Tibetan Plateau through the Yangtze River to Japan and Korea and negative anomalies cover southeast China corresponding to more Tibetan Plateau snow cover. After the early 2000’s, with the reduction of snow cover variability, below-normal and above-normal summer precipitation occurs over northern China-Mongolia and northeast Asia, respectively, corresponding to more Tibetan Plateau snow cover. The change in the influence of the Tibetan Plateau snow on the East Asian summer precipitation is associated with an obvious change in the atmospheric circulation anomaly pattern. Before the early 2000’s, the wind anomalies display a south-north contrast pattern with anomalous convergence along the Yangtze River. After the early 2000’s, an anomalous cyclone occupies Northeast China with anomalous southerlies and northerlies over northeast Asia and northern China, respectively. The Tibetan Plateau snow cover variation after the early 2000’s is associated with the northeast Indian summer precipitation. The model experiments confirm that the weakened influence of summer western Tibetan Plateau snow cover on the East Asian atmospheric circulation and precipitation with the reduced snow cover anomalies.

scholarly journals FLOOD MONITORING USING NDWI AND MNDWI SPECTRAL INDICES: A CASE STUDY OF AGHQALA FLOOD-2019, GOLESTAN PROVINCE, IRAN

2019 ◽  
Vol XLII-4/W18 ◽  
pp. 605-607
Author(s):  
F. Khalifeh Soltanian ◽  
M. Abbasi ◽  
H. R. Riyahi Bakhtyari
Keyword(s):  
Natural Hazards ◽  
Satellite Imagery ◽  
Water Bodies ◽  
Detection Methods ◽  
Spectral Indices ◽  
Landsat Images ◽  
Flood Monitoring ◽  
Golestan Province ◽  
Digital Methods

Abstract. Assessment of changes of water bodies and vegetation by traditional methods is very difficult and costly. The use of satellite data makes it possible to study water bodies and vegetation more accurately and cost effectively. Accordingly, various digital methods have been developed to discover and detect changes of earth's surface features. Flood is one of the important factors contributing to the destruction of natural resources. The purpose of this research is to evaluate the flood areas in the Aghqala area in Golestan province of Iran. The level of water bodies in the spring of 2018 and 2019 was compared and evaluated based on the NDWI and MNDWI indices using Landsat images. The results showed that water bodies’ area in the spring of 2018 was 24.13 km2 which increased to 185.34 km2 at 2019 using NDWI; while the MNDWI due to the excessive sensitivity to the water considered agriculture wetlands as an area of water bodies. Therefore, the NDWI yielded more logical results. Also, change detection methods based on spectral and radiometric information using indices are more accurate than the classification maps and more changes can be shown. Using satellite imagery to monitor changes is essential to facilitate the planning of natural hazards management.

scholarly journals Tracking the impacts of the Aru glacier collapses on downstream lakes

2020 ◽  
Author(s):  
Yanbin Lei ◽  
Tandong Yao ◽  
Lide Tian ◽  
Yongwei Sheng ◽  
Jingjuan Liao ◽  
...  
Keyword(s):  
Tibetan Plateau ◽  
Lake Level ◽  
In Situ Observation ◽  
Lake Surface ◽  
Level Increase ◽  
Lake Morphology ◽  
Western Tibetan Plateau ◽  
Ice Avalanche

Abstract. Two giant glaciers at the Aru range, western Tibetan Plateau, collapsed suddenly on 17 July and 21 September 2016, respectively, causing fatal damage to local people and their livestock. The ice avalanches, with a total volume of 150 × 106 m3, had almost melted by September 2019. Based on in-situ observation, bathymetry survey and satellite data, here we show the impacts of the two glacier collapses on the downstream lakes, the outflow Aru Co and the terminal Memar Co, in terms of lake morphology, water level and water temperature in the subsequent four years (2016–2019). After the first glacier collapse, the ice avalanche slid into Aru Co along with a large amount of debris, which significantly modified the lake’s shoreline and bathymetry. Lake surface temperature (LST) at Aru Co and Memar Co exhibited a significant decrease of 2–4 oC in the first 1–2 weeks after the first glacier collapse due to the intruding ice into Aru Co and its melting. Memar Co significantly deepened by 12.5 m between 2000 and 2018, with accelerated lake level increase after the glacier collapses. Memar Co expanded rapidly at a rate of 0.80 m/yr between 2016 and 2019, which is about 30 % higher than the average rising rate between 2003 and 2014. The meltwater from ice avalanches was found to contribute to about 26.4 % of the increase in lake storage between 2016 and 2019. This study implies that the Aru glacier collapses had long-term and dramatic impacts on the downstream lakes.

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