Quantitative Assessment of Remotely Sensed Global Surface Models Using Various Land Classes Produced from Landsat Data in Istanbul

Digital elevation model （DEM） is the most popular product for three-dimensional （3D） digital representation of bare Earth surface and can be produced by many techniques with different characteristics and ground sampling distances （GSD）. Space-borne opti- cal and synthetic aperture radar （SAR） imaging are two of the most preferred and modern techniques for DEM generation. Using them, global DEMs that cover almost entire Earth are produced with low cost and time saving processing. In this study, we aimed to assess the Satellite pour robservation de la Terre-5 （SPOT-5）, High Resolution Stereoscopic （HRS）, the Advanced Space-borne Thermal Emission and Reflection Radiometer （ASTER）, and the Shuttle Radar Topography Mission （SRTM） C-band global DEMs, produced with space-borne optical and SAR imaging. For the assessment, a reference DEM derived from 1 ： 1000 scaled digital photogrammetric maps was used. The study is performed in 100 km2 study area in Istanbul including various land classes such as open land, forest, built-up land, scrub and rough terrain obtained from Landsat data. The analyses were realized considering three vertical accuracy types as fundamental, supplemental, and consolidated, defined by national digital elevation program （NDEP） of USA. The results showed that, vertical accuracy of SRTM C-band DEM is better than optical models in all three accuracy types despite having the largest grid spacing. The result of SPOT-5 HRS DEM is very close by SRTM and superior in comparison with ASTER models.

Area,lake-level and volume variations of typical lakes on the Tibetan Plateau and their response to climate change,1972-2019

Most lakes have undergone significant changes on the Tibetan Plateau in recent decades,affecting water resources on the Tibetan Plateau and its surrounding areas.In this paper,we investigated the variations of 25 lakes in five sub-regions on the Tibetan Plateau from 1972 to 2019 based on SRTM DEM data and Landsat imagery.We used a method to derive lake-levels based on DEM and lake boundaries delineated from Landsat imagery,and then calculated the changes in lake area,level,and volume in 1972 to 2019.We also analyzed the potential impacts of temperature,precipitation,glacial and permafrost melting in lake changes during this period.The results show that the lakes tended to shrink until 2010 in southern and western plateau,after which they began to expand gradually but the overall trend is still shrinking.Limited meltwater from glaciers and permafrost and low precipitation are the main reasons for their shrinkage.The lakes in the central plateau,northwest plateau and northeast plateau tend to expand overall.The reason for the expansion of the lakes is not only precipitation but also the melting of glaciers and permafrost.Overall,the lake changes have gone through 3 phases,namely a slight decrease during 1972-2000,a rapid increase during 2000-2010,and a slowdown in the last decade(2010-2019).Multiple factors such as temperature,precipitation,the state of glaciers and permafrost have contributed to the changes in the lake.

Mapping wetlands in Indonesia using Landsat and PALSAR data-sets and derived topographical indices

Wetlands play an important role in the provision of ecosystem services,ranging from the regulation of hydrological systems to carbon sequestration and biodiversity habitat.This paper reports the mapping of Indonesia’s wetland cover as a single thematic class,including peatlands,freshwater wetlands,and mangroves.Expert-interpreted training data were used to identify wetland formations including areas of likely past wetland extent that have been converted to other land uses.Topographical indices(Shuttle Radar Topography Mission-derived)and optical(Landsat)and radar(PALSAR)image inputs were used to build a bagged classification tree model based on training data in order to generate a national-scale map of wetland extent at a 60 m spatial resolution.The resulting wetland map covers 21.0%(39.6 Mha)of Indonesia’s land,including 25.2% of Sumatra(11.9 Mha),22.9% of Kalimantan(12.2 Mha),and 28.9% of Papua(11.8 Mha).Results agree with existing image-interpreted products from Indonesia’s Ministries of Forestry and Agriculture and Wetlands International(89% overall agreement),and with the Ministry of Forestry forest inventory data for Sumatra and Kalimantan(91% overall agreement).An internally consistent algorithm-derived national wetland extent map can be used to quantify changing rates of land conversion inside and outside of wetlands.Additionally,wetlands extent can be used to efficiently allocate field resources in national assessments of wetland sub-types such as peatlands,which are a current focus of policies aiming to reduce carbon emissions from land use change.