The distribution characteristics of the impact craters can provide a large amount of information on impact history and the lunar evolution process. In this research, based on the digital elevation model (DEM) data originating from Change'E-1 CCD stereo camera, three automatic extraction methods for the impact craters are implemented in two research areas: direct extraction from flooded DEM data (the Flooded method), object-oriented extraction from DEM data by using ENVI ZOOM function (the Object-Oriented method) and novel object-oriented extraction from flooded DEM data (the Flooded Object-Oriented method). Accuracy assessment, extracted degree computation, cumulative frequency analysis, shape and age analysis of the extracted craters combined display the following results. (1) The Flooded Object-Oriented method yields better accuracy than the other two methods in the two research areas; the extraction result of the Flooded method offers the similar accuracy to that of the Object-Oriented method. (2) The cumulative frequency curves for the extracted craters and the confirmed craters share a similar change trajectory. (3) The number of the impact craters extracted by the three methods in the Imbrian period is the largest and is of various types; as to their age earlier than Imbrain, it is difficult to extract because they could have been destroyed.
WAN CongCHENG WeiMingZHOU ZengPoZHAO ShangMinXIA Yao
Inland lakes are important water resources in arid and semiarid regions. Understanding climate effects on these lakes is critical to accurately evaluate the dynamic changes of water resources. This study focused on the changes in Sayram Lake of Xinjiang, China, and addressed the effects of climate fluctuations on the inland lake based on long-term sequenced remote sensing images and meteorological data from the past 40 years. A geographic information system (GIS) method was used to obtain the hypsometry of the basin area of Sayram Lake, and estimation methods for evaporation from rising temperature and water levels from increasing precipitation were proposed. Results showed that: (1) Areal values of Sayram Lake have increased over the past 40 years. (2) Both temperature and precipitation have increased with average increases of more than 1.8℃ and 82 mm, respectively. Variation of the water levels in the lake was consistent with local climate changes, and the areal values show linear relationships with local temperature and precipitation data. (3) According to the hypsometry data of the basin area, the estimated lake water levels increased by 2.8 m, and the water volume increased by 12.9×10 8 m3 over the past 40 years. The increasing area of Sayram Lake correlated with local and regional climatic changes because it is hardly affected by human activities.
HuiXia CHAIWeiMing CHENGChengHu ZHOUShangMin ZHAOHaiJiang LIU
Inland lakes and alpine glaciers are important constituents of water resources in arid and semiarid regions. Understanding their variations is critical for both an accurate evaluation of the dynamic changes of water resources and the retrieval of climatic information. On the basis of earlier researches, this study investigated the growth of the Sayram Lake and the retreat of its water-supplying glaciers in the Tianshan Mountains using long-term sequenced remote sensing images. Our results show that over the past 40 years, the surface area and the water level of the lake has increased by 12.0±0.3 km2 and 2.8 m, respectively, and the area of its water-supplying glaciers has decreased continuously since the early 1970 s with a total reduction of about –2.13±0.03 km2. Our study has indicative significance to the research of regional climate change.
CHENG WeimingWANG NanZHAO ShangminFANG YueZHAO Min
