A dataset of lake level changes in China between 2002 and 2023 using multi-altimeter data

Lake water levels are an important indicator of water balance and water cycles,and are essential for climate and environmental change studies and water resource evaluation.Currently,lake level measurements are scarce or inconsistent throughout the country,and traditional gauge measurements of many lakes are not feasible,so satellite altimetry is a vital alternative to gauge lake levels.However,the accuracy and sam-pling frequency of lake level time series are usually low because of time and space coverage limitations;therefore,it is necessary to utilize multialtimeter data to monitor lake levels and obtain lake level changes over long time series.In this study,we extracted the water level changes in 988 lakes(>10 km^(2))in China between 2002 and 2023 based on ICESat/-2,Cryosat-2,Jason-1/2/3,and Sentinel-3A/3B altimetry data using waveform retracking,lake level extraction,lake level time series construction,the fusion of multi-altimeter lake level time series,and outlier removal.A total of 55%of the lakes in this dataset have been monitored for more than 10 years,and 34%have more than 12 times the annual average water level monitoring.At the same time,in situ data from 21 lakes were used for validation,and the average root mean square error(RMSE)for each of the datasets of ICESat/-2,Cryosat-2,Jason-1/2/3,and Sentinel-3A/3B versus the in situ lake levels are 0.223 m,0.163 m,0.207 m,0.596 m,0.295 m,0.275 m,0.243 m,and 0.317 m,respectively,and the mean RMSE of the fused lake levels reaches 0.332 m.During the monitoring period,the water levels in Chinese lakes generally increased.The overall annual average rate of change at the 20 and 10-year scales was 0.123 m/a and 0.151 m/a,respectively,among which the overall water levels in large lakes increased significantly.The lakes with a faster rate of decline in the water level were primarily small.The water storage in each lake region in China shows an upward trend,with the most significant increase in the Tibetan Plateau region,where the average annual water level change rate has remained above 0.15 m/a over the past two decades.This dataset has high spatiotemporal coverage and accuracy and can support the estimation of changes in lake water storage,analysis of lake level trends,plateau flooding,and the relationship between lake ecosystems and water resources.

Lake variations in response to climate change in the Tibetan Plateau in the past 40 years

The Qinghai-Tibetan Plateau plays an important role in global climate and environmental change and holds the largest lake area in China,with a total surface area of 36,900 km^(2).The expansion and shrinkage of these lakes are critical to the water cycle and ecological and environmental systems across the plateau.In this paper,surface areas of major lakes within the plateau were extracted based on a topographic map from 1970,and Landsat MSS,TM and ETM+satellite images from the 1970s to 2008.Then,a multivariate correlation analysis was conducted to examine the relationship between the changes in lake surface areas and the changes in climatic variables including temperature,precipitation,evaporation,and sunshine duration.Initial results suggest that the variations in lake surface areas within the plateau are closely related to the warming,humidified climate transition in recent years such as the rise of air temperature and the increase in precipitation.In particular,the rising temperature accelerates melting of glaciers and perennial snow cover and triggers permafrost degradation,and leads to the expansion of most lakes across the plateau.In addition,different distributions and types of permafrost may cause different lake variations in the southern Tibetan Plateau.

Exploring the influence of various factors on microwave radiation image simulation for Moon-based Earth observation

Earth observation technologies are important for obtaining geospatial information on the Earth’s surface and are used widely in many disciplines,such as resource surveying,environmental monitoring,and evolutionary studies.However,it is a challenge for existing Earth observation platforms to acquire this type of data rapidly on a global scale due to limitations in orbital altitude and field of view;thus development of an advanced platform for Earth observation is desirable.As a natural satellite of the Earth,placement of various sensors on the Moon could possibly facilitate comprehensive,continuous,and longterm observations of the Earth.This is a relatively new concept and the study is still at the preliminary stage with no actual Moon-based Earth observation data available at this time.To understand the characteristics of Moon-based microwave radiation,several physical factors that potentially influence microwave radiation imaging,e.g.,time zone correction,relative movement of the Earth-Moon,atmospheric radiative transfer,and the effect of the ionosphere,were examined.Based on comprehensive analysis of these factors,the Moon-based microwave brightness temperature images were simulated using spaceborne temperature data.The results show that time zone correction ensures that the simulation images may be obtained at Coordinated Universal Time(UTC)and that the relative movement of the Earth-Moon affects the positions of the nadir and Moon-based imaging.The effect of the atmosphere on Moon-based observation is dependent on various parameters,such as atmospheric pressure,temperature,humidity,water vapor,carbon dioxide,oxygen,the viewing zenith angle and microwave frequency.These factors have an effect on atmospheric transmittance and propagation of upward and downward radiation.When microwaves propagate through the ionosphere,the attenuation is related to frequency and viewing zenith angle.Based on initial studies,the simulation results suggest Moon-based microwave radiation imaging is realistic and viable.

Simulation of Moon-based Earth observation optical image processing methods for global change study

Global change affected by multiple factors,the consequences of which continue to be far-reaching,has the characteristics of large spatial scale and long-time scale.The demand for Earth observation technology has been increasing for large-scale simultaneoiis observations and stable global observation over the long-term.A Moon-based observation platform,which uses sensors on the nearside lunar surface,is considered a reasonable solution.However,owing to a lack of appropriate processing methods for optical sensor data,global change study using this platform is not sufficient.This paper proposes two optical sensor imaging processing methods for the Moon-based platform:area imaging processing method(AIPM)and global imaging processing method(GIPM),primarily considering global change characteristics,optical sensor performance,and motion law of the Moon-based platform.First,the study proposes a simulation theory which includes the construction of a Moon-Sun elevation angle model and a global image mosaicking method.Then,coverage images of both image processing methods are simulated,and their features are quantitatively analyzed.Finally,potential applications are discussed.Results show that AEPM,whose coverage is mainly affected by lunar revolution,is approximately between 0%and 50%with a period of 29.5 days,which can help the study of large-scale instant change phenomena.GIPM,whose coverage is affected by Earth revolution,is conducive to the study of long term global-scale phenomena because of its sustained stable observation from 67°N-67°S on the Earth.AIPM and GIPM have great advantages in Earth observation of tripolar regions.The existence of top of the atmosphere(TOA)albedo balance line is verified from the GIPM perspective.These two imaging methods play a significant role in linking observations acquired from the Moon-based platform to Earth large-scale geoscience phenomena,and thus lay a foundation for using this platform to capture global environmental changes and new discoveries.

Augmented virtual environment: fusion of real-time video and 3D models in the digital earth system

An Augmented virtual environment(AVE)is concerned with the fusion of real-time video with 3D models or scenes so as to augment the virtual environment.In this paper,a new approach to establish an AVE with a wide field of view is proposed,including real-time video projection,multiple video texture fusion and 3D visualization of moving objects.A new diagonally weighted algorithm is proposed to smooth the apparent gaps within the overlapping area between the two adjacent videos.A visualization method for the location and trajectory of a moving virtual object is proposed to display the moving object and its trajectory in the 3D virtual environment.The experimental results showed that the proposed set of algorithms are able to fuse multiple real-time videos with 3D models efficiently,and the experiment runs a 3D scene containing two million triangles and six real-time videos at around 55 frames per second on a laptop with 1GB of graphics card memory.In addition,a realistic AVE with a wide field of view was created based on the Digital Earth Science Platform by fusing three videos with a complex indoor virtual scene,visualizing a moving object and drawing its trajectory in the real time.

Improved alpine grassland mapping in the Tibetan Plateau with MODIS time series: a phenology perspective

The Tibetan Plateau is primarily composed of alpine grasslands.Spatial distributions of alpine grasses,however,are not well documented in this remote,highly uninhabited region.Taking advantage of the frequently observed moderate resolution imaging spectroradiometer(MODIS)images(500-m,8-day)in 2010,this study extracted the phenological metrics of alpine grasses from the normalized difference vegetation index time series.With the Support Vector Machine,a multistep classification approach was developed to delineate alpine meadows,steppes,and desert grasses.The lakes,permanent snow,and barren/desert lands were also classified with a MODIS scene acquired in the peak growing season.With ground data collected in the field and aerial experiments in 2011,the overall accuracy reached 93%when alpine desert grasses and barren lands were not examined.In comparison with the recently published national vegetation map,the alpine grassland map in this study revealed smoother transition between alpine meadows and steppes,less alpine meadows in the southwest,and more barren/deserts in the high-cold Kunlun Mountain in the northeast.These variations better reflected climate control(e.g.precipitation)of different climatic divisions on alpine grasslands.The improved alpine grassland map could provide important base information about this cold region under the pressure of rapidly changing climate.