Real-time Kinematic Global Positioning System Research Articles

Computation of datum shift parameters between two navigation datasets

Geophysical surveys require precise navigation data which is usually acquired through real-time kinematic GPS. The acquired data needs to be transformed from the GPS reference datum to the local datum, by computing datum shift parameters using control points in the survey area. Oil and gas industry archives contain data from seismic surveys, conducted over the years by various data acquisition crews using different datum shift parameters. Sometimes these parameters are not documented in the navigation data headers. This leads to geo-referencing problems when combining data from different surveys. This paper reviews the transformation models and presents a simple approach for computing Molodensky-based datum shift parameters, by identifying common points between two surveys on a map. A real example is included to show the successful implementation of this method.

Visual-LiDAR Odometry Aided by Reduced IMU

This paper proposes a method for combining stereo visual odometry, Light Detection And Ranging (LiDAR) odometry and reduced Inertial Measurement Unit (IMU) including two horizontal accelerometers and one vertical gyro. The proposed method starts with stereo visual odometry to estimate six Degree of Freedom (DoF) ego motion to register the point clouds from previous epoch to the current epoch. Then, Generalized Iterative Closest Point (GICP) algorithm refines the motion estimation. Afterwards, forward velocity and Azimuth obtained by visual-LiDAR odometer are integrated with reduced IMU outputs in an Extended Kalman Filter (EKF) to provide final navigation solution. In this paper, datasets from KITTI (Karlsruhe Institute of Technology and Toyota technological Institute) were used to compare stereo visual odometry, integrated stereo visual odometry and reduced IMU, stereo visual-LiDAR odometry and integrated stereo visual-LiDAR odometry and reduced IMU. Integrated stereo visual-LiDAR odometry and reduced IMU outperforms other methods in urban areas with buildings around. Moreover, this method outperforms simulated Reduced Inertial Sensor System (RISS), which uses simulated wheel odometer and reduced IMU. KITTI datasets do not include wheel odometry data. Integrated RTK (Real Time Kinematic) GPS (Global Positioning System) and IMU was replaced by wheel odometer to simulate the response of RISS method. Visual Odometry (VO)-LiDAR is not only more accurate than wheel odometer, but it also provides azimuth aiding to vertical gyro resulting in a more reliable and accurate system. To develop low-cost systems, it would be a good option to use two cameras plus reduced IMU. The cost of such a system will be reduced than using full tactical MEMS (Micro-Electro-Mechanical Sensor) based IMUs because two cameras are cheaper than full tactical MEMS based IMUs. The results indicate that integrated stereo visual-LiDAR odometry and reduced IMU can achieve accuracy at the level of state of art.

Motion Predicting of Autonomous Tracked Vehicles with Online Slip Model Identification

Precise understanding of the mobility is essential for high performance autonomous tracked vehicles in challenging circumstances, though the complex track/terrain interaction is difficult to model. A slip model based on the instantaneous centers of rotation (ICRs) of treads is presented and identified to predict the motion of the vehicle in a short term. Unlike many research studies estimating current ICRs locations using velocity measurements for feedback controllers, we focus on predicting the forward trajectories by estimating ICRs locations using position measurements. ICRs locations are parameterized over both tracks rolling speeds and the kinematic parameters are estimated in real time using an extended Kalman filter (EKF) without requiring prior knowledge of terrain parameters. Simulation results verify that the proposed algorithm performs better than the traditional method when the pose measuring frequencies are low. Experiments are conducted on a tracked vehicle with a weight of 13.6 tons. Results demonstrate that the predicted position and heading errors are reduced by about 75% and the reduction of pose errors is over 24% in the absence of the real-time kinematic global positioning system (RTK GPS).

Flight Tests of Autopilot Integrated with Fault-Tolerant Control of a Small Fixed-Wing UAV

A fault-tolerant control scheme for the autopilot of the small fixed-wing UAV is designed and tested by the actual flight experiments. The small fixed-wing UAV called Xiang Fei is developed independently by Nanjing University of Aeronautics and Astronautics. The flight control system is designed based on an open-source autopilot (Pixhawk). Real-time kinematic (RTK) GPS is introduced due to its high accuracy. Some modifications on the longitudinal and lateral guidance laws are achieved to improve the flight control performance. Moreover, a data fusion based fault-tolerant control scheme is integrated in altitude control and speed control for altitude sensor failure and airspeed sensor failure, which are the common problems for small fixed-wing UAV. Finally, the real flight experiments are implemented to test the fault-tolerant control based autopilot of UAV. Real flight test results are given and analyzed in detail, which show that the fixed-wing UAV can track the desired altitude and speed commands during the whole flight process including takeoff, climbing, cruising, gliding, landing, and wave-off by the fault-tolerant control based autopilot.

GPS RTK定位技术在驾考系统中的应用

全球定位系统(GPS)因其高精度三维定位测速及定时的功能在精密工程测量中得到迅速广泛的应用。利用高精度GPS载波相位实时动态差分(RTK)定位技术的特点，在机动车驾驶技能考试中，可精确地计算考车的轮廓位置点，解决了考车行驶过程中的距离测量问题。根据RTK技术在考车上架设的双GPS天线和具体考试项目里车线之间距离的检测方法，并结合考场电子地图各项目的特征点和各项目的评判规则，华众设计的全自动智能驾考系统，可实现精确评判。 Global positioning system (GPS) has been widely used in precision engineering measurement be-cause of its high precision three dimensional positioning velocity test and timing function. Using the characteristics of high precision GPS real-time kinematic (RTK) positioning technology in the motor vehicle driving skills test can accurately calculate the contour points of the test vehicle, this solves the problem of distance measurement in the course of test vehicle. Based on RTK Technology in the test vehicle mounted dual GPS antenna and the detection method of the distance between the test vehicle and the line in the examination of specific project, and combined with the examination of electronic map the feature points and the purposes of evaluation rules, Huazhong design the automatic intelligence of the driving test system , which can realize accurate judgment.

Development of Real-Time PPP-Based GPS/INS Integration System Using IGS Real-Time Service for Hydrographic Surveys

AbstractThe multibeam echosounding technique is used to provide seafloor mapping at a relatively high-quality level and requires an accurate positioning and orientation system. Integration of a global positioning system (GPS) and an inertial navigation system (INS) is widely used for positioning and orientation control and is performed by using an inertial unit integrated with a real-time kinematic (RTK) GPS solution with two GPS receivers to provide the required accuracy. However, the RTK-based GPS/INS system is presently limited to a distance of approximately 10 km and cannot be used for offshore hydrographic surveys. Recently, precise-point positioning (PPP) technology has shown promise toward the development of an autonomous GPS solution for positioning applications in which only one GPS receiver is used. This paper investigates a real-time PPP-based GPS/INS integrated system position and orientation solution using the international GPS service (IGS) real-time service (RTS) for hydrographic surveys. T...

Assessment of ground-based monitoring techniques applied to landslide investigations

A landslide complex in the Whitby Mudstone Formation at Hollin Hill, North Yorkshire, UK is periodically re-activated in response to rainfall-induced pore-water pressure fluctuations. This paper compares long-term measurements (i.e., 2009–2014) obtained from a combination of monitoring techniques that have been employed together for the first time on an active landslide. The results highlight the relative performance of the different techniques, and can provide guidance for researchers and practitioners for selecting and installing appropriate monitoring techniques to assess unstable slopes. Particular attention is given to the spatial and temporal resolutions offered by the different approaches that include: Real Time Kinematic-GPS (RTK-GPS) monitoring of a ground surface marker array, conventional inclinometers, Shape Acceleration Arrays (SAA), tilt meters, active waveguides with Acoustic Emission (AE) monitoring, and piezometers. High spatial resolution information has allowed locating areas of stability and instability across a large slope. This has enabled identification of areas where further monitoring efforts should be focused. High temporal resolution information allowed the capture of ‘S’-shaped slope displacement-time behaviour (i.e. phases of slope acceleration, deceleration and stability) in response to elevations in pore-water pressures. This study shows that a well-balanced suite of monitoring techniques that provides high temporal and spatial resolutions on both measurement and slope scale is necessary to fully understand failure and movement mechanisms of slopes. In the case of the Hollin Hill landslide it enabled detailed interpretation of the geomorphological processes governing landslide activity. It highlights the benefit of regularly surveying a network of GPS markers to determine areas for installation of movement monitoring techniques that offer higher resolution both temporally and spatially. The small sensitivity of tilt meter measurements to translational movements limited the ability to record characteristic ‘S’-shaped landslide movements at Hollin Hill, which were identified using SAA and AE measurements. This high sensitivity to landslide movements indicates the applicability of SAA and AE monitoring to be used in early warning systems, through detecting and quantifying accelerations of slope movement.

Crop height variability detection in a single field by multi-temporal terrestrial laser scanning

Information on crop height, crop growth and biomass distribution is important for crop management and environmental modelling. For the determination of these parameters, terrestrial laser scanning in combination with real-time kinematic GPS (RTK–GPS) measurements was conducted in a multi-temporal approach in two consecutive years within a single field. Therefore, a time-of-flight laser scanner was mounted on a tripod. For georeferencing of the point clouds, all eight to nine positions of the laser scanner and several reflective targets were measured by RTK–GPS. The surveys were carried out three to four times during the growing periods of 2008 (sugar-beet) and 2009 (mainly winter barley). Crop surface models were established for every survey date with a horizontal resolution of 1 m, which can be used to derive maps of plant height and plant growth. The detected crop heights were consistent with observations from panoramic images and manual measurements (R2 = 0.53, RMSE = 0.1 m). Topographic and soil parameters were used for statistical analysis of the detected variability of crop height and significant correlations were found. Regression analysis (R2 < 0.31) emphasized the uncertainty of basic relations between the selected parameters and crop height variability within one field. Likewise, these patterns compared with the normalized difference vegetation index (NDVI) derived from satellite imagery show only minor significant correlations (r < 0.44).

Evaluation of Error Reduction Techniques on a LIDAR-Derived Salt Marsh Digital Elevation Model

ABSTRACT McClure, A.; Liu, X.; Hines, E., and Ferner, M.C., 2016. Evaluation of error reduction techniques on a LIDAR-derived salt marsh digital elevation model. Accurate elevation information is a necessity for conservation and management of tidal salt marshes where elevation differences can be as little as 2 m and where sea-level rise is a critical threat. This study applied an existing method to evaluate and improve the vertical accuracy of a 1-m LIDAR-derived digital elevation model (DEM) using a real-time kinematic (RTK) GPS dataset with a vertical accuracy of ±0.02 m and local vegetation data within a tidal salt marsh. Correction factors were generated for vegetation species within each major vegetation class and produced a modified DEM of the site. Comparison between the original and modified DEM showed that the mean error was reduced from 0.16 m to −0.004 m and the root mean squared error was reduced from 0.212 m to 0.098 m. These results demonstrate that it is possible to significantly reduce ver...

Accuracy of Kinematic Positioning Using Global Satellite Navigation Systems under Forest Canopies

A harvester enables detailed roundwood data to be collected during harvesting operations by means of the measurement apparatus integrated into its felling head. These data can be used to improve the efficiency of wood procurement and also replace some of the field measurements, and thus provide both less costly and more detailed ground truth for remote sensing based forest inventories. However, the positional accuracy of harvester-collected tree data is not sufficient currently to match the accuracy per individual trees achieved with remote sensing data. The aim in the present study was to test the accuracy of various instruments utilizing global satellite navigation systems (GNSS) in motion under forest canopies of varying densities to enable us to get an understanding of the current state-of-the-art in GNSS-based positioning under forest canopies. Tests were conducted using several different combinations of GNSS and inertial measurement unit (IMU) mounted on an all-terrain vehicle (ATV) “simulating” a moving harvester. The positions of 224 trees along the driving route were measured using a total-station and real-time kinematic GPS. These trees were used as reference items. The position of the ATV was obtained using GNSS and IMU with an accuracy of 0.7 m (root mean squared error (RMSE) for 2D positions). For the single-frequency GNSS receivers, the RMSE of real-time 2D GNSS positions was 4.2–9.3 m. Based on these results, it seems that the accuracy of novel single-frequency GNSS devices is not so dependent on forest conditions, whereas the performance of the tested geodetic dual-frequency receiver is very sensitive to the visibility of the satellites. When post-processing can be applied, especially when combined with IMU data, the improvement in the accuracy of the dual-frequency receiver was significant.

Accurate Localization for Making Maps to Mobile Robots Using Odometry and GPS Without Scan-Matching

&lt;div class=""abs_img""&gt; &lt;img src=""[disp_template_path]/JRM/abst-image/00270004/11.jpg"" width=""300"" /&gt; Comparison of mapping results&lt;/div&gt; This paper studies an accurate localization method to make maps for mobile robots using odometry and a global positioning system (GPS) without scan matching. We investigate requirements for GPS accuracy in map-making. To generate accurate maps, SLAM techniques such as scan matching are used to obtain accurate positions. Scan matching is unstable, however, in complex environments and has a high computation cost. To avoid these problems, we studied accurate localization without scan matching. Loop closing is an important property in generating consistent maps. Inconsistencies in maps prevent correct routes to destinations from being generated. Basically, our method adds scan data to a map along a trajectory given by odometry. Odometry accumulates errors due, e.g., to wheel slippage or wheel diameter variations. To remove this accumulated error, we used bundle adjustment, introducing two types of processing. The first is a simple manual input moving a robot to a same position at start and end. This is equal that a robot returns to a start position at end. The second process uses a GPS device to improve map accuracy. Results of experiments showed that an accurate map is generated by using wheel-encoder odometry and a low-cost GPS device. Results were evaluated using a real-time kinematic (RTK) GPS device whose accuracy is within a few centimeters. &lt;/span&gt;

Slip rates and locking depth variation along central and easternmost segments of North Anatolian Fault

While the kinematics of Anatolia plate and the North Anatolian Fault System (NAFS) has been studied extensively, the slip rate and locking depth along the NAFS are usually assumed constant in the analyses due to the lack of sufficient data. This is also partly due to the reasonably good fit of Euler small circle and partly due to the lack of spatial resolution of observations to determine slip rates independently from locking depths. On the other hand, recent geodetic studies show a contrast for locking depth between Marmara and other parts of the NAFS, implying a non-uniform locking depth across the NAFS. In this study, we analyse new GPS data and homogenously combine available data sets covering the eastern part of the NAFS to form the most complete data set. In particular, we incorporate the first results of Turkish Real-Time Kinematic GPS Network (CORS-TR) into our data set. A detailed analysis of three profiles within the NAFS reveals an increase of locking depth in the middle profile to 19.1 ± 3.4 km from 11.9 ± 3.5 km in the easternmost profile while the slip rate is nearly constant (20–22 mm yr−1), which implies a variation of strain rate of ∼100 nanostrain yr−1. Assuming a constant locking depth throughout whole NAFS gives an average locking depth of 14.3 ± 1.7 km. Our best estimates of slip rates in block modelling which takes the variation of locking depths into account are in the range between 22.5 and 22.8 mm yr−1 over eastern part of the NAFS.

The Investigation of the Ardales Cave, Spain – 3D Documentation, Topographic Analyses, and Lighting Simulations based on Terrestrial Laser Scanning

AbstractThis contribution shows the application of terrestrial laser scanning in an integrative approach for the documentation and analyses of the Ardales Cave, southern Spain, which is in many respects an important geoarchaeological site. For the survey of the cave, a combination of the Riegl LMS Z420i laser scanner with a real‐time kinematic global positioning system (RTK‐GPS) from Topcon and further tachymetric measurements were used. The achieved three‐dimensional (3D) model of the cave and the surrounding hill documents the current topography and dimensions of the cave. Additional geoarchaeological data were successfully integrated in a 3D geographical information system (GIS) database and high‐resolution records of a structured‐light scanner were combined with the 3D model of the cave. The 3D model is further used for the estimation of the ceiling thickness that reveals areas for additional entrances. Lighting simulations based on path tracing were conducted for the determination of areas that are reached by natural direct or indirect light. In this case, the weight and size of the instrument was a logistic constraint to reach certain areas and to achieve a complete model of the cave. Overall, the method is feasible for the documentation of this cave and the investigations based on the derived 3D models. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Measurement of desirable minimum one-way bike lane width

Although many countries specify a desirable minimum width for one-way bike lanes, there have been no empirical or methodological studies conducted through extensive field experiments to confirm these specifications. This study devised a measurement method to obtain precise bicycle trajectories using a real-time kinematic global positioning system (RTK GPS). This measurement method achieves very satisfactory accuracy with regard to identifying the desirable minimum bike lane width when considering the bicycle width, Essential Maneuvering Space (EMS), and Comfortable Lateral Clearance (CLC). The width of a bicycle was obtained by investigating common bicycle types in the field. The EMS experiments were performed for speeds of 10, 20, and 30 km/h along test tracks with widths of 1.1, 2.0, and 3.0 m using an RTK GPS. The CLC experiments were repeated 300 times with the same preset speeds as in the EMS tests. Based on the results of this study, the bike lane width should be at least 2.0 m to allow for rider stability on roadways with no curb or gutter. In the future, desirable geometric standards for various types of bike lanes need to be formulated using real data collected with advanced measurement apparatuses.

Georeferenced Scanning System to Estimate the Leaf Wall Area in Tree Crops

This paper presents the use of a terrestrial light detection and ranging (LiDAR) system to scan the vegetation of tree crops to estimate the so-called pixelated leaf wall area (PLWA). Scanning rows laterally and considering only the half-canopy vegetation to the line of the trunks, PLWA refers to the vertical projected area without gaps detected by LiDAR. As defined, PLWA may be different depending on the side from which the LiDAR is applied. The system is completed by a real-time kinematic global positioning system (RTK-GPS) sensor and an inertial measurement unit (IMU) sensor for positioning. At the end, a total leaf wall area (LWA) is computed and assigned to the X, Y position of each vertical scan. The final value of the area depends on the distance between two consecutive scans (or horizontal resolution), as well as the number of intercepted points within each scan, since PLWA is only computed when the laser beam detects vegetation. To verify system performance, tests were conducted related to the georeferencing task and synchronization problems between GPS time and central processing unit (CPU) time. Despite this, the overall accuracy of the system is generally acceptable. The Leaf Area Index (LAI) can then be estimated using PLWA as an explanatory variable in appropriate linear regression models.

Impact of Multi-GNSS on Positioning Accuracy and Multipath Errors in High-Precision Single-Epoch Solutions – A Case Study in Ningbo China

Real-Time Kinematic (RTK) Global Positioning System (GPS) carrier phase-based precise positioning has been widely using in geodesy and surveying applications, and other high accuracy positioning and navigation applications in the last two decades. More Global Navigation Satellite Systems (GNSS) are being developed and it is usually expected that combining GNSS will have a positive impact on positioning accuracy. This paper describes a case study carried out at Ningbo in China on the impact of multi-GNSS on RTK single epoch solutions. Both GPS and GLONASS are fully operational now. Moreover, the Quasi-Zenith Satellite System (QZSS) can be observed at Ningbo. Currently, only one QZSS satellite “MICHIBIKI” is operational. This paper carries out an early assessment of the impact of QZSS on GPS and GLONASS single-epoch high precision positioning (i.e., single-epoch positioning accuracy assessment) and investigates the multipath errors in the GPS, GLONASS and QZSS multi-frequency data.

Acquisition of Grass Harvesting Characteristics Information and Improvement of the Accuracy of Topographical Surveys for the GIS by Sensor Fusion (I) - Analysis of Grass Harvesting Characteristics by Sensor Fusion -

Purpose: This study aimed to install an RTK-GPS (Real Time Kinematic-Global Positioning System) and IMU (Inertial Measurement Unit) on a tractor used in a farm to measure positions, pasture topography, posture angles, and vibration accelerations, translate the information into maps using the GIS, analyze the characteristics of grass harvesting work, and establish new technologies and construction standards for pasture infrastructure improvement based on the analyzed data. Method: Tractor's roll, pitch, and yaw angles and vibration accelerations along the three axes during grass harvesting were measured and a GIS map prepared from the data. A VRS/RTK-GPS (MS750, Trimble, USA) tractor position measuring system and an IMU (JCS-7401A, JAE, JAPAN) tractor vibration acceleration measuring systems were mounted on top of a tractor and below the operator's seat to obtain acceleration in the direction of progression, transverse acceleration, and vertical acceleration at 10Hz. In addition, information on regions with bad workability was obtained from an operator performing grass harvesting and compared with information on changes in tractor posture angles and vibration acceleration. Results: Roll and pitch angles based on the y-axis, the direction of forward movements of tractor coordinate systems, changed by at least <TEX>$9-13^{\circ}$</TEX> and <TEX>$8-11^{\circ}$</TEX> respectively, leading to changes in working postures in the central and northern parts of the pasture that were designated as regions with bad workability during grass harvesting. These changes were larger than those in other regions. The synthesized vectors of the vibration accelerations along the y-axis, the x-axis (transverse direction), and the z-axis (vertical direction) were higher in the central and northwestern parts of the pasture at 3.0-4.5 m/s2 compared with other regions. Conclusions: The GIS map developed using information on posture angles and vibration accelerations by position in the pasture is considered sufficiently utilizable as data for selection of construction locations for pasture infrastructure improvement.

Localising deformation along the elevation of linear structures: An experiment with space-borne InSAR and RTK GPS on the Roman Aqueducts in Rome, Italy

We map and monitor the condition of linear structures using Measurement Points (MPs) from satellite Interferometric Synthetic Aperture Radar (InSAR), and deal with the uncertainty of localising the detected deformation along the building elevation. We combine spatial information of the MPs with elevation measurements collected by Real Time Kinematic (RTK) GPS surveying to understand where structural motions occurred. The MPs are geolocated along the z-direction by exploiting their height information (hMP) compared to the elevation of the surveyed buildings and surrounding ground (hGPS). This approach aims to find a good compromise between the required accuracy and repeatability, and the advantages of reduced time-consumption and cost-effectiveness offered by RTK GPS. Reliability of the method is proved via the experiment on the Roman Aqueducts in the southern peri-urban quarters of the city of Rome, Italy. We focus on the linear man-made structures of the ancient to modern aqueduct systems. These are challenging anthropogenic features to monitor with InSAR due to their huge extent, variety of condition and architectural complexity. Of the total 13,519 MPs retrieved from SqueeSAR™ processing of 87 RADARSAT-1 Fine Beam Mode 3 ascending scenes (2003–2010), the MPs spatially attributed to the local linear features and the surroundings are analysed with regard to: (i) their densities against building type, structure planimetric orientation and vegetation coverage; and (ii) their height distribution against RTK GPS micro-topographic surveying in seven sample areas. Numerical analysis of hMP–hGPS pairs result in high correlation (R2 equals 0.970), and their cross-comparison allows validation of 3D geolocation of the MPs, also demonstrating the usefulness of complementary surveying by laser distance meter device whenever RTK GPS is not feasible. Cross-referenced hMP values are then used to reclassify the MPs and generate final map products to support the design of in-situ inspection activities. We discuss beneficial impacts for condition monitoring and assessment at the scale of single building through the examples of the medieval tower Torre del Fiscale and the Roman arcades of the Claudian Aqueduct. The MP height information improves the understanding of the deformation estimates, and also contributes to address hazard mitigation measures and restorations.

Determination of geodetic control network points using GPS technology for the purpose of monitoring power lines in difficult terrain conditions

Summary The present work discusses the issue of determining geodetic control network in order to monitor the condition of power lines. The problem was presented using the example of the physical survey of an actual infrastructure – a high voltage power line. Difficult terrain conditions constituted a significant factor for determining an appropriate measurement method. The measurement itself was conducted using two methods, independently of one another: the classical traverse method, and the RTK (Real Time Kinematic) GPS method. The following criteria were assumed for the purpose of the comparison: measurement effectiveness and the accuracy of the calculation result. Basic monitoring procedures of power lines were also presented, implemented based on the measurement network established beforehand.

The second Chinese glacier inventory: data, methods and results

AbstractThe second Chinese glacier inventory was compiled based on 218 Landsat TM/ETM+ scenes acquired mainly during 2006–10. The widely used band ratio segmentation method was applied as the first step in delineating glacier outlines, and then intensive manual improvements were performed. The Shuttle Radar Topography Mission digital elevation model was used to derive altitudinal attributes of glaciers. The boundaries of some glaciers measured by real-time kinematic differential GPS or digitized from high-resolution images were used as references to validate the accuracy of the methods used to delineate glaciers, which resulted in positioning errors of ±10 m for manually improved clean-ice outlines and ±30 m for manually digitized outlines of debris-covered parts. The glacier area error of the compiled inventory, evaluated using these two positioning accuracies, was ±3.2%. The compiled parts of the new inventory have a total area of 43 087 km2, in which 1723 glaciers were covered by debris, with a total debris-covered area of 1494 km2. The area of uncompiled glaciers from the digitized first Chinese glacier inventory is ∼8753 km2, mainly distributed in the southeastern Tibetan Plateau, where no images of acceptable quality for glacier outline delineation can be found during 2006–10.