Real-time Kinematic Global Positioning System Research Articles

Investigation on Different Scanning Resolutions for Slope Mapping Studies in Cameron Highlands, Malaysia

The development of laser scanning is one of the surveying methods, which able to produce a digital surface in a short period. The good results of digital surface must be followed by specific procedures, for example, interpolation algorithm and filtering methods. The improvement in information technology has influenced the growing development and application of laser scanning technique in order to fulfill the user needs. Laser scanning resolution might have an effect on the results of slope mapping studies. The objective of this paper is to evaluate the results of different laser scanner resolutions in producing a slope map. This study was conducted at Cameron Highlands, Pahang, Malaysia. Two site locations were identified for this study due to the condition of the slope characteristics that provides a more accurate assessment. Topcon GLS1500 is being used for data collection at both sites, and several control points were established using real-time kinematic global positioning system. The storage of point clouds was increased when the resolution value is decreased. The results of laser scanner were analyzed based on different laser scanner resolutions. It can be concluded that laser scanner resolutions do have an effect on slope mapping accuracies. Determination of the appropriate resolution for specific applications can be identified in this study.

Development and evaluation of an enhanced surrogate safety assessment framework

This study adopted an integrated simulation approach for generating more realistic vehicle trajectories, ultimately for enhancing the surrogate safety assessment methodology under the Connected Vehicle (CV) environment. This integrated simulation divides into two main parts, real time-based simulation approach and post-processing approach. The real-time simulation environment consists of the microscopic traffic simulator to generate various traffic situations, driver warning simulator, GPS/INU simulator, and V2V/V2I communication delays probability model. The post-processing approach includes vehicle dynamics model to incorporate vehicle dynamics to the vehicle trajectories and Surrogate Safety Assessment Model (SSAM) to identify traffic conflicts. This integrated simulation approach was adopted to assess the safety impact of Connected Vehicle (CV)-based traffic applications by considering potential positioning errors and communication delays which are likely to occur in reality. The evaluation results showed that the V2V/V2I communication delays degraded the effectiveness of driver warnings by 3–13% while the driver warnings under ideal conditions (i.e., error-free vehicle positions and no V2V/V2I communication delays) reduced conflicts by 27–42%. In addition, the most accurate GPS/INU device (i.e., Real-Time Kinematic (RTK) GPS) was the best for use with vehicle safety applications as the RTK case was the closest to the ground truth-based warning scenario. Meanwhile, the device with the lowest accuracy (i.e., autonomous GPS) was not very suitable for deployment in the safety application as this case showed even worse results than the base case (i.e., no driver warnings). This integrated simulation approach used for these experiments is a practical and reliable alternative for assessing the safety impact of CV-based traffic applications since it considers the potential positioning errors and communication delays which are likely to affect the performance of CV-based traffic applications in reality and uses vehicle dynamics-incorporated vehicle trajectories which are more realistic than the sore traffic simulator vehicle trajectories.

Paleoseismology of the 2010 Mw 7.1 Darfield (Canterbury) earthquake source, Greendale Fault, New Zealand

The previously unknown Greendale Fault ruptured in the September 2010 moment magnitude (Mw) 7.1 Darfield Earthquake. Surface rupture fracture patterns and displacements along the fault were measured with high precision using real time kinematic (RTK) GPS, tape and compass, airborne light detection and ranging (lidar), and aerial photos. No geomorphic evidence of a penultimate surface rupture was revealed from pre-2010 imagery. The fault zone is up to 300m wide and comprises both distributed (folding) and discrete (faulting) deformation dominated by right-lateral displacement. Surface fracturing accommodates ~30% of the total right-lateral displacement in the central fault zone; the remainder is accommodated by distributed deformation. Ground penetrating radar and trenching investigations conducted across the central Greendale Fault reveal that most surface fractures are undetectable at depths exceeding 1m; however, large, discrete Riedel shears continue to depths exceeding 3m and displace interbedded gravels and sand-filled paleochannels. At one trench site, a Riedel shear displaces surface agricultural markers (e.g., fences and plow lines) and a subsurface (0.6m deep) paleo-channel by 60cm right-laterally and 10cm vertically, indicating the paleochannel has been displaced only in the Darfield earthquake. Optically stimulated luminescence (OSL) dating of the displaced paleochannel yields an age of 21.6±1.5ka. Two additional paleochannels at ~2.5m depth with OSL ages of 28.4±2.4ka and 33±2ka have been displaced ~120cm right-laterally and ~20cm vertically. The doubling of displacement at depth is interpreted to indicate that in the central section of the Greendale Fault the penultimate surface-rupturing event occurred between ca. 20 and 30ka. The Greendale Fault remained undetected prior to the Darfield earthquake because the penultimate fault scarp was eroded and buried during Late Pleistocene alluvial activity. Similar active faults with low slip rates (i.e. lower than sedimentation/erosion rates) are likely to be concealed in alluvial settings globally.

Long Baseline GPS RTK with Estimating Tropospheric Delays

The real-time kinematic (RTK) is one of precise positioning methods using Global Positioning System (GPS) data. In the long baseline GPS RTK, the ionospheric and tropospheric delays are critical factors for the positioning accuracy. In this paper we present RTK algorithms for long baselines more than 100 km with estimating tropospheric delays. The state vector is estimated by the extended Kalman filter. We show the experimental results of GPS RTK for various baselines (162.10, 393.37, 582.29, and 1283.57 km) by using the Korea Astronomy and Space Science Institute GPS data and one International GNSS Service (IGS) reference station located in Japan. As a result, we present that long baseline GPS RTK can provide the accurate positioning for users less than few centimeters.

Effect of Ground Speed and Header Revolutions on the Picking Efficiency ofa Commercial Wild Blueberry Harvester

<abstract><title><italic>Abstract.</italic></title> <bold><sc> </sc></bold>The wild blueberry industry is facing increased harvesting losses with the existing commercial harvester. These machines are no longer able to efficiently harvest the higher yields that result from improvements in plant growth and productivity. This study was designed to evaluate the performance efficiency of a commercial wild blueberry harvester for fruit losses during harvesting. Four wild blueberry fields were selected in the Nova Scotia and New Brunswick provinces of Canada. A 3 × 3 factorial experiment was constructed to examine the joint effect of ground speed and header revolution per minute (rpm) on picking efficiency of the harvester. Eighty-one yield plots (0.91 × 3 m) were selected randomly in each field. The field boundaries, bare spots, weeds, and yield plots were mapped with a real-time kinematics global positioning system (RTK-GPS). The harvester was operated at specific levels of ground speed at 1.2, 1.6 and 2.0 km h^-1 and header rpm of 26, 28 and 30. The total fruit yield, un-harvested berries on the plants, berries on the ground, and berries through the blower, were collected from each plot within the selected fields. The pre-harvest fruit losses were collected from each plot prior to harvest. The treatment combinations were assigned randomly within the selected fields. The slope, plant height, and fruit zone were also recorded manually from each plot. Results indicated that the pre-harvest fruit losses were lower in early season compared to those harvested later. Un-harvested berries on the plants and losses through the blower were significantly lower than losses on the ground. Significant relationship among the fruit yield and total losses (r = 0.54 to 0.82) suggested that losses during harvesting were proportional to fruit yield. A factorial analysis of variance (ANOVA) showed that ground speed, header rpm, and their interaction were found to have significant (p=0.05) effects on the picking efficiency of the harvester. Results of means comparison showed that a combination of 1.2 km h^-1 and 26 rpm resulted in significantly lower losses when compared with other treatment combinations. Results also revealed that a suitable combination of ground speed and header rpm can minimize the fruit losses during harvesting. This can increase harvestable yield and farm profitability.

Field measurement and analysis of climatic factors affecting dune mobility near Grand Falls on the Navajo Nation, southwestern United States

Aeolian sand covers extensive areas of the Navajo Nation in the southwestern United States. Much of this sand is currently stabilized by vegetation, although many drier parts of these Native lands also have active and partly active dunes. Current prolonged drought conditions that started in the mid-1990s are producing significant changes in dune mobility. Reactivation of regional aeolian deposits due to drought or increasing aridity from rising temperatures resulting from climate change could have serious consequences for human and animal populations, agriculture, grazing, and infrastructure. To understand and document the current and future potential for mobility, seasonally repeated surveys were used to track the location of multiple active barchan dunes. By utilizing Real-Time Kinematic GPS field surveys and simultaneously collecting in-situ meteorological data, it is possible to examine climatic parameters and seasonal variations that affect dune mobility and their relative influences. Through analysis of the recorded data, we examined the fit of various climate parameters, and demonstrate that under the current prolonged drought, wind power is the dominant factor controlling dune mobility.

A Kalman filter-based short baseline RTK algorithm for single-frequency combination of GPS and BDS.

The emerging Global Navigation Satellite Systems (GNSS) including the BeiDou Navigation Satellite System (BDS) offer more visible satellites for positioning users. To employ those new satellites in a real-time kinematic (RTK) algorithm to enhance positioning precision and availability, a data processing model for the dual constellation of GPS and BDS is proposed and analyzed. A Kalman filter-based algorithm is developed to estimate the float ambiguities for short baseline scenarios. The entire work process of the high-precision algorithm based on the proposed model is deeply investigated in detail. The model is validated with real GPS and BDS data recorded from one zero and two short baseline experiments. Results show that the proposed algorithm can generate fixed baseline output with the same precision level as that of either a single GPS or BDS RTK algorithm. The significantly improved fixed rate and time to first fix of the proposed method demonstrates a better availability and effectiveness on processing multi-GNSSs.

Enhanced Boundary Condition–Based Approach for Construction Location Sensing Using RFID and RTK GPS

AbstractThe radio frequency identification (RFID) technology has proven its potential in locating and tracking construction resources, a critical task in construction project control. However, the main challenge is how to achieve desired levels of locating accuracy. This paper presents an enhanced boundary condition method that incorporates the tag-reader angle and the reader geometric configuration factors to control the accuracy of a locating system that integrates RFID and real time kinematic (RTK) global positioning system (GPS). Controlled laboratory experiments were conducted to assess their effects and create quality control filters. This study demonstrated the relationship between the detecting range and the tag-reader angle and used it to separate valid/invalid boundary points. Spatial dilution of precision (SDOP) was formulated to measure the geometric configuration of readers forming the boundary constraint. Correlating SDOP to the locating error through a polynomial regression model, a mechani...

Combined GPS and BeiDou Instantaneous RTK Positioning

The Chinese BeiDou-2/COMPASS Navigation Satellite System has attained regional operational status and is expected to reach the same level of popularity as GPS once it has reached its full constellation. This contribution considers combined BeiDou+GPS relative code positioning and single- and multiple-frequency real-time kinematic (RTK) positioning. A combined system increases the redundancy for solving the unknown GNSS parameters and thus allows for more precise position estimates, improved reliability and robustness against failure of any of the systems. The performance is evaluated by ambiguity success rates and by comparing the estimated positions to very precise benchmark coordinates. We make use of the LAMBDA method for integer ambiguity resolution, in combination with the Fixed Failure-rate Ratio Test to validate the resolved ambiguities. The combined model will be shown to allow for improved ambiguity resolution performance and positioning robustness and accuracy over the BeiDou- and GPS-only solutions. Copyright © 2014 Institute of Navigation.

Experimental assessment of post-processed kinematic Precise Point Positioning method for structural health monitoring

Monitoring the response of engineering structures, such as tall buildings, tower and large-scale bridges, under severe loading conditions, such as strong earthquake or wind storm, is an important requirement to verify their design and construction and to evaluate structural condition and reliability. In the last two decades, high-rate real-time or post-processed kinematic differential Global Positioning System (DGPS) has been widely used in dynamic displacement measurements of civil engineering structures. In recent years, interest has increased for Precise Point Positioning (PPP) due to its capability to generate positioning solutions as accurate as DGPS. In this study, the potential of post-processed kinematic PPP in terms of monitoring dynamic displacement response of a structure has been explored based on free damped oscillation events obtained from a model structure, which is able to vibrate in the fundamental and higher modes of vibration. A number of experiments have been carried out and five events, each of which is different character, have been selected to compare PPP results with DPGS results in the time and frequency domain. The results clearly demonstrate that the PPP method, like the DGPS method, offers great potential for the measurement of horizontal and vertical dynamic movement of structures. The impact of a short period (one minute) of observation length on the result of the kinematic PPP method was also investigated in terms of sensing the dynamic movement of a structure. Twenty selected one-minute data-sets extracted from a one-hour original data-set were processed by Canadian spatial reference system PPP and each one-minute PPP solution was compared with the corresponding segment obtained from the one-hour PPP solution. The results show that the one-minute PPP solution is able to extract the fundamental natural frequency of the oscillation in the horizontal and vertical component just like the one-hour PPP solution after the offset is removed and the lower frequency trend component is filtered out.

Compaction quality assessment of earth-rock dam materials using roller-integrated compaction monitoring technology

Abstract The compaction quality of earth-rock dams is normally controlled through compaction parameters (i.e., compaction passes, roller velocity, vibration status, and compacted thickness) during construction and random spot tests after construction. However, using limited spot samples to represent the construction quality of the entire work area can be unreliable and misleading. Additionally, given the time-consuming process, the spot testing method leads to delays in rectifying compaction quality issues at the jobsite. This research utilized roller-integrated compaction monitoring (RICM) technology combined with real-time kinematic global positioning systems (RTK-GPS), adopted compaction value (CV) as a real-time monitoring index for the dam compaction quality, and subsequently proposed a CV-based assessment method to estimate the compaction quality of earth-rock dam materials. Furthermore, the Kriging interpolation method was adopted to obtain estimates for both CVs and compaction quality at any location on the working area, enabling the analysis of the passing rate of compaction quality for the entire work area. A case study on the NZD Project in China indicated that the CV is highly correlated with the compaction parameters, the compactness of the gravel-mixed cohesive soil, and the dry density of rock-fill dam materials; therefore, it can serve as a reliable index for monitoring compaction quality. Quick and continuous assessments of compaction quality on the entire work area can be achieved using the proposed method, which provides a basis for informing the construction with timely feedback information to effectively avoid quality defects and to improve the construction quality of earth-rock dams.

Using multiple sensors to detect uncut crop edges for autonomous guidance systems of head-feeding combine harvesters

This study proposes a method for detection of uncut crop edges using multiple sensors to provide accurate data for the autonomous guidance systems of head-feeding combine harvesters widely used in the paddy fields of Japan for harvesting rice. The proposed method utilizes navigation sensors, such as a real-time kinematic global positioning system (RTK-GPS), GPS compass, and laser range finder (LRF), to generate a three-dimensional map of the terrain to be harvested at a processing speed of 35 ms and obtain the crop height. Furthermore, it can simultaneously detect the uncut crop edges by RANdom SAmple Consensus (RANSAC). The average of the lateral offset value and crop height of the uncut crop edge detected by the proposed method were 0.154 m and 0.537 m, respectively.

Storm-driven cusp behaviour on a high energy gravel beach

ABSTRACT Poate, T.G., Masselink, G., McCall, R.T., Russell, P.E., Davidson, M.A., 2014. Storm-driven cusp behaviour on a high energy gravel beach. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 645–650, ISSN 0749-0208. Gravel and mixed sand-gravel beaches are characterised by steep reflective profiles which provide effective forms of wave absorption and therefore coastal defence to many mid-latitude regions, including northwestern Europe and North America. In the UK the combination of energetic wave conditions and large tides creates very dynamic and responsive morphology often dominated by cuspate features. Recent storm-responsive field campaigns at Loe Bar, Cornwall, UK, have captured highly energetic wave conditions (Hs = 2.5–5.8 m) using temporary video camera installations, low tide 3D topographic surveys with real time kinematic GPS, local tide level measurements and inshore di...

Mine surface deformation monitoring using modified GPS RTK with surveying rod: initial results

The reasonable and effective exploitation and optimal utilisation of coal resources as well as ensuring the safe operation of main buildings, railways, high-voltage power lines, and other facilities of mining-influenced areas are the main technical requirements of the coal industry. The key problem is to implement certain methods and techniques to acquire deformation information, summarise the deformation laws, and ultimately serve mine production and construction. Considering the surface deformation of mining areas, traditional measurement techniques (automatic/digital levels, theodolites and total stations, etc.) are generally used to measure the well-arranged (several hundreds of) monitoring points repetitively, obtain deformation information, and calculate the deformation parameters. These parameters are used to design protective coal pillars. However, surface deformation is expensive to monitor or measure; it cannot be measured by traditional techniques in several coal mine areas, particularly in mountainous regions. Hence, effective techniques must be employed to obtain deformation data. Although global positioning system real-time kinematic (GPS RTK) technology provides an effective solution to this problem, the traditional GPS RTK with surveying rod can only determine deformation at centimetre level or low positioning precision because the rod is subject to vertical deviation and shaking error; thus, it cannot satisfy the precision requirement of surface deformation monitoring. A new GPS RTK surveying method that involves rod measuring is proposed in this study to address these issues. This method can effectively avoid the effects of the vertical deviation and shaking error of the surveying rod, weaken the impact of multipath error in U direction, and further improve positioning precision. Experiment results show that at 1 s sampling interval, the standard deviations estimated by the proposed method toward N, E, and U directions are 11·4, 8·9, and 4·9 mm for 10 s observation, respectively, and 8·9, 5·1, and 4·0 mm for 20 s observation, respectively. The impact of the major error source was reduced, and positioning precision improved significantly. This particular result provides strong technical support for fast and high-precision mine surface deformation monitoring.

Limitations in Extraction of Survey Data from Real-Time Kinematic GPS ADCP Systems

A total of 595 real-time kinematic global positioning system (RTK-GPS) water surface elevations (WSE) were measured using georectified and nongeorectified survey systems along a 21-km-long river reach to evaluate vertical coordinate accuracy of a nongeorectified RTK-GPS acoustic Doppler current profiler (ADCP) system. A georectified survey of a series of quality control benchmarks produced a vertical root-mean-square error (RMSE) of 0.033 m, which was considered globally accurate for river survey purposes. The WSE measured simultaneously at the same locations comparing the nongeorectified to the georectified system resulted in a RMSE=0.741 m. Evaluation of intersetup precision of the nongeorectified WSE confirmed relative accuracy to each initialized arbitrary vertical datum but were found not to be globally accurate. Only 7% of the nongeorectified base station setups resulted in RMSE less than the combined manufacturer’s tolerances when compared to the georectified system at the same spatial locations. When vertical datum corrections were applied to the nongeorectified system from the globally accurate RTK-DGPS system, 80% of the base station setups demonstrated RMSE within the combined manufacturer’s tolerances. Datum corrections varied greatly, ranging from −2.43 to +1.80 m. This study demonstrates that when using nongeorectified RTK-GPS ADCP systems for purposes other than discharge measurement, such as in the extraction of bathymetry data for use in hydraulic assessments and models, great care must be exercised when verifying WSEs

3-Dimentional Mapping Coastal Zone using High Resolution Satellite Stereo Imageries

The metropolitan coastal zone mapping is critical for coastal resource management, coastal environmental protection, and coastal sustainable development and planning. The results of geometric processing of a Shanghai coastal zone from 0.7-m-resolution QuickBird Geo stereo images are presented firstly. The geo-positioning accuracy of ground point determination with vendor-provided rigorous physical model (RPM) parameters is evaluated and systematic errors are found when compared with ground control points surveyed by GPS real-time kinematic (GPS-RTK) with 5cm accuracy. A bias-compensation process in image space that applies a RPM bundle adjustment to the RPM-calculated 3D ground points to correct the systematic errors is used to improve the geo-positioning accuracy. And then, a area-based matching (ABM) method is used to generated the densely corresponding points of left and right QuickBird images. With the densely matching points, the 3-dimentinal coordinates of ground points can be calculated by using the refined geometric relationship between image and ground points. At last step, digital surface model (DSM) can be achieved automatically using interpolation method. Accuracies of the DSM as assessed from independent checkpoints (ICPs) are approximately 1.2 m in height.

The evaluation of unmanned aerial system-based photogrammetry and terrestrial laser scanning to generate DEMs of agricultural watersheds

Agricultural watersheds tend to be places of intensive farming activities that permanently modify their microtopography. The surface characteristics of the soil vary depending on the crops that are cultivated in these areas. Agricultural soil microtopography plays an important role in the quantification of runoff and sediment transport because the presence of crops, crop residues, furrows and ridges may impact the direction of water flow. To better assess such phenomena, 3-D reconstructions of high-resolution agricultural watershed topography are essential. Fine-resolution topographic data collection technologies can be used to discern highly detailed elevation variability in these areas. Knowledge of the strengths and weaknesses of existing technologies used for data collection on agricultural watersheds may be helpful in choosing an appropriate technology. This study assesses the suitability of terrestrial laser scanning (TLS) and unmanned aerial system (UAS) photogrammetry for collecting the fine-resolution topographic data required to generate accurate, high-resolution digital elevation models (DEMs) in a small watershed area (12ha). Because of farming activity, 14 TLS scans (≈25pointsm−2) were collected without using high-definition surveying (HDS) targets, which are generally used to mesh adjacent scans. To evaluate the accuracy of the DEMs created from the TLS scan data, 1098 ground control points (GCPs) were surveyed using a real time kinematic global positioning system (RTK-GPS). Linear regressions were then applied to each DEM to remove vertical errors from the TLS point elevations, errors caused by the non-perpendicularity of the scanner's vertical axis to the local horizontal plane, and errors correlated with the distance to the scanner's position. The scans were then meshed to generate a DEMTLS with a 1×1m spatial resolution. The Agisoft PhotoScan and MicMac software packages were used to process the aerial photographs and generate a DEMPSC (Agisoft PhotoScan) and DEMMCM (MicMac), respectively, with spatial resolutions of 1×1m. Comparing the DEMs with the 1098 GCPs showed that the DEMTLS was the most accurate data product, with a root mean square error (RMSE) of 4.5cm, followed by the DEMMCM and the DEMPSC, which had RMSE values of 9.0 and 13.9cm, respectively. The DEMPSC had absolute errors along the border of the study area that ranged from 15.0 to 52.0cm, indicating the presence of systematic errors. Although the derived DEMMCM was accurate, an error analysis along a transect showed that the errors in the DEMMCM data tended to increase in areas of lower elevation. Compared with TLS, UAS is a promising tool for data collection because of its flexibility and low operational cost. However, improvements are needed in the photogrammetric processing of the aerial photographs to remove non-linear distortions.

A Robust Estimation Method for Correcting Dynamic Draft Error in PPK GPS Elevation Using ADCP Tilt Data

Abstract Measuring temporal and spatial variations in water level with high resolution and accuracy can provide fundamental insights into the hydrodynamics of marine and riverine systems. Real-time kinematic global positioning systems (RTK GPS), and by extension postprocessed kinematic (PPK) positioning, have provided the opportunity to achieve this goal, by allowing fast and straightforward measurements with subdecimeter accuracy. However, boat-mounted GPS are subject to movements of the water surface (e.g., waves, long-period heaves) as well as to the effects of dynamic draft. The latter contaminate the records and need to be separated and removed from the data. A method is proposed to postcorrect the elevation data using tilt information measured by an attitude sensor—in this case, an acoustic Doppler current profiler (ADCP) equipped with internal pitch and roll sensors. The technique uses iteratively reweighted least squares (IRLS) regressions to determine the position of the center of rotation (COR) of the boat that leads to optimal corrections. The COR is also allowed to change in time by performing the IRLS analyses on data subsamples, thus accounting for changes in weight distribution, for example, due to personnel movements. An example of application is presented using data collected in the Saint Lawrence fluvial estuary. The corrections exhibit significant reductions associated with the boat motion while keeping subtle variations in water levels likely related to local hydrodynamics.

Accuracy assessment of topographic mapping using UAV image integrated with satellite images

Unmanned Aerial Vehicle or UAV is extensively applied in various fields such as military applications, archaeology, agriculture and scientific research. This study focuses on topographic mapping and map updating. UAV is one of the alternative ways to ease the process of acquiring data with lower operating costs, low manufacturing and operational costs, plus it is easy to operate. Furthermore, UAV images will be integrated with QuickBird images that are used as base maps. The objective of this study is to make accuracy assessment and comparison between topographic mapping using UAV images integrated with aerial photograph and satellite image. The main purpose of using UAV image is as a replacement for cloud covered area which normally exists in aerial photograph and satellite image, and for updating topographic map. Meanwhile, spatial resolution, pixel size, scale, geometric accuracy and correction, image quality and information contents are important requirements needed for the generation of topographic map using these kinds of data. In this study, ground control points (GCPs) and check points (CPs) were established using real time kinematic Global Positioning System (RTK-GPS) technique. There are two types of analysis that are carried out in this study which are quantitative and qualitative assessments. Quantitative assessment is carried out by calculating root mean square error (RMSE). The outputs of this study include topographic map and orthophoto. From this study, the accuracy of UAV image is ± 0.460 m. As conclusion, UAV image has the potential to be used for updating of topographic maps.

Changes in the glacier extent and surface elevation along the Ningchan and Shuiguan river source, eastern Qilian Mountains, China

We investigate the changes at nine glaciers in the Ningchan and Shuiguan river source, eastern Qilian Mountains, between 1972 and 2010. According to analysis of topographic maps and multispectral satellite data, all nine glaciers in the study area have retreated, by a maximum of 250±57.4m and a minimum of 91±57.4m. The total glacier area decreased by 1.20km2, corresponding to 9.9% of the glacierized area in 1972. Comparing the two DEMs generated from the topographic maps and Real-Time Kinematic GPS data, the mean glacier thinning rate was 0.64myr−1 between 1972 and 2010. The most significant thinning generally occurred on the termini. The ice-volume loss was about 106.8±46.7×10−3km3 (equal to 90.8±39.7×10−3km3 w.e.), which suggested a mean water discharge of 0.1±0.05m3/s during 1972–2010. Based on analysis of meteorological data, the summer temperature (June–August) tends to increase over a similar time period. The consistency of temperature increase and glacier shrinkage allows us to suggest that air temperature plays an important role in glacier changes in this region.