Differential GPS Research Articles

Design of control system for driverless tractor

This paper uses Tianjin TieNiu crawler tractor as the experimental platform to design an unmanned agricultural machinery control system based on RTK-GPS (Differential GPS Technology). The article expounds the overall design of the control system and proposes a path tracking control algorithm. Simulation and experimental results show that the control algorithm can complete the path tracking requirements of unmanned agricultural machinery. The system can control the unmanned agricultural machinery to follow a predetermined route. The speed is 0.55m/s, the maximum error of linear path tracking of agricultural machinery is 4.09cm, the average error is 2.20cm, the maximum error of large diameter circular path tracking is 20.67cm, the average error is 8.34cm, and the maximum error of continuous small diameter turning path tracking is 23.14cm, the average error is 7.38cm, both meet the operational requirements.

Crime Scene Mapping using Differential GPS and Geospatial Techniques for Simulated Outdoor Crime Scenes

Outdoor crime scene management is difficult to accomplish,especially when the crime transpired in a big area, uneven space, or an area with a lack of reference points. It is important to visualize the location of the evidence to get an idea of how the crime took place and in what manner. In this research, two simulated outdoor crime scenes were created,where both manual tape measurement and Differential Global Positioning System (DGPS) unit were applied to see if the differential GPS offers an accurate and reliable alternative for mapping the scene over the baseline method. A eographic Information System(GIS) was used to derive a map of the simulated outdoor scenes. The result indicates that the DGPS unit provides a consistent reading when compared to manual tape measurement, giving an average reading difference of 0.06 cm and 0.13 cm. The study concluded that the DGPS unit can be a viable alternative for mapping outdoor crime scenes.

Forest structure parameter extraction using SPOT-7 satellite data by object- and pixel-based classification methods

Using satellite data to extract forest structure mapping parameters assists forest management. In this research, structural parameters including species, density, canopy, and gaps were extracted from SPOT-7 satellite data over Hyrcanian forests (Iran). A detailed ground inventory was initially conducted, over 12 × 1ha (100m × 100m) plots, in which tree coordinates were plotted, using a differential global positioning system (DGPS), along with data on tree species, diameter-at-breast-height and height, as well as canopy dimensions, and canopy gap shapes, sizes, and positions, for each plot. Then, spectral transformations, vegetation indices, and simple spectral ratios were extracted from SPOT-7 data, and a supervised, pixel-based classification method and a support-vector machine algorithm were used to classify and determine tree species types. In addition, canopy tree borders and gaps were classified, using an object-based method, and tree densities per unit area were determined, using the canopy gravity center. Finally, the original ground data was used to perform an accuracy assessment on the extracted information, with the results showing that forest type could be determined with 95% accuracy and a Kappa coefficient of 0.8. Canopy and gap coverage achieved an overall accuracy of 91% (Kappa coefficient: 0.7), and tree densities per hectare were determined, on average, to be 47 trees fewer than reality. In conclusion, we have shown that forest structural parameters could be extracted, with good accuracy, using a combination of pixel- and object-based methods applied to SPOT-7 imaging.

Analysis and Integration of Surface and Subsurface Information of Different Bridges

Road transportation is one of the major sources of transportation. Bridges are one of the vital engineering structures which have a major impact on the road transportation system. Bridges provide connectivity between two sides of the river banks or untouched paths to ease the travel. The strength of the bridge can get deteriorated due to heavy traffic and aggressive weather conditions. Evaluation of the condition of the bridges traditionally can be more expensive and time-consuming. The other way is by using remote sensing techniques that are nondestructive and advantageous. Terrestrial laser scanning (TLS) and close-range photogrammetry (CRP) are more suitable noninvasive techniques to generate a detailed 3D point cloud model of real objects. Point clouds obtained from TLS and CRP are merged together to produce point cloud dataset (PCD). The PCD can be georeferenced with the help of differential global positioning system points near the structure and total station points on the surface of the structure. The surface analysis for the features like corrosion, vegetation, biological crust, water presence, etc. can be extracted using the PCD and images obtained from digital single-lens reflex camera. Ground-penetrating radar (GPR) can be utilized for generating subsurface 2D and 3D profile scans. Subsurface analysis features like the presence of pier/abutment, water, voids, rebars, crack, asphalt layer, deck layer, etc. can be extracted with the GPR scan profiles. The surface and subsurface information can be visualized together to understand the surface or subsurface features corresponding to each other’s location. Accuracy assessments of the classified images and the classified points of the PCD are done in this research, and the accuracies obtained were 79.69% and 92.494%, respectively. The ground-truth validations were done with the help of laser distometer and measuring tape to precisely compare the values.

Large-earthquake rupturing and slipping behavior along the range-front Maidan fault in the southern Tian Shan, northwestern China

Slipping behavior of active thrust faults are not well explored because of their variable vertical displacements governed by dip-angle changes along the fault striking. The range-front Maidan fault (MDF) is a thrust fault in the southern Tian Shan, and exhibits clear paleoearthquake rupturing during the late Quaternary. In this study, based on field investigation, trench exposing, detailed terrace surveying with differential GPS, and optically stimulated luminescence (OSL) dating, we revealed that the latest paleoearthquake on the MDF occurred at ~1.76 ka, and generated a vertical displacement of ~3.0 m. Then, we analyzed the vertical displacements on different terraces of the Yushanguxi River versus the corresponding terrace 10Be exposure ages. We suggest that the large-earthquake on the MDF is an irregular recurrence. The MDF still has a high seismic risk in spite of only ~1.76 ka elapsed time for the latest paleoearthquake. We propose that the growth and uplift of the western Tian Shan orogen is caused by fault thrusting and crustal shortening of a series of block-like patterns.

Adaptive smartphone-based sensor fusion for estimating competitive rowing kinematic metrics.

Competitive rowing highly values boat position and velocity data for real-time feedback during training, racing and post-training analysis. The ubiquity of smartphones with embedded position (GPS) and motion (accelerometer) sensors motivates their possible use in these tasks. In this paper, we investigate the use of two real-time digital filters to achieve highly accurate yet reasonably priced measurements of boat speed and distance traveled. Both filters combine acceleration and location data to estimate boat distance and speed; the first using a complementary frequency response-based filter technique, the second with a Kalman filter formalism that includes adaptive, real-time estimates of effective accelerometer bias. The estimates of distance and speed from both filters were validated and compared with accurate reference data from a differential GPS system with better than 1 cm precision and a 5 Hz update rate, in experiments using two subjects (an experienced club-level rower and an elite rower) in two different boats on a 300 m course. Compared with single channel (smartphone GPS only) measures of distance and speed, the complementary filter improved the accuracy and precision of boat speed, boat distance traveled, and distance per stroke by 44%, 42%, and 73%, respectively, while the Kalman filter improved the accuracy and precision of boat speed, boat distance traveled, and distance per stroke by 48%, 22%, and 82%, respectively. Both filters demonstrate promise as general purpose methods to substantially improve estimates of important rowing performance metrics.

Static connectivity of stacked deep-water channel elements constrained by high-resolution digital outcrop models

High-resolution digital outcrop models of stacked deep-water channel elements are constructed from the Laguna Figueroa section of the well-exposed Upper Cretaceous Tres Pasos Formation in Chilean Patagonia. The models are based on greater than 1600 m (>5250 ft) of centimeter-scale measured sections, greater than 100 paleoflow measurements, and thousands of differential global positioning system points (10-cm [4-in.] accuracy) from an outcrop belt that is approximately 2.5 km (∼1.5 mi) long and 130 m (425 ft) thick. The models elucidate the effects bed-to-geobody–scale architecture has on static sandstone connectivity among a series of stacked deep-water channel elements and how that connectivity is altered by grid cell size. Static connectivity analyses show that channel element base drapes can strongly influence sandstone connectivity and that smaller channel element widths are more likely to produce disconnected sandstone geobodies. Net-to-gross (NTG) is not directly correlated with connectivity because of the presence of thin channel element base drapes, which do not significantly contribute to NTG. Upscaling the models consistently increases channel element contact (up to 10%) but decreases sandstone connectivity (up to 2%–3%). Channel element stacking patterns strongly impact connectivity. For example, connectivity is reduced in cases of high lateral channel element offsets. Increasing drape coverage markedly decreases connectivity. Evaluating connectivity in a vertical, along-system profile is critical to understanding flow units and reservoir piping. Ultimately, this work constrains uncertainty related to the impact of subseismic-scale stratigraphic architecture on reservoir connectivity by providing concrete knowledge that can be used to guide the model building process.

EDAS (EGNOS Data Access Service) Differential GNSS Corrections: A Reliable Free-of-Charge Alternative for Precision Farming in Europe

Abstract EDAS (EGNOS Data Access Service) is the EGNOS internet broadcast service, which provides free of charge access to the data collected and generated by the EGNOS infrastructure. EDAS disseminates over the Internet, both in real time and via an FTP archive, the raw data of the GPS, GLONASS (no commitment on GLONASS data is provided (1)) and EGNOS GEO satellites collected by the receivers located at the EGNOS reference stations, which are mainly distributed over Europe and North Africa. The EDAS services offer several types of GNSS data in various protocols and formats, such as DGNSS corrections. This paper reports on the results of some in-field tests conducted by ESSP and Topcon Agriculture to confirm the suitability of EDAS DGNSS corrections for precision farming in Europe. The European Commission (EC) is the owner of EGNOS system (including EDAS) and has delegated the exploitation of EGNOS to the European GNSS Agency (GSA). EDAS service provision is performed by ESSP, as EGNOS Services Provider, under contract with the GSA, the EGNOS program manager. In the ENC 2018 article “EDAS (EGNOS Data Access Service): Differential GPS corrections performance test with state-of-the-art precision agriculture system”, ESSP and Topcon Agriculture presented the results of the first in-field test conducted in a dynamic and real-life environment in the summer of 2017. The test results indicated that the EDAS DGNSS corrections could enable a reliable pass-to-pass accuracy performance for a wide range of precision agriculture applications and become an attractive solution for cereal farms, when the farm is located in the vicinity of an EGNOS reference station. In particular, Topcon Agriculture acknowledged that the observed performance was sufficient to support the following precision agriculture applications: spraying and spreading of any crop type, tilling and harvesting of cereal. Then, ESSP and Topcon Agriculture engaged in additional testing activities to further characterise the EDAS DGPS performance in different scenarios (i.e. at various European locations and with a variety of distances between the designated farm and the target EGNOS reference station). In each test, multiple runs with the rover tractors have been performed over the reference patterns predefined in the Topcon guidance systems. Data recorded during the tests has been analysed in detail, looking at the key performance indicators (e.g. cross track error and pass-to-pass performance) that characterize the EDAS DGPS performance for precision agriculture applications. Different techniques for the computation of the pass-to-pass accuracy performance have been used, including a procedure to measure live in the field and a post-processing alternative. The diversity of scenarios available allows drawing conclusions on the applicability of EDAS DGPS corrections (in terms of maximum distance from the target EGNOS station) for precision agriculture and also understanding the impact of operationally relevant aspects such as the quality of the mobile internet coverage (highly variable across Europe). The EDAS system and its architecture, the main types of data disseminated through EDAS services and the online information available to the EDAS users are introduced in this paper. In particular, the EDAS Ntrip service is described in detail, since it provides the differential corrections to the GPS and GLONASS satellites at the EGNOS reference stations in RTCM format, which are the basis for the present study. The article also reports on the results of the latest tests, which have been performed using Topcon receivers, vehicles and auto-steering systems. In all cases, two different Topcon guidance systems on board tractors were running simultaneously to assess the EDAS DGPS positioning performance with respect to a the reference provided by a top-performing RTK-based Topcon solution. The objective of this paper is to draw conclusions on the use of EDAS DGPS corrections as a reliable free-of-charge alternative for precision farming in Europe (especially for cereal farms), based on the available performance results from the testing campaign and the feedback from the involved precision agriculture experts.

Suitability Analysis for DGPS Radio Beacon Establishment at Port Klang Malaysia

Differential Global Positioning System (DGPS) is a positioning technique which provide safety in navigation to support maritime activities. Marine Department of Malaysia has established Sistem Pelayaran Satelit (SISPELSAT) as safety to aid maritime navigation activities system over the coast of Peninsular Malaysia. The aim of this study is to investigate the location suitability for a new SISPELSAT radio beacon station at Port Klang, Selangor. The work involves three (3) parts; (1) multipath analysis, (2) GPS and Medium Frequency (MF) signal interference investigation, and (3) DGPS correction transmission signal simulation coverage. It has found that, the location has an acceptable multipath value of MP1 and MP2 at 0.4097m and 0.3654m respectively. Meanwhile, no signal interferences on GPS and MF radio signals have found at the proposed location. In addition, the signal simulation shows that the location of Port Klang station are able to provide optimum DGPS coverage for the area of Melaka Straits

A rapid assessment method for ground layer coastal vegetation

We aim to test a rapid ecological assessment method to monitor regenerating coastal vegetation without sacrificing accuracy. We estimated species frequency in vegetation plots using traditional point intercept methods. We also tested a rapid, digital method to take high-resolution digital photographs of plots. We navigated among plot locations using a sub-meter Differential Global Positioning System instead of using permanent plot markers, and analyzed plot photographs in a point intercept manner (i.e., grid) in Geographic Information Systems software. We assessed species frequency in 52 permanent plots using traditional and digital methods. Traditional methods required 39.2 min per plot and digital methods required 4.6 min per plot. Estimates of frequency from traditional methods were substantially higher than those from digital methods for permanent plots, so we used an independent assessment of vegetation coverage to calibrate the utility of digital methods. A logistic regression equation can be used to compare historical traditional estimates to those collected digitally. Digital point intercept methods were successfully used for rapid ecological assessment. The primary advantages of digital methods include overwhelming efficiency compared to traditional methods, a resultant increase in sample size, and the ability to recover more accurate estimates of species frequency. Disadvantages of digital methods include a restriction of use for ground layer vegetation and positional inaccuracies introduced through sub-meter navigation. While traditional methods are less accurate in estimating species frequency, they are ideal for capturing accurate temporal trends in vegetation growth since they rely upon the use of permanent plot markers.

Multisensor validation of tidewater glacier flow fields derived from synthetic aperture radar (SAR) intensity tracking

Abstract. Following the general warming trend in Greenland, an increase in calving rates, retreat and ice flow has been observed at ocean-terminating outlet glaciers. These changes contribute substantially to the current mass loss of the Greenland Ice Sheet. In order to constrain models of ice dynamics as well as estimates of mass change, detailed knowledge of geometry and ice flow is needed, in particular on the rapidly changing tongues of ocean-terminating outlet glaciers. In this study, we validate velocity estimates and spatial patterns close to the calving terminus of such an outlet derived from an iterative offset-tracking method based on synthetic aperture radar (SAR) intensity data with a collection of three independent reference measurements of glacier flow. These reference datasets are comprised of measurements from differential GPS, a terrestrial radar interferometer (TRI) and repeated unmanned aerial vehicle (UAV) surveys. Our approach to SAR velocity processing aims at achieving a relatively fine grid spacing and a high temporal resolution in order to best resolve the steep velocity gradients in the terminus area and aims to exploit the 12 d repeat interval of the single-satellite Sentinel-1A sensor. Results from images of the medium-sized ocean-terminating outlet glacier Eqip Sermia acquired by Sentinel-1A and RADARSAT-2 exhibit a mean difference of 11.5 % when compared to the corresponding GPS measurements. An areal comparison of our SAR velocity fields with independently generated velocity maps from TRI and UAV surveys showed good agreement in magnitude and spatial patterns, with mean differences smaller than 0.7 m d−1. In comparison with existing operational velocity products, our SAR-derived velocities show an improved spatial velocity pattern near the margins and calving front. There 8 % to 30 % higher surface ice velocities are produced, which has implications on ice fluxes and on mass budget estimates of similarly sized outlet glaciers. Further, we show that offset tracking from SAR intensity data at relatively low spatio-temporal sampling intervals is a valid method to derive glacier flow fields for fast-flowing glacier termini of outlet glaciers and, given the repeat period of 12 d of the Sentinel-1A sensor (6 d with Sentinel-1B), has the potential to be applied operationally in a quasi-continuous mode.

Bedrock hardness values and morphological zonation of a shore platform in South Africa

Shore platforms found along rock coasts worldwide are often interpreted as wave abrasion acting on uniform bedrock surfaces. Whilst this viewpoint may apply at the macroscale, there are complex feedbacks among bedrock properties (rock type, mineralogy, rock structures), weathering and erosion processes and rates, and microtopography at the meso- to microscale. In turn, these influence wave runup, backwash processes, and the extent of wave-splash and physical, chemical, and biological weathering processes that result. This study investigates the relationships among bedrock hardness properties, microtopography, and shore platform denudation processes from a site on the Indian Ocean-facing coast of South Africa. Three shore-normal transects (45–57 m in length) were surveyed across the sandstone platform using a differential global positioning system (GPS). These data were integrated with rock surface hardness measurements along the transects taken using a Proceq Equotip instrument. Results show that platform morphology and hardness values vary considerably, corresponding to the most dominant denudation processes found at different positions in the tidal frame. The lowest hardness values (most extensive rock weathering) are found on the landward third of the platform but away from the land margin. The highest and greatest variability of hardness values are found on bedrock highs immediately above the highest astronomical tide level, in the lower third of the profile. This position suggests a dominant role of wave-splash and wetting/drying. Variations in hardness values and microtopography through the transects were used to develop an evolutionary model linking rock hardness values to specific weathering and erosion processes of the rocky shore platform.

Contrasting thinning patterns between lake- and land-terminating glaciers in the Bhutanese Himalaya

Abstract. Despite the importance of glacial lake development in ice dynamics and glacier thinning, in situ and satellite-based measurements from lake-terminating glaciers are sparse in the Bhutanese Himalaya, where a number of proglacial lakes exist. We acquired in situ and satellite-based observations across lake- and land-terminating debris-covered glaciers in the Lunana region, Bhutanese Himalaya. A repeated differential global positioning system survey reveals that thickness change of the debris-covered ablation area of the lake-terminating Lugge Glacier (-4.67±0.07 m a−1) is more than 3 times more negative than that of the land-terminating Thorthormi Glacier (-1.40±0.07 m a−1) for the 2004–2011 period. The surface flow velocities decrease down-glacier along Thorthormi Glacier, whereas they increase from the upper part of the ablation area to the terminus of Lugge Glacier. Numerical experiments using a two-dimensional ice flow model demonstrate that the rapid thinning of Lugge Glacier is driven by both a negative surface mass balance and dynamically induced ice thinning. However, the thinning of Thorthormi Glacier is minimised by a longitudinally compressive flow regime. Multiple supraglacial ponds on Thorthormi Glacier have been expanding since 2000 and have merged into a single proglacial lake, with the glacier terminus detaching from its terminal moraine in 2011. Numerical experiments suggest that the thinning of Thorthormi Glacier will accelerate with continued proglacial lake development.

RTDGPS Accuracy Improvement Using PSO-LSWSVM and Low-Cost GPS Receivers

The position of mobile devices is determined by Real Time Differential Global Positioning System (RTDGPS). This system is composed of fixed and mobile station. The accuracy of this system depends on the speed of updating the correction data. Yet, this system often faces the problem of the reference GPS receiver’s signal cut off and internal or non- internal delays which increase the latency time and decrease the updating speed. The prediction models are used to compensate these delays. In this paper, the Particle Swarm Optimization Least Square Wavelet Support Vector Machine (PSO-LSWSVM) is used for predicting the DGPS correction. An experimental setup is designed in order to carry out the operations of reference and user stations. Low-cost receivers were used in both stations. The accuracy of PSO-LSWSVM was evaluated through various simulations and experimental. The practical tests showed that the accuracy of the designed RTDGPS is 0.42 m with PSO-LSWSVM and is equal to 0.73 m without it. In comparing with other method that recently is introduced; it has a higher positioning accuracy.

Mapping an Agricultural Field Experiment by Electromagnetic Induction and Ground Penetrating Radar to Improve Soil Water Content Estimation

A growing interest in proximal sensing technologies for estimating soil water content (SWC) will be highlighted. On this matter the objectives of this study were: (1) to use both the combined electromagnetic induction (EMI) sensor and Ground Penetrating Radar (GPR) to characterize an innovative field experiment located in southern Italy, in which different agricultural practices are tested, including a soil hydraulic arrangement; (2) to implement a geostatistical approach in order to merge different geophysical sensor data as auxiliary variables for SWC estimation. The multi-sensor recorded data were: (1) SWC data measured by gravimetric method; (2) Differential Global Positioning System height; (3) apparent electrical conductivity measured by an EMI sensor; (4) depths of soil discontinuities individuated by GPR radargrams interpretation; and (5) amplitude of GPR signal data at two different frequencies. Geostatistical techniques were used both to map all variables and improve the SWC estimation. The findings of this research indicate that: (1) the GPR radargrams identified four reflection events as a consequence of interfaces; (2) the EMI and GPR mapping provided identification of areas with high potential for water stagnation; and (3) the outputs of geophysical sensors can be effectively used as auxiliary tools to supplement the sampling of the target variable and to improve water content estimation.

Tectonic deformation in the Santorini volcanic complex (Greece) as inferred by joint analysis of gravity, magnetotelluric and DGPS observations

SUMMARYTectonic activity is very difficult to study in the Santorini volcanic complex (SVC) as it comprises a cluster of small/awkwardly shaped islands covered by pyroclastic deposits from which tell-tale markers are swiftly erased, while seismicity is generally absent. We address the problem by combining geophysical exploration methods to evaluate the long-term effects of tectonic deformation and time-lapse differential GPS to directly evaluate the magnitude and kinematics of present-day deformation. The former comprise 3-D gravity modelling to investigate the footprint of tectonics on the pre-volcanic Alpine basement and natural-field EM induction to map conductivity anomalies epiphenomenal to fluid circulation in faults. Our analysis identified the following principal tectonic elements:The Trans-Santorin Divide (TSD), a segmented NNW–SSE dextral strike-slip fault splitting the SVC sideways of the line joining Cape Exomytis, the Kammeni Islets and the Oia–Therassia Strait. It is collocated with a major vertical conductive zone and forms a series of dents and depressions in the basement. The Columbo Fault Zone (CFZ) is a pair of parallel NE–SW subvertical normal-sinistral faults straddling the northern SVC and terminating against the TSD; it may be associated with fluid injection into the shallow crust but appears to have limited effect on crustal conductivity (compared to TSD). The Anhydros Fault Zone (AFZ) is detected by its footprint on the basement, as a set of parallel northerly dipping NE–SW faults between the Athinios–Monolithos line and Fira. If it has any heave, it is left-lateral. It does not have distinguishable electrical signature and does not contribute to present-day horizontal deformation. The CFZ and AFZ are antithetic and form a graben containing the volcanic centre of Kammeni Islets.E–W extension was identified lengthwise of a zone stretching from Cape Exomytis to Athinios and along the east flank of the caldera to Imerovigli. N–S normal faulting confirmed therein, may have contributed to the localization of the east caldera wall. NNE–SSW compression was observed at SW Thera; this may have produced E-W failure and contributed to the localization of the south caldera wall. The footprint of the caldera on the basement is a parallelogram with N–S long and WNW–ESE short dimensions: if the east and south flanks collapsed along N–S normal and E–W inverse failures, then the west and north flanks may have formed analogously. Present-day deformation is localized on the TSD and CFZ: this can only be explained if the former is the synthetic (dextral) Riedel-R shear and the latter the antithetic (sinistral) Riedel-R′ shear, generated by N–S σ1 and E–W σ3 principal stress axes. Accordingly, NW–SE right-lateral shearing of the broader area is expected and indicated by several lines of indirect evidence. The geographic extent of this shearing and its role in the regional tectonics of the south Aegean remains to be confirmed and appraised by future research.Contemporary volcanic centres develop at the interface of the TSD with the CFZ/AFZ graben; volcanism appears to be controlled by tectonics and the SVC to be shaped by tectonic rather than volcanic activity.

High‐precision target echo generation technology based on one‐dimensional linear array radar

The high-precision target echo generation in the field of radar systems is particularly important for large-scale, comprehensive testing of radars. Conventional echo generation techniques often use planar array air feed to simulate echoes. However, it is complicated and expensive to achieve the echo generation with traditional planar array. Therefore, this study proposes a high-precision target generation technique based on one-dimensional linear arrays. The simulation system achieves the target radial high-precision simulation through DRFM technology; the target azimuth high-precision simulation is achieved through differential GPS technology; and the target elevation high-precision simulation is realised through vertical one-dimensional linear array antenna switching. The semi-physical simulation system presented here has the advantages of simple control, low cost, low link loss, easy maintenance, and high simulation target accuracy. Finally, the system was tested in the field to verify the theoretical concept of the article.

A new 3D laser-scanning and GPS combined measurement system

Terrestrial laser scanning (TLS) is widely used because of its ability to quickly acquire high-density and high-precision 3D image and topographic data. However, it can only acquire independent coordinate system points, which restricts its application in large-scale deformation monitoring. In this study, we constructed a measurement system to acquire global coordinate point cloud data by combining TLS and GPS (Global Positioning System). The coordinate values of retro-reflective targets could be acquired in different coordinate systems, the GPS coordinate and the TLS station coordinate, synchronously. Our experiments showed that, after registration with the homonymy points acquired by 30-min short-baseline differential GPS using the ICP algorithm, the positional accuracy of the TLS retro-reflective target center in the global coordinate was better than 10 mm. This high precision meets, for instance, the requirements of coal mining subsidence monitoring. We used our new combined measurement system to acquire and process the point cloud data of a frame structure. The measurements demonstrated the practicability and robustness of the new measurement system.

High bandwidth airborne acoustic detection system (HBADS) for circular synthetic aperture acoustic imaging of canonical ground targets

High Bandwidth Acoustic Detection System (HBADS) is an active acoustic sensor technology developed by the US Army’s Night Vision and Electronic Sensors Directorate. The stripmap airborne synthetic aperture acoustic (SAA) array (mounted on an all-terrane vehicle) contains two horizontal rows of eight evenly spaced microphones oriented in a side scan configuration. An audio speaker (located near the array center) transmits a linear FM chirp having a 2 kHz to 15 kHz effective bandwidth. Experiments are performed with the vehicle in motion to image canonical ground targets in clutter or foliage. A laptop computer controls the 16 channel data acquisition system. The system includes an inertial navigation system (two differential GPS antennas), a wheel coder, a camera, and a unit for measuring temperature, pressure, and humidity. Experiments include imaging spherical targets located on the ground in a grassy field and similar targets camouflaged by natural vegetation along the roadside using both stripmap SAR and circular path C-SAR radar-like configurations. Typical parameters are chirp pulse = 10 or 40 ms, slant range resolution c/(2*BW) = 1.3 cm (air sound speed c ≈ 340 m/s), microphone diameter D = 2 cm, (azimuthal resolution is D/2), and maximum vehicle speed ≈ 2 m/s.High Bandwidth Acoustic Detection System (HBADS) is an active acoustic sensor technology developed by the US Army’s Night Vision and Electronic Sensors Directorate. The stripmap airborne synthetic aperture acoustic (SAA) array (mounted on an all-terrane vehicle) contains two horizontal rows of eight evenly spaced microphones oriented in a side scan configuration. An audio speaker (located near the array center) transmits a linear FM chirp having a 2 kHz to 15 kHz effective bandwidth. Experiments are performed with the vehicle in motion to image canonical ground targets in clutter or foliage. A laptop computer controls the 16 channel data acquisition system. The system includes an inertial navigation system (two differential GPS antennas), a wheel coder, a camera, and a unit for measuring temperature, pressure, and humidity. Experiments include imaging spherical targets located on the ground in a grassy field and similar targets camouflaged by natural vegetation along the roadside using both stripmap SAR a...

Structure from motion photogrammetry in ecology: Does the choice of software matter?

Image‐based modeling, and more precisely, Structure from Motion (SfM) and Multi‐View Stereo (MVS), is emerging as a flexible, self‐service, remote sensing tool for generating fine‐grained digital surface models (DSMs) in the Earth sciences and ecology. However, drone‐based SfM + MVS applications have developed at a rapid pace over the past decade and there are now many software options available for data processing. Consequently, understanding of reproducibility issues caused by variations in software choice and their influence on data quality is relatively poorly understood. This understanding is crucial for the development of SfM + MVS if it is to fulfill a role as a new quantitative remote sensing tool to inform management frameworks and species conservation schemes. To address this knowledge gap, a lightweight multirotor drone carrying a Ricoh GR II consumer‐grade camera was used to capture replicate, centimeter‐resolution image datasets of a temperate, intensively managed grassland ecosystem. These data allowed the exploration of method reproducibility and the impact of SfM + MVS software choice on derived vegetation canopy height measurement accuracy. The quality of DSM height measurements derived from four different, yet widely used SfM‐MVS software—Photoscan, Pix4D, 3DFlow Zephyr, and MICMAC, was compared with in situ data captured on the same day as image capture. We used both traditional agronomic techniques for measuring sward height, and a high accuracy and precision differential GPS survey to generate independent measurements of the underlying ground surface elevation. Using the same replicate image dataset (n = 3) as input, we demonstrate that there are 1.7, 2.0, and 2.5 cm differences in RMSE (excluding one outlier) between the outputs from different SfM + MVS software using High, Medium, and Low quality settings, respectively. Furthermore, we show that there can be a significant difference, although of small overall magnitude between replicate image datasets (n = 3) processed using the same SfM + MVS software, following the same workflow, with a variance in RMSE of up to 1.3, 1.5, and 2.7 cm (excluding one outlier) for “High,” “Medium,” and “Low” quality settings, respectively. We conclude that SfM + MVS software choice does matter, although the differences between products processed using “High” and “Medium” quality settings are of small overall magnitude.