scholarly journals Impact of UAS Image Orientation on Accuracy of Forest Inventory Attributes

2020 ◽  
Vol 12 (3) ◽  
pp. 404 ◽  
Author(s):  
Luka Jurjević ◽  
Mateo Gašparović ◽  
Anita Simic Milas ◽  
Ivan Balenović
Keyword(s):  
Carrier Phase ◽  
Single Frequency ◽  
Pedunculate Oak ◽  
Dual Frequency ◽  
3D Point Clouds ◽  
Sensor Orientation ◽  
Forested Areas ◽  
Gnss Measurements ◽  
Image Orientation ◽  
Gnss Data

The quality and accuracy of Unmanned Aerial System (UAS) products greatly depend on the methods used to define image orientations before they are used to create 3D point clouds. While most studies were conducted in non- or partially-forested areas, a limited number of studies have evaluated the spatial accuracy of UAS products derived by using different image block orientation methods in forested areas. In this study, three image orientation methods were used and compared: (a) the Indirect Sensor Orientation (InSO) method with five irregularly distributed Ground Control Points (GCPs); (b) the Global Navigation Satellite System supported Sensor Orientation (GNSS-SO) method using non-Post-Processed Kinematic (PPK) single-frequency carrier-phase GNSS data (GNSS-SO1); and (c) using PPK dual-frequency carrier-phase GNSS data (GNSS-SO2). The effect of the three methods on the accuracy of plot-level estimates of Lorey’s mean height (HL) was tested over the mixed, even-aged pedunculate oak forests of Pokupsko basin located in Central Croatia, and validated using field validation across independent sample plots (HV), and leave-one-out cross-validation (LOOCV). The GNSS-SO2 method produced the HL estimates of the highest accuracy (RMSE%: HV = 5.18%, LOOCV = 4.06%), followed by the GNSS-SO1 method (RMSE%: HV = 5.34%, LOOCV = 4.37%), while the lowest accuracy was achieved by the InSO method (RMSE%: HV = 5.55%, LOOCV = 4.84%). The negligible differences in the performances of the regression models suggested that the selected image orientation methods had no considerable effect on the estimation of HL. The GCPs, as well as the high image overlaps, contributed considerably to the block stability and accuracy of image orientation in the InSO method. Additional slight improvements were achieved by replacing single-frequency GNSS measurements with dual-frequency GNSS measurements and by incorporating PPK into the GNSS-SO2 method.

scholarly journals UAV-LiCAM SYSTEM DEVELOPMENT: CALIBRATION AND GEO-REFERENCING

2018 ◽  
Vol XLII-1 ◽  
pp. 107-114 ◽  
Author(s):  
C. Cortes ◽  
M. Shahbazi ◽  
P. Ménard
Keyword(s):  
Particle Filtering ◽  
System Development ◽  
Low Cost ◽  
Base Station ◽  
Dual Frequency ◽  
Body Frame ◽  
Integrated Sensor ◽  
Sensor Orientation ◽  
Wide Range ◽  
Gnss Measurements

<p><strong>Abstract.</strong> In the last decade, applications of unmanned aerial vehicles (UAVs), as remote-sensing platforms, have extensively been investigated for fine-scale mapping, modeling and monitoring of the environment. In few recent years, integration of 3D laser scanners and cameras onboard UAVs has also received considerable attention as these two sensors provide complementary spatial/spectral information of the environment. Since lidar performs range and bearing measurements in its body-frame, precise GNSS/INS data are required to directly geo-reference the lidar measurements in an object-fixed coordinate system. However, such data comes at the price of tactical-grade inertial navigation sensors enabled with dual-frequency RTK-GNSS receivers, which also necessitates having access to a base station and proper post-processing software. Therefore, such UAV systems equipped with lidar and camera (UAV-LiCam Systems) are too expensive to be accessible to a wide range of users. Hence, new solutions must be developed to eliminate the need for costly navigation sensors. In this paper, a two-fold solution is proposed based on an in-house developed, low-cost system: 1) a multi-sensor self-calibration approach for calibrating the Li-Cam system based on planar and cylindrical multi-directional features; 2) an integrated sensor orientation method for georeferencing based on unscented particle filtering which compensates for time-variant IMU errors and eliminates the need for GNSS measurements.</p>

scholarly journals Comparison of Multi-GNSS Time and Frequency Transfer Performance Using Overlap-Frequency Observations

2021 ◽  
Vol 13 (16) ◽  
pp. 3130
Author(s):  
Pengfei Zhang ◽  
Rui Tu ◽  
Yuping Gao ◽  
Ju Hong ◽  
Junqiang Han ◽  
...  
Keyword(s):  
Carrier Phase ◽  
Satellite System ◽  
Single Frequency ◽  
Navigation Satellite ◽  
Transfer Performance ◽  
Dual Frequency ◽  
Time Transfer ◽  
Difference Series ◽  
Frequency Transfer ◽  
Global Navigation Satellite

The modernized GPS, Galileo, and BeiDou global navigation satellite system (BDS3) offers new potential for time transfer using overlap-frequency (L1/E1/B1, L5/E5a/B2a) observations. To assess the performance of time and frequency transfer with overlap-frequency observations for GPS, Galileo, and BDS3, the mathematical models of single- and dual-frequency using the carrier-phase (CP) technique are discussed and presented. For the single-frequency CP model, the three-day average RMS values of the L5/E5a/B2a clock difference series were 0.218 ns for Galileo and 0.263 ns for BDS3, of which the improvements were 36.2% for Galileo and 43.9% for BDS3 when compared with the L1/E1/B1 solution at BRUX–PTBB. For the hydrogen–cesium time link BRUX–KIRU, the RMS values of the L5/E5a/B2a solution were 0.490 ns for Galileo and 0.608 ns for BDS3, improving Galileo by 6.4% and BDS3 by 12.5% when compared with the L1/E1/B1 solution. For the dual-frequency CP model, the average stability values of the L5/E5a/B2a solution at the BRUX–PTBB time link were 3.54∙× 10−12 for GPS, 2.20 × 10−12 for Galileo, and 2.69 × 10−12 for BDS3, of which the improvements were 21.0%, 45.1%, and 52.3%, respectively, when compared with the L1/E1/B1 solution. For the BRUX–KIRU time link, the improvements were 4.2%, 30.5%, and 36.1%, respectively.

Advances in smartphone positioning in forests: dual-frequency receivers and raw GNSS data

2020 ◽  
Author(s):  
Julián Tomaštík ◽  
Juliána Chudá ◽  
Daniel Tunák ◽  
František Chudý ◽  
Miroslav Kardoš
Keyword(s):  
Real Time ◽  
Mean Shift ◽  
Global Navigation Satellite Systems ◽  
Single Frequency ◽  
Dual Frequency ◽  
Post Processing ◽  
Open Area ◽  
Satellite Systems ◽  
Gnss Data ◽  
Mean Square Errors

Abstract Smartphones with their capability to receive Global Navigation Satellite Systems (GNSS) signals can be currently considered the most common devices used for positioning tasks, including forestry applications. This study focuses on possible improvements related to two crucial changes implemented into Android smartphone positioning in the last 3 years – dual-frequency (L1/L5) GNSS receivers and the possibility of recording raw GNSS data. The study comprises three experiments: (1) real-time measurements of individual points, (2) real-time recording of trajectories, and (3) post-processing of raw GNSS data provided by the smartphone receiver. The real-time tests were conducted using final positions provided by the internal receiver, i.e. without further processing or averaging. The test on individual points has proven that the Xiaomi Mi8 smartphone with a multi-constellation, dual-frequency receiver was the only device whose accuracy was not significantly different from single-frequency mapping-grade receiver under any conditions. The horizontal accuracy of most devices was lower during leaf-on season (root mean square errors between 5.41 and 12.55 m) than during leaf-off season (4.10–11.44 m), and the accuracy was significantly better under open-area conditions (1.72–4.51 m) for all tested devices when compared with forest conditions. Results of the second experiment with track recording suggest that smartphone receivers are better suited for dynamic applications – the mean shift between reference and measured trajectories varied from 1.23 to 5.98 m under leaf-on conditions. Post-processing of the raw GNSS data in the third experiment brought very variable results. We achieved centimetre-level accuracy under open-area conditions; however, in forest, the accuracies varied from meters to tens of meters. Observed loss of the signal strength in the forest represented ~20 per cent of the open-area value. Overall, the multi-constellation, dual-frequency receiver provided more robust and accurate positional solutions compared with single-frequency smartphones. Applicability of the raw GNSS data must be further studied especially in forests, as the provided data are highly susceptible to multipath and other GNSS adverse effects.

scholarly journals On the Feasibility of Interhemispheric Patch Detection Using Ground-Based GNSS Measurements

2018 ◽  
Vol 10 (12) ◽  
pp. 2044 ◽  
Author(s):  
Rafal Sieradzki ◽  
Jacek Paziewski
Keyword(s):  
Continuous Monitoring ◽  
Dual Frequency ◽  
Degree Polynomial ◽  
Opposite Situation ◽  
Gnss Measurements ◽  
Gnss Data ◽  
Dusk Sector ◽  
Northern And Southern Hemispheres ◽  
Different Parts

Dual-frequency GNSS data processing is currently one of the most useful techniques for sounding the ionosphere. Hence, this work was aimed at the evaluation of ground-based GNSS data for the continuous monitoring of polar patches in both hemispheres. In this contribution, we proposed to use epoch-wise relative STEC values in order to detect these structures. The applied indicator is defined as a difference between an undifferenced geometry-free linear combination of GNSS signals and the background ionospheric variations, which were assessed with an iterative algorithm of four-degree polynomial fitting. The occurrence of patches during the St. Patrick geomagnetic storm was performed for validation purposes. The first part of the work confirmed the applicability of the relative STEC values for such investigations. On the other hand, it also revealed the limitations related to the inhomogeneous distribution of stations, which may affect the results in both hemispheres. This was confirmed with a preliminary cross-evaluation of GNSS and in situ SWARM datasets. Apart from the periods with a well-established coincidence, the opposite situation, when both methods indicated different parts of the polar ionosphere, was also observed. The second part of this contribution depicted the feasibility of continuous patch detection for both regions, and thus the interhemispheric comparison of the analyzed structures. It has demonstrated the strong disproportion between patches in the northern and southern hemispheres. This discrepancy seems to be related to the different amount of plasma propagating from the dusk sector, which is justified by the values of relative STEC at mid-latitudes. The observed structures are also strongly dependent on the orientation of the interplanetary magnetic field.

scholarly journals A Tale of Five Bridges; the use of GNSS for Monitoring the Deflections of Bridges

2014 ◽  
Vol 8 (4) ◽  
Author(s):  
Gethin Wyn Roberts ◽  
Christopher J. Brown ◽  
Xu Tang ◽  
Xiaolin Meng ◽  
Oluropo Ogundipe
Keyword(s):  
Carrier Phase ◽  
Suspension Bridge ◽  
Single Frequency ◽  
Gps Data ◽  
Dual Frequency ◽  
Bridge Monitoring ◽  
Gnss Receivers ◽  
Rtk Gps ◽  
Millennium Bridge ◽  
Gathering Data

AbstractThe first Bridge Monitoring surveying was carried out in 1996 by the authors, through attaching Ashtech ZXII GPS receivers onto the Humber Bridge’ parapet, and gathering and further analysing the resulting 1 Hz RTK GPS data. Various surveys have subsequently been conducted on the Humber Bridge, the Millennium Bridge, the Forth Road Bridge, the Severn Suspension Bridge and the Avonmouth Viaduct. These were all carried out using survey grade carrier phase/pseudorange GPS and later GNSS receivers. These receivers were primarily dual frequency receivers, but the work has also investigated the use of single frequency receivers, gathering data at 1 Hz, 10 Hz, 20 Hz and even 100 Hz. Various aspects of the research conducted are reported here, as well as the historical approach. Conclusions are shown in the paper, as well as lessons learnt during the development of this work. The results are compared to various models that exist of the bridges’ movements, and compare well. The results also illustrate that calculating the frequencies of the movements, as well as looking at the magnitudes of the movements, is an important aspect of this work. It is also shown that in instances where the magnitudes of the movements of the bridge under investigation are small, it is still possible to derive very accurate frequencies of the movements, in comparison to the existing models.

Impact of New GPS Signals on Positioning Accuracy for Urban Bus Operations

2020 ◽  
Vol 73 (6) ◽  
pp. 1284-1305
Author(s):  
Mireille Elhajj ◽  
Washington Ochieng
Keyword(s):  
Carrier Phase ◽  
Signal To Noise Ratio ◽  
Three Dimensional ◽  
Dimensional Accuracy ◽  
Single Frequency ◽  
Measurement Unit ◽  
Dual Frequency ◽  
Positioning Accuracy ◽  
Phase Measurements ◽  
The Impact

This paper analyses for the first time the impact of new GPS signals on positioning accuracy for dynamic urban applications, taking bus operations as an example. The performance assessment addresses both code measurement precision and positioning accuracy. The former is based on signal-to-noise ratio and estimation of multipath and noise by a combination of code and carrier phase measurements. The impact on positioning accuracy is derived by comparing the performance achievable with the conventional single frequency GPS only positioning both relative to reference trajectories from the integration of carrier phase measurements with data from a high grade inertial measurement unit. The results show that L5 code measurements have the highest precision, followed by L1 C/A and L2C. In the positioning domain, there is a significant improvement in two-dimensional and three-dimensional accuracy from dual frequency code measurements over the single frequency measurements, of 39% and 48% respectively, enabling more bus operation services to be supported.

scholarly journals Applications of GNSS-Pro software for processing GNSS short baseline networks in Vietnam

2016 ◽  
Vol 19 (2) ◽  
pp. 27-35
Author(s):  
Lau Ngoc Nguyen ◽  
Huong Thi Thanh Nguyen ◽  
Hoa Minh Ha
Keyword(s):  
Carrier Phase ◽  
Dual Frequency ◽  
Short Baseline ◽  
Phase Measurements ◽  
Satellite Systems ◽  
Results Of Treatment ◽  
Software Packages ◽  
Gnss Network ◽  
Fixed Solution ◽  
Gnss Data

In the framework of a Natural Resources and Environment Ministry level project, chaired by the Vietnam Institute of Geodesy and Cartography, we have established GNSS-Pro software for processing GNSS short baseline networks. The software can process carrier phase measurements from single or dual frequency receivers for the two satellite systems GPS and GLONASS simultaneously. This paper presents the results of treatment an illustrated cadastral GNSS network in Hai Duong province by GNSS-Pro and compared with other commonly used software packages such as Leica Geo Office (LGO) and Trimble Business Center (TBC). Result comparisons showed that although GNSS data collected in the unfavorable conditions, GNSS-Pro still offers fixed solution for all baselines with centimeter level accuracy.

scholarly journals Snow Depth Estimation with GNSS-R Dual Receiver Observation

2019 ◽  
Vol 11 (17) ◽  
pp. 2056 ◽  
Author(s):  
Yu ◽  
Wang ◽  
Li ◽  
Chang ◽  
Li
Keyword(s):  
Snow Depth ◽  
Carrier Phase ◽  
Mean Squared Error ◽  
Depth Estimation ◽  
Combination Method ◽  
Estimation Methods ◽  
Single Frequency ◽  
Dual Frequency ◽  
Combination Methods ◽  
Receiver System

Two estimation methods using a dual GNSS (Global Navigation Satellite System) receiver system are proposed. The dual-frequency combination method combines the carrier phase observations of dual-frequency signals, whereas the single-frequency combination method combines the pseudorange and carrier phase observations of a single-frequency signal, both of which are geometry-free strictly combination and free of the effect of ionospheric delay. Theoretical models are established in the offline phase to describe the relationship between the spectral peak frequency of the combined sequence and the antenna height. A field experiment was conducted recently and the data processing results show that the root mean squared error (RMSE) of the dual-frequency combination method is 5.04 cm with GPS signals and 6.26 cm with BDS signals, which are slightly greater than the RMSE of 4.16 cm produced by the single-frequency combination method of L1 band with GPS signals. The results also demonstrate that the proposed two combination methods and the SNR method achieve similar performance. A dual receiver system enables the better use of GNSS signal carrier phase observations for snow depth estimation, achieving increased data utilization.

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