Geodetic GPS Research Articles

Application of analytic hierarchy process, frequency ratio, and statistical index to landslide susceptibility: an approach to endangered cultural heritage

This paper presents the applicability of the analytic hierarchy process, frequency ratio, and statistical index in landslide susceptibility mapping for an area from north-eastern Romania. The dependent factor (in this case the landslides) was determined by combining seven conditioning factors: elevation, slope angle, curvature, normalised difference vegetation index, roughness, distance to rivers, and landforms. A landslide inventory was prepared using topographic plans and orthophotos and by carrying out field surveys with the total station (Leica TCR1201) and geodetic GPS (Leica System 1200) in RTK mode. The final susceptibility maps were made with the help of GIS and validated by carrying out the receiver operating characteristics (ROC) curves. ROC plots for training data have shown that the susceptibility map generated using the analytic hierarchy process with AUC value of 79.46 has a better prediction accuracy compared with frequency ratio method (AUC = 75.24), and statistical index method, which had an AUC value of 61.46. The prediction rate of the three models is over 50% (79.64% for the analytic hierarchy process model, 75.65% for the frequency ratio model, and 66.36% for the statistical index model). More than a half of the cultural heritage sites are located in areas with a very high and high vulnerability to landslides. Taking into consideration that multi-stratified settlements are located in areas with low and medium landslide susceptibility, this fact can indicate a possible awareness of prehistoric people from natural hazards. The final susceptibility maps can be used for land use planning, risk reduction, hazard mitigation, to evaluate the present state of cultural heritage sites in danger and to predict which of the sites will be in more danger in the future.

3D Land Mapping and Land Deformation Monitoring Using Persistent Scatterer Interferometry (PSI) ALOS PALSAR: Validated by Geodetic GPS and UAV

Complex topography and geological formation are the primary causes of frequent land deformation occurrence at Kelok Sembilan area, West Sumatra, Indonesia. This paper presents a research work on land mapping and land deformation monitoring carried out using persistent scatterer interferometry (PSI) synthetic aperture radar (SAR) technique at Kelok Sembilan bridge region. In this paper, 13 ascending Advanced Land Observation Satellite Phased Array L-band Synthetic Aperture Radar (ALOS PALSAR) scenes, taken from July 2007 to November 2010, were processed using PSI-SAR technique. Then, the land deformation analysis was performed in two of the critical landslide areas near the Kelok Sembilan bridge. For validation purpose, the results were compared with in situ ground measurement data obtained using both differential global positioning system technique, and 3-D photogrammetry technique based unmanned aerial vehicle. The land deformation analysis showed that both of the investigation areas are suffering a severe land movement of approximately −100 mm every year. In addition to that, the validation results showed erroneousness of less than 0.3%.

Development of a Geoid Model by Geometric Method

Engineering projects require orthometric heights of points where as Global Navigation Satellite System (GNSS) provide height above ellipsoid. Thus, to make use of GNSS in engineering surveying, the relationship between ellipsoidal height and orthometric height as a function of position needs to be established through geoid modeling. In this study, an attempt has been made to develop a geoid model using the geometric method. Observations were taken in a network of sixteen stations spread over 600 km2 around Dehra Dun, India. GPS observations were taken using dual frequency geodetic GPS receivers and leveling done using digital levels with 0.1 mm accuracy. Orthometric height of stations from developed model have been found to be near to those from field levelling which is considered most accurate. Further, the values have been compared with those obtained from the recent GOCE–GRACE–LAGEOS geoid model EIGEN6C3stat. It has been found that the geometric model provides far better accuracy than that obtained from the global geoid model. Therefore, it can be concluded that the geometric method of geoid modeling can better be used for reduction of GPS observed ellipsoidal height to orthometric height in a local area. This model may gainfully be employed in a project area as a substitute for densification of leveling lines, thereby reducing the project cost substantially.

An Investigation of the Accuracy of Coulomb Stress Changes Inferred From Geodetic Observations Following Subduction Zone Earthquakes

AbstractEarthquake clustering along plate boundaries suggests that earthquakes may interact, and static Coulomb stress change (CSC) is commonly invoked as one possible mechanism for stress transfer between earthquakes and nearby faults. Previous work has addressed the precision of CSC predictions that are influenced by observational noise, inversion regularization, and simplified modeling assumptions. Here we address the accuracy of CSC predictions informed by geodetic observations in subduction zones where inversion model resolution is poor. We conduct synthetic tests to quantify the degree to which the sign and magnitude of CSC can be reliably inferred from slip distributions inverted from various geodetic observations (interferometric synthetic aperture radar (InSAR), GPS, and seafloor observations). We find that in an idealized subduction zone, CSC can only be confidently inferred for receiver faults far (tens of kilometers) from the earthquake source, though this distance shortens with the addition of synthetic seafloor observations. We apply this methodology to the 2010 Mw8.8 Maule earthquake and identify 13 aftershocks from a population of 475 documented events for which we can confidently resolve coseismic stress changes. These results demonstrate that the low model resolution of fault slip inversions in subduction zones limits our ability to address fundamental questions about earthquake sources and stress interactions. Nonetheless, our results highlight that stress change predictions are considerably more accurate after the introduction of seafloor geodetic observations. Additionally, we show that InSAR observations are not required to substantially improve stress change approximations in regions where GPS may be the only viable observation, such as in island arcs settings.

UNMANNED AERIAL VEHICLES FOR GEOLOGICAL APPLICATIONS

Remote Sensing and photogrammetric techniques have always been used in geological applications. Current advancements in the technology behind Unmanned Aerial Vehicles (UAVs), in accordance with the consecutive increase in affordability of such devices and the availability of photogrammetric software, makes their use for large or small scale land mapping more and more popular. With the UAVs being used for mapping, the problems of increased costs, time consumption and the possible accessibility problems -due to steep terrain-, are all solved at once. In this study, a custom-made UAV with 2 cameras onboard, is used to monitor two complex –regarding their topography- regions in Western Greece. One open pit limestone mine and a landslide occurring on sandy-clayous sediments. Both regions were mapped using surveying instruments like tachymeters and geodetic GPS, as well as using the aforementioned UAV system. 3D models of both regions were created using off-the-shelf photogrammetric software. For the creation of the 3D models, multiple targets were placed on the ground, to indicate GCPs with precisely known coordinates that could be identified in the high-resolution air photos, in order to maintain low Root Mean Square Error, while creating the DSMs and Orthophotos. In addition, the fish-eye effect caused by the cameras’ wide-angle lens was taken into consideration, regarding whether or not it affects the models’ overall geometric accuracy. Finally, the 3D models were compared to the survey measurements and the results are presented in this paper.

Vulnerabilidade costeira e dinâmica sedimentar - Campo de dunas de Mangue Seco, Guamaré/RN, NE do Brasil.

Buscamos determinar taxas de migração de três dunas, baseando-se em medições da variação de volume entre junho de 2013 a maio de 2014. A área em estudo localiza-se no Parque Eólico Alegria, município de Guamaré, litoral setentrional do Estado do Rio Grande do Norte, Nordeste/Brasil. Utilizou-se uma combinação de medições de GPS geodésico e coleta de sedimentos para caracterizar sua morfodinâmica. Foi gerado o MDT (Modelo Digital do Terreno), utilizando a krigagem e foi calculado o seu volume. O volume no mês de junho de 2013 foi de 132.470 m3. Comparou-se com os volumes nos meses consecutivos e os resultados mostraram que houve aumento da duna entre junho-julho de 2013 (+31.545m3) e agosto-setembro de 2013 (+10.341m3), e redução entre julho-agosto de 2013 (-7.700m3). Apesar da redução entre julho-agosto, o volume calculado da duna é superior ao volume inicial. Perfis transversais na duna mostram que as modificações ocorreram a sotavento e barlavento. A velocidade do vento para início do transporte sedimentar (Uct), mostrou que estes de NE são mais efetivos, e o aumento no volume das dunas está relacionado à sua ocorrência. O MDT gerado mostra que as dunas são barcanas. Entre junho-setembro de 2013 e janeiro-maio de 2014, as dunas migraram 6 metros para SW e ~5m para NW, o que resulta em 1,5 m/mês e 1,25 m/mês, respectivamente. De acordo com a estação meteorológica de Macau/RN, da velocidade Uct e dos perfis transversais, a maior velocidade de migração ocorreu entre junho-julho e agosto-setembro. A variação morfológica da duna é influenciada pela variação na frequência de ocorrência dos ventos de NE.

Application of UAV photogrammetry for the multi-temporal estimation of surface extent and volumetric excavation in the Sa Pigada Bianca open-pit mine, Sardinia, Italy

In open-pit mines, monitoring of topographic and volumetric changes through time is found to be of great importance to support excavation stages and to plan rehabilitation strategies. In this work, we describe a geomatic approach to assess changes in surface mine extent and to quantify excavated volume in the Sa Pigada open-pit mine, Sardinia, Italy. We performed two drone-based photogrammetric surveys in 2013 and 2015, and by means of the Structure from Motion (SfM) technique, we obtained related 3D dense point clouds and digital orthophotos. Images were georeferenced thanks to a series of ground control points surveyed with geodetic GPS. Distances between the two clouds were estimated with the recent Multiscale Model to Model Cloud Comparison (M3C2) plug-in included in the CloudCompare open-source software. Starting from cloud-to-cloud distances, we calculated the excavated volume of mineral resources between the two surveys. Results of the M3C2 comparison supported the analysis of the two orthophotos, through which accurate limits of the 2013 and 2015 active mine areas, rehabilitated area and temporary dumps were identified and drawn in a digital map. Results obtained in this study suggest that the applied geomatic techniques are suitable for performing accurate change detection analysis in open-pit environments and represent a valid support for scientists and technicians allowing to monitor with high spatial and temporal resolutions. This approach can be also considered a valid tool to reduce environmental impact from mining.

A 10-Year Comparison of Water Levels Measured with a Geodetic GPS Receiver versus a Conventional Tide Gauge

AbstractA standard geodetic GPS receiver and a conventional Aquatrak tide gauge, collocated at Friday Harbor, Washington, are used to assess the quality of 10 years of water levels estimated from GPS sea surface reflections. The GPS results are improved by accounting for (tidal) motion of the reflecting sea surface and for signal propagation delay by the troposphere. The RMS error of individual GPS water level estimates is about 12 cm. Lower water levels are measured slightly more accurately than higher water levels. Forming daily mean sea levels reduces the RMS difference with the tide gauge data to approximately 2 cm. For monthly means, the RMS difference is 1.3 cm. The GPS elevations, of course, can be automatically placed into a well-defined terrestrial reference frame. Ocean tide coefficients, determined from both the GPS and tide gauge data, are in good agreement, with absolute differences below 1 cm for all constituents save K1 and S1. The latter constituent is especially anomalous, probably owing to daily temperature-induced errors in the Aquatrak tide gauge.

A polarimetric analysis of COSMO-SkyMed and RADARSAT-2 offset tracking derived velocities of David-Drygalski Glacier (Antarctica)

This paper deals with the comparison of coregistration offset tracking velocities in the inner part of the David Glacier (Antarctica), obtained with SAR sensors characterized by different wavelengths and spatial resolutions: Cosmo-SkyMED (X band) and RADARSAT-2 (C band). Particular attention has been devoted to understand the role of polarization and penetration depth of the incident wavelength, which represent key parameters in determining the effective incidence angle and so, for this reason, affecting also derived velocities. Metric validation of offset tracking derived velocities was obtained with respect to a geodetic GPS point available in the study area and to a velocity field derived from Landsat imagery coregistration.

Using combined GRACE and GPS data to investigate the vertical crustal deformation at the northeastern margin of the Tibetan Plateau

In this paper, two types of geodetic measurements, GRACE and GPS, are combined to study the vertical crustal deformation on the northeastern margin of the Tibetan Plateau. The GRACE and GPS derived results show that significant seasonal variations occur at 40 regional continuous GPS stations of the Crustal Movement Observation Network of China (CMONOC). The consistency between the seasonal variations in the GRACE and GPS data can be efficiently enhanced by decreasing the nonlinear deformation in the GPS time series with applying longer observation period. The vertical components of more than 78% of the total number of GPS stations exhibit correlations of more than 0.8 with respect to the corresponding GRACE components, and approximately 73% of the GPS vertical time series exhibit a significant root mean square reduction of approximately 40%, which increases to 60% when corresponding seasonal components derived from the GRACE measurements are subtracted. We consider that the vertical seasonal variations in the study area are caused by mass transfer related to hydrological loading, whereas the horizontal components are related to both mass transfer and other factors, such as the thermal elastic response of the GPS monuments and GPS data processing strategical deficits. These factors distinguish the main differences between the two measurements and exert larger influences in the eastward direction than in the northward direction, contributing to the total displacement. Finally, we use seasonal variations derived from the GRACE results to modify the vertical time series of corresponding GPS campaign stations to mitigate the influences of seasonal loading as much as possible in the dispersed time series. The results show that this modification can significantly reduce the scatter of campaign time series and improve the derived velocities uncertainties remarkably.

Vegetation Sensing Using GPS Interferometric Reflectometry: Experimental Results With a Horizontally Polarized Antenna

Measurement of vegetation state is required both for modeling and for satellite data validation. GPS Interferometric Reflectometry (GPS-IR) is a passive microwave remote sensing technique that has been applied to several applications, such as sensing soil moisture, snow depth, ocean roughness and wind speed, and vegetation growth. Previous studies proposed that geodetic GPS data could be used to measure vegetation biophysical parameters, for example, vegetation height and vegetation water content (VWC). However, the measurement range and accuracy are limited because the geodetic GPS antenna is designed to suppress reflections. In this paper, the antenna design for vegetation sensing via GPS-IR is discussed. Then, a customized dipole antenna is developed specifically for vegetation sensing. A field experiment is conducted at Boulder, CO, USA to evaluate the performance of the proposed antenna. The GPS metric, which is the normalized signal-to-noise ratio (SNR) amplitude ${A_{{\rm{norm}}}}$ , shows a linear relationship with in situ measurements of VWC over a range of 0—6 kg/m2, which is much greater than the range from the geodetic data (0—1.0 kg/m 2). The sensitivity of ${A_{{\rm{norm}}}}$ to VWC change is −0.11 (W/W)/(kg/m2), and the average measurement error of VWC is ∼12.4%. Thus, the horizontally polarized antenna is suitable for vegetation monitoring in most environments, including agricultural settings. The effects of soil moisture on GPS SNR amplitude are also documented, but these are minor compared to the decrease in amplitude resulting from vegetation growth.

Tightly Coupled Integration of GPS Ambiguity Fixed Precise Point Positioning and MEMS-INS through a Troposphere-Constrained Adaptive Kalman Filter.

Precise Point Positioning (PPP) makes use of the undifferenced pseudorange and carrier phase measurements with ionospheric-free (IF) combinations to achieve centimeter-level positioning accuracy. Conventionally, the IF ambiguities are estimated as float values. To improve the PPP positioning accuracy and shorten the convergence time, the integer phase clock model with between-satellites single-difference (BSSD) operation is used to recover the integer property. However, the continuity and availability of stand-alone PPP is largely restricted by the observation environment. The positioning performance will be significantly degraded when GPS operates under challenging environments, if less than five satellites are present. A commonly used approach is integrating a low cost inertial sensor to improve the positioning performance and robustness. In this study, a tightly coupled (TC) algorithm is implemented by integrating PPP with inertial navigation system (INS) using an Extended Kalman filter (EKF). The navigation states, inertial sensor errors and GPS error states are estimated together. The troposphere constrained approach, which utilizes external tropospheric delay as virtual observation, is applied to further improve the ambiguity-fixed height positioning accuracy, and an improved adaptive filtering strategy is implemented to improve the covariance modelling considering the realistic noise effect. A field vehicular test with a geodetic GPS receiver and a low cost inertial sensor was conducted to validate the improvement on positioning performance with the proposed approach. The results show that the positioning accuracy has been improved with inertial aiding. Centimeter-level positioning accuracy is achievable during the test, and the PPP/INS TC integration achieves a fast re-convergence after signal outages. For troposphere constrained solutions, a significant improvement for the height component has been obtained. The overall positioning accuracies of the height component are improved by 30.36%, 16.95% and 24.07% for three different convergence times, i.e., 60, 50 and 30 min, respectively. It shows that the ambiguity-fixed horizontal positioning accuracy has been significantly improved. When compared with the conventional PPP solution, it can be seen that position accuracies are improved by 19.51%, 61.11% and 23.53% for the north, east and height components, respectively, after one hour convergence through the troposphere constraint fixed PPP/INS with adaptive covariance model.

QUALITY TEST VARIOUS EXISTING DEM IN INDONESIA TOWARD 10 METER NATIONAL DEM

Indonesia has various DEM from many sources and various acquisition date spreaded in the past two decades. There are DEM from spaceborne system (Radarsat, TerraSAR-X, ALOS, ASTER-GDEM, SRTM), airborne system (IFSAR, Lidar, aerial photos) and also terrestrial one. The research objective is the quality test and how to extract best DEM in particular area. The method is using differential GPS levelling using geodetic GPS equipment on places which is ensured not changed during past 20 years. The result has shown that DEM from TerraSAR-X and SRTM30 have the best quality (rmse 3.1 m and 3.5 m respectively). Based on this research, it was inferred that these parameters are still positively correlated with the basic concept, namely that the lower and the higher the spatial resolution of a DEM data, the more imprecise the resulting vertical height.

QUALITY TEST VARIOUS EXISTING DEM IN INDONESIA TOWARD 10 METER NATIONAL DEM

Abstract. Indonesia has various DEM from many sources and various acquisition date spreaded in the past two decades. There are DEM from spaceborne system (Radarsat, TerraSAR-X, ALOS, ASTER-GDEM, SRTM), airborne system (IFSAR, Lidar, aerial photos) and also terrestrial one. The research objective is the quality test and how to extract best DEM in particular area. The method is using differential GPS levelling using geodetic GPS equipment on places which is ensured not changed during past 20 years. The result has shown that DEM from TerraSAR-X and SRTM30 have the best quality (rmse 3.1 m and 3.5 m respectively). Based on this research, it was inferred that these parameters are still positively correlated with the basic concept, namely that the lower and the higher the spatial resolution of a DEM data, the more imprecise the resulting vertical height.

Water Surface Height Determination with a GPS Wave Glider: A Demonstration in Loch Ness, Scotland

AbstractA geodetic GPS receiver has been installed on a Wave Glider, an unmanned water surface vehicle. Using kinematic precise point positioning (PPP) GPS, which operates globally without directly requiring reference stations, surface heights are measured with ~0.05-m precision. The GPS Wave Glider was tested in Loch Ness, Scotland, by measuring the gradient of the loch’s surface height. The experiment took place under mild weather, with virtually no wind setup along the loch and a wave field made mostly of ripples and wavelets. Under these conditions, the loch’s surface height gradient should be approximately equal to the geoid slope. The PPP surface height gradient and that of the Earth Gravitational Model 2008 geoid heights do indeed agree on average along the loch (0.03 m km−1). Also detected are 1) ~0.05-m-sized height changes due to daily water pumping for hydroelectricity generation and 2) high-frequency (0.25–0.5 Hz) oscillations caused by surface waves. The PPP heights compare favorably (~0.02-m standard deviation) with relative carrier phase–based GPS processing. This suggests that GPS Wave Gliders have the potential to autonomously determine centimeter-precise water surface heights globally for lake modeling, and also for applications such as ocean modeling and geoid/mean dynamic topography determination, at least for benign surface states such as those encountered during the reported experiment.

3D VISUALIZATION OF CULTURAL HERITAGE USING TERRESTRIAL LASER SCANNER (A Case Study : Monument of Heroes, Surabaya, East Java)

Research subjects reported was the visualization of three-dimensional (3D) surface models in three-dimensional mapping survey using terrestrial laser scanning (TLS). Tugu Pahlawan (Heroes Monument), located in Surabaya city center near the office of the Governor of East Java was chosen as the research object.Laser technology instruments used for comparison is GeoMax Zoom 300 (Terrestrial Laser Scanner) and Gowin TKS-202 (Electronic Total Station) as well as for geodetic GPS coordinates and altitude reference measurement Heroes Monument are georeferenced. Coordinate measurement results Electronic Total Station and Terrestrial Laser Scanner are then converted into global coordinates (UTM) using georeferencing process from Geodetic GPS measurement results. Coordinates, diameter and height of Tugu Pahlawan calculated for each model. Statistical test is used as data validation terrestrial laser scanner with electronic total station.With 90% confidence interval on statistical tests, 80% of them into confidence intervals. Height of Tugu Pahlawan according to archived data is 41.448 m, in contrast with the results of measurements from Total Station is 41.144 m, while the results of TLS is 41.447 m. Statistical test results concluded that the height of heights TLS is outside the confidence interval. Expected in the future, such as the visualization of 3D surface models can be used for documentation, preservation and reconstruction of cultural heritage.

Snow depth estimation accuracy using a dual-interface GPS-IR model with experimental results

Measuring snow depth using the GPS interferometric reflectometry is an active microwave remote sensing technique and an emerging approach because of its relatively large spatial coverage and high temporal sampling capability. The current geodetic GPS networks are capable of measuring snow depth in the vicinity of the antenna installation at no additional hardware cost. However, the performance is constrained by the geodetic GPS antenna which was originally designed to minimize the reception of the reflected signal. In our prior work, we proposed a horizontally polarized antenna which has equal gain for both direct and reflected signals and tested its performance for a single snow event. In order to comprehensively assess its performance, we set up a horizontally polarized snow monitor (HPSM) using the improved antenna at Marshall, Colorado, USA, over the 2013---2014 water year. The data from the HPSM clearly shows that the proposed design has high sensitivity to even very light snowfalls. However, some anomalies are observed from the HPSM measurements, which tend to either overestimate or underestimate the actual snow depth. We explain the observed measurement anomalies by replacing the traditional air---snow single-interface model with an air---snow---soil dual-interface model. The effectiveness of the new model is validated by comparing the simulated results to the HPSM measurements. Utilizing the dual-interface model, we simulate the error curve for snow depth estimation given various snow depths and snow permittivities. The error curve shows that the estimation biases can be observed only for shallow snow with a relatively small permittivity value.

Snow Depth Variations Estimated from GPS-Reflectometry: A Case Study in Alaska from L2P SNR Data

Snow is a water resource and plays a significant role in the water cycle. However, traditional ground techniques for snow monitoring have many limitations, e.g., high-cost and low resolution. Recently, the new Global Positioning System-Reflectometry (GPS-R) technique has been developed and applied for snow sensing. However, most previous studies mainly used GPS L1C/A and L2C Signal-to-Noise Ratio (SNR) data to retrieve snow depth. In this paper, snow depth variations are retrieved from new weak GPS L2P SNR data at three stations in Alaska and evaluated by comparing with in situ measurements. The correlation coefficients for the three stations are 0.79, 0.88 and 0.98, respectively. The GPS-estimated snow depths from the L2P SNR data are further compared with L1C/A results at three stations, showing a high correlation of 0.94, 0.93 and 0.95, respectively. These results indicate that geodetic GPS observations with SNR L2P data can well estimate snow depths. The samplings of 15 s or 30 s have no obvious effect on snow depth estimation using GPS SNR L2P measurements, while the range of 5°–35°elevation angles has effects on results with a decreasing correlation of 0.96 and RMSE of 0.04 m when compared to the range of 5°–30° with correlation of 0.98 and RMSE of 0.03 m. GPS SNR data below 30° elevation angle are better to estimate snow depth.

DEVELOPMENT AND EVALUATION OF A UAV BASED MAPPING SYSTEM FOR REMOTE SENSING AND SURVEYING APPLICATIONS

Abstract. In recent years, unmanned aerial vehicles (UAVs) have increasingly been used in various application areas, such as in the remote sensing or surveying. For these applications the UAV has to be equipped with a mapping sensor, which is mostly a camera. Furthermore, a georeferencing of the UAV platform and/or the acquired mapping data is required. The most efficient way to realize this georeferencing is the direct georeferencing, which is based on an onboard multi-sensor system. In recent decades, direct georeferencing systems have been researched and used extensively in airborne, ship and land vehicle applications. However, these systems cannot easily be adapted to UAV platforms, which is mainly due to weight and size limitations. In this paper a direct georeferencing system for micro- and mini-sized UAVs is presented, which consists of a dual-frequency geodetic grade OEM GPS board, a low-cost single-frequency GPS chip, a tactical grade IMU and a magnetometer. To allow for cm-level position and sub-degree attitude accuracies, RTK GPS (real-time kinematic) and GPS attitude (GPS compass) determination algorithms are running on this system, as well as a GPS/IMU integration. Beside the direct georeferencing, also the precise time synchronization of the camera, which acts as the main sensor for mobile mapping applications, and the calibration of the lever arm between the camera reference point and the direct georeferencing reference point are explained in this paper. Especially the high accurate time synchronization of the camera is very important, to still allow for high surveying accuracies, when the images are taken during the motion of the UAV. Results of flight tests demonstrate that the developed system, the camera synchronization and the lever arm calibration make directly georeferenced UAV based single point measurements possible, which have cm-level accuracies on the ground.

Tightly coupled integration of ionosphere-constrained precise point positioning and inertial navigation systems.

The continuity and reliability of precise GNSS positioning can be seriously limited by severe user observation environments. The Inertial Navigation System (INS) can overcome such drawbacks, but its performance is clearly restricted by INS sensor errors over time. Accordingly, the tightly coupled integration of GPS and INS can overcome the disadvantages of each individual system and together form a new navigation system with a higher accuracy, reliability and availability. Recently, ionosphere-constrained (IC) precise point positioning (PPP) utilizing raw GPS observations was proven able to improve both the convergence and positioning accuracy of the conventional PPP using ionosphere-free combined observations (LC-PPP). In this paper, a new mode of tightly coupled integration, in which the IC-PPP instead of LC-PPP is employed, is implemented to further improve the performance of the coupled system. We present the detailed mathematical model and the related algorithm of the new integration of IC-PPP and INS. To evaluate the performance of the new tightly coupled integration, data of both airborne and vehicle experiments with a geodetic GPS receiver and tactical grade inertial measurement unit are processed and the results are analyzed. The statistics show that the new approach can further improve the positioning accuracy compared with both IC-PPP and the tightly coupled integration of the conventional PPP and INS.