Global Positioning System Inertial Measurement Unit Research Articles

High Temporal and Spatial Resolutions of Sea Surface Current from Low-Altitude Remote Sensing

Jung, D.; Lee, J.S.; Baek, J.Y.; Nam, J.; Jo, Y.H.; Song, K.M., and Cheong Y.I., 2019. High temporal and spatial resolutions of sea surface current from low-altitude remote sensing. Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 282-288. Coconut Creek (Florida), ISSN 0749-0208.The Saemangeum coast in Korea, which is the study area, is divided from the outer side and the inner side of the dyke. Because exchanging seawater are occurred by only two gates (Sinsi and Garyeok), coastal erosion and sedimentation, migration of suspended solids, and chemical component exchange occur extensively along the gates. Therefore, it is critical to observe the movement of seawater flowing through the gates. In this study, an algorithm to extract high-resolution sea surface current information using a Helikite (the compound word for Helium and Kite) and a drone was examined. First, direct georeferencing was performed using Global Positioning System/Inertial Measurement Unit (GPS/IMU) data from the aircraft to assign ground coordinates into the images without a Ground Control Point (GCP). Subsequently, the sea surface current was estimated using a Robust Optical Flow (ROF) algorithm. ROF computes motion by analyzing changes in the brightness values of successive images. The accuracy of the estimated sea surface current was verified by comparing with observations from a surface drifter, and the results showed that the correlation coefficient was 0.57 and the Root Mean Square Error (RMSE) was 8.85 cm/s. Generally, the ROF-based flow rates were underestimated compared to the field measurements. Furthermore, image aliasing occurred due to a 5-s time interval and the currents that had a strong wave frequency could not be completely captured. To fully restore the sea surface current that appeared on the images, it is necessary to obtain the images at various sampling frequencies using video recordings.

Applying Time-Differenced Carrier Phase in Nondifferential GPS/IMU Tightly Coupled Navigation Systems to Improve the Positioning Performance

This paper presents how the time-differenced carrier phase (TDCP) can be implemented in nondifferential global positioning system/inertial measurement unit (GPS/IMU) tightly coupled navigation systems to improve positioning performance. The TDCP is expressed as a conventional TDCP, representing the carrier phase difference between two successive GPS epochs, and a modified TDCP, which is defined in this paper as the carrier phase difference between current and reference GPS epochs. Both of these two TDCP expressions are implemented in a GPS/IMU tightly coupled navigation Kalman filter as observations: The conventional TDCP with a more accurate approximation of the velocity integration is applied to estimate velocity, whereas the modified TDCP is used for position estimation. When initialized with a high-accuracy reference position, the proposed navigation strategy can achieve submeter positioning accuracy in the nondifferential mode without estimating ambiguities. Compared with the conventional TDCP-only method, the inherent position drift problem of the TDCP observations can also be avoided. The absolute positioning accuracy of the proposed conventional+modified TDCP measurement update method is determined by the reference position, since the TDCP, including conventional and modified TDCP, is a relative measurement. However, even when initialized with a low-accuracy reference position, the relative positioning accuracy (or precision) of the proposed method is still very high, and the reference positioning accuracy can be maintained, owing to the proposed method. The proposed method can greatly improve the positioning accuracy, as compared with traditional pseudorange+Doppler GPS/IMU tightly coupled navigation systems.

Submarine groundwater discharge revealed by aerial thermal infrared imagery: a case study on Jeju Island, Korea

AbstractSubmarine groundwater discharge (SGD) is a global phenomenon that carries large volumes of groundwater and dissolved chemical species such as nutrient, metals, and organic compounds to coastal zones. We report the influence of SGD on the coastal waters of Jeju Island, Korea, using high‐resolution aerial thermal infrared (TIR) mapping techniques and field investigations. An aircraft‐based system was implemented using a cost‐effective TIR camera for aerial TIR mapping. Ground‐based calibrations and system integration with GPS/IMU (global positioning system/inertial measurement unit) were performed for the aerial systems. The aerial surveys showed distinct low‐temperature signatures of SGD along the coasts of Jeju Island, revealing large groundwater inputs from the coastal aquifers to the ocean. Multiple aerial surveys over a range of seasons and tidal stages revealed that SGD rates dynamically affect the sea surface temperature (SST) of the coastal zone. The in‐situ measurements supported that SGD has a substantial influence on the coastal water chemistry as well as SST. Our observations highlight the extent to which aerial‐based TIR mapping can serve as a powerful tool for studying SGD and other coastal processes. Copyright © 2016 John Wiley & Sons, Ltd.

Test of Global Positioning System–Inertial Measurement Unit Performance for Surveying Road Alignment

In an effort to shift road alignment surveying from manual to automatic methods, moving objects—such as a vehicle on which a Global Positioning System–inertial measurement unit (GPS-IMU) is mounted—are being used to perform surveys and obtain more accurate results. Two road alignment survey methods are compared: an affordably priced microelectromechanical system (MEMS) GPS-IMU and a high-priced fiber-optic–type GPS-IMU. Cross-section angle values from a stationary laser scanner survey and a GPS-IMU survey are compared to determine whether the roll attitude value of GPS-IMU can be used to ensure a more accurate comparison of the cross-section angle. In addition, GPS-IMU performance is compared under various test conditions to survey road alignment, and results indicate that the fiber-optic GPS-IMU is needed to ensure accuracy within the 10% margin of error required for road alignment. In a test conducted to verify whether the roll value of a vehicle can be used as is to survey the cross-section angle of a road, the values from GPS-IMU, drawing, and laser were within a 1% margin of error. Thus, it would be possible to use the roll value obtained from a vehicle as is to survey the road cross-section angle accurately.

IMM-Based Lane-Change Prediction in Highways With Low-Cost GPS/INS

The prediction of lane changes has been proven to be useful for collision avoidance support in road vehicles. This paper proposes an interactive multiple model (IMM)-based method for predicting lane changes in highways. The sensor unit consists of a set of low-cost Global Positioning System/inertial measurement unit (GPS/IMU) sensors and an odometry captor for collecting velocity measurements. Extended Kalman filters (EKFs) running in parallel and integrated by an IMM-based algorithm provide positioning and maneuver predictions to the user. The maneuver states Change Lane (CL) and Keep Lane (KL) are defined by two models that describe different dynamics. Different model sets have been studied to meet the needs of the IMM-based algorithm. Real trials in highway scenarios show the capability of the system to predict lane changes in straight and curved road stretches with very short latency times.

Kinematic Terrestrial Light-Detection and Ranging System for Scanning

Highway corridor surveys are becoming more difficult and expensive to carry out because of the need to minimize lane closures, traffic disruptions, and safety hazards posed to the surveyors and public. Roadway surveyors are at risk when working in the traffic corridor if they are unable to move with the flow of traffic. Safety for the traveling public is also a concern when lanes are closed or blocked by slow-moving vehicles. Costs for the placement of safety features to protect a survey crew can in some instances be greater than the cost of the survey itself. To mitigate these problems, a survey data acquisition tool is needed that can collect topographic and infrastructure information without disrupting traffic flow. Terrapoint has developed a novel kinematic laser scanning system that can be deployed on a passenger vehicle or small watercraft. Light-detection and ranging (LIDAR) digital imagery and video are collected from the survey platform while it is moving at traffic speeds. The system is georeferenced with a high-accuracy Global Positioning System–inertial measurement unit. Terrapoint's mobile LIDAR scanner has successfully surveyed existing highway corridors all over North America. It has also proven sufficiently accurate for scanning airport runway surfaces so as to predict areas where water will pool. Moving with the traffic flow and not requiring an escort, the system scans a 360° swath that includes the pavement surface and objects to the sides and above the survey vehicle.