A comprehensive method for GNSS data quality determination to improve ionospheric data analysis

Land Cover Classification from Very High-Resolution UAS Data for Flood Risk Mapping

Monitoring the world's areas that are more vulnerable to natural hazards has become crucial worldwide. In order to reduce disaster risk, effective tools and relevant land cover (LC) data are needed. This work aimed to generate a high-resolution LC map of flood-prone rural villages in southwest Niger using multispectral drone imagery. The LC was focused on highly thematically detailed classes. Two photogrammetric flights of fixed-wing unmanned aerial systems (UAS) using RGB and NIR optical sensors were realized. The LC input dataset was generated using structure from motion (SfM) standard workflow, resulting in two orthomosaics and a digital surface model (DSM). The LC system is composed of nine classes, which are relevant for estimating flood-induced potential damages, such as houses and production areas. The LC was generated through object-oriented supervised classification using a random forest (RF) classifier. Textural and elevation features were computed to overcome the mapping difficulties due to the high spectral homogeneity of cover types. The training-test dataset was manually defined. The segmentation resulted in an F1_score of 0.70 and a median Jaccard index of 0.88. The RF model performed with an overall accuracy of 0.94, with the grasslands and the rocky clustered areas classes the least performant.

Monitoring the Vector Error Between a Reference Station and a GNSS on-Board Receiver in the GBAS System in the Polish Air Transport

The article presents research results concerning the determination of the vector error between a reference station and the GNSS on-board receiver in the GPS satellite measurements for GBAS system, taking into account the ZTD troposphere delay parameter. Based on the conducted studies, it was found that the highest value of the vector error between a reference station and the GNSS on-board receiver can exceed 0.18 m, for a distance of over 40 km and the ZTD value equalling to 2428.1 mm. The error results of vector measurement can be used in the RTK-OFT differential technique in the GBAS system.

An Online SBAS Service to Improve Drone Navigation Performance in High-Elevation Masked Areas

Owing to the high demand for drone operation in high-elevation masked areas, it is necessary to develop a more effective method of transmitting and applying Satellite-Based Augmentation System (SBAS) messages for drones. This study proposes an onboard module including correction conversion, integrity information calculation, and fast initialization requests, which can enable the application of an online SBAS to drone operation. The proposed system not only improves the position accuracy with timely and proper protection levels in an open sky, but also reduces the initialization time from 70–100 s to 1 s, enabling a drone of short endurance to perform its mission successfully. In SBAS signal-denied cases, the position accuracy was improved by 40% and the uncorrected 13.4 m vertical error was reduced to 5.6 m by applying an SBAS message delivered online. The protection levels calculated with the accurate position regardless of the current location could denote the thrust level and availability of the navigation solution. The proposed system can practically solve the drawbacks of the current SBAS, considering the characteristics of the low-cost receivers on the market. Our proposed system is expected to be a useful and practical solution to integrate drones into the airspace in the near future.

Dynamic Performance Evaluation of Various GNSS Receivers and Positioning Modes with Only One Flight Test

The performance of global navigation satellite system (GNSS) receivers in dynamic modes is mostly assessed using results obtained from independent maneuvering of vehicles along similar trajectories at different times due to limitations of receivers, payload, space, and power of moving vehicles. However, such assessments do not ensure valid evaluation because the same GNSS signal environment cannot be ensured in a different test session irrespective of how accurately it mimics the original session. In this study, we propose a valid methodology that can evaluate the dynamic performance of multiple GNSS receivers in various positioning modes with only one dynamic test. We used the record-and-replay function of RACELOGIC’s LabSat3 Wideband and developed a software that can log and re-broadcast Radio Technical Commission for Maritime Services (RTCM) messages for the augmented systems. A preliminary static test and a drone test were performed to verify proper operation of the system. The results show that the system could efficiently evaluate the performances of stand-alone, differential GNSS, and real time kinematics positioning for three GNSS receivers in two different positioning modes by repeatedly re-radiating the recorded signals acquired through only one flight. Our proposed system is expected to be useful in evaluating dynamic navigation performance accurately and conveniently in a valid manner.

Assessment of Ionospheric Gradient Impacts on Ground-Based Augmentation System (GBAS) Data in Guangdong Province, China

Ionospheric delay is one of the largest and most variable sources of error for Ground-Based Augmentation System (GBAS) users because inospheric activity is unpredictable. Under normal conditions, GBAS eliminates ionospheric delays, but during extreme ionospheric storms, GBAS users and GBAS ground facilities may experience different ionospheric delays, leading to considerable differential errors and threatening the safety of users. Therefore, ionospheric monitoring and assessment are important parts of GBAS integrity monitoring. To study the effects of the ionosphere on the GBAS of Guangdong Province, China, GPS data collected from 65 reference stations were processed using the improved “Simple Truth” algorithm. In addition, the ionospheric characteristics of Guangdong Province were calculated and an ionospheric threat model was established. Finally, we evaluated the influence of the standard deviation and maximum ionospheric gradient on GBAS. The results show that, under normal ionospheric conditions, the vertical protection level of GBAS was increased by 0.8 m for the largest over bound σvig (sigma of vertical ionospheric gradient), and in the case of the maximum ionospheric gradient conditions, the differential correction error may reach 5 m. From an airworthiness perspective, when the satellite is at a low elevation, this interference does not cause airworthiness risks, but when the satellite is at a high elevation, this interference can cause airworthiness risks.