The CartoDEM Version 3 Release 1 openly accessible datasets are currently the most reliable datasets for relatively plain regions in India specifically. The aim of the presented study is to evaluate ...CartoDEM with respect to two openly accessible spaceborne LiDAR datasets from two LiDAR sensors: the Advanced Topographic Laser Altimeter System (ATLAS) on board the Ice, Cloud, and Land Elevation Satellite-2 (ICESat-2) and Global Ecosystem Dynamics Investigation (GEDI) over the International Space Station (ISS). The differences and deviations were computed for CartoDEM and LiDAR footprint elevations for the two datasets, namely, ICESat-2 and GEDI. The difference values were filtered for footprints with differences between 0 and 2.5 in the DEM and LiDAR elevation values. Besides this, an overall estimate was also calculated for the elevation values obtained over the surface, i.e., the ground, as well as objects such as the trees or buildings. The RMSEs were observed to be 1.16 m and 1.74 m for the ICESat-2 and GEDI datasets for the points/footprints on the terrain, whereas when considering similar parameters for the two datasets, the RMSEs were found to be 1.78 m and 5.48 m for the ICESat-2 and GEDI footprints on the surface (terrain/object), respectively. This study reveals that CartoDEM is highly accurate in the plain regions when validated with respect to the ICESat-2 datasets, which work via the photon counting technique. Further, it was observed that ICESat-2’s performance is better than that of the GEDI mission for terrain height. Thus, it was observed that the spaceborne LiDAR datasets from ICESat-2 can be utilized for the validation of DEMs and can be useful for applications where an input to a DEM is required for engineering or modeling applications.
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
O posicionamento em tempo real por meio do emprego dos sinais de satélites foi um avanço nas navegações aérea, marítima e terrestre com o surgimento do GPS (Global Positioning System). Contudo as ...precisões horizontais e verticais de 100 m e 150 m (nível de probabilidade de 95%) alcançadas, estando a SA (Selective Availability) ativada, passaram a não ser satisfatórias para muitas aplicações e os usuários buscaram galgar outros níveis de precisões. Esforços foram investidos no chamado posicionamento diferencial DGPS (Differential GPS), o qual possibilitou obter precisões em torno de dez vezes melhores do que as do posicionamento absoluto. Posteriormente, usando-se a fase da onda portadora, conseguiu-se realizar posicionamento com maior acurácia por meio do método RTK (Real Time Kinematic), atingindo qualidade centimétrica. Na sequência, houve uma evolução para posicionamentos em rede, empregando, por exemplo, o algoritmo de VRS (Virtual Reference Station). Vários erros nas observáveis dos satélites passaram a ser modelados com uma solução de multiestações em tempo real. A partir de 2012, surgiram serviços e produtos que favoreceram o desenvolvimento do RT-PPP (Real-Time Precise Point Positioning) baseado no conceito SSR (State Space Representation). A busca da solução das ambiguidades no RT-PPP deu origem ao PPP-RTK com menor tempo de fixação das ambiguidades e convergência para a solução acurada do posicionamento. Neste artigo apresenta-se como foi a evolução do posicionamento em tempo real, algumas das aplicações no âmbito nacional e as perspectivas desta modalidade de posicionamento para o futuro.
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.
The cold case search for clandestine graves can be challenging due to the length of time elapsed since the crime and the search environment changing itself. This paper reports on a cold case search ...for “Christine”, a young girl who was reported missing in the mid-1970s in the East Midlands, UK. Once a search sub-area was determined by case reports and new intelligence in rural woodland, a police ground search proved unsuccessful. A multi-phased geoforensic search investigation, using remote sensing and UAV drones, metal detector, EM and dGPS surveys, was subsequently undertaken, with collected data processed and analysed. Results showed 36 discrete dGPS-surveyed metal detector and 3 EM priority targets to be identified which were all intrusively investigated but nothing case-relevant was found. Study implications suggest careful multi-phase remote and geoforensic investigations can give confidence in cold case no-body searches, saving police operational time and costs in such cold case investigations.
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•Present low successful detection rates for missing person cold cases.•Geoforensic surveys can assist with police historic investigations.•Remote sensing, EM, metal detector and dGPS surveys mapped specific survey area in wooded terrain.•Resulting anomalies intrusively investigated.•Cost effective confirmation of no body in search area.•Possible standard operating procedure for analogous cases.
Cooperative Positioning (CP) is considered to be a promising method for close formation flight, which can fully exploit the navigation information in a network. This work proposes a new CP framework ...based on relative position estimation and optimized belief propagation (BP), aiming to enhance the absolute positioning accuracy for low-cost UAVs. Relative estimation is used to augment the BP estimation, which can fully exploit the onboard sensors. For BP, it is widely used as a CP estimator. This work proposes an optimized BP based on vectorized message passing and message evaluation, which can make an effective balance between computational load and estimation accuracy. Simulation results show that the proposed CP framework has better estimation accuracy than traditional CP methods, and has lower computational load than the best existing non-parametric BP (NBP) method with equivalent accuracy.
In microwave design, Bayesian optimization (BO) techniques have been widely applied to the optimization of the frequency response of components and devices. The common approach in BO is to model and ...maximize an objective function over the design parameters, in order to find the optimal spectral response. Such an approach avoids the direct modeling of spectral responses, which is a challenging task for the typical data-efficient surrogate models used in BO. Simple objective functions may lead to a suboptimal solutions, while complicated objectives require more powerful and less data-efficient surrogate models. To resolve this issue, this article proposes to adopt a deep Gaussian process (DGP) to directly model all relevant <inline-formula> <tex-math notation="LaTeX">S </tex-math></inline-formula> coefficients over the frequency and the design parameter ranges of interest. Subsequently, an objective probability distribution is retrieved from the DGP model and maximized using a BO scheme. The proposed approach is tested on two suitable microwave examples and compared to the standard BO approach. Results show increased accuracy in identifying the optimal frequency response for the given design parameters and the desired objective, while maintaining high data efficiency.
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