Study of the performance of aids to navigation systems : phase 1, closed loop model of the process of navigation /

Final report; March 1978.

Study of the performance of aids to navigation systems : phase I, a control theory approach /

Final report; July 1978.

Use of auditory cues for wayfinding assistance in virtual environment: music aids route decision

This paper addresses the crucial problem of wayfinding assistance in the Virtual Environments (VEs). A number of navigation aids such as maps, agents, trails and acoustic landmarks are available to support the user for navigation in VEs, however it is evident that most of the aids are visually dominated. This work-in-progress describes a sound based approach that intends to assist the task of 'route decision' during navigation in a VE using music. Furthermore, with use of musical sounds it aims to reduce the cognitive load associated with other visually as well as physically dominated tasks. To achieve these goals, the approach exploits the benefits provided by music to ease and enhance the task of wayfinding, whilst making the user experience in the VE smooth and enjoyable.

Complete list of lights and other marine aids.

Mode of access: Internet.

List of lights and other marine aids.

Issued as subseries CG-162 of the U.S. Coast Guard.

Towards forecasting and mitigating ionospheric scintillation effects on GNSS

The effect of the ionosphere on the signals of Global Navigation Satellite Systems (GNSS), such as the Global Positionig System (GPS) and the proposed European Galileo, is dependent on the ionospheric electron density, given by its Total Electron Content (TEC). Ionospheric time-varying density irregularities may cause scintillations, which are fluctuations in phase and amplitude of the signals. Scintillations occur more often at equatorial and high latitudes. They can degrade navigation and positioning accuracy and may cause loss of signal tracking, disrupting safety-critical applications, such as marine navigation and civil aviation. This paper addresses the results of initial research carried out on two fronts that are relevant to GNSS users if they are to counter ionospheric scintillations, i.e. forecasting and mitigating their effects. On the forecasting front, the dynamics of scintillation occurrence were analysed during the severe ionospheric storm that took place on the evening of 30 October 2003, using data from a network of GPS Ionospheric Scintillation and TEC Monitor (GISTM) receivers set up in Northern Europe. Previous results [1] indicated that GPS scintillations in that region can originate from ionospheric plasma structures from the American sector. In this paper we describe experiments that enabled confirmation of those findings. On the mitigation front we used the variance of the output error of the GPS receiver DLL (Delay Locked Loop) to modify the least squares stochastic model applied by an ordinary receiver to compute position. This error was modelled according to [2], as a function of the S4 amplitude scintillation index measured by the GISTM receivers. An improvement of up to 21% in relative positioning accuracy was achieved with this technnique.

Generating VRS data using atmospheric models: How far can we go?

Nowadays, with the expansion of the reference stations networks, several positioning techniques have been developed and/or improved. Among them, the VRS (Virtual Reference Station) concept has been very used. In this paper the goal is to generate VRS data in a modified technique. In the proposed methodology the DD (double difference) ambiguities are not computed. The network correction terms are obtained using only atmospheric (ionospheric and tropospheric) models. In order to carry out the experiments it was used data of five reference stations from the GPS Active Network of West of São Paulo State and an extra station. To evaluate the VRS data quality it was used three different strategies: PPP (Precise Point Positioning) and Relative Positioning in static and kinematic modes, and DGPS (Differential GPS). Furthermore, the VRS data were generated in the position of a real reference station. The results provided by the VRS data agree quite well with those of the real file data.

Otimização da distância de extração de madeira com forwarder

The activities and management operations of wood harvesting do not have good computational tools available to help the forest technicians with the task of cost reduction. In many cases, machines of high investment are used in wood harvesting without adequate operation planning; consequently, the cost per hour of these machines, which is high, could be reduced. Using technological resources such as the Geographic Information Systems (GIS) integrated with the Global Positioning System (GPS), which are the basis of precision harvesting. In this research, a technological tool capable of calculating and optimizing the average skidding distance of the forwarder was developed. It was used in stands of different sizes and formats through mathematical techniques and available functionalities in the Geographic Information System GRASS. The developed tool, called optimized model, divides the stand in small parts in relation to shorter skidding distances. The main variable considered was the alignment of plantation. The model was tested in eucalypt stands located in the State of São Paulo. Sixteen stands were randomly selected: eight with a rectangular polygon form, and eight with irregular polygon form. The main variables were collected in these stands. Results showed that the optimized model developed, is efficient and flexible. It was possible to divide the stands in small parts resulting in smaller skidding medium distances. The stands with irregular form had shorter skidding medium distances than the rectangular stands.

Light list.

Mode of access: Internet.

Light list.

"CG-162".

Light list.

Title varies slightly.

Sailing directions (enroute), Strait of Malacca and Sumatera /

Includes index.

Vessel bridge-to-bridge radiotelephone act : hearing before the Merchant Marine Subcommittee of the Committee on Commerce, United States Senate, Ninety-first Congress, second session, on H.R. 6971 ... H.R. 15549 ...

Mode of access: Internet.

Importância das Servidões Militares Aeronáuticas e o seu Impacto na Economia Real

As Servidões Militares Aeronáuticas (SMA) pressupõem restrições que lhes são intrínsecas, suscetíveis de impactar na Economia Real Portuguesa (ERP). Na Força Aérea (FA) as SMA denotam especial importância, em razão das constantes evolução e atualização das Operações Aéreas e tramitação legal imposta, com vista a uma minimização dos encargos restritivos dos bens que, territorialmente, lhes estão associados. Assim, salienta-se a pertinência das SMA enquanto processo que tem reflexos na ERP, uma vez serem utilizadas pela FA no processo de Licenciamento Urbano. Desta feita, foi avaliada a importância das SMA na FA, através de estudo de caso, utilizando um raciocínio hipotético-dedutivo, o qual norteou as entrevistas semiestruturadas, conceptualizadas no respetivo mapa. Estas entrevistas permitiram verificar que: a FA elabora as SMA segundo pressupostos reais e atualizados; a FA emite pareceres positivos relativos aos pedidos de licenciamento que estejam de acordo com o preconizado nos Decreto-Lei das SMA vigentes e nas respetivas áreas territoriais de aplicação; os processos de emissão de pareceres na FA podem ser melhorados concluindo-se, assim, que o processo de conceção das SMA na FA influencia o desenvolvimento da ERP. Abstract: It is assumed that the Aeronautical Control of Obstacles (ACO) imposes certain inner limitations that are susceptible to cause impact on the Portuguese Real Economy (PRE). The ACO area is of special relevance for the Portuguese Air Force (PoAF) due to the permanent evolution and update of the Air Operations and the legal procedures aimed at the decrease of the property limitations associated to them. The ACO is, therefore, of the utmost importance, considering that its process has a significant impact on PRE because of its use by the PoAF within the Building Control process. The scope of this research lies on the importance of the ACO for the PoAF. The research is based on the case study method and the hypothetical-deductive reasoning which set the guidelines for the semi-structured interviews within the conceptual framework, which made possible to verify the PoAF: develops the ACO according to real and updated assumptions; issues positive official assessments to the requests for building licensing that comply with the ACO Legal Decrees within its territorial area of applicability; process of issuing official assessments may be improved, concluding that the development of the ACO within the PoAF influences the development of the PRE.

Coast Guard aids to navigation.

Mode of access: Internet.