The Global Positioning System

GPS, the Global Positioning System, will rapidly become the most widely used radionavigation system in the world when it becomes operational later in this decade. The advantages of GPS (e.g., excellent accuracy, worldwide availability, all-weather performance, and operational simplicity) will assure its rapid acceptance, and the large market thus generated will assure many equipment choices and attractive prices. This paper describes the current GPS development status, including an evaluation of the progress being made toward full deployment. The paper next explores the surprising number of interim GPS applications making use of the present constellation of test and evaluation Navstar satellites. Differential GPS, which can provide navigational accuracy of five meters in local areas, will be evaluated and progress toward standardization of signal formats discussed. Finally, this paper looks toward the future, projecting when GPS will be ready for widespread use and predicting some of the types of equipment which will be available

The Navy Navigation Satellite System: Description and Status

TRANSIT, the Navy’s Navigation Satellite System, has been in continuous operation since January 1964, but only a very limited number of shipboard prototype navigation sets have been available. Production equipment is just now becoming available, both for military and for commercial applications, and the months ahead will see greatly expanded use of the system. This paper describes the overall system, with emphasis on the user’s equipment, compulation requirements, and accuracy considerations. A look is also taken into the system’s future, including expanded applications

Forest–savanna–<i>morichal</i> dynamics in relation to fire and human occupation in the southern Gran Sabana (SE Venezuela) during the last millennia

The southern Gran Sabana (SE Venezuela) holds a particular type of neotropical savanna characterized by the local occurrence of morichales (Mauritia palm swamps), in a climate apparently more suitable for rain forests. We present a paleoecological analysis of the last millennia of Lake Chonita (4°39′N–61°0′W, 884 m elevation), based on biological and physico-chemical proxies. Savannas dominated the region during the last millennia, but a significant vegetation replacement occurred in recent times. The site was covered by a treeless savanna with nearby rainforests from 3640 to 2180 cal yr BP. Water levels were higher than today until about 2800 cal yr BP. Forests retreated since about 2180 cal yr BP onwards, likely influenced by a higher fire incidence that facilitated a dramatic expansion of morichales. The simultaneous appearance of charcoal particles and Mauritia pollen around 2000 cal yr BP supports the potential pyrophilous nature of this palm and the importance of fire for its recent expansion. The whole picture suggests human settlements similar to today – in which fire is an essential element – since around 2000 yr ago. Therefore, present-day southern Gran Sabana landscapes seem to have been the result of the synergy between biogeographical, climatic and anthropogenic factors, mostly fire