Determination of GPS orbits to submeter accuracy

Orbits for satellites of the Global Positioning System (GPS) were determined with submeter accuracy. Tests used to assess orbital accuracy include orbit comparisons from independent data sets, orbit prediction, ground baseline determination, and formal errors. One satellite tracked 8 hours each day shows rms error below 1 m even when predicted more than 3 days outside of a 1-week data arc. Differential tracking of the GPS satellites in high Earth orbit provides a powerful relative positioning capability, even when a relatively small continental U.S. fiducial tracking network is used with less than one-third of the full GPS constellation. To demonstrate this capability, baselines of up to 2000 km in North America were also determined with the GPS orbits. The 2000 km baselines show rms daily repeatability of 0.3 to 2 parts in 10 to the 8th power and agree with very long base interferometry (VLBI) solutions at the level of 1.5 parts in 10 to the 8th power. This GPS demonstration provides an opportunity to test different techniques for high-accuracy orbit determination for high Earth orbiters. The best GPS orbit strategies included data arcs of at least 1 week, process noise models for tropospheric fluctuations, estimation of GPS solar pressure coefficients, and combine processing of GPS carrier phase and pseudorange data. For data arc of 2 weeks, constrained process noise models for GPS dynamic parameters significantly improved the situation

China and the Global Market for Forest Products: Transforming Trade to Benefit Forests and Livelihoods

China's spectacular economic growth over the last decade is having a dramatic impact throughout the world. It has become a leading nation in terms of its demand for forest products, and its influence is being felt as far afield as Cameroon and Cambodia, Indonesia and the United States. Burgeoning domestic consumption, in a nation with very limited per capita forest resources, has fueled the rapid rise in China's imports of forest products. Growing demand in the US, Europe and elsewhere for low-cost wood products manufactured in China has also contributed to the country's ever-increasing demand for foreign timber. China has rapidly become the wood workshop of the world, capturing almost a third of the global trade in furniture over the last eight years. In many supplier countries, particularly those with weak governance records, the increasing trade flows into China are associated with unsustainable harvesting, illegal logging and the abuse of forest communities' rights. However, China's growing demand also creates the possibility that millions of low-income forest producers can benefit from this new market. Trees and forests are the primary asset of millions of the world's poorest people and when governments enable the poor to use them wisely, they can be an important instrument of rural development. China is now in the world's spotlight, with governments, industry and development agencies eager to learn more about the global impact the country is having on forests and forest industries. Until recently, they have been hampered by a scarcity of reliable information and a lack of rigorous, publicly accessible analysis of macro-level trends. The primary source of market information to date has been proprietary analysis, the costs of which have precluded their use by all but the largest international investors and trade associations. This paper and the body of research it represents aims to help fill the knowledge gap. It is an overview of the key findings of many research studies conducted by Forest Trends, the Center for Chinese Agricultural Policy (CCAP), the Center for International Forestry Research (CIFOR) and their many partners in China and the Asia-Pacific region. As an overview, it necessarily focuses on broader and more globally critical issues. The synthesis of this research presents a wake-up call for the global forestry community. One of our key findings is that domestic and export demand for Chinese manufactured wood products will continue to grow dramatically, at least over the medium term and probably well beyond. So, in turn, will the demand for both home-grown and imported timber. Furthermore, China should be seen as the harbinger of even greater change, as India and other populous developing countries increase their demand for forest products. It is now clear that the global forest market is undergoing dramatic changes, and that these changes have important implications for forests, forest people and industry globally. We hope this paper helps governments, industry and civil society gain a clearer understanding of their respective roles in the global timber market. It is also hoped that it will help them to take an important leadership role in helping to transform the forest products market to one that not only ensures sustainable forestry and conservation, but to one that provides satisfactory livelihood opportunities for forest dependent communities, and promotes sustainable economic development for all nations

First Epoch Geodetic Measurements with the Global Positioning System Across the Northern Caribbean Plate Boundary Zone

The first geodetic survey across the northern Caribbean plate boundary zone with the Global Positioning System (GPS) was conducted in June 1986. Baseline vectors defined by the six station regional GPS network ranged from 170 to 1260 km in length. Repeatability of independent daily baseline estimates was better than 8 mm plus 1.3 parts in 108 of baseline length for horizontal components. The wet tropospheric path delay during the experiment was both high, sometimes exceeding 30 cm at zenith, and variable, sometimes exceeding 5 cm variation over several hours. Successful carrier phase cycle ambiguity resolution (“bias fixing”) could not be achieved prior to construction of a regional troposphere model. Tropospheric calibration was achieved with water vapor radiometers at selected sites, and with stochastic troposphere models and estimation techniques at remaining sites. With optimum troposphere treatment and single-day orbital arcs, we resolved most biases on baselines up to about 550 km in length. With multiday orbital arcs we resolved most biases in the network regardless of baseline length. Our results suggest that constraints on plate boundary zone deformation in the Greater Antilles, and on the North America-Caribbean relative plate motion vector, can be obtained with a series of GPS experiments spanning less than 10 and 15 years, respectively

The China forest products trade: overview of Asia-Pacific supplying countries, impacts and implications

Over 70 % of China's timber product imports are supplied by countries in the Asia Pacific region, and China is the dominant forest product market for many of these countries. Unsustainable harvesting practices, illegal logging, and negative impacts on community livelihoods plague many of these supplying countries. The countries may be divided into those still harvesting and exporting timber from natural forests on a large scale and those which have gone past their highest levels of natural forest timber harvesting and are now more aggressively pursuing plantation development and processing. Apart from Russia, China's top Asia Pacific timber suppliers could at best maintain current supply, with natural forest resources being depleted in less than 20 years. Resource limits also constrain expansion and/or long-term continuation of processed product export to China. Greater attention and action on the part of governments, market leaders, and international organizations is needed to address negative impacts, shifting supply to a sustainable, legal, and equitable basis and to determine from where China's long-term supply will come

The China forest products trade: Overview of Asia-Pacific supplying countries, impacts and implications

Over 70 % of China’s timber product imports are supplied by countries in the Asia Pacific region, and China is the dominant forest product market for many of these countries. Unsustainable harvesting practices, illegal logging, and negative impacts on community livelihoods plague many of these supplying countries. The countries may be divided into those still harvesting and exporting timber from natural forests on a large scale and those which have gone past their highest levels of natural forest timber harvesting and are now more aggressively pursuing plantation development and processing. Apart from Russia, China’s top Asia Pacific timber suppliers could at best maintain current supply, with natural forest resources being depleted in less than 20 years. Resource limits also constrain expansion and/or long-term continuation of processed product export to China. Greater attention and action on the part of governments, market leaders, and international organizations is needed to address negative impacts, shifting supply to a sustainable, legal, and equitable basis and to determine from where China’s long-term supply will come