- Global Positioning System (GPS)
The International Institute of Tropical Forestry (IITF), USDA Forest Service, has been using the Global Positioning System (GPS) since 1992 for research activities, at both local and international levels. GPS is been use for research plot locations. Currently, new and historical research plots are being registered using GPS, documented and transferred to our Geographic Information System (GIS) database. Many years ago, the USFS established in Puerto Rico several plantations for experimental purposes (i.e., species adaptability studies, provenance studies, spacing effect on plantations, etc.). All of these plantations have now been registered-using GPS. Wildlife scientists incorporate GPS and GIS technologies as well. Radio telemetry is being used to track the Puerto Rican Boa, an endangered snake endemic to Puerto Rico. GPS and GIS are then used to study their movements, activity range, and habitat use. The pearly-eyed thrasher, a non-native, competes with Amazona vittata an endemic endangered parrot of Puerto Rico. Location of their nests, and point count sites have been located using GPS as part of the research. After Hurricane Georges struck Puerto Rico on September 21, 1998, we assessed hurricane damage on 3,758 urban trees. A total of 123 species were represented in the sample. For all trees studied we collected information on species, diameter at breast height (dbh), tree height, and type and degree of damage. All trees were located with GPS. This method allowed for a continuous study of recovery of these trees in the urban environment.
The IITF is committed to promoting urban forestry. A program has been established to encourage the community in the identification of Champion Trees. These are the biggest trees by species. Candidates are judged by their height, diameter at breast height (dbh), and crown width. All current Champion Trees have been located using GPS and mapped. At the beginning of the twentieth century Puerto Rico had lost a little more than 90% of its forest. An inventory of remnants of primary forest was done and mapped using GPS. The IITF also carries out research in remote sensing. GPS is used to collect ground-truth data for accuracy assessments, and field verifications. Within the Caribbean National Forest, there is a research area dedicated to long term and detailed watershed studies, Bisley. GPS has been used to locate water meters, meteorological stations, trails, research plots, and riverbank elevations, among others.
Another important aspect of our work scope has been with IITF’s efforts in International Cooperation. Since 1993 we have been assisting several Brazilian and Central American research agencies and institutions, with training and cooperative work in the use and applications of GPS technology for environmental and natural resources management. Also in Puerto Rico we have assisted several State Government agencies in the use and applications of GPS (Puerto Rico Telephone Company, PR Planning Board, Department of Natural Resources and the Environment, University of Puerto Rico). Our more current international work has been in the application of GPS and GIS technologies in the study of the ecology of Swietenia macrophylla (mahogany) through the establishment of permanent study plots (25 ha) across the natural range of the species.
The IITF also operates a GPS reference station. A reference station is used to improve the accuracy of GPS data collected by roving receivers. The central component of a reference station is a GPS receiver at a fixed location. Clock errors, orbital errors, and transmission delays cause differences between the known position of the reference station and the autonomous positions it calculates from GPS signals. These differences also apply to positions recorded at the same time by roving receivers within about 250 km of the reference position. Data from a roving receiver can be corrected using the reference station’s data if the rover:
- is in range,
- uses some or all of the satellites the reference station uses, and
- collects data only when the reference station is operating
The data recorded by a reference station is often referred to as ‘base data’, and a reference station may also be called a ‘base station’. Base data may be stored to disk and used later during post processing. IITF’s base data is at