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Publication Number: FHWA-RD-03-092
Date: May 2006
Verification of LTPP Virtual Weather Stations Phase I Report: Accuracy and Reliability of Virtual Weather Stations
Several climatic measurements are taken during the Long-Term Pavement Performance (LTPP) program. Onsite weather data are collected during the Seasonal Monitoring Program (SMP) for 63 General Pavement Studies (GPS) and Specific Pavement Studies (SPS) sections. Climatic data are also collected for 35 SPS–1, –2, and –8 sections using onsite automated weather stations (AWS). In the Information Management System (IMS) database, the climatic conditions for 880 SPS and GPS sites are estimated using data from as many as 5 nearby national weather stations. These estimates are referred to as virtual weather stations (VWS).
The study of onsite and estimated climatic data in the LTPP database can help determine the reliability and accuracy of climatic data and identify any possible discrepancies in the data. It will also help determine the quality of VWS estimates and the accuracy with which the site’s weather conditions can be estimated.
The climatic database for the LTPP program was originally developed by the Strategic Highway Research Program (SHRP) in 1992(1) and was later revised and expanded by the LTPP program in 1997.(2) The climatic data in the LTPP database were derived from the U.S. National Climatic Data Center (NCDC) and the Canadian Climatic Center (CCC) databases. For each GPS test section and SPS project site, up to five nearby weather stations were selected and used to estimate site-specific climatic conditions. These estimates are referred to as VWS. The VWS climatic data are estimated by averaging data from up to five nearby weather stations (see figure 1) using a 1/R2 weighting scheme as shown in figure 2.
Figure 1. Diagram. Schema of VWS concept.
Figure 2. Equation. Estimating climatic data.
Vm = Calculated data element for day m for the
Ri = Distance of weather station i from the pavement project site.
The monthly and yearly estimates of several climatic parameters for every LTPP section are developed and stored in several tables in the climatic module (CLM) of the LTPP database. Between 13 and 57 years of data through 1996 are available for the LTPP test sections.
The objectives of the study are to:
The project was conducted in four tasks: