A comparison and validation of observations from three different instruments attached to moving vehicles during DOCS and the IMO study

The Demonstration of CAN-bus Study (DOCS) and the Integrating Mobile Observations (IMO) field projects were run during 2011 and 2012 through collaboration between the National Center for Atmospheric Research (NCAR), the Federal Highway Administration (FHWA), the Minnesota Department of Transportation (MnDOT), and the Nevada Department of Transportation (NDOT) for the purpose of demonstrating how weather, road condition, and other related vehicle data could be collected, transmitted, processed, and used for decision support applications and activities. As part of this study, three different external instruments attached to various heavy and light duty vehicles collected mobile observations: the Vaisala Surface Patrol HD (air temperature, relative humidity, surface temperature), the M. S. Foster & Associates RoadWatch (air temperature, surface temperature), and the Airmar LB150 (air temperature, barometric pressure, relative humidity, wind speed/direction).

In six cases, three from DOCS and three from NDOT, the instruments were mounted to the same vehicle, and the nearest Road Weather Information System (RWIS) stations were matched with vehicle location to serve as verification. Air and surface temperatures were generally within 2 – 3°C of each other and the RWIS station, although the Surface Patrol HD had occasional issues with noisy data and taking surface temperature observations on snow-covered pavement. Relative humidity was well correlated overall but biased low for the NDOT cases. Barometric pressure was typically within 3 hPa of the RWIS station. The Airmar was not able to properly correct for wind speed and direction when mounted to the vehicles. Although there were some notable issues, overall, these three external sensors were closely matched and well correlated with the nearby RWIS stations, and all three proved useful for taking air, dewpoint, and surface temperature and barometric pressure measurements on moving vehicles.