A list of the upper-air sites operated by the U.S. is given in Appendix C. Pibal observations are taken mainly by Department of Defense operations in the field, and are used primarily for artillery support. 1.7.1 Network of U.S. Stations . The U.S. network of stations comprises more than ten percent of the global rawinsonde network. Regardless of the purpose for the observations, agencies that do acquire rawinsonde and pibal observations and communicate them for general use shall comply with the provisions of this Handbook. 1.7.2 Network Design and Configuration .
Many factors influence the size of the U.S. network and the locations of stations.
Operational requirements play a central role in determining the network of stations and types of observing systems needed to describe the state of the atmosphere. Budgetary realities, in terms of existing and planned appropriations, determine agencies' ability to establish and sustain operations over an extended period of time. Logistics determine the ability to supply and maintain each station on a continuing basis. Geography determines an optimum location for each station, taking into account terrain, climatology, urban development, and other physical considerations. 1.7.3 Transmission of Observations .