NTCIP 1204 v04.26b PDF

Environmental sensor stations (ESS) include a wide array of sensors, including those that monitor weather, roadway surface, water level, and air quality conditions. These sensors are typically connected to a nearby microprocessor termed a remote processor unit (RPU). An environmental sensor station (ESS) consists of the RPU plus its suite of sensors.
Typically, this equipment is fixed or permanently located at a site along a travel corridor. In some cases, the "stations" may be portable, or even mobile. For NTCIP 1204 v04 purposes, all three types of stations are called ESS. In the transportation community, these devices are frequently used to improve roadway maintenance and traffic operations.
Environmental sensors are also frequently co-located with pavement treatment systems (PTS) and, in fact, may use the same controller. Thus, for NTCIP 1204 v04 purposes, the term ESS may also include a PTS.