The National Weather Service’s Ceilometer Planetary Boundary Layer Project

The National Weather Service (NWS) along with the Federal Aviation Administration (FAA) and the U.S. Navy owns an extensive suite of Automatic Surface Observing System (ASOS) stations. These stations span the USA with close to 1,000 sites and monitor atmospheric surface conditions (temperature, dewpoint, wind, etc.) and cloud base levels. The NWS, FAA and Navy are in the process of updating the hardware and software for these stations as part of a Service Life Extension Program (SLEP). In that regard, the NWS's Office of Science and Technology (OS&T) and Office of Operational Systems (OOS) are investigating the potential of adding functionality to ASOS's cloud base height indicator, the Vaisala CL31 ceilometer. The OS&T NextGen Program and OOS's Sterling Field Support Center (SFSC) are collaborating with the NOAA Center of Atmospheric Sciences (NCAS) - Howard University Beltsville, MD Research Campus (HUBC), University of Maryland Baltimore County (UMBC) and others on this project.

For the test, a network of CL31 ceilometers around the Washington DC metropolitan area was assembled. The CL31 ceilometers were set up separate from other ASOS equipment at the SFSC, HUBC and the Atmospheric Research Laboratory (ARL) NOAA Center of Weather and Climate Prediction (NCWCP) campuses. At these locations, profiles of backscatter were collected for a year and used to determine PBL heights and examine data quality. High-powered LIDAR systems like the Micro Pulse LIDAR (MPL) and the Howard University Raman Lidar (HURL) as well as newer versions of the Vaisala ceilometer (CL51) were used to evaluate the quality of the backscatter data, and radiosonde soundings were used to evaluate reliability of derived PBL heights. Three PBL height algorithms were used with the CL31 ceilometers. They are Compton et al. 2013, Hicks et al. 2014 and Vaisala's BL-View algorithms.