Laser Beam Ceilometer Comparisons March 1998–April 1999

The Automated Surface Observing System (ASOS) uses the Vaisala CT12K laser beam ceilometer for cloud height detection up to 12,000 feet. Because the CT12K ceilometer is out of production and will only be maintained by Vaisala until 2005, the National Weather Service (NWS) ASOS Planned Product Improvement (PPI) Program has been exploring new cloud height detection technologies. Laser beam ceilometers that can measure clouds as high as 25,000 feet (25K) were acquired for comparison with the CT12K ceilometer.

An intensive ceilometer performance evaluation began on March 2, 1998 and ended on April 19, 1999. Twenty-five thousand foot ceilometers from three manufacturers were under test and evaluation at Sterling, Virginia. Performance statistics focused on cloud heights below 12,000 feet with special emphasis on ceiling layers around the Instrument Flight Rules (IFR) and Marginal Visual Flight Rules (MVFR) criteria. The test results indicated that the 25K ceilometers attained as much as a 15% improvement over the CT12K ceilometer at IFR and MVFR ceiling heights when compared to ceiling light and pilot balloon observations.