Campbell Scientific has introduced a new operating system, OS12 for the CS135 ceilometer. It is fully backwards compatible. OS12 is available free of charge.
OS12 has introduced improvements to the optical overlap correction function. This has corrected previous over-sensitivity to signal returns at very low altitudes.
This change results in the reduced detection of false, fixed-level, low cloud height reports during some types of rain and the reporting of cloud layers when there are returns from low lying layers of mist or pollution.