Standard Guide for Mixing Layer Height Determination by Laser-Based Ceilometer

Abstract

5.1 Ceilometers are devices used by national weather services, regulators, and researchers around the globe to determine the cloud base altitude by means of a backscattered light beam. Cloud base altitude is defined as the base height of the lowest opaque cloud layer (1).3 The ceilometer light source is based on laser technology; therefore, it is a type of atmospheric lidar instrument. Lidar is the acronym for light detection and ranging, and was developed as a remote sensing technique after the invention of lasers in the 1960s (2). 5.2 Lidars are used to precisely measure distances and properties of distant objects. The performance of a ceilometer as a type of lidar system relies on how efficiently a photon can travel through the atmosphere and return to its point of origin due to aerosol backscattering. Having a time-sampling period adjustable over a wide range and adjustable height-sampling intervals, the ceilometer can provide observations on the vertical structure of the planetary boundary layer. 5.3 The instrument’s high temporal and spatial resolution are especially helpful in aerosol (particle pollution) and cloud studies when investigating the evolution of specific layers in the atmosphere since significant changes in atmospheric properties can occur over periods of a minute or less and over distances of tens of meters. Using lidar as a remote sensing tool includes the unobtrusive nature of the probing, which does not contaminate the measured parcel of air, and the option of integrating layer-specific stratified data into column density information. Ceilometers, as laser instruments, have potential safety issues that can be addressed through existing standards, such as IEC criteria for electronic systems, and should comply with national and regional safety regulations.