MicroPulse DIAL (MPD)

Science motivation

Water vapor is one of the fundamental thermodynamic variables that define the state of the atmosphere. It is highly variable in space and time and influences many important processes related to weather and climate. The ability to continuously measure water vapor in the lower troposphere with high vertical resolution has been identified as a priority observation needed by the weather forecasting, atmospheric science, and climate science communities. 

Currently, radiosondes and satellite-based measurements form the backbone of observations used for weather forecasting. However the limited spatial and temporal observations prohibit forecasting of mesoscale high-impact weather events like thunderstorms. Passive sensors like radiometers can provide useful measurements or temperature and water vapor close to the surface but their coarse vertical resolution make them unsuitable to detect elevated water vapor layers; whereas, GPS receivers only provide the integrated column water vapor amount. Raman lidars and high-power water vapor Differential Absorption Lidar (DIAL) can provide the high spatial and temporal measurements of water vapor that are desired, however, they are inherently large and expensive instruments to build, operate, and maintain.

Development of the MPD testbed

Researchers at Montana State University (MSU) and NCAR/EOL have pioneered, demonstrated, and validated a micropulse, diode-laser-based, differential absorption lidar for water vapor profiling in the lower troposphere.  This development effort was initially just called by the name of the technique: Water Vapor Differential Absorption Lidar (WV-DIAL). Building on the proven design, we have developed five compact field deployable units, now called MicroPulse DIAL (MPD).  These instruments are capable of measuring water vapor in the lower troposphere with the appropriate vertical range, resolution, and measurement time needed for monitoring, verification, and data assimilation.  The five unit testbed is enabling the first tests of larger scale ground-based water vapor profiling networks.  The MPD instrument design and validation are discussed in Spuler et al. 2015 and Weckwerth et al. 2016, respectively. 

NCAR demonstrated that the same low-cost, high reliability diode-laser-based architecture can be used to build a low-cost high spectral resolution lidar (HSRL).  HSRL is distinguished from elastic backscatter lidar in that it is able to directly retrieve the optical properties of aerosols and clouds without assumptions about particle scattering properties, coupling of retrieval errors between altitude regions or significant correction factors for low altitude returns.  The diode-laser-based HSRL is ideal for aerosol and cloud characterization and is discussed in Hayman and Spuler 2017

We are actively researching temperature profiling as a further extensions to the MPD architecture.  A demonstration of the temperature profilng has been done as discussed in Stillwell et al. 2020

Example data from the RELAMPAGO field campaign