Initial Characterization of a Compact Ceilometer for the Ameriflux Network

The development and enhancement of sensor networks to gather atmospheric data for weather and climate forecasting on large spatial and temporal scales is crucial to the advancement of our understanding of many important processes that drive such predictive models. A prime example is the height of the atmospheric boundary layer (ABL). This is an important variable as it is used to parameterize boundary layer transport in numerical weather prediction models and boundary layer effects related to fluxes and concentrations of both trace gases and aerosols in inversion models. Increased knowledge of the boundary layer structure and the diurnal evolution of its height is the goal of recent activity in Europe to establish networks of aerosol lidars and ceilometers to monitor boundary layer height, as well as other parameters. The value of these networks has led to the desire to add aerosol profiling ceilometers to the AmeriFlux network, especially to aid in regional flux monitoring efforts. Given that AmeriFlux sites utilize instrumented towers, whose automated sensors are exposed to the full range of weather and must operate often with limited electrical power, a new class of laser ceilometer is needed to add boundary layer height measurement capability to the AmeriFlux network.

We are developing an ultra-compact laser ceilometer for retrievals of both ABL height and cloud base height that is compatible with the demands imposed by the wide environmental conditions experienced by, and automated operation required of, site instrumentation throughout the AmeriFlux network. For deployment at an AmeriFlux tower site, substantial reductions in size, weight, and power, compared to existing designs, are needed. Compact size, a high degree of ruggedization, and thermal management with a very small available power budget are similar to design restrictions placed on aircraft and spacecraft payloads. Our design for a compact ceilometer considers thermo-mechanical stability and thermal management in the entire environmental envelope as the foundation for the sensor design.

In this presentation, we will review the elements of the design, including the coupled thermal, mechanical and optical modeling. The majority of the presentation will review initial characterization of the first engineering prototypes. Initial characterization includes several activities, the first of which is an intercomparison of a prototype operating locally in tandem with a commercial grade ceilometer. This work will yield system retrieval statistics and lessons learned from retrieval algorithm refinement. The second element of system characterization is accelerated environmental testing of a prototype in an environmental chamber. In these tests, a variety of optical diagnostics are used to monitor system alignment in response to temperature cycling through the required operational temperature range. Lastly, we will report on initial results arising from deployment of a prototype at an Ameriflux site and intercomparisons at the site with a commercial grade ceilometer.