Latest Results of Field Tests of the New Open-Path and Enclosed Systems for CO2 and H2O Flux Measurements

In 2014-2015, improved open-path and enclosed-path gas analyzers were developed, based on established LI-7500A and LI-7200 models, with the focus on improving stability in the presence of contamination, refining temperature control and compensation, and providing more accurate gas concentration measurements. In addition to optical and electronic redesign, both analyzers incorporate automated on-site flux calculations using EddyPro® software run by a weatherized remotely-accessible microcomputer, the SmartFlux system. The ultimate goal of such development was to reduce errors in CO2 and H2O fluxes and in long-term carbon and water budgets.

Field tests of both systems were conducted over six periods, each 5-14 months long, at 6 sites with diverse environments, setups, and types of contamination, using 26 gas analyzers.

The open-path LI-7500RS performed significantly better than the original LI-7500A model in terms of contamination-related drifts in concentrations measurements. Improvements in CO2 drifts were strong, with RS models often drifting less than the original. Improvements in H2O contamination-related drifts were particularly significant, with modified models often drifting many times less than the original.

The enclosed LI-7200RS performed substantially better than the original LI-7200 in terms of the drifts in H2O. Improvements in CO2 contamination-related drifts were modest, being similar or just a bit better than the original.

Results from field tests suggest that both RS systems can help improve flux data coverage and likely reduce site maintenance:

-          Frequency of cleaning and site visits for service and maintenance should decrease, especially for the open-path design

-          Amount of highest quality data with smallest error bars on fluxes is expected to increase for both  open-path and enclosed-path designs

-          Amount of total data coverage over long periods of deployment should also increase substantially 

The presentation will describe details and results from field tests of these new models in comparison with older models and control reference instruments.