From the arctic tundra to the arid deserts, the LI-7500RS is designed for the most demanding environments.

Stability and Drift Resistance

The accumulation of dust, pollen, chemical residues, and other contaminants on optics of open-path gas analyzers can lead to measurement drift and cause gaps in datasets. Typically, this is not a problem when an instrument is regularly maintained. If an instrument is not maintained, however, there is risk that the accumulation will affect measurements.

Innovations to the optics and electronics ensure that the LI-7500RS collects more accurate and dependable data—even as contaminants begin to accumulate on the optics.

Experimental data from 13 instruments at numerous sites with a wide range of contamination levels consistently show that the LI-7500RS provides significantly more stable measurements than the LI-7500A. Figures 1 and 2 show contamination-related drift data from an urban site adjacent to heavy road traffic.

Figure 1. CO2 measurements from three LI-7500RS analyzers and three LI-7500A analyzers (average and spread). The y-axis shows the deviation from a control reference. CO2 measurements from the LI-7500RS analyzers drifted considerably less and had smaller instrument-to-instrument variability than those from the original LI-7500A models. Data show the typical improvement expected from the LI-7500RS analyzer.
Figure 2. Water vapor measurements from three LI-7500RS analyzers and three LI-7500A analyzers (average and spread). The y-axis shows the deviation from a control reference. Measurements from the LI-7500RS analyzers drifted several times less, and had smaller instrument-to-instrument variability when compared with original LI-7500A models.

Minimized Flow Distortion

In eddy covariance systems, airflow distortion can occur when a gas analyzer is inside or too close to the sonic anemometer path. If the gas analyzer is too close, it can disrupt airflow before wind enters the anemometer, leading to errors in the computation. If it is too far away, the instruments will sample different eddies, which also leads to errors.

The LI-7500RS can be positioned at the ideal distance from the anemometer, either down wind or under it. This makes it possible to minimize wind flow distortion and maximize frequency response, ensuring that flux results are minimally affected by flow distortion.

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