Integrates with LI-COR Eddy Covariance Systems

The LI-7700 integrates easily with LI-COR eddy covariance systems without requiring any additional components. Using GPS clocks and the Precision Time Protocol (PTP), methane data are synchronized with wind speed and other measurements with sub-microsecond accuracy. Methane fluxes are computed on the SmartFlux® System at the same time as CO₂ and H₂O fluxes.

For other applications, the LI-7700 can be ordered with the optional LI-7550 Analyzer Interface Unit, which provides analog, RS-232 serial, and SDM data outputs, as well as other functions.

The LI-7700 instrument

How it works

The only open path methane analyzer designed for field deployment in eddy covariance systems, the LI-7700 features innovations that ensure high performance, low-maintenance operation in the most demanding environments. A technological marvel, the LI-7700 maintains accuracy over a wide range of temperature and pressure fluctuations. The LI-7700 is capable of 40 measurements per second.

Wavelength Modulation Spectroscopy

The LI-7700 optical source is a single-mode tunable near-infrared laser, which operates at ambient temperature. Using Wavelength Modulation Spectroscopy (WMS), the laser scans across a single absorption feature of methane with high resolution. The wavelength is modulated across the absorption band at sub-MHz frequency. The LI-7700 demodulates the resulting signal at twice the modulation frequency. It compares the demodulated signal to a reference signal shape to determine CH₄ concentration.

Pressure- and temperature-induced changes in line shape and population distribution, as well as changes in laser power and mirror reflectivity, are compensated using computational fitting algorithms. This ensures that measurements remain accurate over a wide range of pressure and temperature conditions.

Specifications