LI-COR LI-7700 Open Path CH4 Analyzer - Sigmatech Inc. Philippines

Open Path CH4 Analyzer

LI-7700

The LI-7700 Open Path CH₄ Analyzer features an open sample path that measures methane density in ambient air.

Features

The LI-7700 is designed specifically for eddy covariance flux measurements to evaluate methane emissions from the terrestrial landscape. It provides low-maintenance long-term operation in demanding field deployments.

Low power consumption: Draws 8 watts of power nominally, making it ideal for use with solar power supplies in remote locations.

Improved optics and temperature controls increase long-term stability and reduce drift—even when the instrument is not cleaned for weeks at a time.

Logs complete eddy covariance data sets—including wind speed measurements from a sonic anemometer and supporting meteorological, radiation, and soil data from a LI-COR Biomet System.

Heated mirrors reduce condensation on optics, which prevents data loss during humid conditions.

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.

LI-7700 Wavelength Modulation Spectroscopy

Components

Included Component

Washing Unit

Standard with each LI-7700, the washing unit includes a washer fluid reservoir, pump, spray nozzle, tubing, and power cable for the washer. The washing unit provides the self-cleaning capability for the lower mirror.

Optional Component

LI-7550 Analyzer Interface Unit

The LI-7550 Analyzer Interface Unit expands the data storage and output options of the LI-7700, including analog, RS-232 serial, and SDM output to use the LI-7700 with Campbell® Scientific, Inc. systems.

Performance

The following data are excerpts from a poster presented at AmeriFlux in 2011.

View the Full Poster

Frequency response

Spectral and co-spectral analysis is a powerful tool to evaluate the performance of an eddy covariance flux system—more specifically, the performance of the sonic anemometer and the gas analyzer. As shown, the normalized power spectrum of the LI-7700 follows the theoretical curve, indicating the LI-7700 has sufficient resolution and response time for eddy covariance flux measurements.

Zero-flux test: ensemble averaged hourly flux, Nebraska

The data are from a methane eddy-covariance flux system at a zero-flux site. Chamber-based soil methane emission measurements over a few years at this site show no methane emission.

For additional information on the performance of the LI-7700, see the following publications:

McDermitt D., G. Burba, L. Xu, T. Anderson, A. Komissarov, B. Riensche, J. Schedlbauer, G. Starr, D. Zona, W. Oeschel, S. Oberbauer, and S. Hastings, 2010. A new low-power, open-path instrument for measuring methane flux by eddy covariance. Applied Physics B: Lasers and Optics, 102: 391-405.

Matteo D., J. Verfaillie, F. Anderson, L. Xu, D. Baldocchi. 2011. Comparing laser-based open- and closed-path gas analyzers to measure methane fluxes using the eddy covariance method. Agricultural and Forest Meteorology, 151: 1312-1324.

Specifications

LI-7700 Specifications

Resolution (RMS noise): 5 ppb @ 10 Hz and 2000 ppb CH₄
Measurement Range: 0 to 25 ppm @ -25 °C, 0 to 40 ppm @ 25 °C
Data Communication: Ethernet (up to 40 Hz)
Detection Method: Wavelength Modulation Spectroscopy 2f detection
Linearity: Within 1% of reading
Operating Pressure Range: 50 to 110 kPa
Output Bandwidth: up to 20 Hz
Operating Temperature Range: -25 to 50 °C
Power Requirements: 10.5 to 30 VDC
Power Consumption: 8 W nominal, 16 W during cleaning cycle
Dimensions:
- Sensor: 14.33 cm dia (5.64 inches), 82.8 cm height (32.6 inches)
- Optical Path: 0.5 m physical path (1.65 ft), 30 m measurement path (98.4 ft)
Weight: 5.2 kg (11.5 lbs)
User Interface: Windows®based software supports all setup, configuration, and calibration functions through Ethernet connection

7700-101 Mirror Cleaner Specifications

Pump Operating Temperature Range: -10 °C to 50 °C
Weight: 3.2 kg (7 lbs)
Dimensions: 44.5 × 32.8 × 15 cm (17.5 × 12.9 × 6 inches)
Fluid Capacity: 4 liters (1.1 U.S. Gallon)

LI-7550 Specifications

Data Storage: Removable USB Storage Device. 16 Gigabyte Provided (expandable with user supplied Industrial Grade USB Flash Drive)
Data Communication:
- Ethernet: up to 40 Hz
- Synchronous Devices for Measurement (SDM): up to 33.3 Hz
- RS-232: 57,600 baud, 20 records per second max.
- DAC: 0-5 V, 40 Hz
Bandwidth: Up to 20 Hz
Inputs: Ethernet, 4 analog inputs, differential ±5 V, 16 bit
Operating Temperature Range: -25° to 50° C
Power Requirements: 10.5 to 30 VDC
Power Consumption: 10 W nominal
Dimensions: 35 × 30 × 15 cm (13.8 × 12 × 6 inches) external dimensions
Weight: 4.4 kg (10 lbs)

Specifications subject to change without notice.

Downloads

Publications and Posters

See publications that use LI-COR eddy covariance analyzers.

Get the Publications List

Posters

Using Flux Measurements for Immediate Societal Benefits
Burba, G., 2022. Using Flux Measurements for Immediate Societal Benefits. American Geophysical Union Fall Meeting, Chicago, Illinois, 12-16 December.

2155 Past & Present Eddy Covariance Measurement Locations, & Still Counting
Burba G., 2019. Illustrative Maps of Past and Present Eddy Covariance Measurement Locations: II. High-Resolution Images. Retrieved August 6, 2019, www.researchgate.net 9 pp. DOI: 10.13140/RG.2.2.33191.70561

Tovi, New Software for Flux Data Analysis: from Gap Filling to Flux & Footprint Partitioning
G. Burba, I. Begashaw, A. Forgione, N. Franken, F. Griessbaum, P. Isaac, D. Johnson, J. Kathilankal, A. McQuistan, A. Parkinson, M. Sun, A. Templeton, L. Woodford, and G. Fratini, 2019. Tovi, New Software for Flux Data Analysis: from Gap Filling to Flux & Footprint Partitioning. European Geosciences Union General Assembly, Vienna, Austria, 07-12 April.

Eddy Covariance flux errors due to synchronization issues during data acquisition
Gerardo Fratini, Simone Sabbatini, Kevin Ediger, Brad Riensche, George Burba, Giacomo Nicolini, Domenico Vitale, and Dario Papale, 2019. Eddy Covariance flux errors due to synchronization issues during data acquisition. European Geosciences Union General Assembly, Vienna, Austria, 07-12 April.

Investigation on the Importance of Fast Air Temperature Measurements in the Sampling Cell of Short-Tube Closed-Path Gas Analyzer for Eddy Covariance Fluxes
James Kathilankal, Gerardo Fratini, George Burba, 2014. American Geophysical Union Fall Meeting, San Francisco, California, 15-19 December.

A New Tool for Automated Data Collection and Complete On-Site Flux Data Processing for Eddy Covariance Measurements
Israel Begashaw, James Kathilankal, Jiahong Li, Kevin Beaty, Kevin Ediger, Antonio Forgione, Gerardo Fratini, David Johnson, Michael Velgersdyk, Liukang Xu, George Burba, 2014. American Geophysical Union Fall Meeting, San Francisco, California, 15-19 December.

Direct Continuous Measurements of Methane Emissions From a Landfill
George Burba, Liukang Xu, Xiaomao Lin, Jim Amen, Karla Welding, Dayle McDermitt, 2014. American Geophysical Union Fall Meeting, San Francisco, California, 15-19 December.

Expanding Spatial and Temporal Coverage of Arctic CH4 and CO2 Fluxes
Patrick Murphy, Walter Oechel, Virginie Moreaux, Salvatore Losacco, and Donatella Zona, 2013. American Geophysical Union Fall Meeting, San Francisco, California, 9-12 December.

Efficacy of Using Eddy Covariance Method for Gas and Energy Flux measurements in Disciplines and Applications beyond Micrometeorology.
Burba, G., and D. Anderson, 2011. Efficacy of Using Eddy Covariance Method for Gas and Energy Flux measurements in Disciplines and Applications beyond Micrometeorology. European Geosciences Union General Assembly, Vienna, Austria, 03-06 April. Submitted

Combining the strengths of open-path and closed-path designs into a single CO₂/H₂O gas analyzer
Burba, G., M. Furtaw, D. McDermitt, and R. Eckles, 2009. Combining the strengths of open-path and closed-path designs into a single CO₂/H₂O gas analyzer. American Geophysical Union Fall Meeting, San Francisco, California, 14-18 December.

Solution for Minimizing Surface Heating Effect for Fast Open-path CO₂ Flux Measurements in Cold Environments
Burba, G., D. McDermitt, J. Hupp, D. Anderson, and R. Eckles, 2010. Solution for Minimizing Surface Heating Effect for Fast Open-path CO₂ Flux Measurements in Cold Environments. American Geophysical Union Fall Meeting, San Francisco, California, 13-17 December.

Calculating CO₂ and H₂O Eddy Covariance Fluxes from Low-power Gas Analyzer Using Fast Mixing Ratio
Burba, G., A. Schmidt, R. Scott, J. Kathilankal, B. Law, D. McDermitt, D. Anderson, R. Eckles, M. Furtaw, and M. Velgersdyk, 2010. Calculating CO₂ and H₂O Eddy Covariance Fluxes from Low-power Gas Analyzer Using Fast Mixing Ratio. American Geophysical Union Fall Meeting, San Francisco, California, 13-17 December.

Eddy Covariance Measurements of Methane Flux at Remote Sites with New Low-Power Lightweight Fast Gas Analyzer
Burba, G., L. Xu, J. Schedlbauer, D. Zona, T. Anderson, D.K. McDermitt, S. Oberbauer, W. Oechel, A. Komissarov, and B. Riensche, 2010. . European Geosciences Union General Assembly, Vienna, Austria, 02-07 May.