LI-7500 Open Path
CO2 / H2O Analyzer
The Proven Leader in
Eddy Covariance Measurements
Advantages
The LI-7500 is a high speed, high precision, non-dispersive infrared gas analyzer that accurately measures densities of carbon dioxide and water vapor in turbulent air structures. With the eddy covariance technique, these data are used in conjunction with sonic anemometer air turbulence data to determine the fluxes of CO2 and H2O.
Key Features
- Low power consumption: 10 W during normal operation
- High Speed: up to 40hz
- High Precision: 0.16 ppm CO2, .0067 ppt H2O
- Excellent stability
- Absense of tubing eliminates delays and sorption effects
- Suitable for harsh environments
A weatherproof box houses the control unit's high speed Digital Signal Processing (DSP) electronics. Serial data are output at selectable speeds of up to 20 Hz, and linearized, user-configurable Digital-to-Analog Converters (DACs) output analog signals that are updated at 300 Hz.
Eddy Covariance
The LI-7500 is designed for the eddy covariance technique. With the eddy covariance method, the flux, Fc of gas c (e.g. CO2, H2O) is given by 
where c' is the density fluctuations of the gas (mmol/m3), and w' is the vertical wind velocity fluctuations (m/s). The LI-7500 has the high speed and high precision required for this method. The flux of CO2 and H2O is obtained from the vertical wind speed (measured with a sonic anemometer) and the concentration of the gas (measured with the LI-7500).
Advantages of the LI-7500 for Eddy Covariance Measurements
- LI-7500 integrates easily with any fast sonic anemometer (ATI, CSI, Gill, Kaijo, Metek, RM Young).
- Basic station (LI-7500, sonic anemometer, and datalogger) requires 20 W or less. Can be powered by solar panel and batteries, or a household generator.
- Basic station (LI-7500, sonic anemometer, and datalogger) is below 20 lbs.
Applications
Scientists have used the LI-7500 to measure CO2 and H2O flux and density over many environments, including natural and agricultural ecosystems, urban areas, and water bodies. Ecosystems commonly measured include grasslands, deciduous forests, tropical environments, scrublands, deserts, wetlands, and others.
Wetlands: In wetland ecosystems, where access to mains power is often limited, the low power and low maintenance features of the LI-7500 make it an obvious choice for CO2/H2O density measurements.
Urban Flux: Urban environments occupy a significant and growing portion of Earth’s surface. CO2/H2O flux from urban ecosystems cannot be ignored. The LI-7500 is ideally suited for these applications with its excellent stability and undampened measurements. 
Learn More...
Aircraft Eddy Covariance: Scientists have mounted the LI-7500 to fixed wing and rotary-wing aircraft and successfully measured CO2 and H2O flux. Be sure to check FAA guidelines before attempting this kind of measurement. Learn More...
Agro-ecosystem Flux: Agricultural ecosystem flux varies with crop type, management regime, season, region, and many other variables. The long term stability and low power requirements make the LI-7500 an ideal instrument for these applications.
CO2 and H2O Flux over Water Bodies: Lakes, tidal zones, seas, and oceans are very relevant to the global carbon cycle. The LI-7500 is used on stationary platforms, buoys, and boats to measure CO2 and H2O flux in these environments. The low power demands and relative insensitivity to vibration make the LI-7500 an ideal instrument for these applications.
Carbon Capture and Sequestration: The eddy covariance method is an effective way to monitor large areas where CO2 may escape from the subsurface. Before attempting to detect a leak from an underground storage location, the baseline CO2 flux must be established. The LI-7500 is an excellent instrument for all stages of CCS monitoring – including pre-injection, injection, and post-injection phases. Learn More...
For considerations for measuring flux in extremely cold environments, click here.
Software
The LI-7500 has two software components: the embedded instrument firmware and the Windows® interface software. The internal firmware controls the instrument, while the Windows interface software is used to configure the LI-7500.
The intuitive, tab-based interface provides full control over instrument parameters, from instrument calibration to data output settings. With a few mouse clicks, you can easily configure the two fully-linearized DACs, SDM output, bandwidth, and time delay settings. In addition, you can set up PC data logging, view the live data stream, and examine complete diagnostic information.
World-wide Standard
The LI-7500 is the most widely used open path CO2/H2O analyzer in the world. Since its introduction in 1999, scientists have come to know that the LI-7500 provides high precision, accuracy, and stability.
The LI-7500 has been directly cited in over 1500 scientific publications. Data collected with the LI-7500 have been cited in UNFAO (United Nations Food and Agriculture Organisation) publications, IPCC Reports, and the journals Science and Nature.
References from Google Scholar™
Common Internet searches can be performed with Google, and many articles can be found with Google Scholar:
The LI-7500 is used by major flux networks around the world including...
| FLUXNET | AMERIFLUX | ASIAFLUX | FLUXNET-CANADA |
| CARBOEUROPE | EUSTACH-LBA | KOFLUX | OZFLUX |
| CHINAFLUX | GREENGRASS | CARBOMONT | Other Links: ILTER |
LI-7500 images courtesy of National University of Singapore, Princeton University, National Institute for Agro-Sciences
Ordering Information
LI-7500 Open Path CO2/H2O Analyzer
High precision and high speed analyzer for Eddy Covariance measurements. Includes Calibration Shroud, IRGA Cable (3 meters), Serial Cable and USB Adapter, DAC, Auxiliary Input, SDM Cables (4 meters), Windows® Software and Instruction Manual.
LI-7500DP Open Path CO2/H2O Analyzer Package Includes:- LI-7500 Open Path CO2/H2O Analyzer
- LI-610 Portable Dew Point Generator.
| Part No. | Description |
|---|---|
| 184-05637 | U-Bolt for 6575-033 Bracket |
| 222-01824 | Bev-a-line Tubing |
| 392-05618 | SDM Interface Cable |
| 392-05619 | Power Cable |
| 392-05620 | RS-232 Cable (to connect to external port on control box) |
| 392-05621 | Analog Input Cable |
| 392-05622 | DAC Output Cable |
| 439-04214 | 5 Amp Fast Fuse 125 V |
| 6575-033 | Control Unit Mounting Bracket |
| 7500-950 | Internal Chemical Bottles Kit (2 small bottles) |
| 9975-005 | Sensor Head Cable |
| 9975-005-06 | Sensor Head Cable, 6 meters |
| 9975-006 | Control box |
| 9975-007 | Standard Spares Kit |
| 9975-008 | Head assembly |
| 9975-012 | Calibration Tube Assembly (Shroud) |
| 9975-014 | Shroud Gasket Kit |
| 9975-015 | Cable to Connect Internal RS-232 to PC |
| 9975-016 | Standard RS-232 Cable Kit |
The LI-7500A
The updated LI-7500A builds upon the strengths of the field proven LI-7500 by reducing energy use and heat dissipation in cold environments, integrating more auxiliary data with CO2 and H2O measurements, and providing removable USB data storage. The LI-7500A is designed to provide simple set-up and reliable, long-term performance in remote areas and extreme environments.
The LI-7500A operates with the new LI-7550 Analyzer Control Unit (included) to enable the collection of synchronized eddy covariance data sets that include CO2/H2O, sonic anemometer, and auxiliary data. The LI-7550 provides 4 auxiliary inputs, versatile data outputs, and removable USB data storage at rates up to 20 Hz. This provides a new level of integration for eddy covariance systems and makes instrument setup and high speed data collection easier than ever before.
Key updates include:
- Low chopper motor housing temperature setting for use in cold climates
- Saves energy in cold environments
- Reduces dissipation of heat into the optical path
Operation with the New LI-7550 Analyzer Interface Unit
- High speed analog inputs for auxiliary sensors including a sonic anemometer
- Flexible, easily configured USB data logging at up to 20 Hz
- Ethernet connectivity – allows for remote setup and data transfer
- Longer data cables – 5 meter
- Extended sensor head cables – 5 or 10 meter
