Frequently Asked Questions
Q What benefits for eddy covariance flux measurements does the LI‑7700 offer?
A The LI‑7700 provides in situ methane density measurements at high speeds, with high resolution and good frequency response. Since it requires no pumps or tubing, there is no impact of sorption or time delays due to tubing. With low power consumption, the LI‑7700 is the only open path methane analyzer capable of running on a basic solar power system.
Q Will the LI‑7700 be affected by condensation build up if I'm in an area with high humidity?
A The LI‑7700 has features that reduce data loss due to condensation build-up. Heated top and bottom mirrors and a radiation shield reduce or eliminate condensation on the mirrors. The radiation shield also reduces power consumption for the heated mirrors. The mirror heaters typically are configured to remain at or slightly above ambient temperatures.
Q What are the benefits of the Wavelength Modulation Spectroscopy technology used in the LI‑7700?
A Wavelength Modulation Spectroscopy (WMS) allows the LI‑7700 to measure methane at ambient pressure with a relatively short optical path length. WMS provides a highly sensitive measurement, with little sensitivity to mirror contamination. This reduces the need to keep the optics clean, making the LI‑7700 ideal for remote deployments.
Q Will I have any issues mounting the LI‑7700 on my tower?
A At just over a ½ meter tall, and weighing in at about 11 lbs (5.2 kg), the LI‑7700 should be easy to deploy on a tower. It mounts to a tower with standard mounting hardware
Q I have a remote research location with limited power, is the LI‑7700 suitable for this location?
A The LI‑7700 is designed for use in remote flux monitoring systems and engineered for long-term field deployment. Low power consumption allows the LI‑7700 to operate from a solar panel power supply. Total power consumption is under 10 Watts during normal operation and 20 Watts during the cleaning cycle.
Q Do I need any pumps or tubing for the LI‑7700?
A No, because of its open path design it does not require any pumps or tubing. This helps reduce the total amount of power needed for the instrument.
Q What happens if the mirrors get dirty while out in the field? Will I need to go clean them?
A The LI‑7700 has an automated mirror cleaning mechanism, which includes a fluid pump and a mirror spin motor that removes the cleaning solution and debris from the mirror. The mirror cleaning mechanism is user-settable to initiate cleaning cycles at a prescribed interval or based on the strength of the laser signal. When the mirror spins, the pump sprays cleaning solution onto the mirror and cleans it without requiring human intervention. WMS technology proves to be very stable even as contaminants accumulate on the mirror. This allows for extended field deployment without the need for frequent site visits to clean the optics. There will be times though when the mirror needs to be wiped off.
Q What environmental conditions is the LI‑7700 suitable for?
A The LI‑7700 is built for use in remote locations where methane flux is important — from swamps to arctic environments. The instrument features a wide operating temperature range (-25°C to 50°C.), low power requirements, and self-cleaning optics that keep mirrors free of obstructions. This combination of innovative technologies makes the LI‑7700 ideal for use in difficult and inaccessible environments.
Q How often will I have to calibrate the LI‑7700?
A LI‑COR recommends checking the instrument zero and span every six months. WMS laser based technology is very stable, with little drift over time. This reduces the need to zero or span the instrument. The LI‑7700 can be calibrated in the field.
Q What kind of data logger is necessary for measurements?
A An external data logger is not necessary if you have a direct Ethernet link from a computer to the LI‑7700 or if you are using an LI‑7550 Analyzer Interface Unit. The LI‑7550 Analyzer Interface Unit allows collection of CO2/H2O, sonic anemometer or auxiliary data. Data can be output via Ethernet or stored on a removable USB device. Additional high speed digital to analog converters, SDM, and RS-232 outputs enable integration with a variety of data storage devices.
Q How much data can be stored in the LI‑7550?
A The LI‑7550 offers onboard data storage through a removable USB drive. An industrial grade 4 GB USB flash drive is included and stores approximately 20 days of 10Hz data (logging the full compliment of data). The 4GB drive can log up to 50 days of data by logging only 10 variables. An optional 16 GB industrial grade USB flash drive is available allowing storage of up to 80 days of 10 Hz data (part number 616-10723). The LI‑7550 can also log data to a USB hard drive (>1 TB) if the drive has power supplied from an external source.