Using Metek Multi-Path Anemometers in Eddy Covariance Systems

Printable PDF: Using Metek Multi-Path Anemometers in Eddy Covariance Systems


Download this content as a pdf that can be saved to your computer or printed.

This document describes how to use the Metek Multi-Path Class A and Cage sonic anemometers in LI-COR eddy covariance systems. The topics covered are installing the anemometer at your site, connecting the anemometer to the SmartFlux 2 or 3 System, and configuring the software for the eddy covariance site.

Important: Be sure to read and understand the documentation provided with the sonic anemometer.

Table 1‑1. Power and data cables to connect Metek anemometers with the SmartFlux Systems.
Cable Type Length Part Number
Cage Data and Power 5 m 7900-482-5
Cage Data and Power 25 m 7900-482-25
Cage Data and Power 50 m 7900-482-50
Class A Data and Power 5 m 7900-492-5
Class A Data and Power 25 m 7900-492-25
Class A Data and Power 50 m 7900-492-50
USB to RS-232/RS-485 1.8 m 392-16348

Installing the anemometer and analyzer

Metek anemometers can be mounted to a horizontal cross-arm with a crossover fittings and post hardware.

Figure 1‑1. The Metek Cage anemometer (left) is mounted with a crossover fitting (part number 7900-334). The Class A anemometer (right) is mounted with the mounting kit (part number 7900-336).

Orientation, horizontal offsets, and vertical offset

Mount the anemometer with the north spar (for cage models) or the opening (for Class A models) facing magnetic north, then rotate it so that one spar is oriented downwind from the prevailing wind direction. Measure and record the north offset and height.

Figure 1‑2. Overhead view of Cage (top) and Class A (bottom) anemometers. The north offset is the degrees of clockwise rotation past magnetic north.
  • North offset (°): The degrees of rotation from magnetic north.
  • Height (m): The distance between the ground and the center of the anemometer sample volume.

Horizontal separation distances (Figure 1‑3) are measured in a Cartesian coordinate system, which EddyPro® uses to determine the distance between the gas sample and the anemometer. The center of the anemometer is the center (0, 0) of the coordinate system. Distances from the anemometer are provided along the north-south and east-west axes. The sensor head or air inlet should be 10-20 cm from the anemometer in the horizontal plane.

Figure 1‑3. Overhead view of Cage (top) and Class A (bottom) anemometers. Horizontal separation distances are cm east-west and north-south from the anemometer sample midpoint.

For deployments that are close to a plant canopy, the center of the analyzer and sonic anemometer should be at equal heights, as shown in Figure 1‑4. If mounted over 15 m above ground level, horizontal and vertical sensor separation can be as large as 30-50 cm. Measure and record the horizontal and vertical separation distances.

Figure 1‑4. Vertical separation (0 cm in the illustration) If non-zero, measure the distance and record it.
  • Northward Separation (cm): North (positive values) or south (negative values) distance between the sample path or intake and the anemometer.
  • Eastward Separation (cm): East (positive values) or west (negative values) distance between the sample path or intake and the reference anemometer.
  • Vertical Separation (cm): Vertical distance between the sample path or inlet and the reference anemometer. Negative if the center of the analyzer or the inlet is below the center of the reference anemometer sample volume; positive if the inlet is above.

Connecting to the SmartFlux 2 or 3 System

The Metek Cage and Class A anemometers are automatically configured by the SmartFlux System when connected and powered on. The anemometer cable connects to port 1, 2, or 3 on the SmartFlux System (port 1 shown). Port 1 accepts 11-pin and 9-pin terminal strips. Ports 2 and 3 accept 9-pin terminal strips.

Important: Disconnect the power supply to the SmartFlux System before connecting anemometer cables.

SmartFlux Terminal # SmartFlux Label Wire color
9 RS-422/485 RX- Green
8 RS-422/485 RX+ Yellow
7 RS-422/485 TX- Brown
6 RS-422/485 TX+ White
2 Power Out - Pink
1 Power Out + Gray
Figure 1‑5. Wiring the Metek Class A MP (left) or Cage MP (right) anemometer to the SmartFlux System. The Class A has weatherproof electronics box between the head and SmartFlux System. For both anemometers, the wind-sensing components can be powered through the SmartFlux System.

Powering the heater from the biomet enclosure

Heaters are powered by the system power supply, typically.

Heater Wire Color Connects to
Power GND Black | Purple Terminals 1 to 3
Power (+24 VDC) Blue | Red Terminals 5 to 7
Ground   System ground

Important: Refer to the Metek MP instruction manuals for details about operating the heater in low-voltage and over-voltage conditions.

Figure 1‑6. The Class A (left) or Cage (right) anemometer and SmartFlux System are joined with the gas analyzer using a network switch.

Configuring the eddy covariance system

Several things need to be configured in software before your system will log valid eddy covariance data sets. These are described below.

Enter sonic anemometer information

In the gas analyzer PC software, click Site Setup > Sonic Anemometer tab, and select Anemometer connected to a digital port on the SmartFlux 2 or 3 System.

  • Port: The port on the SmartFlux system that the anemometer is connected to (1 in this example).
  • Manufacturer: Metek.
  • Model: Class A MP or Cage MP.
  • Serial Number: Optional, the anemometer serial number.
  • Software Version: Optional, the anemometer software version.
  • Wind Data Format: U, V, W is the only option.
  • North Offset: Degrees clockwise of magnetic North. Measured at the site (see Figure 1‑2).
  • Height: Distance of the anemometer sample volume above the ground. Measured at the site.

Enter gas analyzer information

The following information is required:

Additional system settings

Although not related to the sonic anemometer, configure the following settings to finish configuring the eddy covariance system. Under Site Setup > USB Log File > USB Log File Options, set the following:

  • Log Rate (Samples per Second): 10.0 (or higher).
  • File Duration: 30 minutes.

Under Site Setup > Site Description, set the following:

  • Site Name: A name of your choice.
  • Station Name: A name of your choice.
  • Canopy Height (m): The distance between ground level and the top of the plant canopy.
  • Check Use SmartFlux GPS coordinates.

At this point, you've configured the minimum required settings to log complete eddy covariance data sets with an LI-7500A/RS/DS. There are additional settings to configure if you are using an LI-7200/RS, a biomet system, or an LI-7700, or if you want to process data using EddyPro Advanced settings. These are described in corresponding product documentation.