A met tower, short for meteorological evaluation tower, is a tall structure equipped with weather instruments used to measure wind conditions at a specific site. Its primary purpose is determining whether a location has enough consistent wind to justify building a wind farm. Before a developer commits millions of dollars to installing turbines, a met tower collects at least one full year of wind data to prove the site’s energy potential to investors and lenders.
How a Met Tower Works
A met tower is essentially a tall pole bristling with sensors at multiple heights. The most important instrument is the anemometer, which measures wind speed. Most towers carry several anemometers mounted at different levels, often at 40, 60, and 80 meters or higher, to capture how wind behaves as you go up from the ground. Wind vanes sit alongside them to record wind direction. Additional sensors measure air temperature and barometric pressure, both of which affect air density and therefore how much energy a turbine can extract from the wind.
All of this data feeds into a logger housed at the base of the tower, typically recording measurements every one to ten seconds and averaging them over ten-minute intervals. The resulting dataset paints a detailed picture of wind patterns across seasons, time of day, and weather events.
Why Multiple Heights Matter
Wind speeds increase with altitude because the ground surface creates friction that slows airflow. This change in speed from one height to another is called wind shear, and it’s one of the most important things a met tower measures. Engineers use a standard formula called the power law to estimate wind speeds at turbine hub height based on measurements taken lower on the tower. The formula uses a shear exponent, typically assumed to be around 0.2, though it varies by terrain and atmospheric conditions.
Getting wind shear wrong can make or break a project’s financial projections. If the actual shear is lower than expected, the turbines at hub height will see less wind than predicted, producing less electricity and less revenue. By mounting sensors at three or more heights, a met tower lets developers calculate the real shear exponent for that specific site rather than relying on assumptions.
Tower Types and Construction
Most met towers fall into two broad categories: lattice (also called truss) towers and tubular steel towers. Lattice towers are the more common choice for wind assessment. They use a framework of steel angles bolted together, supported by guy wires anchored to the ground. They’re relatively lightweight, can be shipped in compact sections, and are often tilted up from the ground without a crane. A typical lattice met tower reaches 50 to 80 meters, though taller versions exist.
Tubular towers are sturdier and more self-supporting, but they cost more, require heavier equipment to install, and become increasingly expensive as height grows because thicker walls and wider diameters are needed. Tubular designs are more common for the turbines themselves than for temporary measurement towers. Some projects use a hybrid approach: a lattice base with a tubular upper section.
How Long Data Collection Takes
A met tower typically stays in place for at least 12 months, and often longer. One full year is the minimum needed to capture seasonal variation, since a site that’s windy in winter but calm in summer looks very different from one with steady year-round wind. Banks and investors financing wind projects generally require at least a year of on-site data before they’ll commit funding. Developers often file permits with the FAA years before their target construction date to allow time for this data collection alongside environmental reviews, land-use approvals, and financing.
Aviation Safety Requirements
Because met towers are tall, thin, and often located in rural or agricultural areas where low-altitude flying is common, they pose a real hazard to aircraft. The FAA requires that any structure exceeding 200 feet (about 61 meters) above ground level be marked or lit to make it visible to pilots. For met towers, this typically means high-visibility orange and white paint and marker balls or sleeves on the guy wires.
The FAA estimated in 2024 that marking a new met tower costs about $14,300, covering marker balls (around $2,000), sleeves ($101), installation labor, and the cost of a pre-painted tower. Dismantling a tower after the measurement campaign runs between $5,000 and $22,500, with $9,000 being the most common estimate. These aren’t trivial expenses, but they’re a small fraction of the overall cost of developing a wind project.
LiDAR as an Alternative
As modern wind turbines have grown taller, with hub heights exceeding 100 meters and rotor diameters stretching between 100 and 200 meters, building met towers tall enough to measure at those altitudes has become extremely expensive. This has pushed the industry toward remote sensing technologies, particularly LiDAR (Light Detection and Ranging). A ground-based LiDAR unit fires laser pulses into the atmosphere and measures the reflected light from tiny particles carried by the wind, calculating speed and direction at various heights without any physical tower.
LiDAR units are portable, can be deployed at sites that are difficult to access, and work well offshore where building a tower would be impractical. Studies comparing LiDAR to tower-mounted instruments have found excellent agreement in mean wind speed measurements, with correlation values above 0.99 at 40 meters. LiDAR also captures turbulence intensity more accurately than traditional cup anemometers, though it samples data at a lower frequency (1 measurement per second versus 10 for sonic anemometers on towers).
The main limitation of LiDAR is in complex terrain, such as mountainous or heavily forested areas. The technology assumes the wind field is horizontally uniform across its measurement volume. In rugged landscapes where wind flows are disrupted by ridges and valleys, that assumption breaks down, introducing larger errors. For flat or gently rolling terrain, LiDAR is increasingly accepted as a standalone measurement tool. In complex terrain, many developers still install a met tower alongside LiDAR to cross-validate the data.
What the Data Gets Used For
The wind data from a met tower feeds into nearly every decision in wind farm development. Energy production estimates, which determine whether a project is financially viable, depend directly on accurate wind speed and direction measurements. Turbine selection is influenced by the site’s turbulence characteristics and wind shear profile, since different turbine models are designed for different wind conditions. The layout of turbines across a site is optimized using wind direction data to minimize wake effects, where one turbine’s downwind turbulence reduces the output of turbines behind it.
Perhaps most critically, the data is what convinces lenders and investors to finance the project. A well-documented measurement campaign with high-quality instruments and proper calibration reduces the uncertainty in energy estimates, which directly lowers the perceived financial risk. Poor or insufficient data can increase the cost of financing or kill a project entirely.