Calibration with measurements

In wind resource assessment and energy yield modelling, accurately representing the wind climate at your project site is critical. Whiffle Wind uses high-resolution Large Eddy Simulation to generate site-specific time series and wind resource grids that capture atmospheric dynamics such as turbulence, wake effects, and terrain-induced flow features. These detailed simulations help reduce uncertainty in wind resource estimates and provide a strong foundation for feasibility studies and energy yield predictions.

Like any numerical model, simulation output can show systematic differences when compared with on-site measurements. Minor biases in mean wind speed can become significant when translated into long-term financial projections.

Calibration is the process of identifying and adjusting these systematic differences to better align simulated data with measured observations. When applied carefully, it improves confidence in model results while preserving the physical consistency of the simulation. This article explains how to set up and run calibration in Whiffle Wind.

Good to know

Calibration is currently limited to long-term corrected measurements and long-term statistics in Whiffle Wind.

You can request a calibrated time series by setting up a simulation in Whiffle Wind and selecting Run via support on the Overview step. In the information field, indicate that you would like a calibrated time series. Alternatively, you can contact [email protected] to discuss options.

Step 1. Uploading Measurements

1. Navigate to the Measurements tab and click the “+ New measurement” button.

2. Your measurements should be a time series with 10-minute end-of-interval timestamps, including both mean wind speed and mean wind direction at each height. The data should meet the following requirements:

   • Long-term corrected wind speeds

   • Timestamps in UTC following the ISO 8601 format

   • NaN values for missing or erroneous data points

3. A template can be downloaded directly from the upload form, or you can prepare your data using the example table below:

timestamp	wind_speed_50m_mean[m_s]	wind_direction_50m_mean[deg]	wind_speed_80m_mean[m_s]	wind_direction_80_mean[deg]
2015-12-22 00:10:00	7.842	214.3	8.654	216.1
2015-12-22 00:20:00	7.961	215.7	NaN	217.4
2015-12-22 00:30:00	NaN	213.9	8.821	215.8

Notes:

• The timestamp column is required.

• Wind speed values should be in meters per second (m/s).

• Wind direction values should be in degrees (°).

Step 2. Filling in the Location and Heights

After uploading your measurements, a form will appear where you can set the name and location of the measurement.

For each column in your CSV file:

• A corresponding row will be created in the form.

• Select the type of measurement: Mean wind speed or Mean wind direction.

• Enter the height for that measurement.

Requirements:

• Exactly one wind speed and one wind direction must be provided at each height.

• Each location can have a maximum of 6 sensor heights.

• All measurements used in a simulation must have the same sensor heights.

Finally, mark the measurement as final. A finalised measurement can be used in your simulation but can no longer be edited, ensuring full traceability of your data.

Step 3. Setting Up a Simulation

1. Navigate to the Simulations tab and click “+ New simulation”. For detailed instructions on setting up a simulation, see our guide here.

2. On the Site step, open the calibration panel and select your previously uploaded measurements.

3. On the Period step, choose between Statistics and Time series. Currently, calibration is only available for Statistics. A calibrated Time series can be requested through support.

4. On the Output step, the heights for the calibrated and non-calibrated WRG will be displayed. These heights are based on the heights defined in your measurements.

5. Start the simulation. Once complete, you can download the following for each height

   • A calibrated WRG (Wind Resource Grid)

   • A non-calibrated WRG

This allows you to compare results and see the impact of calibration on your simulation outputs.

FAQ

Does calibration cost extra?

No. The cost for running a calibration is the same as a standard statistics run in Whiffle Wind.

Which method is used?

We apply an “Adjust-to-Mast” bias correction that calibrates the modelled wind resource grid to match the measured mast wind climate. For each wind-direction sector, we compute the ratio between the measured and modelled sector mean wind speed (at each mast), then apply a distance-squared (1/d²) weighted blend of those ratios to every location on the site. This results in adjusted wind speeds matching the statistics at the mast locations. The method preserves the model’s spatial patterns while removing systematic bias relative to the measurements.

What if I’m interested in a calibrated time series?

You can request a calibrated time series by setting up a simulation in Whiffle Wind and selecting Run via support on the Overview step. In the information field, indicate that you would like a calibrated time series. Alternatively, you can contact [email protected] to discuss options.