This module will address the RS ET errors, testing and field data validation. The module assumes particular importance as the focus of the webinars will be: on the source of errors encountered in RS ET determinations and relative significance; the way to mitigate these errors and reduce biases; the challenges to benchmark, validate and calibrate the RS ET algorithms; the limitations of using field data for RS ET testing; the benefits of CIMEC (‘Calibration using Inverse Modelling of Extreme Conditions’) approaches to reduce impacts of bias in energy balance components.