The city of Amersfoort wants to investigate apparent temperature (temperature equivalent perceived by humans) and heat stress. To determine apparent temperature, multiple measurements have to be combined: air temperature, humidity, wind and solar irradiance. The apparent temperature monitoring service will be calculating the apparent temperature based on the best available information from sensors. A relatively dense network of temperature and humidity sensors was installed and has been operated by a citizen initiative ‘Meet je Stad’ (Measure your City) since 2017. As these sensors have been hand built at costs as low as possible, the accuracy of the sensors is limited. In order to use the data for calculating apparent temperature, the time series have to be validated and corrected. # Data collection There is a harvester which periodically downloads meteorological information from the Measure your City website. This data is harmonized according to the FIWARE data model “Weather observed”. Variables collected are temperature (degrees Celsius), relative humidity (percentage) and, depending on the type of sensor, illuminance (Lux).