Abstract: A method and apparatus are disclosed for calibrating a first sensor in a changing operating environment by a calibration process. Sensor data are received from the first sensor and sensor values are received from a known calibrating sensor. A sensor specific model is maintained for the first sensor. Calibration needs are detected by estimating a drift and an error, taking into account a difference of sensor values to the known calibrating sensor and further taking into account a sensor profile of the first sensor. A correction factor or a correction model is estimated to the sensor data using said difference and used for calibrating the sensor. The correction factor or the correction model is derived from the sensor specific model.