An additive manufacturing method, comprising: monitoring a temperature of a first portion of a build plane during an additive manufacturing operation from a Eulerian reference frame using a first optical temperature sensor; monitoring a temperature of a second portion of the build plane that includes the first portion during the additive manufacturing operation from a Lagrangian reference frame using a second optical temperature sensor (309, 311); detecting a change in phase of material within the first portion of the build plane as a heat source passes through the first portion of the build plane using sensor data produced by the first optical temperature sensor; calibrating the second optical temperature sensor by cross-correlating (204, 402) the sensor data produced by the first optical temperature sensor during the change in phase with information collected by the second optical temperature sensor during the detected phase change, by correcting the peak temperature measured in the Lagrangian reference frame by a correlation factor which is derived by comparing the Lagrangian data to the Eulerian data over a given time step; predicting at least one of a cooling rate or a melt pool size using data from the second optical temperature sensor in combination with process models; and changing an amount of energy supplied by the heat source in accordance with the calibrated temperature information provided by the second optical temperature sensor. monitoring a temperature of a first portion of a build plane during an additive manufacturing operation from a Eulerian reference frame using a first optical temperature sensor; monitoring a temperature of a second portion of the build plane that includes the first portion during the additive manufacturing operation from a Lagrangian reference frame using a second optical temperature sensor (309, 311); detecting a change in phase of material within the first portion of the build plane as a heat source passes through the first portion of the build plane using sensor data produced by the first optical temperature sensor; calibrating the second optical temperature sensor by cross-correlating (204, 402) the sensor data produced by the first optical temperature sensor during the change in phase with information collected by the second optical temperature sensor during the detected phase change, by correcting the peak temperature measured in the Lagrangian reference frame by a correlation factor which is derived by comparing the Lagrangian data to the Eulerian data over a given time step; predicting at least one of a cooling rate or a melt pool size using data from the second optical temperature sensor in combination with process models; and changing an amount of energy supplied by the heat source in accordance with the calibrated temperature information provided by the second optical temperature sensor. calibrating the second optical temperature sensor by cross-correlating (204, 402) the sensor data produced by the first optical temperature sensor during the change in phase with information collected by the second optical temperature sensor during the detected phase change, by correcting the peak temperature measured in the Lagrangian reference frame by a correlation factor which is derived by comparing the Lagrangian data to the Eulerian data over a given time step; predicting at least one of a cooling rate or a melt pool size using data from the second optical temperature sensor in combination with process models; and changing an amount of energy supplied by the heat source in accordance with the calibrated temperature information provided by the second optical temperature sensor.