Devices and corresponding methods can be provided to measure temperature and/or emissivity of a target. Emissivity of the target need not be known or assumed, and any temperature difference between a sensor and the target need not be zeroed or minimized. No particular bandpass filter is required. Devices can include one or two sensors viewing the same target as the target views different respective viewed temperatures. The respective viewed temperatures can be sensor temperatures, and a single sensor can be set to each of the respective viewed temperatures at different times. An analyzer can determine the temperature and/or emissivity of the target based on the respective viewed temperatures and on plural net heat fluxes detected by the sensors and corresponding to the respective viewed temperatures.