The ESA global detection of hot spots by ERS-2's Along Track Scanning Radiometer (ATSR-2) and Envisat's Advanced Along Track Scanning Radiometer (AATSR) in 2005. These twin radiometer sensors work like thermometers in the sky, measuring thermal infrared radiation to take the temperature of Earth's land surfaces. Temperatures exceeding 312º K (38.85 ºC) are classed as burning fires.