The KT19 Pyrometer, also known as the KT-19 Skin Surface Temperature Sensor (KSSTS), measures the brightness temperature of the surface beneath an aircraft. By knowing the emissivity of the target—sea ice has an emissivity very close to one—the KT-19 can estimate the surface temperature. Thick sea ice is sometimes as cold as -20° or -30° Celsius (-4° or -22° Fahrenheit) while open water is around -2° Celsius (28° Fahrenheit). 

The KT19 as calibrated for NASA’s IceBridge mission can accurately measure the temperature of sea ice leads larger than 40 meters (130 feet). For larger leads covered in thin ice, the KT19 can provide surface temperature data that can be used to estimate ice thickness. Leads smaller than 40 meters have a reduced effect due to the KT19 footprint, and correspondingly the KT19 measures a colder signal for those leads, but many small leads can still be detected.