Temperature retrieval for Earth´s surfaces using BIRD (Bi-spectral InfraRed detection)

The Earth´s surface temperature is a key parameter for the understanding of the energetic and hydrological balance of the Earth. Continuous measurements of the global temperature distribution provide information on its changes and impact on the global climate. With the BIRD small satellite mission (size: 158 cm×64 cm×52 cm, mass: 85 kg) a new generation of imaging infrared sensors to be used in space will be tested. The main scientific tasks include the developing of temperature retrieval methods for high-temperature-events like fires, volcanos etc. as well as for “normal” Earth´s surface temperature like the temperature of vegetation, etc.-the fire surrounding temperature. BIRD, a multi-spectral sensor system, is slated to be launched in 2000. It consists of two IR cameras (3.4-4.2 μm (MIR-Mid InfraRed) and 8.5-9.3 μm (TIR-Thermal InfraRed)) as well as a stereo camera WAOSS (Wide-Angle Optoelectronic Stereo Scanner) where the spectral ranges lie within the visible (VIS) and the near infrared (NIR). Two temperature retrieval methods customized for the BIRD channel constellation are established. One method is based on a multi-spectral regression (referred to as “regression”-approach) using brightness temperatures of both channels at the top of the atmosphere. The other approach recovers land surface emissivity and temperature from ground radiances utilizing a “Temperature Independent Spectral Index for Emissivity” (referred to as “TISIE”-approach). Both methods lead to equivalent temperature retrieval errors, but the “TISIE”-approach does not need an a priori knowledge of the emissivity