HOUSTON, TX, April 7 -- On April 15 NASA will deploy Landsat 7, the first major satellite in a program to check the health of the Earth and understand the complex interactions that drive global change.Every 16 days, Landsat 7 will fly over and document the condition of the entire globe. Landsat images are extremely detailed, capturing features on the planet as small as 30 m (compared with the geostationary GOES satellites, which can only resolve objects of 4 km or greater). The instrument onboard Landsat 7 is the Enhanced Thematic Mapper Plus, a passive sensor that measures solar radiation reflected or emitted by the Earth. The sensor has eight bands sensitive to different wavelengths of visible and infrared radiation.