NOAA-18(2005-2012) is a weather forecasting satellite run by NOAA. NOAA-N (18) was launched on May 20, 2005, into a sun-synchronous orbit at an altitude of 854 km above the Earth, with an orbital period of 102 minutes. It hosts the AMSU-A, MHS, AVHRR and High Resolution Infrared Radiation Sounder (HIRS) instruments, as well as the SBUV/2 ozone-monitoring instrument. It is the first NOAA POES satellite to use MHS in place of AMSU-B. APT transmission frequency is 137.9125 MHz (NOAA-18 changed frequencies with NOAA-19 on June 23, 2009).