NOAA-18

NOAA-18, also known as NOAA-N before launch, is a decommissioned, polar orbiting, weather satellite series (NOAA K-N) operated by the National Environmental Satellite Service (NESS) of the National Oceanic and Atmospheric Administration (NOAA). NOAA-18 also continued the series of Advanced TIROS-N (ATN) spacecraft begun with the launch of NOAA-8 (NOAA-E) in 1983 but with additional new and improved instrumentation over the NOAA A-M series and a new launch vehicle (Titan 23G). NOAA-18 is in an afternoon equator-crossing orbit and replaced NOAA-17 as the prime afternoon spacecraft. NOAA-18 was decommissioned as of 17:49 UTC, June 6, 2025.

NOAA-18 was launched by the Delta II launch vehicle on 20 May 2005 at 10:22:01 UTC from Vandenberg Air Force Base, at Vandenberg Space Launch Complex 4 (SLW-4W), in a Sun-synchronous orbit, at 854 km above the Earth, orbiting every 102.12 minutes. NOAA-18 is in an afternoon equator-crossing orbit and has replaced the NOAA-17 as the prime afternoon spacecraft.

The goal of the NOAA/NESS polar orbiting program is to provide output products used in meteorological prediction and warning, oceanographic and hydrologic services, and space environment monitoring. The polar orbiting system complements the NOAA/NESS geostationary meteorological satellite program (GOES). The NOAA-18 Advanced TIROS-N spacecraft is based on the Defense Meteorological Satellite Program (DMSP Block 5D) spacecraft and is a modified version of the ATN spacecraft (NOAA 6-11, 13-17) to accommodate the new instrumentation, supporting antennas and electrical subsystems. The spacecraft structure consists of four components: 1° the Reaction System Support (RSS); 2° the Equipment Support Module (ESM); 3° the Instrument Mounting Platform (IMP); and 4° the Solar Array (SA).

All of the instruments are located on the ESM and the IMP. The spacecraft power is provided by a direct energy transfer system from the single solar array which consists of eight panels of solar cells. The in-orbit Attitude Determination and Control Subsystem (ADACS) provides three-axis pointing control by controlling torque in three mutually orthogonal momentum wheels with input from the Earth Sensor Assembly (ESA) for pitch, roll, and yaw updates. The ADACS controls the spacecraft attitude so that orientation of the three axes is maintained to within ± 0.2° and pitch, roll, and yaw to within 0.1°. The ADACS consists of the Earth Sensor Assembly (ESA), the Sun Sensor Assembly (SSA), four Reaction Wheel Assemblies (RWA), two roll/yaw coils (RYC), two pitch torquing coils (PTC), four gyros, and computer software for data processing. The ATN data handling subsystem, consists of the TIROS Information Processor (TIP) for low data rate instruments, the Manipulated Information Rate Processor (MIRP) for high data rate AVHRR, digital tape recorders (DTR), and a cross strap unit (XSU).

The NOAA-18 instrument complement consists of:

The AVHRR/3 on the Advanced TIROS-N (ATN) NOAA K-L series of polar orbiting meteorological satellites is an improved instrument over previous AVHRRs. The AVHRR/3 adds a sixth channel and is a cross-track scanning instrument providing imaging and radiometric data in the visible, near-IR and infrared of the same area on the Earth. Data from the visible and near-IR channels provide information on vegetation, clouds, snow, and ice. Data from the near-IR and thermal channels provide information on the land and ocean surface temperature and radiative properties of clouds. Only five channels can be transmitted simultaneously with channels 3A and 3B being switched for day/night operation. The instrument produces data in High Resolution Picture Transmission (HRPT) mode at 1.1 km resolution or in Automatic Picture Transmission (APT) mode at a reduced resolution of 4 km. The AVHRR/3 scans 55.4° per scan line on either side of the orbital track and scans 360 lines per minute. The six channels are: 1) channel 1, visible (0.58-0.68 μm); 2) channel 2, near-IR (0.725-1.0 μm); 3) channel 3A, near-IR (1.58-1.64 μm); 4) channel 3B, infrared (3.55-3.93 μm; 5) channel 4, infrared (10.3-11.3 μm); and 6) channel 5 (11.5-12.5 μm).

The improved HIRS/4 on the Advanced TIROS-N (ATN) NOAA K-N series of polar orbiting meteorological satellites is a 20-channel, step-scanned, visible and infrared spectrometer designed to provide atmospheric temperature and moisture profiles. The HIRS/4 instrument is basically identical to the HIRS/3 flown on previous spacecraft except for changes in six spectral bands to improve the sounding accuracy. The HIRS/4 is used to derive water vapor, ozone, and cloud liquid water content. The instrument scans 49.5° on either side of the orbital track with a ground resolution at nadir of 17.4 km. The instrument produces 56 IFOVs for each 1,125 km scan line at 42 km between IFOVs along-track. The instrument consists of 19 IR and 1 visible channel centered at 14.95, 14.71, 14.49, 14.22, 13.97, 13.64, 13.35, 11.11, 9.71, 12.45, 7.33, 6.52, 4.57, 4.52, 4.47, 4.45, 4.13, 4.0, 3.76, and 0.69 μm.

The AMSU-A is an instrument on the Advanced TIROS-N (ATN) NOAA K-N series of operational meteorological satellites. The AMSU consists of two functionally independent units, AMSU-A and AMSU-B. The AMSU-A is a line-scan instrument designed to measure scene radiance in 15 channels, ranging from 23.8 to 89 GHz, to derive atmospheric temperature profiles from the Earth's surface to about 3 millibar pressure height. The instrument is a total power system having a field of view (FOV) of 3.3° at half-power points. The antenna provides cross track scan 50° on either side of the orbital track at nadir with a total of 30 IFOVs per scan line. The AMSU-A is calibrated on-board using a blackbody and space as references. The AMSU-A is physically divided into two separate modules which interface independently with the spacecraft. The AMSU-A1 contains all of the 5 mm oxygen channels (channels 3-14) and the 80 GHz channel. The AMSU-A2 module consists of two low-frequency channels (channels 1 and 2). The 15 channels have a center frequency at: 23.8, 31.4, 50.3, 52.8, 53.6, 54.4, 54.94, 55.5, six at 57.29, and 89 GHz.