Environmental Satellites

The satellite research group in the NOAA ETL Ocean Remote Sensing Group uses data from various meteorological satellites to study seasonal to interannual climate variability. These satellites measure various types of electromagnetic radiation reflected and emitted by materials on planet Earth, including the land, oceans, and atmosphere. The kind of radiation measured by meteorological satellites includes visible-wavelength energy (light) and non-visible energy (e.g., infrared and microwave radiation). Data from both geostationary and polar-orbiting satellites are gathered and analyzed daily.

GENERAL INFORMATION ON METEOROLOGICAL SATELLITES

Geostationary satellites

Geostationary satellites have orbits that match the rotation of the Earth, so they continually "hover" over the same location with respect to to the Earth's surface. Because they constantly observe the same region of the Earth, geostationary satellites are ideal platforms for observing changes in cloud patterns and other weather phenomena. However, because they orbit at very high altitudes (38,500 km) above the equator, they cannot provide the same level of detail as lower-altitude satellites.

At present, the United States operates two geostationary satellites, GOES-East and GOES-West. GOES stands for "Geostationary Operational Environmental Satellite". The GOES-East satellite (also known as GOES-8) is positioned over the equator at 75 degrees west longitude, giving good coverage of North and South America. The GOES-West satellite (also known as GOES-10) is located over the equator at 135 degrees west longitude, giving good coverage of the eastern Pacific. Similar geostationary satellites covering other portions of the globe are operated by Europe, Japan, India, Russia, and China.

Polar-orbiting satellites

In contrast to geostationary satellites, polar-orbiting satellites generally orbit at relatively low altitudes (typically 700 to 800 km), constantly changing their position relative to the Earth's surface. They move in circular orbits that take them near the north and south poles, typically completing one orbit in around 100 minutes. The relatively low altitudes of polar-orbiting satellites allow them to capture more detailed images of the planet than geostationary satellites. However, because polar-orbiting satellites view the Earth in relatively narrow swaths, complete coverage of our planet requires time (one or many days) for the satellite to complete many orbits, or requires that observations from multiple satellites be combined.

Polar-orbiting satellites include the Defense Meteorological Satellite Program (DMSP), NOAA Polar-orbiting Operational Environmental Satellites (POES), Landsat satellites, and the French SPOT satellites. The DMSP and NOAA/POES satellites are operational meteorological satellites that normally provide complete global coverage on a daily basis. Landsat and SPOT do not provide daily global coverage, but offer the advantage of higher-resolution, multi-spectral images of our planet.

SATELLITES CURRENTLY USED BY THE ETL SATELLITE CLIMATE RESEARCH GROUP

 The data currently used for climate research include data collected by DMSP satellites, GOES satellites, and GMS satellites.

DMSP

The Defense Meteorological Satellite Program (DMSP) is a Department of Defense program that designs, builds, launches, and maintains several near- polar orbiting satellites monitoring the meteorological, oceanographic, and terrestrial physics of the Earth. DMSP satellites orbit at an altitude of approximately 830 km, collecting images across a 3,000-km swath under both daytime and nighttime conditions. Each satellite views any point on the Earth twice a day and completes an orbit in about 101 minutes. Complete global coverage is provided every six hours. DMSP satellites carry various kinds of data-collection instruments, several of which provide data used for climate research, including the Special Sensor Microwave Imager (SSM/I), the SSM/T, and the SSM/T2.

The SSM/I instrument gathers microwave data at four different wavelengths and two different polarizations. SSM/I data are used to derive geophysical parameters such as ocean surface wind speed, precipitation over land and water, atmospheric water vapor, and sea surface temperatures. The SSM/T and SSM/T2 instruments are atmospheric sounding instruments that measure microwave temperatures at various levels of the atmosphere, supplying information about atmospheric conditions at various altitudes.

GOES

The geostationary operational environmental satellite (GOES) series of satellites is owned and operated by the National Oceanic and Atmospheric Administration (NOAA). The objective of the GOES system is to maintain a continuous data stream from two satellites to support the requirements of the U.S. National Weather Service. Currently, GOES satellites provide half-hourly observations of the Earth and its environment. These are continuously transmitted to ground terminals and processed for rebroadcast to primary weather services and research communities around the world.

Each GOES satellite carries two major instruments: an imager and a sounder. Imager data, which consist of measurements of five different wavelengths of visible and infrared (IR) energy, are acquired on a three-hourly basis via NOAA's Forecast Systems Laboratory. Of the five wavelengths sampled by the imager, the visible, water vapor IR, and thermal IR wavelengths are used to monitor clouds, atmospheric water vapor, and (in cloud-free areas) sea surface temperatures.

GMS

The Geosynchronous Meteorological Satellite (GMS) is operated by Japan. GMS-5 is located above the equator at 140 degrees east longitude, providing good coverage of the western Pacific. The GMS satellite is similar to the U.S. GOES-West and GOES-East satellites, except that it does not carry a sounding instrument. We will be using GMS imager data in much the same way we are using GOES imager data.

OTHER METEOROLOGICAL SATELLITES OF INTEREST

 Several other satellite platforms exist that are designed primarily for weather imaging and atmospheric research. These include the Meteosat satellite operated by the European Community, the Feng-Yun satellite operated by China, the GOMS satellite operated by Russia, and India's INSAT satellite.

Meteosat is a geostationary satellite operated by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT). EUMETSAT has now launched three satellites of the operational Meteosat series and a fourth of the same design is under construction. EUMETSAT's newest satellite, Meteosat-7, was successfully placed into geostationary orbit on April 9, 1997. Meteosat provides data captured at visible, thermal IR, and water vapor IR wavelengths.

Feng-Yun is the first geostationary meteorological satellite of China, launched on June 10, 1997. The spacecraft was positioned at 105 east degrees longitude on June 17. The visible wavelength sensor started working on June 21 and sent back its first visible image of the full disk of the Earth on that date. The Feng-Yun satellite carries an imaging instrument that senses radiation in one visible wavelength and two infrared wavelengths that are similar to GOES-9 sensors. As of this writing (September 1997), the thermal IR and water vapor IR sensors are not yet active.

GOMS (aka Elektro) is Russia's first geosynchronous weather imaging satellite. GOMS-1 is operational for the Eastern Hemisphere, but visible imagery can't be broadcast because of problems with the sensor package. According to NASA, GOMS-1 infrared data became operational in June 1996, and GOMS IR images are posted on-line.

The Indian INSAT satellite is located above the equator at approximately 90 degrees east longitude, providing images of the Indian Ocean and central Asia. According to NASA, INSAT imagery is encrypted to hide it from the surrounding nations, and is currently unavailable for real-time analysis. However, archived data are reportedly easily acquired. The U.S. National Oceanographic and Atmospheric Adminstration (NOAA) has been negotiating for years to get regular access to real-time INSAT imagery.