Читать книгу Earth Observation Using Python - Rebekah B. Esmaili - Страница 16

Most Earth‐observing satellites orbit our planet either in either geostationary or low‐Earth orbiting patterns. These types of satellites tend to be managed and operated by large international government agencies, and the data are often freely accessible online:

 Geosynchronous equatorial orbit (GEO) satellites. Geostationary platforms orbit the Earth at 35,700 km above the Earth’s surface. GEO satellites are designed to continuously monitor the same region on Earth, and thus can provide many images over a short period of time to monitor change. National Oceanic and Atmospheric Administration (NOAA) operates the Geostationary Environmental Satellite System (GOES) satellites for monitoring North and South America. GOES‐16 and ‐17 have an advanced baseline instrument (ABI) onboard to create high‐resolution imagery in visible and infrared (IR) wavelengths. The GOES‐16 and ‐17 satellites are also equipped with the Geostationary Lightning Mapper (GLM) to detect lightning. Instruments designed for space weather include the Solar Ultraviolet Imager (SUVI) and X‐ray Irradiance Sensors (EXIS). The European Organization for the Exploitation of Meteorological Satellites (EUMETSAT) operates and maintains the Meteosat series GEO satellites that monitor Europe and Africa. The Japan Aerospace Exploration Agency (JAXA) operates and maintains the Himawari satellite that monitors Asia and Oceania.

 Low‐Earth orbit (LEO) satellites. Polar orbiting satellites provide approximately twice daily global observations at the equator (with more observations per day at the poles). Figure 1.3 displays the equatorial crossing time for historic and existing LEO satellites, which refers to the local time at the equator when observations are made. Overpasses from some LEO satellites shift during a mission, while others are periodically adjusted back to maintain a consistent overpass time throughout the duration of a mission. Polar orbiting satellites are called low‐Earth orbit satellites because they are much closer to the Earth’s surface (at 400–900 km) than GEO satellites, which are approximately 40 times further away from the earth or at ~35,000 km. The lower altitude of LEO satellites facilitates their higher spatial resolution relative to GEO, although the temporal resolution tends to be lower for LEO satellites. The Suomi‐NPP and NOAA‐20 are two satellites that were developed and maintained by NASA and NOAA, respectively. They are each equipped with an imager, the Visible Infrared Imaging Radiometer Suite (VIIRS), and infrared and microwave sounders, the Cross‐track Infrared Sounder (CrIS) and an Advanced Technology Microwave Sounder (ATMS). The MetOp series of LEO satellites (named MetOp‐A, ‐B, and ‐C) were developed by the European Space Agency (ESA) and are operated by EUMETSAT.

Figure 1.3 Equatorial crossing times for various LEO satellites displayed using Python.