卫星全球气候观测系统OA

Satellite remote sensing has become an indispensable component of the Global Climate Observation System(GCOS).At present,satellite observations primarily rely on two types of platforms:geostationary Earth orbit(GEO)satellites and low Earth orbit(LEO)satellites.GEO satellites provide continuous monitoring of the atmosphere,land surface,and oceans with high temporal resolution,although their observational capability is lim-ited at high latitudes.In contrast,LEO satellites offer near-global coverage and high spatial resolution but generally have lower temporal sampling frequencies. Spaceborne instruments can be broadly classified into passive and active sensors.Passive instruments only re-ceive electromagnetic waves emitted by the Earth and atmosphere,while active instruments can both emit and re-ceive scattered echoes from target objects.Early satellite instruments primarily operated in the visible light and in-frared spectral regions because these wavelengths correspond to the major portions of Earth's reflected solar radia-tion and emitted thermal radiation,enabling observations with relatively high spatial resolution.However,visible and infrared radiation cannot penetrate cloud cover.Microwave sensors,by contrast,can observe the Earth's surface under cloudy conditions and provide information on the internal structure of clouds and precipitation sys-tems.Owing to the relatively weak microwave emission from the Earth,microwave sensors require larger sampling footprints to achieve adequate signal strength,resulting in lower spatial resolution than visible and infrared instru-ments.Active remote sensing systems,including spaceborne LIDAR and microwave radar,determine the location and characteristics of targets by transmitting electromagnetic signals and analyzing the returned echoes.In addition,the Gravity Recovery and Climate Experiment(GRACE)mission measures variations in the Earth's gravity field to monitor mass changes in the hydrosphere,cryosphere,and oceans.Global Navigation Satellite Sys-tem(GNSS)receivers carried aboard LEO by satellites provide high-vertical-resolution observations of atmos-pheric temperature and humidity through radio occultation techniques and can be used to calibrate and validate satellite microwave sounding data. Although the former Soviet Union launched the world's first artificial satellite,US satellite programs have made particularly important contributions to the global climate observing system through their long-term continui-ty,extensive data records,and open data policies.Since 1978,the Advanced Very High Resolution Radiometer(AVHRR)aboard the National Oceanic and Atmospheric Administration(NOAA)satellite series has provided Earth observation data at approximately 1.1 km spatial resolution,supporting applications such as land surface temperature retrieval,vegetation phenology monitoring,land-cover classification,and snow and ice mapping.How-ever,the absence of orbit maintenance systems and onboard calibration devices for visible sensors resulted in or-bital drift and sensor degradation,creating challenges for long-term climate applications.Since 1972,the Landsat program has provided 30 m spatial resolution observations for monitoring deforestation,urban expansion,agricul-tural activities,and inland water bodies.NASA's Earth Observing System(EOS),initiated in 1998,addressed many of the orbital and sensor stability issues encountered by earlier satellite systems while incorporating the strengths of the Landsat program.The US Defense Meteorological Satellite Program(DMSP)operates satellites in a dawn-dusk sun-synchronous orbit and provides observations of clouds,land and ocean surface conditions,and three-dimensional atmospheric temperature and humidity fields.Its microwave imaging instruments are widely used for precipitation retrieval and soil and vegetation moisture monitoring.European satellite missions have made distinct contributions to radar remote sensing and collaborate closely with the United States in polar-orbiting mete-orological observations through data-sharing and cost-sharing initiatives.The Sentinel satellite series,developed under the European Copernicus Earth Observation Program,supports the monitoring of land,oceans,the atmos-phere,and climate change.The Tropical Rainfall Measuring Mission(TRMM)and the Global Precipitation Measurement(GPM)mission,jointly developed by the United States and Japan,significantly improved the accu-racy of tropical and global precipitation observations through the deployment of precipitation radar and advanced microwave sensors.Although China entered the field of meteorological satellite observation later than some other major spacefaring nations,its Fengyun satellite program has developed rapidly and is currently the only operational system simultaneously maintaining morning,afternoon,dawn-dusk,and inclined-orbit meteorological satellites. More than five decades of satellite observations have provided an invaluable foundation for climate change research.Nevertheless,challenges remain in constructing long-term,high-quality climate data records due to orbital drift,sensor degradation,instrument replacement,calibration inconsistencies,and the sparse temporal sampling of low-Earth orbit satellites.This review summarizes the characteristics of major satellite orbits,spaceborne instru-ments,and key Earth observation missions and briefly discusses calibration approaches,current challenges,and future directions for satellite-based global climate observing systems.