A geocentric orbit , Earth-centered orbit , or Earth orbit involves any object orbiting Earth , such as the Moon or artificial satellites . In 1997, NASA estimated there were approximately 2,465 artificial satellite payloads orbiting Earth and 6,216 pieces of space debris as tracked by the Goddard Space Flight Center . More than 16,291 objects previously launched have undergone orbital decay and entered Earth's atmosphere .
7-600: The Moderate Resolution Imaging Spectroradiometer ( MODIS ) is a satellite-based sensor used for earth and climate measurements. There are two MODIS sensors in Earth orbit : one on board the Terra ( EOS AM) satellite, launched by NASA in 1999; and one on board the Aqua (EOS PM) satellite, launched in 2002. MODIS has now been replaced by the VIIRS , which first launched in 2011 aboard
14-462: A v-groove black body . MODIS has used the marine optical buoy for vicarious calibration. The following MODIS Level 3 (L3) datasets are available from NASA, as processed by the Collection 5 software. (global vegetation phenology ) Modis has 36 spectral bands Geocentric orbit A spacecraft enters orbit when its centripetal acceleration due to gravity is less than or equal to
21-574: Is about 36 MJ /kg, which is six times the energy needed merely to climb to the corresponding altitude. Spacecraft with a perigee below about 2,000 km (1,200 mi) are subject to drag from the Earth's atmosphere, which decreases the orbital altitude. The rate of orbital decay depends on the satellite's cross-sectional area and mass, as well as variations in the air density of the upper atmosphere. Below about 300 km (190 mi), decay becomes more rapid with lifetimes measured in days. Once
28-626: The Aral Sea , and the detection and mapping of wildland fires in the United States. The United States Forest Service 's Remote Sensing Applications Center analyzes MODIS imagery on a continuous basis to provide information for the management and suppression of wildfires. MODIS utilizes four on-board calibrators in addition to the space view in order to provide in-flight calibration: solar diffuser (SD), solar diffuser stability monitor (SDSM), spectral radiometric calibration assembly (SRCA), and
35-570: The Suomi NPP satellite. The MODIS instruments were built by Santa Barbara Remote Sensing. They capture data in 36 spectral bands ranging in wavelength from 0.4 μm to 14.4 μm and at varying spatial resolutions (2 bands at 250 m, 5 bands at 500 m and 29 bands at 1 km). Together the instruments image the entire Earth every 1 to 2 days. They are designed to provide measurements in large-scale global dynamics including changes in Earth's cloud cover , radiation budget and processes occurring in
42-552: The centrifugal acceleration due to the horizontal component of its velocity. For a low Earth orbit , this velocity is about 7.8 km/s (28,100 km/h; 17,400 mph); by contrast, the fastest crewed airplane speed ever achieved (excluding speeds achieved by deorbiting spacecraft) was 2.2 km/s (7,900 km/h; 4,900 mph) in 1967 by the North American X-15 . The energy required to reach Earth orbital velocity at an altitude of 600 km (370 mi)
49-685: The oceans, on land, and in the lower atmosphere . Support and calibration is provided by the MODIS characterization support team (MCST). With its high temporal resolution although low spatial resolution, MODIS data are useful to track changes in the landscape over time. Examples of such applications are the monitoring of vegetation health by means of time-series analyses with vegetation indices, long term land cover changes (e.g. to monitor deforestation rates), global snow cover trends, water inundation from pluvial, riverine, or sea level rise flooding in coastal areas, change of water levels of major lakes such as
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