MODIS (Terra and Aqua) description. Thirty-six band spectroradiometer measuring VIS and IR radiation (0.4 and 14.5 mm with a spatial resolution of 250 m, 500 m, and 1 km at nadir) for deriving products ranging from land vegetation and ocean chlorophyll fluorescence to cloud and aerosol properties, fire occurrences, snow cover on land, and sea ice in the oceans. The Terra orbit follows the Worldwide Reference System, as do the orbits of Landsat-7 (United States Geological Survey, USGS; Landsat = Land Remote Sensing Satellite), Earth Observing-1 (EO-1, NASA), and Satellite de Aplicaciones Cientificas-c (SAC-C, Argentina Comision Nacional para el Ahorro de Energis (CONAE)), all crossing the equator within 30min of each other. These four spacecraft form the 'Morning Constellation', thus facilitating joint use of Terra data and the data from its companion missions. Terra, launched in December 1999, flies in anear-polar, Sun-synchronous orbit that descends across the equator in the morning at around 10.30 a.m. ± 5min. The Aqua spacecraft, launched in May 2002, flies in ascending orbit with a 1.30p.m. equatorial crossing time which enables the study of diurnal variability with the MODIS (moderate-resolution imaging spectroradiometer) and CERES (clouds and the Earth's radiant energy system) instruments onboard both Terra and Aqua. The MODIS and CERES measurements extend the measurements of their heritage sensors - the advanced very high resolution radiometer (AVHRR), the coastal zone color scanner (CZCS), and the Earth radiation budget experiment (ERBE) - but with a higher quality of calibration and characterization. Other benefits include having more spectral bands, and other collocated instruments on board, which can be used to improve the satellite retrieval algorithms and improve the atmospheric correction that often needs to be applied to obtain accurate surface features.
Data continuity from the MODIS instruments on Terra and Aqua are expected from the VIIRS (visible and infrared imaging radiometer suite) instrument on the operational National Oceanic and Atmospheric Administration (NOAA) NPOESS (National Polar Orbiting Environmental Satellite System) series to be launched beginning in the early part of the next decade. Retrospective data continuity is via the Landsat series of satellites.
SeaWiFS/Orbview. Sea-viewing wide field-of-view sensor (SeaWiFS) launched on 1 August 1997, and began taking measurements of the World Ocean in September 1997. Abbreviated SeaWiFS/Orbview, technical details: Sun-synchronous, altitude: 705 km; equatorial crossing: noon±20min; inclination: 98.2°; period: 99min; design life: 5 years; launch: 1 Aug 1997; status: operational. The eight SeaWiFS spectral bands are: Band-1: 402-422 nm; Band-2: 433-453 nm; Band-3: 480-500 nm; Band-4: 500-520 nm; Band-5: 545565 nm; Band-6: 660-680 nm; Band-7: 745-785 nm; Band-8: 845-885 nm. Science focus areas include: carbon cycle, ecosystems, and biogeochemistry; climate variability and change; water and energy cycles. (Note the overlap between SeaWiFS and MODIS spectral bands.)
Landsat. High spatial resolution visible and infrared radiance/reflectance from terrestrial surfaces. Type: circular Sun-synchronous orbit at an altitude of 705 km with inclination 98.2°, period 98.9 min, and repeat cycle 16 days/233 orbits. The main instrument cluster is the enhanced thermatic mapper plus (ETM+) on Landsat-7 and legacy instruments (the thematic mapper, TM) on previous satellites of the Landsat. Next-generation instruments are to be found on the experimental satellite EO-1 which carries an advanced land imager (ALI), a hyperspectral instrument (hyperion), and a linear etalon imaging spectral array (LAC). ETM+ includes eight reflective spectral bands and spatial resolutions: three 30 m VIS bands; one 30 m N-IR band; two 30 m shortwave infrared (SEIR) bands; one 15 m panchromatic band; and one emissive 60 m thermal infrared (TIR) band. EO-1, launched in November 2000, is currently functional. The ALI instrument on EO-1 provides data continuity with ETM+.
Note 1. EOS-Terra and EOS-Aqua also carry several other instruments. They are not detailed in this article because their primary mission objectives pertain to observations of other aspects of the earth/climate system than ecology or ecosystems.
Note 2. Instruments on board Europe's Environmental Satellite, European Space Agency (ENVISAT, ESA), Japan's Advanced Earth Observation Satellite (ADEOS), and the satellites of other countries also measure various aspects of the Earth system, including ecosystems. For brevity, they are not detailed in this article either.
observations called the Global Observing System of Systems (GEOSS) with secretariat hosted by the WMO in Geneva, Switzerland.
This article is not intended to be a treatise on ecology or remote sensing technology. Rather, we provide a few selected examples of how remote sensing technology is used to observe and monitor global ecosystems. Substantial use is made of'public domain' material readily available via the Internet. While extensive use is made of data from National Aeronautics and Space Administration (NASA) Earth Observing System (EOS) series of satellites and predecessor space-based platforms, it is underscored that many other space agencies of other countries and regions increasingly have advanced capabilities to monitor the global biosphere from space. Broad coverage of international satellite programs and applications are detailed on the web site of the UN Office for Outer Space Affairs which coordinates the work of the UN Committee on the Peaceful Uses of Outer Space (UNCOPUOS) and its Space Applications program (http://www.uncosa.unvien-na.org/pdf/reports/IAM2006E.pdf).
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