ASTER

ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) is an imaging instrument that is flying on Terra, a satellite launched in December 1999 as part of NASA's Earth Observing System (EOS). ASTER was built in Japan for the Ministry of Economy Trade and Industry (METI). It is a result of a cooperative effort between METI, NASA, and the Earth Remote Sensing Data Analysis Center (ERSDAC). The ASTER team consists of scientists from the United States, Japan, France, and Australia, and managed by the Japan Resources Observation System Organization (JAROS).

The main objective of ASTER mission is to obtain global, regional, and local images of the Earth in 14 different wavelengths of the electromagnetic spectrum (spectral bands), ranging from visible to thermal infrared light. ASTER is the only high spatial resolution instrument on Terra that is important for change detection, calibration and/or validation, and land surface studies. It can obtain detailed maps of land surface temperature, emissivity, reflectance and elevation to study glaciology, urban change, evaporation/surface fluxes, hydrology, volcanology, and geology.

There are three separate subsystems that make up the ASTER instrument. Each subsystem operates in a different spectral region, has its own telescope(s), and built by 3 different Japanese companies: NEC Corporation, Mitsubishi Electric Company (MELCO), and Fujitsu Ltd. The telescopes are VNIR (Visible Near Infrared, a backward looking telescope which is only used to acquire a stereo pair image), SWIR (Short Wave Infrared, a single fixed aspheric refracting telescope), and TIR (Thermal Infrared). ASTER high-resolution sensor is capable of producing stereoscopic (three-dimensional) images and detailed terrain height models. Unlike other instruments on Terra, ASTER can be scheduled based on on-demand data acquisition requests, collecting an average of 8 minutes of data per 98-minute orbit. ASTER needs roughly 5 years to assemble a global data set of Earth surface in a very detailed digital elevation map at resolutions of up to 15 meters per pixel.

MODIS

MODIS (Moderate Resolution Imaging Spectroradiometer) is a key instrument that plays a vital role in the development of validated, global, interactive Earth system models. It was launched together with other instruments aboard Terra and Aqua satellites as part of the Earth Observing System (EOS). The instrument is provided by NASA and was built by Hughes Corporation's Santa Barbara Remote Sensing (SBRS). Its operation is managed by NASA's Goddard Space Flight Center (GSFC).

MODIS has one of the most comprehensive onboard calibration subsystems, which includes a solar diffuser, a solar diffuser stability monitor, a spectroradiometric calibration assembly, a plate-type black body, and a space viewport, ever flown on a remote sensing instrument. The first MODIS flight instrument, ProtoFlight Model or PFM, is integrated on the Terra (EOS AM-1) satellite. The second MODIS flight instrument, Flight Model 1 or FM1, was launched aboard Aqua (EOS PM-1). The orbit of Terra and Aqua is timed; Terra passes across the equator in the morning and Aqua passes in the afternoon. This allows MODIS to operate continuously during the day and night portions of each orbit; only the thermal infrared band data that is collected during the night portion of an orbit.

Scientists use MODIS data to understand the Earth as a system, facilitating their ability to predict global climate changes accurate enough. These predictions can assist policy makers in making sound decisions concerning the protection and management of the environment and resources, and differentiate between the impact of human activities and natural activities on the environment. Data is acquired using a cross-track scanning multi-spectral radiometer with 36 spectral bands including ultra-violet, visible, infrared, and microwave.

MODIS provides exceptionally low out-of-band response, allowing responses to be custom tailored to the needs of the user community worldwide. Its sensor monitors changes on the land surface over the entire Earth almost every day, thereby building upon and extending the heritage begun by Landsat.

Landsat 7 ETM+ Landsat 7, the latest in a series of Landsat earth observation satellites dating back to 1972, was launched on April 15, 1999. It is part of a global research program known as NASA's Earth Science Enterprise.

The Landsat Program was managed cooperatively by the National Aeronautics and Space Administration (NASA), the National Oceanic and Atmospheric Administration (NOAA), and the USGS. The Program is part of the NASA's global change initiative - the Earth Observing System, administered by the NASA Office of Mission to Planet Earth.

The spaceraft was manufactured by Lockheed Martin Missiles and Space, while the Enhanced Thematic Mapper Plus (ETM+) instrument was built by Raytheon (formerly Hughes) Santa Barbara Remote Sensing. Landsat 7 is operated by USGS that also performs data processing, archiving and distribution. Data products are available from the EROS Data Center in South Dakota and are distributed at the cost of fulfilling user requests (COFUR) price.

The Enhanced Thematic Mapper Plus (ETM+) is an eight-band multispectral scanning radiometer capable of providing high-resolution imaging information of the Earth's surface. This new feature makes ETM+ a more versatile and efficient instrument for global change studies, land cover monitoring and assessment, and large area mapping. Its repetitive, synoptic coverage of continental surfaces is needed for observation of seasonal changes on regional, continental and global scales.

ETM+ detects spectrally filtered radiation at visible, near-infrared, short wave, and thermal infrared frequency bands from the sun-lit Earth. It produces approximately 3.8 gigabits of data for each scene, which is roughly equivalent to nearly 15 sets of encyclopedias at 29 volumes per set. A solid-state recorder capable of storing 380 gigabits of data (100 scenes) is used to store selected scenes from around the world for playback over a U.S. ground station. Real-time data from ETM+ can be transmitted to cooperating international ground stations and to the U.S. ground stations.

REFERENCES

EROS

• Lantmateriet. (2002). EROS Satellite System. Retrieved on July 20, 2002 from http://www.satellus.se/eros/imagenet/satellites.asp.
• Space and Tech. (2001). EROS A1 - Summary. Retrieved on July 20, 2002 from http://www.spaceandtech.com/spacedata/logs/2000/2000-079a_erosa1_sumpub.shtml.
• Canada Centre for Remote Sensing. (2002). EROS Technical Specification. Retrieved on July 28, 2002 from http://www.ccrs.nrcan.gc.ca/ccrs/data/satsens/eros/erostek_e.html.
• The Geographic Information Systems (GIS) Portal. (2001). ImageSat International Cancels Plans for EROS A2. Retrieved on August 2, 2002 from http://www.gisdevelopment.net/news/2001/feb/ngb017.htm.
  ImageSat International. (2002). About Us. Retrieved on August 22, 2002 from http://www.imagesatintl.com/1024/company/about.html.

TERRA

• NASA – Visible Earth. (2001). First Global Carbon Monixide (Air Pollution) Measurements. Retrieved on August 10, 2002 from http://visibleearth.nasa.gov/cgi-bin/viewrecord?8086.
• ILS. (2002). Earth Observing System (EOS) Terra Spacecraft Size and Application, Atlas Launch Pad Modifications Set Record Firsts. Retrieved on August 10, 2002 from http://www.ilslaunch.com/newsarchives/newsreleases/rec34/prebody.html.
• NASA - Earth Observatory. (2002). MODIS instrument on NASA's Terra satellite improves global vegetation mapping, makes new observations possible. Retrieved on August 10, 2002 from http://earthobservatory.nasa.gov/Newsroom/EVI_LAI_FPAR/.

AQUA

• NASA/GSFC. (2002). AQUA Homepage - Executive Summary. Retrieved on July 27, 2002, from http://aqua.gsfc.nasa.gov/.
• NASA/GSFC. (2002). AQUA Project Science. Retrieved on July 27, 2002 from http://aqua.nasa.gov/.
• Jet Propulsion Laboratory. (2002). NASA's Aqua Spacecraft to Study Earth's Water Cycle. Retrieved on August 10, 2002 from http://www.jpl.nasa.gov/releases/2002/release_2002_95.html.

ASTER

• NASA. (2002). TERRA, the EOS Flagship - ASTER. Retrieved on July 19, 2002 from http://terra.nasa.gov/About/ASTER/about_aster.html and http://terra.nasa.gov/Brochure/Sect_4-2.html.
• Jet Propulsion Laboratory. (2002). ASTER. Retrieved on July 19, 2002 from http://asterweb.jpl.nasa.gov/.
• EROS Data Center - Products. (2002). Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Retrieved on July 19, 2002 from http://edc.usgs.gov/products/satellite/aster.html.

MODIS

• NASA. (2002). MODIS Web. Retrieved on July 24, 2002 from http://modis.gsfc.nasa.gov/about/index.html.
• NASA. (2002). TERRA, the EOS Flagship - MODIS. Retrieved on July 24, 2002 from http://terra.nasa.gov/About/MODIS/about_modis.html and http://terra.nasa.gov/Brochure/Sect_4-5.html.
• Earth Observatory. (2001). MODIS instrument on NASA's Terra satellite improves global vegetation mapping, makes new observations possible. Retrieved on July 24, 2002 from http://earthobservatory.nasa.gov/Newsroom/EVI_LAI_FPAR/.

LANDSAT 7

• Landsat 7 Basic Facts, http://landsat.gsfc.nasa.gov/project/L7basix.html.
• About Landsat-7, http://earthobservatory.nasa.gov/Library/Landsat/landsat.html.
• Benefits of Landsat 7 over other Remote Sensing Missions. Retrieved from http://landsat.gsfc.nasa.gov/project/reason.htm.
  Retrieved from http://earthobservatory.nasa.gov/Library/Landsat/landsat.html.
  Retrieved from http://landsat.gsfc.nasa.gov/project/reason.htm.