A		Advanced
S		Spaceborne
T		Thermal
E		Emission and Reflection
R		Radiometer

ASTER will obtain high resolution (15 to 90 m) images of the Earth in the visible, near-infrared (VNIR), shortwave-infrared (SWIR), and thermal infrared (TIR) regions of the spectrum.

ASTER is a cooperative effort between NASA and Japan's Ministry of International Trade and Industry (MITI), with the collaboration of scientific and industrial organizations in both countries. Management of the ASTER Team is provided by the Japan Resources Observation System Organization (JAROS). As shown in the figure, ASTER consists of three distinct telescope subsystems: VNIR, SWIR, and TIR. It is a high spatial, spectral, and radiometric resolution, 14-band imaging radiometer. Spectral separation is accomplished through discrete bandpass filters and dichroics. Each subsystem operates in a different spectral region, has its own telescope(s), and is built by a different Japanese company.

The VNIR subsystem, built by NEC Corporation, consists of two telescopes—one that looks backward (along track) and one that looks at nadir. The nadir-looking telescope is a reflecting-refracting improved Schmidt design and pairs with the backward looking telescope to produce same-orbit stereo images. The VNIR subsystem operates in three visible and near-infrared bands with 15 m resolution and a 60 km swath width. The telescope pair is pointable crosstrack over a ± 24° angle to increase the revisit frequency of any given Earth location and special targets of opportunity (e.g., volcanic activity and natural disasters). Light from either of two onboard halogen lamps will be used periodically for calibration of this subsystem.

The SWIR subsystem, built by Mitsubishi Electric Company (MELCO), operates in six shortwave infrared channels with 30 m resolution and a 60 km swath width. It contains a pointing mirror that can point ± 8.54° from nadir to allow coverage of any point on Earth over the spacecraft's 16-day cycle. This mirror is also periodically used to direct light from either of two onboard calibration lamps into the subsystem's telescope—a fixed, aspheric refracting telescope.

The TIR subsystem, built by Fujitsu Ltd., operates in five thermal infrared channels with 90 m resolution and a 60 km swath width. It contains a scan mirror that is used for both scanning and pointing up to ± 8.54° from nadir. As in the SWIR, this mirror is also periodically used to view the onboard blackbody for calibration. Light from the TIR scan mirror is reflected into a Newtonian catadioptric telescope system with an aspheric primary mirror and lens for aberration correction.

The ASTER instrument operates for a limited time during the day and night portions of an orbit. The full configuration (all bands plus stereo) collects data for an average of 8 minutes per orbit. Reduced configurations (limited bands, different gains, etc.) can be implemented as requested by investigators.

The ASTER Team Leaders are Hiroji Tsu in Japan, and Anne Kahle in the U.S. For more information about the instrument, see http://asterweb.jpl.nasa.gov.

ASTER is the highest spatial resolution instrument on the Terra spacecraft, and the only one that does not acquire data continuously. ASTER data products include:

• spectral radiances and reflectances of the Earth's surface;
• surface temperature and emissivities;
• digital elevation maps from stereo images;
• surface composition and vegetation maps;
• cloud, sea ice, and polar ice products; and
• observation of natural hazards (volcanoes, etc.).

ICELAND ICE CAP. The Vatnajokull ice cap and its glaciers are clearly shown in this simulated ASTER image created from Landsat data. Monitoring of glacial movement contributes to understanding climate change.

ASTER Instrument Characteristics Spectral range   VNIR 0.5-0.9 µm SWIR 1.6-2.5 µm TIR 8-12 µm Spatial resolution 15 m (VNIR: 3 bands), 30 m (SWIR: 6 bands), 90 m (TIR: 5 bands) Duty cycle 8% Data rate 8.3 Mbps (avg), 89.2 Mbps (peak) Mass 450 kg Power 525 W (avg), 761 W (peak)

These are simulations of an ASTER scene, 60 x 60 km, taken from an aircraft over Death Valley, CA. The images are draped over digital elevation data to produce the 3-D perspective view. The left image illustrates ASTER's multispectral thermal infrared bands that will provide new surface compositional information and more accurate surface temperature determinations. Colors on the image relate to differences in surface materials—red areas are quartz-rich outcrops and alluvial fans; dark green, gray, and blue areas are other volcanic and sedimentary rock types; light green areas are salt deposits on the valley floor. The right image was produced using the visible, middle infrared, and short wavelength infrared bands that are used for the color display of the surface compositional information. Image colors depict different surface materials—green areas are vegetated; blue areas are wet or have standing water; orange areas are iron-rich volcanic rocks; brown, pink, blue gray areas are volcanic and sedimentary rocks.

These simulated ASTER images were made from coregistered AVIRIS imaging spectrometer data (the VNIR and the SWIR images), and Thermal Infrared Multispectral Scanner data (the TIR image). The VNIR image has a spatial resolution of 15 m, and combines ASTER bands 3, 2, and 1 in red, green, and blue (RGB). The SWIR image has a resolution of 30 m, and combines SWIR bands 8, 6 and 4 as RGB. The TIR image uses bands 14, 12 and 10 displayed as RGB, and has a resolution of 90 m. (Images displayed here are reduced in resolution.) The size of the area depicted is 12 x 50 km. Bad Water in Death Valley is the lowest place in the United States. It is in the right middle of each image. The three versions of ASTER data illustrate the different compositional information available in various wavelength regions. For example, the bright red areas in the top image are vegetation patches at Furnace Creek Ranch and on the Furnace Creek Fan. The turquoise area in the left corner of the middle image depicts ground covered by limestone fragments. In the thermal image (bottom), surfaces with the mineral, quartz, present are depicted in red.