ASTER

ASTER System

Overview/History

ASTER stands for Advanced Spaceborne Thermal Emission and Reflection Radiometer. ASTER is not actually a satellite; it is an imaging instrument that is onboard Terra, the first Earth Observing System satellite that was launched in 1999. ASTER is a joint project of NASA, Japan’s Ministry of Economy, Trade and Industry (METI), and Japan Space Systems. The purpose of ASTER data is to create maps of elevation, land surface temperature, and reflection. ASTER is newer and more capable than Landsat Thematic Mapper because of its high resolution images.

ASTER is known as the zoom lens for Terra. The ASTER system has three instrument subsystems, with each of them operating a different region and telescope. The three subsystems are: the Visible and Near Infrared (VNIR), the Shortwave Infrared (SWIR), and the Thermal Infrared (TIR).

The VNIR subsystem has two telescopes to minimize distortion. VNIR provides the most data of the three ASTER instruments because all four bands are gathering data at the same time. The SWIR subsystem uses only one aspheric refracting telescope and contains a calibration system. Spectral separation is achieved by using six optical bandpass filters. The TIR subsystem also uses one telescope and operates in five bands in the thermal infrared region. TIR is different from VNIR and SWIR because it uses a mirror to scan resulting in a high data rate. The TIR subsystem can collect useful data during the day and night.

Spatial/Spectral/Time Resolution

ASTER records high spatial resolution data in 14 bands, from visible to thermal infrared wavelengths, along with stereo viewing capability for creating digital elevation models. The VNIR has a resolution of 15m. SWIR has a resolution of 30m, and TIR has a resolution of 90m. Each subsystem has a swath width of 60km.

Pros

ASTER images are in high in quality because of its high spatial resolution and broad wavelengths. Data can be acquired to make surface temperature maps at night. Using ASTER is a cheaper and faster way to make maps when compared to ground-based methods.

Cons

ASTER data can be complex and large in size, which can take a lot of resources to manage. Some people claim ASTER data is not as high resolution as it claims to be. Like all remote sensing technology, it has its limits and does not always operate perfectly. Cooling the SWIR subsystem has been a challenge for the ASTER team.

Examples of Use

ASTER data is useful in a wide range of scientific research and applications. An example listed on NASA’s website shows how ASTER data is used to monitor land surface and land cover change. The high resolution photos are very useful in analyzing deforestation, desertification, and urbanization. Also interesting and valuable from ASTER is information on hazards such as the effects of wildfires, flooding, and tsunami damage. ASTER detected warm spots on the Chikurachki Volcano in the Kurile Islands nearly two months before it erupted. ASTER can work as a very sensitive geo-thermometer, which is a good thing because it can warn of severe changes in the Earth’s surface.