1. Mission Continuity: Landsat 7 is the latest in a long history of land remote sensing spacecraft, spanning 33 years of multispectral imaging of the Earth's surface, starting with the launch of Landsat 1 in 1972. In particular, the ETM+ continues the database of Earth imagery begun in 1982 by the Landsat 4 Thematic Mapper, providing the same spectral bands for consistent change detection.
2. Global Survey Mission: Landsat 7 data is acquired systematically to build and periodically refresh a global archive of sun-lit, substantially cloud-free images of the Earth's landmass. Approximately one quarter of the Earth's landmass is imaged every 16 days, using a planning scenario that emphasizes seasonal changes in vegetation and uses cloud predictions from NOAA to avoid imaging cloudy areas, thus optimizing the data acquisition strategy. If the data user wants a particular image, chances are that it is already in the data archive. Also, as environmental changes occur on the Earth's surface, it is highly probable that recent prior data already exists and can be quickly retrieved to compare with newly acquired data.
3. Affordable Data Products: Landsat 7 data products are available from the USGS Center for Earth Resources Observation and Science (EROS), Sioux Falls, South Dakota. These products are distributed at "the Cost of Fulfilling User Requests", known as the COFUR price. This is a significant price reduction from commercial data sales, allowing renewed use of Landsat data in academic institutions for scientific research. This has again stimulated the use of multispectral imagery in a variety of applications, fostering new uses not only for Landsat data but for other remote sensing data as well.
4. Absolute Calibration: Landsat 7 data from the ETM+ is calibrated to better than 5%, and serves as an on-orbit standard for cross-calibration of other Earth remote sensing missions. NASA orbited the EOS-AM1 spacecraft and EO-1 in formation with Landsat 7 to take advantage of this enhanced calibration.
These features, combined with all the traditional utility of Landsat data proven over 33 years, makes Landsat 7 data important for a wide and diverse remote sensing community.
References:
- NASA, Landsat 7.
