ABSTRACT
The first multispectral imagery of Earth from satellite, specifically designed for Earth resources surveys, started with Landsat 1, which had a spatial resolution of approximately 40 m from the Return Beam Vidicon (RBV) camera and of about 80 m from the optomechanical scanner multispectral scanner system (MSS). Since then, to cater to the increasing needs of the user community, efforts have been made to provide space imagery with better and better performance capabilities. One area where consistent efforts are being put in is to generate images with improved spatial resolution. The Thematic Mapper launched in 1982 had a resolution of 30 m. The launch of SPOT in 1986 gave panchromatic (PAN) imagery with 10-m spatial resolution, whereas the Indian Remote Sensing Satellite (IRS) 1C launched in 1995 produced PAN imagery with about 6-m resolution. However, during this period, highly classified spy satellites have been operating with spatial resolution of a few tens of centimeters resolution. These Earth observation satellites were funded by their respective governments. The U.S. policy of allowing private entrepreneurs to launch and operate satellites with resolution up to 1 m opened a new era in Earth observation. The first such class of satellite was IKONOS launched in 1999. The IKONOS could provide PAN imagery with a spatial resolution of 1 m and 4-band multispectral (B, G, R, near infrared [NIR]) imagery with 4-m spatial resolution. Thus the gap between civilian and military remote sensing capabilities started narrowing. The major improvement has been for the PAN band. Figure 7.1 gives the improvement of spatial resolution of the PAN channel since the launch of SPOT-1. In this chapter, we shall discuss the design considerations and challenges for realizing spaceborne cameras with a resolution of 1 m or better, which we shall refer to as a high-resolution system.
