A major evolution in spectral imaging has occurred with the advent of three commercial remote sensing systems. IKONOS, Quickbird, and Orbview-3 provide spectral imagery at a resolution of 4 m or better15 and have similar spectral responses, all modeled after the first four Landsat spectral bands. The calibration values for IKONOS are given in Fig. 5.14. Note that the panchromatic-sensor spectral response extends well into the near infrared, and that the response in blue is relatively poor.
The response functions for the other commercial sensors are all very similar. The subtle differences become important when spectral quantities are estimated, such as vegetation health or area coverage.
The markets and applications for these sensors are still being created. Their improved spatial resolution (a factor of ten greater than Landsat) is ideal for studies of fields and forests by those who wish to observe and characterize vegetation; presently, the largest market is in agriculture.
Figure 5.14 The panchromatic sensor has almost no blue response, to avoid image degradation caused by atmospheric scattering. Note the fairly high NIR coverage of the panchromatic sensor. Blue: 0.45-0.52
Green: 0.52-0.60
Red: 0.63-0.69
NIR: 0.76-0.90
