2.2 Characteristics of Optical Sensors Radiation

Optical sensors are characterized specified by spectral, radiometric and geometric performance. Figure 2.2.1 summarizes the related elements for the three characteristics of optical sensor. Table 2.2.1 presents the definitions of these elements.

The spectral characteristics are spectral band and band width, the central wavelength, response sensitivity at the edges of band, spectral sensitivity at outer wavelengths and sensitivity of polarization.

Sensors using film are characterized by the sensitivity of film and the transmittance of the filter, and nature of the lens. Scanner type sensors are specified by the spectral characteristics of the detector and the spectral splitter. In addition, chromatic aberration is an influential factor. The radiometric characteristics of optical sensors are specified by the change of electro-magnetic radiation which passes through an optical system. They are radiometry of the sensor, sensitivity in noise equivalent power, dynamic range, signal to noise ratio (S/N ratio) and other noises, including quantification noise.

The geometric characteristics are specified by those geometric factors such as field of view (FOV), instantaneous field of news (IFOV), band to band registration, MTF (see 2.3), geometric distortion and alignment of optical elements.

IFOV is defined as the angle contained by the minimum area that can be detected by a scanner type sensor. For example in the case of an IFOV of 2.5 milli radians, the detected area on the ground will be 2.5 meters x 2.5 meters,if the altitude of sensor is 1,000 m above ground.


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