136.

[Cover] [Contents] [Index]

Page 22

relatively old model, it generates quite robust calibration results (Colby, 1991).

Figure 1.11 shows the geometrical relationships between the Sun, the sensor, and an arbitrary surface element. The Lambertian model assumes that the surface reflects the incident radiation uniformly in all directions. If we treat wavelength as a constant and ignore atmospheric interactions, the variation in radiance detected by the sensor is mainly caused by the local incidence angle θ_i (i.e. the angle formed between the solar radiation path and local surface normal). In this case, sensor-detected radiance L can be normalised in terms of:

(1.18)

where L_n denotes the normalised radiance. The cos(θ_i) term can be derived from the spherical law as follows:

(1.19)

Figure 1.11 Geometrical relationships between the Sun, the sensor and the target position (modified from Smith et al. (1980), figure 1). (Reproduced by permission of the American Society for Photogrammetry and Remote Sensing).

[Cover] [Contents] [Index]