58.

[Cover] [Contents] [Index]

Page 15

1.3.2.1 Modelling the atmospheric effect

The 5S model (Simulation of the Sensor Signal in the Solar Spectrum) developed by Tanré et al. (1986, 1990) is the best-known atmospheric calibration model. An improved version is the 6S (Second Simulation of the Sensor Signal in the Solar Spectrum) model, which is capable of simulating a non-Lambertian surface to model the signal measured by the sensor. The 6S model also includes data for calculating atmospheric absorption using an increased number of atmospheric gases. In what follows, the core of the model is described in order to provide an introduction to atmospheric modelling.

Assume unit solar irradiance incident on top of the atmosphere. A fraction of the incident solar irradiance is scattered from the path between the Sun and the ground target into the atmospheric volume, with the remainder of the radiation being incident on the ground target as direct solar radiation (Figure 1.8a). This transmitted fraction denoted by T(θ_s) is defined as:

(1.3)

Figure 1.8 Five kinds of radiative interaction with the atmosphere.

[Cover] [Contents] [Index]