**2. Modelling the interaction of the solar spectrum with the atmosphere**

An analytical model for simulating radiative transfer in water coupled with an atmospheric model can adequately simulate the signal of a body of water to the attitude of the satellite to analyze the effects of atmospheric parameters and shallow water. This model determines the scattered radiation by a body of water in the software simulation of satellite data *SDDS* (Bachari, 1997), its main function is the calculation of the spectral radiance reflected from the sea water level sensor.

The purpose of modeling is to understand how different components of the measurement system combine to make a measurement. The form and content of a model depends on their purpose. The model is constructed to describe and characterize the measurement system to understand the phenomena which he is registered and to predict their behavior under the effect of an external action or as a result of a partial modification of the system itself same. The model developed is to break the middle-ground atmosphere into subsets in interaction with the solar spectrum and the sensor onboard the satellite.

The source irradiates the object and the latter reflects the radiation in all directions, some of this radiation is captured. The radiation received by a radiometer on board the satellite, is composed of two main terms: brightness caused by the surface in the field of vision sensor and a brightness that is not caused by the surface in the field of vision. The first term is useful information, it is due to the direct and indirect solar radiation. The second term, considered the noise is due to the light scattered by the atmosphere. (Gordon & Clark, 1981; Becker & Rffy, 1990)
