**1. Introduction**

194 Atmospheric Model Applications

Zermeno, G.A., Hipps, L.E. (1997). Downwind evolution of surface fluxes over a vegetated

(Amsterdam) 192: 189-210.

surface during local advection of heat and saturation deficit. J. Hydrol.

All bodies emit and reflect the flow of energy in the form of electromagnetic radiation. The relative variation of the energy reflected or emitted as a function of wavelength, is the spectral signature of the object considered in a given state. The spectrum can be used to identify and determine its status. For a satellite, making measurements in a number of spectral bands, the spectral signature of an object will correspond to different levels of radioactivity recorded in each of them.

The principle of remote sensing is the detection of electromagnetic radiation that carries information from the soil-atmosphere either by reflection or by transmission from a radiometer on board the satellite. The signal received by the radiometer is the result of physical, biological and geometrical objects on the ground. For a better use of satellite measurements, we must answer the following questions: At what point on the earth's surface so far is it? What is the value of measuring that?

Answering these questions requires the definition: What exactly are the physical quantities measured by the measurement system? What disturbs the measurement system does what it is supposed to measure? Which model can you describe the disturbances? How does one characterize the quality of measurement?

To understand this complex phenomenon, we have developed an analytic model (SDDS) of radiatif transfer simulation in water coupled to an atmospheric model in order to simulate measure by satellite. This direct model permits to follow the solar radiance in his trajectory Sun-Atmosphere - Sea - Depth of sea- sensor. The goal of this simulation is to show for every satellite of observation (SPOT, Landsat MSS, Landsat TM) possibilities that can offer in domain of oceanography. (Bachari,1997)

An interaction model of the solar spectrum with the Earth-atmosphere system is developed to calculate the various components of solar radiation at ground and upper atmosphere. (Bachari, 1999; Houma and al.,2010)

Solar Radiation Modeling and Simulation of Multispectral Satellite Data 197

E0λ : is the solar spectrum outside Earth's atmosphere, λ: wavelength of emission of radiation, 1: Astronomical Unit (1UA= 1.496x 108 km), f: is the correction factor of distance

In clear sky atmosphere, the concentration of gases and aerosols varies with the changing weather conditions and geographical position. Gases and aerosols absorb and scatter solar radiation on a selective basis throughout the optical path. Gases, principally ozone, carbon dioxide and water vapor are the bodies responsible for absorption of the solar spectrum. Air molecules and aerosols are the body responsible for the dissemination of solar radiation in all directions. (Prieur & Morel, 1975). The effects of absorption and scattering functions are

Tλ = Iλ/ I0λ (2)

Diffusion occurs during the interaction between the incident radiation and particles or large gas molecules in the atmosphere (water droplets, dust, smoke ...). Where the suspended particles are negligible compared to the wavelength, the phenomenon that occurs is

The diffusion of a particle occurs independently of other particles. The radiation will be distributed in all directions, the forward scattered radiation is equal to the radiation

This model is to calculate the solar spectral irradiance (irradiance) direct normal and horizontal diffuse to the conditions of a cloudy sky not. This code calculates a range of 0.3 and 4.0 microns with a pitch of 10 nm. This code introduces a number of parameters such as solar zenith angle, the angle of inclination, atmospheric turbulence, the amount of water

Monochromatic distribution of a direct solar beam can be computed as a function of a number of variables, including optical mass and a wide variety of atmospheric parameters-

In the ultraviolet and visible region, it is essentially ozone absorption, Rayleigh scattering, and aerosols that control attenuation of the direct beam. The transmittance by aerosols is minimum at the short wavelengths and increases slowly as the wavelength increases. (Morel

The equation of the light arriving directly from the sun at ground level for a wavelength λ is

d o rawou I H DT T T T T λ λ λλ λλ λ = (3)

vapor precipitated amount of ozone, pressure and albedo (Guyot & Fagu ,1992).

for exemple, water-vapor content, ozone layer thickness, and turbidity parameters.

sun-soil (this factor depends on the number of days and cos (θz) is the zenith angle).

presented by the transmittance according to Bouguer's law (Bouguer, 1953):

Iλ is the spectral radiation output and I0λ is the radiation spectral λ input.

Rayleigh scattering. (Fröhlich & Brusa, 1981**)**

**3.1 Model description of irradiance** 

**3.2 Direct spectral irradiance on the ground** 

scattered backward.

& Gentili, 1993)

as follows:

Where

In this research, we are interested in applying the model to simulate the radiative transfer through the atmosphere under realistic conditions for assessing the significance of the effects of the atmosphere and conditions on shooting satellite images. The main objective of this application is the analysis of satellite measurements, along with their variations atmospheric parameters. The spectral signature of water is used here to simulate the action of the satellites. (Gordon, 1974)
