**5. Simulation of satellite data for SDDS**

Based on this physical model, we developed a simulation system of satellite data to correct the scattered radiation of atmospheric effects.

A library of spectral signatures is introduced, it covers the main ground objects that have a reflectance in the bands of the electromagnetic spectrum. The combination of spectral signatures and different radiances allows us to calculate the spectral radiance reflected from the surfaces. The simulation results depend on the choice of input parameters. The software allows to show the influence of the effects of various parameters and geometric characteristics of the structures on the signal reaching the sensors onboard the satellite SPOT, LANDSAT and IRS1C.

To highlight the effect of a given parameter on the satellite measurement, are assigned fixed data for all variables in the case of a clear sky and for geometrically well defined.

The second part is from satellite SPOT, LANDSAT and IRS1C, applying the method of covariance matrix (a method that can provide a correction locally specific in the sense that it relates to the pixels of a given region of the image), one can estimate the atmospheric noise through a program to input data images from different channels and outputs the atmospheric noise of these channels.The physical quantity measured by the shooting system (sensor) is a solar radiation reflected by the soil-atmosphere averaged in some way in the spectral band considered the sensor. It depends on angle of illumination and shooting.

To determine the different radiation received at the satellite, the data input parameters are astronomical, geographical and atmospheric.

#### **5.1 Atmospheric correction of remotely sensed data**

Atmospheric correction is a major issue in visible or near-infrared remote sensing because the presence of the atmosphere always influences the radiation from the ground to the sensor.

As introduced before, the atmosphere has severe effects on the visible and near-infrared radiance.

**First**, it modifies the spectral and spatial distribution of the radiation incident on the surface.

**Second**, radiance being reflected is attenuated.

**Third**, atmospheric scattered radiance, called path radiance, is added to the transmitted radiance.

Solar Radiation Modeling and Simulation of Multispectral Satellite Data 207

Fig. 7. Contribution of the atmosphere on the multispectral channels SPOTXS.

calculated by replacing the zenith angle from the viewing angle.

depends on the angle of illumination and shooting. (Bachari et al., 1997)

**6. Analysis of variation in luminance** 

Fig. 8. Simulation of the scattered radiation as SDDS

Tat-sat(λ) is the spectral transmittance of the atmosphere, such that its optical path is

To dissect the effects of the various elements contributing to satellite measurements, we developed a software simulation of satellite data (SDDS) using the visual language Basic.6. The tool is based on modeling of radiation and atmospheric effects. The monitoring of the solar spectrum as a double drive-ground and ground sun-sensor is implemented based on the concepts of codes 5S, 6S, to simulate different radiances reaching the sensor. For the operation of the system we used the extinction coefficients of the solar spectrum in the developed Lowtran.6 and a bank of spectral signatures extracted from the software ENVI.4.3 (2007).

The physical quantity measured in the system shooting (sensor) is a solar radiation reflected by the soil-atmosphere averaged in some way in the spectral band considered the sensor. It

The atmosphere transmittance is:

$$T\_{\theta} = \exp(-\pi/\mathcal{C}os(\theta))\tag{18}$$

Where τ is the atmospheric optical thickness and θ can be sonar zenith angle or satellite angle view.

The optical thickness is composed of:

$$
\tau\_{\lambda} = \tau\_{a\lambda} + \tau\_{R\lambda} + \tau\_{d\lambda} \tag{19}
$$

���: Thickness selective absorption

���: Thickness scattering by small particle (molecular) is named Rayleigh diffuse

���: Thickness scattering by medium particle is named Mie diffuse

For a given spectral interval, the solar irradiance reaching the earth's surface is

$$E\_g = \int\_{\lambda\_1}^{\lambda\_2} (E\_S T\_i \text{Cov} \left( l \right) + E\_d ) d\lambda \tag{20}$$

The scattering is dominated by aerosols while back scattering is mainly due to Rayleigh scattering. A number of path radiance determination algorithms exists. For a nadir view as Landsat MSS, TM and SPOT HRV are usually used. In this section, we only tried to introduce some basic concepts of this complex topic. This is only a single-scattering correction algorithm for nadir viewing condition. More sophisticated algorithms which count multiple-scattering do exist. Some examples of these algorithms are LOWTRAN7, 5S (Simulation of the Satellite Signal in the Solar Spectrum 5S) and 6S (Second Simulation aircraft, altitude of target).

There are FORTRAN codes available for these algorithms. The 5S and 6S are proposed by Tanre (Tanre et al., 1990).

For small wavelengths the atmospheric contribution is very important, we wish to point out that the impact angle is also important he was noticed by a degradation of the signal that reaches the sensor signals for all contributors to the signal exciting the radiometer. The simulation analysis shows the need to correct the satellite images of atmospheric effects in order to identify objects on the ground. (Figure7)

The composition of the atmosphere disturbs the path of electromagnetic radiation between the source on the one hand, between the earth and the satellite on the other. Atmospheric effects resulting absorption and diffusion, performed jointly by the two major components: gases and aerosols.

When a signal is recorded, it is the part of the spectral radiation scattered by air molecules and aerosols to the outside of the system soil – atmosphere (Popp, 1994).

This signal Hλ(b) is called atmospheric noise :

$$\mathbf{H}^{\chi}(\mathbf{b}) = \mathbf{E}(\chi)\mathbf{L}^{\text{up\\_out}}(\chi) \tag{21}$$

���: Thickness scattering by small particle (molecular) is named Rayleigh diffuse

For a given spectral interval, the solar irradiance reaching the earth's surface is

��

�� <sup>=</sup> � (��������(�) � ��)�� ��

The scattering is dominated by aerosols while back scattering is mainly due to Rayleigh scattering. A number of path radiance determination algorithms exists. For a nadir view as Landsat MSS, TM and SPOT HRV are usually used. In this section, we only tried to introduce some basic concepts of this complex topic. This is only a single-scattering correction algorithm for nadir viewing condition. More sophisticated algorithms which count multiple-scattering do exist. Some examples of these algorithms are LOWTRAN7, 5S (Simulation of the Satellite Signal in the Solar Spectrum 5S) and 6S (Second Simulation -

There are FORTRAN codes available for these algorithms. The 5S and 6S are proposed by

For small wavelengths the atmospheric contribution is very important, we wish to point out that the impact angle is also important he was noticed by a degradation of the signal that reaches the sensor signals for all contributors to the signal exciting the radiometer. The simulation analysis shows the need to correct the satellite images of atmospheric effects in

The composition of the atmosphere disturbs the path of electromagnetic radiation between the source on the one hand, between the earth and the satellite on the other. Atmospheric effects resulting absorption and diffusion, performed jointly by the two major components:

When a signal is recorded, it is the part of the spectral radiation scattered by air molecules

Hλ(b)=E(λ)Tat-sat(λ) (21)

and aerosols to the outside of the system soil – atmosphere (Popp, 1994).

���: Thickness scattering by medium particle is named Mie diffuse

θ

�� = ���(�� ��� ⁄ ) (�) (18)

�� = ��� � ��� � ��� (19)

can be sonar zenith angle or satellite

(20)

The atmosphere transmittance is:

The optical thickness is composed of:

���: Thickness selective absorption

aircraft, altitude of target).

Tanre (Tanre et al., 1990).

gases and aerosols.

order to identify objects on the ground. (Figure7)

This signal Hλ(b) is called atmospheric noise :

is the atmospheric optical thickness and

Where τ

angle view.

Fig. 7. Contribution of the atmosphere on the multispectral channels SPOTXS.

Tat-sat(λ) is the spectral transmittance of the atmosphere, such that its optical path is calculated by replacing the zenith angle from the viewing angle.

To dissect the effects of the various elements contributing to satellite measurements, we developed a software simulation of satellite data (SDDS) using the visual language Basic.6. The tool is based on modeling of radiation and atmospheric effects. The monitoring of the solar spectrum as a double drive-ground and ground sun-sensor is implemented based on the concepts of codes 5S, 6S, to simulate different radiances reaching the sensor. For the operation of the system we used the extinction coefficients of the solar spectrum in the developed Lowtran.6 and a bank of spectral signatures extracted from the software ENVI.4.3 (2007).
