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Prediction of emission and scattering coefficient from cloud layer contain gases ,ice and water vapor from optical and infrared band

Abstract Now a day the effect of cloud layer in ice and water vapor on the propagation of electromagnetic waves has become a subject of interest. Hence considerable attention has been devoted to evaluate the influence of natural occurring obscurant on the performance of electromagnetic wave (optical, infrared and millimeter wave) propagation. It may be mentioned that like other precipitation sand and dust particles present in the atmosphere ice, sheet, water vapor, different gases, also effect the propagation of electromagnetic waves. These particles affect the phase and amplitude of the wave during propagation. In this paper an attempt has been made to evaluate the scattering Aledo, coefficient, reflection coefficients from cloud layer using Radiative Transfer Model at optical, infrared radiation. After estimation of reflection coefficient and scattering coefficients, calculate temperature brightness with wavelength for different effective radius of particles of gases such as ozone, carbondiodixe, ammonia, water vapor

.
KEY WORDS: EMISSON COEFFICENT, ANGLE OF INCIDENCE, OPTICAL THERMAL AND REFLECTED INFRARED FREQUENCY, MOISTURE AND DEPTH OR THICKNESS, MODIS BANDS
1. Introduction

In this paper an attempt has been made for estimation of emissivity of optical, infrared, radiation signal using the MODIS band from cloud layer. The expression for emissivity and reflection coefficients from cloud layer which contain moisture, ice particles , sleet , rain , water developed have been developed both for vertical and horizontal polarization. Reflection and Emission coefficient depends on frequency, angle of incidence, dielectric constant of water , moisture water content and thickness ,surface roughness, chemical compositions, physical temperature , atmospheric temperature . It is found that Reflection coefficient of optical and infrared signal decreases with increases in wavelength an increases effective radius of particle. And scattering albedo also decreases with increases in wavelength increase with angle of incidence and visibilities. The dielectric constant for real and imaginary part increases with moisture content. At last also find temperature brightness from cloud layer for different gases , which has different values depend upon polarization properties . The intent of this document is to present algorithms for inferring certain optical and thermodynamical properties of cloud layers, specifically, optical thic k- ness, effective particle radius, and particle phase from multi wavelength reflected solar and emitted thermal radiation measurements. It is well known that clouds strongly modulate the energy balance of the Earth and its atmosphere through their

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interaction with solar and terrestrial radiation, as demonstrated both from satellite observations a n d from modeling studies. However, clouds vary considerably in their horizontal and vertical extent, in part due to the circulation pattern of the atmosphere with its requisite updrafts and downdrafts, and in part due to the distribution of oceans and continents and their numerous and varied sources of cloud condensation nuclei (CCN). A knowledge of cloud properties and their variation in space and time, therefore, is crucial to studies of global climate change (e.g., trace gas greenhouse effects), a corresponding cloud feedback working to enhance global warming. The main objective of this work is the development of routine methods for simultaneously retrieving the cloud optical thickness and effective particle radius from daytime multi wavelength reflected solar and emitted thermal radiation measurements. Retrieval of cloud particle phase from visible and near-infrared solar reflection measurements will also be discussed. The scattering albedo , temperature brightness and reflection coefficient is obtained by help of Radiative Transfer model , shows energy transfer between surface and clouds , and top of cloud which has higher temperature sue to extent solar radiation ,. These coefficients predict by optical and infrared wavelengths at different angle of incidence generally these values collaborate with MODIS data which has six bans of range MODIS is a

36-band scanning spectroradiometer. Four of these visible (0.645 mm) and near-infrared (1.64,

2.13, and 3.75 mm) spectral bands will be used in our daytime shortwave cloud retrieval algorithm over land surfaces, with 0.858 or 1.240 mm replacing 0.645 mm over ocean and bright snow/sea ice surfaces, respectively. Other bands in the thermal region, such as the 8.55, 11.03,

12.02, 13.335, 13.635, 13.935 and 14.235 mm bands, will be used for cloud cover and cloud top properties (including cloud top altitude, cloud top temperature and thermodynamic phase) In addition, the 11.03 m band will be used to make the thermal emission correction to the

3.75 m band during the day. The 0.645, 2.13 and 3.75 m bands will be used to retrieve the cloud optical thickness and effective particle radius over land (with 0.645 m
replaced by 0.858 m over oceans and 1.24 m over snow and sea ice surfaces); a combination of the 0.645, 1.64, and possibly the 2.13 m bands will be used for cloud
thermodynamic phase determination.

2.. Theoretical description

Radiative Transfer Model

In order to describe the characteristics of spectra measured by a passive infrared spectrometer, a model may be used in which the atmosphere is divided into plane-parallel Homogeneous layers along the optical path. In many cases a model with three layers is sufficient to describe the basic characteristics of the spectra (Figure 1). Radiation from the background, for example the sky or a surface (background layer), propagates through the vapor cloud (cloud layer, a mixture of the released molecules and air), and the atmosphere between the cloud and the spectrometer (atmospheric layer). The radiation containing the signatures of all layers is measured by the spectrometer. The cloud and atmospheric layers are considered homogeneous with regard to all physical and chemical properties. Application of the three layer model6 yields

LS (1τat )Bat  τat (1τc )Bc  τcLb 

for the spectral radiance at the entrance aperture of the spectrometer LS. Here, τat is the transmittance of the atmosphere between the spectrometer and the cloud, Bat is the spectral

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Radiance of a blackbody at the temperature of the atmosphere, Tat, τc is the transmittance of the cloud, and Bc is the spectral radiance of a blackbody at the temperature of the cloud, Tc. Lb is the radiance that enters the layer of the cloud from the background. The quantities in Equation (1) are frequency-dependent. Because the scattering coefficient in the infrared spectral region is small under many measurement conditions, the contribution of scattering is neglected in this model. If the temperatures of the cloud layer and the atmospheric layer are equal, Equation (1)

can be simplified:

LS Bat τat τ c Lb Bat . ………………………….. 2

To retrieve the cloud optical thickness and effective particle radius, a radiative transfer model is first used to compute the reflected intensity field. It is convenient to normalize the reflected intensity (radiance) I(0, , ) in terms of the incident solar I is the measured intensity at the top-of-atmosphere, Icloud-top is the cloud top intensity, including surface effects, in the absence of an atmosphere, and tatm is the above-cloud transmittance in either the or 0 directions flux F0at different wavelength (), such that the reflection function R(c, re; , 0, ) is defined

by R(c’, re; , 0, ) = I(0, , ) re c / 0F0 (λ ) …………………………………3 where c is the total optical thickness of the atmosphere (or cloud), re the effective particle radius, defined by (Hansen and Travis 1974)

re = r 3n(r )d r / r 2 n(r )d r , ……………………………….4

where n(r) is the particle size distribution and r is the particle radius, 0 the cosine of the solar zenith angle 0, the absolute value of the cosine of the zenith angle , measured with respect to the positive direction, and the relative azimuth angle between the direction of propagation of the emerging radiation and the incident solar direction. When the optical thickness of the atmosphere is sufficiently large, numerical results for the reflection function must agree with known asymptotic expressions for very thick layers (van de Hulst 1980). Numerical simulations as well as asymptotic theory show that the reflection properties of optically thick layers depend essentially on two parameters, the scaled optical thickness c
c= (1 0g)c …………………………………….5
where g is the asymmetry factor and 0 the single scattering albedo of a small volume of cloud air.
Putting the value of re ,cin equ 3 we get reflection coefficient of optical and infrared signal from cloud layer.

R(c’, re; , 0, ) = I(0, , ) r 3n(r )d r / r 2 n(r ) d r (1 0g)c / 0F0 (λ )

………….6

Then transmittance of signal is given as τc from the cloud is

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τc = 1- R(c’, re; , 0, ) ………………………7

Now then we calculate scattering Aledo from cloud thickness layer at different wavelength at solar zenith angle of 10 degree is defined as
0 = 1+c/c g ………………………………..8
Putting he value of τc in 8
0 = 1+c/ 1- R(c’, re; , 0, ) g

0 = 1+c/ 1- I(0, , ) r 3n(r )d r / r 2 n(r )d r (1 0g)c / 0F0 (λ ) g

…………………………9
Putting in radiative transfer equation we ret transfer of heart and energy between land, surface, cloud layer, top of clouds, and different gases.
Now calculate for Brightness temperature from cloud layer as a function of wavelength for nadir observations and for various values of the effective radius of cloud droplets, where the cloud optical thickness tc(0.75 mm) = 5 for all cases. Results apply to water clouds having a modified gamma distribution embedded in a midlatitude summer atmosphere with cloud top temperature Tt = 14°C, cloud base temperature Tb = 17°C, and an underlying surface temperature Ts = 21°C

LS Bat τat τ c Lb Bat .

Brightness temperature Bat = LS- τat τ c Lb/1+ τat τ c ……………………………10

Bat = LS- τat 1- R(c’, re; , 0, ) Lb/1+ τat 1- R(c’, re; , 0, )

For ice particles:

Cloud is composed of 50% bullet rosettes,30% hollow columns, and 20% solid plate ice crystals From ice particles present in cloud layer causes volume scattering, an volume extinction coefficient is given as dp =ke -1 ……………………………….11
K is sum of absorption and scattering coefficients the penetration depth is given by
stiles dp = λ√ε/έ ……………………..12

Volume scattering is given from ice particles,

σvolvv = 0.75f L cosθi[1-exp(-2ked/cosθt)] …………………………..13 where L denote the width and the maximum dimension of an ice crystal,

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respectively, and n(L) is the size distribution as a function of L, f is frequency θi is angle of incidence , θt is angle of transmission .

3.. Result and discussion In this paper an attempt has been made to evaluate the scattering, reflection coefficients from cloud layer using Radiative Transfer Model at optical, infrared radiation. After estimation of reflection coefficient and scattering coefficients, calculate temperature brightness with wavelength for different gases. The sensor-measured intensity at visible wavelengths (0.66 m) is primarily a function of cloud optical thickness, whereas near-infrared intensities (1.6, 2.1, and 3.7 m) are sensitive both to optical thickness and, especially, cloud particle size. As a consequence, Rayleigh scattering in the atmosphere above the cloud primarily affects the cloud optical thickness retrieval since the Rayleigh optical thickness in the near-infrared is negligible. Because the Rayleigh optical thickness in the visible wavelength region is small (about

0.044 at 0.66 m), it is frequently overlooked in retrieving cloud optical thickness for to investigate the Rayleigh scattering effects on cloud optical thickness retrievals . from fig
1, eq 6 it is observed that reflection coefficient of signal decreases with increases wavelength up to infrared region .We simplified the air-cloud system as a two-layer
atmosphere with molecules above the cloud, and carried out simulations with an adding- doubling code as from graph temperature brightness has different values for different
molecules varies with wavelength , its values for water has high at 5-6 micrometer , for carbon dioxide it has 4-5 micrometer . , for ozone it has high 10-12 micrometers from
equ 10 fig 3 it is observed that temperature brightness fro atmosphere cloud layer top cloud layer increases with wavelength . , For ice crystal two thing come from equ 13 fig 4
that with increases in frequency, back scattering or volume scattering from ice particles increases, due to lambertian surface and with increases in angle of incidence the back
scattering decrsses from cloud model. , and from equ 9 fig 2 it is observed that second scattering coefficients decreases with increases in wavelength at different effective
particle thickness.

5 10 15 20 25

optical thickness in micrometer

λ =065

1.65

2.72

3.72

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Fig 1 shows variation of reflection coefficient and optical effective radius of particle at different wavelength

0.6

0.5

0.4

0.3

0.2

0.1

re=4

WAVELENGTH MICROMETER

Fig 2 shows variation of scattering albedo in db and wavelength at different effective radius of particles re in micrometer.

2000

1500

1000

500

3 6 9 12 15 18

WAVELENGTH MICROMETER

re=4

Fig 3 shows variation of temperature brightness and wavelength at different effective radius of particles re in micrometer.

10 8 λ=065

6 1.65

2.72

4

3.72

2

0

angle of incidence

Fig 4.shows variation of scattering coefficient and optical effective radius of particle at different wavelength

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Prediction of emission and scattering coefficient from cloud layer contain gases ,ice and water vapor from optical and infrared band

2.. Theoretical description

For ice particles:

10

8 λ=065

6 1.65

2.72

4

3.72

2

0

References

13, 777–794.