Validation of RKAS Soil Dielectric Model at C and X-Band Microwave Frequencies

In the present study an attempt is made to validate soil dielectric model which was formed to estimate the values of dielectric constant of dry and moist soil at various volumetric moisture contents at C and X-Band microwave frequencies. Eight Soil samples are collected from various parts of Haryana. Dielectric constants are measured using waveguide cell technique at C and X-Band microwave frequencies at varying volumetric moisture contents and then compared with estimated values obtained from model. The model has good accuracy and practicality.


INTRODUCTION
In the present era of technology, microwave remote sensing is a major tool to understand and analyze natural resources like soil.The soil has physical properties like porosity, bulk density, texture, grain size, color etc; Chemical properties like pH, organic matter, nutrients available, inorganic matter etc; Electrical properties like permeability, dielectric constant, dielectric loss, electrical conductivity etc.In microwave remote sensing of soil, its electrical parameters play important role as it depends on soil moisture, texture of soil and frequency at which measurements are made.Dielectric constant is a function that depends on texture of soil, moisture content and frequency at which observations are made [1]- [8] and play very important role to understand and analyze soil.
For the estimation of value of dielectric constant of soil from its physical constituents and volumetric moisture content present in it, a mathematical model was formed which is named as RKAS model [9].In our previous study [9], the model is formed using results of six soil samples from  Table 1.

TABLE I. TEXTURE OF SOIL SAMPLES ON WHICH TESTING OF VALIDATION IS DONE
The samples of soil collected first sieved and coarse particles are removed.The texture structure of four samples is presented in Table 1 for which measurements are made.The fine particles obtained are then oven dried for several hours to remove moisture completely and make it dry.Now to prepare moist soil samples measured quantity of distilled water is added to dried soil.The gravimetric soil moisture content in percentage term is calculated using the following relation [11]: Where , is the weight of wet soil and is the weight of dry soil.

A. Measurement of dielectric constant of soil
In the present work, technique used for the measurement constant is waveguide cell technique [12].A microwave bench operating at C-Band is used at 5.

IV. CONCLUSION
From the study on the variation of dielectric constant of soil with volumetric moisture content, it is found that dielectric constant is strongly depend on volumetric moisture content.Table 2 and Table 3 shows the variations of dielectric constant of soil of Kaithal, Rewari, Jind, Panipat, Sonipat, Jhajjar,

1 IKG
Hisar, Ramgarh, Rohtak, Siswal, Balsmand and Naraingarh at various moisture contents and compared with Hallikainen et al.Model [10].In the present paper, an attempt is made to validate the mathematical model for soil samples from eight different locations of Haryana with different textured soil.These eight locations are Kaithal, Rewari, Jind, Panipat, Sonipat, Jhajjar, and Mahendargarh and Sirsa districts of Haryana.Validation of RKAS Soil Dielectric Model at C and X-Band Microwave Frequencies Rajeev Kumar 1 , Arvind Sharma 2 , Anupamdeep Sharma 3 Punjab Technical University, Jalandhar, Punjab, India, 2 Anupamdeep Sharma, National Institute of Pharmaceutical Education and Research, Raiberraily (UP), India 487 Testing of validation of the model is done in two steps: 1.Comparison of modeled results of dielectric constant at various volumetric moisture contents with measured results at different frequencies.2. Comparison of modeled results of dielectric constant at various volumetric moisture contents with other available model at different frequencies.II.EXPERIMENTAL DETAILS Soil samples are collected from eight different locations of Haryana -Kaithal, Rewari, Jind, Panipat, Sonipat, Jhajjar, Mahendargarh and Sirsa.Texture of these eight samples are given in 488source at room temperature and another microwave bench operating at X-Band is used at 12 GHz in TE10 mode with reflex Klystron as microwave source were used for measurements.The microwaves are allowed to be incident on the sample.A part of incident signal reflects and superimpose with incident signal to give rise to standing wave pattern.The dielectric constant is measured by using the shift in minima of standing wave pattern that takes place due to the change in guide wavelength on the introduction of sample in the waveguide.Dielectric constant can be calculated using the following relation:where is real part of admittance, is wavelength in air filled guide, a = inner width of rectangular waveguide.

Fig. 1 .
Fig. 1.Block Diagram of Experimental Set up of Microwave Bench.

Mahendargarh and Sirsa with volumetric moisture content at 5
GHz and 12 GHz.Values obtained under laboratory conditions and modeled values are presented here.The values obtained experimentally are compared with RKAS model as well as with Hallikainen model.It is seen that the values obtained from RKAS model are accurate and the percentage error is in allowable range.

TABLE II .
COMPARISON OF MODELED AND OBSERVED VALUES OF DIELECTRIC CONSTANT AT C-BAND