DIELECTRIC PROPERTIES OF NORTH INDIAN OCEAN SEAWATER AT 5 GHZ

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DIELECTRIC PROPERTIES OF NORTH INDIAN OCEAN SEAWATER AT 5 GHZ Powered By Docstoc
					International Journal of Advances in Engineering & Technology, Jan 2012.
©IJAET                                                              ISSN: 2231-1963



       DIELECTRIC PROPERTIES OF NORTH INDIAN OCEAN
                    SEAWATER AT 5 GHZ
                          A.S. Joshi1, S.S. Deshpande2, M.L.Kurtadikar3
                   1
                 Research Scholar, J.E.S. College, Jalna, Maharashtra, India.
                   2
                Rashtramata Indria Gandhi College, Jalna, Maharashtra, India.
 3
   P.G. Department of Physics and Research centre, J.E.S. College, Jalna, Maharashtra, India.




ABSTRACT
This study presents dielectric properties of North Indian Ocean seawater. In all, fourteen seawater samples are
collected from Arabian Sea, Lakshadweep Sea, Tip of Bay of Bengal Sea, deep Indian Ocean and Equatorial
region. The Von Hipple method is used to measure dielectric properties, both real part ε' and imaginary ε'', at 5
GHz and 30 °C using automated C-Band microwave bench set up. The dielectric constant ε' and dielectric loss
ε'' are calculated using least square fitting technique. The salinity measurement of seawater samples are done
on autosalinometer. Making use of salinity values of all samples and for 5 GHz and 30 °C, static dielectric
constant and dielectric loss are estimated by Klein-Swift model and Ellison et al. model. Experimental and
theoretical results are compared. This study emphasizes latitude and longitudinal variations of salinity and
dielectric properties. The laboratory data obtained are significant for microwave remote sensing applications in
physical oceanography.

KEYWORDS: Seawater Permittivity, Salinity, North Indian Ocean, 5 GHz microwave frequency.

      I.     INTRODUCTION
Indian Ocean is third largest ocean of the world and has unique geographic setting. The Tropical India
Ocean (TIO), in particular is significant to oceanographers and meteorologists as it experiences the
seasonally reversing monsoon winds and is land locked on northern side. Remote sensing [1-2] of
ocean sea surface salinity, sea surface temperature is important in the areas like seawater circulations,
climate dynamics, atmosphere modeling, environmental monitoring etc. For microwave remote
sensing applications over ocean radar and radiometer, precise values of emissivity and reflectivity are
required. The surface emissivity is a complex function of dielectric constant of surface seawater. This
complex function is composed of two parts, the real part is known as the dielectric constant (ε′) and is
a measure of the ability of a material to be polarized and store energy. The imaginary part (ε′′) is a
measure of the ability of the material to dissipate stored energy into heat. The two are related by the
expression:
                                    ∗= ′− ′′                       …1
The dielectric constant in turn is governed by electrical conductivity and microwave frequency under
consideration. The conductivity is governed by salinity and temperature of seawater [3-4]. There are
variations in salinity and temperature of ocean resulting variation in dielectric properties and hence in
emissivity at that particular location. These variations follow certain pattern latitude and longitude of
the location, due to dynamic features of the ocean.
 This work focuses on measurement of dielectric properties of seawater samples at 5 GHz at 30°C.
The study emphasizes on latitude and longitudinal variations in salinity and dielectric properties.
Knowing the dielectric constant and dielectric loss, the parameters like emissivity, brightness



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International Journal of Advances in Engineering & Technology, Jan 2012.
©IJAET                                                              ISSN: 2231-1963
temperature, scattering coefficient can be interpreted, as they are interdependent. Making use of the
measured salinity values of all samples, static dielectric constant and dielectric loss are estimated by
Klein-Swift model [5-6] and Ellison et al. model [7-8] for 5 GHz and 30 °C. The laboratory data
obtained are significant for interpretation of microwave remote sensing applications, and helps in
designing active and passive microwave remote sensors.

    II.     MATERIAL AND METHODOLOGY
2.1. Seawater Sampling
By participating in ORV Sagar Kanya scientific cruise SK-259, organized by NCAOR in May-June
2009 that is summer monsoon period, seawater samples were collected from Arabian Sea,
Lakshadweep Sea, Tip of Bay of Bengal Sea, deep Indian Ocean and from equatorial regions of
Tropical Indian Ocean. Surface seawater at different locations were drawn through bucket
thermometer and two bottles of the samples were preserved around 4°C by standard procedure. Out of
two bottles, one of the samples was used to determine the salinity parameter at that location using an
Autosalinometer 8400B in the laboratory onboard Sagar Kanya vessel and the other sample of the
same location was brought to the Microwave Research Lab, J.E.S. College, Jalna, Maharashtra for
dielectric measurement.
2.2. Temperature and Salinity Measurement
The bucket thermometer is used to measure the temperature of surface seawater. Salinity
measurements of seawater samples were done using 8400B AUTOSAL onboard ORV Sagar Kanya
laboratory. This instrument is semi-portable, semi-automatic and is used in the land based or sea-
borne laboratory to determine salinity levels of saline seawater samples and standard seawater sample
by measuring their equivalent conductivity. The instrument reading is displayed in terms of
conductivity ratio. Inputting the conductivity ratio to the software available in the computer lab,
salinity value of the sample is calculated. The software calculates salinity using the following
formula. The equation is based on the definitions and the algorithm of practical salinity formulated
and adopted by UNESCO/ICES/SCOR/IAPSO Joint Panel on oceanographic tables and standards,
Sidney, B.C., Canada, 1980 [9-10].

                      a +a R        +a R     +a R
                S=                                                                 …2
                          +a R     +a R      + ∆S

                             T − 15                   b +b R         +b R
          ∆S =                                 ∗                                         …3
                      1 + 0.0162 T − 15             +b R      +b R    +b R

 Where     a = 35.0000, b = 0.0000,
 For, 2 ≤ S ≤ 42, and for − 2°C ≤ T ≤ 35 °C.
                             Table 1. Values of the coefficients a and b

                                      i         a              b
                                      0      0.0080         0.0005
                                      1     -0.1692        -0.0056
                                      2     25.3851        -0.0066
                                      3     14.0941        -0.0375
                                      4     -7.0261         0.0636
                                      5      2.7081        -0.0144

2.3. Measurement of Dielectric Properties
There are several methods of dielectric measurement of liquid [11]. In present work, the dielectric
properties of seawater samples are measured using Von Hipple Method [12] for which automated C-


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International Journal of Advances in Engineering & Technology, Jan 2012.
©IJAET                                                              ISSN: 2231-1963
Band microwave bench , as shown in figure 1, is used. The MW bench consists of a low power
tunable narrow band VTO-8490 solid-state microwave source; having frequency range of 4.3-5.8
GHz. Tuning voltage is kept at 7 volts, throughout the experiment, which corresponds 5 GHz
frequency. The other components of the bench setup are: an isolator, coaxial to waveguide adapter,
attenuator, SS tuner, slotted line and the liquid dielectric cell.




                            Figure 1. Block diagram of a C-band microwave bench.

Microwave generated by the VTO propagate through the rectangular waveguide to the liquid cell. A
desired power level in the line is adjusted with the attenuator. A slotted section with a tunable probe is
used to measure the power along the slot line. The crystal detector (1N23) in the probe is connected to
a microammeter and to the PC to read, acquire and store the data. The empty liquid dielectric cell is
connected at the output end of the bench. The bench is tuned to get symmetrical standing wave pattern
in the slot line. The positions of minima are noted from the pattern from which wavelength λg of the
wave-guide can be calculated. The probe position on the slot line is kept constant at the first minima
of the standing wave pattern in the slot line. The liquid dielectric cell is then filled with the sample
under consideration. The plunger of the liquid cell is initially set in a position such that the thickness
of the liquid column below the plunger is zero. By moving the plunger away from this position, data
of microwave power is recorded for different plunger positions. The data of plunger positions and the
corresponding power are acquired and stored in a file which is further used to calculate dielectric
constant ε and dielectric loss ε using the least square fit program. The parameters α, β, P0, δ are used
as the fitting parameters, where α= attenuation factor, β=propagation constant, P0=maximum power,
and δ= phase factor. The computer program also takes care of calculating error in dielectric constant,
∆ε′, and error in dielectric loss, ∆ε′′.
The dielectric properties of seawater samples can be calculated using the relations
                              1     α −β
                   ε′ = λ       +                                                   …4
                             λ        4π

and

                   ε′′ =                                                           …5
                           λ αβ
                           2π

where λ is the free space wavelength which can be calculated using the formula
                1     1    1
                   = +                                                       …6
                λ     λ    λ

Whereλ = 2a = 2 ∗ 4.73 cm = 9.46 cm, ‘a’ being the broader side of the C-band rectangular wave-
guide.




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International Journal of Advances in Engineering & Technology, Jan 2012.
©IJAET                                                              ISSN: 2231-1963

   III.     RESULTS AND DISCUSSIONS
The Sea Surface Temperature of collected samples is found to be between 27 °C to 30 °C (Table 1.).
Winds over the North Indian Ocean reverse twice during a year. They blow from the southwest during
May – September and from the northeast during November – January with the transition-taking place
during the months in between. Forced by these winds, circulation in the Indian Ocean has a general
eastward direction during summer (May – September) and westward during winter (November –
January). During summer, period when seawater samples were collected the monsoon current flows
eastward as a continuous current from the western Arabian Sea to the Bay of Bengal [13-14]. These
circulations are shown in Figure 2.




Figure 2. Schematic diagram of major surface currents in the TIO during the southwest (summer) monsoon.
The thickness represents the relative magnitude of the current (adapted from Shenoi et al., 1999a) [15].

The Arabian Sea has high salinity (usually in the range 35 to 37) due to excess of evaporation over
rainfall. In Table 2, the samples S-01 and S-03 are from Arabian Sea and have higher salinity values
compared to other samples.
                     Table 2. The temperature and salinity values of seawater samples.
            Sample          Latitude          Longitude          Temperature             Salinity
                                                                     °C
             S-01           N 080 30'          E 750 47'             30                  35.0238
                                0                  0
             S-02           N 08 06'           E 78 31'               27                 34.6434
             S-03           N 070 36'          E 760 18'              30                 35.1564
                                0                  0
             S-04           N 07 39'           E 78 38'               27                 34.9782
             S-05           N 060 49'          E 760 52'              30                 34.7117
                                0                  0
             S-06           N 06 00'           E 79 09'              27.5                35.0079
             S-07           N 050 11'          E 780 00'              29                 34.6353
                                0                  0
             S-08           N 05 12'           E 79 39'               28                 34.5746
             S-09           N 040 33'          E 780 25'              29                 34.7316
                                0                  0
             S-10           N 04 25'           E 80 16'               28                 34.5082

             S-11           N 030 00'          E 810 20'              27                 34.4115
                                0                  0
              S12           N 02 46'           E 81 28'              28.5                34.3808
              S13           N 010 27'          E 820 24'              28                 34.8350
                                0                  0
              S14           N 00 37'           E 82 40'               29                 34.9186




    223                                                                     Vol. 2, Issue 1, pp. 220-226
International Journal of Advances in Engineering & Technology, Jan 2012.
©IJAET                                                              ISSN: 2231-1963
In contrast, the Bay of Bengal has much lower salinity due to the large influx of fresh water from river
discharge and high amount of rainfall. The samples S-02 and S-04 although located on similar latitude
as S-01 and S-03 respectively, differ longitudinal wise and for these Lakshadweep Sea samples,
drawn at mouth of Bay of Bengal Sea, decrease in salinity is seen.
The samples S-05, S-07, S-08 are from deep IO and S-06, S-08, S-10, although located on similar
latitude, differing in longitude, are towards east, and are from border of Bay of Bengal Sea and
Arabian Sea. The salinity values of these samples are found less than the former ones.
As we move towards Equator there is slight decrease in salinity in case of the samples S-11, S-12, but
near the equatorial regions, S-13, S-14, a sudden slight increase in salinity value is found. This is due
to high evaporation in low-pressure equatorial regions [16].
The dielectric constant ε', dielectric loss ε'', error in dielectric constant ε' and error in dielectric loss
  ε'', at 5 GHz, at 30 °C and with varying salinity, latitude and longitude wise in North Indian Ocean
are given in Table 3. The magnitude of dielectric constant is found to be 66. It is found that dielectric
constant is decreased with increase in salinity. The dielectric loss values are in range of 53 to 58.

       Table 3. The experimentally measured values of dielectric constant ′ , dielectric loss ′′ , error in
             dielectric constant ∆ ′ , error in dielectric loss ∆ ′′of all seawater samples at 5 GHz.

  Sample           Latitude         Longitude        Salinity         ε'           ε''              ε'          ε''
   S-01            N 080 30'         E 750 47'       35.0238       66.5285       53.8442       6.6474      2.3641
   S-02            N 080 06'         E 780 31'       34.6434       66.7812       53.9340       7.4309      2.6384
                       0                  0
   S-03            N 07 36'          E 76 18'        35.1564       66.5103       56.9364       6.9828      2.5926

   S-04            N 070 39'         E 780 38'       34.9782       66.5876       53.8652       7.5291      2.6767
                       0                  0
   S-05            N 06 49'          E 76 52'        34.7117       66.7164       53.9111       6.9207      2.4583

   S-06            N 060 00'         E 790 09'       35.0079       66.5675       56.4844       7.0274      2.5917
                       0                  0
   S-07            N 05 11'          E 78 00'        34.6353       66.8153       57.7529       6.6314      2.4801

   S-08            N 050 12'         E 790 39'       34.5746       66.8288       53.9509       7.6745      2.7241
                       0                  0
   S-09            N 04 33'          E 78 25'        34.7316       66.7093       53.9086       6.9227      2.9227
   S-10            N 040 25'         E 800 16'       34.5082       66.8354       53.9645       7.8615      2.7907
                       0                  0
   S-11            N 03 00'          E 81 20'        34.4115       66.9019       58.549        6.4895      2.4498
    S12            N 020 46'         E 810 28'       34.3808       66.954        55.9341       6.0384      2.0061
                       0                  0
    S13            N 01 27'          E 82 24'        34.8350       66.6813       55.7891       7.2306      2.6381
    S14            N 000 37'         E 820 40'       34.9186       66.6072       56.7009       7.5652      2.7969



The values calculated in Tables 4 and 5 are by using Klein and Swift and Ellison et al. models
respectively. Comparison of measurement results with these respective models shows that real part,
dielectric constant ε' values are well in agreement. However, our experimental loss factor is higher by
a magnitude of about 20 as compared with the theoretical models. The percentage error in
measurement in dielectric constant and loss is of the order of 7 and 2 respectively.

Table 4. The calculated relaxation time, τ ps , static dielectric constant ε , dielectric constant ε and dielectric
loss ε using Klein-Swift Model at 5 GHz.

  Sample           Latitude         Longitude       Salinity                                   ε'             ε''
                       0                 0
    S-01           N 08 30'          E 75 47'        35.0238     69.6620       7.0859       66.6042       34.7258
                       0                 0
    S-02           N 08 06'          E 78 31'        34.6434     69.7340       7.0875       66.6715       34.5412
    S-03           N 070 36'         E 760 18'       35.1564     69.6369       7.0853       66.5807       34.7901


    224                                                                         Vol. 2, Issue 1, pp. 220-226
International Journal of Advances in Engineering & Technology, Jan 2012.
©IJAET                                                              ISSN: 2231-1963
    S-04           N 070 39'         E 780 38'      34.9782      69.6707       7.0861       66.6123      34.7037
                       0                 0
    S-05           N 06 49'          E 76 52'       34.7117      69.7211       7.0872       66.6594      34.5743
    S-06           N 060 00'         E 790 09'      35.0079      69.6650       7.0859       66.6068      34.7187
                       0                 0
    S-07           N 05 11'          E 78 00'       34.6353      69.7355       7.0875       66.6729      34.5372
    S-08           N 050 12'         E 790 39'      34.5746      69.7469       7.0877       66.6836      34.5077
                       0                 0
    S-09           N 04 33'          E 78 25'       34.7316      69.7173       7.0871       66.6559       34.584
    S-10           N 040 25'         E 800 16'      34.5082      69.7595       7.0880       66.6953      34.4755
                       0                 0
    S-11           N 03 00'          E 81 20'       34.4115      69.7777       7.0884       66.7123      34.4284
    S12            N 020 46'         E 810 28'      34.3808      69.7835       7.0885       66.7177      34.4135
                       0                 0
    S13            N 01 27'          E 82 24'       34.8350      69.6977       7.0867       66.6376      34.6342
    S14            N 000 37'         E 820 40'      34.9186      69.6819       7.0863       66.6228      34.6747


Table 5. The calculated relaxation time τ ps , static dielectric constant ε , dielectric constant ε and dielectric
loss ε using Ellison et. al. model at 5 GHz.

  Sample           Latitude         Longitude       Salinity                                   ε'           ε''
                       0                 0
    S-01           N 08 30'          E 75 47'       35.0238      67.9616       7.4153       64.8768      33.8678
                       0                 0
    S-02           N 08 06'          E 78 31'       34.6434      68.0491       7.4230       64.9537      33.7003

    S-03           N 070 36'         E 760 18'      35.1564      67.9311       7.4126       64.8500      33.9261
                       0                 0
    S-04           N 07 39'          E 78 38'       34.9782      67.9721       7.4162       64.8861      33.8477

    S-05           N 060 49'         E 760 52'      34.7117      68.0334       7.4216       64.9399      33.7304
                       0                 0
    S-06           N 06 00'          E 79 09'       35.0079      67.9652       7.4156       64.8800      33.8608

    S-07           N 050 11'         E 780 00'      34.6353      68.0510       7.4232       64.9554      33.6967
                       0                 0
    S-08           N 05 12'          E 79 39'       34.5746      68.0649       7.4244       64.9676      33.6700

    S-09           N 040 33'         E 780 25'      34.7316      68.0288       7.4212       64.9359      33.7391
                       0                 0
    S-10           N 04 25'          E 80 16'       34.5082      68.0802       7.4258       64.9811      33.6408

    S-11           N 030 00'         E 810 20'      34.4115      68.1025       7.4278       65.0006      33.5982
                       0                 0
    S12            N 02 46'          E 81 28'       34.3808      68.1095       7.4284       65.0068      33.5847
    S13            N 010 27'         E 820 24'      34.8350      68.0050       7.4191       64.9150      33.7846
                       0                 0
    S14            N 00 37'          E 82 40'       34.9186      67.9858       7.4174       64.8981      33.8214




ACKNOWLEDGEMENTS
We are thankful to ISRO for providing the C-Band Microwave Bench Setup under RESPOND project
of Dr. M.L. Kurtadikar. Special thanks to NCAOR, Goa, for allowing participation in SK-259 cruise
of ORV Sagar Kanya, for seawater sample collection.

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[3] Smyth, C.P., (1955). Dielectric Behaviour and structure, McGRAW-HILL Book company Inc, New York.


    225                                                                         Vol. 2, Issue 1, pp. 220-226
International Journal of Advances in Engineering & Technology, Jan 2012.
©IJAET                                                              ISSN: 2231-1963
[4] Hasted, J.B, (1973). Aqueous Dielectrics, Chapman and Hall Ltd, London.
[5] Stogryn, A., (1971) Equation for calculating the dielectric constant of saline water, IEEE transactions on
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Authors
Anand Joshi was born in Aurangabad, India in 1981. He received B.Sc. degree in Physics,
Mathematics, Computer Science and M.Sc. degree in Physics from Dr. Babasaheb Ambedkar
Marathwada University, Aurangabad, Maharashtra, India in 2002 and 2004 respectively. He is
currently pursuing a Ph.D.(Physics) degree under the guidance of Dr. M.L.Kurtadikar,
Postgraduate Department of Physics and Research Centre, J.E.S. College, Jalna, Maharashtra,
India. His research interests include Dielectric measurements, Microwave Remote sensing
Applications and Astrophysics.
Santosh Deshpande was born in Parbhani, India in 1974. He received M.Sc. degree in Physics
from Swami Ramanand Teerth Marathwada University, Nanded, Maharashtra and M.Phil
degree in Physics from Algappa University, Tamil Nadu, India in 2000 and 2008 respectively.
He is currently working as Assistant Professor of Physics in the RMIG College, Jalna,
Maharashtra, India. He is also pursuing a Ph.D. degree under the guidance of Dr.
M.L.Kurtadikar, Postgraduate Department of Physics and Research Centre, J.E.S. College,
Jalna, Maharashtra, India. His research interests include Dielectric measurements, Microwave
Remote sensing Applications and Astrophysics.
Mukund L. Kurtadikar was born in Nanded, India in 1951. He received the Master of
Science (Physics) and Ph.D. (Physics) degrees from Marathwada University of Aurangabad,
India in 1973 and 1983 respectively. He is currently working as Associate Professor of Physics
in the Postgraduate Department of Physics of J. E. S. College, Jalna, Maharashtra, India. His
research interests include Microwave Remote Sensing Applications, dielectric measurements of
soils, seawater, rocks, snow, vegetation etc. He also works on Photometry of Variable Stars
using Small Optical Telescope and Scientific Exploration of Historic Monuments. He is a
Science Communicator.




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