DIELECTRIC PROPERTIES OF NORTH INDIAN OCEAN SEAWATER AT 5 GHZ Copyright IJAET

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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 å' and imaginary å'', at 5 GHz and 30 °C using automated C-Band microwave bench set up. The dielectric constant å' and dielectric loss å'' 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.

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DIELECTRIC PROPERTIES OF NORTH INDIAN OCEAN SEAWATER AT 5 GHZ Copyright IJAET

  1. 1. 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.ABSTRACTThis study presents dielectric properties of North Indian Ocean seawater. In all, fourteen seawater samples arecollected from Arabian Sea, Lakshadweep Sea, Tip of Bay of Bengal Sea, deep Indian Ocean and Equatorialregion. The Von Hipple method is used to measure dielectric properties, both real part ε and imaginary ε, at 5GHz and 30 °C using automated C-Band microwave bench set up. The dielectric constant ε and dielectric lossε are calculated using least square fitting technique. The salinity measurement of seawater samples are doneon autosalinometer. Making use of salinity values of all samples and for 5 GHz and 30 °C, static dielectricconstant and dielectric loss are estimated by Klein-Swift model and Ellison et al. model. Experimental andtheoretical results are compared. This study emphasizes latitude and longitudinal variations of salinity anddielectric properties. The laboratory data obtained are significant for microwave remote sensing applications inphysical oceanography.KEYWORDS: Seawater Permittivity, Salinity, North Indian Ocean, 5 GHz microwave frequency. I. INTRODUCTIONIndian Ocean is third largest ocean of the world and has unique geographic setting. The Tropical IndiaOcean (TIO), in particular is significant to oceanographers and meteorologists as it experiences theseasonally reversing monsoon winds and is land locked on northern side. Remote sensing [1-2] ofocean sea surface salinity, sea surface temperature is important in the areas like seawater circulations,climate dynamics, atmosphere modeling, environmental monitoring etc. For microwave remotesensing applications over ocean radar and radiometer, precise values of emissivity and reflectivity arerequired. The surface emissivity is a complex function of dielectric constant of surface seawater. Thiscomplex function is composed of two parts, the real part is known as the dielectric constant (ε′) and isa measure of the ability of a material to be polarized and store energy. The imaginary part (ε′′) is ameasure of the ability of the material to dissipate stored energy into heat. The two are related by theexpression: ∗= ′− ′′ …1The dielectric constant in turn is governed by electrical conductivity and microwave frequency underconsideration. The conductivity is governed by salinity and temperature of seawater [3-4]. There arevariations in salinity and temperature of ocean resulting variation in dielectric properties and hence inemissivity at that particular location. These variations follow certain pattern latitude and longitude ofthe 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 220 Vol. 2, Issue 1, pp. 220-226
  2. 2. International Journal of Advances in Engineering & Technology, Jan 2012.©IJAET ISSN: 2231-1963temperature, scattering coefficient can be interpreted, as they are interdependent. Making use of themeasured salinity values of all samples, static dielectric constant and dielectric loss are estimated byKlein-Swift model [5-6] and Ellison et al. model [7-8] for 5 GHz and 30 °C. The laboratory dataobtained are significant for interpretation of microwave remote sensing applications, and helps indesigning active and passive microwave remote sensors. II. MATERIAL AND METHODOLOGY2.1. Seawater SamplingBy participating in ORV Sagar Kanya scientific cruise SK-259, organized by NCAOR in May-June2009 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 ofTropical Indian Ocean. Surface seawater at different locations were drawn through bucketthermometer and two bottles of the samples were preserved around 4°C by standard procedure. Out oftwo bottles, one of the samples was used to determine the salinity parameter at that location using anAutosalinometer 8400B in the laboratory onboard Sagar Kanya vessel and the other sample of thesame location was brought to the Microwave Research Lab, J.E.S. College, Jalna, Maharashtra fordielectric measurement.2.2. Temperature and Salinity MeasurementThe bucket thermometer is used to measure the temperature of surface seawater. Salinitymeasurements of seawater samples were done using 8400B AUTOSAL onboard ORV Sagar Kanyalaboratory. 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 sampleby measuring their equivalent conductivity. The instrument reading is displayed in terms ofconductivity 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 followingformula. The equation is based on the definitions and the algorithm of practical salinity formulatedand 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 -0.01442.3. Measurement of Dielectric PropertiesThere are several methods of dielectric measurement of liquid [11]. In present work, the dielectricproperties of seawater samples are measured using Von Hipple Method [12] for which automated C- 221 Vol. 2, Issue 1, pp. 220-226
  3. 3. International Journal of Advances in Engineering & Technology, Jan 2012.©IJAET ISSN: 2231-1963Band microwave bench , as shown in figure 1, is used. The MW bench consists of a low powertunable narrow band VTO-8490 solid-state microwave source; having frequency range of 4.3-5.8GHz. Tuning voltage is kept at 7 volts, throughout the experiment, which corresponds 5 GHzfrequency. 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. Adesired power level in the line is adjusted with the attenuator. A slotted section with a tunable probe isused to measure the power along the slot line. The crystal detector (1N23) in the probe is connected toa microammeter and to the PC to read, acquire and store the data. The empty liquid dielectric cell isconnected at the output end of the bench. The bench is tuned to get symmetrical standing wave patternin the slot line. The positions of minima are noted from the pattern from which wavelength λg of thewave-guide can be calculated. The probe position on the slot line is kept constant at the first minimaof the standing wave pattern in the slot line. The liquid dielectric cell is then filled with the sampleunder consideration. The plunger of the liquid cell is initially set in a position such that the thicknessof the liquid column below the plunger is zero. By moving the plunger away from this position, dataof microwave power is recorded for different plunger positions. The data of plunger positions and thecorresponding power are acquired and stored in a file which is further used to calculate dielectricconstant ε and dielectric loss ε using the least square fit program. The parameters α, β, P0, δ are usedas 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 4πand ε′′ = …5 λ αβ 2πwhere λ is the free space wavelength which can be calculated using the formula 1 1 1 = + …6 λ λ λWhereλ = 2a = 2 ∗ 4.73 cm = 9.46 cm, ‘a’ being the broader side of the C-band rectangular wave-guide. 222 Vol. 2, Issue 1, pp. 220-226
  4. 4. International Journal of Advances in Engineering & Technology, Jan 2012.©IJAET ISSN: 2231-1963 III. RESULTS AND DISCUSSIONSThe 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 duringMay – September and from the northeast during November – January with the transition-taking placeduring the months in between. Forced by these winds, circulation in the Indian Ocean has a generaleastward direction during summer (May – September) and westward during winter (November –January). During summer, period when seawater samples were collected the monsoon current flowseastward as a continuous current from the western Arabian Sea to the Bay of Bengal [13-14]. Thesecirculations 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 overrainfall. In Table 2, the samples S-01 and S-03 are from Arabian Sea and have higher salinity valuescompared 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
  5. 5. International Journal of Advances in Engineering & Technology, Jan 2012.©IJAET ISSN: 2231-1963In contrast, the Bay of Bengal has much lower salinity due to the large influx of fresh water from riverdischarge and high amount of rainfall. The samples S-02 and S-04 although located on similar latitudeas 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 similarlatitude, differing in longitude, are towards east, and are from border of Bay of Bengal Sea andArabian 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, butnear the equatorial regions, S-13, S-14, a sudden slight increase in salinity value is found. This is dueto 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 Oceanare given in Table 3. The magnitude of dielectric constant is found to be 66. It is found that dielectricconstant 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 2.7969The values calculated in Tables 4 and 5 are by using Klein and Swift and Ellison et al. modelsrespectively. 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 bya magnitude of about 20 as compared with the theoretical models. The percentage error inmeasurement 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 dielectricloss 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
  6. 6. 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 34.6747Table 5. The calculated relaxation time τ ps , static dielectric constant ε , dielectric constant ε and dielectricloss 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 33.8214ACKNOWLEDGEMENTSWe are thankful to ISRO for providing the C-Band Microwave Bench Setup under RESPOND projectof Dr. M.L. Kurtadikar. Special thanks to NCAOR, Goa, for allowing participation in SK-259 cruiseof ORV Sagar Kanya, for seawater sample collection.REFERENCES[1] Fawwaz T Ulaby, Richard K Moore and Adrian K Fung (1986). Vol. 3 Artech House Inc.[2] Eugene A. Sharkov (2003). Passive Microwave Remote Sensing of the Earth, Springer, Praxis Publishing, UK.[3] Smyth, C.P., (1955). Dielectric Behaviour and structure, McGRAW-HILL Book company Inc, New York. 225 Vol. 2, Issue 1, pp. 220-226
  7. 7. 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 microwave theory and Techniques, vol.19, pp 733-736.[6] Klein, L.A., and. Swift ,C.T ,(1977). An improved model for the dielectric constant of seawater at microwave frequencies, IEEE J. Oceanic Eng., OE-2: pp 104-111.[7] Ellison, W., Balana, A., Delbos, G., Lamkaouchi, K., Eymard, L., Guillou, C., and Prigent, C., (1996). Study and measurements of the dielectric properties of sea water, Tech. Rep. 11197/94/NL/CN, European Space Agency.[8] Ellison, W., Balana, A., Delbos, G., Lamkaouchi, K., Eymard, L., Guillou, C., and Prigent, C. (1998). New permittivity measurement of seawater,” Radio Science, Vol. 33: pp 639-648.[9] Lewis, E.L. (1978). Salinity: its Definition and calculation. J. Geophys. Res. 83:466.[10] Lewis, E.L. (1980). The practical salinity scale 1978 and its antecedents. IEEEJ. Oceanic Eng. OE-5:3.pp 14.[11] Udo Kaatze (2010). Techniques for measuring the microwave dielectric properties of materials, IOP publishing, Metrologia, Vol. 47, pp 91-113.[12] Von Hipple A (1954). Dielectrics & Waves, Wiley, New York.[13] Prasanna Kumar S, Jayu Narvekar, Ajoy Kumar, C Shaji, P Anand, P Sabu, G Rijomon, J Josia, K.A. Jayaraj, A Radhika and K.K. Nair (2004). Intrusion of Bay of Bengal water into Arabian Sea during winter monsoon and associated chemical and biological response, American Geophysical Research, vol. 31, L15304, doi:10.1029/2004 GL020247.[14] Gangadhara Rao, L.V., Shree Ram, P., (April 2005). Upper Ocean Physical Processes in the Tropical Indian Ocean, monograph prepared under CSIR scientist scheme, National Institute of Oceanography regional centre, Visakhapatnam, pp 4-32.[15] Shenoi, S.S.C, Saji, P.K and Almeida, A.M (1999a). Near-surface Circulation and kinetic energy in the tropical Indian Ocean derived from Lagrangian drifters, J Mar. Res. Vol. 57, pp. 885-907.[16] Shankar .D, Vinayachandra P.N, Unnikrishnan (2002). The Monsoon Currents in the North Indian Ocean, Progress in Oceanography, 52(1) pp 63-120.AuthorsAnand 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 AmbedkarMarathwada University, Aurangabad, Maharashtra, India in 2002 and 2004 respectively. He iscurrently 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 sensingApplications and Astrophysics.Santosh Deshpande was born in Parbhani, India in 1974. He received M.Sc. degree in Physicsfrom Swami Ramanand Teerth Marathwada University, Nanded, Maharashtra and M.Phildegree 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, MicrowaveRemote sensing Applications and Astrophysics.Mukund L. Kurtadikar was born in Nanded, India in 1951. He received the Master ofScience (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 Physicsin the Postgraduate Department of Physics of J. E. S. College, Jalna, Maharashtra, India. Hisresearch interests include Microwave Remote Sensing Applications, dielectric measurements ofsoils, seawater, rocks, snow, vegetation etc. He also works on Photometry of Variable Starsusing Small Optical Telescope and Scientific Exploration of Historic Monuments. He is aScience Communicator. 226 Vol. 2, Issue 1, pp. 220-226

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