Characterization of Optical Properties of Mandovi and Zuari Estuarine Waters A thesis submitted to Goa University for the award of the Degree of Doctor of Philosophy In Physics by Thayapurath Suresh Under the guidance of Prof. J.A.E. Desa Department of Physics Goa University, Goa 403206 January 2020 DECLARATION As required under the University Ordinance OB.9A, I state that the present thesis entitled, “Characterization of Optical Properties of Mandovi and Zuari Estuarine Waters”, submitted to Goa University for the award of the degree of Doctor of Philosophy in Physics is a record of original and independent work carried out by me during the period January 2014 – January 2020, under the supervision of Prof. J.A.E. Desa, Department of Physics, Goa University, and that it has not formed the basis for the award of any Degree or Diploma to me or to any other candidate of this or any other University. Date : January 2020 Place : Goa University, Goa Thayapurath Suresh CERTIFICATE It is hereby certified that this thesis entitled, “Characterization of Optical Properties of Mandovi and Zuari Estuarine Waters” submitted to Goa University for the award of the degree of Doctor of Philosophy in Physics is a record of original and independent work carried out by Mr. Thayapurath Suresh during the period January 2014 – January 2020, and that it has not formed the basis for the award of any Degree or Diploma to any candidate of this or any other University. Place : Goa University Date : January 2020 Prof. J.A.E. Desa Prof. K. R. Shenvi Priolkar ( Guide ) (Co-Guide) Department of Physics Department of Physics Goa University Goa University I would like to dedicate this thesis to my Amma and Achan, my children Adi, and Nami, and Ettan and Echi … and to all my colleagues ACKNOWLEDGEMENTS I would like express my gratitude to Dr. Elgar Desa my mentor and Guru, who introduced me to this exciting, and fascinating world of marine optics and ocean color remote sensing without which I would not have engaged myself in this field. Thank you for the knowledge imparted in this subject, time you spent with me educating me, for the encouragement and also being there whenever required. Thank you, Dr. Ehrlich Desa for your support. Dr. Erwin Desa my guide, thank you for accepting me as your student. He has always been supportive, encouraging and was optimistic of my completing the PhD. Thank him for his helping nature and calm unperturbed approach towards all his students. Thank you, Dr. Kaustubh Priolkar, my co-guide for your support. Some people in your life matters a lot and always there to render help at all times and it was my staff Miss Albertina Dias who was the shining photon, without whom I would have never registered, continued and reached to this stage. She was there with me all through with a magic wand in her hand. Dr. Madhubala Talaulikar helped me during the early days of studies when we were new to this subject, setting up the laboratory, organizing and participating in the field measurements and analyzing the data with her sound knowledge of programming and engaging in fruitful discussions. I am indebted to the duo, Ashvesh Gimonkar and Mithilesh Mane whose sincere, sustained efforts facilitated in the field measurements, calibration and upkeep of the instruments. Thanks are also due to the Reshmitha, Shreya, Nupoor and others who helped me with the field measurements and analysis. I shall always cherish the moments of field measurements on boats, birthday celebrations, fishing, and picnics. With you all being there, working was so pleasant, enjoyable and fruitful. I am grateful to Space Application Centre (ISRO), Ahmedabad, National Remote Sensing Centre (ISRO), Hyderabad, ESSO-INCOIS and Naval Research Board, New Delhi for the support and interactions with the staff. Thank you Dr. Shanmugham, IIT Madras for the discussions, suggestions, encouragement and help. I am thankful to the Directors of CSIR- National Institute of Oceanography, where I was employed, who always encouraged and supported me to undertake projects in ocean color applications. Thank you all at my division of Marine Instrumentation Division for your continued support and encouragements. Thank you Dr. Mithun of lbrary, staff of ship cell, ITG and others at NIO who always helped me whenever required. ABSTRACT The research topic was in the field of marine optics and ocean color applications. The focuses of the studies were to understand the light properties of the optically complex waters of Goa, which included the two estuaries Mandovi and Zuari and the coastal waters off Goa (Latitude 15.35 to 15.55° N, Longitude 73.65 to 74.047° E). This study was carried-out using large data of measured spectral optical, physical, biological and ancillary parameters of these waters to understand the spatial and temporal variations optical properties and their associations with other parameters, physical and biological features and also the development of new algorithms to derive optical parameters that could be used for ocean color satellite applications. There were three types of data used for the studies, which included measured, derived from the radiative transfer simulations and satellite data. There were measured data from 500 field measurements, and these were from 27 regular time-series stations which included, Mandovi(12), Zuari(8), and coastal (9) where measurements carried-out all through the year at periodic intervals. There were distinct spatial and temporal variations of optical, biological, physical, and ancillary parameters of coastal and estuarine waters. Two parameters that have been used to indicate the penetration of light in water were first optical depth or penetration depth Z90 (m) and Secchi depth, Zsd. There was sufficient light available in these waters till the bottom during all seasons, and average %PAR at was about 22%. The values of Z90 and Zsd show that light penetrates the deepest in coastal waters, and among estuaries, the light penetrations in Mandovi were deeper than Zuari. The wavelength at maximum Z90(λ) was about 577 nm in the estuaries and was higher compared to the coastal waters, which was at about 545 nm. The bulk refractive index was higher in the estuaries, indicating more mineral particles. The particle sizes were relatively smaller in the estuaries. vi Monsoons play an important role in modulating the physical, biological, and optical parameters of these estuaries. However, during monsoon, despite the availability of nutrients and sufficient light, the chlorophyll was low and high discharge, and flow rates were presumed to be responsible for it. Contributions of CDOM and detritus were significant in the estuaries, with the highest values observed during monsoon. A new method developed to determine the iso layers could identify the MLD and ILD of these estuaries and the studies of the physical features such as MLD, ILD, thermal inversions, and bottom heating and their association with optical and biological parameters attempted for the first time in these waters provided encouraging results. The time-series observations at a station could show the variations of optical parameters with the tides. Cluster analysis of these large measured data of complex coastal and estuarine waters could identify distinct classes with each class having similar optical, biological, and physical properties, and the classes differed from each other in all these aspects. These classes were mostly season invariant but spatially apart. There were spatial and temporal variations of Secchi depths or transparencies of waters of the estuaries and coastal waters of Goa, and the study provided an understanding of the parameters that control the transparency, visibility, or light penetrations in these waters. The transparencies of coastal waters increased during algal blooms such as Noctiluca and Trichodesmium. The transparencies of water decreased by a large factor during the monsoon season due to the increase in optical properties that control the transparencies of water. The amount of rainfall was inversely proportional to the transparencies. Transparency of light given by Secchi depth, Zsd was found to be close to Z90. The wavelength of the deepest penetrating light in water varied inversely with the transparency, Zsd. Algorithms were developed to derive optical parameters from optically complex waters which were slope of the spectral CDM, adg(λ), absorption of CDM, adg(412), spectral total absorption at(λ), volume scattering function (VSF) or phase function and underwater vertical and horizontal visibilities. The new algorithms derived were also validated with satellite data. vii CONTENTS Abstract ..................................................................................................................................... vi Contents .................................................................................................................................. viii List of Figures ......................................................................................................................... xiv List of Tables .......................................................................................................................... xix List of sysmbols and acronyms .............................................................................................. xxi CHAPTER 1. Introduction .................................................................................................. 1 1.1 Overview of the structure of the thesis ..................................................................