Ocean Science

The  advent  of  satellite  remote  sensing  has  initiated  a  new  era  of monitoring the Earth’s atmospheric and oceanic processes. The satellite sensors provide vital information to study and understand the important constituents of the atmosphere and ocean and their dynamics. The  satellite  data  products  are  operationally  used  by  India Meteorological Department (IMD), National Centre for Medium Range Weather  Forecasting  (NCMRWF),  Indian  Institute  of  Tropical Meteorology (IITM) and  Indian National Centre for Ocean Information Services  (INCOIS)  for  providing  information  and  advisory  services  on weather, climate and ocean.Earth and Climate Sciences Area (ECSA) of NRSC emphasis on Studying earth as a coupled system involving Land–air-Ocean interactions through satellite , ground observations and modeling. The functional components of ECSA include Land Surface Processes & Climate Modeling, Terrestrial Sciences, Atmospheric Sciences & Ocean Sciences. The modeling studies of ocean demand for the Observations of the variation of the Energetics of Ocean Heat Transport, Sea ice formation and the Salinity. The Essential Climate Variables include Sea-surface temperature, Sea-surface salinity, Sea level, Sea state, Sea ice, Current, Ocean colour (for biological activity), Carbon dioxide partial pressure at Surface level & Temperature, Salinity, Current, Nutrients, Carbon, ocean tracers, Phytoplankton at sub-surface level.

Ocean Colour Remote Sensing

The prime objective of ocean-colour remote sensing is quantitative estimation of the ocean water constituents from the spectrum of the solar reflected radiation from the ocean waters. In the solar radiation incident on the Earth’s surface, only the VIS-NIR part of the spectrum (~ 400 to 700 nm) penetrates into water. This radiation, after entering into the water, undergoes multiple scattering and absorption by water molecules and the ocean water constituents and a small of this radiation part is scattered out of water, which is detected by the remote sensing sensors in space. From this radiance - called water-leaving radiance - detected in a selected set of wave bands, the concentrations of the water constituents are estimated through a retrieval procedure. The purpose of the OCEANSAT-II Ocean Colour Monitor-II (OCM-II) mission is to provide continuity to the OCEANSAT-I OCM mission and to obtain quantitative information of ocean colour variables e.g., (i) chlorophyll-a concentration, (ii) vertical diffuse attenuation of the light (Kd) characterized at 490-nm, (iii) estimation of the total suspended matter concentration in coastal waters etc. and to make that data readily available to the user community. This Algorithm Theoretical Basis Document (ATBD) describes the algorithms used for the retrieval of geophysical parameters for OCEANSAT-II Ocean Colour Monitor (OCM)-II data. The document describes atmospheric correction procedure adopted for the atmospheric correction of the OCM-II data as well the in-water algorithms used for the estimation of ocean colour variables e.g. chlorophyll-a concentration, vertical diffuse attenuation (Kd) at 490-nm, total suspended matter (TSM) and atmospheric variable like aerosol optical depth (AOD) over oceanic regions measured at 865-nm wavelength.

Potential Fishing Zone

Ocean Colour Monitor (OCM)-II instrument is designed to measure ocean-colour, the spectral variation of water leaving radiance that can be related to concentration of phytoplankton pigments, suspended matter and coloured dissolved organic matter in coastal and oceanic waters, and the characterization of atmospheric aerosols. OCEANSAT-II OCM-II payload is a follow on system from OCEANSAT-I OCM, which was launched in May 1999 by Indian Space Research Organization (ISRO). OCEANSAT-II OCM-II is almost identical to OCEANSAT-I OCM but having minor spectral shift for band 6 and 7 from OCEANSAT-I OCM configuration. The spectral band 6, which was located at 670-nm in OCEANSAT-I OCM has been shifted to 620-nm for better quantification of suspended sediments. The spectral band 7, which was located at 765-nm in OCEANSAT-I OCM has been shifted to 740-nm to avoid oxygen absorption in case of OCEANSAT-II OCM-II. The OCEANSAT- II OCM will collect data in eight spectral bands. The imaging principle of OCM is based on push-broom technique, which is the same as for the linear imaging self-scanner (LISS) cameras used in earlier missions of IRS series. There is a separate refractive optics for each band. Each band has a linear charge coupled devices (CCD) array in the focal plane of the optics as the detector. The detector outputs are processed by the payload electronics, which provide serial digital data stream for each band to the data handling system. Each band has separate detector, optics and camera electronics and uses 6K 2 Port CCD out of which 3730 are imaging pixels. The sensor provides high radiometric performance at low radiance and has provision for along track tilt (± 20º) to avoid sun glint.

The geophysical products are generated from OCEANSAT-II OCM data. The normalized water-leaving radiance in 412, 443, 490, 510 and 555-nm bands will be the output of the atmospheric correction procedure and will be subsequently used in the estimation of bio-geo-physical variables. The chlorophyll-a product can be used as a proxy to the presence of phytoplankton in the seawater as chlorophyll-a is the dominant pigment found in most of the phytoplankton. The diffuse attenuation coefficient (Kd) product is an apparent optical property, which defines the rate of decrease of downwelling irradiance falling with depth in the water column. The total suspended matter (TSM) product will provide quantitative measure of the inorganic particulate matter present in the suspended form mainly in the coastal waters. The aerosol optical depth (AOD) is a measure of the atmospheric turbidity, which will be characterized at 865-nm, as this wavelength is almost insensitive to reflectance from ocean waters.

Several validation and data collection ship campaigns were conducted all along the East Coast of India for validating the Geophysical data products derived from OCM-2. Among those cruises few cruises were exclusively conducted for identifying the algal blooms and to study the spectral characteristics of the coastal waters along the east coast using Hyperspectral under water radiometer. However, this in-situ data will serve as a base for building the spectral library for the coastal ocean waters in development and validation bio-optical algorithms for estimating the optically active constituents in the coastal ocean waters which is very complex in nature. The atmospheric parameters like AOD were measured during the cruise period for validating the atmospheric correction algorithm for Oceansat-2 OCM applications. This AOD data also will serve as a database for developing the atmospheric correction algorithm over coastal ocean regions.

Major Highlights

  • Potential Fishing Zone (PFZ) Forecast
  • Ocean State Forecast
  • High-resolution Regional Weather Prediction
  • Monsoon Prediction
  • Tropical Cyclone & Storm Surge Prediction
  • Coral Reef Bleach Alert

Major Benefits

  • About 40,000 users are regularly benefited through PFZ forecasts
  • Space inputs have improved weather and cyclone track prediction
  • Monitoring and conservation of coral reefs
  • Ocean state forecast is useful for Indian Navy, Indian Coast Guard, cargo and passenger shipping agencies, off-shore oil & gas exploration agencies, fishermen and ports

Operational Products / Services

Research Areas

  • Water quality in coastal and inland lakes
  • High-resolution coastal and ocean state forecast
  • Polar environment monitoring
  • Prediction of high intensity rainfall events, e.g.thunderstorms
  • Aerosol and cloud interaction

Ocean Science