Integration of GIS and Oceanic Remote Sensing

Oceanic Remote Sensing Remote sensing is a technique based on measuring the electromagnetic energy reflected or emitted by the surface of geographic space (Caloz and Collet, 2003). Satellites are able to sense an array of parameters including ocean color, sea-surface temperature, sea-surface irradiance, sea-surface topography, and winds (Simpson, 1992). Satellite ocean color remote sensing is based on sensing the radiance exiting the ocean surface that contains a wealth of spectral information regarding the absorption and scattering processes of the constituents within the water column that include water itself, phytoplankton, colored dissolved organic matter, and suspended sediments (Kirk, 1994). The goal of remote sensing of ocean color is to derive quantitative information on the types and concentrations of these substances present in the water from variations in spectral form and magnitude of the emergent flux from the ocean. Ocean color is determined by remote sensing reflectance (Rrs); the ratio of water leaving radiance (Lu) to downwelling irradiance (Kirk, 1994). It is a measure of how much of the downwelling light that is incident onto the water surface is eventually returned through the surface and is a product of the specific absorption spectra of the water column constituents. Most commonly, ocean color information is used to determine chlorophyll concentration that is used as a proxy for phytoplankton biomass. This information is then used to quantitatively determine the ocean’s role in biogeochemical cycles, determine the magnitude and variability of primary production, and timing of phytoplankton blooms. However, current progressive research is also trying to discern many other parameters from ocean color revealing information about suspended sediments, organic matter concentration, coccolith concentration, various pigment concentrations, attenuation of light, total absorption, and chlorophyll fluorescence which is used as a proxy for phytoplankton physiological stress. Sea-surface temperature is derived from emergent infrared radiance from spectral bands in the near-infrared and infrared portion of the electromagnetic spectrum. This information is used in investigations such as climate research and primary production. Sea-surface topography is measured with an microwave radar altimeter, in which the satellite sends a microwave signal and determines the amount of time is takes for the signal to return to the sensor based on specific determination of the location of the satellite. The objectives of sea-surface topography is to provide a global data set that allows time-dependent and time-average large-scale ocean currents to be characterized with a relatively high degree of accuracy so the general circulation of the ocean can be determined (Simpson, 1992). Winds are measured with a microwave radar scatterometer where a radar signal is transmitted to the surface of the ocean and then is backscattered to the sensor. The roughness of the sea-surface influences to strength of the signal and is used to determine the relative direction and speed of wind acting on the surface of the ocean. This information is used in air-sea interaction research, climate research, hurricane forecasting, and ocean circulation. Sea-surface irradiance is determined from atmospheric parameters that determine the amount of sunlight that reaches to surface of the ocean and is an important factor in climate and also primary production studies. In addition to the reflected and emitted electromagnetic energy, the remote sensor receives light originating from reflection of skylight, along with scattering and attenuation within the atmosphere. At least eighty percent of the upward radiance measured by a satellite sensor originates from atmospheric scattering (Kirk, 1994). These additional sources of detected light need to be corrected for in order to deduce information about the underwater light field and surface of the ocean. Once the signal has been corrected it is subjected to many steps of processing and sophisticated algorithms to deduce oceanographic information.