Applications to hydrosphereSea Surface Temperature April 06, 2005 derived from satellite dataWhat is hydrosphere?The totality of water surrounding the Earth, comprising all the bodies of water, ice, and water vapor in the atmosphere i.e. water held in oceans, rivers, lakes, glaciers, ground water, plants, animals, soil, and air.Remote Sensing of Water: Objectives To introduce some of the fundamental principles associated with remote sensing surface water and its constituents,Remote Sensing of Water: Hydrological CycleWater covers 70% of the earth's surfaceThe global water cycle has three major pathways: precipitation, evaporation/transpiration and vapor transport. Water precipitates from the sky as rain or snow, most of which (385,000 cubic kilometers per year) falls into the oceans. It returns to the atmosphere by evaporation. Some flows from the land to the sea as runoff or groundwater; in the other direction, water vapor is carried by atmospheric currents from the sea to the land. Net flow is measured in thousands of cubic kilometers per year.Remote Sensing Surface Water Biophysical Characteristics How can remote sensing be used to inventory and monitor the spatial extent, organic/inorganic constituents, depth and temperatures of water in rivers, lakes, reservoirs, seas and oceans?Water Surface, Subsurface, Volumetric and Bottom RadianceThe total radiance (Lt) recorded by the sensor onboard an aircraft or satellite is a function of the electromagnetic energy from four sources:1. Lpnever reaches the surface (unwanted path radiance)2. Lsreaches the air-water interface called the free-surface layer or boundary layer3. Lvpenetrates the surface and interacts with water and organic/inorganic constituents (subsurface volumetric radiance)4. Lbreaches the bottomSpectral Response of Pure Water as a Function of Wavelength Least amount of absorption and scatteringof incident light takes place in the blue wavelength region (400-500 nm) Minimum located at 460-480 nm, penetrate water column further than any other type of light Nearly all incident near-and middle infrared (740 –3000 nm) radiant flux entering a pure body of water is absorbed Scattering of violet and blue and absorption of 520 – 700 nm results in pure water appearing blueSpectral Response of Pure Water as a Function of Wavelength Scattering in the water column is important in the violet, dark blue and light blue portions of the spectrum (400–500 nm) This is the reason water appears blue to our eyes Almost all of the incident near- and middle infrared (740-2500 nm) radiant flux entering a pure water body is absorbed with negligible scatteringMonitoring the Surface Extent of Water Bodies The best wavelength region for discriminating land from water is the near-and middle-infrared regions at wavelengths between 740-2500 nm Water bodies appear very dark in these regions as they absorb almost all of the incident radiant flux Soils and vegetation reflect significant amounts of near- and middle-infrared  This causes land surfaces to appear relatively bright in near- and middle-infrared imageryIkonos Near Infrared ImageBand 4: 0.77 - 0.88 µm (near infra-red) 4 metersMonitoring the Surface Extent of Water Bodies If have organic and inorganic constituents in the water column (especially those near the surface) more infrared scattering will occur Water may then appear almost as bright as land featuresMississippi River Delta: What is water and what is sediment?Landsat TMSpectral Response of Water as a Function of Organic and Inorganic Constituents The spectral reflectance of suspended sediment in surface water is a function of both the quantity and characteristics (particle size, absorption) of material in water Remote sensing data must be validated with in situ measurements This can be done using a secchi disk or a spectroradiometerMeasurements of Suspended Sediment A secchi disk is used to measure suspended sediment in water bodies by lowering it into water column and determining the depth at which it disappears, then the depth is correlated with the amount of the suspended material The accuracy of the measurement is a function of the visual acuity of the observer, which can vary dramaticallyMeasurements of Suspended Sediment using a Spectroradiometer Spectroradiometer can also be used to collect spectral reflectance data of pure water and water with various suspended sediment and chlorophyll a concentrations252 bands between 368 and 1114 nmMeasurements using a Spectroradiometer Spectral reflectance of water drops continuously after about 580 nm due to absorption in the water column As suspended sediment is increased, reflectance increases at all wavelengths for both clayey and silty soils Peak reflectance shifts toward longer wavelengths in the visible region as more suspended sediments are addedMeasurements of Suspended Sediment using a Spectroradiometer Results suggest that the visible wavelength range of 580-690 nm may provide information on the type of suspended sediments (soil) in surface waters; and the near infrared wavelength range of 714-880 nm may be a useful wavelength range for determining the amount of suspended materials in surface waters where suspended minerals are the predominant constituentChlorophyll in Water Plankton is the generic term used to describe all the living organisms (plant and animal) present in a water body Phytoplankton – plant organisms Zooplankton – animal organisms Bacterioplankton – bacteriaChlorophyll in Water Phytoplankton use carbon dioxide and produce oxygen during the photosynthetic process Thus, water bodies and oceans act as a carbon sink (dead phytoplankton and zooplankton), a place that disposes of global carbon Uncertainties remain as to how much carbon inland water bodies and ocean accumulate As such, phytoplankton are very important to our knowledge of the global carbon cycleChlorophyll in Water Phytoplankton contain chlorophyll pigments As chlorophyll concentration increases in the water column there is a significant decrease in the relative amount of energy reflected in the blue and red wavelengths but an increase in green wavelength reflectance Different spectral response if have suspended mineral sediment and chlorophyllChlorophyll in Ocean Water Satellites can determine plankton content by analyzing the color variations (mainly in the visible) of