OS2 3 Zhu

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Published on January 4, 2008

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The use of in situ, laboratory and airborne measurements to estimate the chlorophyll-a concentration in the St. Lawrence River:  The use of in situ, laboratory and airborne measurements to estimate the chlorophyll-a concentration in the St. Lawrence River Yushan Zhu Vodacek Anthony Michael Twiss Center for Imaging Science Digital Imaging and Remote Sensing Lab Rochester Institute of Technology 04/05/2006 Outline:  Outline In situ measurements: HOBI Labs HydroRad-4(RIT), bbe FluoroProbe 2 (Clarkson University) Field collected water sample was analyzed in lab by spectrophotometer (Cary 500) Airborne image was taken at the same time by MISI Summary Further studies Study Area – St. Lawrence River:  Study Area – St. Lawrence River Block section of St. Lawrence north of Wilson Hill Island: 44°53.425 to 44°54.484 75°06.870 to 75°06.873 Time: July 21, 2005 Yellow points: HydroRad-4 Red points: bbe fluoroprobe MISI image after MNF:  MISI image after MNF HydroRad-4:  HydroRad-4 HydroRad-4 is a versatile system for in-situ radiometric measurements constructed from four Ocean Optics spectrometer 2048 pixels ; wavelength from: 350nm~700nm; spectral resolution 3.0nm The four sensors are used as two pairs This method of deployment was effective for determine the scalar irradiance, net irradiance, and average cosine Approximately total absorption can also be derived using Gershun’s equation HydroRad-4:  HydroRad-4 1+cos - collector Example of measurements by HydroRad-4:  Example of measurements by HydroRad-4 bbe FluoroProbe 2 (Clarkson University):  bbe FluoroProbe 2 (Clarkson University) Highly sensitive measuring instrument for in situ chlorophyll analysis Algae differentiation uses 5 LEDs for fluorescence excitation. (450, 525, 570, 590, 610nm) Give the concentration for different type of algae: green algae, bluegreen algae, diatoms, and cryptophyta Laboratory measured parameters from water samples:  Laboratory measured parameters from water samples The field collected water samples were analyzed in lab to get following results Total Suspended Solids (TSS) Colored Dissolved Organic Matter absorption (CDOM) Particle and pigment absorption TSS:  TSS TSS: 1L water sample filter through GF/F glass-fiber filter (0.2 µm); weight the difference of GF/F filter Cary spectrometer:  Cary spectrometer Absorption can be measured by Cary 500 Typical of high performance laboratory spectrometers range from UV to NIR It has a dual-beam design: The instrument alternately measures the spectral radiance from a reference material and from the sample material of interest The instrument uses a common light source, monochromators, and detector for both beams. A chopper wheel controls which beam the detector is viewing during the measurement cycle The spectral transmission of a material can be determined by the two measured beams CDOM absorption:  CDOM absorption Use two 10cm length cuvettes, one with pure water and the other with filtered sample water through GF/F and membrane (0.2um) filter. When the same light beam penetrated two cell, the difference tells the CDOM absorption Particle and pigment absorption :  Particle and pigment absorption A pair of filters is used: one is wetted with pure water as a reference; the other is filtered with sample water. The difference of the two filters can tell the optical density of concentrated cultures After the sample filter is washed by MeOH, the pigment will extracted out and the difference now is only about particle absorption Absorption spectra measured for aquatic particles concentrated onto glass-fiber filters require a correction for increase in path length caused by multiple scattering in the glass-fiber filter Particle and pigment absorption:  Particle and pigment absorption Compare the results of in situ and laboratory measurements:  Compare the results of in situ and laboratory measurements The absorption obtained from in situ measurements (HydroRad – 4) can tell the information about the CHL concentration well Modular Imaging Spectrometer Instrument - MISI:  Modular Imaging Spectrometer Instrument - MISI MISI is designed by Digital Imaging and Remote Sensing Group at RIT Line scanner: scanner mirror spinning to project the image of the detector along a line on the ground perpendicular to the aircraft ground track High spatial resolution: 1.0 m GIFOV at 1km of altitude High spectral resolution: two separate 36-channel spectrometers to cover the spectrum from 440nm to 1020nm in 10nm spectral bands. Procedure: Raw Data -> oversampling correction, roll compensation -> glint remove -> spectral, radiometric calibration -> atmosphere calibration MISI Images (before and after deglint):  MISI Images (before and after deglint) The reflection of solar radiation on non-flat water surfaces is a serious problem for the image. The wave and glint patterns can clearly see from the left image In order to eliminate most of the glint patterns, deglint algorithm is applied After deglint, the image is more smooth, eliminate most of the information from sun glint, and get more information about water itself Sun glint remove algorithm:  Sun glint remove algorithm Since water is relatively opaque to NIR wavelength, which mean it has maximum absorption and minimal water leaving radiance The amount of sun glint in the visible bands is linearly related to the brightness in the NIR band because the real index of refraction is nearly equal for NIR and visible wavelength The amount of light reflected from the water surface in the NIR is good indicator of the amount of light that will be reflected in visible wavelengths Regions of the image are selected where a range of sun glint is evident Algorithm by J.D.Hedley Different TSS, CDOM, CHL concentration simulated by HydroLight:  Different TSS, CDOM, CHL concentration simulated by HydroLight Hydrolight: radiative transfer numerical model that computes radiance distributions and derived quantities for natural water bodies. The Chl-a has strong absorption of blue light between 400nm and 500nm and red light at approximately 680nm Summary:  Summary The apparent and inherent optical properties of the St. Lawrence river were obtained using in situ and laboratory measurements The average concentrations of Chl-a and TSS are 1ug/l and 1mg/l. CDOM absorption is only about 0.1 at 440nm Chl-a concentration can’t be mapped by airborne image for now because of the less variance of Chl-a, TSS, and CDOM Further studies:  Further studies Continue field studies in this summer, more measurements will be done for different water samples which have more concentration ranges for Chl, TSS, and CDOM Suitable Chl concentration estimation algorithms for coastal and inland waters need to develop using MISI data Then algal growth model output can be compared with these chlorophyll map derived from MISI to validate and calibrate the models. Slide22:  ?

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