DEVELOPMENT OF A SPECTRAL ATTENUATION METER AND A SPECTRAL BACK SCATTERING METER

THIS PROJECT WILL DESIGN, CONSTRUCT, AND EVALUATE PROTOTYPE SPECTRAL ATTENUATION AND BACKSCATTERING METERS. THESE INSTRUMENTS, ALONG WITH A SPECTRAL ABSORPTION METER CURRENTLY BEING DEVELOPED, ARE NEEDED FOR RESEARCHERS TO UNDERSTAND THE RADIATIVE TRANSFER PROPERTIES LINKING THE REMOTELY SENSED OCEAN COLOR SPECTRA TO THE STATE OF THE OCEANIC BIOSPHERE. THESE STUDIES ARE CRUCIAL TO THE GLOBAL MONITORING NECESSARY TO DOCUMENT PROCESSES RELATED TO THE GREENHOUSE EFFECT AND OZONE DEPLETION. PRESENTLY, NO SUCH IN-SITU INSTRUMENTS ARE AVAILABLE COMMERCIALLY. PHASE I WILL BE DEVOTED TO THE DESIGN AND TESTING OF A PROTOTYPE SPECTRAL ATTENUATION METER WHICH WILL EMPLOY A WHITE LIGHT SOURCE MODULATED BY A TUNING FORK LIGHT CHOPPER AND FED INTOA HOLOGRAPHIC GRATING MONOCHROMATOR. THE LIGHT OUTPUT FROM THE MONOCHROMATOR WILL BE COLLIMATED AND THEN SPLIT INTO TWOBEAMS OF EQUAL INTENSITY BY A BEAM SPLITTER MOUNTED IN THE OPTICAL PATH; THIS WILL MAKE AN OPTICAL BRIDGE DESIGN POSSIBLE. MUCH OF THE NEEDED ELECTRONICS AND LIGHT SOURCE DESIGN IS CURRENTLY IN PROGRESS OR PROPOSED FOR THE DEVELOPMENT OF A BLUE LIGHT EMITTING DIODE TRANSMISSOMETER AND A SPECTRAL ABSORPTION METER. THE TASK IS TO MELD THESE TECHNOLOGIES INTO A SPECTRAL ATTENUATION METER. BEFORE DECIDING AMONG SEVERAL POSSIBLE DESIGNS FOR A SPECTRAL BACKSCATTERING METER, THEORETICAL ANALYSES MUST BE COMPLETED TO DETERMINE WHAT ANGULAR RANGE AND RESOLUTION ARENEEDED FOR REMOTE SENSING STUDIES. SUBSEQUENTLY, A PROTOTYPE WILL BE BUILT AND TESTED. THE MOST PROMISING DESIGN IS ONE BASED ON A CASSEGRAINIAN TELESCOPE. THE DETECTOR WILL BE WELL COLLIMATED, AND A XENON PULSED LIGHT SOURCE WITH VARIABLE COLLIMATION ANGLE WILL BE LOCATED IN FRONT OF THE TELESCOPE LENS. BY SUCCESSIVELY INCREASING THE COLLIMATION ANGLE OF THE LIGHT SOURCE, SCATTERING CAN BEMEASURED AT SUCCESSIVE ANGLES BY SUBTRACTION. THE ANGULAR RANGE OF THE DEVICE WILL BE FROM APPROXIMATELY 165 DEGREES TO 178 DEGREES SCATTERING. BY PULSING THE LIGHT SOURCE USING A SYNCHRONOUS DETECTOR, SCATTERED LIGHT CAN BE SEPARATED FROM AMBIENT LIGHT.