Voss_COAST_Cal_prest090505 by zhangyun

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									Calibration and Status of MOBY
      Dennis Clark, NOAA/NESDIS
          Carol Johnson, NIST
           Steve Brown, NIST
        Mark Yarbrough, MLML
         Stephanie Flora, MLML
          Mike Feinholz, MLML
     Mike Ondrusek, NOAA/NESDIS
            Ken Voss, UM
      Calibration/Processing Requirements for an ocean color
                            instrument

PRE-LAUNCH CHARACTERIZATION: It is critical that any instrument be
thoroughly characterized before launch. Some parts are impossible to
vicariously calibrate, or do on orbit (polarization). Geosynchronous orbit will
make various techniques used to vicariously calibrate polar orbiters obsolete.

VICARIOUS CALIBRATION: Necessary to adjust satellite sensor’s gain by
using the difference in a match pair of satellite and in situ Lwn measurements.
Prelaunch characterization cannot do everything.

PRODUCT VALIDATION: Assure products are Climate Data Record (CDR)
quality.

REPROCESSING: to reflect improved knowledge of the instruments
performance changes. Necessary for CDR’s.
  MOBY
Instrument
 and spectral
Time Series of
MODIS ocean
 color bands
Accuracy ~4 -
     5%
            Spectral Band Pass Matching
High Resolution Spectra Convolved to Sensor’s Spectral Band Pass.
Single site can service multiple sensors (VIIRS, GOES-R, etc.)
                 MOBY Calibration Process
Site only useful if calibrated and maintained to highest possible standards.


                                                  NIST Collaborations
                                          Training
                                          NIST Primary Lamp Standards
                                          Annual On Site Calibration Systems Check
                                          Pre/Post Cal. System monitoring with NIST
                                          Cal. Radiometers
                                          SIRCUS - Stray Light Characterizations on
                                          MOBY and Shipboard Spectrometers
                                          MOCE Calibration Systems (OL420 &
                                          OL425) now Calibrated at NIST
                                          Initiating the development of new
                                          Radiometric Calibration Sources for
                                          Oceans
Currently MOBY team Goals are:

• Transition MOBY vicarious calibration
  capabilities for NPP/NPOESS (e.g., VIIRS)
• Adapt MOBY technology for coastal validation
  activities for GOES-R (e.g. HES)

Have some funding from Research to Operations
 (R20) to start this process
Currently Concentrating on 2
           issues:
– Relocate power generation to mooring buoy
  • enables a large reduction in size of optical buoy &
    associated deployment/servicing costs
– Simultaneous measurements to reduce
  environmental sources of measurement
  uncertainty, system complexity
  • required a new optical system design
Tether Redesign and Prototype
• Electromechanical swivel
  – design compete, order in progress
• Tether flounder plate
  – preliminary mechanical design complete,
    strain relief design in progress
• Electromechanical tether
  – final design complete, majority of components
    ordered
Tether Testing
         Optical System Goals
• In MOBY, currently the scans are discrete and
  sequential; in the new system, they are simultaneous
• Currently MOBY requires 20 min for upwelling radiance
  measurements (multiple Es and Lu scans). This is a
  undesirable sampling feature. There can be variability
  due to changing solar zenith angle and atmospheric
  conditions, requiring normalization procedures that
  introduce measurement uncertainty.
• The new system eliminates this problem by
  simultaneous observations with multiple inputs. In
  addition, a comparable sequence as for MOBY takes
  about 20 sec, not 20 min.
Instrument Layout, at Sea Testing
     Optical System Breadboard
• ISA f/2 spectrograph
• Andor 1024x256 cooled CCD array
• Four separate optical fiber inputs along
  entrance slit                                             Spectralon sphere


                       Input fibers

                                                                           Input fibers

  CCD & Fiber bundle
  spectrograph

                                Lens, aperture, & shutter

                           Shutter drive circuit
Breadboard System Performed
            Well

              Spectral stray light from optical system is better than
              MOBY.

              Stability, system response, and signal to noise ratio
              all adequate for ocean color measurements.
At Sea Tests
   The breadboard system was
   implemented with four inputs and tested
   in Case 1 waters off Oahu in August
   2005. The inputs were Es, Eu, Lu
   (0.75m) and Lu (3.25 m).
        Status of optical redesign
• Breadboard System
   –   Superior stray light (compared to MOBY)
   –   A simple 2D stray light model was implemented
   –   Satisfactory dynamic range and sensitivity
   –   Successfully balanced individual throughputs
       resulting in the same integration time, independent of
       Es or Lu
• All fiber optical input simplifies optical design
• Outstanding issues:
   – Desirable to have six or eight fiber inputs
   – Increased spectral resolution

								
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