Transcript Ocean Color Research to Operations

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
Fiber bundle
CCD &
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