Calibration and Status of MOBY Dennis Clark NOAANESDIS

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 (OL 420 & OL 425) 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 (R 20) 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 1024 x 256 cooled CCD array • Four separate optical fiber inputs along entrance slit

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. 75 m) and Lu (3. 25 m).

Status of optical redesign • Breadboard System – – Superior stray light (compared to MOBY) A simple 2 D 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