R&O Buoy Spectrograph System
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Transcript of R&O Buoy Spectrograph System
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
R&O Buoy
Spectrograph System
Steve Brown
NIST
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Research and Operations Objectives
– Transition MOBY vicarious calibration capabilities for NPP/NPOESS VIIRS & GOES-R HES– Like to maintain high spectral resolution for good matching to
satellite bands
– Adapt MOBY technology for complex coastal validation activities for GOES-R (e.g. HES)– Two spectrographs: one blue and one red
– Reduce MOBY operational costs– Reduce the size of the buoy– Operational for longer periods of time between servicing (extend
period from 3 mos. to 6 mos.)• Anti-bio-fouling more critical• Instrument stability and monitoring more critical
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Reduce the measurement uncertainty
– Laboratory– Calibration source
– Stray light
– Environmental– Bio-fouling
– Self shading or shadowing
– Noise from wave-focusing, etc.
• MOBY: single channel spectrograph with optical fiber multiplexer
– each arm, each sensor data taken sequentially
– It can take 20 minutes for a scan.
• New Buoy: Simultaneous Data Acquisition
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
MOBY Uncertainty Elements Addressed with the new Optical System
– Reduce the stray or scattered radiation in the system
– Eliminate dichroic filter– Two separate spectrograph systems
• One for blue water
• Second to be added for coastal regions
– Systems designed for simultaneous acquisition (all ports)– Ideally like to have 8 ports to minimize self-shading effects
– Minimum # of ports required is 4
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
R&O Optical System Breadboard (Spring 2005)
– ISA (Jobin Yvon) f/2 spectrograph with reflective concave holographic grating; 25 m slit
– Andor 1024x256 cooled CCD array, 25 m pixels
– Four separate 1 mm diameter optical fiber inputs along entrance slit
Lens, aperture, & shutter
CCD & spectrograph
Fiber bundle
Input fibers
Shutter drive circuit
Lens, aperture, & shutter
CCD & spectrograph
Fiber bundle
Input fibers
Shutter drive circuit
Spectralon sphere
Input fibers
Spectralon sphere
Input fibers
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Multi-track fibers
– Breadboard system had 1 mm fibers separated by ~500 m
Image expanded to 1 % full scale
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Breadboard System Performed Well in the Laboratory'along-track' scattering – in the dispersion direction
– Stability, system response, and signal to noise ratio adequate for ocean color measurements
– Spectral stray light from optical system is better than MOBY
– Spatial stray light correction algorithm (to account for cross-track coupling) developed and successfully implemented
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Cross-track CouplingWhite LED Illuminating Track 2 ONLY
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NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
At-Sea TestsThe 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).
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
At-Sea Testing: Deployment
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
At-Sea Testing: Klaus Wyrtki
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Preliminary Conclusions (end of August 2005)– Breadboard System
– All-fiber input simplified optical design– Superior stray light (compared to MOBY)
• A simple 2D stray light model was implemented– Satisfactory dynamic range and sensitivity demonstrated– Successfully balanced individual throughputs resulting in the same integration time,
independent of Es or Lu
– Simultaneous acquisition successful. • A full measurement, comparable to a MOBY data set, takes about 20 sec, not
20 min.• Meaningful reduction in measurement uncertainty achieved (Ken Voss)
– Outstanding issues:– Desirable to have eight fiber inputs to reduce shadowing effects– Increased spectral resolution
• Resolution degraded for top and bottom channels– Desirable to change CCD from Andor to Apogee Alta system
• Heritage: U of Miami Group is experienced with Apogee systems; some control software has been written
• Size: Andor power supply a disadvantage for buoy operation
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Spectral Resolutioncompared with MOBY
Image Qualitybetween Tracks
Breadboard System
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Spectrograph vendor search– Multi-channel input:
• minimum of 4 channels; 8 channels preferable– High throughput, f/# 2.4 or lower– High resolution
• Approx. 1 nm ideal• 2 nm might be acceptable
– Software control over the acquisition• Ethernet-based
– Compact – size is an issue
– Time and money concerns, looking for Commercial Off-the-Shelf (COTS) systems if possible
– Ruggedized or ruggedizable for field deployment– Heritage matters
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Image Plane– Defined by choice of CCD
– 1024 by 256 element, 25 m pitch CCD– 25 mm (dispersion) x 6 mm (for multi-channel acq)
– Systems 1:1 imaging– 25 m pixel > 25 m entrance slit
System f/#– For simplicity and to maximize throughput, we wanted the f/# of
the system to match or be slightly smaller than the f/# of the input fiber– Fused silica fiber, NA of 0.22 or f/#=2.3
– Spectrograph f/# of 2.4 or smaller
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
System resolution defined by spectral band pass matching requirements
– High Resolution Spectra Convolved to Sensor’s Spectral Band Pass.
– Single site can service multiple sensors
–MODIS, MERIS, SeaWiFS > VIIRS, GOES-R HES, etc.
MODIS&SeaWiFS: 10 nm bands VIIRS: 20 nm bands HES: 20 nm threshold
10 nm goal MOBY: 1 nm bands > R&O: 2 nm bands
NASA new Ocean Color Satellite SeaWiFS-like: 10 nm bandsNASA: Vicarious calibration buoy: ~ 1 nm resolution
R&O - 2 nm resolution maybe okNASA - 1 nm resolution
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Spectral Bandpass Matching Illustration
MODIS Terra In-Band Wavelength Uncertainty
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MODIS-Terra In-Band Wavelength Uncertainty
-3.0 nm-2.0 nm-1.0 nm0.0 nm1.0 nm2.0 nm3.0 nm
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Multi-track fiber consideration
– 4 input channels – keep 1 mm core diameter fiber
– or go to 500 m fiber
– 8 input channels– 500 m fibers; 250 m spacing
Future consideration
– New 1024 by 512, 25 m pitch chip coming out for the Apogee system (est. release this fall)– 12 mm slit height&image plane possible
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Vendor Search
– Newport, ISA (JY), Zeiss, TECUSA, Headwall, Satlantic, Kaiser, Optronic, Instrument Systems …
– Headwall, Jobin Yvon, & Kaiser– Headwall provided aircraft instruments
• Same optical configuration as MOBY
– Kaiser
• Axial transmissive system
• Developed an in-situ ocean Raman system for MBARI
– Jobin-Yvon
• We had evaluated a JY system and it performed well.
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Headwall Photonics
– Image plane not matched (6 mm horizontal, dispersion direction)
– Spectral coverage not well-matched to MOBY requirements
– Resolution: 2 nm at best
– Has required resolution– Needs custom grating– No characterization data
– Better horizontal image plane
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Jobin Yvon
– CP140– COTS not a perfect match:
spectral coverage&resolution
– Custom gratings possible, but expensive (>10 K) with several months delivery
– f/2.4; simple, compact, good optical quality
– Aberrations affect imaging away from center 2 mm
– We need to develop input and CCD mounts/holders, etc.
– CP200– possible better imaging
(larger system)
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Volume Transmissive Gratings
Axial Transmissive Design– Offer both standard and custom gratings – No imaging degradation over the full slit: > 10 mm
– High Throughput: f/#=1.8– High Spectral Resolution: ~ 1 nm– Minimal # of optical elements: No Moving
Parts
Improved Thermal Stability over Czerny-Turner design
Stray light < 1e-4
50 channel system demonstrated
Rugged Compact Design– Been deployed in an underwater Raman system (by MBARI)
HolographicTransmission
Grating
EntranceSlit
Multi-elementLenses
Output Plane
COTS: Kaiser Optical Systems
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
Kaiser Optical Systems
– Each grating a ‘master’– Relatively inexpensive and quick to modify grating
specifications
• Respond to changing vicarious calibration requirements
– Different gratings can be placed vertically within a single larger grating plane– Visible and NIR system within the same instrument
NOAA Research and Operations Marine Optical Buoy Design Review July 18-19, 2006
R&O Prototype: Status on Spectrograph Systems
– The JY/Andor prototype is in-house– Successful characterization measurements & field
trials with JY system
– One Kaiser system, new JY system ordered– Two Apogee camera systems ordered– Multi-track fiber inputs ordered (Romack)
– One 8-channel input system
– One 6-channel input system
All due in ~ September