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SST from VIIRS on NPP: prelaunch preparations and post-launch validation. Peter J Minnett & Robert H Evans Meteorology & Physical Oceanography Rosenstiel School of Marine and Atmospheric Science University of Miami Miami FL USA. Outline.
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SST from VIIRS on NPP: prelaunch preparations and post-launch validation Peter J Minnett & Robert H Evans Meteorology & Physical Oceanography Rosenstiel School of Marine and Atmospheric Science University of Miami Miami FL USA
Outline • Description of VIIRS – Visible/Infrared Imager/Radiometer Suite • SST retrievals • Cal/Val approach All information about VIIRS is from publicly accessible sources.
NPP payload From http://modis.gsfc.nasa.gov/sci_team/meetings/201001/presentations/plenary/gleason.pdf
VIIRS • The Visible/Infrared Imager/Radiometer Suite collects visible/infrared imagery and radiometric data. • Applications include atmospheric clouds, earth radiation budget, clear-air land/water surfaces, sea surface temperature, ocean color, and low light visible imagery. • Primary instrument for satisfying 22 Environmental Data Records (EDRs) and 2 Key Performance Parameters (KPPs): Imagery & sea surface temperature. • Multiple VIS and IR channels between 0.3 and 14 μm • Imagery (I) Spatial Resolution: ~370m @ nadir / 750m @ edge of swath • Moderate (M) Spatial Resolution: ~740m @ nadir / 1500m @ edge of swath • Swath width ~3000km
VIIRS Components • Spectral Bands: – Visible/Near IR: 9 plus Day/Night Band – Mid-Wave IR: 8 – Long-Wave IR: 4 • Imaging Optics: 18.4 cm Aperture, 114 cm Focal Length • Band-to-Band Registration (All Bands, Entire Scan) > 80% per axis • Orbital Average Power: 240 W • Mass: 275 Kg
VIIRS innovations • Rotating telescope primary optics • Two-sided “Half-Angle Mirror” (HAM) • Multiple detectors (16) per spectral band • On-board pixel aggregation
Risk reduction by using components derived from heritage instruments: • Rotating Telescope from SeaWiFS • Black-body from MODIS • Multiple Focal Plane Arrays and Multiple Detector Assemblies from MODIS
Pixel Aggregation • Each “pixel” has three rectangular detectors in the scan direction • Detectors have a 3x1 aspect ratio • These are aggregated in threes, then twos, then no aggregation, across the scan. • This is an attempt to provide near uniform spatial resolution across the swath.
VIIRS vs MODIS spatial resolution From http://www.ipo.noaa.gov/ams/2010/posters/AGU_AMS-RAY_NGAS-VIIRSHeritageSystems-SNODGRASS_GUENTHER_ANDREAS-WE_PRINT-PR.pdf
VIIRS SST Bands Spectral bands are a subset of MODIS bands GSD = Ground sampling distance These are very promising
VIIRS SST Uncertainty Estimates • The sources of error the VIIRS SSTs fall into two categories: • associated with imperfections in the instrument • arise from imperfections in the atmospheric correction algorithm. • The instrumental effects include: • The inherent noise in the detectors, the Noise Equivalent Temperature Difference (NEΔT) • Band-to-band registration (BBR) • Modulation Transfer Function (MTF) • Imperfections in the knowledge of angular dependence of the reflectivity of the “Half Angle Mirror” • Calibration errors, such as imperfections in the knowledge of the emissivity and surface temperature of the on-board black body target, and of stray radiation falling on the detectors. • Uncertainties will be established soon after launch using multiple techniques.
VIIRS SST algorithms Daytime NLSST algorithm: where a0, a1, a2, a3 are coefficients derived by regression analysis, T11 is the measured brightness temperature at 11 µm (VIIRS band M15), T12 is the measured brightness temperature at 12 µm (VIIRS band M16), RSST is a modeled, first guess SST, and z is the sensor zenith angle. Night-time NLSST algorithm: where a0, a1, a2, a3 are coefficients derived by regression analysis (but are different from those in Equation 12), T3.7 is the measured brightness temperature at 3.7 µm (VIIRS band M12).
Post launch validation The approach will be based on experience gained from AVHRR, (A)ATSR and MODIS, and will involve comparisons with: • Other validated satellite data sets (e.g. AVHRR, AATSR, MODIS…) • Drifting and moored buoys • Ship-based radiometers – M-AERI, M-AERI Mk2, ISAR…..
SST validation using ship-board radiometers Radiometers installed on ships for the validation of MODIS skin SSTs. Top: the ISAR mounted above the bridge of the M/V JinguMaru. Middle: M-AERI mounted on the NOAA S Ronald H. Brown. Bottom: M-AERI mounted on an upper deck of the Explorer of the Seas.
M-AERI cruises since the launch of Terra used for the validation of MODIS skin SSTs M-AERI validation data
ISAR VOS cruises for SST validation Real-time transmission of data via Iridium, on-the-fly validation is feasible.
SST radiometers - 20093rd Miami IR Radiometry Workshop Traceability to SI references is a prerequisite for CDRs
Validation with buoys Buoys provide many more opportunities of “matchups ” than radiometers.
GHRSST Diagnostic Data Set Location of the 250 HR-DDS global data comparison locations for SST in situ and satellite retrievals.
DDS time series Example of time series of DDS data including multiple satellite data, in situ measurements, NWP analysis fields and OI fields. This allows rapid comparison between VIIRS SSTs and other SSTs.
Gather in situ Buoy MAERI, ISAR Real time or retrospective A Acquire, load SDR and reference field inputs Generate extraction files Quality control B C 0 1 In situ data → LUT generation to product validation F E Process SDR, Navigate → EDR, Matchup records D Analyze Matchups → Quality Test Hypercube LUT Update L2gen with revised LUT and tables 1 2 G H I Analyze Diff wrt Reference, Time Series Hovmueller plots Process VIIRS SDR → EDR, Diagnostics Correct algorithm as necessary, update and re-process 2 0
Current status at L-351 • Instrument level T/V testing completed, and some optical cross-talk issues identified – but not expected to be dominant source of SST error • Instruments integrated on NPP spacecraft at Ball Aerospace & undergoing testing • Post-launch SST validation plans being set up: coordination between May (NAVOCEANO), Ignatov (NOAA –STAR), Emery (U. Colorado) & Evans – Minnett (U Miami) • New validation sensors (M-AERI Mk2) being developed • Real-time data transmission being tested • Software being installed and tested, including match-ups “on the fly” • Data streams being established and tested • Anticipated validation data: • Satellite fields (MODIS, AVHRR, AATSR) • Buoys • Radiometers (2 M-AERIs; 2 M-AERI Mk2s, 2 ISARS) • Logical framework for feedback to improve retrievals being established
Summary • VIIRS has the potential to provide high quality SSTs. • Post launch validation will focus on comparison with: • Satellite SST fields • Buoys • Radiometers • Contribution to SST CDR requires validation with NIST-traceable radiometers – facilitated through Miami Infrared Radiometry Workshops.
Major VIIRS Objectives • High resolution imagery with near constant resolution across scan • Increased resolution of SST retrievals • Disaster monitoring (Volcanic ash, Suspended Matter, Floods, Fires, …) • Increased accuracy/resolution of aerosols and cloud properties • Climate relevant accuracies……
In situ and proxy data tasks A1 A2 In Situ Measurements MAERI In Situ Measurements ISAR A E1 I1 Matchup database RTE simulation In Situ Measurements MAERI E I
Telescope / HAM Synchronization Angles Note – successive rotations of the Rotating Telescope Assembly use alternate sides of the HAM
VIIRS Bands Spectral bands are a subset of MODIS bands
ISAR validation data Real-time transmission of data via Iridium, on-the-fly validation is feasible
Temperatures are traced to NIST • On-board black-body cavities have thermometers calibrated to NIST-traceable thermometers (SSEC) • Periodic calibration using a 3rd black body in M-AERI zenith view. • Periodic calibration of M-AERI system with a NIST-designed Water-Bath Black-Body target at RSMAS, using NIST-traceable reference thermometers. • RSMAS Water-Bath Black-Body target characterized with NIST EOS TXR NIST EOS TXR TXR characterizing the RSMAS WBBB
NIST water-bath black-body calibration target See: Fowler, J. B., 1995. A third generation water bath based blackbody source, J. Res. Natl. Inst. Stand. Technol., 100, 591-599
M-AERI Cold finger, Dewar and detectors Aft optics Input aperture Stirling cycle cooler Interferometer
Wavelength calibration Wavelength calibration provided by a HeNe laser