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

NASA SST Science Team Meeting Seattle, November 2010 Outline Description of VIIRS – Visible/Infrared Imager/Radiometer Suite SST retrievals Cal/Val approach All information about VIIRS is from publicly accessible sources.

NASA SST Science Team Meeting Seattle, November 2010 NPP payload From

NASA SST Science Team Meeting Seattle, November 2010 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 μ m Imagery (I) Spatial Resolution: nadir / edge of swath Moderate (M) Spatial Resolution: nadir / edge of swath Swath width ~3000km

NASA SST Science Team Meeting Seattle, November 2010 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

NASA SST Science Team Meeting Seattle, November 2010 VIIRS innovations Rotating telescope primary optics Two-sided “Half-Angle Mirror” (HAM) Multiple detectors (16) per spectral band On-board pixel aggregation

NASA SST Science Team Meeting Seattle, November 2010 VIIRS

NASA SST Science Team Meeting Seattle, November 2010 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 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

NASA SST Science Team Meeting Seattle, November 2010

NASA SST Science Team Meeting Seattle, November 2010 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.

NASA SST Science Team Meeting Seattle, November 2010 VIIRS vs MODIS spatial resolution From VIIRSHeritageSystems-SNODGRASS_GUENTHER_ANDREAS-WE_PRINT-PR.pdf

NASA SST Science Team Meeting Seattle, November 2010 VIIRS SST Bands GSD = Ground sampling distance Spectral bands are a subset of MODIS bands These are very promising

NASA SST Science Team Meeting Seattle, November 2010 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.

NASA SST Science Team Meeting Seattle, November 2010 VIIRS SST algorithms Daytime NLSST algorithm: where a 0, a 1, a 2, a 3 are coefficients derived by regression analysis, T 11 is the measured brightness temperature at 11 µm (VIIRS band M15), T 12 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 a 0, a 1, a 2, a 3 are coefficients derived by regression analysis (but are different from those in Equation 12), T 3.7 is the measured brightness temperature at 3.7 µm (VIIRS band M12).

NASA SST Science Team Meeting Seattle, November 2010 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…..

NASA SST Science Team Meeting Seattle, November 2010 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 Jingu Maru. 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.

NASA SST Science Team Meeting Seattle, November 2010 M-AERI validation data M-AERI cruises since the launch of Terra used for the validation of MODIS skin SSTs

NASA SST Science Team Meeting Seattle, November 2010 M-AERI Mk 2

NASA SST Science Team Meeting Seattle, November ISAR VOS cruises for SST validation Real-time transmission of data via Iridium, on-the- fly validation is feasible.

20 SST radiometers rd Miami IR Radiometry Workshop Traceability to SI references is a prerequisite for CDRs

NASA SST Science Team Meeting Seattle, November 2010 Validation with buoys Buoys provide many more opportunities of “matchups ” than radiometers.

NASA SST Science Team Meeting Seattle, November 2010 GHRSST Diagnostic Data Set Location of the 250 HR-DDS global data comparison locations for SST in situ and satellite retrievals.

NASA SST Science Team Meeting Seattle, November 2010 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.

In situ data → LUT generation to product validation Gather in situ Buoy MAERI, ISAR Real time or retrospective Gather in situ Buoy MAERI, ISAR Real time or retrospective Generate extraction files Quality control Acquire, load SDR and reference field inputs Process SDR, Navigate → EDR, Matchup records Process SDR, Navigate → EDR, Matchup records Analyze Matchups → Quality Test Hypercube LUT Analyze Matchups → Quality Test Hypercube LUT Update L2gen with revised LUT and tables Process VIIRS SDR → EDR, Diagnostics Analyze Diff wrt Reference, Time Series Hovmueller plots Analyze Diff wrt Reference, Time Series Hovmueller plots Correct algorithm as necessary, update and re- process A B C D G E I F H

NASA SST Science Team Meeting Seattle, November 2010 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

NASA SST Science Team Meeting Seattle, November 2010 VIIRS & NPP

NASA SST Science Team Meeting Seattle, November 2010 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.

NASA SST Science Team Meeting Seattle, November 2010 Additional slides in reserve

NASA SST Science Team Meeting Seattle, November 2010 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……

NASA SST Science Team Meeting Seattle, November 2010 In situ and proxy data tasks In Situ Measurements MAERI In Situ Measurements MAERI In Situ Measurements ISAR In Situ Measurements ISAR A A A1A1 A1A1 A2A2 A2A2 Matchup database RTE simulation Matchup database RTE simulation In Situ Measurements MAERI In Situ Measurements MAERI E1E1 E1E1 E E I1 I 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

NASA SST Science Team Meeting Seattle, November 2010

NASA SST Science Team Meeting Seattle, November 2010 ISAR validation data Real-time transmission of data via Iridium, on-the-fly validation is feasible

NASA SST Science Team Meeting Seattle, November 2010 Temperatures are traced to NIST 1.On-board black-body cavities have thermometers calibrated to NIST- traceable thermometers (SSEC) 2.Periodic calibration using a 3 rd black body in M-AERI zenith view. 3.Periodic calibration of M-AERI system with a NIST-designed Water-Bath Black-Body target at RSMAS, using NIST-traceable reference thermometers. 4.RSMAS Water-Bath Black-Body target characterized with NIST EOS TXR NIST EOS TXR TXR characterizing the RSMAS WBBB

NASA SST Science Team Meeting Seattle, November NIST water-bath black-body calibration target See: Fowler, J. B., A third generation water bath based blackbody source, J. Res. Natl. Inst. Stand. Technol., 100,

NASA SST Science Team Meeting Seattle, November 2010 M-AERI Input aperture Interferometer Cold finger, Dewar and detectors Stirling cycle cooler Aft optics

NASA SST Science Team Meeting Seattle, November 2010 The innards

NASA SST Science Team Meeting Seattle, November 2010 Wavelength calibration Wavelength calibration provided by a HeNe laser