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Sea-Surface Temperature from Suomi-NPP VIIRS: Algorithm Development and Uncertainty Estimation Peter J. Minnett, Robert H. Evans, Guillermo P. Podestá , Katherine A. Kilpatrick Rosenstiel School of Marine and Atmospheric Science, University of Miami. Outline.

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slide1

Sea-Surface Temperature from Suomi-NPP VIIRS: Algorithm

Development and Uncertainty Estimation

Peter J. Minnett, Robert H. Evans, Guillermo P. Podestá, Katherine A. Kilpatrick

Rosenstiel School of Marine and Atmospheric Science, University of Miami

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

outline
Outline

Focus on possible contribution to the SST Climate Data Record.

Overview of VIIRS characteristics relevant for SST retrievals

Form of the atmospheric correction algorithms.

Uncertainties:

  • comparisons vs drifting buoys.
  • comparisons vs ship radiometers.

Future directions.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

introduction
Introduction

VIIRS is the first of a new class of satellite radiometer, using design elements from MODIS and SeaWiFS.

At least two more VIIRS will be flown on the NOAA JPSS satellites replacing the AVHRRs on the NOAA-n polar orbiters.

The European radiometer to replace the AVHRRs on MetOp-A and MetOp-B, called METimage, will have a similar optical design, but will have SST channels more similar to MODIS.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

suomi npp
Suomi NPP
  • Launched on 28 October, 2011.
  • Equator crossing - 1:30 p.m.
  • Altitude of 824 km.
  • 16-day repeat cycle
  • Five key instruments:
  • Advanced Technology Microwave Sounder (ATMS)
  • Cross-track Infrared Sounder (CrIS)
  • Ozone Mapping and Profiler Suite (OMPS)
  • Clouds and the Earth's Radiant Energy System (CERES)
  • Visible Infrared Imaging Radiometer Suite (VIIRS)

Photo courtesy Ball Aerospace.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

viirs
VIIRS
  • Rotating telescope with “Half-Angle Mirror” fore-optics.
  • 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.
  • Scan Range of earth view: ±56º from nadir.
  • Swath width: 3000 km.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

viirs components
VIIRS Components

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

viirs spectral bands
VIIRS spectral bands

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

viirs sst rsrs
VIIRS SST RSRs

Green - MODIS Red -VIIRS

Purple lines are the VIIRS broad-band imaging bands with nadir resolution of 0.375km.

Moeller, C., et al. VIIRS F1 "best" relative spectral response characterization by the government team. in SPIE 8153, 2011.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

viirs pixel aggregation
VIIRS pixel aggregation

HSI: Horizontal Sampling Interval

Schueler, C. F., Lee, T. F. and Miller, S. D., "VIIRS constant spatial-resolution advantages". International Journal of Remote Sensing, 34(16): 5761-5777 (2013).

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

viirs vs modis spatial resolution
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

sst retrieval
SST retrieval
  • Cloud screening – required to identify all pixels with contamination by cloud (or aerosols)
  • Atmospheric correction – required to correct for the effect of the intervening atmosphere
effect of the atmosphere
Effect of the atmosphere

Temperature deficit VIIRS M15 (λ=10.76µm)

Temperature deficit VIIRS M16 (λ=12.01µm)

viirs atmospheric correction algorithms
VIIRS Atmospheric Correction Algorithms

Miami V6:

  • SST2b = a0 + a1T11 + a2(T11 – T12) Tsfc + a3(T11-T12)Sq
  • SST3b = a0 + a1T11 + a2(T3.7 – T12) Tsfc + a3Sq

Miami V7:

  • SST2b = a0 + a1T11+ a2(T11– T12) Tsfc+ a3(T11-T12)Sq+

a4Sq+ a5Sqχ

χ = fn(lat)

  • SST3b = a0 + a1T11+ a2(T3.7– T12) Tsfc+ a3Sq+ a4Sqχ

χ = 0.1 for |lat| ≤ 40°; 2.0 for |lat| > 40°

Sq= sec(θ)-1

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

spatial distribution of errors
Spatial distribution of errors

Comparisons with buoys

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

simple global statistics
Simple Global Statistics

Statistics of the differences between the VIIRS skin SST retrievals and the subsurface temperatures measured from drifting buoys.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

zenith angle dependence
Zenith angle dependence

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

spatial comparisons windsat
Spatial comparisons – WindSat

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

time dependences
Time dependences

SST 2b day

SST 2b night

SST 3b night

Comparisons to buoy temperatures

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

time dependences in latitude bands
Time dependences – in latitude bands

Comparisons to buoy temperatures

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

slide23

Ship radiometers: M-AERIs

M-AERIs, new and old, on R/V Knorr. Transit from Woods Hole to Cape Town, and an Agulhas mooring recovery cruise.

Mean 0.024K, stdev = 0.201K, n = 78

VIIRS v7.0 algorithm

Reference SST WindSat 5day average.

Skin SST measurements from R/V Knorr. January – March 2013.

M-AERIs are Fourier Transform Infrared interferometers with two internal blackbody calibration targets.

Pre- & post-deployment lab calibration against NIST-traceable calibrators.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

slide24

Ship radiometers: ISARs

M/V Andromeda Leader

M/V Horizon Spirit

Mean -0.058 K, stdev = 0.417K, n = 337

ISARs are autonomous filter radiometers with two internal blackbody calibration targets.

Pre- & post-deployment lab calibration against NIST-traceable calibrators.

Data relayed in real-time by Iridium.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

spatial distribution of errors radiometers
Spatial distribution of errors - radiometers

Comparisons with ship radiometers

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

summary
Summary
  • VIIRS is a good SST radiometer.
  • Errors are pleasingly stable in time.
  • Spatial comparisons with WindSat microwave SSTs give more uniform agreement than with infrared OI SSTs.
  • Full swath retrievals are improved by the use of additional zenith angle terms.
  • Form of algorithms provides continuity with heritage sensors.
  • Comparison with ship-board radiometers provides mechanism for contributing the SST Climate Data Record.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

future directions
Future directions
  • Continue to populate matchup data base, leading to error hypercube.
  • Continue refinement of atmospheric correction algorithm.
  • Compare with AMSR2 microwave SSTs.
  • Continue matchups with ship radiometers – provide pathway to contributing to the SST CDR.
  • Continue to work with NOAA STAR VIIRS Team.

SPIE Ocean Sensing and Monitoring. Baltimore, May 6, 2014

acknowledgements
Acknowledgements

Funding from NASA and NOAA JPSS

Thank you.