AATSR SST Validation using the M-AERI Peter J. Minnett Rosenstiel School of Marine and Atmospheric Science, University of Miami, Florida, USA Marianne Edwards Space Research Centre, University of Leicester Leicester, UK ENVISAT Validation Workshop Frascati 12 December 2002

Overview SST variability The M-AERI Validation cruises Past experience Future directions

M-AERI data for satellite SST validation Skin SST is source of signal detected by infrared satellite radiometers. Use of M-AERI for validation is comparing “like with like.” For example, satellite SST accuracy determined with buoy data includes near surface SST variability, which can be significant during the day.

Near surface temperature gradients – reality Profile measured at 12:51 local time on 4 October Off Baja California, R/V Melville MOCE-5 cruise. Blue line = SkinDeEP* profile Blue circle = M-AERI skin temp. Red cross = Float bulk SST at ~0.05m Green star = Ship thermosalinograph at ~3m From Ward, B. and P. J. Minnett, An autonomous profiler for near surface temperature measurements. Gas Transfer at Water Surfaces. M. A. Donelan, W.M. Drennan, E.S. Saltzmann and R. Wanninkhof (Eds.) American Geophysical Union Monograph

Time evolution of near-surface thermal gradients SkinDeEP profiles on 12 October Off Baja California, R/V Melville. From Ward, B. and P. J. Minnett, An autonomous profiler for near surface temperature measurements. Gas Transfer at Water Surfaces. M. A. Donelan, W.M. Drennan, E.S. Saltzmann and R. Wanninkhof (Eds.) American Geophysical Union Monograph

Fourier Transform Interferometers

Michelson interferometer

Interference

Fourier transforms of interferograms are spectra

M-AERI spectra From Minnett, P. J., R. O. Knuteson, F. A. Best, B. J. Osborne, J. A. Hanafin and O. B. Brown (2001). "The Marine-Atmospheric Emitted Radiance Interferometer (M-AERI), a high-accuracy, sea-going infrared spectroradiometer." Journal of Atmospheric and Oceanic Technology. 18(6): Air TemperatureSkin SST Both temperatures measured by one instrument, one calibration.

The M-AERI

M-AERI black- body cavities

M-AERI calibration targets

Marine-Atmospheric Emitted Radiance Interferometer (M-AERI)

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

M-AERI at sea

M-AERI in the Arctic

M-AERI in the Mediterranean One of a series of cruises in collaboration with CNR Institute of Atmospheric Physics and Climate, Rome.

Time-series of M-AERI measurements on Explorer of the Seas The Explorer of the Seas is a Royal Caribbean Cruise Liner, operating a bi-weekly schedule out of Miami. It is outfitted as an oceanographic and atmospheric research vessel, very suitable for satellite validation. For more details see

M-AERI data from Explorer of the Seas

Comparison of M-AERI with AATSR Over 140 M-AERI files (days) between May and September converted and uploaded to the NILU database. Explorer of the Seas cruise track

Past M-AERI results…. AVHRR Pathfinder MODIS

AVHRR-MAERI SST validation experience Cruise Name NMean K St. Dev. K CSP N GASEX FPO NOW 1998 (Arctic) Total, all data Total, excluding NOW data M-AERI validation of Pathfinder SSTs Using skin temperatures reduces the uncertainties by about a factor of two. See Kearns et al, 2000, Bull. Am. Met. Soc., 81,

MODIS SST Buoy and MAERI retrieval Statistics Version 4.5 (new delivery) MODIS SST Buoy and MAERI retrieval Statistics Version 4.5 (new delivery) BUOY M-AERI SST - new coefficients Median StdDev Number of Points –Terra all –Terra night –Terra day –Aqua all –Aqua night –Aqua day SST4 new coeffs, new formulation –Terra night –Aqua night SST - new coefficients MedianStdDevNumber of Points – Terra all – Terra night – Terra day – Aqua all – Aqua night – Aqua day SST4 new coeffs, new formulation – Terra night – Aqua night

Terra MODIS SST Validation Terra MODIS SST Validation Both SST and SST4 products show no trends with time (Jan 01-Sept 02), satellite zenith angle (not shown) or latitude vs drifting buoys. Dotted lines are ± 0.2K and enclose 50% of the retrievals Thermal, µm SST SST residual vs time by lat band Mid-wave, 4 µm SST SST4 residual vs time by lat band

Issues Accuracy of M-AERI data well established. M-AERI data-flow to Leicester, and to NILU, established. Narrow swath of AATSR is going to be a handicap in developing a large M-AERI – AATSR validation data base (clouds cause ~90% data loss). Much larger numbers of buoys are an attractive proposition, especially at night, and can complement radiometer measurements. Inter-satellite comparisons should be made, e.g. AATSR and MODIS; EOS Terra is in a compatible orbit (overpass time).

Night-time behavior of the skin effect  T = – 0.3 * exp(-U/3.7) From Donlon, C. J., P. J. Minnett, C. Gentemann, T. J. Nightingale, I. J. Barton, B. Ward and J. Murray (2002). "Towards improved validation of satellite sea surface skin temperature measurements for climate research." J. Climate 15:

Aqua-day Terra-day Terra/Aqua Global DAY SST - Sept 29, 2002

Wind speed dependence of diurnal & skin effects Envisat, Terra and Aqua overpass times. Note, local time varies across the swath.

Future plans Validate AATSR SSTs 2003 cruises: –Explorer of the Seas (2 weeks dry dock in January, 2003) –Polar Sea: Melbourne – Yokohama – Seattle, March – April –Urania: Mediterranean, April-May –Franklin: Canadian Arctic, September 2003, for 12 months (?) –Tangaroa: November, NZ SOLAS (?) –Polar Star: Seattle – Sydney, November -December AVHRR, MODIS, AIRS, AMSR SSTs