ghrsst 8 th science team melbourne, may 2007 ghrsst sea ice working group peter minnett rsmas...

GHRSST 8th Science Team Melbourne, May 2007

GHRSST Sea Ice Working GHRSST Sea Ice Working GroupGroup

Peter MinnettPeter Minnett

RSMASRSMAS

University of MiamiUniversity of Miami


BackgroundBackground

• GHRSTT SI WG was set up at the 6GHRSTT SI WG was set up at the 6 thth Science Team Meeting in Exeter.Science Team Meeting in Exeter.

• Objectives:Objectives:– To determine best ice-mask for high latitude SST To determine best ice-mask for high latitude SST

fieldsfields– To improve accuracy of high latitude SST fields To improve accuracy of high latitude SST fields


MembershipMembership

• Peter Minnett (U. Miami)Peter Minnett (U. Miami)

• Chelle Gentemann (RSS & U. Miami)Chelle Gentemann (RSS & U. Miami)

• SSøøren Andersen (DMI)ren Andersen (DMI)

• John Stark (UK Met O)John Stark (UK Met O)

• With input from Ron Vincent (Royal Military With input from Ron Vincent (Royal Military College of Canada) & Steinar Eastwood College of Canada) & Steinar Eastwood (Norwegian Met Service [met.no])(Norwegian Met Service [met.no])


IR - IssuesIR - IssuesThere are four specific issues associated with the accurate retrieval There are four specific issues associated with the accurate retrieval

of sea surface temperature (SST) at high latitudes using infrared of sea surface temperature (SST) at high latitudes using infrared radiometry:radiometry:

• The discrimination between ice-free and ice-covered water at the The discrimination between ice-free and ice-covered water at the resolution (temporal and spatial) of the GHRSST SST retrieval resolution (temporal and spatial) of the GHRSST SST retrieval schemes.schemes.

• The discrimination between ice-free and ice-covered water at the The discrimination between ice-free and ice-covered water at the resolution (temporal and spatial) of the GHRSST SST global resolution (temporal and spatial) of the GHRSST SST global analyses schemes.analyses schemes.

• The accurate correction of the effects of the atmosphere on the The accurate correction of the effects of the atmosphere on the infrared radiation as it propagates from the sea surface to the infrared radiation as it propagates from the sea surface to the satellite radiometer.satellite radiometer.

• How feasible is the reconstruction of SST in the marginal ice How feasible is the reconstruction of SST in the marginal ice zone based on ice concentration, typically needed in climate–zone based on ice concentration, typically needed in climate–related, long-term data sets such as HadISST?related, long-term data sets such as HadISST?


μμW - IssuesW - IssuesMicrowave radiometry is very good at all-Microwave radiometry is very good at all-weather determination of SST and ice cover, weather determination of SST and ice cover, but:but:– Spatial resolution is poorSpatial resolution is poor– Side-lobe contamination – more of an issue for Side-lobe contamination – more of an issue for

SST than for ice coverSST than for ice cover– Calibration of AMSR-E is potentially an issueCalibration of AMSR-E is potentially an issue


GHRSST Sea Ice RequirementsGHRSST Sea Ice Requirements• Ice mask, not ice properties: Ice mask, not ice properties:

– 1- 4 -10km resolution @ 6hrs1- 4 -10km resolution @ 6hrs

• Procedure very analogous to cloud screeningProcedure very analogous to cloud screening• Could make use of ice properties retrievals, Could make use of ice properties retrievals,

but it is not clear that objectives are the samebut it is not clear that objectives are the same• ComplementaryComplementary to the GCOS SST & Sea Ice to the GCOS SST & Sea Ice

Working Group which is comparing different Working Group which is comparing different ice concentration products in order to obtain ice concentration products in order to obtain better knowledge of their error properties.better knowledge of their error properties.


GHRSST Sea Ice Requirements - IIGHRSST Sea Ice Requirements - II• Atmospheric correction algorithm improvements for Atmospheric correction algorithm improvements for

high-latitude, near ice edge factors high-latitude, near ice edge factors – Dry atmospheresDry atmospheres

– Large air-sea temperature differencesLarge air-sea temperature differences

– Temperature dependence of infrared emissivity Temperature dependence of infrared emissivity • see Newman, S. M., J. A. Smith, M. D. Glew, S. M. Rogers, and J. see Newman, S. M., J. A. Smith, M. D. Glew, S. M. Rogers, and J.

P. Taylor, 2005: Temperature and salinity dependence of sea P. Taylor, 2005: Temperature and salinity dependence of sea surface emissivity in the thermal infrared. surface emissivity in the thermal infrared. Quarterly Journal of the Quarterly Journal of the Royal Meteorological SocietyRoyal Meteorological Society, , 131,131, 2539-2557. doi: 2539-2557. doi: 10.1256/qj.04.15010.1256/qj.04.150


Sea IceSea Ice

• Sea ice includes ice pack, land fast ice and Sea ice includes ice pack, land fast ice and tide-water glaciers that extend beyond the tide-water glaciers that extend beyond the conventional, time-invariant land-mask.conventional, time-invariant land-mask.

• Highly variable in space and timeHighly variable in space and time

• Does not necessarily have a well defined edgeDoes not necessarily have a well defined edge– Comparable to cloud edge Comparable to cloud edge


OLS image of katabatic winds blowing over open water in the Ross Sea, Antarctica. Streamers of frazil ice forming at the surface are oriented in the direction of air flow. (Courtesy of Arctic Antarctic Research Center - arcane.ucsd.edu)


Large tabular icebergs calved off

Antarctica provide a dynamic ice edge


Data sourcesData sources

• High resolution (<1 km) SAR and visible High resolution (<1 km) SAR and visible imagery imagery

• High resolution (~1 km) infrared imageryHigh resolution (~1 km) infrared imagery

• Medium resolution (~12 km) high frequency Medium resolution (~12 km) high frequency microwave imagery (ice cover)microwave imagery (ice cover)

• Low resolution (~50-100 km) low frequency Low resolution (~50-100 km) low frequency microwaves (SST)microwaves (SST)


Spatial Spatial resolutionresolution

Spatial resolution in the micro-wave images relatively poor.

Generally over-sampled to a 25km grid.

Microwave data less influenced by clouds, and contain complementary information to the visible or infrared imagery.


Terra MODIS true colorTerra MODIS true color

June 29, 2004. 21:59 UTCJune 29, 2004. 21:59 UTC


Terra MODIS true colorTerra MODIS true color

June 16, 2004. June 16, 2004.


MODIS MODIS cloud & cloud & ice maskice mask


Example of SAR imageExample of SAR image


Summary – ice maskSummary – ice mask• During summer, cloud screening algorithms using During summer, cloud screening algorithms using

reflected sunlight can be applied to IR datareflected sunlight can be applied to IR data• During winter, lack if reflected sunlight means IR During winter, lack if reflected sunlight means IR

techniques have to be applied (e.g. spatial coherence), techniques have to be applied (e.g. spatial coherence), or reduced-resolution microwave ice product:or reduced-resolution microwave ice product:– DrDr Gentemann has an “operational” 9-km, daily Gentemann has an “operational” 9-km, daily μμww ice ice

maskmask– Aqua has MODIS and AMSR-E so elapsed time not an Aqua has MODIS and AMSR-E so elapsed time not an

issue; all other combinations of ir/mw sensors have issue; all other combinations of ir/mw sensors have uncertainties with ice movement between overpassesuncertainties with ice movement between overpasses

– SAR images, very high resolution, but difficult to interpret, SAR images, very high resolution, but difficult to interpret, and displacement between overpasses can be an issue. and displacement between overpasses can be an issue.


Atmospheric correction algorithmsAtmospheric correction algorithms

• And now for the high latitude effects on SST:And now for the high latitude effects on SST:– Atmospheric transmissivity (water vapor Atmospheric transmissivity (water vapor

distribution)distribution)– Air-sea temperature differencesAir-sea temperature differences


Variability of atmospheric transmissionVariability of atmospheric transmission


Ocham’s razor – simple is goodOcham’s razor – simple is good

AVHRR NLSST algorithms:AVHRR NLSST algorithms:NLSST = NLSST = aa + + bbTT44 + + cc(T(T44 – T – T55) + ) + dd[(T[(T44 – T – T55) * (sec) * (sec – 1)] – 1)]

CASSTA (Composite Arctic Sea Surface CASSTA (Composite Arctic Sea Surface Temperature Algorithm; Vincent et al, 2007 a, b) Temperature Algorithm; Vincent et al, 2007 a, b) uses the form:uses the form:

Arctic SST = Arctic SST = aa + + bbTT44

with coefficients derived by AVHRR BT & ship-with coefficients derived by AVHRR BT & ship-based skin-SST measurementsbased skin-SST measurements


Marine-Atmospheric Emitted Radiance Marine-Atmospheric Emitted Radiance Interferometer (M-AERI)Interferometer (M-AERI)


Temperatures are traced to NISTTemperatures are traced to NIST

1.1. M-AERI on-board black-body cavities have M-AERI on-board black-body cavities have thermometers calibrated to NIST-traceable thermometers calibrated to NIST-traceable thermometers.thermometers.

2.2. Periodic calibration using a 3Periodic calibration using a 3rdrd black body black body in M-AERI zenith view.in M-AERI zenith view.

3.3. Periodic calibration of M-AERI system with Periodic calibration of M-AERI system with a NIST-designed Water-Bath Black-Body a NIST-designed Water-Bath Black-Body target at RSMAS, using NIST-traceable target at RSMAS, using NIST-traceable reference thermometers.reference thermometers.

4.4. RSMAS Water-Bath Black-Body target RSMAS Water-Bath Black-Body target characterized with NIST EOS TXRcharacterized with NIST EOS TXR

NIST EOS TXR

TXR characterizing the RSMAS WBBB


Dry Arctic Dry Arctic AtmospheresAtmospheres


North Water Polynya Expedition North Water Polynya Expedition March-July 1998March-July 1998

M-AERI


AVHRR SST retrievals in the NOW regionAVHRR SST retrievals in the NOW region

From Vincent, R. F., R. F. Marsden, P. J. Minnett, K. A. M. Creber, and J. R. Buckley, 2007: Arctic Waters and Marginal Ice Zones: Part 1 - A Composite Arctic Sea Surface Temperature Algorithm using Satellite Thermal Data.

In reparation.

Preliminary results


AVHRR SST retrievals in the NOW regionAVHRR SST retrievals in the NOW regionFrom Vincent, R. F., R. F. Marsden, P. J. Minnett, K. A. M. Creber, and J. R. Buckley, 2007: Arctic Waters and Marginal Ice Zones: Part 1 - A

Composite Arctic Sea Surface Temperature Algorithm using

Satellite Thermal Data. In reparation.


Radiometric measurements of air-Radiometric measurements of air-sea temperature differencesea temperature difference


Air-sea temperature differencesAir-sea temperature differencesOver most of the Over most of the oceans the air-sea oceans the air-sea temperature difference temperature difference is very constrained. is very constrained. Close to the ice, the Close to the ice, the spread of values is spread of values is greater.greater.


Dependence on air-sea temperature differenceDependence on air-sea temperature difference


Dependence on air-sea temperature differenceDependence on air-sea temperature difference

Simulations have 5 air-sea temperature differences under each atmosphere: 0, ±1, ±2K


SummarySummary• Ice mask for IR SST can be derived in the summer Ice mask for IR SST can be derived in the summer

using the same tools as the cloud mask.using the same tools as the cloud mask.– Use information in the data streams for SST, not necessary to wait for an Use information in the data streams for SST, not necessary to wait for an

ice product. ice product.

– New approaches may need to be defined for winter measurements New approaches may need to be defined for winter measurements

• Ice amount can be retrieved from microwave channelsIce amount can be retrieved from microwave channels– Use information in the data streams for SST, not necessary to wait for an Use information in the data streams for SST, not necessary to wait for an

ice product. ice product.

• Physics of high-latitude SSTs reasonably well Physics of high-latitude SSTs reasonably well understood in terms of the problems, solutions are understood in terms of the problems, solutions are being developed. being developed. – Requires better characterization of polar conditions; more in situ Requires better characterization of polar conditions; more in situ

measurements.measurements.

ghrsst 8 th science team melbourne, may 2007 ghrsst sea ice working group peter minnett rsmas...

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