Generation of a MODIS Sea Surface Temperature Composite Methodology and Validation

Earth-Sun System DivisionNational Aeronautics and Space Administration

SPoRT SAC Nov 21-22, 2005

Generation of a MODIS Sea Surface Temperature Composite

Methodology and Validation

Stephanie Haines

November 21, 2005



Outline

Motivation to generate a high-resolution SST

composite

Methodology used to create several versions of

MODIS SST composites

Case Study analysis of May 2004– Comparison to RTG– Latency effects

Validation against buoy data

Conclusions and future work



Motivation Coastal NWS offices wanted high resolution SST product

Single pass of MODIS provides limited coverage

– Simple composite generated from multiple passes of MODIS data

• Main assumption is that SST does not change significantly from one day

to the next

• High resolution (1 km), full coverage

• Small scale features in SST gradients retained

Alternative to the Real-Time Global (RTG) SST analysis for

model assimilation

– Lower boundary layer forcing important in mesoscale models

– RTG is a 0.5 degree daily interpolation of in situ and satellite data



Methodology

Use the 1km SST EOS MODIS product to produce a detailed and spatially continuous SST field while minimizing cloud contamination and latency effects

Retain 5 clear (as determined by a cloud mask) SST values for each pixel separately for day and night

Average some of clear values to obtain a more consistent field

– Version 2 discards the coldest 2 of the 5 and averages the remaining 3 (current operational method)

– Version 3 has reduced latency by only considering the 3 most recent, to reduce cloud contamination the coldest is discarded (experimental method)



Case Study Period

May 2004

– relatively clear and dry period

– General warming trend of SSTs

– Version 2 method used with EOS SST product from the DAAC

– EOS cloud mask applied

Loop of daytime composites shows

– Spatially continuous pattern

– 1 km resolution

– Realistic spatial trends, varying with time



Comparison of MODIS to RTG

Large scale patterns of MODIS match well to RTG Strong SST gradient off east coast not in RTG product RTG is a daily product, therefore no diurnal information The MODIS composites show diurnal differences Operational applications of version 2 revealed some latency issues as a result of

persistent cloud cover – reran May 2004 case with version 3

RTG-SST

290 292 294 296 298 300 302 304 306

MODIS Daytime MODIS Nighttime

29th May 2004



Latency Effect on SST

Version 3 developed because of latency issues with version 2

Only small differences seen between the two MODIS versions, although there are differences in the latency

Even with several days latency, the composites capture both large scale and small scale SST gradients

0 2 4 6 8 10 12 14 16 18 20

MODIS LATENCY V2 MODIS LATENCY V3

290 292 294 296 298 300 302 304 306

MODIS SST V3RTG-SST MODIS SST V2

8th May 2004



Verification Against Buoy Data SST composites capture

majority of trends in the buoy data with high correlation values both day and night

Daytime

Nighttime RTG too warm at night, with the largest bias of 0.53

Reduced latency improves the composite (average latency improvement between versions 2 and 3 is 1-2 days)

RTG compares very well to buoy data during the day. Both MODIS composites have a warm bias



Conclusions and Future Work Version 2 worked very well for May 2004, but persist cloud cover and

cooling SSTs revealed issues with current compositing method Version 3 has reduced latency compared to version 2 and Will be creating a Version 4 algorithm that further improves the product Add AMSR-E SST data

– Aqua only– Plan to make AMSR-E SST available in real-time 2006– Provides SST values in cloudy conditions

AQUA MODIS AMSR-E MODIS+AMSR-E

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Generation of a MODIS Sea Surface Temperature Composite Methodology and Validation

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