Martin Rutherford Technical Director Oceanography and Meteorology Royal Australian Navy 02 Jun 2009 Towards a Bias Corrected L4 Median
Scope n Motivation – Spoilt with choice! n Creating a simple median using ArcGIS n Analysing the Median n Bias corrections n What next!
Motivation n 1984 – CSIRO -Weekly ‘best image’ based on cloud content -AVHRR only -Hard copy by priority post -Customers were happy (previously had nothing) n 1992 – BoM regional SST image -Updated after each AVHRR pass -Weighted blend based on age, but no OI -Sourced using McIDAS, delivered via the web -Customers were happy (timely, fewer gaps)
Motivation n NAVO MCSST K10 -Global daily 10 km analysis -OI, no cloud holes -Processed as web map service and posted on internet -Customers were happy (more timely, higher resolution) n Added OSTIA as web map service -Added K10 – OSTIA differences ~ confidence -Customers NOT happy (which one do they use?)
Lessons Learned n Customers want: -Web-based delivery -Frequent updates -High resolution -A measure of confidence/uncertainty -Animation n Customers do NOT want: -Choice
A (Not so) Simple Median n Use Python and GIS tools to: -Download all L4 products -Interpolate to common grid -0.1, 0.25, 0.5?? -Bilinear, cubic ?? -Calculate median and standard deviation -Display as Web Map Service -Deliver as GIS compatible layer
Best Spatial Resolution ?
Best Interpolation Method ?
Decision Point ! n Re-sample to 0.1 Degree n Use Cubic Interpolation
The Daily Product
Contributing to the Median
Calculating the Bias n Find daily (Interpolated - Median) n Bias = Median of daily (Interpolated – Median)
Bias: ABOM GAMSSA
Bias: EUR ODYSSEA
Bias: NAVO K10
Bias: NCDC AVHRR
Bias: NCDC AVHRR + AMSR
Bias: REMSS MW+IR
Bias: UKMO OSTIA
Applying the Bias n Apply bias correction to daily Interpolated n Find new daily median
Testing for Impact n Compare Standard Deviation n Compare contributions to median
Testing for Impact – Std. Dev.
ABOM GAMSSA ‘Bias’
GAMSSA Uncorrected Contribution
GAMSSA Corrected Contribution
EUR ODYSSEA ‘Bias’
ODYSSEA Uncorrected Contribution
ODYSSEA Corrected Contribution
NAVO K10 ‘Bias’
K10 Uncorrected Contribution
K10 Corrected Contribution
NCDC AVHRR ‘Bias’
AVHRR Uncorrected Contribution
AVHRR Corrected Contribution
NCDC AVHRR + AMSR ‘Bias’
AVHRR + AMSR Uncorrected Contribution
AVHRR + AMSR Corrected Contribution
UKMO OSTIA ‘Bias’
OSTIA Contribution
OSTIA Corrected Contribution
REMSS MW + IR ‘Bias’
REMSS Uncorrected Contribution
REMSS Corrected Contribution
Percentage of Observations in Median
What Next? n Seek GHRSST Science Team Advice!! n Re-do all calculations! n Publish uncorrected median and Std. Dev. n Compare with GMPE
Bigger Questions! n Should users be correcting GHRSST products? n Has this technique any merit?? n How do I provide the ‘best’ information for my users from existing GHRSST products: -Global -10km or better -0.5 K or better -Six hourly -Near real time -Including diurnal variability
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