Real time Arctic SST retrieval from satellite IR data

issues and solutions(?)Pierre Le Borgne, Gérard Legendre, Anne Marsouin, Sonia Péré, Hervé Roquet

Centre de Météorologie Spatiale, Météo-France, Lannion, France

Earthtemp Arctic SST workshop 18-19 December, Exeter

Outline

METOP-A/AVHRR derived daytime SST in September 2013

-Data-METOP-A (daytime)-Atmospheric profile data set

-Validation results (5years)

-Regional algorithms

-Use of NWP outputs

-Conclusions

Earthtemp Arctic SST workshop 18-19 December, Exeter

Data : METOP-A SST

METOP-A:1km resolution SST, Global coverage since 2007

METOP SST (see http://www.osi-saf.org )– Cloud mask (Maia, L. Lavanant, MF/CMS)– Ice mask (Ice probability, S. Eastwood, met.no)– Cloud/ice control– Daytime algorithm

SST = a T11 + (b TCLI + c S) (T11 - T12) + d S + e

MDB: 5 year Matchups at full resolution;

buoy location in central pixel within 3 hrs

Earthtemp Arctic SST workshop 18-19 December, Exeter

DATA: ECMWF output derived BT simulations (CEP+)

ECMWF operational forecasts   RTTOV version 10.2 applied onto each profiles BTs at 3.7, 10.8 and 12 m

Training dataset

60N

Earthtemp Arctic SST workshop 18-19 December, Exeter

Daytime « Arctic » validation results

Error vs clear sky coverage:Clouds induce negative errors(no evidence of ice related errors)

Error vs T11-T12

5 year MDB

All cov

n

QL

3-5

17405 0.05 0.66

Simulated Error vs T11-T12

Simul.CEP+

n

534 0.22 0.34

Earthtemp Arctic SST workshop 18-19 December, Exeter

Validation conclusions

Significant influence of cloud contamination – Improved cloud/ice detection effort: met.no

Errors determined by the shape of atmospheric profiles:

(ex: summer temperature inversion cases lead to large positive errors)

Errors well reproduced by simulations

Earthtemp Arctic SST workshop 18-19 December, Exeter

Solutions

1) Multisensor Bias corrections (Hoyer et al, 2013, RSE, in press)

AATSR and NAVOCEANO GAC data as reference

2) Regional algorithms

NLC SST = (a + b S) T11 + (c + d TCLI + e S) (T11 - T12) + f +g

S

CASSTA SST = (a + b S) T11 +c +d S

3) NWP derived correction methods

Earthtemp Arctic SST workshop 18-19 December, Exeter

Regional algorithms ?

5 Year MDB +Cloud filtering reinforced: cov> 0.8; QL 4-5

Three regimes?

Earthtemp Arctic SST workshop 18-19 December, Exeter

Regional algorithms

Regional algorithms applied on the 5 year MDB

6143 cases (cov>0.8)

QL 4-5

Operational

NLC

Simulation derived regional NLC

Optimal regional NLC

Optimal

CASSTA

(T10.8)

0.28 0.25 0. 0.

0.45 0.50 0.44 0.64

Simulation dataset (CEP+) not adequate to determineregional algorithms

T10.8 based algoNot convincing

Earthtemp Arctic SST workshop 18-19 December, Exeter

NLC vs CASSTA on MDB

T108-T120 max

0. 0.1 0.2 0.5

OptimalNLC

0.76 0.73 0.75 0.59

OptimalCASSTA

0.77 0.74 0.78 0.68

Residual standard deviation on MDB

Earthtemp Arctic SST workshop 18-19 December, Exeter

NWP derived methods

Simulations must be « exact »: they should produce the same BTs as would be observed, given a surface temperature and atmospheric profiles:

A BT simulation adjustment step is necessary

We need to compare observations and simulations

(in consistent conditions)

Earthtemp Arctic SST workshop 18-19 December, Exeter

Simulations too cold

Earthtemp Arctic SST workshop 18-19 December, Exeter

Low wind zones: DW!

Earthtemp Arctic SST workshop 18-19 December, Exeter

OSTIA and DW in the Arctic?

Filter: 7 ms-1?

June 2012 June 2013June 2011

Earthtemp Arctic SST workshop 18-19 December, Exeter

Relative number of clear sky cases with wind > 7ms-1

July 2012

Earthtemp Arctic SST workshop 18-19 December, Exeter

Daytime prototype results in 2012 summer Arctic

June July August 2012, lat > 60°N

1070 cases Operational NLC

Operational NLC + bias correction

Optimal HL NLC

OSTIA

d -0.10 -0.13 -0.12 -0.31

s 0.60 0.55 0.52 0.37

Earthtemp Arctic SST workshop 18-19 December, Exeter

Trends with latitude

Operational NLC Operational NLC + bias correction

Optimal HL NLC OSTIA

Earthtemp Arctic SST workshop 18-19 December, Exeter

Operational SST retrieval methods in Arctic

Global daytime algorithm leads to SST overestimations by several tenths of K for T108-T120 below 0.5K

Regional algorithms may solve the problem, however simulation derived algorithms necessitate dedicated profile data sets

DW induced differences between OSTIA and observed SST make NWP derived simulation adjustments quite difficult in permanent daylight conditions

Drastic wind filtering (> 10ms-1) has lead to satisfactory results.

Earthtemp Arctic SST workshop 18-19 December, Exeter

Further work

CMS to write a paper on 5 (7) years of METOP-A Arctic results X(?) to build up a profile database adapted to Arctic studies CMS to prepare regional HL algorithms as a backup to simulation

derived BTs for METOP-B CMS & DMI to compare METOP biases (NWP derived vs Jacob’s

method) …….

Earthtemp Arctic SST workshop 18-19 December, Exeter

10.8 micron simulation error on the 1st of June 2012

Earthtemp Arctic SST workshop 18-19 December, Exeter

Summertime error origin

(see alsoLeBorgne et al, EUMETSAT Oslo 2011)

0.5<T11-T12 <0.7

Air temp. dt/dq

0.5<T11-T12 <0.7

Normal case=0.04, =0.16

0.<T11-T12 <0.3

Air temp.dt/dq

0.<T11-T12 <0.3

Summer ArcticCase=0.55, =0.21

Earthtemp Arctic SST workshop 18-19 December, Exeter

Trends with T108-T120

Operational NLCOperational NLC + bias correction

Optimal HL NLC

Earthtemp Arctic SST workshop 18-19 December, Exeter

Earthtemp Arctic SST workshop 18-19 December, Exeter

Anomalies in Sept 2013

METOP-A/AVHRR derived daytime SST in September 2013