Validation of the MSG-2 SEVIRI Operational Evapotranspiration Product at Selected European Sites

Transcription

1 Validation of the MSG-2 SEVIRI Operational Evapotranspiration Product at Selected European Sites George P. Petropoulos 1, Matthew R. North 1, Gareth Ireland 1, Prashant K. Srivastava 2,3, Salim Lamine 1 1 Geography and Earth Sciences, Aberystwyth University, Aberystwyth, Wales, UK 2 NASA Goddard Space Flight Centre, Greenbelt, MA, USA 3 Earth System Science Interdisciplinary Centre, University of Maryland, Baltimore, MA, USA

2 Background Importance of accurate estimation of Evapotranspiration (ET) cannot be overstated... Involved in numerous physical processes & feedbacks within the climate system Major relevance to global water and energy & biochemical cycles Of practical value in many disciplines & practical applications However, the strong spatial & temporal variability of parameters needed for the accurate evaluation of ET, make deriving its spatially distributed estimates a challenging & daunting task

3 Background Ground instrumentation require often a large array of surface based data unworkable over large areas small scale of measurement: only localised estimates Implementation expensive, time-consuming, labour-intensive...use of Ground Monitoring Networks... Eddy Covariance Lysimeter FLUXNET Network

4 Background The advent of Earth Observation has lead to numerous methods being developed to estimate ET rates. Some techniques have shown promise for operational exploitation, with releavnt products being available already One example is the MSG SEVIRI ET product: Spatial resolution: 3 km Temporal resolution: 30, daily ET obtained: Ghilain et al., 2012 Available from: MSG-2 SEVIRI

5 Background A few SEVIRI validation studies have been conducted so far, particularly so evaluating the product accuracy on continental scale (Ghilain et al., 2011; 2012; Sepulcre-Canto et al., 2014; Petropoulos et al., 2015). Knowledge gained from such studies can for example: Determine a product suitability for different applications Increase product credibility before that is used practically Allow for identification, quantification and understanding of errors Assist to directing efforts towards the re-evaluation the ET retrieval parameters and algorithm structure

6 Aim and Objectives Evaluate the accuracy of the SEVIRI MET operational product evapotranspiration estimates at a range of European ecosystems for years 2010 and Examine agreement in respect to Season variations 2. Investigate ET agreement for a range of Fractional Vegetation Cover (FVC) thresholds 1. Appraisal product accuracy for a range of land use/land cover (LULC) types in Europe

7 Study Sites In total 7 sites representing different biophysical conditions from the CarboEurope network was used in the study. UK_EBU IT_MBO FR_MAU IT_CAS ES_LJU ES_AGU IT_REN

8 Study Sites Characteristics of the CarboEurope flux tower sites used as experimental sites in validating the SEVIRI MET product Site Name Llano de los Juanes Aguamarga Monte Bondone Renon/ Ritten (Bolzano) Castellaro (only 2010) Easter Bush- Scotland Mauzac (only 2011) Abbreviation ES-LJu ES-Agu IT-Mbo IT-Ren IT-Cas UK-Ebu FR-Mau Coordinates (Lat/Long) / / / / / / / Country SPAIN SPAIN ITALY ITALY ITALY UK FRANCE Land Use Olive Plantation Grass Steppe Grassland Forest Agricultural Site Grasslands Agricultural Site Ecosystem Type/ Land Cover Olive Orchards Annual Broadleaf Shrub Grasslands Evergreen Needle-leaf Forest Cropland Grasslands Cropland Dominant Species/Genus Olea europaea, Macchia Sumac (Rhus), Toyon (Heteromeles) and Coffeeberry (Rhamnus) species Nardetum alpinum Picea Cereal Crop C3 grasses Cereal Crop Elevation (Metres) 1622m 195m 1547m 1794m 89m 190m N/A Climate Warm temperate with dry, hot summer Arid Steppe cold Snow fully humid warm summer Snow fully humid cool summer Warm temperate fully humid with warm summer oceanic with mild winters and cool and moist summers Warm temperate fully humid with warm summer

9 Methodology

10 Methodology mm h -1 mm h -1 a) SEVIRI MET product over Italy for p.m. on the 21st of July 2011 b) SEVIRI MET product over Spain for p.m. on the 21st of July 2011 Agreement was assessed based on: P denotes the predicted values (SEVIRI ET) and O denotes the observed (CarboEurope) values Name Description Definition Bias / MBE Scatter / MSD RMSE MAE R 2 Bias (or Mean Bias Error) Scatter (or Mean Standard Deviation) Root Mean Square Error Mean Absolute Error Linear Correlation Coefficient of Determination of Pi to Oi 2 R = N 1 bias = MBE = ( P i O i ) N i= 1 N 1 scatter = ( Pi Oi ( Pi Oi )) ( N 1) N i= 1 i= RMSE = bias + scatter N 1 MAE = N P O ( P P)( O O) i i N i= 1 i= 1 i ( O O) i i N 2 i= Pi O) 2

11 Results LULC Analysis Year 2010 Year 2011 Sites Bias Scatter RMSD MAE Slope Intercept R2 All Sites Combined

12 Results LULC examples

13 Results FVC Analysis

14 Results FVC example

15 Results Seasonality YEAR 2010 YEAR 2011

16 Results Seasonality All Days YEAR 2010 YEAR 2011

17 Conclusions LULC: For all sites, average RMSD was mm h -1 whilst the average correlation (R 2 ) for all ecosystems was With the exception of IT_CAS 2010, cropland sites exhibited consistently good estimation of ET (RMSD <0.086 mm h -1 ). FVC: the most accurate estimation of ET is found in environments of lower FVC, i.e. grassland & cropland sites. In such environments lower (thus more predictable) rates of ET occur (Fernandez-Prieto et al., 2012). SEASON: Summertime conditions yielded the highest correlation between predicted and observed data (R 2 = 0.509) but the largest error and scatter (0.05 mm h -1 & mm h -1 respectively). Winter yielded the poorest correlated results, but the lowest error and scatter (0.02 mm h -1 and mm h -1 respectively). IN OVERALL: Findings well-aligned to previous validations undertaken on different years (e.g. Ghilain et al., 2011; SEVIRI ATBD). Detailed error budget analysis challenging, several factors to be accounted for including: modelling approach uncertainties & on modelling inputs, site characteristics variability, in-situ uncertainty...

18 Future Work Studies such as this are important steps in the validation of operational satellite products and are vital for the future development of SEVIRI s operational capacity on a global scale. Further work should look to expand SEVIRI MET operational product validation at a wide range of settings, including: inter-comparisons to other similar products exploration of correlations to other variables (e.g. Rg, LST) downscaling ET from SEVIRI Results also support ongoing efforts globally towards the operational development of related products using EO instruments which were launched recently or planned be launched in the next 1-2 years.