VALIDATION AND INTER-COMPARISON OF FOUR GLOBAL … · Criteria of selection QA Criteria Perfor mance Comments Product Completeness-Main limitations over Northern latitudes in wintertime

VALIDATION AND INTER-COMPARISON OF FOUR GLOBAL SURFACE ALBEDO PRODUCTS USING THE SALVAL TOOL.

www.eolab.esContact: Jorge Sánchez-Zapero.

EOLAB CTO & Research Engineer

(+34)963769448 jorge.sanchez@eolab.es

https://www.linkedin.com/in/jorgesanchezzapero/

EOLAB – Earth Observation LaboratoryParc Científic Universitat de València. C/ Catedrático Agustín Escardino, nº 9, 46980 Paterna, Valencia, Spain

ABSTRACT

METHODOLOGY

J. Sánchez-Zapero (1), F. Camacho (1), L. de la Madrid (1), Z. Wang (2), M. O. Roman (3)

(1) EOLAB, Valencia, Spain. (jorge.sanchez@eolab.es, lorena.delamadrid@eolab.es, fernando.camacho@eolab.es)

(2) University of Maryland College Park, College Park, MD, USA. (zhuosen.wang@nasa.gov)

(3) NASA/GSFC, Greenbelt,MD, USA.(miguel.o.roman@nasa.gov)

ProductPlataform/

SensorPeriod

SpatialResolution

Temp. Frec.

Comp. Period

Projection Spectral albedos

C_GLS V1SPOT/VGT 1999-2014

1km10

days30

daysPlate

carrée

▪VIS [0.4-0.7μm]▪NIR[0.7-4.0μm]▪BB [0.3-4.0μm]PROBA/VGT 2014-Present

MCD43A3 C6TERRA+AQUA/

MODIS2000-present 500m Daily

16 days

Sinusoidal ▪VIS [0.3-0.7μm]▪NIR[0.7-5.0μm]▪BB [0.3-5.0μm]

GLASS

NOAA/AVHRR 1981-1999 ~5km

8 days17

daysSinusoidal

▪BB [0.3-3.0μm]TERRA+AQUA/MODIS

2000-2010 1km

EBF DBF NLFCrop

Shrub

Herb.

BA

LANDVAL 9 6 10 26 21 16 11

Global 7 8 16 17 24 10 14

0

5

10

15

20

25

30

Pe

rcen

tage

NOAM

SOAM

EURO

AFRI ASIAOCE

A

LANDVAL 25 12 14 21 22 5

Global 19 11 9 24 31 6

05

101520253035

Pe

rce

nta

ge

Quality Criteria Validation Metrics

CompletenessGap size distribution (annual maps, temporal variations per biome/continent). Length of gaps.

Spatial Consistency

Visual inspection global maps.

Monthly maps and histograms of residuals.

PDFs & histograms of residuals per biome and continent.

Indicator of spatial homogeneity and correlation (CV, MoranIndex)

Temporal ConsistencyQualitative inspection of temporal variations

Cross-correlation and auto-correlation.Intra-annual Precision Histograms of the smoothness

Inter-annual PrecisionBox-plots per bin and median absolute anomaly of 95th and 5th percentiles for two consecutive years

Stability

Box-plots per bin and median absolute anomaly of 95th and 5th

percentilescomparing each year to the long term average

The slope of the evolution of inter-annual precision

Systematic errors (Bias)

Mean differences (bias)

Major Axis Regression linear fit (slope, offset)

Histogram of differences

Box plots of differences per bin

Total Error (Accuracy)

Pearson’s coefficient (power of the linear fit)

Root Mean Square Deviation (RMSD)

Box-plots of absolute bias per bin

Surface albedo is defined as the fraction of incident solar irradiance reflected by Earth's surface over the whole solar spectrum, and represents an Essential Climate Variable (ECV) as established by the Global Climate

Observing System (GCOS). The uncertainty of satellite-based albedo products must be evaluated over global conditions with the aim to determinate the compliance of user requirements (GCOS) and the usability.

Moreover, the availability of numerous products creates a need to understand the level of consistency between satellite products.

This work presents the validation and inter-comparison of four global surface albedo products: SPOT/VGT V1 of the Copernicus Global Land Service, NASA MODIS MCD43 C6, Global LAnd Surface Satellites (GLASS),

and PROBA-V V1 for the continuity of the Global Land Service. The results are generated using the Surface ALbedo VALidation (SALVAL) tool. SALVAL has two main objectives: (i) to provide transparency and

traceability in the validation procedure, designed to be compliant with the CEOS-LPV (Comitee on Earth Observations Satellites - Land Product Validation) sub-group and QA4EO (Quality Assurance for Earth

Observation) recommendations, and (ii) to provide a tool to benchmark new products or update product validation results as the time serie expands, reaching Validation Stage 4 in the CEOS LPV hierarchy.

designed to represent globally the variability of land surface types over optimal conditions in terms of spatial homogeneity and topography

Evaluated over

2001-2004 period: SPOT/VGT V1, MODIS C6 & GLASS SPOT/VGT V1 vs PROBA-V V1 during the overlapperiod (Nov’13-May’14) for the continuity of theGlobal Land Service

Product Completeness

ConclussionsConclussions

Evaluation of the sampling per biome type and continental region

ParameterThresho

ldPurpose

Distance to open water bodies [km]

5

Avoid open water bodies and their

changing reflectance

behavior with viewing geometry

Minimum fraction of

majority land cover type at 5

km distance

60%Avoid areas with

heterogeneous land cover.

Land Cover Majority at

5km

Exclude 'Water bodies' and 'Urban areas'

Vertical range [m] within a distance of

5km

<300m

Avoid areas with significant terrain

variability close to a site.

Location (Latitude)

60ºS to 80ºN

Exclude sites over extreme latitudes, where Global Land products does not

provide data

Network # of sites

SAVS 1.0521

(including256 BELMANIP2.1)

Calibration Sites

20

Additional sites (from existing

networks)26

Additional sites (Geo-Wiki)

158

Total 725

Criteria of selection

QA

Criteria

Perfor

manceComments

Product

Completeness - Main limitations over Northern latitudes in wintertime and Equatorial areas. Similar results than SPOT/VGT (and MODIS)

Spatial Consistency +Global distributions showed systematic positive bias (PROBA-V > SPOT/VGT) for NIR and BB, and bias 0 for VI.

Global distributions of residuals showed ~36% of cases within the optimal level for VI, and 50% for NI and BB

Temporal

Consistency + Reliable temporal variations for most of the cases compared with satellite reference products and ground observations.

Intra-Annual

Precision + Similar smoothness than both references (SPOT/VGT and MODIS C5), showing slightly higher δ values in NI.

Overall Spatio-

Temporal

Consistency±

PROBA-V vs SPOT/VGT shows high correlation (R>0.93) and low scattering, with almost no mean bias in VI and systematic positive

mean bias of ~5% in NI and BB (except in snow). 39%, 43% and 42% (67%, 73%, and 75%) of pixels showed optimal (target level) for

VI, NI and BB.

Comparison of PROBA-V and SPOT/VGT per biome type showed low bias (<3%, random sign) for VI, and positive bias for NI and BB in

all biome types. The exception was the snow class, with negative bias.

Accuracy

Assessment -PROBA-V:N=274; B=0.032 (22.1%); RMSD=0.042; Snow free conditions. 4% of pixels within GCOS.

Improved results for MODIS C5 using the same sampling: B=0.006 (4.9%); RMSD= 0.029; 18.1% of pixels within GCOS.

Product Completeness

Spatial Consistency

Temporal Consistency

Temporal Realism Accuracy Assessment

Intra-AnnualPrecision

Spatio-Temporal Consistency

Spatio-Temporal Consistency

SPOT/VGT V1 vs MODIS C5 SPOT/VGT V1 vs GLASS GLASS vs MODIS C5

Spatial Consistency

Intra-Annual Precision

Inter-Annual Precision

Temporal Consistency

QA

Criteria

SPOT/

VGT

MODIS

C6GLASS Comments

Product

Completeness - - +SPOT/VGT & MODIS showed main limitations over Northern latitudes in

wintertime and Equatorial areas. GLASS is gap-filled product

Temporal

Consistency ± + +Good temporal agreement between the three satellite products.

SPOT/VGT: Some limitation observed to detect spurious snowfall events,

and slight seasonality over desertic calibration sites.

Intra-Annual

Precision + + + Similar smoothness all products

Inter-Annual

Precision ± + +

2004 vs 2003

SPOT/VGT: RMSD 2,6% over calib. Sites. Median abs. Anomaly: 3%

MODIS C6: RMSD 2,6% over calib. Sites. Median abs. Anomaly: 2,3%

GLASS: RMSD 2,6% over calib. Sites. Median abs. Anomaly: 2,2%

QA

Criteria

SPOT/VGT V1

Vs

MODIS C6

SPOT/VGT V1

Vs

GLASS

GLASS

Vs

MODIS C6

Comments

Spatial

Consistency + ± +

Residuals:

VGT vs MOD: 15% GCOS / 75% Target

VGT vs GLASS: 14% GCOS / 53% Target

GLASS vs MOD: 39% GCOS / 82% Target

Overall

Spatio-

Temporal

Consistency

+ + +

VGT vs MOD

VGT vs GLASS

GLASS vs MOD

R 0,95 0,94 0,97

Bias 1,9% -0,4% 1,7%

RMSD 0,04 (19%)

0,05 (22%)

0,03 (16%)

%GCOS/Target 40/69 42/71 54/77