METEOSAT SURFACE ALBEDO FIRE PERTURBATION PRODUCT (MSAFPP) EVALUATION Bernardo W. Mota 1 José M.C. Pereira 1 Yves Govaerts 2 Ana C.L. Sá 1 João M.N. Silva

METEOSAT SURFACE ALBEDO FIRE PERTURBATION PRODUCT (MSAFPP)

EVALUATION

Bernardo W. Mota1

José M.C. Pereira1

Yves Govaerts2

Ana C.L. Sá1

João M.N. Silva1

1 Instituto Superior de Agronomia

2 EUMETSAT

Global Geostationary Fire Monitoring Applications Workshop March 23-25, 2004, EUMETSAT

Objectives

• The objectives of the study were:

– to evaluate the Meteosat Surface Albedo Fire Perturbation Product (MSAFPP).

– to develop a quantitative relationship between MSAFP probability and area burned. If successful, this will allow for the processing of 20+ years of Meteosat archive data, yielding monthly estimates of area burned in Africa.


Data

• The MSAFPP is based on a temporal analysis of the Meteosat Surface Albedo (MSA) data set generated with the algorithm of Pinty et al. (2000), applied to all daylight Meteosat-5 data acquired in 2000.

• A total of 37 ten-day composite periods were produced. The product was generated at the Meteosat full spatial resolution over Africa, ranging from about 2.5 km at the subsatellite point up to about 5 km.

•The derived surface albedo, , is the hemispherical integration of the BRF for a given position of the Sun fixed at 30º, estimated within the Meteosat radiometer visible (VIS) band ( 0.4 - 1.1 m).

• Fire-induced albedo perturbations are detected from an analysis of albedo temporal variations, looking for the presence of a significant decrease preceding very low values, and followed by a slow albedo increase (Govaerts et al., 2002).


Data

• Evaluation of the MSAFPP was performed with data from the year 2000, and relied on the following datasets:

– JRC/IES Global Burned Areas (GBA) 2000 monthly burned area maps, at 1 km spatial resolution.

– 13 Landsat scenes, with binary classification (burned / unburned). 5 scenes from the northern Hemisphere and 8 scenes from the southern Hemisphere.

– The European Space Agency ATSR World Fire Atlas, screened for non-vegetation fire hotspots. The product contains daily, night-time active fires, at 1 km spatial resolution.


Methods

• The MSAFPP, GBA2000, ATSR-WFA and Landsat scenes were co-registered, and the burned area class of the Landsat scenes was used as a spatial template for the extraction of temporal profiles.

• The MSAFPP and ATSR-WFA products were aggregated to monthly datasets, corresponding to the temporal resolution of GBA2000.

• Temporal profiles of MSAFPP, GBA 2000, and ATSR-WFA data from each Landsat scene were plotted together, to assess the similarity of their behavior. MSAFP probability values <0.5 were equalled to zero.

• The MSAFPP and GBA2000 data for the whole of Africa were aggregated in 0.25º cells, and the GBA2000 fraction of area burned in each cell was plotted as a function of the mean MSAFP probability for the cell.


Methods


Location of the 13 Landsat scenes used in the MSAFPP evaluation.

Methods


The GBA 2000 product was validated against burned area maps derived from the 13 Landsat scenes, with the results shown above (Silva et al., in preparation).

These results support the use of GBA2000 as a reference dataset for assessing the MSAFPP.

• Results


Example of the temporal profile analysis for the D.R. Congo site. The multiple MSAFPP profiles show the effect of different thresholds for the exclusion of low fire perturbation probability observations.

Results


The temporal profiles of MSAFPP, GBA2000 and ATSR-WFA are quite similar. The MSAFPP peak in May in the Sudan Landsat scene needs further analysis, to clarify the mismatch with GBA2000 and ATSR-WFA.

• Results


There is good correspondence between profiles in the SE Sudan and DRC sites. In Zambia there is an MSAFPP peak in May without correspondence in the fire data. In Nampula (N Mozambique), fire occurrence detected by GBA2000 and ATSR-WFA is not captured by MSAFPP, probably due to fire fragmentation and vegetation type (low albedo wet miombo).

• Results


At most of these S hemisphere sites, MSAFPP displays earlier peaks than GBA2000 and ATSR-WFA. The reasons for this effect are unclear. To some extent, they may be an artefact of temporal compositing of the various datasets.

• Results


In January, fires affect the Sudanian and Guinean savannas of the N hemisphere, that have high pre-fire albedo.

Fires cause a substantial drop in albedo, and MSAFP probability is high.

In June, fires affect primarily the wetter Zambezian miombo woodlands of the S hemisphere.

Forest cover is relatively high, and pre-fire albedo is low. Fire-induced albedo change tends to be lower than in the N hemisphere, and MSAFP probabilities never are very high.

Monthly relationships are good, but slopes vary. The main sources of variation are likely to be the magnitude of surface albedo change, and fire fragmentation patterns.

• Results


At the annual level the relationship between MSAFPP and area burned (as given by GBA2000) is very good.

The negative y-intercept is quite low, and reflects the influence of factors other than biomass burning on surface albedo dynamics.

All MSAFPP values were taken into account in this analysis. If low probability values (e.g. <0.5) are excluded, the relationship is expected to improve.

• Conclusions

• At the local level, defined by the Landsat scenes, and using the MSAFPP pixel as the unit of analysis, the correspondence between temporal profiles of MSAFPP on one side, and GBA2000 and ATSR-WFA varies substantially between locations.

• It tends to be better in the northern hemisphere than in the southern hemisphere sites, and appears to be affected by vegetation type and fire spatial patterns.

• At various sites, MSAFP probabilities show earlier peaks than GBA2000 and ATSR-WFA. This effect may be partly an artefact (temporal resolution, compositing), but it may also correspond to effective surface changes not clearly understood.


• Conclusions

• The continental level analysis, comparing MSAFPP and GBA2000 in 0.25º cells, performed at monthly and annual time frames, shows good correspondence between the two datasets.

• The slopes of the relationships between the two products vary in space and in time, apparently as a function of the magnitude of the surface albedo changes induced by burning, and of fire fragmentation patterns.

• The conversion of MSAFPP into estimates of area burned appears feasible. The ideal levels of spatial and temporal aggregation of the data to produce this estimate need further investigation.

• Also, the uncertainty generated by the use of a single relationship to implement the MSAFPP-based burned area estimation remains to be determined.


• References

• Govaerts, Y.M., J.M.C. Pereira, B. Pinty, and B. Mota (2002) Impact of fires on surface albedo dynamics over the African continent. Journal of Geophysical Research-Atmospheres, 107 (D22), 4629, doi:10.1029/2002JD002388.

• Pinty, B., F. Roveda, M.M. Verstraete, N. Gobron, Y. Govaerts, J.V.Martonchik, D.J. Diner, and R.A. Kahn (2000)Surface albedo retrieval from Meteosat, 1, Theory, J. Geophys. Res., 105, 18,099–18,112.

• Silva, J.M.N., A.C.L. Sá, J.M.C. Pereira, J.F.C.L. Cadima and J.-M. Grégoire (2004). Comparison of burned area estimates derived from SPOT-VEGETATION and Landsat ETM+ data for thirteen sites in Africa: influence of spatial pattern and vegetation type. In preparation.


Documents

METEOSAT SURFACE ALBEDO FIRE PERTURBATION PRODUCT (MSAFPP) EVALUATION Bernardo W. Mota 1 José M.C. Pereira 1 Yves Govaerts 2 Ana C.L. Sá 1 João M.N. Silva