Comparison of NDVI derived from NOAA/AVHRR LAC and PAL data

NOAA/AVHRR satellite imagery has been widely used for vegetation studies at global and regional scales, to study for example the exchange of matter and energy between the ecosystem and the atmosphere or to generate land cover maps. PAL and LAC products are usually processed as maximum composite yielding an image every 10 days, with 8 and 1 km spatial resolution, respectively. However differences in the processing algorithms and on the data available to generate the products, radiometric data and spectral indices derived are not equal. The objective of this analysis was to generate mathematical relationships between data provided by LAC and PAL imagery, in order to make them comparables for vegetation studies. We work with 36 NDVI 10 day composites for the 1992-93 growing season from each of the databases for southern South America. The LAC images were degraded to the same spatial resolution of the PAL images (8km) in order to make both sources comparables. We worked on the values of individual pixels and on the annual NDVI average (NDVII). Our results showed that the relationship between NDVI-I from both sources differed from de 1:1 line: NDVI-I LAC = 0.77 x NDVI-I PAL + 0.092 (r=0.82). We detect non-random spatial differences that can be partially associated to differences on the processing. Our results suggest that a direct relationship between NDVI sources is useful in order to make the sources compatible for vegetation studies.