2.1. Satellite data
The boundary of the Barents Sea was taken according to . Based on the natural conditions determining formation of bio-optical characteristics, the whole basin was divided into three sub-regions: the Northern (1), Middle (2) and Southern (3) Fig.1.
The Northern region is predominantly occupied by the flow of cold Arctic Basin Water whereas the Middle is under influence of the warm Norwegian Current. The boundary between them was taken along 75° N, in the vicinity of the Polar Front. Of course, a real position of the Polar Front is very changeable and not a straight line . The Southern region is a shallow basin comprising the Cheshskaya Bay and the Pechora Sea; the latter is under strong influence of the Pechora river run-off.
The mean monthly distributions of the bio-optical characteristics in the White Sea with spatial distributions of 3 x 3 km, computed from MODIS-Aqua data, are given in Section 3.
Fig.2 shows the monthly coverage of the sub-regions by satellite data in different months from 1998 to 2010. The coverage was calculated for the chlorophyll data product (Chl). It should be noted that the presented diagrams do not take into account the number of used images (a bin is considered to be covered even if only one image per month).
The coverage from SeaWiFS and MODIS-Aqua are shown on Fig.2 by different hatching. One can see that the coverage by MODIS-Aqua, especially since 2006, is much better than by SeaWiFS data. As mentioned in Introduction, since July 2002 MODIS-Aqua data were used for the computations.