Self-Organizing Maps and Unsupervised Classification - Neural Networks: Methodology and Applications - page 424

Fig. 7.20. Outline of the physical phenomena that are relevant to explain the
observations. The observations consist in the set of reflectance spectra that are
measured by the SeaWifs radar. That radar uses eight wavelengths for analyzing
the surface

of ocean color data processing. They come from a SeaWifs image. This image
was over West Africa and the Canarie islands on January 5th, 1999. Two
pictures of that zone, which were obtained on the same day with different
resolutions, are available: a LAC ( Local Area Coverage ) image, with 2141 ×

793 = 1 , 697 , 813 pixels (Fig. 7.21) and lower resolution, GAC ( Global Area
Coverage ) image with 536

199 = 106 , 664 pixels. The topological map design
was performed from a sampled LAC image. Sampling was performed by line
decimation of the original LAC image. Thus the training set had 238

×

793 =
188 , 734 pixels. The quality of the resulting vector quantization, was assessed
from the full LAC picture. Since 90% of the pixels had no contribution to

×

Table 7.1. Spectral bands of SeaWifs

Bands Wavelengths

K (nanometers) λ k

1 412

2 443

3 490

4 510

5 555

6 670

7 765

8 865