VIRTIS view of the Earth (VIS-2)
VIRTIS was one of the instruments aboard Rosetta that were active during the spacecraft's third Earth swingby on 13 November 2009. This image was taken by VIRTIS several hours after closest approach, when the spacecraft was at about 230 000 km from the Earth's surface and receding again from the planet.
One of the two channels of the VIRTIS instrument is the Mapper (VIRTIS-M), a hyperspectral imager that collects image data simultaneously in 864 narrow, adjacent spectral bands (colours). The observations in different sets of narrow bands can be combined to generate different views of the Earth.
This image (called "VIS-2" in the related composite image "VIRTIS spectral images of the Earth", linked from the right-hand menu) has been taken over the American continents in the visible-near infrared spectral range (350-1000nm). It is essentially the same as figure "VIS-1" (see related images), but now the set of spectral bands (colours) that were used for the RGB channels of the image were selected to give maximum contrast to the various components: ground, clouds and sea.
North and South America are clearly seen in this false-colour picture centred on the Gulf of Mexico. Additionally, the contrast between clouds and sea is increased. This enhancement is obtained by using a combination of colours with the blue (B), green (G) and red (R) channels respectively at 0.474 µm (for the sea water), 0.785 µm and 1.0 µm (to increase the contrast of the land).