Vents de sable vus du ciel
Page 1 sur 1
Vents de sable vus du ciel
Quand les glaciers reculent un peu la terre brisée, laminée sèche et se transforme en poudre que les vents emmènent au-dessus de la mer.
On n'est pas au Sahara, on est dans l'Alaska!
Dernière édition par Ulysse92 le Mar 25 Jan 2011 - 0:02, édité 1 fois
Question directe à NASA Earth Observatory
Sur la 1ère photo on voit des bandes noires verticales perpendiculaires aux vents de sable
Je me suis donc demandé si c'était la houle
et j'ai posé la question le 19 novembre 2010
What are the dark lines perpendicular to the wind on the sea?
Is it swell? It seems so regular...
on m'a répondu le 22 novembre
This is the reply I got from one of our data folks...
MODIS and a lot of other sensors have a small field of view and scan back and forth to build a picture. By the time it reaches the end of one scan line across, the spacecraft has moved and it makes a new scan (and there's some fancy stuff to compensate for the forward motion of the spacecraft during the scan. One image overlaps with the previous one slightly so there are not gaps in the imagery. However, the calibration and sensitivity of the detectors at the top end of one scan
are not absolutely perfectly matched to those at the bottom of the previous (though the match is quite good). On dark surfaces, there can be a slightly visible pattern, or in very bright areas (you can see the same scan line pattern in sunglint features from MODIS, for example), but unless the area has low contrast, the pattern is usually not very obvious.
The fact that it is perpendicular to the wind direction in this image is coincidence: the scan line patterns are actually perfectly perpendicular to the direction of motion of the spacecraft. If you look around in that image, you'll notice areas where the wind direction is quite different and the scan line pattern remains the same.
Thanks for reading and viewing so closely...
Mike Carlowicz
Editor - NASA Earth Observatory
Pour ceux qui parlent pas bien anglais ces traits foncés sont le résultat du collage côte à côte de plusieurs photos... car le satellite effectue des balayages périodiques
Je me suis donc demandé si c'était la houle
et j'ai posé la question le 19 novembre 2010
What are the dark lines perpendicular to the wind on the sea?
Is it swell? It seems so regular...
on m'a répondu le 22 novembre
This is the reply I got from one of our data folks...
MODIS and a lot of other sensors have a small field of view and scan back and forth to build a picture. By the time it reaches the end of one scan line across, the spacecraft has moved and it makes a new scan (and there's some fancy stuff to compensate for the forward motion of the spacecraft during the scan. One image overlaps with the previous one slightly so there are not gaps in the imagery. However, the calibration and sensitivity of the detectors at the top end of one scan
are not absolutely perfectly matched to those at the bottom of the previous (though the match is quite good). On dark surfaces, there can be a slightly visible pattern, or in very bright areas (you can see the same scan line pattern in sunglint features from MODIS, for example), but unless the area has low contrast, the pattern is usually not very obvious.
The fact that it is perpendicular to the wind direction in this image is coincidence: the scan line patterns are actually perfectly perpendicular to the direction of motion of the spacecraft. If you look around in that image, you'll notice areas where the wind direction is quite different and the scan line pattern remains the same.
Thanks for reading and viewing so closely...
Mike Carlowicz
Editor - NASA Earth Observatory
Pour ceux qui parlent pas bien anglais ces traits foncés sont le résultat du collage côte à côte de plusieurs photos... car le satellite effectue des balayages périodiques
Dernière édition par Ulysse92 le Mar 25 Jan 2011 - 0:05, édité 3 fois
Sujets similaires
» Vu du ciel un quai géant
» l'arbre à vents
» Festival champignons Août 2011 au Suc des Vents
» Ciel mon téléscope
» dessins cochons vus du ciel
» l'arbre à vents
» Festival champignons Août 2011 au Suc des Vents
» Ciel mon téléscope
» dessins cochons vus du ciel
Page 1 sur 1
Permission de ce forum:
Vous ne pouvez pas répondre aux sujets dans ce forum
|
|