Regarding cloud ( if set to 0), is it that acquisition will not be planned if cloud is more that 0?

The cloud figure is a qualifier parameter, just that. The acquisition will not be planed if you have configured the sensor with a Cloud Constraint and the cloud figure is out of the defined bounds See more here: http://1.help.taitussoftware.com/SaVoir/help/content/6.advanced/constraints/clouds/clouds.htm