Spaced Out ::

I had another good question in class last week as to why the Landsat missions have/had a ~10am UTC equatorial crossing time. In fact the full list of satellite times are below (Source: wikipedia):

So why is that? Although I didn’t know, I thought it was something to do with optimum reflectance from the Earth’s surface in relation to the original mission objectives, and that it’s stuck ever since

I’ve asked a couple of colleagues and the consensus seems to be to acquisition (globally) of “good”, usable, imagery but that it’s a trade off between about solar elevation angle, cloud formation and dew/frost cover. As you see from the table above, later Landsats have progressively gone for slightly later times.

Some further comments include because it places the local time for most of the imaged land areas (primarily in the northern hemisphere) in the 10am-2pm range when the sun is at a high elevation (in order to minimize shadow). Additionally, there is a consideration for cloud. “Conventional wisdom” is that we avoidthe afternoon buildup of cumulus clouds over interior regions with the10am crossing time. This doesn’t necessarily help out in coastal areas though.

Thanks to those who answered my query and any further thoughts would be welcome!