[alma-config] topography mask

[Simon Radford]

Friends,

How should we incorporate topography constraints in the configuration
design process? 

To date, we have discussed using a binary "go"-"no go" mask computed
from the digital elevation models. Although simple in principle, this
will be hard in practice. No single parameter characterizes the ease or
difficulty of putting an antenna station at a given location. Rather,
several different characteristics must be considered. These include, but
are probably not limited to, the overall and local surface gradients,
the local surface roughness, the subsurface geology and hydrology, and
road access. Given sufficient money, most of these features (or
impediments) can be mitigated or circumvented. But how should the cost
threshold be defined? Is it uniform across the site? Is it uniform for
all configurations? A binary mask must encode all of these factors.

Instead of a binary mask, therefore, I suggest we develop and use a
continuous, "cost" mask, where each pixel is assigned a relative
construction cost, which avoids the difficulty of defining a cost
threshold. Then the configuration design task is to minimize this cost
consistent with other goals, such as imaging, etc. This approach has the
flexibility to accommodate a few "high cost" stations if they are
balanced by other "low cost" stations and improve the overall
configuration quality.

How to calculate the cost mask is not, unfortunately, immediately
obvious. But it would appear a tractable problem that might tie in with
Mark Gordon's work. 

I welcome your reactions.

Simon