Re: New ground proximity warning.

Date:         13 Dec 96 04:26:01 
From:         "Mark A. Brown" <mark@optima.nal.go.jp>
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Dear all,

Re terrain models for CFIT avoidance

In at least one terrain referenced nav system for military a/c that I know
of, a database is employed along with a laser radar that scans ahead of the
vehicle. It is reported to be able to pick out a power pylon at a distance
of several  miles in pouring rain. Otherwise its a bit embarressing when
your deadly foe just stops your multi-zillion zloty whizzbang wonderplane
with a lo-tech high wall or barrage balloons.

I'd agree with Robert in that high accuracy isn't needed for situational
awareness. Even in areas of the map which are not too good, one has an MSA.
The database designer could simply use the "worse case" terrain model or just
use a "plateau" at 2000 ft (or 1000ft) below the MSA for the area.

Some pilots might suggest that this could be dangerous due to what you
see out of the window not matching expectation, I suppose. However, the
display is supposed to improve SA, not be a substitute for looking
out of the window, and if you can see out clearly anyway (VMC), you wouldn't
need the display.

Some parts of the world are mapped very well. I've got some data
from an agency in Japan which can supply you with satellite derived height
data for the whole of Japan on various grid densities (250 metres, 50 metres,
1 km). The heights are in decimeters (0.1m) although I don't know if this is
the true accuracy.
I'll be using this data for experiments with a 3D version of EGPWS, maybe
adding a velocity vector (if the VV is on the hillside and the hillside
is close, you could be in trouble!) and autopilot programmed flight path
(for vertical path awareness) as well as experimenting with colour-coding.

Back to lurking,
Mark.