From: Rick v100 (rickv100@yahoo.com)
Date: Fri Jul 15 2005 - 03:24:40 PDT
Thus the reason why the National Security Service and
other government agenices have the best supercomputers
available to process the data.
Rick
--- david gudmunsen <kroctec@btopenworld.com> wrote:
> I hope that I may be able to partially illuminate
> the subject as it relates
> to the "Great site" correspondence.
>
> First of all I should point out that the imagery
> that is and is becoming
> available to us comes from a great variety of
> sources and there are great
> differences in terms of coverage and both spectrally
> and spacially. The
> spectral content and spatial resolution are normally
> determined by the
> purpose of the data, how big a pocket ($s) the
> primary user of the data sets
> is and from there on the value of future sales which
> may be used to offset
> investment costs. the older and more the data has
> and is being used the
> cheaper it becomes to the point where we even get
> some stuff for free: High
> res 3D data is crazy money.
>
> From a spectral point of view there is just about
> everything used out there
> from simple black & white photographic, ultra
> violet, visible colour, near &
> far infra red, radar and x-ray also both analogue
> and digital.
>
> Spacially the resolution largely depends on how far
> the instrument (camera)
> is from the subject, the ground speed and also the
> type of instrument.
> Typically analogue aerial cameras have format sizes
> between 150mm and 300mm.
> For example Leica make a range of instruments: 240mm
> film camera that will
> ideally resolve about 5cm on the ground, a laser
> based instrument using
> LIDAR (light detecting and ranging) horizontal and
> vertical resolution to
> about 13cm and a CCD based scanner which can also
> under ideal circumstances
> resolve about 5cm on the ground.
>
> When it comes to satellite mounted instruments there
> is so much variety
> spacially ranging from 50cm to about 10km for
> digital for commercial data.
> Better than 8cm for some low orbit steerable
> military satellites. The early
> Landsat instruments were about 120m per pixel and
> the more recent I think
> are 10m per pixel.
>
> Low orbit satellites operate at altitues from about
> 120 miles to typically
> 1500 miles and satellites below 22500 miles are also
> called low orbit, they
> will circle the earth in times that vary from about
> 2 hours at 120 miles
> altitude to 24 hours (geostationary or
> geosynchronous) at 22500 miles
> altitude. To get complete earth coverage you need a
> satellite in a low polar
> orbit, to get continuous coverage you need a
> geostationary satellite.
>
> A note on coverage is that there are some areas of
> the world which are never
> 'clear sky' ie there is always cloud cover.
>
> None of the forgoing has anything much to do with
> communications satellites
> which are a very different subject. Also the
> greatest problem is the sheer
> number crunching capacity required for processing
> such massive data sets and
> the time it takes compared to the speed of data
> aquisitiion. Storage is also
> a further problem.
>
> Anyone who is particularly interested in the subject
> can email me privately
> and I wil do my best to point them in appropriate
> directions.
>
> Best regards from David Gudmunsen
>
>
> ===Mil-Veh is a member-supported mailing list===
> To unsubscribe, send e-mail to:
> <mil-veh-off@mil-veh.org>
> To switch to the DIGEST mode, send e-mail to
> <mil-veh-digest@mil-veh.org>
> To reach a human, contact <ack@mil-veh.org>
>
This archive was generated by hypermail 2.1.4 : Fri Oct 28 2005 - 23:22:17 PDT