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Peter Broomhall raised the following points on the ACIS:
(see http://www.dvtech.com/astract/Abstrct.html )
>>I see the comment " the soil auger configuration loosens soil around
the shaft so soil is not compacted against sensors ". I see from the home page
on Capacitance sensors the major drawback is " extremely critical to have good
sensor -tube-soil contact for reliable estimation of soil moisture " Does
this not do the opposite therefore reducing accuracy ?
I suppose there is a fine line between disturbing the soil too much when
placing tubes, and compacting the soil. The former, I would feel, will
in time settle back to a more representative condition than would a soil
compressed around a tube. The loosened soil would however be more likely
to provide a preferential path for water flow. Depending on the soil
type, good sensor/tube soil contact will vary. Some settling time prior
to using the equipment would seem to be the way to go.
Correcting for the compaction and change in bulk density does not seem
to be a practical way out. Better insertion methods must be found.
Peter - could you fill us in on the "installation process developed for
the EnviroSCAN"?
>>Then based on the auger having a 3 inch diameter, it may well be
the soil inside the spirals represents 50 % of the sphere of influence.
Would this not again influence the accuracy of the sensor ?
The web page and the spiral auger design appear to indicate that the
soil in the spiral will be part of the measured volume. The volume that
the spiral displaces will always be the same, but the increase in bulk
density due to compression/compaction of the soil will vary with
texture. (Some soils will compact a lot in the immediate vicinity, and
others less over a larger distance away). It is not therefore a constant
that can be ignored.
So there does appear to be a problem, with this aspect of the sensor
(assuming we have deducted how it is inserted correctly.)
Despite this, the idea of a sensor integrated into a spiral auger still
appeals as compared to an access tube.
>From the ACIS web page
" The capacitance sensing design approach also allows the user to
determine whether soil or rocks are
compacted against the sensors, alerting the user of this condition
and allowing adjustment of the probe's
orientation to avoid potentially inaccurate readings."
But how exactly this is done is not stated. Perhaps someone who has used
the system could elaborate!?
I must say that the overall setup appears to be well executed,
particularly the telemetry and base unit.
--
Regards
=======================================================
Bruce Metelerkamp SOIL WATER RESEARCH OFFICER
Institute for Commercial Forestry Research,
University of Natal, PO Box 100281
Scottsville, ZA3209
Rep. of South Africa
Voice:27 331 62314 Private Voice Mail 0881236337
E-mail: bruce@icfr.unp.ac.za FAX:27 331 68905
brooz@pobox.com
Bruce.Metelerkamp@pobox.com
URL http://www.icfrnet.unp.ac.za/~metele
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