| Densitometry
Equipment
LignoStation and LignoVision
LignoStation is an
"all in one system for surface preparation, high resolution assessment
of tree-ring variables and wood density. The LignoStation follows a new
concept: It produces high resolution digital scans, directly and
automatically. The whole system is computer controlled. Thus you can
focus on your scientific work, while the system does the routine work
for you. Note: This product is developed in co-operation with the
University of Freiburg, Germany and is in development." Details: (1)
Density assessment by a high frequency probe (no x-ray source used); (2)
Image resolution: <= 20 microns (=1/50 mm); (3) Optical scans with
high-resolution camera; (4) Samples: increment cores or stem discs; and
(5) Maximum measurement length: 500 mm
Coupled with LignoStation is (1) LignoTrim: High resolution wood
surface cutter; (2) LignoScan: High resolution, electromagnetic wood density
scanner; (3) LignoScop: High resolution wood surface
microscope-camera scanner; and (4) LignoVision. LignoVision is software that
represents a system for tree-ring scanning that works with any scanner and
allows automatic tree-ring detection plus an easy manual editing function.
Ring-width as well as early and latewood width can be separately stored.
Besides surface scanning, it can also be used for analysis of x-ray
images. The software also supports multiple image sources, such as optical
scanner, CCD-camera, and x-ray scanner.
Ian
Campbell of the Canadian Forest Service reminds us that DendroScan is
software available for $99.95 + $5 shipping Canadian from the University
of British Columbia Press:
UBC
Press
University of British Columbia
6344 Memorial Road
Vancouver, BC
Canada V6T 1Z2
Phone: 604-822-5959
Fax: 1-800-668-0821
The
book gives detailed instructions for the assembly and use of an x-ray
densitometry lab, using stuff most universities already have like a
scanner, a darkroom, a table saw, and an x-ray machine. It includes a
pre-calibrated density wedge and a floppy with the DendroScan program,
which converts scanned grey-scale images of x-ray negatives (or positives)
into density, identifies ring boundaries, and measures and counts the
rings. DendroScan is also able to use images scanned directly from
well-sanded wood, and will give ring measurements and counts - but not
densities. It has also been used for other rhythmically banded objects,
including annually laminated lake sediments and growth increments in seal
teeth. If anyone has any questions, please don't hesitate to contact:
Ian Campbell
Canadian Forest Service
5320-122 St. Edmonton
Alberta, Canada
T6H 3S5
Phone: 403-435-7300
Fax: 403-435-7359
Julian
Sceicz adds this regarding densitometry saws: The version Ian Campbell
mentioned as being designed by Forintek is I think the same as the one now
produced by AcuSaw Ltd. Glen MacDonald and Gordon Jacoby purchased these
saws a few years ago, and as part of setting up a tree-ring lab here at
Queen's I also recently bought one. The saw is a beautifully made twin
blade job which uses compressed air to run. They are custom built, which
means you can't be in a hurry - mine took over a year from ordering to
delivery. Cost is ca. $11,000 Canadian. Contact address:
AcuSaw Ltd.
2302 West 33rd Ave.
Vancouver, B.C.
Canada V6M 1C3
Phone/Fax: 604-261-3931
Gordon
Jacoby adds this about the AcuSaw and densitometry/image analysis: The
AcuSaw saw mentioned by some previous messages works very well. The length
of cut is limited to about 20 cm. Unmounted cores can be cut down to about
1 mm thickness after some adjusting of the saw. If a milling machine is
available, a twin-bladed saw such as used (and described) by Fritz
Schweinguber can be made for much less than the $11,000 Canadian
investment for this saw.
A
densitometric/image analysis system can be assembled with a frame-grabber
board for a Mac (and assumably a PC), a videocamera mounted on a
microscope to look at xrays on a light table, and image analysis software
from NIH (free). We used a similar system for several years using
proprietary software based on NIH. The software was purchased from
Analytical Vision Inc., 213 Merwin road, Raleigh, NC 27606, (919-85-8117).
This system and an expert operator (who has unfortunately retired)
produced excellent data but was slow as each frame was analyzed
separately, sometimes over a hundred frames for one core. Our system is
mostly described in Thetford, D'Arrigo, and Jacoby, "An image
analysis system for determining densitometric and ring-width time
series", Canadian Journal of Forest Research 21, 1544-1548,
1991. We have no other diagrams, schematics, or specifications drawn or
compiled.
Yves
Bégin provides a thorough description of the densitometry system used at
the Centre d'études nordiques of Laval University:
SAMPLING:
(1) An increment borer of at least 7 mm diameter is needed, but we use 1.2
mm when possible or more simply entire cross-sections.
(2) Cores are kept preferably in an alcohol bath for conservation.
SAMPLE PREPARATION:
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(1)
A double bladed saw (Dendrocut from Walesch Electronics) is used. Cores
placed on home-made wood supports are sticked perpendicular to normal
presentation for measuring ring widths. Advantage: very precise and
regular. All sample thicknesses are measured afterward (average
imprecision 0.02mm) with a range between 0.7 to 2.5 mm. Best: 1.5 - 2 mm
thick. The machine is also easy to handle and comes with a binocular
microscope allowing the measurement of the angle of the axial cells with
the core axis. The same measuring system is mounted on the saw. A vacuum
is needed to evacuate saw dust. Compare to other systems (Home-made most
of it) - the great advantage is precision. Not much is said in the
literature about precision. The use of microtome sections must be avoided
because of their imprecision and they are too thin to integrate wood
anatomical structures. One should mention to the readers that the range of
density variations is due to the imprecision of the cut. Disadvantage
(minor): the device is heavy (at least 100 kg), the potentiometers are
fragile, the saw needs to be frequently sharpened, and cleaned with
alcohol.
(2)
A Soxhlet extractor with alcohol (96%/vol) is used to extract the resin
and other substances from samples. Price: about 1000$US including a
heating plate and tubes. Available from any chemistry supplier. Picea,
Abies need generally 24 hrs, Larix and Pinus more. Samples are marked with
China ink, insoluble in alcohol and transparent to X-ray.
(3)
Samples are cut obliquely in small pieces and pressed in Bell Canada
telephone directories (not expensive!) to avoid bending. How about densest
populated countries? Internet directories not very useful!
(4)
The dried thin sections are placed in a home-made rack made of two layers
of good quality cellophane that contracts when heated with a hair dryer
(available in home hardware stores to insulate windows in winter). The
rack is made of two embeded wood rectangles, one applying pressure over
the other through a system of nuts. Ink numbers are placed face down for
xeroxing the montage. This sketch is very useful to position samples
afterward with the densitometer. Finally, the montage is kept at least
half an hour in the X-ray room to equilibrate with atmosphere. According
To Ernst Shär (Birmensdorf), the equilibrium is rapidly reached (10-15
min, 50% Humidity in the air and 20°C, 8-9 % humidity in the wood). Many
details available in: Schweingruber, F.H, Schär, E., et al., 1978. The
X-ray technique as applied to dendroclimatology. Tree-Ring Bulletin
38: 61-91.
X-RAYING:
(1) X-Ray room
We
benefited from an old X-ray room from Dr. Poliquin (retired from Laval
University) which i s coated with lead sheets, but a concrete-walled room
is sufficient to stop the rays for safety (e.g. Birmensdorf). The
atmosphere is controlled into the room. T° and Humidity are kept to 20°C
and 50% with an air exchanger with the exterior. A hygro-thermostat is
needed. T he room is lighted with a special red-light calibrated
especially for the film by Kodak (expensive: 500$ US). Finally, a
rectangular plate placed over a marber plate helps place the montage under
the source in the dark.
(2) X-Ray source
We
fixed an old Balteau device that is generally used in hospital.
Specifications: Baryllium window of 5mm with 20mv and 12ma. A source and a
sink for cold water is needed in the X-ray room. This type of device is
best because it is not expensive (available in any hospital stockroom for
cheap prices). Their advantage, compared to modern systems, is that the
source is far from the target (2.3 m at Laval, 2.5 m at Birmensdorf). With
shorter distances, the obliquity of the rays with longitudinal wood cell
walls produces a shadow on the film. Some labs correct this problem by
bending the extremity of their samples, but there is a risk of imprecision
by doing so.
(3) Duration of film exposure
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We
use Kodak RPM 12 X 12 inches double-side coated. Cheap in box of 50.
Irradiation duration: 45 min for 0.7 mm sections, 50 min for 1mm, 55 min
for 1.5 mm and 60 min for 2 mm. The films are carried out within opaque
boxes and processed in standard solution (for free) in X-O-Mat standard
processing machine in hospital (90 sec).
MEASUREMENT OF DENSITY:
Laval
University is one of the 5 labs having a dendro-2003 densitometer from
Walesch Electronics (see also one in Germany, China?, New York and
Marseille). One word: The best machine for precision measurements.
Disadvantage: expansive, extremely heavy, many mechanical parts are
fragile. The operator overseas needs to develop a good knowledge of the
machine with several years of use. However, Walesch gives remarkable
service after purchase. Software used to handle data needs to be improved,
especially with the recent developments in the definition of parameters
(e.g. where do we place the limit between earlywood and latewood?).
If
you're interested in the Dendrocut precision sawing device and the
Dendro-2003 densitometry system, the address for Walesch Electronics is:
Walesch Electronics
Gestenrietstrasse 2
CH-8307 Effretikon
Switzerland
Phone: +41 52 326266 or +41 52 322644 |
