Campbell Scientific CS725 Snow Water Equivalency Sensor - Manual (Page 27)

CS725 Snow Water Equivalency Sensor
It is reasonable to have small amounts of wood material within the 6 m
clearance radius. Be aware that reducing the amount of material near the
CS725 or increasing the distance will reduce its influence on the readings.
8.1 Collimator
The need for a collimator is typically dictated by the characteristics of the
intended site. The presence of wooded vegetation, man-made structures and
the expected SWE for a given site are all a factor.
It is possible to use the sensor and obtain accurate measurements without using
the collimator option. The following table is a guideline for determining if a
site can be used without a collimator.
TABLE 8-1. Collimator Guidelines
Site Characteristics Maximum
SWE
<300 mm Maximum
SWE 300 to
400 mm Maximum
SWE
>400 mm
Very open site with no
proximity to trees, buildings or
tall vegetation within a 48 m
(160 ft) radius. Optional Optional Optional
No trees, buildings or tall
vegetation within a 24 m
(80 ft) radius. Optional Optional Required
No trees, buildings or tall
vegetation within a 12 m
(40 ft) radius. Optional Required Required
Site with minimum clearance
radius of 6 m (20 ft) radius. Required Required Required
Always confirm that your sensor has the Collimator Installed
parameter set properly. The SWE calculations are different for a
sensor with and without a collimator. NOTE
8.2 Soil Moisture Considerations
Moisture in the soil can influence the CS725 readings. It is important to avoid
low lying spots were water will pool or saturate the soil during the snow melt.
Sandy or rocky soil types will have more stable soil moisture levels throughout
the measurement season. Bog type ground conditions should be avoided due to
the potentially high moisture content and variations.
8.3 Obtaining Site Qualifying Counts
There is variability in the natural occurring radiation levels from site to site.
For this reason, it is recommended to qualify the site prior to setting up the
permanent installation for the CS725. You may find that your site has low
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