UNIDATA recommends no adjustments are normally required.
Pan corrosion
changes the interior surface colour and texture. The difference
between a black painted and unpainted galvanised iron pan is approximately
10%.
UNIDATA pans are constructed of white fibreglass to minimise discolouring
or deterioration with poor water quality.
3.2.2
Operating Errors
Evaporation pans are normally manually operated and require daily reading
and resetting. This is difficult or impossible at remote sites and data quality is
compromised.
Water level too high
will result in rainfall splashing or blowing from the
tank when it is near full, and overflowing when it is full.
Water level below the reference mark
increases the shading from the sides
of the tank and reduces evaporation by up to 2.5%/10mm below the reference
level, in temperate regions.
Water level very low
records increased evaporation as the temperature of
water in the pan increases.
UNIDATA recommends these errors be avoided by automatically controlling
the water level.
Automatic Evaporation System
EVAPORATION MONITORING TECHNIQUES 13
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UNIDATA
14 EVAPORATION MONITORING TECHNIQUES