Apogee SP-510-SS Посібник користувача - Сторінка 15

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MAINTENANCE AND RECALIBRATION

Moisture or debris on the filters (diffuser for upward-looking pyranometer, glass window for downward-looking

pyranometer, silicon windows for pyrgeometers) is a common cause of errors. The upward-looking sensors have a

domed housing for improved self-cleaning from rainfall, but materials can accumulate on the diffuser or window

(e.g., dust during periods of low rainfall, salt deposits from evaporation of sea spray or sprinkler irrigation water)

and partially block the optical path. Materials can also accumulate on the downward-looking detectors. Dust or

organic deposits are best removed using water or window cleaner and a soft cloth or cotton swab. Salt deposits

should be dissolved with vinegar and removed with a soft cloth or cotton swab. Never use an abrasive material or

cleaner on the diffuser.

Although Apogee sensors are very stable, nominal accuracy drift is normal for all research-grade sensors. To

ensure maximum accuracy, we generally recommend sensors are sent in for recalibration every two years,

although you can often wait longer according to your particular tolerances.

Upward-Looking Pyranometer (Shortwave Radiation)

The Clear Sky Calculator (www.clearskycalculator.com) can be used to determine the need for pyranometer

recalibration. It determines total shortwave radiation incident on a horizontal surface at any time of day at any

location in the world. It is most accurate when used near solar noon in spring and summer months, where

accuracy over multiple clear and unpolluted days is estimated to be ± 4 % in all climates and locations around the

world. For best accuracy, the sky must be completely clear, as reflected radiation from clouds causes incoming

radiation to increase above the value predicted by the clear sky calculator. Measured values of total shortwave

radiation can exceed values predicted by the Clear Sky Calculator due to reflection from thin, high clouds and

edges of clouds, which enhances incoming shortwave radiation. The influence of high clouds typically shows up as

spikes above clear sky values, not a constant offset greater than clear sky values.

To determine recalibration need, input site conditions into the calculator and compare total shortwave radiation

measurements to calculated values for a clear sky. If sensor shortwave radiation measurements over multiple days

near solar noon are consistently different than calculated values (by more than 6 %), the sensor should be cleaned

and re-leveled. If measurements are still different after a second test, email

to discuss test results and possible return of sensor(s).