Delta Electronics SS1-UM-1.05 Finding North, and setting the shade ring, Levelling the BFS

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Finding North, and setting the shade ring

If you are taking measurements which require only the incident total radiation on the canopy, you can ignore the compass orientation of the BFS and you should set the shade ring horizontal so that it is not in use.

If, however, you want the Direct and Diffuse components of the incident radiation, you must elevate the shade ring so that its shadow falls across the Diffuse sensor (the one directly in line with the shade ring pivots), covering it completely.

If you are moving the BFS frequently, the compass orientation of the BFS need not be accurately set to north. If you want the shadow to track correctly for longer periods of time, set the BFS to point true north more carefully. The same instructions apply if you are using the BFS in the southern hemisphere.

The shadow may not track perfectly throughout the course of a whole day, owing to limitations imposed by the simple and robust design of the BFS. You should inspect the BFS from time to time and readjust the ring if necessary.

In overcast conditions, the exact elevation of the shade ring is not critical (and it is quite difficult to estimate!). If there is any chance of direct sun breaking through, you must wait for it to do so before setting the elevation.

Levelling the BFS

The BFS is equipped with a miniature bubble level. The tripod supplied has 3-axis adjustment to facilitate levelling.

It is more important to level the BFS accurately than the probe.

The usual routine for setting up the tripod will be:

•Orientate the BFS to face true north.

•Level the BFS.

•Elevate the shade ring to bring the shadow completely across the Diffuse sensor (the northernmost one).

Extension cables, and the location of the BFS

Extension cables of 10, 25 and 50 m can be fitted between the BFS and the probe, which will extend your range of operation from the BFS. There is a trade-off between range and convenience: the greater your range, the fewer times you need to re-site the BFS, but the more time you are likely to spend handling the cable.

Extension cables can be joined together. A combination of two shorter cables may be preferable to one long one.

You should bear in mind that the SunScan will read the BFS and probe simultaneously. If the different locations are widely spaced apart, the light levels could momentarily be different - cloud shadows can easily travel at 20 m.s-1.

The solution is to be aware of this possibility in fast changing conditions and avoid taking readings at critical moments.

Very long cable lengths may introduce a small systematic error in BFS readings. Up to 100 metres, this should not be significant (< 10 ∝ mol.m-2.s-1). At 200 metres it could add about 20 ∝ mol.m-2.s-1to the readings, which may need subsequent adjustment .

50 • Measurement options

Document code: SS1-UM-1.05

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Contents SunScan SS1-UM-1.05Trademarks CopyrightAcknowledgements CE conformityContents LAI theory Menus and Screens More Psion and file handling notesMeasurement options Technical Reference sectionAppendices IndexSunScan Canopy Analysis System How to use the manualsIntroduction Organisation of this manualBeam Fraction sensor Field accessoriesSunScan probe Data Collection TerminalWorkabout and SunScan probe Getting StartedPreliminary checks Checking the Workabout hardware SunData s/w Diskette Installing the SunData s/w in your PCInstalling the s/w What the s/w doesSetting up your PCs COM port Running SunDataWorkabout to PC Communication checksSunScan probe to PC Running SunData in Windows Working with the Workabout SunScan TutorialAbout this tutorial What to do if you get lost Starting SunData in the WorkaboutUsing a PC instead of the Workabout Starting the PC softwareThis page is intentionally blank Setting up a measurement session Working through the menu optionsFile Saving Hot KeysUsing the Emulator mode Taking readingsConnecting the SunScan probe Without a Beam Fraction SensorConnecting the Beam Fraction Sensor Measuring Leaf Area Index without a Beam Fraction Sensor Reviewing your data file AveragesTo the PC Transferring the data file to your PCFrom the Workabout Initiating the file transfer from the Workabout Meanwhile, on the PC RS232 communication problems Conclusion of the TutorialSunData Screens on the Workabout File SettingsMenus and Screens Contd UtilsQuit Workabout User Guide More Psion and file handling notesNavigating Psion directories and screens Navigating the Psion directories and screensPsion subdirectory usage in file select dialogs Flashcards reformatting Re-installing the SunData application iconDeleting unwanted Workabout files Data memory management Configuration and data file handlingSunData Configuration files Restoring a configuration Default .cfgCreating a configuration file Data files.CSV file Displaying data files on your PC.PRN file Data file layouts and data groups Page Above-canopy reference requirements Measurement optionsExperiment design Canopy type and LAI estimates Canopy Sampling volumeCanopy type and BFS practicalities Preferred light and weather conditions Planning for the sun’s positionAbsorption Advice on Absorption and Eladp valuesSetting Eladp Relationship between Mean Leaf Angle and Eladp Estimating Eladp in the fieldLAI, PAR and All displays Workabout setupSunScan System Measurement modes Autolog function Probe GO button Measurement procedures in the fieldProbe handling in the field Levelling the probeUse of the tripod Using the tripodBFS handling in the field WorkaboutExtension cables, and the location of the BFS Finding North, and setting the shade ringLevelling the BFS Checking the probe/BFS matching PAR calibrationsFactory light calibration Recalibrate optionEffect of the shade ring on the BFS Routine maintenance and cleaningRestoring the factory calibration Comparing the calibration with other PAR sensorsEnvironmental and moisture protection SunScan probe and Beam Fraction SensorLAI theory Ingredients of the LAI computation methodTheory versus reality Derivation of Wood’s SunScan canopy analysis equationsMajor assumptions Transmission of Diffuse Light Beers law for canopy absorptionCampbells Ellipsoidal LAD equations Transmission fraction τ Is given by I/I0 Modelling the canopy transmission Diffuse light transmission cosine corrected sensorDetail Diffuse light cosine response sensor Functions used to model canopy transmissionAccuracy of LAI calculations Diffuse light hemispherical response sensorModelling incomplete PAR absorption and scattering Exp 0.1 . x . atan 0.9 Atan L Q SpherSummary Scientific referencesCalculating zenith angles Jones, Hamlyn G Plants and Microclimate second edition. CUP Checking the batteries Maintenance and repairTechnical Reference section SunScan probe batteriesChecking the desiccant Factory calibration method Re-setting the factory calibrationChecking the PAR calibration Psion Workabout TroubleshootingProblems running the SunData application While running SunDataInsufficient power to write data reported Technical Support Beam Fraction Sensor type BF1 SpecificationsSunScan Probe Type SS1 Data Collection Terminal type DCT1 Psion WorkaboutSpares Kit type SPS1 Carrying Case type SCC1Telescopic Tripod type BFT1 Logging CablesPAR Performance Spectral responseCosine responses of probe and BFS SunScan system cosine responseAppendices Logging the probe as a Linear Quantum SensorLogging the Beam Fraction sensor Workabout SunData s/w Upgrading the SunScan systemSunData PC s/w Revision HistoryPsiWin File transfer between Workabout and PCChoice of different programs Workabout Remote LinkExample using Slink Slink and RcomDrives on the PC are referred to as REMA, Remc REM = remote Example using Rcom Documentation of Rcom and SlinkSending a file to a Communication program Using the Workabout Comms applicationAlternative file transfer mechanisms Sending a file to a serial printerGlossary Page Index AccuracyIndex Field use 39, 46, 48, 50, 51, 58
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