Delta Electronics SS1-UM-1.05 user manual Advice on Absorption and Eladp values, Setting Eladp

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Advice on Absorption and ELADP values

Absorption

Absorption is the percentage of incident PAR that is absorbed by the leaf.

Most leaves have Absorption values in the range 0.8 - 0.9, so the default value of 0.85 will usually be appropriate.

Only adjust the Absorption value if you have good reason to, for example if you are working with very thick, dark leaves, or very thin transparent ones.

If you set the Absorption value to 1.0, the LAI calculations will be equivalent to simpler models that assume completely black leaves.

ELADP

ELADP is the Ellipsoidal Leaf Angle Distribution Parameter.

The ELADP is a way of characterising the horizontal or vertical tendency of leaves in a canopy.

The canopy leaf elements are assumed to be distributed in space in the same directions and proportions as the surface area of an ellipsoid of revolution, symmetrical about the vertical axis. The Leaf Angle Distribution can then be described by a single parameter, the ratio of the Horizontal to Vertical axes of the Ellipsoid.

V

H

ELADP = HV

This is also equal to the ratio of the vertically projected area to the horizontally projected area of the ellipsoid (or of the canopy elements).

•An ELADP of 1.0 gives a spherical Leaf Angle Distribution, where all leaf angles are equally represented.

•A high ELADP (e.g. 1024) represents a broad flat ellipsoid, i.e. the leaf elements are all horizontal

•A low ELADP (0.0) represents a tall thin ellipsoid, i.e. all the leaf elements are vertical.

Most crops have ELADPs in the range 0.5 - 2.0.

Setting ELADP

The default setting of 1.0 (spherical leaf angle distribution) is a good starting point.

If you are unable to estimate the ELADP any other way, set ELADP to 1.0. You can check how much this affects your results in the field by making several measurements in one place within a canopy using different ELADP values, and comparing the LAI values calculated.

44 • Measurement options

Document code: SS1-UM-1.05

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Contents SunScan SS1-UM-1.05Copyright AcknowledgementsTrademarks CE conformityContents Menus and Screens More Psion and file handling notes Measurement optionsLAI theory Technical Reference sectionAppendices IndexHow to use the manuals IntroductionSunScan Canopy Analysis System Organisation of this manualField accessories SunScan probeBeam Fraction sensor Data Collection TerminalWorkabout and SunScan probe Getting StartedPreliminary checks Checking the Workabout hardware Installing the SunData s/w in your PC Installing the s/wSunData s/w Diskette 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 More Psion and file handling notes Navigating Psion directories and screensWorkabout User Guide 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 Default .cfg Creating a configuration fileRestoring a configuration Data files.CSV file Displaying data files on your PC.PRN file Data file layouts and data groups Page Above-canopy reference requirements Measurement options Experiment 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 Measurement procedures in the field Probe handling in the fieldProbe GO button Levelling the probeUsing the tripod BFS handling in the fieldUse of the tripod WorkaboutExtension cables, and the location of the BFS Finding North, and setting the shade ringLevelling the BFS PAR calibrations Factory light calibrationChecking the probe/BFS matching Recalibrate optionRoutine maintenance and cleaning Restoring the factory calibrationEffect of the shade ring on the BFS 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 Functions used to model canopy transmission Accuracy of LAI calculationsDiffuse light cosine response sensor 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 Maintenance and repair Technical Reference sectionChecking the batteries SunScan probe batteriesChecking the desiccant Factory calibration method Re-setting the factory calibrationChecking the PAR calibration Troubleshooting Problems running the SunData applicationPsion Workabout While running SunDataInsufficient power to write data reported Technical Support Specifications SunScan Probe Type SS1Beam Fraction Sensor type BF1 Data Collection Terminal type DCT1 Psion WorkaboutCarrying Case type SCC1 Telescopic Tripod type BFT1Spares Kit type SPS1 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 Upgrading the SunScan system SunData PC s/wWorkabout SunData s/w Revision HistoryFile transfer between Workabout and PC Choice of different programsPsiWin 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 SlinkUsing the Workabout Comms application Alternative file transfer mechanismsSending a file to a Communication program Sending a file to a serial printerGlossary Page Index AccuracyIndex Field use 39, 46, 48, 50, 51, 58