AccuPAR LP-80 v8

AccuPARPAR/LAI ceptometer

model LP-80

Operator’s ManualVersion 8

Decagon Devices, Inc.

Decagon Devices, Inc.2365 NE Hopkins Court

Pullman, WA 99163tel: (509) 332-2756fax: (509) 332-5158www.decagon.com

TrademarksAccuPAR and Ceptometer are

registered trademarks of Decagon Devices, Inc. © 2006-2009

AccuPAR LP-80Table of Contents

i

Table of Contents1. Introduction . . . . . . . . . . . . . . . .1

Customer Service and Tech Support . . . . . . . . 1Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . . . . . 2Repair Instructions . . . . . . . . . . . . . . . . . . . . . . . 3

2. About the LP-80 . . . . . . . . . . . . 5Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Overview of the LP-80 . . . . . . . . . . . . . . . . . . . 6Components of the LP-80 system . . . . . . . . . . . 7Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Keyboard Operation . . . . . . . . . . . . . . . . . . . . . 8Turning on the instrument . . . . . . . . . . . . . . . . . 9

3. Definitions . . . . . . . . . . . . . . . . 11PAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Tau (t) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12LAI (L) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12External Sensor . . . . . . . . . . . . . . . . . . . . . . . . . 12Zenith Angle (z) . . . . . . . . . . . . . . . . . . . . . . . . . 13Fraction of Beam Radiation (Fb) . . . . . . . . . . . 13Leaf Distribution Parameter (x) . . . . . . . . . . . . 14

4. PAR/LAI Menu . . . . . . . . . . . . .16Taking Measurements . . . . . . . . . . . . . . . . . . . 16


ii

5. Log Menu . . . . . . . . . . . . . . . . .19

6. File Menu . . . . . . . . . . . . . . . . .21View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Send . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 New . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29Delete All . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30

7. Setup Menu . . . . . . . . . . . . . . .31Set Baud Rate . . . . . . . . . . . . . . . . . . . . . . . . . .34Calibrate Probe . . . . . . . . . . . . . . . . . . . . . . . . .35External Sensor Const. . . . . . . . . . . . . . . . . . . .36Power Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . .37About . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38

8. PAR and LAI Theory . . . . . . . . 39PAR (photosynthetically active radiation) . .39Average and Intercepted PAR . . . . . . . . . . . .39Using PAR to determine Leaf Area Index . . .45Extinction Coefficient & Canopy Structure .49LAI measurements & Non-Random Distribution 57Zenith Angle and Equation of Time . . . . . . . . 61

9. Measurement Tips . . . . . . . . 66Above Canopy (External) Sensor . . . . . . . . . 66Sample Size . . . . . . . . . . . . . . . . . . . . . . . . . . . .67Clumping in Canopies . . . . . . . . . . . . . . . . . . . .67LAI Sampling in Row Crops . . . . . . . . . . . . . . . 68

10. Care and Maintenance . . . . . 70Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70


iii

Cleaning the Probe and Controller . . . . . . . .70Re-calibration . . . . . . . . . . . . . . . . . . . . . . . . . . 71General Precautions . . . . . . . . . . . . . . . . . . . . . 71

Declaration of Conformity . . . . 73

Appendix A: External Sensor Info . 74Specifications . . . . . . . . . . . . . . . . . . . . . . . . . .74Spectral Response . . . . . . . . . . . . . . . . . . . . . .74Cosine Response . . . . . . . . . . . . . . . . . . . . . . . .75Temperature Response . . . . . . . . . . . . . . . . . .75Long-term stability . . . . . . . . . . . . . . . . . . . . . .76

Appendix B: Further Readings . 77

Index . . . . . . . . . . . . . . . . . . . . . 85

AccuPAR LP-80Introduction

1

1. Introduction

Welcome to Decagon’s AccuPAR model LP-80 PAR/LAICeptometer. The AccuPAR measures PhotosyntheticallyActive Radiation (PAR) in the 400-700nm waveband, andcan invert these readings to give you Leaf Area Index foryour plant canopy. This manual is designed to help youaccomplish your research goals, and understand how toget the most out of your AccuPAR.

Customer Service and Tech SupportWhen contacting us via fax or email, include the followinginformation: Your AccuPAR’s serial number, your name,address, phone and fax number, and a description of yourproblem

Phone:Call Monday - Friday, between 8 a.m. and 5 p.m. PST. US and Canada (toll-free): 1-800-755-2751Outside of the US and Canada: (509) 332-2756

Fax:(509) 332-5158

E-mail:[email protected].


2

WarrantyThe AccuPAR has a one year warranty on parts and labor.It is activated upon the arrival of the instrument at yourlocation.

Seller’s LiabilitySeller warrants new equipment of its own manufactureagainst defective workmanship and materials for a periodof one year from date of receipt of equipment (the resultsof ordinary wear and tear, neglect, misuse, accident andexcessive deterioration due to corrosion from any causeare not considered to be a defect); but Seller’s liability fordefective parts shall in no event exceed the furnishing ofreplacement parts f.o.b. the factory where originallymanufactured. Material and equipment covered herebywhich is not manufactured by the Seller shall be coveredonly by the warranty of its manufacturer. Seller shall notbe liable to Buyer for loss, damage, or injuries to persons(including death), or to property or things of whatsoeverkind (including, but not without limitation, loss ofanticipated profits), occasioned by or arising out of theinstallation, operation, use, misuse, nonuse, repair, orreplacement of said material and equipment, or out of theuse of any method or process for which the same may beemployed. The use of this equipment constitutes Buyer’sacceptance of the terms set forth in this warranty. Thereare no understandings, representations, or warranties ofany kind, express, implied, statutory or otherwise,(including, but without limitation, the implied warranties


3

of merchantability and fitness for a particular purpose),not expressly set forth herein.

Repair InstructionsIf your AccuPAR needs to be sent in for service or repair,call Decagon at (509) 332-2756 or 1-800-755-2751 (USand Canada). We will ask you for your address, phonenumber, and serial number. For non-warranty repairs, wewill also ask for a purchase order number, a repair budget,and billing address.

When shipping your instrument back to us, include adocument listing the complete shipping address, name anddepartment of the person responsible for the instrument,and (most importantly) a description of the problem. Thiswill better help our technicians and our shippingdepartment to quickly expedite repair on your instrumentand ship it back to you.

Pack your AccuPAR carefully. Ship it back in the blackcarrying case, preferably inside a cardboard box. Ship to:

Decagon Devices Inc.2365 NE Hopkins CourtPullman, WA 99163

Repair Costs:Manufacturer’s defects and instruments under warrantywill be repaired at no cost. For non-warranty repairs, costs


4

for parts, labor, and shipping will be billed to you. We havea $75 minimum charge for repair that takes one hour orless. For repair over one hour the labor rate is $75/hour.

AccuPAR LP-80About the LP-80

5

2. About the LP-80

The AccuPAR model LP-80 is a menu-driven, battery-operated linear PAR ceptometer, used to measure lightinterception in plant canopies, and to calculate Leaf AreaIndex (LAI). It consists of an integrated microprocessor-driven datalogger and probe. The probe contains 80independent sensors, spaced 1cm apart. The photosensorsmeasure PAR (Photosynthetically Active Radiation) in the400-700nm waveband. The AccuPAR displays PAR inunits of micromols per meter squared per second (µmolm-2s-1). The instrument is capable of hand-held orunattended measurement.

SpecificationsOperating Environment: • 0° to 50° C (32°-122° F)• 100% relative humidityProbe Length: 86.5 cmNumber of sensors: 80Overall Length: 102 cm (40.25 in)Probe Cross-Section: 19cm x 9.5cm (.75 x .375 in)Micro controller dimensions: 15.8 x 9.5 x 3.3cm (6.2 x

3.75 x 1.3 in.)PAR Range: 0 to >2,500µmol m-2s-1

Resolution: 1µmol m-2s-1


6

Minimum Spatial resolution: 1cmData Storage Capacity: 1MB RAM.Unattended logging interval: User selectable, between 1

and 60 minutes.Instrument weight: 1.21kg (2.7 pounds)Data retrieval: direct via RS-232Keypad: 7-Key menu-driven.Clock: 24-hour ±1 minute per month.Interface Cable: RS-232 cablePower: Four AAA Alkaline cells.External PAR sensor connector: Locking 5-pin sealed

circular connector.

Overview of the LP-80The LP-80’s menu-driven interface is designed for ease ofuse. There are four menus to choose from: PAR/LAIsampling menu, unattended logging menu, file menu, andthe setup menu. You navigate between the menus bypressing the MENU button, and select items within eachmenu using the up and down arrow keys, and the ENTERor ESC keys. An internal bubble level is mounted in theupper right corner of the case to allow you to keep theprobe relatively level when making measurements.

The AccuPAR can be operated in environments withtemperatures from 0 to 50 °C, and in relative humidities ofup to 100%. The instrument is shipped with an RS-232interface cable to allow for downloading data to acomputer, and an external PAR sensor to allow for


7

simultaneous above and below canopy PARmeasurements. The AccuPAR operates on four AAAalkaline batteries.

Components of the LP-80 systemThe AccuPAR and its accessories come to you in a durablefoam-padded carrying case. As you open the case, youshould find the following:• AccuPAR model LP-80 • RS-232 Cable• Operator’s manual• External PAR sensor• #1 Phillips screwdriver

Features

ProbeBubble LevelDisplay

RS-232/Ext. sensor port

ExternalSensorLug


8

Keyboard Operation

Figure 1: LP-80 Keypad

The LP-80’s keypad is a 7-key panel, designed for ease ofuse and intuitive navigability through the operatingsystem. Here is a brief description of the key functions:


9

ON/OFF Key: Located in the upper left corner, it turnsthe instrument on or off. The AccuPAR will turn itself offautomatically after 10 minutes of inactivity.

MENU Key: Cycles between the four menus.

UP and DOWN ARROW KEYS: In PAR samplingmenu, they initiate above (up arrow) and below (downarrow) canopy PAR readings. In other menus, they areused to navigate to items within those menus and tochange numeric values in sub menus.

Round Green Key: The circular key in the upper rightcorner of the keypad (by the AccuPAR logo) also servesthe same function as the Down-arrow key. It is designedas an ergonomic alternative when taking multiple below-canopy PAR samples

ESC: Discards the current PAR reading displayed in thelower half of the PAR sampling menu, backs out of FILEmenu options and stores changes in SETUP menuoptions.

ENTER: Saves the current PAR readings in the PARsampling menu, and selects items in other menus.

Turning on the instrumentWhen you first turn on the instrument, it will be in thePAR sampling menu, in which you will see real-time PAR


10

data displayed in the center portion of the screen. If youhave the external PAR sensor connected, you will also seeits real-time PAR data displayed, and indicated by anabove-canopy icon.

At any time, you can cycle between the four menus bypressing the MENU key. The menus are indicated by thetabs on the top of the screen, with the active menuhighlighted in black. To the right of the menu tabs is thecurrent battery status and the time. Later chapters discusseach menu in detail and how to use the features that eachprovides..

current timebattery statusmenu tabs

AccuPAR LP-80Definitions

11

3. DefinitionsThe AccuPAR uses several variables to calculate Leaf AreaIndex, and displays values for these variables on the screenas measurements are taken. This chapter will discuss thesevariables and their definitions. If you’re not familiar withthem, we recommend that you review this chapter beforeproceeding with measurements.

PARPAR (photosynthetically active radiation) is defined as theradiation in the 400 to 700 nanometer waveband. Itrepresents the portion of the spectrum which plants usefor photosynthesis. Under a plant canopy, radiation levelscan vary from full sun to almost zero over the space of afew centimeters. Therefore, reliable measurement of PARrequires many samples at different locations under thecanopy. The AccuPAR measures PAR either manually orin unattended logging mode. Intercepted PAR data can beused for determining important parameters of canopystructure and for the calculation of LAI. An external pointsensor may be used to collect instantaneous above canopyPAR measurements when sampling under or within acanopy. You also have the option of segmenting the probeto reflect spatial changes in the plant canopy. This is usefulwhen evaluating discontinuous and irregular canopies, orto limit the size of active sensors along the probe.


12

Tau (τ)Tau is another variable in the LAI inversion equations. It isdefined as the ratio of below canopy PAR measurementsto the above canopy PAR value. It is measuredautomatically by the instrument, based upon the PARreadings you make. The current Tau value is displayed andupdated in the lower left corner of the screen in the PARmenu. Further explanation of the significance of Tau isgiven in Chapter 9.

LAI (L)LAI (Leaf Area Index) is defined as the area of leaves perunit area of soil surface. It is a very valuable measurementin helping to assess canopy density and biomass. TheAccuPAR calculates LAI based on the above and below-canopy PAR measurements along with other variables thatrelate to the canopy architecture and position of the sun.These variables are the zenith angle, a fractional beammeasurement value, and a leaf area distribution parameter(also known as x) for your particular canopy. TheAccuPAR automatically calculates both the zenith angleand fractional beam reading, and requires you to input avalue for x in the setup menu.

External SensorAn external PAR sensor is provided with the AccuPAR toallow you to make simultaneous above and below canopyPAR measurements. This is useful if you want to be able


13

to make multiple PAR measurements under the canopy invariable light conditions without having to keep movingthe instrument in and out of the canopy to update theabove canopy PAR reference.

Zenith Angle (z)Zenith angle can be defined as the angle the sun makeswith respect to the zenith, or the point in the sky directlyoverhead, vertical to where you stand. The zenith isdefined as being 0° and the horizon is 90°. The zenithangle of the sun is necessary for calculation of certaincanopy structure parameters, such as LAI. It is calculatedby the AccuPAR based on your global position and thetime of day, and is displayed in the lower right corner ofthe screen when taking above and below PARmeasurements. To make sure this value is accurate, youmust first correctly set the longitude, latitude, date, andtime of day in the setup menu.

Fraction of Beam Radiation (Fb)Fractional beam radiation is the ratio of direct beamradiation coming directly from the sun to radiationcoming from all ambient sources like the atmosphere orreflected from other surfaces. A fractional beam radiationvalue is necessary for calculation of LAI using PAR data.The AccuPAR obtains this value by comparing the abovecanopy PAR measurement to the calculated value ofincoming solar radiation at your location and zenith angle.


14

The current calculated Fb is displayed and updated at thebottom of the screen in the PAR menu.

Leaf Distribution Parameter (x)Leaf Distribution Parameter (also known as Chi, or x)refers to the distribution of leaf angles within a canopy.The parameter x is the ratio of the length of the horizontalto the vertical axis of the spheroid described by the leafangle distribution of a canopy. It can also be measured asthe ratio of the projected area of an average canopyelement (a leaf, for example) on a horizontal plane to itsprojection on a vertical plane. The default value for x is1.0, which assumes the canopy angle distribution to bespherical. Onions are good example of a strongly verticalcrop. For onions, x would be about 0.7. On the otherextreme, strawberries, a crop with a strongly horizontalnature, would have a x value of about 3.

Table one gives some typical values for x. In some cases arange of values is given, indicating the variability that is tobe expected for x in any canopy. Fortunately, the value ofLAI computed is not strongly dependent on the value of xchosen. The AccuPAR uses a value of x=1.0 as its default.


15

Table 1: typical x values

Crop X

Ryegrass 0.67 to 2.47

Maize 0.76 to 2.52

Rye 0.80 to 1.27

Wheat 0.96

Barley 1.20

Timothy 1.13

Sorghum 1.43

Lucerne 1.54

Hybrid Swede 1.29 to 1.81

Sugar Beet 1.46 to 1.88

Rape 1.92 to 2.13

Cucumber 2.17

Tobacco 1.29 to 2.22

Potato 1.70 to 2.47

Horse Bean 1.81 to 2.17

Sunflower 1.81 to 2.31

White Clover 2.47 to 3.26

Strawberry 3.03

Jerusalem Artichoke 2.16

AccuPAR LP-80PAR/LAI Menu

16

4. PAR/LAI MenuThe first menu option is the PAR/LAI sampling menu,which is used for all measurements with the AccuPAR.The default screen is one similar to this:

This screen example indicates that the current real-timePAR level is 10 µmols/m2s (this example was takenindoors), and that no above or below PAR measurementshave been taken. If the external sensor is attached, thereal-time PAR value measured by the external sensor willbe also displayed above the real-time probe PAR data.

Taking MeasurementsTo make an above-canopy PAR measurement, press theup-arrow key in this menu. The resulting value will bedisplayed in the upper right section of the screen. To makemeasurements below the canopy, press the down-arrowkey or the green circular key in the upper right corner ofthe keypad. When at least one of both an above and belowcanopy measurement have been taken, other relevant datais displayed at the bottom of the screen, as shown in this


17

example:

The current calculated Tau (T), LAI value (L) beamfraction (Fb), leaf distribution parameter (x) and zenithangle (z) values are updated and displayed at the bottom ofthe screen with each subsequent PAR measurement. If theexternal sensor is attached, both above and below valueswill be summed each time the down arrow is pressed.Pressing ENTER saves these values to memory. PressingESC discards the values. Both options clear the screen fornew data. The values displayed at the bottom of the screenare dependent on how you have set up your instrument inthe Setup menu. For a more detailed description of thesevariables and their definitions, please refer to chapter 3(Definitions) or chapter 8 (Theory).

With each above or below canopy measurement, a numberappears to the right of the PAR value, indicating thenumber of measurements taken. The displayed PAR valuereflects the average of the samples taken. Therefore, in theabove sample screen, eight above and below canopymeasurements have been made, so the average of the eight

Number ofreadingstaken

Averagecanopyreading

belowcanopyreading

above

Average


18

above-canopy PAR values is 1037 µmols, while theaverage of the eight below-canopy value is 330 µmols.

Note: When the external sensor is connected, only readings from theexternal sensor are used to calculate LAI: though “ABV” data isgenerated whenever the up key is pressed, if the external sensor wasconnected at the time, the numbers displayed in the 8 segmentcolumns of downloaded data have no bearing on the current LAIcalculation.

AccuPAR LP-80Log Menu

19

5. Log MenuWhen you advance to the LOG menu, the followingscreen appears:

This menu allows you to put the instrument in anunattended par datalogging mode. In this mode, theAccuPAR will automatically measure and store PAR dataat an interval that you specify.

Note: LAI and Tau are not computed in this mode becausemanually sampling PAR beneath a canopy at random locationsproduces a more accurate LAI value than leaving the LP-80 in oneplace and collecting data in PAR mode. You can select the measurement interval by pressing theup or down arrows. This will allow you to select any valuebetween 1 and 60 minutes. In the above example, it is setto make and store a measurement every 15 minutes. Toactivate or deactivate the logging mode, press the Enterbutton. When the logging mode is enabled the screen will

AccuPAR LP-80Log Menu

20

change to the following:

The data that is taken in this mode will be stored in thecurrent file that is open at the time of activation.

Note: you can move from this menu to other menus while the loggingmode is activated, but the instrument will not log measurementsunless it is in the Log menu. Also, when the Log mode is activated, itcontinues to be active whether or not the AccuPAR’s display is on.

AccuPAR LP-80File Menu

21

6. File Menu

The File menu allows you configure and interact with datathat you store with your AccuPAR. When you advance tothis menu, the following screen appears: From this menu

you can view files and their relevant data, send the data toyour computer terminal for download and analysis, createa new file, or delete all files. To select one of the options inthis menu, scroll to the desired item and press theENTER key.

ViewWhen you select “View” from the File menu, you will seea screen such as this one:


22

The list on the left shows the status of the current files:Closed, Open, or Empty. The file labeled as “Open” is thefile you are currently storing data to. “Closed” files areones that contain previously-stored data. “Empty” simplyshows that there is room for other files to be created. Thetime and date that each file was created is displayed next toits status. In the above example, the file listed as “Open”was created Jan. 7, 2002 at the beginning of the day. Eachday at 00:00, the AccuPAR will create a new file. It willthen use that file as the default file for data taken that day.If you want to create a separate file, you can do so fromthe NEW option of the File menu.

You can scroll between different files using the up anddown arrows. To view the data from a selected file, pressthe ENTER key while it is highlighted. The stored datawill be displayed. Use the up and down arrows to scrollthrough the stored data. The values are shown in columnswith their corresponding labels as shown.

SendThe Send option allows you to download stored data to


23

your computer via the RS-232 cable that came with yoursystem. You can download the data using AccuLink (freesoftware included with your shipment), WindowsHyperterminal or any similar terminal software.

There are three options for downloading data:“Download Summary”, “Download Raw”, or“Download All”. These options are chosen in the Setupmenu under “Download Options.” “DownloadSummary” displays the average above and below canopyPAR data for each measurement, with the correspondingvalues for Tau, LAI, Fb, etc. “Download Raw” displaysthe PAR values for each measurement that went into theaveraged value. It also breaks down each measurement byprobe segment. “Download All” displays all the raw datafollowed by the summary data.

Downloading using AccuLink 2.0AccuLink is a program designed specifically fordownloading data from the AccuPAR. To installAccuLink, double-click on the “AccuLink2_0.exe” icon onthe CD that came with your LP-80. The program willbegin to install in the “Program Files” folder of your harddrive.

1. Once the software is installed, click on the Accu-Link.exe to start the program. The following screen will appear:


24

2. Connect the RS232 from a serial port on your com-puter to the AccuPAR’s external port.

3. Select the correct COM port from the drop-down menu and select the highest baud rate your computer can use.

4. Be sure to configure the LP80’s baud rate to match this baud rate value. See “Set Baud Rate” section for further information.

5. Click on the “Connect” icon to connect to the Accu-PAR. All files in the AccuPAR will be displayed on the screen.

6. To view the content of an individual file, click on a file and then click on the “View” icon. The data for that file will be displayed on screen according to how you have set the download options (e.g. Download Sum-mary, Download Raw, etc.) in the Setup menu.


25

7. To save the data to a specific folder or location, click on the “Save” icon and specify a target location for the data. You can also specify the file type in the “Prefer-ences” sub-menu of this option.

Downloading using Windows HyperterminalHere are the steps involved for downloading usingWindows Hyperterminal, which comes with all Windowsoperating systems since Windows 95:

1. Open Windows Hyperterminal: From the Start menu, select Programs > Accessories > Communications > Hyperterminal. Click on the Hypertrm.exe icon.

2. At the dialog box prompt, select a name for the new connection, and an icon (if desired).

3. At the “Connect To” dialog box, select an available COM port at the bottom of the screen in the “Con-nect Using” box.

4. In the Communication Properties Dialog box, select the settings as shown below: 19200 Bits per second (or whatever the baud rate is set for in the AccuPAR’s Setup menu), 8 Data bits, no Parity, 1 Stop bit, and no


26

Flow Control.

5. Once the terminal window opens, click on the File menu and select “Properties.” Click on the “Settings” tab, and then click on the “ASCII Setup” button. Check the box that says “Append line feeds to incom-ing line ends” and then click OK.

6. To set up the terminal program to capture the data, click on the Transfer menu and select “Capture Text.” Select the directory where you want to place the data text file and then click “Start.”

7. Select “Send” from the AccuPAR’s File menu. The list of current files will appear as in the “View” menu. Use the up and down arrows to select the file you wish to download, then press the ENTER key to send the data to your computer. The data will appear on the screen.


27

8. To finish capturing the text, click on the “Transfer” menu again and select “Capture Text > Stop.” Before closing Hyperterminal, save the session with a name you will be able to recognize. The next time you need to download, you will just need to open the Hyperter-minal folder and select the name you saved.

9. You may now open the text file in a word processing program or a spreadsheet program like Microsoft Excel.

The following is an example of the data format displayedin the “Download Summary” mode. The number at thetop is the time and date the file was created. The followinglines display the data stored in the file.

The columns are in the following order: download mode(in this case, SUM for summary), minutes into the currentday, average above canopy PAR value, average belowcanopy PAR value, Tau, LAI, Chi, Fb, and zenith angle.

The next example shows what is displayed in the“Download Raw” mode. When you download the rawdata, the data for each measurement that went into theaverage will be displayed. In other words, the data for each“button push” will be displayed rather than their average.

Jun-05-03 13:14SUM,799,2102.39, 412.70, 0.19, 3.09, 1.00, 0.90, 25SUM,799,2102.60, 411.70, 0.19, 3.00, 1.00, 0.90, 25SUM,799,2097.80, 334.39, 0.15, 3.36, 1.00, 0.90, 25


28

This fact can be seen by comparing the raw data below tothe summary for the same data shown above.

Again, the number at the top of the displayed data is thetime and date the file was created. The following linesdisplay the raw data stored in the file for each PARmeasurement, shown in the following order: minutes intothe day, PAR value for segment 1, segment 2, etc. throughsegment 8 and finally the external PAR sensor value (iftaken with the external sensor attached):

Note: Segment 1 is the segment of Sensors closest to the controller,and segment 8 is the segment closest to the tip of the instrument.


29

*Column 1: Above or below canopy designation andminutes into day. Ex. 799 minutes would be 1:14pm when12:01am is 1 minute.

NewTo create a new file to store your data, press the Newoption from the File menu. A dialog box will appearasking if you want to create a new file. Press the ENTERkey to create the file, or press ESC to escape. By default,the AccuPAR will create a new file at midnight (0:00) eachday. Therefore, the data you store on that day will beallocated to that file, unless you specify otherwise.

Jun-05-03 13:14 - Date and time of file creation

Col. 1* Seg. 1 Seg. 2 Seg. 3 Seg. 4 Seg. 5 Seg. 6 Seg. 7 Seg. 8 Ext. Sen.BLW,799, 727.20, 723.29, 733.20, 748.29, 733.59, 751.40, 776.20, 782.20,2092.50BLW,799, 540.09, 535.00, 545.70, 558.70, 542.40, 561.59, 588.90, 592.00,2102.10BLW,799, 492.60, 486.39, 496.29, 508.29, 491.10, 509.20, 535.40, 536.90,2106.39BLW,799, 492.60, 486.39, 496.29, 508.29, 491.10, 509.20, 535.40, 536.90,2106.39BLW,799, 268.70, 266.89, 281.20, 290.60, 289.29, 298.70, 315.39, 315.50,2106.39BLW,799, 268.70, 266.89, 281.20, 290.60, 289.29, 298.70, 315.39, 315.50,2106.39BLW,799, 249.00, 248.69, 264.20, 272.70, 275.29, 281.60, 290.89, 290.20,2101.80BLW,799, 249.69, 248.10, 262.29, 271.10, 274.10, 281.29, 291.20, 291.00,2100.19BLW,799, 249.69, 248.10, 262.29, 271.10, 274.10, 281.29, 291.20, 291.00,2100.19BLW,799, 294.39, 291.50, 303.29, 312.70, 306.50, 319.70, 341.10, 343.20,2105.80BLW,799, 513.29, 512.59, 527.29, 543.50, 531.00, 554.70, 585.90, 590.79,2102.39BLW,799, 394.60, 394.29, 409.50, 423.10, 410.79, 429.60, 457.20, 458.50,2100.69BLW,799, 332.89, 334.10, 351.70, 366.10, 357.39, 375.50, 403.50, 405.60,2101.80BLW,799, 404.39, 403.70, 418.89, 432.60, 419.89, 439.79, 469.60, 472.29,2101.39BLW,799, 283.10, 283.00, 298.79, 309.29, 305.00, 318.00, 339.50, 342.00,2097.00BLW,799, 283.10, 283.00, 298.79, 309.29, 305.00, 318.00, 339.50, 342.00,2097.00BLW,799, 283.10, 283.00, 298.79, 309.29, 305.00, 318.00, 339.50, 342.00,2097.00BLW,799, 283.10, 283.00, 298.79, 309.29, 305.00, 318.00, 339.50, 342.00,2097.00


30

Delete AllTo delete all stored files, select “Delete All” from the Filemenu. A dialog box will appear asking if you want todelete all files. To proceed, press the ENTER button. Toescape, press the ESC button. If you proceed, you will seethe words “Please Wait..” while the instrument deletes thefiles. This may take a minute or so to complete. Once allthe files have been deleted, a new file will be automaticallycreated.

AccuPAR LP-80Setup Menu

31

7. Setup Menu

The setup menu is where you configure and set most ofthe parameters that affect the functionality of yourAccuPAR. When you scroll to this menu, the followingscreen appears:

Use the up and down arrows to scroll among the menuitems.

Set Time/Date:Set your current time and date in this menu. Theinstrument uses the time and date provided here tocalculate its zenith angle and Fb values, so make sure it isaccurate. Use the up and down arrow keys to change thevalues of each item, and use the ENTER key to move to

Scrolling further down:


32

the next item. At the “Daylight Savings” box, press the uparrow to check the box, or the down arrow to un-check it.Once you have set the time and date correctly, press theESC key to exit the menu and store the result in memory.

Set LocationYou will need to set the correct longitude and latitude foryour location in order for your LAI calculations to becorrect. This is due to the fact that zenith angle calculationis based not only on the time and date, but the longitudeand latitude of the site. When you select this menu item,you will see a large scrolling menu with various countriesand cities listed:

Scroll to your country using the up and down arrows, andselect a city closest to your location and in your time zoneby pressing the ENTER button. The longitude, latitude,and time offset settings will be displayed. Press theENTER key to advance to the individual settings, and usethe up and down arrows to change the values tocorrespond to your exact location. Once the values are setcorrectly, press the ESC button.

Set xThis menu is used to set the x (leaf distribution) parameter


33

for the plant canopy you plan to measure. See the nextchapter for further explanation of the x parameter. Tochange the value of the x parameter, use the up and downarrow keys. When the value is correct, press the ESCbutton.

Set Active SegmentsFor some measurement purposes, you may not want touse the entire length of the probe. For such applications,you can turn off sections of the probe, starting from thebase and continuing down the probe to the end. Whenyou select this menu, the following screen will appear:

This screen shows that all 8 segments are on, which is thedefault setting. To reduce this amount, press the up-arrowkey until you reach the desired number of active segments.The icon on the right side of the screen will illustrate theactive segments as you reduce or increase them. Once youhave selected your desired number of segments, press theESC button. If you have selected active segments smallerthan 8, the segment icon will also appear in the PAR/LAIsampling menu to remind you that it is in segmentedmode.


34

Note: If LP-80 segments are deactivated, those segments will stillshow numbers when they dump their data. These deactivated segmentnumbers will not be used in LAI calculation.

Set Download OptionsAs mentioned in the “File Menu” section of this chapter,you can select the data to be downloaded to a computer.When you select this menu, you have 3 options:Download Summary, Download All, Download Raw, and.Here is a brief description of the three options:

• Download Summary: Downloads the average above and below canopy PAR values for each stored item, along with the associated Tau, LAI, x, etc. for the read

• Download All: Downloads both the summary data and the Raw data for each stored reading.

• Download Raw: Downloads the individual PAR data for each reading that went into the averaged value. For each reading, it also displays the individual readings that each of the 8 probe measurement segments mea-sured.

For a more detailed description and illustration of theseoptions, refer to chapter 7 (File Menu).

Set Baud RateThis menu is also used to set up the Send menu. This


35

allows you to select the transfer rate of your AccuPARwhen it downloads data. The baud rate that you set heremust match the baud rate of your computer’s terminalprogram. Upon entering this screen you will see thefollowing:

To change the value, press the up or down arrow key.When you get the desired value, press the ESC button andthat value will be stored for future downloads.

Calibrate ProbeThe AccuPAR is equipped with a calibrated external PARsensor. As mentioned earlier, this is used for makingsimultaneous above and below canopy PARmeasurements. It is also used to calibrate your AccuPAR’sprobe, ensuring that the PAR response between theexternal sensor and the probe are the same. When youselect this option, the following screen appears:


36

For best results, attach the external PAR sensor to the LP-80 by inserting the bolt attached to the external sensorthrough the hole in the bubble level. This will ensure thatthe sensor and probe are both level. The directions stateto level the probe and sensor, however you can alsocalibrate the AccuPAR on a flat board or platform thatyou can prop up at an angle to get more direct light fromthe sun.

Direction #3 means that the PAR level must be above600µmols m-1 s-1. Values below this will not update thecalibration, so check the PAR levels before proceedingwith the calibration. In general, a clear day where the sunis visible will be above 600µmols. Overcast days aretypically less than 600µmols.

When you have it ready to calibrate, move out of theprobe area to minimize reflection off your body, and pressthe ENTER button to perform the calibration (it isimportant not to affect light levels on the probe throughshading or reflection). The probe response will bedisplayed graphically. If you have no external sensorattached while performing the calibration, the calibrationgraph will not appear and the display will return to setup.

External Sensor Const.This menu option stands for “External Sensor Constant.”This menu is for adjusting the calibration constant of theexternal sensor. Therefore, you should only adjust this


37

value either when using a new external sensor, or after theexternal sensor has been re-calibrated. To check to makesure this value is correct, check the tag attached to theexternal sensor’s cable. The value shown shouldcorrespond with the value shown in this menu. If youneed to adjust the value, press the up or down arrow keysto the correct value, then press the ESC key.

As with most electronic components, the sensitivity of theexternal sensors drift over time and therefore periodicallyneed re-calibration. Therefore we recommend that youhave your external sensor re-calibrated. If you use itheavily each year, we suggest this be done on a yearlybasis. If you only make periodic measurements, one re-calibration every 2 to 3 years should be adequate. ContactDecagon for more details about re-calibrating the externalsensor.

We recommend you calibrate, or match, the LP-80 to theexternal sensor at least once an hour to maintain a stablecalibration between the two sensors.

Power FilterArtificial lighting uses AC electrical power in your officeor home and can add a significant amount of noise to theAccuPAP LP80’s sensor measurments. The power filtersetting is designed to elminate this electrical noise thatcomes from the AC powered light source. You should setthe value of the Power Noise Filter to match the frequency


38

of the power cycle where you live. In North America andmost of Asia, this is 60 Hz (the default vaule). In most ofEurope the electrical frequency is 50 Hz.

AboutThe About menu shows you data about the operatingsystem of the AccuPAR, and more importantly, the statusof the operating code, i.e. if the program has beencorrupted or if it is good. Here is an example of the Aboutscreen:

The top portion describes the name of the instrument,copyright info, and version number. At the very bottom,the code status is displayed (“Good”). This indicates thatthe code has not been corrupted. Next to the code status,the instrument temperature is displayed. This is useful introubleshooting the performance of the AccuPAR in hotweather, since the instrument incorporates a temperature-compensation device for the LCD screen.

AccuPAR LP-80PAR and LAI Theory

39

8. PAR and LAI Theory

The AccuPAR is useful for a number of applications,including the measurement of average and interceptedPAR. From these measurements, LAI can be calculatedand other attributes of the canopy structure can bedetermined.

PAR (photosynthetically active radiation)PAR is defined as the radiation in the 400 to 700nanometer waveband. It represents the portion of thesolar spectrum which plants use for photosynthesis.Under a plant canopy, radiation levels can vary from fullsun to almost zero over the space of a few centimeters.Therefore, reliable measurement of PAR requires manysamples at different locations under the canopy.

Average and Intercepted PARMonteith (1977) observed that dry matter production of aplant canopy is directly related to the amount ofphotosynthetically useful radiation intercepted by thecanopy. Dry matter production is modeled as the productof three terms:

P = efS(equation 1)


40

where P is the amount of dry matter produced, S is theflux density of incident radiation intercepted by the crop, fis the fraction of incident radiation intercepted by thecrop, and e is a conversion efficiency. Conversionefficiency and fractional interception (f) are determined bycrop physiology and management.

Incident solar radiation is the only environmental factor. Iff and S are monitored over the period of growth of a crop,and P is measured at harvest, e can be determined. Theresults of experimental treatments or the influence ofgenetics can be interpreted in terms of their effect on eand f.

The radiation incident on a canopy can be absorbed by thecanopy, transmitted through the canopy and absorbed orreflected at the soil surface, or reflected by the canopy. Inprinciple, only PAR absorbed by the canopy is useful inproducing dry matter, so f should be the fractionalabsorption. If t is the fraction of incident radiationtransmitted by the canopy, r is the fraction of incidentradiation reflected to a sensor above the canopy, and rs isthe reflectance of the soil surface, then the absorbedradiation fraction is calculated from:

(equation 2)

f 1 t– r– trs+=


41

The last two terms are often ignored and fractionalinterception is approximated by:

(equation 3)

The error resulting from this approximation is usuallysmall when t, r, and rs are measured in the PAR wavebandbecause most of the PAR is absorbed. The error becomesmuch more significant when measurements of total solarradiation are used because of large scattering coefficientsof leaves for near infrared radiation.

As a first-order estimate of error, assume that

(equation 4)

where rc is the reflectance of the vegetation. Equation 2becomes:

(equation 5)

The error resulting from using equation 3 is approximately

f 1 t–=

r 1 t–( )rc trs+=

f 1 t–( ) 1 rc–( )=


42

equal to rc, which is typically less than 0.05 in the PARwaveband. Since the AccuPAR’s sensors are sensitive onlyto radiation in the PAR waveband, equation 3 willgenerally be accurate for making measurements ofintercepted radiation. However, measurement of the otherterms needed for equation 2 is simple and will also beexplained.

Sampling for Fractional InterceptionThe functions needed to perform these calculations areavailable in the PAR sampling menu of the AccuPAR. Themeasurements needed for fractional interception are thosefrom which t, r, and rs are calculated. If S is the PARreading from an upward-facing AccuPAR above the plantcanopy, R is the reflected PAR above the plant canopy(inverted AccuPAR above the crop), T is the upward-facing AccuPAR below the plant canopy, and U is thereflected PAR from the soil surface, then t, r, and rs can becalculated from:

(equation 6)

(equation 7)

t T S⁄=

r R S⁄=


43

(equation 8)

Assume only t needs to be known. Measure S above thecrop canopy. Level the AccuPAR above the canopy andpress the up-arrow key. The reading displayed in the upperright portion of the screen is the value for S.

Measure T by placing the AccuPAR below the plantcanopy, being careful to place it below all of the leaves. Tryto keep the instrument level. Press the down-arrow key tomake below-canopy measurements. The resulting valuesare displayed below the above-canopy values on thescreen. Since the light below the canopy is extremelyvariable, several samples at different locations will benecessary for a reliable reading. The number of necessarysamples can be determined by taking, for example, 10individual readings and computing the coefficient ofvariation from:

(equation 9)where S is the standard deviation of the 10 readings:

rs U T⁄=

CVS

T---=

SΣ Ti T–( )2

n 1–-------------------------=


44

where n is the number of samples taken. The fractionalerror in the measurement of T will be CV divided by thesquare root of the number of samples.

Once you have taken the first below-canopy PAR reading,you will see the current τ value displayed in the lower leftcorner of the screen. With each subsequent below-canopymeasurement, the τ value will be updated. After you havetaken sufficient measurements, use the displayed τ value inthe lower left corner for t (see equation 6).

This calculation would normally be generated by acomputer program after the data from all of the sampleshave been sent to the computer. However, it is importantto set up some kind of sampling scheme beforehand orkeep detailed notes of sampled areas of the field plot ortreatment so that they can be compared to stored readings.

To find r, level the AccuPAR above the canopy and pressthe up-arrow. Then invert the AccuPAR at a height of 1-2meters above the crop canopy. Leveling is not critical forthis measurement since the radiation reaching the sensoris not directional. Press the down-arrow key in the PARsampling menu. Multiple readings are typically notnecessary, since R is not usually variable. r for equation 7 isshown in the T location at the bottom of the AccuPARscreen.


45

To find rs, invert the AccuPAR over the soil below thecanopy and take measurements at several locations.Average and store these measurements as before. Thisreading is the value U. Calculate rs from equation 8 usingU and T. A value in the range of 0.1 to 0.2 should beobtained, but it is possible that the light level below thecanopy will be so low that U will not be accuratelymeasured. If a value outside of the expected range isobtained, there will be negligible error in f by assuming r =0.15. As mentioned before, evaluation of interceptedradiation normally involves the measurement of t.

Only measurements below the canopy have beendiscussed. Obviously, measurements throughout thecanopy are possible. Profiles of interception with heightcan be useful in determining at what location most of thephotosynthesis is occurring in the canopy.

Using PAR to determine Leaf Area IndexThe PAR measured by the AccuPAR within a plantcanopy is a combination of radiation transmitted throughthe canopy and radiation scattered by leaves within thecanopy. A complete model of transmission and scatteringis given by Norman and Jarvis (1975), but it is verycomplex and not suitable for inversion.


46

The Norman-Jarvis model was used to test and fit twosimpler models which are more easily inverted. Equation10 is a simple light scattering model suggested byGoudriaan (1988). It gives the fraction of transmittedPAR, τ (ratio of PAR measured below the canopy to PARabove the canopy), below a canopy of LAI, L, as

(equation 10)

where fb is the fraction of incident PAR which is beam, a isthe leaf absorptivity in the PAR band (AccuPAR assumes0.9 in LAI sampling routines), and K is the extinctioncoefficient for the canopy. The extinction coefficient canbe modeled in various ways. Assuming an ellipsoidal angledistribution function (Campbell 1986), then

(equation 11)

where θ is the zenith angle of the sun and x is a leaf angledistribution parameter. When x=1, the angle distributionis spherical, and K simplifies to

(equation 12)

τ fb aKL–( ) 1 fb–( ) 0.87 aL–( )exp+exp=

Kx

2 Θ2tan+

x 1.744 x 1.182+( ) 0.733–+

---------------------------------------------------------------=

K1

2 Θcos----------------=


47

John Norman suggested a different equation forpredicting scattered and transmitted PAR.

(equation 13)

where A = 0.283 + 0.785a - 0.159a2.

Both equations predict canopy PAR within a few percentof values from the complete Norman-Jarvis model.Equation 10 is slightly more accurate, but equation 13 ismuch easier to invert to obtain L. The difference inaccuracy of the two equations is smaller than otheruncertainties in the method, so equation 13 will be used todetermine LAI. Inverting equation 13 gives the following:

(equation 14)

Applications and ExamplesThis section describes the method of manually collectingPAR data for the determination of LAI in a barley and pea

τA 1 0.47fb–( )L

11

2K-------–

fb 1–

------------------------------------

exp=

L

11

2K-------–

fb 1– τln

A 1 0.47fb–( )-------------------------------------------------=


48

canopy. This example has been included to show how theAccuPAR automatically calculates LAI in the field.

PAR was measured above a barley canopy of 391 µmol(µmol m-2s-2) on an overcast day. The average of severalmeasurements below the canopy was 62 µmol. Thetransmission, τ, is therefore 62/391 = 0.159. Since the daywas overcast, fb = 0. If a = 0.9, then A = 0.86. Fromequation 14, L = -ln(0.159)/0.86 = 2.14. Because themeasurement was made under overcast skies, it was notnecessary to have canopy structure information or solarelevation angle. Measurements on overcast days are thesimplest for LAI determination and do not requireassumptions about canopy structure.

The next example uses measurements on a sunny day.1614 µmol was measured above a pea canopy and 80µmol under the canopy. The fraction of PAR transmittedby the canopy was therefore τ = 80/1614 = 0.05. Thesolar zenith angle was 30°, and the beam fraction was0.881. The A value for equation 14 is again 0.86. “x” forthe canopy is unknown, but unless leaves have obvioushorizontal or vertical tendencies, a spherical distributioncan be assumed and x be set equal to 1. (The AccuPARdefault value for leaf distribution parameter is 1.0, which isapplicable for many canopies). For a zenith angle of 30°,this gives K = 0.577. Substituting these values intoequation 14 results in L = 5.2.


49

The AccuPAR program utilizes these same equationswhen the instrument is used to automatically calculateLeaf Area Index. In the AccuPAR’s setup menu, you enteryour local time, date, and leaf distribution parameter, andit automatically calculates zenith angle and beam fraction.It then couples these parameters with collectedintercepted PAR data to determine LAI.

Extinction Coefficient and Canopy StructureIf the the elements of a canopy are randomly distributedin space, then the probability of a ray of light, or otherprobe, penetrating the canopy without interception can becalculated from theory. The probability of penetrationwithout interception is equal to the sunfleck fraction,which is the beam transmission coefficient, τ(θ), for thecanopy. The parameter, θ, is the zenith angle (anglemeasured from the vertical) of the probe or solar beam. τusually varies with zenith angle. The transmissioncoefficient for a canopy of randomly placed elements is:

(equation 16)

where L is the leaf area index of the canopy (area of leavesper unit area of soil surface) and K is the extinctioncoefficient for the canopy, which depends on the leafangle distribution of canopy elements and the zenith angle

τ θ( ) KL–( )exp=


50

of the probe.

A number of expressions have been proposed for K. Themost useful is from Campbell (1986) where the angledistribution of canopy elements is assumed to beellipsoidal. One can picture the angle distribution of areain a plant canopy to be similar to the angle distribution ofarea on the surface of oblate or prolate spheroids, orspheres. The equation for K is:

(equation 17)

The parameter, x, is the ratio of the length of thehorizontal to the vertical axis of the spheroid, and can bemeasured as the ratio of the projected area of an averagecanopy element on a horizontal plane to its projection ona vertical plane.

Kx

2 Θ2tan+

x 1.744 x 1.182+( ) 0.733–+

---------------------------------------------------------------=


51

Figure 4: Extinction Coefficient vs. Zenith Angle

Figure 4 shows the extinction coefficient plotted as afunction of zenith angle for various values of x. There aretwo important things to note. First, at a zenith angle ofabout 57°, the extinction coefficient is near unity for allcanopies. When leaves are horizontal (large x), theextinction coefficient, K, is unity for all elevation angles,but as x decreases, K becomes smaller at large zenithangles and larger at small zenith angles.

Equation 16 can be used in various ways to determine theleaf area index, and also the leaf angle distribution for acanopy. The simplest application is that of Bonhomme etal. (1974). Since K= 1 for zenith angles near 57°, theinversion of equation 16 is simple and gives:

0

0.5

1

1.5

2

2.5

3

0 30 60 90

Zenith Angle, Degrees

Ext

inct

ion

Coe

ffici

ent,

K

0

0.5

1

4

1000


52

(equation 18)

If a measurement is made when the zenith angle is about57°, equation 18 can be used directly to find L.

If measurements of the transmission coefficient, τ, aremade at several elevation angles, a simple method fromLang (1987) can be used. The measurements of τ are used

to compute y = cos Θ ln τΘ. These are regressed on Θ (inradians), giving a slope, B and intercept, A. The leaf areaindex is given by:

(equation 19)

An approximate value for x is x=exp(-B/0.4L).

Example: Readings were obtained as follows:

Table 2: Sample readings

Θ-deg Θ-rad τ -cosΘ lnτ35 0.61 0.21 1.28

41 0.72 0.18 1.29

55 0.96 0.10 1.32

L τ57( )ln–=

L 2 A B+( )=


53

Linear Regression gives:

A = 1.21B = 0.12L = 2(1.21 + 0.12) = 2.64x = exp(-0.12 / 0.4 x 2.64) = 0.9

A more precise method for finding x is as follows. Wewould like to find values for x and L which minimize:

(equation 20)

subject to the constraint, x>0, where τi are transmissioncoefficients measured at several zenith angles, Θi, and theKi are the extinction coefficients for the correspondingangles.

Correction of PAR for Sun Angle

Canopy transmission (τ), measured at one zenith angle,can be used to predict transmission or radiationinterception for other zenith angles. For example, ameasurement might be made at Θ=32° from which cover(1 - transmission at Θ=0) is to be calculated. Fromequation 16:

F τln i KiL+( )2

∑=


54

(equation 21)

so:τ(Θ1) = τ(Θ2)p

(equation 22)

We can calculate p from equation 17:

(equation 23)

If Θ1 = 0,

If x is not known, assume x=1.

Example: From the measurements in the previousexample, find the canopy cover. Take Θ = 35°, τ = 0.21.The x value is 0.9.

τ1ln

τ2ln----------

K1

K2------ p= =

px

2 Θ1tan( )2+( )

x2 Θ2tan( )2

+( )--------------------------------------

12---

=

px

2( )x

2 Θ2tan( )2+( )

--------------------------------------

12---

=


55

τ(0) = 0.210.79 = 0.29

Cover = 1 - τ(0) = 1 - 0.29 = 0.71

Intercepted radiation averaged over an entire day can beestimated from:

f = 1-τd(equation 24)

where τd is the transmission coefficient averaged over all

elevation angles. τd can be calculated from:

-lnτd = uLv

(equation 25)

where u and v are functions of x which can be calculatedfrom:

u = 1 - 0.33exp(-0.57x)(equation 26)

p0.9

2( )0.9

235tan( )2( )

------------------------------------

12---

=


56

v = 1 - 0.33exp(-0.97x)(equation 27)

The next table shows typical values.

Combining equations 16 and 25 gives:

τd = τ(Θ)q

(equation 28)where q = uLv-1/K

Example: Calculate a value for fractional dailyinterception for the crop in the previous two examples.

u= 1 - 0.33exp(-0.57 x 0.9) = 0.80v= 1 - 0.33exp(-0.97 x 0.9) = 0.87

Table 3: values of u and v for equation 25

x u v

0.1 0.69 0.73

0.5 0.75 0.82

1.0 0.81 0.89

2.0 0.90 0.95

4.0 0.96 0.98

8.0 0.99 0.99


57

q = 0.80 x 2.64-0.13/0.59 = 1.2

τd = 0.211.2 = 0.15

f= 1 - τd = 1 - 0.15 = 0.85

LAI measurements and Non-Ran-dom DistributionThere has been much discussion concerning inversionmethods to obtain leaf area index. Since all inversionmethods rely on the assumption that elements of a canopyare randomly dispersed in space, errors in themeasurement of leaf area index may result from a non-random arrangement of canopy elements. This isespecially true for canopies with heliotropic leaves, coniferforests, row crops before canopy closure or for canopieswhich never close, as in desert vegetation. The degree oferror in measurement is a result of the canopy’s deviationfrom this random dispersion assumption.

In past studies, LAI has been used to relate both actualbiomass area and the interception of PAR by a plant

K0.9

235tan( )2

+( )

12---

0.9 1.774 0.9 1.182+( ) 0.733–+

------------------------------------------------------------------------ 1.141.94---------- 0.59= = =


58

canopy. Another proposed view regarding LAI in whichL, the actual biomass area, was related to a new term, Le,which represents the actual orientation of the canopyelements relating to the interception of PAR at a givenangle. In situ measurements of LAI using hemisphericalphotography were equated with this new term “effectiveplant area index” (Le), which was defined as:

where Le represents the actual leaf area index (equal to aharvested leaf area measurement) and Ω refers to aclumping index resulting from the non-randomdistribution of canopy elements.

When a canopy displays random dispersion, Ω is unity;however, when a canopy is clumped, Ω is not unity. In thisequation, Le refers to the actual canopy elementorientation. For example, in a randomly dispersed canopy,L would be equal to Le (figure 1), in an under-dispersedcanopy (clumped), L would be greater than Le (figure 2),and in an over-dispersed canopy, L would be less than Le(figure 3). Refer to the next page for illustrations.

The purpose of this discussion is to expose you topossible errors that may occur when making LAImeasurements in situ. When setting up an experiment, youshould carefully examine the desired end result. If you are

Le ΩL=


59

interested in the interception of PAR within a canopy, theresult of the inversions given in this manual will be correctin reaching Le. The leaf or plant area index that iscalculated through inversion will be an accurate portrayalof the canopy’s structure and orientation with respect tolight interception. In this instance, while clumping effectswithin the canopy remain present, these effects do notcause error with regard to light interception and theeffective area index for that situation. Alternately, if youare interested in obtaining the actual biomass representedby L in this discussion, all measurements should beperformed so that the effects of clumping are minimized.Clumping effects can be minimized by segmenting theAccuPAR’s probe in small groups such that the areasampled by a group is relatively random (see Lang andYueqin, 1986). This can also be done by measuring only atcertain times of day or at positions within the canopy thatdirectly minimize the clumping effects.


60


61

Zenith Angle and Equation of TimeThe formulas for calculating elevation angle are relativelystraightforward. The zenith angle is calculated from:

Ψ = arccos(sinLsinD+cosLcosDcos0.2618(t-to)) (equation 30)

where L is the latitude, D is the solar declination, t is thetime, and to is the time of solar noon. The earth turns at arate of 0.2618 radians per hour, so the 0.2618 factorconverts hours to radians. Time, t, is in hours (local solartime), ranging from 0 to 24. Latitude of a given site iseasily found in an atlas or using a GPS system. Users inthe Southern hemisphere should enter latitude as anegative number. Solar declination ranges from +0.409radians (+23.45°) at summer solstice to -0.409 radians (-23.45°) at winter solstice. It can becalculated from:

D = arcsin[0.39785sin[4.869+0.0172J +0.03345sin(6.224+0.0172J)]]

(equation 31)

where J is the day of the year. Some values are given inTable 1. The time of solar noon is calculated from:

to = 12 - LC - ET

(equation 32)


62

where LC is the longitude correction and ET is theEquation of Time. LC is +4 minutes, or +1/15 hour foreach degree east of the standard meridian and -1.15 hourfor each degree west of the standard meridian. Standardmeridians are at 0°, 15°, 30°...etc. Generally, time zonesrun approximately +7.5° to -7.5° on either side of astandard meridian, but this varies depending on politicalboundaries, so check an atlas to find both standardmeridian and longitude. Typically, longitudes in theEastern Hemisphere are given as negative values.

The Equation of Time is a 15 to 20 minute correctionwhich depends on the day of the year. It can be calculatedfrom:

ET=[-104.7sinφ+596.2sin2φ +4.3sin3φ-12.7sin4φ- 429.3cosφ-2.0cos2φ+19.3cos3φ]/3600

(equation 33)

where φ = (279.575 + 0.986 J)π/180. Some values for ETare given in Table 4.

Example Calculation:Find the zenith angle for Pullman, WA at 10:45 PDT onJune 30. Convert the time of observation to standard timeby subtracting one hour and convert minutes to decimalhours, so t = 9.75 hours.


63

June 30 is J = 181.Pullman latitude is 46.77°, or 0.816 radians, and longitudeis 117.2°.The standard meridian for Pullman is 120°.The local meridian is 2.8° east of the standard meridian, soLC = 2.8/15 = 0.19 hours.From Equation 33 or Table 4, ET = -0.06 hours. Equation32 then gives to = 12 - 0.19 - (-0.06) = 11.87.Declination from Table 4 or Equation 31 is 0.4 radians.Substituting these values into Equation 30 gives:

θ = arccossin(0.816) sin(0.4) + cos(0.816) cos (0.4) cos[0.2618(9.75 - 11.87)] = 0.61 radians, or 34.9°.

Table 4: Solar Declination and Equation of Time

Date Day of Year D in radians ET hour

Jan 1 1 -0.403 -0.057

Jan 10 10 -0.386 -0.123

Jan 20 20 -0.355 -0.182

Jan 30 30 -0.312 -0.222

Feb 9 40 -0.261 -0.238

Feb 19 50 -0.202 -0.232

Mar 1 60 -0.138 -0.208

Mar 11 70 -0.071 -0.117

Mar 21 80 -0.002 -0.122

Mar 31 90 0.067 -0.072


64

Apr 10 100 0.133 -0.024

Apr 20 110 0.196 0.017

Apr 30 120 0.253 0.046

May 10 130 0.304 0.060

May 20 140 0.346 0.059

May 30 150 0.378 0.043

Jun 9 160 0.399 0.015

Jun 19 170 0.409 -0.019

Jun 29 180 0.406 -0.055

Jul 9 190 0.392 -0.085

Jun 19 200 0.366 -0.103

Jun 29 210 0.331 -0.107

Aug 8 220 0.286 -0.097

Aug 18 230 0.233 -0.065

Aug 28 240 0.174 -0.022

Sep 7 250 0.111 0.031

Sep 17 260 0.045 0.089

Sep 27 270 -0.023 0.147

Oct 7 280 -0.091 0.201

Oct 17 290 -0.157 0.243

Oct 27 300 -0.219 0.268

Nov 6 310 -0.275 0.243

Nov 16 320 -0.324 0.255

Nov 26 330 -0.363 0.213

Dec 6 340 -0.391 0.151




65

Automatic Calculation of Zenith AngleThe AccuPAR automatically determines zenith angleusing the above equation and parameters. However, to getthe accurate zenith angle for your location, you need toenter the site latitude, longitude and universal time offsetin the Setup menu. Once these values are entered, theAccuPAR determines zenith angle without further input.The sun’s zenith angle will then be calculated and stored atthe end of each data set.

Dec 16 350 -0.406 0.075

Dec 26 360 -0.408 -0.007



AccuPAR LP-80Measurement Tips

66

9. Measurement Tips

Above Canopy (External) SensorThe AccuPAR is supplied with an external PAR sensorwhich connects to the port on the right side of theAccuPAR. The external sensor allows you to takesimultaneous above and below canopy PAR readingswithout having to move the instrument above and belowthe canopy you are measuring.

For above-canopy PAR data collection, considerconnecting the external point sensor to the AccuPAR.This ensures an accurate measurement of interceptedPAR, especially on days where radiation levels vary rapidly.Ideally, you can mount the sensor on a tripod and level itwith a bubble level.

When it is not feasible to use an external point sensor toobtain above-canopy measurements, such as in timber ortropical crops, you have two choices:

1. Use a separate datalogger with an attached PAR sensorsuch as a point quantum sensor, or configure anotherAccuPAR to log in the unattended mode (one readingper minute, for example) in a clearing outside the can-opy. After collecting PAR data within the canopy, you


67

can correlate the data from the two instruments afterdownloading it from each to a computer.

2. You can use your AccuPAR as an above-canopy refer-ence by regularly collecting above-canopy PAR data ina large clearing within the canopy structure.

Note: For LAI data in tall canopies, use the intercepted PARinversions and not the gap fraction theory. Intercepted PARinversions may be found in Chapter 8.

Sample SizeWhen evaluating experimental protocols for measuringaverage intercepted PAR and determining average LAI fora large area, make sure that a sufficient number of samplesand sampling locations are used. This will reduce errorscaused by canopy structure variations.

Clumping in CanopiesWhen evaluating discontinuous canopies or canopies withdefinite clumping, the AccuPAR can be configured suchthat its active sampling area is reduced, or you candownload the data collected by the AccuPAR’s probesegments. In this way you can gather information thatbetter describes the changes in canopy structure withregard to location. To reduce the sampling size of theprobe, refer to the “Set Active Segments” option in thesetup menu (see chapter 7). To see the individual PARreadings for each of the eight probe segments, select“Download All” or “Download Raw” from the


68

“Download options” section of the Setup menu, thendownload the stored data (select “Send” in the File menu).

LAI Sampling in Row CropsOne of the common uses for the AccuPAR is measuringthe leaf area index of row crops. When doing so, it isimportant to take measurements in such a way as to give agood row-to-row representation of the entire below-canopy PAR environment both under the plants andbetween rows. We suggest a sampling regime such asshown below, where the probe either extends from mid-row to mid-row, or extends from mid-row to the middleof the open space between rows, depending on row widthand canopy size.

Scenario 1: The two ends of the AccuPAR probe are in the middleof each row, getting a good representative sample of the entire areabelow and between rows.


69

Scenario 2: The base of the probe is in the center of the row, while theend is in the center of the open space between rows. When samplingthe next row, the same orientation is maintained, giving an accuraterepresentation of the overall area.

Mid-line of open space between rows

AccuPAR LP-80Care and Maintenance

70

10. Care and Maintenance

BatteriesThe AccuPAR uses four standard 1.5V AAA alkalinebatteries. These batteries are easily obtained and shouldlast for at least 2 years before they have discharged. Thebattery icon in the upper right corner of the screen (nextto the time) shows you the current power level of yourbatteries.

Replacing BatteriesIf the alkaline batteries require replacement, remove thefour screws on the bottom of the AccuPAR case and liftthe cover carefully. The batteries are located on both sidesof the circuit board. Be sure to orient them properly;placing them the wrong way in the battery holder candamage the AccuPAR. The battery holders indicate whichdirection they should be placed.Note: Data will not be lost when the batteries are replaced. Thememory and program sections of the AccuPAR are non-volatile.After replacing the batteries, press the reset button at thetop left corner of the board.

Cleaning the Probe and ControllerThe white probe diffuser should always be clean to ensureaccurate readings. To clean the probe, use a small amount


71

of isopropyl alcohol and a soft cloth. Rub the surface untilit is clean.

To clean the controller, use a soft cloth and water to washheavy dirt, then use ethyl or isopropyl alcohol to finishcleaning. Make sure to only use a soft cloth when cleaningthe LCD window. Tissues made from wood fiber willscratch the surface.

Re-calibrationThe AccuPAR calibrates its sensors against the externalsensor supplied with the instrument. Therefore, providedyour external sensor’s calibration is good, you simply re-calibrate the AccuPAR in the Setup menu (see chapter 9)as often as you wish. However, as is the case with allelectronic components, shifts in the external sensor’ssensitivity will occur over time. As a result, we recommendthat you periodically send your external sensor in toDecagon’s factory for re-calibration, depending on howoften you use it. If you use it heavily each year, we suggestonce a year. For periodic measurements, one re-calibrationevery 2 to 3 years should be adequate. Before sending theinstrument in, contact Decagon via phone or email so wecan prepare for its arrival.

General PrecautionsThe AccuPAR is a low maintenance instrument. There areonly a few suggestions to keep in mind


72

• Keep the probe clean. The accuracy of readings may decline if there is any debris on the probe which pre-vents light from entering the sensors.

• Although the AccuPAR is splash-resistant, don't immerse the instrument in water, or leave the it in contact with rain for long periods of time.

• When transporting the AccuPAR, keep the instrument in its padded hard-sided carrying case to prevent dam-age.

AccuPAR LP-80Declaration of Conformity

73

Declaration of ConformityApplication of Council 89/336/EECDirective:

Standards to which EN50082 : 1998conformity is declared: EN55022 : 1998

Manufacturer’s Name: Decagon Devices, Inc.Manufacturer’s Address: 2365 NE Hopkins Court

Pullman, WA 99163USA

Type of Equipment: AccuPAR Linear PAR/LAI Ceptometer.

Model Number: LP-80

Year of First Manufacture: 2003

This is to certify that the AccuPAR model LP-80, manu-factured by Decagon Devices, Inc., a corporation based in Pullman, Washington, USA meets or exceeds the stan-dards for CE compliance as per the Council Directives noted above. All instruments are built at the factory at Decagon and pertinent testing documentation is freely available for verification.

AccuPAR LP-80Appendix A

74

Appendix A: External Sensor InformationThe external quantum sensor provided with the AccuPARmodel LP-80 is calibrated to provide an output ofapproximately 0.1mV per µmol m-2s-1 This sensor offersgood accuracy, however you should be aware of potentialsources of error. The biggest error is often caused bysmall changes in the position of the sensor. The sensormust be exactly horizontal for the most accuratemeasurements.

SpecificationsOutput: approx. 0.1mV per µmol m-2s-1 Dimensions: 24 mm diameter, 27mm tallCable length: 2mRange: 0 to 4000 µmol m-2s-1 (full sunlight ~ 2000)Warranty: 1 year parts and labor.

Spectral ResponseAn ideal quantum sensor would give equal emphasis to allphotons between 400 and 700 nm and would excludephotons above and below these wavelengths. The mostaccurate way to measure this radiation is with aspectroradiometer. However, quantum sensors that


75

approximate the ideal response with filters are accurate towithin ±3% for common light sources. The spectralresponse of the external sensor is such that itunderestimates the 400 to 500 nm wavelengths (bluelight), overestimates the 550-650 nm wavelengths (yellowand orange), and has little sensitivity above 650 nm (redlight). Fortunately common light sources are mixtures ofcolors and many spectral errors offset each other.

Cosine ResponseSome of the radiation coming into a sensor at low angles isreflected, which causes the reading to be less than itshould be. to partly correct for this problem, moreexpensive sensor are enclosed in a black cylinder with asmall raised translucent disk in the top. This cosinecorrected head helps to capture radiation at low angles. theApogee sensor is flush mounted in a PVC grey body thatblocks the radiation at very low angles. the small gapbetween the edge of the sensor and the grey body allowsthe correct amount of low angle radiation to be capturedby the sensor. The cosine error for typical applications isless than 1%.

Temperature ResponseIncreasing temperature increases the output of mostradiation sensors. This sensor was calibrated at 20°C Ourmeasurements indicate that it reads 0.6% low at 10°C and0.8° high at 30°C. The temperature error is insignificantfor most applications.


76

Long-term stabilityThe output of all radiation sensors tends to drift over timeas the detector ages. The average decrease of the sensor is1% every year. Therefore, we recommend returning thesensor for recalibration at least every 3 years.

AccuPAR LP-80Appendix B

77

Appendix B: Further ReadingsThe following is a list of references that offer more detailconcerning plant canopy characteristics and research.

Anderson, M.C. (1971) Radiation and crop structure. InPlant Photosynthetic Production, Manual of Methods (edsA. Sestak, J. Catsky and P.G. Jarvis), Junk, TheHague, pp. 412-66.

Andrade, F.H., Calviño, P., Cirilo, A. and P. Barbieri (2002)Yield Responses to Narrow Rows Depend onIncreased Radiation Interception. In AgronomyJournal, 94:975-980

Bonhomme, R., Varlet-Grancher, C. and Chartier, P.(1974). The use of hemispherical photographs fordetermining the leaf area index of young crops.Photosynthetica, 8 (3), pp. 299-301.

Campbell, G.S. (1977) An Introduction to EnvironmentalPhysics, Springer-Verlag New York Inc., New York,pp. 159.

Campbell, G.S. (1986) Extinction coefficients for radiation in


78

plant canopies calculated using an ellipsoidal inclinationangle distribution. Agric. For. Meteorol., 36: 317-21.

Campbell, G.S., and J.M Norman. (1988) The descriptionand measurement of plant canopy structure. inPlant Canopies: Their Growth, Form and Function (ed.G. Russell), Society for Experimental Biology,Seminar Series 29, Cambridge University Press,New York.

Chen, H.Y.H. Interspecific responses of planted seedlingsto light availability in interior British Columbia:survival, growth, allometric patterns, and specificleaf area. Canadian Journal of Forest Research 27:1383-1393 (1997).

Chen, Jing M. and Cihlar, Josef. Plant Canopy gap-sizetheory for improving optical measurements ofleaf-area index. Applied Optics 34(27): 6211-6222.

Cohen, S., Striem, M.J., Bruner, M., and I. Klein.Grapevine Leaf Area Index Evaluation by GapFraction Inversion. Proceedings of the 3rd Intl.Symposium on Irrigation Hort. Crops, Ferreiraand Jones (eds.) Acta Horticulturae. 537, ISHS 2000pp.87-91

Cohen, Shabtai, R.Sudhakara Rao and Yehezkel Cohen.Canopy transmittance inversion using a line


79

quantum probe for a row crop. Agricultural andForest Meteorology 86: 225-234

Flénet F, J.R. Kiniry, J.E. Board, M.E. Westgate and D.C.Reicosky. Effect of row spacing, time of day, andstage of crop development on light extinctioncoefficient of corn, sorghum, soybean, andsunflower. Agronomy Journal (1995)

Goudriaan, J. (1977) Crop Micrometeorology: A SimulationStudy, Center for Agriculture PublicationDocumentation, Wageningen, The Netherlands.

Goudriaan, J. (1988) The bare bones of leaf angledistribution in radiation models for canopyphotosynthesis and energy exchange. Agriculturaland Forest Meteorology, 43:155 - 169.

Hyer, E. and S.J. Goetz (2004). Comparison and sensitivityanalysis of instruments and radiometric methodsfor LAI estimation: assessments from a borealforest site. Agricultural and Forest Meteorology, 122 (3/4): 157-174

Jobidon, Robert. Measurement of Light Transmission inYoung Conifer Plantations: A new Technique forAssessing Herbicide Efficacy. Northern Journal ofApplied Forestry 9(3): 112-115.


80

Jobidon, Robert. Light Threshold for Optimal BlackSpruce (Picea mariana) Seedling Growth andDevelopment Under Brush Competition. CanadianJournal of Forest Research Vol. 24, No. 8:1629-1635.

Kiniry, J.R., C.R. Tischler, G.A. Van Esbroeck. (1999)Radiation Use Efficiency and leaf CO2 exchangefor diverse C4 Grasses. Biomass and Bioenergy.17:95-112.

Kiniry, J.R., J.A. Landivar, M. Witt, T.J. Gerik, J. Cavero,and L.J. Wade. Radiation-use efficiency responseto vapor pressure deficit for maize and sorghum.European Journal of Agronomy Oct. 1995.

Kiniry, J.R. and D.P. Knievel. Response of Maize SeedNumber to Solar Radiation Intercepted Soon afterAnthesis. Agronomy Journal 87(2): 228-234

Kiniry, J.R. Radiation-Use Efficiency and Grain Yield ofMaize Competing with Johnsongrass. AgronomyJournal 86(3): 554-556.

Kiniry, J.R. (1998) Biomass Accumulation and Radiationuse Efficiency of Honey Mesquite and EasternRed Cedar. Biomass and Bioenergy Vol.15 No. 6: 467-473


81

Lang, A.R.G., (1986) Leaf area and average leaf angle fromtransmission of direct sunlight. Aust. J. Bot.,34:349-355.

Lang, A.R.G.,(1987) Simplified estimate of leaf area indexfrom transmittance of the sun’s beam. Agric. For.Meteorol., 41: 179-186.

Lang, A.R.G. (1991) Application of some of Cauchy’stheorems to estimation of surface areas of leaves,needles and branches of plants, and lighttransmittance. Agric. For. Meteorol., 54: (in press).

Lang, A.R.G., R.E. McMurtrie, and M.L. Benson. (1991)Validity of leaf area indices of Pinus radiata forestsestimated from transmittances of the sun’s beam.Agric. For. Meteorol., (accepted).

Lang, A.R.G., and R.E. McMurtrie. (1991) Total leaf areasof single trees of Eucalyptus grandis estimatedfrom transmittance of the sun’s beam. Agric. For.Meteorol., (accepted).

Lang, A.R.G. and Xiang Yueqin (1986) Estimation of leafarea index from transmission of direct sunlight indiscontinuous canopies. Agric. For. Meteorol., 37:229-43.


82

Lang, A.R.G., Xiang Yueqin and J.M. Norman. (1985)Crop structure and the penetration of directsunlight. Agric. For. Meteorol., 35: 83-101.

Lemur, R. (1973) A method for simulating the direct solarradiation regime in sunflower, Jerusalem artichoke,corn and soybean canopies using actual standstructure data. Agric. Meteorol., 12: 229-47.

Levy, P.E. and P.G. Jarvis (1998) Direct and indirectmeasurements of LAI in millet and fallowvegetation in HAPEX-Sahel Agric. For. Meteorol.,97: 199-212

Maas, S. Cotton canopy structure, light absorption, andgrowth in the San Joaquin Valley of California.Proceedings of the 1996 Beltwide Cotton Conferences,(2)1235-1237.

Martens, Scott N., S.L. Ustin and R.A. Rousseau.Estimation of tree canopy leaf area index by gapfraction analysis. Forest Ecology and Management 61(1993): 91-108

Norman, J.M. (1979) Modeling the complete crop canopy.in Modification of the Aerial Environment of Crops (edsB.J. Barfield and J. Gerber), American Society ofAgricultural Engineers, St. Joseph, MI, pp. 249-77.


83

Norman, J.M., and G.S. Campbell. (1989) Canopy structure. Plantphysiological ecology: Field methods and instrumentation. R.E.Pearcy, J.R. Ehleringer, H.A. Mooney and P.W. Rundel(eds). London, Chapman and Hall. pp. 301-325.

Norman, J.M. and P.G. Jarvis. (1974) Photosynthesis inSitka Spruce (Picea sitchensis (Bong.) Carr.) III.Measurements of canopy structure andinterception of radiation. J. Appl. Ecol., 12:839-878.

Norman, J. M., E.E. Miller, and C.B. Tanner. (1971) Lightintensity and sunfleck-size distributions in plantcanopies. Agron. J., 63:743-748.

Norman, J. M. and J.M. Welles. (1983) Radiative transfer inan array of canopies. Agron. J., 75:481-488.

Norman, J. M., S.G. Perry, A.B. Fraser, and W. Mach.(1979) Remote sensing of canopy structure. Proc.14th Conf. Agric. For. Meteor., p.184-185, Am.Meteor. Soc., Boston.

Welles, Jon M., and Shabtai Cohen. Canopy Structuremeasurement by gap fraction analysis usingcommercial instrumentation. Journal of ExperimentalBotany. 47(302): 1335-1342.

White, J.D., Running, S.W., Nemani, R., Keane, R.E., andK.C. Ryan. Measurement and remote sensing of LAI


84

in Rocky Mountain montane ecosystems. CanadianJournal of Forest Research 27: 1714-1727 (1997)

Wilhelm, W.W., K. Ruhe, and M.R. Schlemmer.Comparison of Three Leaf Area Index Meters in aCorn Canopy. Crop Science 40:1179-1183 (2000)

AccuPAR LP-80Index

85

IndexAAbout menu 38Accessories 7

BBatteries

replacing 70type 70

Beam fraction 13Biomass

production 57

CCalibration 71

external sensor 36Canopy

distribution 50studies

(tall) 67Canopy elements

non-random distribution 57Canopy structure

error reduction 67Care 70CE compliance 73Chi 14Cleaning 70Clumping 58, 67

minimizing effects 59

AccuPAR LP-80Index

86

Code status 38Code version number 38Conifer forests 57

DDate

setting 31Declaration of Conformity 73Delete 30Download

all 34options 23raw 34summary 34

Download Summary 27Downloading

setting options for 34Downloading data 22Dry matter production 39

EE-mail address 1Erasing files 30Error

in readings 57, 58measurement 41, 45

External sensor 12calibration constant 36specifications 74

Extinction coefficient 50

AccuPAR LP-80Index

87

FFax number 1Fb 13File

send 22view 21

Filedeleting files 30

Fraction of beam radiation 13Fractional interception 42

GGeographical location

setting 32

IIntercepted PAR 49

KK (extinction coefficient) 50Keyboard 8

LLAI

equation for calculating 47LAI calculation

examples 48Leaf angle distribution 50, 51Leaf distribution

random 49Leaf distribution parameter 14, 46, 48, 50

AccuPAR LP-80Index

88

MMaintenance 70Measurement

taking PAR and LAI samples 16

OOvercast sky conditions 48

PPAR

and dry matter production 39definition 11, 39for LAI 58

PAR/LAI sampling menu 16Partitioning probe 33

RRecalibration 71References 77Repair

costs 3instructions 3

Row crops 57

SSample size 67Segment mode icon 33Seller’s liability 2Send 22Set active segments 33Set download options menu 34

AccuPAR LP-80Index

89

Set location 32Specifications 5Spherical distribution 46

TTau 12Telephone number 1Temperature 38Timber

studies 66Time

setting 31Time/date set 31

VViewing stored data 21

WWarranty 2

XX parameter

setting 32X (leaf distribution parameter) 14, 46, 50

ZZenith angle 46

defined 13equation 61example calculation 62setting location for 32

AccuPAR LP-80 v8

Documents

Transcript of AccuPAR LP-80 v8