Decagon Devices AccuPAR LP-80 User manual

AccuPAR
PAR/LAI ceptometer
model LP-80
Operator’s Manual
Ve r si o n 1 . 0
Decagon Devices, Inc.

Decagon Devices, Inc.
950 NE Nelson Court
Pullman, WA 99163
tel: [phone]
fax: [phone]
www.decagon.com/lp80
[e-mail]
Trademarks
AccuPAR and Ceptometer are
registered trademarks of Decagon
Devices, Inc. © 2003

LP-80
Table of Contents
i
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 1
Customer Service and Tech Support . . . . . . . . 1
Warranty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Seller’s Liability . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Repair Instructions . . . . . . . . . . . . . . . . . . . . . . . 3
2. About the LP-80 . . . . . . . . . . . . . . . . . . . . . 5
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Overview of the LP-80 . . . . . . . . . . . . . . . . . . . 6
Components of the LP-80 system . . . . . . . . . . . 7
Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Keyboard Operation . . . . . . . . . . . . . . . . . . . . . 8
Turning on the instrument . . . . . . . . . . . . . . . . . 9
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . .11
PAR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Tau (t) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
LAI (L) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
External Sensor . . . . . . . . . . . . . . . . . . . . . . . . . 13
Zenith Angle (z) . . . . . . . . . . . . . . . . . . . . . . . . . 13
Fraction of Beam Radiation (Fb) . . . . . . . . . . . 14
Leaf Distribution Parameter (x) . . . . . . . . . . . . 14
4. PAR/LAI Menu . . . . . . . . . . . . . . . . . . . . 17
Taking Measurements . . . . . . . . . . . . . . . . . . . 17
5. Log Menu . . . . . . . . . . . . . . . . . . . . . . . . . 20
7. File Menu . . . . . . . . . . . . . . . . . . . . . . . . . 22
View . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

LP-80
Table of Contents
ii
Send . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
New . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Delete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Delete All . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
7. Setup Menu . . . . . . . . . . . . . . . . . . . . . . . 30
Set Baud Rate . . . . . . . . . . . . . . . . . . . . . . . . . .34
Calibrate Probe . . . . . . . . . . . . . . . . . . . . . . . . .34
External Sensor Const. . . . . . . . . . . . . . . . . . . .36
About . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
8: PAR and LAI Theory . . . . . . . . . . . . . . . . 38
PAR (photosynthetically active radiation) . . 38
Average and Intercepted PAR . . . . . . . . . . . .38
Using PAR to determine Leaf Area Index . . .45
Extinction Coefficient and
Canopy Structure . . . . . . . . . . . . . . . . . . . . . . .49
LAI measurements and
Non-Random Distribution . . . . . . . . . . . . . . . .57
Zenith Angle and Equation of Time . . . . . . . .62
9. Measurement Tips . . . . . . . . . . . . . . . . . . 67
Above Canopy (External) Sensor . . . . . . . . .67
Sample Size . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
Clumping in Canopies . . . . . . . . . . . . . . . . . . . .68
10. Care and Maintenance . . . . . . . . . . . . . 70
Batteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70
Cleaning the Probe and Controller . . . . . . . . 71
Re-calibration . . . . . . . . . . . . . . . . . . . . . . . . . . 71
General Precautions . . . . . . . . . . . . . . . . . . . . .72

LP-80
Table of Contents
iii
Appendix A:
External Sensor Information . . . . . . . . . . . 73
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . .73
Spectral Response . . . . . . . . . . . . . . . . . . . . . .73
Cosine Response . . . . . . . . . . . . . . . . . . . . . . . .74
Temperature Response . . . . . . . . . . . . . . . . . .74
Long-term stability . . . . . . . . . . . . . . . . . . . . . .75
Appendix B: Further Readings . . . . . . . . . 76
Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83

AccuPAR LP-80
Introduction
1
1. Introduction
Welcome to Decagon’s AccuPAR model LP-80 PAR/
LAI Ceptometer. The AccuPAR measures
Photosynthetically Active Radiation (PAR) in the
400-700nm waveband, and can invert these readings
to give you Leaf Area Index for your plant canopy.
This manual is designed to help you accomplish
your research goals, and understand how to get the
most out of your AccuPAR.
Customer Service and Tech Support
When contacting us via fax or email, include the
following information: Your AccuPAR’s serial
number, your name, address, phone and fax
number, and a description of your problem
Phone:
Call Monday through Friday, between 8 a.m. and 5
p.m. PST.
US and Canada (toll-free): 1-800-755-2751 .
Outside of the US and Canada: [phone].
Fax:
[phone].

AccuPAR LP-80
Introduction
2
E-mail:
[email protected].
Warranty
The AccuPAR has a one year warranty on parts and
labor. It is activated upon the arrival of the
instrument at your location.
Seller’s Liability
Seller warrants new equipment of its own
manufacture against defective workmanship and
materials for a period of one year from date of
receipt of equipment (the results of ordinary wear
and tear, neglect, misuse, accident and excessive
deterioration due to corrosion from any cause are
not considered to be a defect); but Seller’s liability
for defective parts shall in no event exceed the
furnishing of replacement parts f.o.b. the factory
where originally manufactured. Material and
equipment covered hereby which is not
manufactured by the Seller shall be covered only by
the warranty of its manufacturer. Seller shall not be
liable to Buyer for loss, damage, or injuries to
persons (including death), or to property or things
of whatsoever kind (including, but not without
limitation, loss of anticipated profits), occasioned by
or arising out of the installation, operation, use,
misuse, nonuse, repair, or replacement of said
material and equipment, or out of the use of any

AccuPAR LP-80
Introduction
3
method or process for which the same may be
employed. The use of this equipment constitutes
Buyer’s acceptance of the terms set forth in this
warranty. There are no understandings,
representations, or warranties of any kind, express,
implied, statutory or otherwise, (including, but
without limitation, the implied warranties of
merchantability and fitness for a particular purpose),
not expressly set forth herein.
Repair Instructions
If your AccuPAR needs to be sent in for service or
repair, call Decagon at [phone] or 1-800-
755-2751 (US and Canada).We will ask you for
your address, phone number, and serial number.
For non-warranty repairs, we will also ask for a
purchase order number, a repair budget, and billing
address.
When shipping your instrument back to us, include
a document listing the complete shipping address,
name and department of the person responsible for
the instrument, and (most importantly) a description
of the problem. This will better help our technicians
and our shipping department to quickly expedite
repair on your instrument and ship it back to you.
Pack your AccuPAR carefully. Ship it back in the
black carrying case, preferably inside a cardboard

AccuPAR LP-80
Introduction
4
box. Ship to:
Decagon Devices Inc.
950 NE Nelson Court
Pullman, WA 99163
Repair Costs:
Manufacturer’s defects and instruments under
warranty will be repaired at no cost. For non-
warranty repairs, costs for parts, labor, and shipping
will be billed to you. We have a $65 minimum
charge for repair that takes one hour or less. For
repair over one hour the labor rate is $65/hour.

AccuPAR LP-80
About 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 light interception in plant canopies, and to
calculate Leaf Area Index (LAI). It consists of an
integrated microprocessor-driven datalogger and
probe. The probe contains 80 independent sensors,
spaced 1cm apart. The photosensors measure PAR
(Photosynthetically Active Radiation) in the 400-
700nm waveband. The AccuPAR displays PAR in
units of micromols per meter squared per second
(µmol m-2s-1). The instrument is capable of hand-
held or unattended measurement.
Specifications
Operating Environment:
• 0° to 50° C (32°-122° F)
• 100% relative humidity
Probe Length: 86.5 cm
Number of sensors: 80
Overall Length: 102 cm (40.25 in)
Probe Cross-Section: 19cm x 9.5cm (.75 x .375 in)
Microcontroller 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

AccuPAR LP-80
About the LP-80
6
Resolution: 1µmol m-2s-1
Minimum Spatial resolution: 1cm
Data 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-232
Keypad: 6-Key menu-driven.
Clock: 24-hour ±1 minute per month.
Interface Cable: RS-232 cable
Power: Four AA Alkaline cells.
External PAR sensor connector: Locking 3-pin
sealed circular connector.
Overview of the LP-80
The LP-80’s menu-driven interface is designed for
ease of use. There are four menus to choose from:
PAR/LAI sampling menu, unattended logging menu,
file menu, and the setup menu. You navigate
between the menus by pressing the MENU button,
and select items within each menu using the up and
down arrow keys, and the ENTER or ESC keys. An
internal bubble level is mounted in the upper right
corner of the case to allow you to keep the probe
relatively level when making measurements.
The AccuPAR can be operated in environments with
temperatures from 0 to 50 °C, and in relative
humidities of up to 100%. The instrument is shipped

AccuPAR LP-80
About the LP-80
7
with an RS-232 interface cable to allow for
downloading data to a computer, and an external
PAR sensor to allow for simultaneous above and
below canopy PAR measurements. The AccuPAR
operates on four AA alkaline batteries.
Components of the LP-80 system
The AccuPAR and its accessories come to you in a
durable foam-padded carrying case. As you open
the case, you should find the following:
• AccuPAR model LP-80
• RS-232 Cable
• Operator’s manual
• external PAR sensor
• #1 Phillips screwdriver
Features
Probe
Bubble Level
Display
RS-232/
Ext. sensor port

AccuPAR LP-80
About the LP-80
8
Keyboard Operation
Figure 1: LP-80 Keypad
The LP-80’s keypad is a 6-key panel, designed for
ease of use and intuitive navigability through the
operating system. Here is a brief description of the
key functions:

AccuPAR LP-80
About the LP-80
9
ON/OFF Key: Located in the upper left corner, it
turns the instrument on or off. The AccuPAR will
turn itself off automatically after 10 minutes of
inactivity.
MENU Key: Cycles between the four menus.
UP and DOWN ARROW KEYS: In PAR sampling
menu, they initiate above (up arrow) and below
(down arrow) canopy PAR readings. In other
menus, they are used to navigate to items within
those menus and to change numeric values in sub
menus.
ESC: Discards the current PAR reading displayed in
the lower half of the PAR sampling menu, backs out
of FILE menu options and stores changes in SETUP
menu options.
ENTER: Saves the current PAR readings in the PAR
sampling menu, and selects items in other menus.
Turning on the instrument
When you first turn on the instrument, it will be in
the PAR sampling menu, in which you will see real-
time PAR data displayed in the center portion of the
screen. If you have the external PAR sensor
connected, you will also see its real-time PAR data

AccuPAR LP-80
About the LP-80
10
displayed, and indicated by an above-canopy icon.
At any time, you can cycle between the four menus
by pressing the MENU key. The menus are
indicated by the tabs on the top of the screen, with
the active menu highlighted in black. To the right of
the menu tabs is the current battery status and the
time. Later chapters discuss each menu in detail and
how to use the features that each provides.
.
current time
battery statusmenu tabs

AccuPAR LP-80
Definitions
11
3. Definitions
The AccuPAR uses several variables to calculate Leaf
Area Index, and displays values for these variables
on the screen as measurements are taken. This
chapter will discuss these variables and their
definitions. If you’re not familiar with them, we
recommend that you review this chapter before
proceeding with measurements.
PAR
PAR (photosynthetically active radiation) is defined
as the radiation in the 400 to 700 nanometer
waveband. It represents the portion of the spectrum
which plants use for photosynthesis. Under a plant
canopy, radiation levels can vary from full sun to
almost zero over the space of a few centimeters.
Therefore, reliable measurement of PAR requires
many samples at different locations under the
canopy. The AccuPAR measures PAR either
manually or in unattended logging mode.
Intercepted PAR data can be used for determining
important parameters of canopy structure and for
the calculation of LAI. An external point sensor may
be used to collect instantaneous above canopy PAR

AccuPAR LP-80
Definitions
12
measurements when sampling under or within a
canopy. You also have the option of segmenting the
probe to reflect spatial changes in the plant canopy.
This is useful when evaluating discontinuous and
irregular canopies, or to limit the size of active
sensors along the probe.
Tau (τ)
Tau is another variable in the LAI inversion
equations. It is defined as the ratio of below canopy
PAR measurements to the above canopy PAR value.
It is measured automatically by the instrument,
based upon the PAR readings you make. The
current Tau value is displayed and updated in the
lower left corner of the screen in the PAR menu.
Further explanation of the significance of Tau is
given in Chapter 9.
LAI (L)
LAI (Leaf Area Index) is defined as the area of
leaves per unit area of soil surface. It is a very
valuable measurement in helping to assess canopy
density and biomass. The AccuPAR calculates LAI
based on the above and below-canopy PAR
measurements along with other variables that relate
to the canopy architecture and position of the sun.
These variables are the zenith angle, a fractional
beam measurement value, and a leaf area
distribution parameter (also known as x) for your

AccuPAR LP-80
Definitions
13
particular canopy. The AccuPAR automatically
calculates both the zenith angle and fractional beam
reading, and requires you to input a value for x in
the setup menu.
External Sensor
An external PAR sensor is provided with the
AccuPAR to allow you to make simultaneous above
and below canopy PAR measurements. This is
useful if you want to be able to make multiple PAR
measurements under the canopy in variable light
conditions without having to keep moving the
instrument in and out of the canopy to update the
above canopy PAR reference.
Zenith Angle (z)
Zenith angle can be defined as the angle the sun
makes with respect to the zenith, or the point in the
sky directly overhead, vertical to where you stand.
The zenith is defined as being 0° and the horizon is
90°. The zenith angle of the sun is necessary for
calculation of certain canopy structure parameters,
such as LAI. It is calculated by the AccuPAR based
on your global position and the time of day, and is
displayed in the lower right corner of the screen
when taking above and below PAR measurements.
To make sure this value is accurate, you must first
correctly set the longitude, latitude, date, and time
of day in the setup menu.

AccuPAR LP-80
Definitions
14
Fraction of Beam Radiation (Fb)
Fractional beam radiation is the ratio of direct beam
radiation coming directly from the sun to radiation
coming from all ambient sources like the
atmosphere or reflected from other surfaces. A
fractional beam radiation value is necessary for
calculation of LAI using PAR data. The AccuPAR
obtains this value by comparing the above canopy
PAR measurement to the calculated value of
incoming solar radiation at your location and zenith
angle. The current calculated Fbis displayed and
updated at the bottom 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 horizontal to the vertical axis of the spheroid
described by the leaf angle distribution of a canopy.
It can also be measured as the ratio of the projected
area of an average canopy element (a leaf, for
example) on a horizontal plane to its projection on
a vertical plane. The default value for xis 1.0, which
assumes the canopy angle distribution to be
spherical. Onions are good example of a strongly
vertical crop. For onions, xwould be about 0.7. On
the other extreme, strawberries, a crop with a

AccuPAR LP-80
Definitions
15
strongly horizontal nature, would have a xvalue of
about 3.
Table one gives some typical values for x. In some
cases a range of values is given, indicating the
variability that is to be expected for xin any
canopy. Fortunately, the value of LAI computed is
not strongly dependent on the value of xchosen.
The AccuPAR uses a value of x=1.0 as its default.