LAI-2200 Introduction

• Non-destructive measurements of Leaf Area Index
• Calculates mean foliage inclination angle and canopy gap fraction
• Fast, cost effective measurements
• On-site evaluation of LAI data
• For use in a variety of canopy types

Leaf Area Index (LAI) is the ratio of foliage area to ground area. The measurement of LAI is of fundamental importance to agricultural and ecological research, as LAI is an indicator of plant growth. LAI directly affects the interception and absorption of light by the canopy and influences the heat balance and evaporation from the landscape.

The LAI-2200 calculates the interception of blue light (320-490 nm) at 5 zenith angles from readings taken above and below the canopy. These data are fit to a well-established and scientifically accepted model of radiative transfer in vegetative canopies to compute Leaf Area Index, Mean Tip Angle, and canopy gap fraction.

Data can be read live in the field and later processed using the powerful FV2200 software. The FV2200 software provides significant data processing options, including 3 additional inversion methods and ring masking.

The LAI-2200 can be used to measure almost any canopy type with the appropriate sampling protocol.

LAI-2200 Features

The LAI-2200 Plant Canopy Analyzer was designed based on the proven optical configuration that made the LAI-2000 a powerful and versatile instrument for decades. The new design offers many improvements on the LAI-2000 platform, including:

• Autonomous or wired optical sensor operation to accommodate numerous canopy types and sampling protocols
• Automatic logging feature for measuring tall canopies using two sensors
• Large memory capacity can store over 1.5 million readings
• Plug and play USB data transfer
• Light weight, ergonomic instrument console makes field work easier
• Intuitive, menu-driven set-up for effortless operation
• Long battery life for uninterrupted data collection
• Powerful post-processing software enables detailed data analysis

Advantages

The novel technology used in the LAI-2200 has distinct advantages over other indirect LAI measurements approaches, including:

Applications

Choose from the following Applications to view video demonstrations of the LAI-2200 in action.

The technology of the LAI-2200 Plant Canopy Analyzer has become invaluable to a wide range of applications, including studies of canopy growth, canopy productivity, forest vigor, canopy fuel load, air pollution deposition modeling, insect defoliation studies and remote sensing.

LAI is also one of the fundamental measurements associated with carbon flux studies and global carbon cycle research. The technology of the LAI-2200 and its predecessor, the LAI-2000, is the most commonly used indirect LAI measurememt technology worldwide.

LAI-2200 Specifications

LAI-2270 Control Unit:

• Sensor Inputs: 2 6-pin connectors for LAI-2250 Optical Sensors. 2 3-pin connectors for LI-COR Light Sensors.
• Memory: 128 MB of FAT16 memory.
• Keypad: 22 button tactile response keypad.
• Display: 128x64 graphics display.
• Communications:
  • USB (as mass storage device)
  • RS-485: baud rate 115200, 8 data bits, no parity, 1 start, 1 stop
  • RS-232: selectable baud rates of 9600, 38400, 57600, or 115200. 8 data bits, no parity, 1 start, 1 stop.
• Clock: Year, Month, Day, Hour, Minute. Accuracy of ±3 minutes per month.
• Power Requirements: 4 "AA" alkaline, NiMH, lithium Batteries.
• Battery Life:
  • 140 hours based on 4 "AA" alkaline batteries without optical sensor attached
  • 80 hours based on 4 "AA" alkaline batteries with optical sensor
• Low Battery Warning: Display indicates when battery power is <15%.
• Size: 20.9 x 9.8 x 3.5 cm (8.2" x 3.9" x 1.4").
• Weight: 0.454 kg (1.0 lb) with batteries.

LAI-2250 Optical Sensor:

• Sensor Inputs: 1 6-pin Bulkhead connector for control unit interface.
• Memory:
  • 1 MB flash memory for record storage.
  • 1 KB EEPROM for calibration and configuration storage.
• Keypad: 2 button, tactile response keypad.
• Clock: Year, Month, Day, Hour, Minute. ± 3 minutes per month. Can be synced with control unit clock when joined with a data cable.
• Power Requirements: 2 "AA" (alkaline, NiMH, lithium) Batteries.
• Battery Life: 180 hours of typical operation (based on 2 "AA" alkaline batteries).
• Optics: 1.00° maximum decentering error as measured from center of mass of ring 4. 0.50° maximum magnification error as measured from the center of mass of ring 4.
• Radiation Rejection:
  • > 99% from 490-650 nm;
  • > 99.9% above 650 nm.
• Wavelength Range: 320-490 nm.
• Nominal Angular Coverage:
• Ring 1: 0.0-12.3°
• Ring 2: 16.7-28.6°
• Ring 3: 32.4-43.4°
• Ring 4: 47.3-58.1°
• Ring 5: 62.3-74.1°
• Lens Coating: MgF2 for improved transmission at oblique angles (external and internal lenses).
• View Caps: Provide azimuthal masking of view into quadrants of 10°, 45°, 90°, 180°, and 270°.
• Size: 63.8 L x 2.9 W x 2.9 D cm (25.1" x 1.125" x 1.125") (Endcap: 4.4 W x 5.1 D cm; 1.75" x 2.0").
• Weight: 0.845 kg (1.86 lbs) with batteries.

Environmental Conditions:

• Operating Temperature Range: -20 to 50° C.
• Humidity Range: 0 – 95% RH (non-condensing conditions).
• Storage: -40 to 65 °C.

LAI-2200 Plant Canopy Analyzer

Frequently Asked Questions

*Note with the exception of the first three questions all references made with LAI-2200 can be substituted with the LAI-2000 as well and vice versa.

Q What is the advantage of using the LAI-2200 vs. the LAI-2000?

A If the measurements are done correctly the LAI-2200 and LAI-2000 give the same results. Aside from the new features of the LAI-2200 such as USB connect, increased memory, lighter weight ergonomic design, and a new menu driven software the biggest advantage of the LAI-2200 over the LAI-2000 is the ability to use the optical sensor autonomously. The new LAI-2250 optical sensor can log both above and below readings without the console. This is especially advantageous in tall canopy setting where you need an additional optical sensor to acquire instantaneous A reading to coincide with the B readings.

Q What is the advantage of the LAI-2200TC Tall Canopy Package?

A The LAI-2200TC Tall Canopy Package gives you two optical sensors and one console. Since the optical sensor can log data autonomously you can set up automatic logging for your above canopy A readings without the console while obtaining your B readings simultaneously. The files can be merged later to compute LAI and other canopy parameters. The “Tall Canopy Package” is designed to save people money who would otherwise need two LAI-2200’s to do the work.

Q Can I use the new LAI-2250 Optical Sensor with my current LAI-2000?

A Although we use the same optical assembly head the technology gap between the LAI-2000 and LAI-2200 is different enough that the two systems cannot be interchanged.

Q What types of canopies can I measure with the LAI-2200?

A The LAI-2200 allows you to measure the LAI from crops, grasslands, forests, hedges, and isolated trees.

Q How does the LAI-2200 measure Gap Fraction?

A The LAI-2200 measures Gap Fraction at multiple zenith angles with a single, quick measurement. In contrast with ceptometers and linear sensors, there is no need to wait for the sun angle to change or make multiple measurements to acquire this data.

Q I have a line quantum sensor that I was going to use to measure LAI. What advantages does the LAI-2200 offer?

A Measurements with the LAI-2200 will be much quicker than with a line quantum sensor. A typical measurement with the LAI-2200 takes less than one minute for a short canopy. The line sensor technique relies on direct solar radiation and necessitates waiting for the sun angle to change in order to determine canopy interceptance at several angles. Or, if you assume an extinction coefficient (leaf angle distribution), a line quantum sensor can be used at one angle. The LAI-2200 looks at 5 angles simultaneously for each measurement.

The sample size when using the line sensor technique is limited, since the sensor only samples the portion of the canopy that lies between the sun and the sensor. With its fisheye field-of-view, the LAI-2200 can see 360° (with no view cap). Lastly, the LAI-2200 calculates LAI immediately after the measurement, allowing on-site inspection and verification of the data.

Q How can it correctly measure leaf area if the sensor can’t see all the leaves, or if the leaves overlap?

A Leaf area is not calculated by viewing all the leaves. Rather, it is calculated from how much radiation is extinguished as it passes through the canopy. Random leaf positioning is assumed, implying a certain amount of leaf overlap. In fact, if a particular canopy had leaves positioned so that no leaf overlap were present, it would cause an error in the LAI-2200’s computed result, because radiation is extinguished faster than the ideal in this case.

Q How big a plot is necessary?

A A rough rule of thumb is that plot radius (distance from the sensor location) should be 3 times the plot height. However, in dense canopies less distance may be required, because the sensor may not be able to see that far through the canopy.

Q What if a plot isn’t that big?

A View caps can be used to prevent the sensor from seeing in a particular direction, allowing readings to be made near the edge of a plot, and reducing the total plot size necessary. Another remedy for small plots is to do the analysis neglecting the outer ring. The FV2200 software supports this.

Q How short can a canopy be and still get good measurements?

A There are several considerations when determining if a canopy is too small. First, does the presence of the sensor disturb the canopy? (Are new gaps created when the sensor is pushed in?) Second, the LAI-2200 assumes the foliage elements are small compared to the area of view of each ring. In general, the distance from the optical sensor to the nearest foliage at an angle of 30° should be at least 4 times the leaf width.

Q Will the LAI-2000/2200 work in coniferous forests?

A Work by Gower and Norman (1990) indicates that the LAI-2000/2200 can be successfully used in forest settings. In conifer stands, they found that the LAI-2000/2200 underestimated LAI by 35-40%, apparently due to the fact that the instrument is sensing projected area of shoots, rather than needles. They further found that a correction factor, which is based solely on shoot morphology and can be independently measured, appears to adequately compensate for this. Their suggested technique is to determine the ratio of projected shoot area to total needle area for the particular species being measured, and then multiply the results by this ratio.

Q Can the LAI-2200 differentiate between species - weeds and corn, for example?

A No. It only responds to objects (foliage, etc.) that block the transmission of radiation.

Q Will the LAI-2200 detect insect defoliation?

A Yes, but measurements should be made in the exact same places each time to remove spatial variability from the results.

Q Can I measure a single plant?

A Yes, assuming that the plant is isolated enough and that the leaves are small enough.

Q At the location where my research is conducted, it is almost never cloudy. Can I still take accurate measurements with the LAI-2200?

A Sunlit foliage will cause the LAI-2200 to underestimate LAI. To make measurements under these conditions, two techniques should be used. First, a view cap should be used to mask the portion of the sky that contains the sun. Second, the canopy should be shaded as much as possible within the sensor's field of view. Measurements could be taken at dawn or dusk when the sun is near the horizon which minimizes the sunlit leaf area seen by the sensor. When the sun is low in the sky, it is much easier to shade the canopy.

Q Can I measure canopy PAR absorption with the LAI-2200?

A Not directly. The LAI-2200 is designed to measure foliage structure, which is only one of several factors determining absorption. Also, the spectral range of the sensor does not correspond to the PAR region, so it should not be used as a PAR sensor. The diffuse non-interceptance value (DIFN) calculated by the LAI-2200 is a direct estimate of how much diffuse sky radiation gets through the canopy, and (1 - DIFN) would be the absorbed sky radiation; but all this assumes that the foliage does not scatter radiation. Also, this neglects what happens to direct beam radiation, which is a function of solar position. The direct beam absorption could be inferred, perhaps, from the mean gap fraction measurements at the five zenith angles based on diffuse radiation, but this would still neglect the contribution of scattered radiation. Another approach is to model canopy absorption based on the canopy structure (as measured with the LAI-2200), the foliage reflectance and transmittance, the reflectance of the ground, and measurements of incident total PAR and the fraction thereof that is direct beam.

Q What is Mean Tip Angle (MTA) good for?

A Gap fraction data at different angles potentially hold two types of information: amount of leaf area and leaf orientation distribution. See Perry et al (1988) for a discussion of how much information can be reliably extracted from gap fraction data. The LAI-2200 calculates MTA as a measure of how the leaves are oriented.

Q I've never heard of this "indirect" way to measure LAI. Has the model and the LAI-2000/2200 be thoroughly tested?

A Methods of inverting gap fraction data to get canopy structure have been used for many years. During the development of the LAI-2000/2200, there were a number of verification studies, as described in the work by Welles and Norman (1990) and in an application note available from LI-COR. Verification work started in summer 1988 and has continued on since then. A wide variety of canopies were used in the verification research, ranging in size from forests to prairie grass. The LAI-2000/2200 data was compared to data from other indirect measurement techniques (fisheye photograph analysis, etc.), and to data from canopies which were harvested (100%) and measured with an electronic area meter.

Q How does the LAI-2200 method compare with other indirect methods?

A Other gap fraction methods of determining canopy structure include point quadrats (Warren Wilson and Reeve 1959), high-contrast fisheye photography (Anderson 1970, Bonhomme and Chartier 1972), traversing a light sensor beneath a canopy (Norman et al 1979, Lang et al 1985, Perry et al 1988), and using a linear light sensor (Walker et al 1988). The LAI-2000 method is closest to fisheye photography. The LAI-2200 has the advantage over photography of immediate on-site analysis, but the disadvantage of not having a picture (permanent record) on which to do a number of other types of analyses. The point quadrat technique is only suited to small canopies. The remaining techniques involve using the sun as a canopy probe. The obvious disadvantages are two: the sun must be out, and one must wait for the sun to move to get data at various angles. The LAI-2200 gets all the angle data at once, and does not require the sun to be out. (In fact, it is best if the sun is not out). On the other hand, the LAI-2200 requires an above canopy reference reading, whereas techniques that use the sun do not. LAI can be deduced from measurements of light attenuation at only one solar angle, using an integrating radiometer (Pierce and Running 1988). However, canopy extinction (that is, leaf angle distribution) must be assumed beforehand, and is not deduced from the measurement. An above canopy reference reading is also required.

Q Can I use a LAI-2250 Optical Sensor with a general purpose data logger?

A No. The complexity of the LAI-2250, and the unique data reduction software make it very difficult, if not impossible.

References

Bonhomme, R. and Chartier, P. (1972). The interpretation and automatic measurement of hemispherical photographs to obtain sunlit foliage area and gap frequency. Isr. J. Agric. Res. 22:53-61.

Gower, S.T., and Norman, J.M. (1990). Rapid estimation of leaf area index in forests using the LI-COR LAI-2000. Ecology, 72(5) 1896-1900.

Lang, A.R.G., Xiang, Y., and Norman, J.M. (1985). Crop structure and the penetration of direct sunlight. Agric. & For. Meteor. (35) 83-101.

Perry, S.G., Fraser, A.B., Thomson, D.W., and Norman, J.M. (1988). Indirect sensing of plant canopy structure with simple radiation measurements. Agric. and For. Meteor. (42) 255-278.

Pierce, L.L. and Running, S.W. 1988. Rapid estimation of coniferous forest leaf area index using a portable integrating radiometer. Ecology 69(6) 1762-1767.

Walker, G.K., Blackshaw, R.E., and Dekker, J. (1988). Leaf area and competition for light between plant species using direct sunlight transmission. Weed Technology (2) 159-165.

Warren Wilson, J., and Reeve, J.E. 1959. Analysis of the spatial distribution of foliage by two-dimensional point quadrats. New Phytol. (58) 92-101.

Welles, J.M. (1990). Some indirect methods of estimating canopy structure. In: Instrumentation for Studying Vegetation Canopy for Remote Sensing in Optical and Thermal Regions. (eds. N.S. Goel and J.M. Norman). Remote Sensing Reviews. 5(1) pp. 31-43.

Welles, J.M. and Norman, J.M. (1990). An instrument for indirect measurement of canopy architecture. Agronomy J., 83:818-825.

Ordering Information

LAI-2200 Plant Canopy Analyzer:

Includes one LAI-2250 Optical Sensor with data cable, LAI-2270 Control Unit, carrying case, RS-232 cable, USB cable, view-restrictors, 6 "AA" batteries, belt clip, and Windows FV2200 software.

LAI-2200TC Plant Canopy Analyzer – Tall Canopy Package:

Two LAI-2250 Optical Sensors with data cables, one LAI-2270 Control Unit, carrying case, RS-232 cable, USB cable, view-restrictors, 8 "AA" batteries, belt clip, and Windows FV2200 software.

LAI-2250 Optical Sensor:

For use with the LAI-2200 in Autonomous mode. Additional sensor can take above readings independently of the control unit. Includes 2 "AA" batteries, view restrictors, and data cable.

LAI-2270 Control Unit:

For use with the LAI-2250 Optical Sensor(s). Includes carrying case, RS-232 cable, USB cable, 4 "AA" batteries, belt clip, and Windows FV2200 software.