Plant canopy analyzer（Image analysis）

I. Product Overview

The HD-G20 plant canopy image analyser is used for research on plant canopies at various heights. A fisheye lens and a CCD image sensor are used to acquire images of the plant canopy, and the relevant canopy indices and parameters are obtained with dedicated analysis software. Because the fisheye lens measures canopy data in a single operation, the laborious traditional practice of repeated fixed-point measurements throughout the day is no longer necessary; moreover, image-based canopy measurement can actively avoid canopy gaps that do not conform to the structural parameters being calculated, as well as obstacles that would disturb the measurement.

II. Measuring Principle and Method

The plant canopy image analyser is based on the relationship between canopy porosity and canopy structure. Following the Beer–Lambert law of light attenuation through a medium, and under a series of defined assumptions about the plant canopy, canopy structure parameters are calculated from measured canopy porosity using semi-theoretical, semi-empirical formulae. This principle is used by canopy instruments throughout the world. On this basis, the analyser measures canopy porosity by analysing hemispherical sky images taken beneath the canopy, which is the most accurate, the least labour-intensive, the fastest and the most convenient of all available methods.

III. System Composition

The analyser consists of a fisheye image capture probe (a fisheye lens with a CCD image sensor), a measuring rod (swing arm) with 25 built-in PAR sensors, a notebook computer, image acquisition software and image analysis software. The fisheye probe is mounted at the tip of a very light swing arm and acquires fisheye images with a 150° field of view. Images are displayed and stored on the supplied notebook computer.

IV. Key Features

1. The fisheye lens keeps itself horizontal automatically: the compact fisheye camera designed specifically for plant canopy structure measurement is mounted on a handheld universal balance joint, which keeps the lens horizontal without a tripod.

2. The fisheye lens can reach into the canopy: because the lens is compact and mounted at one end of the swing arm with the measuring rod, it can easily be extended horizontally forwards or vertically upwards to different heights within the canopy for rapid stratified measurement, giving the light transmittance within the stand and the vertical distribution of the leaf area index.

3. Image analysis software: the analysis area can be defined freely (the zenith angle can be divided into 10 zones and the azimuth angle into 10 zones).

4. Unreasonable canopy portions can be masked: when analysing different canopy directions region by region, ground features and unreasonable canopy portions (such as missing plants or edge rows) can be masked at will. Selecting different start and end angles of the zenith angle avoids canopy porosity conditions that do not conform to the canopy structure parameters being calculated, and manual threshold adjustment allows more accurate measurement of the leaf area index and other parameters. The software is compatible with Windows 10 and above only.

V. Measurable Indices

Leaf area index (LAI); mean tilt angle of leaves (MTA); sky diffuse light transmittance; direct radiation transmittance of the plant canopy at different solar elevation angles; extinction coefficient of the canopy at different solar elevation angles; azimuthal distribution of leaf area density.

VI. Technical Parameters