SunScan [Professional]
Introduction
Rapid and reliable estimates of leaf area index (LAI) are important for studies of exchanges of energy and gases in the biosphere-atmosphere continuum. In this case evaluated the field performance of SunScan canopy analysis system for rapid estimation of LAI. Direct and indirect measurements of LAI were made in a maize (Zea mays L.) field at four phenological stages (emergence, vegetative, flowering and physiological maturity). The result showed a generally good performance of this sensor at all the phenological stages, so the evaluated sensor yielded a good and reliable LAI estimates under maize canopy.[1]
Figure 1: Sunscan canopy analysis system.[2]
The SunScan plant canopy analyzer probe consists of 64 PAR Sensors embedded in a 1 m long probe. Whenever a reading is taken, all sensors are scanned and the measurements sent to a hand-held PDA, type RPDA3, via an RS232 interface. The average PAR level from the Probe is read, but all 64 individual readings can be stored for more complete PAR mapping, or making linear transects. Automatic logging can be selected to obtain readings over a period of time at a fixed point. If connected to a data logger the Probe can function as a Linear Quantum Sensor (also known as a line quantum sensor).
The RPDA3 is an exceptionally robust handheld PDA which collects and analyses readings from the SunScan Probe. Raw readings, and derived functions such as LAI, can be displayed, reviewed and stored in the field by the SunData Software; groups of readings can be averaged if required. Readings are stored in the internal memory which holds > 1 million readings, or in widely available micro SD cards which provide removable data storage. Collected data can be transferred easily to a PC.
The SunScan’s unique feature is an optional reference sensor, integrated into the design, to measure simultaneously the direct and diffuse light above the canopy. The BF5 Sunshine Sensor provides these above-canopy reference measurements quickly and conveniently. The BF5 uses an array of photodiodes and a unique shading pattern to calculate whether the sun is shining and to measure the direct and diffuse components of solar radiation. This completely avoids the need for troublesome shade ring adjustments required with conventional diffuse light sensors.
An optional radio link connects the SunScan Probe and the BF5 reference sensor, removing the need for long connecting cables. The link operates over the 434 MHz licence-free frequency and can transmit up to 250 m line-of-sight or 100 m to 200 m in vegetation.
A 2009 paper in the Crop Science journal compared the use of SunScan canopy analyser and LAI-2000 systems for estimating LAI on upland rice grown in Benin. The authors found that the SunScan canopy analyser provided a highly significant measurement of LAI up to 4 m2.m-2 compared to destructive sampling (slope of regression line = 1.00, R2 = 0.96) and in summary concluded that the SunScan can be used to estimate LAI of different upland rice cultivars with various types of canopy development. Comparison of Three Methods for Estimating Leaf Area Index of Upland Rice Cultivars. Crop Sci. 49:1438-1443.
SunScan is ideal for analysing and characterising low regular canopies such as crops. However, for forest and woodland canopies, the Delta-T HemiView system is the correct choice.
References
[1] Philip Gbenro Oguntunde, olawale J. Olukunle, Johnson T. Fasinmirin, Oluremi A. Abiolu (2012) Performance of the SunScan canopy analysis system in estimating leaf area index of maize
[2] Sunscan