Leaf Area Index: Advances in Ground-Based Measurement

Leaf area index (LAI) is a primary parameter for vegetation structure and is one of the important products from remote sensing data. Ground-based LAI estimation of LAI is the important activity for global satellite product validation. In this chapter, the main methods on LAI measurement were reviewed, and the emphasis was put on the new advanced method on LAI measurement. We present two new instruments (LAINet and LAISmart) designed by Beijing Normal University which use either modern communication network or mobile computing platform to obtain LAI with high efficiency and low cost. LAINet is an instrument constructed on the base of wireless sensor network, and the principle of LAINet is capturing sunlight transmittance using a series of wireless sensors in different sun zenith angles. And LAI is estimated from the sensed transmittances. Borrowing the wireless communication technique, the measured data can be transferred to remote computer server, thus, LAINet can reduce the cost of field data collection. LAISmart is a mobile application deployed on the smartphone, and the LAI is calculated by the classification of captured image. By integration of capturing images and real time computing of smartphone, LAISmart provide automatic measurement method compared with the traditional digital hemispherical photography method. In the end of this chapter, the prospect of the methods on the LAI ground-based measurement is summarized, and it is pointed out that the integration of passive and active optical signal to produce low cost and light weight and thus affordable and portable device may be a promising tendency.