Apogee Instruments S2-412 Manuale d'uso - Pagina 4

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INTRODUCTION

Radiation reflected from surfaces (e.g., plant canopies, soil) provides information about the state of the surface.

Reflectance is the ratio of radiation reflected by the surface to radiation incident on the surface.

A common index calculated from reflectance measurements is normalized difference vegetation index (NDVI).

NDVI is calculated from red and near infrared (NIR) reflectance and provides a measure of surface greenness.

The typical application of NDVI sensors is monitoring plant canopies. NDVI is related to leaf area of the plant

canopy and canopy chlorophyll content of leaves and is often used to monitor green up in the spring and

senescence in the fall.

Apogee Instruments S2 series two-band sensors consist of a cast acrylic diffuser (upward-looking sensor) or acrylic

window (downward-looking sensor), pair of photodiodes that measure specific wavelength ranges, and signal

processing circuitry mounted in an anodized aluminum housing. A cable to connect the sensor to a measurement

device is also included. S2 series sensors are designed for continuous irradiance (upward-looking sensor) or

radiance (downward-looking sensor) measurements in indoor and outdoor environments. Reflectance derived

from paired upward-looking and downward-looking sensors can be used to calculate NDVI. Apogee NDVI sensors

are offered with digital SDI-12 output (this manual) or with analog voltage output.