Passive (optical or thermal) Imaging Systems

• Relies on reflected sunlight or emitted thermal energy
• Unable to use through clouds, smoke or at night
• Vegetation response controlled by pigments, canopy structure & biomass

Active (microwave or radar) Imaging Systems

• Relies on a transmitter/sensor configuration
• Able to see through, clouds, smoke and at night
• Vegetation response controlled by water content, canopy structure & biomass