Active Microwave and LIDAR. Three models for remote sensing.
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1. Passive-Reflective: Sensors that rely on EM energy emitted by the sun to illuminate the target. The sensor measures the amount of energy that is reflected from the target. Used for wavelengths of about 0.4-3.0 μm. Most of our work this quarter will focus on the use of this model. We will spend some time discussing two other models…
2. Passive-Emitted: The sun still serves as the source of illumination (hence, still a passive system). The sensors measure the amount of EM energy emitted from the target in the thermal or emissive portion of the spectrum. These systems are intended to determine something about the thermal properties of the target. Used for wavelengths of about 3.0-30 μm
3. Active: These systems do not rely on solar radiation to illuminate the target. The system emits EM energy and then records the amount of this energy that is reflected from the target. These systems operate in parts of the spectrum where emissions from the sun are minimal (longer wavelengths; microwave, radar). Usually for wavelengths of about 1cm-1m; some applications (LIDAR) at about 1 μm
Pulses of energy (usually at about 1 µm) emitted from a laser, energy is reflected from the ground back to the sensor, travel time for the signal is used to measure distance from sensor to the ground feature
Inertial measurement unit (IMU) and GPS are critical for accurately locating ground footprint of laser pulses
Your text mentions continuous wave lasers and pulsed laser. My discussion will focus on use of the pulsed laser.