Active Microwave and LIDAR. Three models for remote sensing 1. Passive-Reflective: Sensors that rely on EM energy emitted by the sun to illuminate the.

Active Microwave and Active Microwave and LIDARLIDAR

Three models for remote sensingThree models for remote sensing 1. 1. Passive-ReflectivePassive-Reflective: Sensors that rely on EM : Sensors that rely on EM

energy emitted by the sun to illuminate the target. energy emitted by the sun to illuminate the target. The sensor measures the amount of energy that is The sensor measures the amount of energy that is reflected reflected from the target. Used for wavelengths of from the target. Used for wavelengths of about 0.4-3.0 μm. about 0.4-3.0 μm. Most of our work this quarter Most of our work this quarter will focus on the use of this model.will focus on the use of this model. We will We will spend some time discussing two other models… spend some time discussing two other models…

Three models for remote sensingThree models for remote sensing 2. 2. Passive-EmittedPassive-Emitted:: The sun still serves as the The sun still serves as the

source of illumination (hence, still a passive source of illumination (hence, still a passive system). The sensors measure the amount of EM system). The sensors measure the amount of EM energy energy emittedemitted from the target in the thermal or from the target in the thermal or emissive portion of the spectrum. These systems emissive portion of the spectrum. These systems are intended to determine something about the are intended to determine something about the thermal properties of the target. Used for thermal properties of the target. Used for wavelengths of about 3.0-30 wavelengths of about 3.0-30 μmμm

Three models for remote sensingThree models for remote sensing 3. 3. ActiveActive:: These systems do not rely on solar These systems do not rely on solar

radiation to illuminate the target. The system radiation to illuminate the target. The system emits EM energy and then records the amount of emits EM energy and then records the amount of this energy that is reflected from the target. this energy that is reflected from the target. These systems operate in parts of the spectrum These systems operate in parts of the spectrum where emissions from the sun are minimal where emissions from the sun are minimal (longer wavelengths; microwave, radar). Usually (longer wavelengths; microwave, radar). Usually for wavelengths of about 1cm-1m; some for wavelengths of about 1cm-1m; some applications (LIDAR) at about 1 applications (LIDAR) at about 1 μmμm

Active SystemsActive Systems

Active Microwave: wavelengths of about 1mm to Active Microwave: wavelengths of about 1mm to 1m; RADAR (1m; RADAR (RaRadio dio DDetection etection aand nd RRanginganging• Capable of obtaining imagery day and night Capable of obtaining imagery day and night

and can penetrate cloudsand can penetrate clouds• Certain wavelengths can penetrate some types Certain wavelengths can penetrate some types

of vegetationof vegetation• Long wavelengths can penetrate dry soil (or Long wavelengths can penetrate dry soil (or

sand) several meters to reveal subsurface sand) several meters to reveal subsurface featuresfeatures

• Not as widely used as optical systemsNot as widely used as optical systems LIDAR: (LIDAR: (LiLight ght DDetection etection aand nd RRanging) anging)

wavelengths of about 1 µm; sometimes called wavelengths of about 1 µm; sometimes called LADAR (LADAR (LaLaser ser DDetection etection aand nd RRanging) anging) • Gaining widespread use in recent yearsGaining widespread use in recent years

LIDARLIDAR Pulses of energy (usually at about 1 µm) Pulses of energy (usually at about 1 µm)

emitted from a laser, energy is reflected emitted from a laser, energy is reflected from the ground back to the sensor, travel from the ground back to the sensor, travel time for the signal is used to measure time for the signal is used to measure distance from sensor to the ground featuredistance from sensor to the ground feature

Inertial measurement unit (IMU) and GPS Inertial measurement unit (IMU) and GPS are critical for accurately locating ground are critical for accurately locating ground footprint of laser pulsesfootprint of laser pulses

Your text mentions Your text mentions continuous wave laserscontinuous wave lasers and and pulsed laser.pulsed laser. My discussion will My discussion will focus on use of the pulsed laser.focus on use of the pulsed laser.

LIDAR: Laser AltimeterLIDAR: Laser Altimeter First applications of LIDAR were to provide height First applications of LIDAR were to provide height

above the ground for aircraftabove the ground for aircraft Extension of this idea and improved aircraft Extension of this idea and improved aircraft

navigation tools (IMU and GPS) made it possible navigation tools (IMU and GPS) made it possible to generate topographic mapsto generate topographic maps

Use of laser footprints of about 10m over forests Use of laser footprints of about 10m over forests revealed revealed multiple returns – several “heights.” multiple returns – several “heights.” Why?Why?

Laser energy reflecting off different layers in the Laser energy reflecting off different layers in the canopy; canopy; potential to obtain data about the potential to obtain data about the vertical distribution of biomass in a forest vertical distribution of biomass in a forest canopy!canopy!

Airborne LIDARAirborne LIDAR

Ground footprint: 0.5m (or less) to Ground footprint: 0.5m (or less) to 10m10m

Ground spacing of pulses: variable, Ground spacing of pulses: variable, generally 3-5m, sometimes <1mgenerally 3-5m, sometimes <1m

Horizontal and vertical accuracy in Horizontal and vertical accuracy in the range of 0.5m or lessthe range of 0.5m or less

Waveform Recording vs. Discrete-return LIDARWaveform Recording vs. Discrete-return LIDAR

Lefsky et al., Fig 1

Canopy heightCanopy height

Lefsky et al., Fig 2

Lefsky et al., Fig 3

Synthetic Synthetic Waveform Waveform created from created from discrete-discrete-return datareturn data

Lefsky et al., Fig 4

Beach Erosion ApplicationBeach Erosion Application

Lefsky et al., Fig 5

Beach profile before and after a major storm