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 target. The sensor measures the amount of energy that is reflected from the target. Used for wavelengths of about μm. Most of remote sensing analyses use this approach. 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 μm. Most of remote sensing analyses use this approach.

Three models for remote sensing 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 μm 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 μm

Three models for remote sensing 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 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

Active Systems Active Microwave: wavelengths of about 1mm to 1m; RADAR (Radio Detection and Ranging Active Microwave: wavelengths of about 1mm to 1m; RADAR (Radio Detection and Ranging Capable of obtaining imagery day and night and can penetrate cloudsCapable of obtaining imagery day and night and can penetrate clouds Certain wavelengths can penetrate some types of vegetationCertain wavelengths can penetrate some types of vegetation Long wavelengths can penetrate dry soil (or sand) several meters to reveal subsurface featuresLong wavelengths can penetrate dry soil (or sand) several meters to reveal subsurface features Not as widely used as optical systemsNot as widely used as optical systems LIDAR: (Light Detection and Ranging) wavelengths of about 1 µm; sometimes called LADAR (Laser Detection and Ranging) LIDAR: (Light Detection and Ranging) wavelengths of about 1 µm; sometimes called LADAR (Laser Detection and Ranging) Gaining widespread use in recent yearsGaining widespread use in recent years

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

LIDAR: Laser Altimeter First applications of LIDAR were to provide height above the ground for aircraft First applications of LIDAR were to provide height above the ground for aircraft Extension of this idea and improved aircraft navigation tools (IMU and GPS) made it possible to generate topographic maps Extension of this idea and improved aircraft navigation tools (IMU and GPS) made it possible to generate topographic maps Use of laser footprints of about 10m over forests revealed multiple returns – several “heights.” Why? Use of laser footprints of about 10m over forests revealed multiple returns – several “heights.” Why? Laser energy reflecting off different layers in the canopy; potential to obtain data about the vertical distribution of biomass in a forest canopy! Laser energy reflecting off different layers in the canopy; potential to obtain data about the vertical distribution of biomass in a forest canopy!

Airborne LIDAR Ground footprint: 0.5m (or less) to 10m Ground footprint: 0.5m (or less) to 10m Ground spacing of pulses: variable, generally 3-5m, sometimes <1m Ground spacing of pulses: variable, generally 3-5m, sometimes <1m Horizontal and vertical accuracy in the range of 0.5m or less Horizontal and vertical accuracy in the range of 0.5m or less

Waveform Recording vs. Discrete-return LIDAR Lefsky et al., Fig 1

Canopy height Lefsky et al., Fig 2

Lefsky et al., Fig 3 Young Mature Old Growth

Synthetic Waveform created from discrete- return data Synthetic Waveform created from discrete- return data Lefsky et al., Fig 4

Beach Erosion Application Lefsky et al., Fig 5 Beach profile before and after a major storm

North Fork Nooksack: LIDAR First Return Shaded Relief

North Fork Nooksack: LIDAR Bare Earth Shaded Relief

Previously unknown Geologic fault line

North Fork Nooksack: LIDAR Canopy Height: 1 st rtn. – last rtn.

Modeling forest canopy structure using LIDAR data

ICESat Launched January 2003 Launched January 2003 Carries the Geoscience Laser Altimeter system (GLAS); first spaceborne laser ranging instrument for earth observation Carries the Geoscience Laser Altimeter system (GLAS); first spaceborne laser ranging instrument for earth observation Laser emits pulses at um and um Laser emits pulses at um and um Ground footprint 70m in diameter spaced 170m intervals Ground footprint 70m in diameter spaced 170m intervals Near polar orbit Near polar orbit

ICESat Applications