In-Depth Notes on Remote Sensing in Geotechnical Engineering

Remote sensing is the process of acquiring information about the Earth's surface without direct contact.
Involves sensing and recording energy emitted or reflected from earth's surface, and processing that data.

A. Energy Source/Illumination: An energy source provides electromagnetic energy to the target.
B. Radiation and the Atmosphere: Energy interacts with the atmosphere during its path to the target.
C. Interaction with the Target: Energy interacts with the target based on the properties of both.
D. Recording of Energy: A sensor collects and records the energy.
E. Transmission, Reception, and Processing: The recorded energy is transmitted for processing into an image.
F. Interpretation and Analysis: The processed image is interpreted to extract information.
G. Application: The extracted information is used to solve problems or enhance understanding.

Remote sensing techniques utilize electromagnetic radiation which has properties governed by wave theory.
Composed of an electric field (E) and a magnetic field (M), both traveling at the speed of light (c).
Key Characteristics:
- Wavelength (λ): Distance between successive wave crests, measured in meters (m) or derivatives (nm, μm, etc.).
- Frequency (v): Number of cycles per second, measured in Hz. Related by the formula: c = rac{λ}{v}

UV Radiation: Shortest wavelengths, interacts with surface materials (rocks/minerals).
Visible Wavelengths: Ranges from approximately 0.4 to 0.7 μm.
Infrared:
- Reflected IR: 0.7 μm to 3.0 μm, similar applications as visible radiation.
- Thermal IR: 3.0 μm to 100 μm, emitted as heat from Earth's surface.
Microwave: 1 mm to 1 m, longest wavelengths for remote sensing.

Passive Sensors: Measure naturally available energy (like sunlight); limited use to daytime.
Active Sensors: Provide their own energy; can operate anytime regardless of natural light conditions.

Images: Any pictorial representation from remote sensing regardless of wavelength/device.
Photographs: Specifically images recorded on photographic film, usually within the visible range (0.3 - 0.9 μm).
The digital representation of images involves pixels which display brightness/color values from different channels (RGB).

Terrain mapping, baseline infrastructure, geologic mapping, structural mapping, geohazard mapping, soil moisture estimation, change detection, flood mapping, land cover and land use analysis.

LiDAR: Measures the time for light pulses to return to the sensor to create 3D maps.
Radar Interferometry: Measures changes in topography using radar signals.
Photogrammetry: Involves measurements from photographs, producing maps/drawings/models.

Based on light travel time, calculates distance:
d = rac{c imes t}{2}
where d is distance, c is the speed of light, and t is time taken for light to return.
Used on various platforms: ground-based, airborne (planes/UAVs), and satellite.

Ground-based LiDAR: Offers high-density point clouds for detailed structures.
Airborne LiDAR: Covers larger areas but tends to have less dense data collection; relies on GPS positioning for accuracy.

Uses electromagnetic pulses to detect object distance through time delay calculations: R = rac{c imes t}{2}
Synthetic Aperture Radar (SAR) uses movement to mimic a larger antenna.
Interferometry techniques measure phase differences for monitoring displacement:
d = rac{λ}{4 ext{π}} imes ∆φ

Elevation models, structural mapping can be generated by photographing from various angles.
Relies on light, cannot penetrate vegetation unlike LiDAR. Digital cameras have advantages over classical film-based systems.

Accessible data acquisition from remote areas, quick image creation, high density information capture, less disruption caused in work environments.

No direct sampling, corrections for atmospheric and shadowing effects are complex, and interpretation may require calibration against direct observations.

Airborne LiDAR for Rock Fall Simulations: Used to analyze terrains and simulate rock fall hazards along railways in Canada.
Terrestrial LiDAR for Landslide Monitoring: Provides high-resolution elevation models over time to detect slope deformations.
Satellite InSAR for Landslide Activity: Continuous monitoring of landslide movements within key transport corridors.

Natural Resources Canada (2014) fundamentals on remote sensing; international and local case studies on applied remote sensing in geotechnical contexts.