Overview of remote sensing, including its definition, history, principles, and the role it plays in various fields such as environmental monitoring, agriculture, urban planning, and disaster management.
Introduction to Remote Sensing
Key concepts, components, and applications
1. What Is Remote Sensing?
- Definition – Acquisition of information about an object or area from a distance, typically using sensors mounted on aircraft or satellites.
- Core Idea – Detect and record electromagnetic energy (or other signals) reflected, emitted, or scattered by the Earth's surface and atmosphere.
2. Electromagnetic Spectrum (EMS) Basics
| Region |
Wavelength (nm) |
Typical Uses in Remote Sensing |
| Ultraviolet (UV) |
10–400 |
Atmospheric ozone monitoring, water quality |
| Visible (VIS) |
400–700 |
True‑color imagery, vegetation health |
| Near‑Infrared (NIR) |
700–1300 |
Plant vigor, water content |
| Short‑Wave Infrared (SWIR) |
1300–3000 |
Soil mineralogy, fire detection |
| Thermal Infrared (TIR) |
3–14 µm |
Surface temperature, heat flux |
| Microwave (Microwaves & Radar) |
1 mm–1 m |
Soil moisture, cloud‑penetrating imaging |
- Energy interaction types – Reflection, absorption, emission, and scattering.
3. Types of Remote Sensing Systems
| Category |
Platform |
Sensor |
Data Characteristics |
| Passive |
Satellites (e.g., Landsat, Sentinel‑2), aircraft |
Optical radiometers, spectrometers |
Record natural energy (sunlight, thermal emission). |
| Active |
Satellites (e.g., Sentinel‑1), aircraft, drones |
Radar (SAR), LiDAR, sonar |
Emit own signal; work day/night & through clouds. |
| Spaceborne |
Orbiting satellites |
Wide swath, repeat coverage |
Global monitoring, long‑term datasets. |
| Airborne |
Planes, balloons, UAVs |
High spatial resolution, flexible timing |
Targeted studies, validation of satellite data. |
4. Sensor Characteristics
| Parameter |
What It Describes |
Why It Matters |
| Spatial Resolution |
Size of ground pixel (e.g., 10 m, 30 m) |
Determines detail that can be discerned. |
| Spectral Resolution |
Number & width of wavelength bands |
Influences ability to differentiate materials. |
| Radiometric Resolution |
Number of digital levels (e.g., 8‑bit = 256 levels) |
Affects detection of subtle differences in energy. |
| Temporal Resolution (Revisit Time) |
Frequency of observations over same area |
Critical for monitoring change (e.g., crop growth). |
| Swath Width |
Width of ground area captured in a single pass |
Impacts coverage speed and data volume. |
5. Data Acquisition Process
- Planning – Select platform, sensor, acquisition date, and area of interest.
- Sensor Capture – Energy is sensed and converted to digital numbers (DN).
- Transmission – Data downlinked to ground stations.
- Pre‑processing – Radiometric correction, geometric correction, and (if needed) atmospheric correction.
- Archiving & Distribution – Data stored in repositories (e.g., USGS EarthExplorer, Copernicus Open Access Hub).
6. Image Processing Workflow
- Radiometric Calibration – Convert DN →