CIVL 334: Introduction to Remote Sensing

• CIVL 334 is a Remote Sensing course.

Course Outcomes

• Understand the basic concepts, history, and applications of Remote Sensing.
• Classify different types of satellite platforms, orbits, and sensors.
• Explain the electromagnetic spectrum, image resolutions, spectral signatures, atmospheric windows, and aerial photography.
• Analyze aerial photographs, calculate image scale and relief displacement.
• Analyze GIS data, map projections, datums, coordinate systems, and image enhancement.
• Learning needs should be identified and initiate responses to those needs.

Introduction to Remote Sensing

• Remote sensing acquires information about an object or phenomenon without direct contact.

Steps of Remote Sensing

• Remote sensing can be described as gathering data or information from a distance.

Remote Sensing Process: 7 Steps

• Energy Source (A): The first requirement, remote sensing needs an energy source that illuminates or provides electromagnetic energy to the target
• Radiation and Atmosphere (B): As the energy travels from its source to the target, interaction with the atmosphere occurs.
• Interaction with the Target (C): This step involves the interaction of energy with the target, depending on the properties of both the target and radiation.
• Recording of Energy by the Sensor (D): A sensor (not in contact with the target) is required to collect and record the electromagnetic radiation scattered or emitted from the target.
• Transmission, Reception, and Processing (E): The energy recorded by the sensor is transmitted, often in electronic form, to a receiving and processing station where the data is processed into an image (hard copy & digital).
• Interpretation and Analysis (F): The processed image is interpreted visually and digitally to extract information about the target.
• Application (G): The final step is applying the information extracted from the imagery to better understand the target and reveal new information.

Components of Remote Sensing

• Platforms
• Sensors
• Orbits

Remote Sensing Platforms

• Ground-based platforms
• Airborne platforms
• Spaceborne platforms

Ground-Based Platforms

• Used to record detailed information about the surface very closely.
• Examples include ground vehicles, towers, air balloons, and kites.
• Typically located up to 50 m above the Earth's surface.

Airborne Platforms

• Collect detailed images and facilitate data collection over any part of Earth's surface at any time.
• More expensive compared to ground-based platforms.
• Examples include aeroplanes, high-altitude aircraft, and helicopters.
• The height of airborne platforms are above 50 km from earth surface

Spaceborne Platforms

• Examples include rocket satellite space shuttles (250 to 300 km above Earth's surface), space stations (300 to 400 km), low-level satellites (700 to 1500 km, also known as polar satellites), and high-level satellites (36,000 km, also known as geostationary satellites).
• Satellites are objects that revolve around another object (e.g., Earth).

Sensors

• A device that measures properties like temperature, pressure, light, or motion.
• Converts these measurements into signals for monitoring or control in remote sensing, automation, healthcare, and other sectors.

Types of Sensors

• Passive Sensors: Detect naturally reflected or emitted radiation; examples include optical sensors and thermal sensors.
• Active Sensors: Emit own energy and measure the reflected response; LiDAR and Synthetic Aperture Radar (SAR) are examples.
• The human eye is a passive sensor.

Passive Sensors

• Detect natural energy (radiation) emitted or reflected by the object or scene being observed.
• Reflected sunlight is the most common source of radiation.
• Examples include: Landsat, MODIS, Aster, and Other imagery sources
• Can be on satellites, manned and unmanned (UAS) aircraft, and some on vehicles on the ground.
• Rely on the sun as the "energy source".

Active Sensors

• Transmit their own signal and measure the energy that is reflected, transmitted, or scattered back from the target.
• Radar and sonar are examples.
• "Energy source is 'provided'".
• Lidar - Light Detection and Ranging using pulsed laser beam (of varying wavelengths)
• SAR – Synthetic Aperture Radar – pulses of radio waves

Orbits

• An orbit is the curved path of an object around a planet, star, or celestial body due to gravity, e.g. satellites orbiting Earth and planets around the Sun.
• Geostationary Orbit
• Polar Orbit
• Sun-Synchronous Orbit

Geostationary Orbits

• Satellites have geostationary orbits at very high altitudes, to view the same part of the Earth's surface.
• Geostationary satellites are at altitudes of approximately 36,000 kilometers.
• These satellites revolve at the same speed as the Earth's rotation, so they appear stationary relative to the Earth's surface.

Polar Orbit

• A polar orbit travels north-south over the poles and takes approximately an hour and a half for a full rotation.
• A satellite can observe the entire Earth's surface in the time span of 24 hours.
• Almost all the satellites that are in a polar orbit are at lower altitudes and often used for applications such as monitoring crops, forests and even global security.

Sun-Synchronous Orbit

• Allows a satellite to pass over a section of the Earth.
• Since there are 365 days in a year and 360 degrees in a circle, it means that the satellite has to shift its orbit by approximately one degree per day.
• These satellites orbit at an altitude between 700 to 2800 km.

Satellites

• A satellite orbits a planet or star, and can be natural (like the Moon) or artificial (like communication or weather satellites).

Types of Satellites Categorized By Orbits

• Geostationary Satellites: Remain fixed over a specific location and useful for weather monitoring (e.g., GOES).
• Polar-Orbiting Satellites: Move over the Earth's poles and capturing global imagery (e.g., Landsat, Sentinel-2).
• Sun-Synchronous Satellites: Cross the same location at a consistent solar time, ensuring uniform lighting conditions (e.g., MODIS, SPOT).

Terminology

• Path or Ground Track: The portion of the Earth's surface traced by a satellite as it moves across the sky.
• Swath: The total width of area on the ground track covered by a satellite sensor is called Swath or Field of view (FOV).
• Row: The latitudinal centerline of a frame of imagery at the time that a satellite scanner is observing.
• Repeat Cycle: The time gap of a satellite repeats its path after a fixed time.
• Nadir Point: An imaginary point directly beneath a satellite scanner.
• Nadir Line: An imaginary line along the nadir point on the ground track.

Understand remote sensing concepts, its history, and applications. Learn about satellite platforms, orbits, and sensors. Explore the electromagnetic spectrum, image resolutions, and aerial photography. Analyze GIS data and image enhancement techniques.