Remote Sensing Types

Active - Passive - Microwave

Active Remote Sensing

Remote Sensing Acquires Information Without Physical Contact

Radars and lidars are the most epic examples of active remote sensing

The earth’s surface and the atmosphere both reflect back emissions by the active sensors. This makes it possible for many space borne active sensor satellites to be involved in a variety of operations like the creation of a three-dimensional body of the cloud which is very resourceful in the weather forecast.

Active Sensors provide their own energy source for emission makes it possible to use it during day or night and over terrains and weather conditions where capturing solar radiation may be challenging.

There are three main types of Active remote sensing. They are:

Active Optical Remote Sensing: This type of remote sensing emits radiation in the visible range which hits the target and the back scattered light is analyzed. LIDAR is a common active optical remote sensor that is used.

Active Microwave Remote Sensing: This is the microwave emitting remote sensor and RADAR is commonly used for measurement of these microwaves.

Active Thermal Remote Sensing: This form of remote sensing is used to detect the thermal infrared radiations. LIDAR is commonly used for thermal remote sensing.

Active Remote Sensing Instruments

Active remote sensing instruments operate with their own source of emission or light, while passive ones rely on the reflected one. Radiation also differs by wavelengths that fall into short (visible, NIR, MIR) and long (microwave).

Each active sensor in remote sensing directs its signal to the object and then checks the response – the received quantity. The majority of devices employ microwaves since they are relatively immune to weather conditions. Active remote sensing techniques differ by what they transmit (light or waves) and what they determine (e.g., distance, height, atmospheric conditions, etc.).

Radar is a sensor assisting in ranging with radio signals. Its specific feature is the antenna emitting impulses. When the energy flow in radar active remote sensing meets an obstacle, it scatters back to the sensor to some degree. Based on its amount and traveling time, it is possible to estimate how far the target is.

Lidar determines distance with light. Lidar active remote sensing implies transmitting light impulses and checking the quantity retrieved. The target location and distance are understood by multiplying the time by the speed of light.

Laser altimeter measures elevation with lidar.

Ranging Instruments estimate the range either with one or two identical devices on different platforms sending signals to each other.

Sounder studies weather conditions vertically by emitting impulses, in case it falls to the active category.

Scatterometer is a specific device to measure bounced (backscattered) radiation.

Applications And Benefits

Apart from a variety of implementations, active remote sensors basically have no restrictions as to research conditions. Active types of remote sensing systems fully function at any time of the day as they do not require sunlight, and they are relatively independent of atmospheric scatterings.

Various types of remote sensing technology find implementations both in scientific branches and far more practical industries. Shuttle Radar Topography Mission collected the Earth’s elevation data.

Lidar active remote sensing in the sky assisted in the elaboration of digital models of our planet’s surfaces.

Data acquired with remote sensing instruments serve agriculturalists and foresters. They are critical in hard-to-reach places in marine sciences and rescue missions.

Sounders assist in developing weather forecasts with vertical profiles of humidity, precipitations, temperature, and absence/presence of clouds.

Sources: GOV USA NASA APPLIED SCIENCES PROGRAM | GOV EU Remote Sensing Types Of Remote Sensing | EOS Data Analytics

Types of Remote Sensing Sensors and Applications

Remote sensing sensors have become an essential tool for monitoring and understanding the Earth’s surface and atmosphere. From monitoring weather patterns and mapping natural resources to tracking the movements of vehicles etc.

Remote sensing sensors are instruments that are used to collect data about the Earth’s surface and atmosphere remotely. These sensors can be placed on aircrafts, satellites, drones, or other platforms and can capture information about the physical properties of the planet, such as temperature, reflectance, and emissions.

Electromagnetic Sensors: Electromagnetic sensors are devices that detect and measure electromagnetic waves, which are oscillating electric and magnetic fields propagating through space. These sensors are employed to gather information about different aspects of the environment, including physical properties, electromagnetic phenomena, and even the presence of certain materials. Some common examples of electromagnetic sensors include magnetic, microwave and radio frequency sensors.

Lidar Sensors: Lidar (Light Detection and Ranging) sensors are a type of remote sensing sensor that use laser pulses to measure distance to the object and can be used to create detailed 3D maps of the Earth’s surface and even the seafloor. This makes them incredibly useful for navigation and terrain analysis.

Some common examples of lidar sensors include airborne lidar and terrestrial lidar. Airborne lidar sensors are typically mounted on aircrafts and used for mapping large areas rapidly. Terrestrial lidar, on the other hand, are mounted on tripods or vehicles and are used to create detailed 3D maps of small areas.

Lidar sensors can also be combined with other remote sensing sensors, such as cameras and multispectral scanners, to provide additional information about the Earth’s surface.

Multispectral & Hyperspectral: Multispectral and hyperspectral imaging cameras go beyond the visible spectrum, capturing images in multiple spectral bands, including visible, near-infrared, mid-infrared, and thermal infrared.

Infrared: These sensors detect electromagnetic radiation with wavelengths longer than visible light but shorter than radio waves, making them capable of detecting heat radiation emitted by objects.

Ultraviolet: These sensors can capture ultraviolet radiation, which is shorter in wavelength than visible light and is often used for specialized applications.

Optical Sensors: Optical sensors primarily operate within the visible spectrum of electromagnetic radiation and are used to create images of the Earth’s surface. They cinclude traditional cameras that produce color images using red, green, and blue channels, as well as, more advanced versions such as multispectral and hyperspectral imaging cameras.

Radar Sensors: Radar sensors are a type of remote sensing sensor that use radio waves to detect the Earth’s surface and measure the distance to objects. These sensors emit electromagnetic waves, which bounce off objects and return to the sensor. By measuring the time it takes for the waves to return, radar sensors can calculate the distance to the object and can be used to create a map of the surrounding environment. Some common examples of radar sensors include synthetic aperture radar (SAR) and interferometric SAR (InSAR).

Synthetic Aperture Radar (SAR): SAR is a type of radar sensor that uses advanced imaging techniques to create high-resolution images of the Earth’s surface. Among others, it can be used to detect and monitor changes in land use, map deforestation or flooded areas and even measure the movement of glaciers.

Interferometric SAR (InSAR): InSAR is a type of radar sensor that measures surface deformation and subsidence. InSAR uses two or more radar images of the same area taken at different times and compares the differences in the images to create a 3D map of the surface deformation. InSAR can be used to monitor volcanic activity, map earthquake zones, and measure the deformation of glaciers and ice sheets.

Visible Spectrum: Visible spectrum sensors capture images using standard colors (red, green, blue) to create colorful representations of the Earth’s surface.

IMAGE RESOLUTION: For earth observation, WE have to consider image resolution.

Remote sensing divides image resolution into three different types:

Spatial resolution

Spectral resolution

Temporal resolution

SPATIAL RESOLUTION: Spatial Resolution is the detail in pixels of an image. High spatial resolution means more detail and smaller pixel size. Whereas, lower spatial resolution means less detail and larger pixel size.

Typically, UAV imagery has one of the highest spatial resolution. Even though satellites are highest in the atmosphere, they are capable of 50cm pixel size or greater.

SPECTRAL RESOLUTION: Spectral Resolution is the amount of spectral detail in a band. High spectral resolution means its bands are more narrow. Whereas low spectral resolution has broader bands covering more of the spectrum.

TEMPORAL RESOLUTION: Temporal Resolution is the time it takes for a satellite to complete a full orbit. UAVs, airplanes, and helicopters are completely flexible. But satellites orbit the Earth in set paths.

Global position system satellites are in medium Earth orbit (MEO). Because they follow a continuous orbital path, revisit times are consistent. This means our GPS receiver can almost always achieve 3 satellites or greater for high accuracy.

TYPES OF ORBITS:

Geostationary Orbits match the Earth’s rate of rotation.

Sun-Synchronous Orbits keep the angle of sunlight on the surface of the Earth as consistent as possible.

Polar Orbits pass above or nearly above both poles of Earth.

It’s the satellite’s height above the Earth’s surface that determines the time it takes for a complete orbit. If a satellite has a higher altitude, the orbital period increases.

We often find the weather, communications, and surveillance satellites in high Earth Orbit. But CubeSats, the ISS, and other satellites are often in Low Earth Orbit.

Dr. Bashir A. Syed, Sc.D.

Dr. Bashir A. Syed, Sc.D., (Died 1 June 2015 in Houston, TX) was Muslim-Pakistani-American Solar Physicist and a NASA Research Scientist in the field of Robotics and solar sciences. He was the member of New York Academy of Sciences.[1] He produced numerous articles on resolving the energy crises in the world[1] and is attributed with establishing the wind power and Solar power plants in the Pakistan. He also inducted a separate research institutions on solar physics and technology at SUPARCO and PAEC.

Bashir Syed joined NASA in 1989 while working at General Electric as a contractor. He was transferred to the International Space Station as a Solar Technologist.[2] As a NASA Scientist he worked in the United States Space Program. Mr. Syed played a major role in the project from the Design Phase till the Construction Phase. He also participated in the Space Shuttle Modification Program.

Dr. Syed worked on the development of NASA's space probes. He is a specialist on Cosmic and Solar Radiation. As a result, Dr. Syed was In Charge of Space Radiation Effects on Space Craft and Their Components. He was heavily involved in the production and development of Mars Pathfinder.

Dr. Syed also worked as an Astronaut Trainer and in the Astronaut Development Program. He also worked in the United States Mercury Project where he did research in Solar Produced Plasmas. Dr. Syed retired from NASA on September 22, 2002. He continued his research in the field of Microtechnology, especially Carbon Nanotubes.[2]

Page updated

Report abuse