The vehicle or carrier for a remote sensor to collect and record energy reflected or emitted from a target or surface is called a platform.
According to Lillesand and Kiefer (2000), a platform is a vehicle, from which a sensor can be operated. Remote sensing should be mounted on suitable stable platforms. These platforms can be ground-based, airborne, or space-borne based.
As the platform height increases the observational area increases. Thus, the higher the sensor is mounted; the larger the synoptic view is obtained.
It is a place where a camera or sensor is mounted and captures the photo of places below upon its.
WHAT IS PLATFORM?
For remote sensing applications, sensors should be mounted on suitable stable platforms. These platforms can be ground based air borne or space borne based. As the platform height increases the spatial resolution and observational area increases. Thus, higher the sensor is mounted; larger the spatial resolution and synoptic view is obtained.
The types or characteristics of platform depend on the type of sensor to be attached and its application. Depending on task, platform can vary from ladder to satellite. For some task sensors are also placed on ground platforms. Though aircrafts and satellites are commonly used platforms, balloons and rockets are also used.
TYPES OF PLATFORMS
- Ground Based Platform
- Air-Borne Platform
- Space- Borne Platform
Ground-based Platforms
Ground-based sensors are often used to record detailed information about the surface which is compared with data collected from aircraft or satellite sensors.
In some cases, this can be used to better characterize the target being imaged by these other sensors, making it possible to better understand the information in the imagery.
To study the properties of a single plant or a small patch of grass, a ground-based platform is used (hand-held or mounted on a tripod).
Ground observation platforms are used to record detailed information about the objects or features of the earth’s surface. These are developed for the scientific understanding on the signal-object and signal-sensor interactions.
Ground observation includes both the laboratory and field study, used for both in designing sensors and identification and characterization of land features.
Ground observation platforms include- handheld platforms, cherry pickers, towers, portable masts, vehicles, etc.
Mobile Hydraulic Platforms
Carried on vehicles.
Extendable to a height of 15 m above the surface.
At the top of the platform, there are
Spectral reluctance meters
Photographic systems
IR or microwave scanners
Linked to data loggers in the vans.
Limitation
Vehicles are limited to roads and the range is confined to a small area along or around the road.
Portable Masts
Used to support cameras and scanners. E.g., Land Rover fitted with an extending aerial.
Limitation: Very unstable in windy conditions.
Towers
Can be dismantled and moved from one place to another.
Offer greater rigidity than masts but are less mobile and require more erecting time.
Cherry Pickers
These platforms are used for ground investigation.
It is mainly used for the observation of surface roughness, vegetation, cover, soil temperature, and soil texture variation.
AIR-BORNE PLATFORMS
Aerial platforms are primarily stable-wing aircraft, although helicopters are occasionally used.
Aircraft are often used to collect very detailed images and facilitate the collection of data over virtually any portion of the Earth’s surface at any time.
Aircraft remote sensing systems may also be referred to as sub-orbital or airborne, or aerial remote sensing systems. At present, airplanes are the most common airborne platform.
Airborne platforms are employed owing to their mobilization flexibility and capability of recording data covering large spatial areas as compared to ground-based sensors. The speed, altitude as well as the orientation of the aircraft must be carefully chosen so as to have minimum influence on the scale resolution and geometric characteristics of the recorded images.
Balloons
Balloons as platforms are not very expensive like aircraft. They have a great variety of shapes, sizes, and performance capabilities.
They provide a large field of view and in general, require no power.
The greatest advantage of balloon platforms is their flight trajectory cannot be controlled and they depend on the meteorological condition.
Balloons are used for remote sensing observation (aerial photography) and nature conservation studies. The balloon floats at a constant height of about 30 km.
Balloon is governed by the wind at the floating altitude. Balloons are rarely used today because they are not very stable and the course of flight is not always predictable, although small balloons carrying expendable probes are still used for some meteorological research.
Altitude range is 22-40 km.
There are three main types of balloon systems.
- Free Balloons
- Tethered Balloons
- Powered Balloons
Drones
Drone is a miniature remotely piloted aircraft. It is designed to fulfill requirements for a low-cost platform, with long endurance, moderate payload capacity, and capability to operate without a runway or small runway.
Drone includes equipment for photography, infrared detection, radar observation, and TV surveillance. It uses satellite communication links. An onboard computer controls the payload and stores data from different sensors and instruments.
Kites
Camera carried aloft by large kites has also seen used to obtain aerial photography.
Aerial photography using kite developed by French man ‘Arthur Butut’.
George E. Lowrance used as many as 17 kites in a connecting train to carry loft cameras heightening.
He called the collection of their kites a captive Airship.
Pigeon
In 1903, Julius Neubronner a breast-mounted aerial camera for carrier pigeons that weight very less.
As a carrier pigeon after starting at first describing a spiral line, it is quite easy to take a number of views of a given portion of the ground from a different point of view.
Air Crafts
Air crafts are used to take aerial photographs at different altitudes.
They allow us to explore smaller areas in detail.
It is possible to obtain very high resolution due to the stereo imaging facility.
Aerial platforms are primarily stable-wing aircraft. Helicopters are also occasionally used for this purpose. Generally, are used to collect very detailed images.
Special aircraft aerial photography results in large-scale images providing detailed information on the terrain, the high-altitude smaller scale images offer advantages to cover a larger study area with low spatial resolution.
SPACE BORNE PLATFORMS
In space, remote sensing is sometimes conducted from the space shuttle or more commonly from satellites.
Satellites are object which revolves around another object in this case, the Earth.
With the help of the satellite, we can collect a number of data that is very useful for urban studies.
Using different types of sensors, we can capture a variety of data (Multi Specter, Hyper Specter)
Space-borne remote sensing is carried out from outer space or at an altitude higher than the Earth’s atmosphere and utilizes space shuttle or more commonly satellites as platforms. Space-borne or satellite platforms are one-time cost affected but relatively lower cost per unit area of coverage can acquire imagery of entire Earth without taking permission.
Space-borne imaging ranges from an altitude of 250 km to 36000 km.
Spaceborne remote sensing provides the following advantages
- Large area coverage;
- Frequent and repetitive coverage of an area of interest;
- Quantitative measurement of ground features using radiometrically calibrated sensors;
- Semi-automated computerised processing and analysis;
- Relatively lower cost per unit area of coverage.
REFERENCES
Panda. B. C., 2005, Remote sensing principles and applications, Viva Books Pvt. Ltd., pp. 73-78.
