Remote sensing platforms are the structures or vehicles that house remote sensing instruments. A number of attributes that may dictate the use of specific sensors are determined by the platform on which a particular sensor is housed.
These characteristics include the sensor’s distance from the object of interest, the frequency with which images are acquired, the timing with which images are acquired, and the location and extent of coverage. Remote sensing platforms are classified into three broad categories.
there are different types of platforms
- Ground based Platform
- Airborne platform
- Satellite platform
A. Ground based Platform
Remote sensing employs a wide range of ground-based platforms. Handheld devices, tripods, towers, and cranes are some of the more common ones. Ground-based instruments are frequently used to measure the quantity and quality of light emitted by the sun, as well as to characterize objects at close range.
Almost all laboratory instruments are used for research, sensor calibration, and quality control. Much of what is learned in the lab is used to better understand how remote sensing can be used to identify different materials. This helps to develop new sensors that improve on existing technologies.
Field instruments are also widely used in research. This type of remote sensing instrument is frequently held in one’s hand or mounted on a tripod or other similar support.
Permanent ground platforms are typically used to monitor atmospheric phenomena, but they can also be used to monitor terrestrial features over time. Towers and cranes are frequently used to support research projects that require a reasonably stable, long-term platform.
Towers can be built on-site and tall enough to project through a forest canopy, allowing measurements to be taken from the forest floor, through the canopy, and above the canopy.
For early remote sensing work, airborne platforms were the only non-ground-based platforms. In 1859, the first aerial photographs were taken with a camera carried aloft by a balloon.
Balloons are rarely used today because they are unstable and the flight path is not always predictable, though small balloons carrying expendable probes are still used for meteorological research.
Airplanes are currently the most common airborne platform. Remote sensing applications are used on nearly every type of civilian and military aircraft.
Simple, low-cost aircraft can be used as platforms when the altitude and stability requirements for a sensor are not too stringent. However, as the need for greater instrument stability or higher altitudes arises, more sophisticated aircraft will be required.
Low-flying aircraft typically fly below altitudes where additional oxygen or pressurization is required (12,500 feet above sea level). They are useful for acquiring high spatial resolution data that is limited to a small area.
A satellite, which is space borne, is the most stable platform aloft. In 1960, the first remote sensing satellite was launched for meteorological purposes. Over a hundred remote sensing satellites have now been launched, with more being launched each year.
The Space Shuttle is a one-of-a-kind spacecraft that can be reused for a variety of missions and serves as a remote sensing satellite.
Satellites are classified according to their orbital geometry and timing. Geostationary, equatorial, and Sun synchronous orbits are the most common for remote sensing satellites.
A geostationary satellite has the same period of rotation as the Earth (24 hours), so it always orbits the same location on Earth.
Geostationary orbits are frequently used by communications and weather satellites, with many of them located over the equator.
A satellite in an equatorial orbit circles the Earth at a low inclination (the angle between the orbital plane and the equatorial plane). The Space Shuttle travels in an equatorial orbit with a 57-degree inclination.
Sun-synchronous satellites travel in orbits with high inclination angles, nearly crossing the poles. The satellite’s orbits are timed so that it always passes over the equator at the same local sun time. As a result, the satellites maintain the same relative position with the sun throughout their orbits.
Many remote sensing satellites are Sun synchronous, which ensures consistent sun illumination during specific seasons. Because a Sun synchronous orbit does not pass directly over the poles, data for the extreme polar regions is not always possible to obtain.
The frequency with which a satellite sensor can acquire data covering the entire Earth is determined by sensor and orbital characteristics. The total coverage frequency of most remote sensing satellites ranges from twice a day to once every 16 days.
The majority of remote sensing satellites are designed to transmit data to ground receiving stations around the world. The receiving station must have a direct line of sight to the satellite in order to receive data directly from it. If there are not enough designated receiving stations around the world, any given satellite may not be able to get a direct view of a station, potentially resulting in data discontinuity problems.