Other techniques in the classification of space visuals:
Other techniques in the classification of space visuals:
Most remote sensing satellites deal with a single image, i.e. without interference between each of the two consecutive images, making it impossible to measure the heights of spatial features on the visuals.
However, some satellites (such as The French Satellite Spot5) offer inter-sensory access to dual visuals and thus the possibility of measuring placements and using them in the development of contour maps and digital altitude models.
On the other hand, there are types of radar satellites (i.e. active rather than passive) whose data allow for the development of placements and the indication of terrain differences on the Earth’s surface.
1) Satellite radar scanning techniques:
In 1999, NASA launched a space-borne radiometric reflection measurement technology or astra in collaboration with Japan.
The sensor in this technique is made through 14 electromagnetic energy ranges ranging from visible light bands to thermal infrared bands.
This technology provides space visuals with a spatial coverage of 60*60 km with a spatial distinguishing capacity of 15 metres for visual sensing, 30 for near-infrared sensing,90 metres for thermal infrared sensing.
However, the most important features of Aster’s technology are that it allows for dual photography (overlap between each of the two consecutive images) enabling the development of spatial parameters to develop topographical maps.
The technology is also available free of charge to users around the world through NASA’s space website at:
The US Space Agency, through Aster technology visuals, has also developed a digital altitude model covering the entire world that illustrates the topography of the Earth’s surface with a spatial degree of spatial distinction (cell size) of 30 meters.
This form is available for free download to users at the link:
In February 2000, NASA launched its space shuttle on a special radar device to measure the earth’s surface levels for most parts of the earth (from a 56-south latitude to a 60-north latitude) and called the space shuttle’s topographic radar mission or SRDM.
By measuring this 11-day mission, it was possible to develop a digital altitude model covering the whole world that illustrates the topography of the earth’s surface with a spatial degree of spatial distinction (cell size) of 30,90,900 metres.
This model is available for free download to users (cell size only 90 and 900 meters) in the link:
The accuracy of global digital height models is several metres (e.g. ±6 metres for the S ARTEM and ±9 m for the Aster model), indicating that they are not suitable for engineering or urban applications or the production of topographic maps with large graphic scales.
On the other hand, the existence of these global models is free of charge and, from an economic point of view, makes them suitable for many users, particularly in regional and environmental applications and topographic maps with medium and small graphic standards.
2) Laser scanning techniques with aircraft:
In the last two decades, a new technology called portable spy and optical measurement systems has been developed or shortly named LiDAR.
This technique is based on placing a laser device on an aircraft where it releases, receives and records lasers after they are reflected from the surface of the Earth, from which spatial parameters can be calculated.
With gps coordinates on board, horizontal geographic coordinates (longitude and latitude) can be measured for each radar beam launch moment, so triple geographical coordinates (longitude, latitude and drop-off circle) are available for all points observed throughout the course of the aircraft.
There are two main types of lidar systems, one dedicated to land-based radar survey and the other for deep-sea radar survey.
Although airborne laser scanning technology began primarily in the 1990s, the proliferation of its applications and uses in topographic surveying has also made it a commercial technology in recent years.
Lidar technology excels in aerial imaging as a semi-automated technology that does not require much user intervention in data collection and contour mapping development,
as the accuracy of laser scanning reaches the limits of ten centimeters or less, and the laser device can measure the levels of several points (up to 12 points) per square meter, which increases the density of points and the accuracy of drawing topographic details, In addition, the economic cost of this technology is much lower than the cost of aerial photography.
3) Satellite-active radar sensor:
There are several active sensor application systems where the satellite releases and records radar rays after they are reflected again from the Earth’s surface.
One such system is the industrial radar port technology, or sar, where the radar device is placed on board the satellite (and sometimes on board a plane) this technique depends on receiving reflected rays from the Earth’s surface through an “Anna” receiver installed on the satellite surface,
i.e. several areas of this dish receive reflected rays, which means that there is more than one image of the ground teacher and therefore the possibility of determining the nature of this teacher with great distinctive ability.
This technique also features radar rays not affected by clouds and clouds in atmospheric layers, making their visuals suitable for agricultural, geology and hydrological applications.
Examples of satellites applying SAR technology include the European ARS2 satellite, the Canadian radarsat-2, the Italian moon Terrasarax and the Japanese moon Alous.