Aerial surveying technology is utilized in a wide range of fields throughout the world. These range from the creation of maps, to terrain analysis and research (rivers, soil erosion, coasts, etc.), urban planning, road planning (roads, rails, etc.), and vegetation research (forests, agriculture, lakes and marshland, etc.).
Aerial Photogrammetric Surveying Technology and Its Applications
Regardless of the field in which aerial photographs are utilized, the position coordinates of the photograph are required in most cases. GPS/IMU (a position and orientation measurement system) is at the heart of the technology needed to obtain such coordinates.
Global Positioning System (GPS) is a widely used technology that has come to be represented by navigational services on maps incorporated into car navigation and mobile phone devices, while Inertial Measurement Unit (IMU) is a device that measures the acceleration and angular velocity of an aircraft. The flight trajectory of the aircraft can then be obtained by combining this information with the position information of the aircraft obtained through the GPS system.
In the past, it had been necessary to establish the reference point aerial signal to be shown on the photograph before the photograph is taken, but this step has since been abolished with the development of the GPS/IMU technology. From a method that sought position coordinates for a photograph from the ground to one that seeks ground position coordinates directly from the air, the transition has been a significant one.
In particular, the potential of this technology has been demonstrated in the photography of sites that people do not have easy or direct access to, such as photographing disaster area.
With the aim of acquiring information with a high level of positional precision, PASCO has incorporated GPS/IMU systems into each of the sensors featured below, and operates these systems on an everyday basis.
1: Photogrammetric Surveying Using RC (Analogue) Cameras
This technology is the origin of aerial surveying. Photography is basically carried out using Leica RC series analogue film cameras. Aerial photographs are, of course, the source of information about roads, buildings, railways, rivers, and other topographic features that make up maps; they are also utilized as part of the basic information that satisfies a wide range of public uses, such as in the formulation of urban plans, road plans, river plans, erosion control plans, and hazard maps.
This technology is used in a variety of applications in both the public and private sector. For instance, the film of these aerial photographs is also used to produce optical prints on photographic paper that are used as photographic maps, and data is sometimes processed such that surfaces appear as they would look from an aerial view, when viewed from any point (ortho-images).
In photography using analogue cameras, there is a need to scan aerial photographs using photograph negatives in order to digitalize the photographs.
2: UCX/UCXp (Digital camera: Area Sensor)
"UltraCam-X" and "UltraCam-Xp" are the products of the evolution of RC (analogue) series cameras to digital cameras.
The key areas of application, similar to those for RC (analogue) cameras, are as basic information for various fields. This information forms the basis of information for map creation.
The basic structure is the same as cameras generally known as "digital cameras." In addition, they are characterized by three features.
- They have a dynamic range that far surpasses the photography range and filming capability of conventional aerial cameras. The shortest shutter interval is 1 second (1.35 seconds for UltraCam-X), and can secure 80% overlap even at ground resolution of 4 cm. As a result, they are able to significantly reduce the occlusion of buildings, thus enabling mapping that is of a higher degree of precision.
- Unlike conventional cameras, it is possible to attach eight lenses to these cameras. Of these, the four panchromatic (monochromatic) lenses located in the center of the camera overcome slight time lags to take split shot images. By combining these split shot images, it is possible to obtain centrally projected images that are the same as typical photographs.
- The four lenses located in the periphery can take colored images (RGB) and near-infrared images (NIR) at the same time that monochromatic images are being captured. In addition, through synthesis with high-resolution monochromatic images (pan-sharpening), it is possible to create colored and near-infrared images that have a similarly high degree of resolution as that for monochromatic images. High-resolution near-infrared images are useful in areas such as vegetation survey.
3: ADS (Digital camera: Line sensor)
While the technology has a wide range of applications in areas such as disaster prevention, roads, soil erosion, forestry, agriculture, urban planning, and rivers as we have described previously, in the acquisition of photographic images, it is possible to acquire panchromatic, colored, and near-infrared digital images of a high level of precision directly through digital data from ADS cameras, in the same way as for area sensors.
Within one flight course, it is possible to acquire images continuously and in a seamless manner.
In addition, due to the characteristics of the ADS sensor, panchromatic images are digitalized three times for all domains in each course.
Compared to area sensors, the ability to reduce collapse of buildings, etc. is yet another characteristic of capturing with this sensor.
Taking advantage of the above characteristics, PASCO captures with a high degree of overlap between courses and produces true ortho-images with the highest quality among ortho-images, as well as creates digital terrain model data through image matching.