Langchop developed a detailed survey satellite on the basis of developing a general survey satellite. A detailed camera is characterized by its high resolution, but its photographic range.
Small in size, it is suitable for tactical reconnaissance. Frame cameras or line cameras are mostly used, with a focal length of 3 m ~ 8 m, a photographic resolution of 60 lines /mm ~ 88 lines /mm, and a shooting height of 150 km ~ 180 km. The highest ground resolution can reach 0. 15 m ~ 0.3 m, and the width can be achieved. General reconnaissance cameras have moderate resolution and large coverage, and are suitable for strategic reconnaissance and surveillance. Panorama camera is often used, with a photographic resolution of 30 lines /mm and a width of tens to hundreds of kilometers. Detailed investigation and census can complement each other and cooperate with each other. 1 reconnaissance satellites are usually equipped with cameras for general surveys and detailed investigations, and sometimes they are equipped with various remote sensing such as mapping and multispectral cameras.
Instrument.
2. Combination of film reconnaissance camera and transmission reconnaissance camera.
The appearance of CCD device promotes the development of transmission reconnaissance camera. Transmission reconnaissance camera has the characteristics of long life, near real-time information acquisition and high reliability, so both the United States and Russia are vigorously developing transmission reconnaissance cameras. The United States mainly uses transmission cameras, supplemented by film cameras carried by the space shuttle; In Russia, both cameras have their own advantages, and satellite multi-body recovery technology is used to make up for the shortcomings of poor real-time photography reconnaissance. For example, the Russian CA- 1 19 film camera is still in service, with a resolution of 2m, and the film taken has been sold to the US Air Force. This shows that the film reconnaissance camera continues to play a role in space reconnaissance, and the recoverable satellite is not outdated. Ground resolution of space camera image
Ground resolution is one of the important design indexes of space camera. The ground resolution of space camera image is an artificially defined ground scale, and the camera working mode and imaging principle are different, so there are different definitions and measurement (evaluation) standards.
The resolution of a film camera is usually expressed by the maximum number of black-and-white line pairs (black and white lines are equal in width and alternately distributed) that can be resolved within the range of photosensitive materials per millimeter, and its value is determined by the camera shooting black-and-white line targets with different widths and densities. The greater the brightness contrast (contrast) between the black line and the white line on the target, the better the resolution of the camera. When the film camera is aimed at the ground for vertical photography from the height of the space track, the scale of the ground scene corresponding to the camera resolution (that is, the width of a pair of lines in a set of black and white lines with the same width and the same contrast with the target line on the ground) is called the spatial resolution of the image.
The resolution of CCD camera is often expressed by the spatial field of view corresponding to CCD pixel; It can also be expressed by the number of CCD elements per square millimeter or the number of CCD elements per millimeter. When the CCD camera is aimed at the ground for vertical photography from the height of space orbit, the ground scene scale corresponding to the camera resolution is called the pixel resolution of the image.
As can be seen from the above, the ground resolution of space camera image is not the actual image resolution of general ground objects, but an artificially defined scale for specific ground objects (black and white lines, film cameras) or regardless of ground object types (CCD cameras). In other words, the ground resolution of space camera image is only the ground scale corresponding to the image detail feature scale.
The essence of ground resolution of space camera image is discussed above, and several problems about it are discussed below.
① For film cameras, there is no concept of image pixel resolution. The film camera records the image of the scene by using photosensitive materials (silver halide crystals distributed on the latex layer of the film). The silver halide crystals in the latex are extremely small in diameter (generally less than 3μm), with different shapes and random distribution.
(2) For CCD camera, we can imitate film camera to define the spatial resolution of image, which is even a multiple of image pixel resolution (taking one-dimensional linear scale).
The spatial resolution of film camera image refers to the width of a pair of lines in a set of black and white lines with equal width and alternating distribution, which have the same contrast with the target line on the ground. If the CCD camera is aimed at this ground object for vertical photography, the pixel resolution of its image is exactly equal to the width of the line. In this case, as long as the contrast between the black and white lines is high enough, the distinguishable black and white lines can be displayed on the image, that is, the spatial resolution of the CCD camera image is twice that of the pixels. On the other hand, if the contrast between black and white lines is too low, the distinguishable black and white lines will not be displayed on the image. Because the CCD element receives electromagnetic radiation energy from the scene corresponding to it, the image is a mosaic of pixels. Therefore, when the contrast of black and white lines is too low, only when several adjacent CCD elements all sense the lines of the same color (black or white) will the distinguishable lines appear on the image. That is, when the contrast of black and white lines is low, the ratio of spatial resolution of CCD camera image to pixel resolution k is an even number not less than 4. See figure 1 for the above relationship.
③ The ground resolution of camera images can be divided into static and dynamic. According to whether there is relative motion between the camera and the ground object, its image
Can be divided into static and dynamic. If the reference object is a black-and-white line as mentioned above, and the direction of the black-and-white line is parallel to the moving direction of the camera relative to the object, there is no difference between the static image and the dynamic image of the camera, that is, the dynamic ground resolution of the camera image is equal to the static ground resolution. (4) It is reported that the French Space Agency has put forward a technology to improve the ground resolution of the Spot-5 earth resources satellite under development by overlapping two images. Specifically, two transmission channels on the satellite are used to transmit the black-and-white images shot by the same CCD camera at the same time, and the two images are superimposed on the ground, so that the original image with a pixel resolution of 5m can be superimposed to obtain an image with a pixel resolution of 2.5 ~ 3 m without narrowing the field of view. The French space agency has applied for a patent for this technology.
As mentioned above, the ground pixel resolution of the image is 5m, which means that the images (pixels) of black and white lines with a width of 5m Gao Fancha are distinguishable on the image. Now, two such images are staggered by half a pixel for overlapping synthesis, as shown in Figure 2. Then, as long as the contrast of black and white lines is high enough, the distinguishable lines (black, gray, white and gray lines are arranged in sequence to form a group) on the superimposed image are only 1/2 of the original pixel width. In this way, the ground pixel resolution of the converted composite image is 2.5m.