General knowledge and interpretation marks of aerial and satellite film interpretation

(a) General knowledge of aerial and satellite film interpretation

The interpretation of aerial photographs is generally carried out with the help of stereoscope. Stereoscope is a simple stereoscopic observation instrument, which is used to create stereoscopic images. Its main function is to separate the sight of people's left and right eyes, so that each eye can only see one photo, that is, the left eye sees the left photo and the right eye sees the right photo. By observing aerial photos with stereoscope, the surface morphology (optical model) of aerial photos can be reproduced under stereoscope, so as to achieve the purpose of intuitive analysis and research.

1. Stereoscopes commonly used at present

(1) Bridge Stereo Bridge Stereo, also known as lens stereo (Figure11), consists of two observation lenses with magnification (about 2 times). The distance between the two lenses can be adjusted to suit the length of each observer's eye baseline. This stereo mirror is small in size and easy to carry in the field. Its disadvantage is that the field of view is small and it is impossible to observe the whole area of the overlapping part of the image pair.

Photo 1 1- 1 lens stereo

Figure 1 1-2 Reflective Stereo

(2) Reflective Stereo The reflective stereomirror (Figure 1 1-2) consists of four mirrors that are parallel to each other (with an included angle of 45) and two mirrors that have magnifying effect. The two lenses are installed between the two parallel mirrors respectively. This stereoscopic lens has a large field of view, which is suitable for observing larger photos and can observe the full range of overlapping parts of images. It is often equipped with a parallax rod (an instrument for measuring left and right parallax) (Figure 1 1-3), which can measure geological and geomorphic elements under a microscope. It's convenient to draw in the mirror. The disadvantage is that it is inconvenient to carry.

Figure 1 1-3 parallax bar

2. Simple use of stereoscope and its stereoscopic observation

(1) Hold the beam of the reflective stereoscope, open the stereoscope, and check whether the four mirror feet are on the same plane; If they are not in the same plane, adjust the screws of the temples to make them rest on the table smoothly.

(2) Overlap the stereo image pairs under the mirror, and then separate them in parallel in left and right order.

(3) finding out the image points with the same name in the stereo image pair, so that two index fingers respectively hold down the two image points with the same name; Then move the photo left and right in parallel under the mirror until the two index fingers overlap under the mirror.

(4) Staring at two photos, you can get a three-dimensional effect. If it is not three-dimensional, just rotate any photo slightly.

The principle of stereoscopic observation under stereoscope is established by simulating the stereoscopic vision of eyes. Therefore, the photos used for stereoscopic observation must be similar to the images obtained by human eyes observing the same object or area from different angles. In other words, the two photos must be continuous stereo image pairs with a certain overlap (about 60%) along the course, and they are images taken from two different angles at the same altitude for the same area. Only by observing this stereo image pair can the stereo effect be obtained. In stereoscopic observation, the placement of stereoscopic image pairs must meet the following requirements.

One is that two photos must be at the same height and look at the same object from two angles.

Secondly, the two photos should be placed according to their relative positions when imaging. In stereoscopic observation, only the left eye can see the left photo and the right eye can see the right photo.

If the positions of the left and right photos are reversed, the three-dimensional model is opposite to the real one, that is, the original convex part becomes concave and the original concave part becomes convex. This phenomenon is called anti-stereoscopic effect. If the photo is rotated 90 degrees according to the relative position when it is imaged, it will not get the stereoscopic impression, which is called zero stereoscopic impression.

In stereo observation, the optical model is often deformed, the terrain fluctuates greatly and the ground slope becomes steep. This vertical exaggeration is called superelevation (or deformation of three-dimensional effect). The main reason for this phenomenon is that the vertical scale of the three-dimensional model is greater than the horizontal scale. Super-high texture makes the surface more stereoscopic, which is convenient for observation and measurement under the mirror. Its deformation degree is often expressed by vertical expansion coefficient (superelevation coefficient). The vertical expansion coefficient is equal to the ratio of the vertical scale to the horizontal scale of the three-dimensional model. When the ratio is equal to 1, the three-dimensional model is similar to a field; When it is greater than 1, the three-dimensional model has a sense of superelevation; When it is less than 1, the fluctuation of the three-dimensional model is less than that of the actual terrain.

3. Marking of aerial photos

Aerial photos are aerial photos taken by various flying tools on the ground according to certain requirements. In order to roughly understand the inclination and shooting time of photographic instruments, several indicating devices, such as circular level and timetable, are generally installed on aerial cameras. These descriptions are recorded in the corner or side of each Zhang Hang photo, and the aerial photos taken by AφA aerial camera are described as follows (Figure 1 1-4).

Figure 1 1-4 aerial photo marking

The (1) frame is located at the four sides or corners of the aerial photo, and the intersection of the corresponding frame lines is the main point (center point) of the photo.

(2) The four straight lines with a "well" shape on the edge of the photo are flattening lines, and their curvature and straightness indicate whether the negative is flattened during photography.

(3) The level is in the corner of the photo, which is used to record the tilt angle of the photo at the moment of photography. Concentric circle representativeness, the bubble deviates from a circle 1 (or half a degree); At the same time, the tilt direction of the camera is judged according to the deviation direction of the bubble.

(4) The shooting time is recorded in the timetable. When the recorded conversion of time becomes a place, the direction of the photo can be determined according to the shadow of the image.

(5) The barometer records the air pressure or altitude at the moment of photography, so as to determine the altitude of the main point.

(6) Others, including camera model, factory number, lens focal length, aerial photography date, negative number and photo number, are recorded on one side of the photo.

(2) Landforms and Quaternary geological interpretation marks of aerial and satellite photos.

Because aerial photography and satellite photos are comprehensive images of the ground landscape restored in a certain proportion, the geometric and optical characteristics of the ground surface are recorded objectively, truly, comprehensively and in detail, and these characteristics show various influences in the photos, such as shape, size, pattern, tone and so on. These characteristics of photos are called interpretation marks. According to these interpretation marks, the process of analyzing aerial and satellite photos by using relevant knowledge, theories, means and methods to reveal the existence and attributes of a ground object or phenomenon on the surface is called the interpretation (or interpretation) of aerial and satellite photos. Geomorphology and Quaternary geological interpretation of aerial photographs is a process of analyzing and studying geomorphology and Quaternary geological phenomena on aerial photographs by using relevant knowledge and theory according to the image characteristics of aerial photographs.

Interpretation marks of aerial photographs can be divided into direct marks and indirect marks. The image features revealed by the interpretation object itself are called direct interpretation marks, and the image features revealed by other geological bodies or objects are called indirect interpretation marks.

On the basis of decades of production and scientific research work, geological remote sensing workers in China have summarized many interpretation marks with universal significance, which are widely used to distinguish the attributes of ground objects. Due to the influence of different natural environments in different regions, different shooting bands and photosensitive materials used in developing and printing, it has the characteristics of variability and limitation. Therefore, when using these signs to interpret, we should comprehensively use various signs, pay attention to mutual verification and comparative analysis, and conduct on-the-spot verification when necessary to ensure the correctness of the interpretation results.

See Remote Sensing Geology in this section for details.