Practice content and steps

There are many kinds of remote sensing images. In order to correctly use remote sensing images and extract useful information from the images for geological interpretation, we must first have a comprehensive understanding of the images used, such as: remote sensor (photography or scanning) and imaging rules, remote sensing platform, information recording method (film or digital), recorded electromagnetic wave wavelength range (working band of remote sensor) and its properties (reflection and emission), and expression form of electromagnetic radiation intensity (color tone).

For example, the images used in this internship are all aerial photography, the remote sensor is a frame aerial camera (or a multi-spectral aerial camera), and the remote sensing platform is an aerial photography tool such as an airplane. Using photosensitive film (full-color black-and-white film, natural color film or color infrared film) to record the electromagnetic wave with the wavelength of 0.3 ~ 1.3 micron, and its intensity is expressed by hue or color. Without correction, the image has the property of central projection.

(A) to understand the characteristics of different types of aerial photos

For the observed aerial photos, the following questions should be answered first: ① Types and imaging rules of imaging remote sensors; ② wavelength range of electromagnetic wave (working wavelength of remote sensor); ③ Types and structural features of photographic film; (4) the meaning of hue or color; ⑤ Basis for distinguishing features.

(2) Contents of technical appraisal of aerial photography.

The technical appraisal of aerial photography shall be obtained from the aerial photography unit at the same time as the aerial photos are collected. The contents include:

① date of aerial photography; ② Aerial photography time; ③ Film type used; 4 altitude; ⑤ The approximate proportion of photos; ⑥ Model and focal length of aerial photographic instruments; ⑦ Internal directional elements; 8 aerial photography quality evaluation.

(3) Understand the notes and attached records of aerial photos.

Observe the notes and attached records on aerial photographs such as H- 162, H- 1433, H-2547 and H-0348;

In the corner or edge of aerial photos, images and text numbers of several indicating devices are often recorded at the same time. They can generally explain the tilt of the photo, the shooting time, the type and focal length of the aerial camera, and the photo number.

1) Frame: located at the center or four corners of the photo edge. Its function is to determine the image principal point of the photo (the intersection of the relative borders is the image principal point of the photo), so as to check the longitudinal and transverse deformation of the photo.

2) Model, focal length, factory number and photographic film number of the aerial camera: "ааа-37" indicates the model of the aerial camera; "F=6920" means that the focal length of the aerial camera is 69.20 mm "N 0125058" is the factory number of the aerial camera; "9820" is the number of the photographic film to calculate the daily workload.

3) Timetable: The shooting time is recorded. From the time table records of two consecutive photos, the shooting time interval can be calculated.

4) Flattening line: used to check whether the negative is flat or not during photography.

5) Circular level: roughly indicates the inclination of the photo when taking a photo. Concentric circles represent degrees, one circle is 0.5, and the inclination is generally not more than 3.

6) Barometric altimetry record: used to indicate the height difference from the altitude, which is only seen in the 23cm×23cm photos.

In addition to the above description, there is also a manual number in the upper right corner of the photo, which is mainly used to indicate the number of survey area, shooting date and number of photos. If the manual number is 73 18-0174, it means that the survey area is "7318" and the photo number (i.e. photo number) is 0174; Another example is the number KT56- 105, which indicates the survey area of KT. The photo number is1956165438+10/5.

(4) Collating and cataloguing aerial photos.

After obtaining aerial photos, it is necessary to sort out and catalogue them in time.

Methods: Take a certain proportion of maps as a unit, put a file bag on each flight zone, and indicate the map number, flight zone number, photo number and photo number where the photos are located, and catalog them in the upper left corner of the back of each photo according to the following format:

K-50- 123 C (table number)

5- 18-3 (No.5 in this figure, *** 18, third from left to right)

Some aerial photographs of K-50- 123 were sorted and catalogued, and the route overlap and lateral overlap were observed.

(5) Experience the central projection of aerial photos.

Observe the displacement law of image points: 3226, 3227.

(6) Stereoscopic observation principle and stereo observation of aerial photography image pairs.

When the stereoscopic observation conditions are met, the two-dimensional image can be transformed into an optical stereoscopic model of three-dimensional space, highlighting the spatial characteristics of the ground objects, which is convenient for human eyes to identify the ground objects and determine the spatial position (Figure 2- 1).

Figure 2- 1 principle of artificial stereoscopic vision

1. Simulated stereoscopic observation conditions

Figure 2-2 schematic diagram of shooting the same area from different angles

(1) It must be two consecutive images with certain overlap-stereo image pairs; (2) Stereo images were taken from two different angles at the same height in the same area (Figure 2-2); ③ The two images should be placed according to their relative positions when imaging. In stereoscopic observation, only the left eye can see the left image and the right eye can see the right image. The main function of various stereoscopes used for stereoscopic observation of aerial photographs is to separate eyes (Figure 2-3); (4) The eye baseline and the photographic baseline on the image are parallel to each other, and the lines of sight corresponding to the feature points with the same name can intersect in pairs, and there is no up-and-down parallax; ⑤ The scale difference between the two images is less than 16%.

Note: Stereoscope is a valuable optical instrument. When you use it, you should care as much as you care for your eyes. Don't touch the optical lens with your hands. When taking and placing the stereoscope, open the box cover with your left hand, hold the metal bracket in the middle with your right hand, and then put the legs of the metal bracket on the experimental platform with your left hand. At this time, your thumb is most likely to accidentally touch the large mirror lens and leave fingerprints. Sweat stains will corrode the lens and cause damage. If there is dirt such as dust or fingerprints on the mirror, please report it to the instructor and don't wipe it with anything yourself.

Figure 2-3 Optical Path Diagram of Reflective Stereoscope

E, e '- eyes; B-eye baseline; B-the distance between the same name image points;

1-large reflector; 2- Magnifier; 3- Small mirror

2. Methods and steps of stereo observation of images

(1) Select a stereo image pair, and determine the intersection points of the image principal points and the adjacent image principal points with the photo baseline.

The intersection of the main optical axis of an aerial camera and the image plane is called the image principal point. Make a line between each aerial photo and the frame, and the intersection point is the main point of the image, as shown in Figure 24, points O 1 and O2. Draw a small circle (about 2mm in diameter) on the back of the photo by penetrating the main point of the image with a needle, and find out the image point with the same name as the main point of the image in the overlapping part of adjacent photos, so as to estimate the point of rotating thorn, which is called the main point of rotating thorn. In Figure 2-4, P 1 and P2 are stereo image pairs, and O 1 is the image principal point of P 1. The same image point O' 1 as O 1 can be found in the overlapping part of two photo images adjacent to P 1 on P2, and then O' 1 can be found on P2. Similarly, O2 is the principal point of P2 image and O2 is the principal point of spine image on P 1. The connecting line (O 1O'2, O2O' 1) between the principal point of each aerial photograph and the principal point of the rotating image of the adjacent photograph is the photograph baseline B (photograph azimuth line), and the connecting line direction is the horizontal axis (X) of the aerial photograph coordinate system. The connecting line between the aerial photograph and the frame is not the horizontal axis of the aerial photograph coordinate system, especially when the route is curved.

Figure 2-4 Determining the photo direction line (photo baseline)

(2) Place the photo under a stereo mirror.

The overlapped image part is placed in the middle (Figure 2-5), that is, two images of the same feature partially overlap, and then are pulled from the overlapped part to the left and right. The left image is placed under the left large reflector, and the right image is placed under the right large reflector, so that the eye baseline is parallel to the photo baseline and parallel to the long axis of the stereo.

Figure 2-5 Photo Placement

(3) Observe in the mirror

At the same time, use your hands to move left and right along the baseline direction of the photos until the image points of the two photos with the same name coincide (Figure 2-6), and stare quietly to establish and feel the three-dimensional effect.

Figure 2-6 Schematic Diagram of Stereoscopic Observation

(4) stereoscopic effect

Including positive stereoscopic effect (Figure 2-7), negative stereoscopic effect and zero stereoscopic effect.

(5) Superelevation or three-dimensional effect deformation

The optical three-dimensional model of ground objects seen under stereoscope is often not completely consistent with the actual situation, and the terrain fluctuates greatly (Figure 2-8). This phenomenon is called superelevation or three-dimensional effect deformation.

Cause: The vertical scale of the optical stereo model is inconsistent with the horizontal scale.

3. Stereoscopic observation principle

Understand the principle and positive and negative stereoscopic observation methods of single photo stereoscopic observation.

4. Alignment and lateral overlap

Understand the course overlap and lateral overlap of aerial photos (Figure 2-9).

Figure 2-7 Schematic Diagram of Orthostereoscopic and Antistereoscopic

Figure 2-8 Vertical exaggeration and tilt angle change

Figure 2-9 Route Overlap and Lateral Overlap