JPS6041916B2 - Satellite image correction system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention removes geometric distortions contained in images of the earth's surface transmitted to the ground by earth observation satellites by using the positions of characteristic points contained in the images. It is related to the method.

If the image data of the earth's surface sent from a satellite is converted into an image as is, the image will be geometrically distorted due to fluctuations in the satellite's orbit and attitude, the rotation of the earth, the curvature of the earth's surface, etc. (Figure 2) a).

Therefore, it is necessary to remove the geometric distortion of this image and reproduce a proper image (for example, Figure 2b). These methods can be roughly divided into two types.
The first method is to clarify the three-dimensional geometric relationship between the satellite 1 and the earth 2 as shown in the first diagram, receive information on the orbit and attitude angle at the time of imaging with the receiver 3, and based on this information, The image correcting device 4 determines the position of arbitrary image data on a proper image, rearranges the image data, and then outputs it to a magnetic tape 5 or makes it into a photograph 6. The second method does not consider a geometric model of the satellite and the Earth, and instead makes characteristic points on the image (highway intersections, airport runways, the tips of capes, etc.) appear as if they were made of rubber. This method considers it as if it were drawn on a board, and moves the position of all image data in accordance with the movement of the feature points. Figure 3 shows how distortion is corrected using this method.

The tip of the cape was selected as a characteristic point. In the figure, 7 is a feature point on the satellite image, 8 is the correct position of the feature point, 9 is an image before correction, and 10' is an image after correction.
In the second method, finding characteristic points on an image is a necessary condition for image correction. Also, in the first method, in order to perform the correction with high accuracy, it is necessary to estimate the orbit and attitude of the satellite by back calculation using the position information of characteristic points on the image. As mentioned above, in order to remove the geometric distortion of images sent from satellites and reproduce them properly, it is necessary to place characteristic points on the satellite image whose latitude and longitude are known. must be found.

However, in conventional satellite image correction methods, the feature points on images used are limited to topography and structures that are stationary on the ground. It was not possible to do so.
The present invention aims to correct geometric distortions in satellite images in areas where characteristic topography and structures cannot be found, such as ocean areas and deserts.

The satellite image correction system according to the present invention measures the position coordinates on the earth of a characteristic object moving on the earth's surface, transmits the coordinates to an image correction device, and measures the position coordinates of a characteristic object moving on the earth's surface, transmits the coordinates to an image correction device, and measures the position coordinates of a characteristic object moving on the earth's surface. This is a satellite image correction system that determines the position of an object and removes distortion included in the satellite image by using the position coordinates and the deviation of the position of the object on the satellite image.

Hereinafter, the present invention will be explained in detail with reference to Examples.

First, the outline of the embodiment will be explained using FIG. 5. FIG. 5 shows the configuration of a system that corrects distortions in ocean satellite images using information on the position of large ships in the image. The embodiment of the present invention is different from the conventional image correction system shown in FIG.
This feature is incorporated into the image correction system. Furthermore, the present invention differs from conventional image correction systems in that it includes an antenna for receiving these position coordinates transmitted from the ship 11 and a line facility for sending the position coordinate data to the image correction device. Next, the flow of data in the embodiment will be explained.

The earth observation satellite 1 images the earth's surface while rotating the earth 2 or while remaining stationary at one point. The obtained image data is
Transmitted to the ground in real time. On the ground, the image data receiving device 3 captures this signal, shapes the signal waveform, and then sends it to the image correction device 4. On the other hand, the position coordinates of the ship 11 navigating the ocean are measured by the ship position measuring device 13 at regular intervals, and transmitted to the ground by the ship position transmitting device 12. The receiving device 18 on the ground transmits the ship position data to the image correction device 4 through a line. Here, the ship position measuring device 13 will be explained.

Measurement of ship position can be carried out, for example, using the Naval Navigation Satellite System (NN).
SSNaviNavigatiOnSatellite
This can be done using a satellite system called ``System''. The principles of ship position measurement are shown in Figures 6 and 7.
This will be explained using figures. The US Navy Navigation Satellites 1 and 4 are equipped with extremely stable crystal oscillators, which constantly transmit radio waves at a constant frequency. The satellite 14 also transmits data regarding the satellite's orbit at regular intervals. The ship 11 includes a radio wave receiving device 15, an orbit data decoding device 16,
A Doppler shift analysis device 17 is loaded. Radio waves from the satellite are received by a receiving device 15, and their frequencies are precisely measured. If the difference Δf between the transmission frequency and the reception frequency from the satellite 14 is measured and plotted when the satellite passes by, the change will be as shown in FIG. 7. Due to the Doppler effect, Δf has a positive value when the satellite 14 is approaching, and has a negative value when it is moving away. When the satellite 14 comes closest to the receiving device 15, Δf becomes 0, and its rate of change becomes maximum. Time T at this time. can be precisely measured and the satellite orbit can be known by the orbit data decoding device 16, so the position coordinates of the ship (receiving device) on the earth can be determined by analysis by the analyzing device 17. As described above, for example, by using the US Naval Navigation Satellite System (NNSS), it is possible to measure the position of a ship at regular intervals when the navigation satellite passes over the sky. Ship positions Xl, X2, . . . at fixed time intervals are stored in the storage device 19 of the image correction device 4.
are recorded one after another.

Interpolate these values with a continuous reading function x(t) at time t,
Find X(T) at time T when the image was captured. As a function for interpolation, for example, a polynomial of time t, X(t
)=XO+X1·t+...+Xn-Tn can be used.

The above calculations are performed for a plurality of ships (FIG. 4, 11) navigating in the sea area included in the image. Once such positional coordinates are determined, these positional coordinates play exactly the same role as the conventional positional coordinates of stationary feature points.
Geometric distortion of the ocean image can be corrected using the position information of these ships 11 by a conventional method. That is, the position of the ship 11 in the distorted image,
The attitude and orbit of the satellite 1 are estimated from the direction and magnitude of the correct positional deviation determined by the position measuring device 13 of the ship 11, and the geometrical relationship between the satellite 1 and the earth 2 in three-dimensional space is determined. At this time, the position of the ship in the image can be found by searching for points where the intensity of the image data exceeds a certain threshold, which is much easier than locating feature points on the ground using a correlation function. Once the geometric relationship between the satellite 1 and the earth 2 is known, the exact position of any image data can be determined using a proper coordinate system, and all that is left to do is to rearrange the image data. It is also possible to use a huge balloon, an airplane, etc. as a moving object instead of the ship 11 of the above embodiment, but it is also necessary to measure the altitude of the object when moving the object.

In addition, as the ship position measuring device of the above embodiment, Kuchiran (
A measurement device that uses radio waves from a LORAN station may be used instead.

As explained above, according to the present invention, satellite images without characteristic topography such as only the ocean can be obtained.
This geometric distortion can be removed.

Japan is surrounded by the ocean, and obtaining appropriate and accurate information about the ocean is important in many areas of society, including the economy and the environment.

The present invention is highly effective as a method for removing distortion from satellite images of ocean areas, which has not been possible until now.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of a conventional satellite image correction system;
The figure is an explanatory diagram using a schematic image of the meaning of satellite image distortion correction. Figure 3 is an explanatory diagram of correcting the entire image by aligning the feature points in the image to the correct position. Figure 4 5 is an explanatory diagram of the satellite image correction of the sea area when the present invention is implemented, FIG. 5 is a configuration diagram of the satellite image correction system of the present invention, and FIG. 6 is a diagram of ship position measurement used in the embodiment of the present invention. FIG. 7 is a block diagram of the apparatus for explaining FIG. 6.

Claims (1)

[Claims] 1. Image data obtained by an imaging means mounted on a satellite rotating around the earth to capture images of the earth's surface is received on earth, and geometric distortions of the received image data are removed to obtain an image of the earth's surface. In a satellite image correction system that reproduces a corrected image, the earth coordinates of a predetermined object moving on the earth's surface at the moment the object was imaged are measured, and the measured earth coordinate values and the image of the object are measured. A satellite image correction system characterized in that geometric distortion of the image data is removed using position information on the image.