KR100425283B1 - Topography Measurement Method using InSAR - Google Patents

Abstract

PURPOSE: A method for measuring an elevation using a geometric characteristic of an interferometric synthetic aperture radar is provided to measure accurately an elevation by performing a phase difference-elevation conversion process. CONSTITUTION: An SAR image process for generating two-dimensional images is performed by receiving predetermined signals from each antenna by pixel unit having sizes and phases. The SAR images are arranged in a range/Doppler region and an interferometric phase difference is detected by pixel unit. An elevation is obtained by performing a phase difference-elevation conversion process and using a predetermined mathematical expression. A filtering for processing the calculated elevation information is performed by processing of one pixel or a spatial filtering process using a multi look method for dividing one region into multiple pixels.

Description

Topographic Measurement Method Using Geometric Characteristics of Synthetic Aperture Radar for Interferometry {Topography Measurement Method using InSAR}

Digital Elevation Model (DEM) is a data type that expresses the altitude information of the terrain for a specific area. It is a continuous change of ups and downs in space by dividing the target area into a grid of a certain size. Is a numerical representation of the grid.

The method of generating a DEM includes i) a method generated from a contour layer of a digital map, ii) a method using a stereo satellite image or an aerial photograph, and iii) a method using a GIS application such as a wireless network design system.

Therefore, SAR may be generated based on the digital map, so that the digital data may include the altitude information, and the SAR may be generated by using ultra wideband VHF SAR data and using corona satellite images. Interferometry) can be used to generate the DEM.

As a DEM generation method based on a digital map, inverse distance weighting, kriging, and triangular network formation are used. However, the method of generating the DEM data from the contour layer of the digital map has a problem that it takes a lot of time and money.

Interferometric Synthetic Aperture Radar (hereinafter referred to as InSAR) is a synthetic aperture radar that has two antennas spaced apart from each other and obtains the topographic altitude from the phase difference of the interference signal received by these antennas. InSAR detects information about the earth's surface using the phase difference between two complex radar signals. Applications using InSAR technology include DEM generation, geophysical hazard analysis, glacier velocity measurement, and land use classification.

The applications using InSAR technology utilize interferometry correlations related to phase and target point characteristics by interferometry that is proportional to the path length difference between one target point and radar position on the earth's surface.

An object of the present invention is to equip two antennas, one of which is used as both a transmitter and a receiver and the other as a bistatic receiver, using a DEM using InSAR geometrical characteristics by a single pass aircraft. We will provide a method for generating the topographic elevation through the phase-altitude conversion.

1 is a block diagram for generating a DEM using the InSAR geometric characteristics by a single pass aircraft disclosed in the present invention

2 is an InSAR geometrical characteristic of a single pass aircraft disclosed in the present invention.

FIG. 3 is a procedure diagram for measuring topographical altitude using InSAR geometric characteristics by a single pass aircraft disclosed in the present invention.

<Description of the symbols for the main parts of the drawings>

A1, A2, # 1, # 2: antenna H: altitude of sensors

B: Baseline Length D: Direct Range

δD: Direct range difference Z: Terrain altitude

θ: observation angle α: direction angle of the baseline with respect to the horizontal plane

B⒳: Horizontal component of baseline B⒵: Vertical component of baseline

P: reference surface Q: target point on the surface

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings in the detailed description. In addition, in the following description of the present invention, if it is determined that a detailed description of a known function or configuration related to the present invention may obscure the gist of the present invention, the detailed description will be omitted. In addition, terms to be described below are terms defined in consideration of functions in the present invention, and may vary according to a user's intention or custom, and the definitions should be made based on the contents throughout the present specification.

FIG. 1 is a block diagram illustrating a process of generating a DEM using InSAR geometric characteristics by a single pass aircraft disclosed in the present invention. FIG. 3 is a procedure for measuring topographical altitude using InSAR geometrical characteristics by a single pass aircraft disclosed in the present invention.

That is, it is equipped with two antennas, one of which is used as both a transmitter and a receiver, and the other as a single path which is used as a bistatic receiver (a receiver in a radar system with a distance between transmitting and receiving). Single Pass) A schematic diagram of generating a DEM using the geometric characteristics of InSAR by an aircraft.

Referring to FIG. 3, first, in step S31, an antenna # 1 returns an echoes signal returned when an electric wave is emitted to a point on the earth from antenna # 1 for a transceiver in an InSAR system by a single pass aircraft. Received at 1 and antenna # 2 respectively. The signal received from each antenna is received in units of pixels having a magnitude and a phase, and generates one two-dimensional image from each antenna. In operation S32, the two SAR images are arranged in a range / doppler area to detect an interferometric phase difference on a pixel-by-pixel basis. The detected interference phase difference is converted into a phase difference-terrain altitude to provide a terrain altitude in units of pixels. Thereafter, in step S33, the accuracy of the terrain elevation information is improved by spatially filtering one pixel or multiple filtering by dividing an area into multiple pixels.

FIG. 2 shows InSAR geometrical characteristics by a single pass aircraft disclosed in the present invention.

Shuttle Radar Topography Mission (SRTM) is an application to measure topographical altitude using InSAR geometrical characteristics by single pass aircraft.

In step S34, the interferometry SAR technology combines two SAR complex images to provide a coherence map using a complex interferogram and the SAR interference picture, before generating the interference picture. Complex image combining is coregistered with sub-pixel accuracy, and after resampling, the first image is multiplied by the complex conjugate of the second image to generate an interference plot, and by the corresponding normalized correlation Create a coherence image. In step S35, a path difference having a direct relationship with the phase difference between the two images is measured from the interference plot. Will be obtained.

(One)

here, Is the radar signal wavelength. The topographic altitude is obtained from the phase difference, which is influenced by the interference baseline among the orbital parameters.

Surface Topography is obtained from the Interferogram Phase through the reverse algorithem only when the baseline formed by the two physical antennas A1 and A2 is accurately measured.

The process of calculating the surface elevation as a function of the Orbital Parameter using the Interferometer Imaging Geometry is as follows.

(2)

(3)

z is the surface elevation measured by both antennas A1 and A2, H is the aircraft's altitude, B is the baseline distance, θ is the look angle, D is the direct distance to the target point on the surface, and α is the horizontal plane. The angle δD of the baseline is the path difference of the reflected waves in the radars A1 and A2.

The phase elevation at each point on one image is measured and the topographic elevation at each point is obtained by the above equations (1), (2) and (3).

FIG. 3 is a procedure for measuring topographical altitude using InSAR geometrical characteristics by a single pass aircraft disclosed in the present invention.

Receive a signal from each antenna in units of pixels having a size and phase to generate a two-dimensional image one by one from each antenna (S31), and the two SAR images are aligned in a range / doppler region in pixel units. Interferometric Phase Difference is detected (S32), topographical altitude is calculated through the conversion of phase difference-terrain altitude (S33), multiple pixels are processed in one pixel, or one region is multi-pixel ( Spatial filtering is performed by dividing the data into multiple pixels (S34) to obtain highly accurate topographical information (S36) to generate a DEM (S35).

In the present invention having the above-described configuration, specific embodiments have been described, but various modifications can be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the claims below, but also by the equivalents of the claims.

The phase shift-terrain altitude conversion equation disclosed in the present invention enables accurate terrain elevation measurement, and even when a stereoscopic optical approach cannot be applied due to clouds or other obstacles, a DEM can be generated to measure terrain elevation. There is.

Claims (2)

Equipped with two antennas, one of which is used for both the transmitter and the receiver, and the other for terrain altitude measurements using InSAR geometrical characteristics by a single pass aircraft used as a bistatic receiver. In the DEM generation method for a) a SAR image processing step of receiving signals from each antenna in pixel units having a size and a phase and generating two two-dimensional images, one for each; b) arranging the two SAR images in a range / doppler region to detect an interferometric phase difference on a pixel-by-pixel basis; c) the topographic elevation is converted into a phase difference-terrain elevation by the following equation; , , (λ is the radar signal wavelength, Z is the surface elevation measured by both antennas A1 and A2, H is the aircraft's altitude, B is the baseline distance, θ is the look angle, and D is the direct Calculating a range according to the firing range, α is the angle of the baseline with respect to the horizontal plane, δD is the path difference of the reflected waves at A1 and A2); and d) filtering the processed topographical elevation information by spatially filtering one pixel into a multiple look or dividing one region into multiple pixels. Topographic Altitude Measurement Method. delete