Geometric correction, ortho correction, image registration, radiometric calibration, radiometric correction, atmospheric correction, topographic correction concept detailed

first, geometric correction

1. Concept

is the process of eliminating or correcting the geometrical errors of remote sensing images;

is to realize the transformation of the coordinate system of digitized data and the correction of deformation error of drawing (yellow apricot Element).

Common GIS software usually has the functions of affine transformation, similarity transformation and two-time transformation.

Affine transformations can scale the coordinate data in the X and Y directions at different scales, while twisting, translating, and rotating. The characteristics of affine transformation are as follows: (1) The linear transformation is still a straight line, (2) The parallel lines are still parallel after the transformation, and (3) the length ratio in different directions is changed.

2, the cause of image deformation

(1) Systematic: caused by the sensor itself, regular and predictable, can be corrected with the sensor model, the satellite ground receiving station has completed the work

(2) Non-systematic: the influence of the sensor platform position and the change of moving state (air height, speed, pitch and yaw)

(3) The impact of the Earth itself on imagery: topography, curvature of the Earth's surface, Earth's rotation

(4) Influence of atmospheric refraction

3. Resampling method

The final goal of the correction is to determine the number of rows and columns of the corrected image, and then find the luminance value for each cell in the new image.

(1) Nearest neighbor law (Nearest Neighbor):

(2) Bilinear interpolation method (Bilinear):

(3) Three-time convolution interpolation (Cubic convolution):

4. Calibration method

The following figure is the correction method provided in the ENVI software:

(1) Image to image geometry correction: The same figure appears in the same position as the corrected image by selecting a point (or control point) with the same name from two images as a datum for a raster file with no geometry correction or geometry correction. Most geometric corrections use this method.

(2) image to Map: The process of planar image geometry through ground control points, which can be entered, retrieved from a vector file, or obtained from a raster file. This method can be used for topographic map correction.

Note: The same specification file, can be generated by the way the header file to achieve batch geometry correction, see C # Remote sensing Data header file batch generator.

(3) Using the satellite's own geo-location file for geometric correction, as shown below:

second, positive shot correction

1. Concept

Positive-shot correction is the process of correcting image space and geometric distortion to produce a multi-center projection plane orthographic image, which can also cause geometric distortion caused by topography besides correcting the distortion of general system factors.

Positive-shot correction is a kind of geometric correction, which is consistent with the geometric correction process of image to map, which requires elevation point or DEM, and has high precision in the area with large terrain fluctuation.

2. Correction method

The ENVI provides no control points (orthorectify sensor type), a control point (orthorectify sensor type with Ground control) and a positive injection process correction tool three correction methods.

(1) Ortho correction without control point

Main Menu →map→orthorectification→quickbird→orthorectify QuickBird

(2) Positive shot correction with control point

Main Menu →map→orthorectification→quickbird→orthorectify QuickBird with Ground Control

(3) Positive injection calibration Process tool

Toolbox →geometric Correction→orthorectification→rpc orthorectification Wrokflow

Third, image registration

1. Concept

2. Methods

(1) georeferencing for georeferencing raster imagery in ArcGIS, with the following toolbar:

Procedure: ① Define coordinate system ② Select control points, input latitude and longitude, etc.

(2) Vector data with spatial adjustment, the following toolbar:

iv. radiometric Calibration

1. Concept

Radiometric calibration is the conversion of voltage or digital quantization values recorded by the sensor into:

The process of ① radiant Brightness (Radiance) (Liang Shunlin, 2009) or

② surface (apparent) reflectivity (reflectance) and

The process of ③ brightness temperature (brightness temperature).

2, Calibration classification

According to different use requirements or application purposes, can be divided into absolute calibration and relative calibration.

Absolute Calibration : The quantitative relationship between radiation luminance value and DN value is established through various standard radiation sources. For general Sensors:

L into =gain*dn + Offset

Relative calibration : refers to the relative values (Tong Qingxi, 2006) that determine the intensity of radiation measured before each cell in the scene, between each detector, between the spectra, and at different times.

The following figure shows the radiometric calibration and atmospheric correction tools provided by the ENVI:

3. Calibration of sensor radiation

(1) Pre-launch Lab calibration

(2) on-board calibration based on the onboard marker

(3) After the launch of the calibration (site calibration):

① Ocean Calibration (Qinghai Lake, China)

② Desert Calibration (next to the desert in Dunhuang, China)

③ Cloud Calibration

④ Other: Dry lakes, permanent ice shells, clouds of shadows on the water, moon

v. Radiation correction

1. Concept

The radiation intensity that enters the sensor is reflected in the image as the luminance value (or grayscale value). The greater the radiation intensity, the greater the luminance value. This value is mainly affected by two physical quantities: one is the radiation intensity of solar radiation to the ground, and the other is the spectral reflectance of the objects. When the solar radiation is the same, the difference of the luminance on the image directly reflects the difference of the ground reflectance. But the actual measurement, found that the radiation intensity value is also affected by other factors, the change is part of the need for correction, it is called radiation distortion .

The causes of radiation distortion are: (1) The error of the sensor itself (2) the effect of the atmosphere on radiation (3) The effect of topography on radiation (topographic correction)

2. Radiation correction Method (Meino)

(1) Histogram minimum value removal method

(2) Regression analysis method

3, for the cause of radiation distortion, complete radiation correction includes: sensor correction, atmospheric correction, topographic correction and sun height angle correction.

Vi. Atmospheric Correction

1. Concept

2. Purpose

The objective of atmospheric correction is to eliminate the influence of factors such as atmosphere and illumination on the reflection of ground objects, and to obtain real physical model parameters such as reflectivity, radiation and surface temperature, to eliminate the influence of water vapor, oxygen, carbon dioxide, methane and ozone in the atmosphere on the reflection of objects, and to eliminate the scattering of atmospheric molecules and aerosols. In most cases, the atmospheric correction is also the process of retrieving the true reflectivity of the object.

3. Method classification

Absolute atmospheric correction method: Mortran model based on radiative transmission, Lowtran model, Actor model and 6S model, etc.

Relative atmospheric correction method: Invariant target method based on statistics and histogram matching method

4. ENVI provides atmospheric correction function

(1) Simplified Dark Cell method (Dark subtraction)

(2) reflectance inversion based on statistical model

① Flat Field method (Flat field,ff), logarithmic residuals (log residuals), internal averaging (Internal Average Relative reflectance), and empirical linearity (empirical line).

(3) Invariant target law

(4) FLASSH Atmospheric correction module

(5) Fast atmospheric correction (Quick atmospheric Correction)

(6) Thermal infrared atmospheric correction

Toolbox →radiometric correction→thermal Atm Correction Tool

Vii. Topographic correction

1. Concept

To eliminate the influence of topography on the reflectance of remote sensing.

2. Methods

(1) Cosine correction method

(2) IPW method

3. ENVI topographic correction

adjourned