METHOD OF CALCULATING TAVI BASED ON A BAND RATIO MODEL AND SOLAR ALTITUDE ANGLE

Abstract

The present invention relates to a method of calculating a Topography Adjusted Vegetation Index (TAVI) based on a band ratio model and a solar altitude angle. The method includes the folio wing steps: obtaining the apparent reflectance data of a remote sensing image through image preprocessing, analyzing the quality of the image and numerical distribution, calculating a Shadow Vegetation Index (SVI), and constructing a TAVI combinational algorithm:

[00001]$\mathrm{TAVI}=\frac{B_{\mathrm{ir}}}{B_r}+f\left(\right).Math.\frac{1}{B_r},$

calculating an adjustment factor f () with the solar altitude angle, and finally obtaining anti-topographic effect TAVI vegetation information. The TAVI in the present invention is composed of two band ratio submodels RVI and SVI, the denominators of both of which are red band data of a remote sensing image, and the adjustment factor f(), which is calculated by a solar altitude angle as a parameter with a sensor factor applied, has great physical significance. The TAVI calculation method does not need digital elevation model (DEM) data and remote sensing image classification when not depending on ground survey data,, and ensures that the interference of the topographic effects with the vegetation information can be effectively eliminated by the TAVI, thereby avoiding the problem of reduced inversion accuracy of ground vegetation information due to different registration accuracy of a remote sensing image and DEM data.

Claims

1. A method of calculating a Topography Adjusted Vegetation Index (TAVI) based on band ratio model and a solar altitude angle, the method comprising the following steps: step S1, preprocessing a remote sensing image and generating apparent reflectance data of the image by performing radiation correction on the remote sensing image; step S2, determining the apparent reflectance data of a red band and a near-infrared band of the remote sensing image, and analyzing whether the reflectance of mountainous vegetation is reasonable at the two bands to decide whether the image is normally available; step S3, calculating a Shadow Vegetation index (SVI) using the following formula: $\begin{array}{cc}\mathrm{SVI}=\frac{1}{B_r}& \left(1.Math.\text{-}.Math.1\right)\end{array}$ wherein SVI is the shadow vegetation index, and B.sub.r is the apparent reflectance data of the reel band of the remote sensing image; step S4, constructing a TAVI combinational algorithm, as specifically shown below: $\begin{array}{cc}\mathrm{TAVI}=\frac{B_{\mathrm{ir}}}{B_r}+f\left(\right).Math.\frac{1}{B_r}& \left(1.Math.\text{-}.Math.2\right)\end{array}$ wherein TAVI is the topography adjusted vegetation index; f() is an adjustment factor; B.sub.ir is the apparent reflectance data of the near-infrared band of the remote sensing image, and B.sub.r is the apparent reflectance data of the red band of the remote sensing image; step S5, reading a solar altitude angle during a pass of a satellite from a header tile of the remote sensing image and calculating the f() by the following formula:
f()=ssin() (1-3) wherein s is a sensor parameter, and a is the solar altitude angle; and step S6, obtaining mountainous anti-topographic effect vegetation index information by substituting the f() calculation result of the formula (1 -3) into the formula (1 -2).

2. The method of calculating a TAVI based on a band ratio model and a solar altitude angle according to claim 1, wherein the remote sensing image includes optical remote sensing image data.

3. The method of calculating a TAVI based on a band ratio model and a solar altitude angle according to claim 1, wherein s, which is the sensor parameter and is set to 1 by default, is dependent on different sensors.

4. The method of calculating a TAVI based on a band ratio model and a solar altitude angle according to claim 1, wherein the step S2 also comprises: calculating mean values, mid-values, variances and other indices of the red band and the near-infrared band.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0026] FIG. 1 is a schematic diagram of an image comparison in a research area in the present invention,

[0027] FIG. 2 is a schematic technical flow diagram of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and an embodiment.

[0029] Referring to FIG. 2, the present disclosure provides a method of calculating a Topography Adjusted Vegetation Index (TAVI) based on a band ratio model and a solar altitude angle. The method includes the following steps,

[0030] At step S1, image preprocessing is performed, which specifically includes: performing radiation correction on a multi-spectral remote sensing image to generate apparent reflectance data of the image.

[0031] At step S2, the quality of the image is analyzed, which specifically includes: determining the apparent reflectance data of a red band and a near-infrared band of the remote sensing image (calculating mean values, mid-values, variances and other indices of the two bands) and analyzing whether the reflectance of mountainous vegetation is reasonable at the two hands to decide whether the image is normally available.

[0032] At step S3, a Shadow Vegetation Index (SVI) is calculated using the following formula:

[00005]$\begin{array}{cc}\mathrm{SVI}=\frac{1}{B_r}& \left(4.Math.\text{-}.Math.1\right)\end{array}$

[0033] where SVI is the shadow vegetation index, and B.sub.r is the apparent reflectance data of the reel band of the remote sensing image.

[0034] At step S4, a TAVI combinational algorithm is constructed, as specifically shown below:

[00006]$\begin{array}{cc}\mathrm{TAVI}=\frac{B_{\mathrm{ir}}}{B_r}+f\left(\right).Math.\frac{1}{B_r}& \left(4.Math.\text{-}.Math.2\right)\end{array}$

[0035] where TAVI is the topography adjusted vegetation index; f() is an adjustment factor; B.sub.ir is the apparent reflectance data of the near-infrared band of the remote sensing image, and B.sub.r is the apparent reflectance data of the red band of the remote sensing image.

[0036] At step S5, the adjustment factor f() is calculated. A solar altitude angle during a pass of a satellite is read from a header file of the remote sensing image and f() is calculated by the following formula:

f()=ssin() (4-3)

[0037] where s is a sensor parameter. In an embodiment of the present invention, s is set to 1 by default. The values of s may be slightly adjusted according to different sensors. The value of the Larsdsat 5 TM data is 0.9, and the value of Landsat 8 OLI is 1.2.Math. is the solar altitude angle.

[0038] At step S6, the TAVI information is calculated. Mountainous anti-topographic effect vegetation index information is obtained by substituting the f() calculation result of the formula (4-3) into the formula (4-2).

[0039] The remote sensing image includes optical remote sensing image data.

[0040] The foregoing are descriptions of the preferred embodiment of the present invention, and any variations and modifications made within the application patent scope of the present invention shall all be encompassed in the scope of the present invention.