Summary of key points: SPOT data download, image band data introduction, and three methods of multispectral data simulation for true color [Reprinted and integrated]

foreword

First of all, I am very grateful to the bloggers who have studied the GIS field for sharing. The link below is the original text for reference. On the basis of fully respecting the original author, I have integrated and compiled this article. If there is any infringement, please contact me to modify and delete it! Thank you so much!

btw whymultispectral dataneed to gosimulate true color:
→→→Mainly aiming at the problem that some remote sensing data lack blue bands and cannot perform true-color image synthesis, a method for simulating true-color images of multi-spectral sensors is proposed.

（以上仅供个人学习使用）
The link to the original text is attached below:
Three methods for simulating true color with spot multispectral data Three methods
for simulating true color with SPOT5 multispectral data Three methods for
color synthesis of remote sensing images

Coursework

Requirements: Completed using SPOT imagery (20m) image data of the past five yearsExtraction of urban impervious surfaces, vegetation and water bodies, which are saved in three folders respectively, and the files are named in chronological order. The website for downloading image data: REGARDS OSS
The detailed steps of downloading image data can refer to the following link: Spot Satellite Introduction and
Data Download I moved over the link for downloading data:
spot1- The download link of spot5 free satellite data is: spot1-spot5 The download link of free satellite data spot-6 paid data is: spot-6 paid data The download link of spot-7 paid data is: spot-7 paid data

Infrared band

The following is an introduction to the near-infrared band and the mid-infrared band:
Original text reference link: What is the difference between near-infrared and mid-infrared?
The main difference between near-infrared and mid-infrared is the band range, and the other spectrum carries information. This leads to the difference in sampling methods and applications between the two.
band range, according to 波长的大小, 红外波段can be divided into three distinct regions:

Infrared band	The size of the wavelength
near infrared region	0.75~2.5μm
mid-infrared region	2.5~25μm
far infrared region	25~1000μm

The near-infrared is produced by molecules 倍频, the mid-infrared belongs to molecules , and the far-infrared belongs to molecules . According to the relationship between wavelength and energy,合频
基频振动光谱
转动光谱某些基团的振动光谱
Enear-infrared>Emid-infrared>Efar-infrared

SPOT satellite parameters

SPOT-1,2,3

Each satellite of SPOT-1, 2, and 3 carries a total of 2 instruments, HRV-1 and HRV-2, and the detailed parameters of each band of the satellites are as follows:

name	band	Wavelength range/μm	resolution
band 1 (xs1)	green band	0.50 - 0.59 μm	20 m
band 2 (xs2)	red band	0.61 - 0.68 μm	20 m
band 3 (xs3)	near infrared band	0.78 - 0.89 μm	20 m
band 4 (swir)	Mid-infrared band	1.58 - 1.75 μm	20 m
panchromatic	panchromatic band	0.51 - 0.73 μm	10 m

SPOT-4

The SPOT-4 satellite carries a total of two instruments, HRVIR-1 and HRVIR-2, and the detailed parameters of each band of the satellite are as follows:

name	band	Wavelength range/μm	resolution
band 1 (xs1)	green band	0.50 - 0.59 μm	20 m
band 2 (xs2)	red band	0.61 - 0.68 μm	20 m
band 3 (xs3)	near infrared band	0.78 - 0.89 μm	20 m
band 4 (swir)	Mid-infrared band	1.58 - 1.75 μm	20 m
panchromatic	panchromatic band	0.50 - 0.73 μm	10 m

SPOT-5

The SPOT-5 satellite carries 2 instruments for stereo view: HRG1 and HRG2. Innovatively introduced the THR super mode, which can create a 2.5 m resolution image from two 5 m resolution images. The detailed parameters of the satellite's band are as follows:

name	band	Wavelength range/μm	resolution
band 1 (xs1)	green band	0.50 - 0.59 μm	10 m
band 2 (xs2)	red band	0.61 - 0.68 μm	10 m
band 3 (xs3)	near infrared band	0.78 - 0.89 μm	10 m
band 4 (swir)	Mid-infrared band	1.58 - 1.75 μm	10 m
panchromatic	panchromatic band	0.48 - 0.71 μm	5 m
panchromatic super-mode	super panchromatic band	0.48 - 0.71 μm	2.5 m

SPOT-6,7

The SPOT-6/-7 are the successors of the SPOT-5 with increased resolution and added blue bands. In addition, these two satellites form a constellation with Pléiades-1 and Pléiades-2 satellites (resolution 0.5m), and the four satellites are 90° apart on the same orbit.

name	band	Wavelength range/μm	resolution
band 1 (xs1)	blue band	0.455 - 0.525 μm	6 m
band 2 (xs2)	green band	0.53 - 0.59 μm	6 m
band 3 (xs3)	red band	0.625 - 0.695 μm	6 m
band 4 (swir)	near infrared band	0.76 - 0.89 μm	6 m
panchromatic	panchromatic band	0.45 - 0.75 μm	1.5 m

Three ways to simulate true color

After our data is downloaded, the next three methods of multispectral data simulation of true color.
First introduce color synthesis: color synthesis technology is to use the visual characteristics of the eyes to synthesize many different colors with a few shades or dyes.
Remote sensing image color synthesis includes four methods 伪彩色合成: , 真彩色合成, 假彩色合成and synthesis. : It is a method of transforming different gray levels in a single-band grayscale image into colors according to a specific functional relationship, and then displaying color images, mainly through模拟彩色
伪彩色合成Density Segmentationto fulfill.

真彩色合成: That is, the wavelength of the wavelength band selected in color synthesis is the same or similar to the wavelength of red, green and blue, and the obtained image color is similar to the true color synthesis method. For example, 3、2、1assigning three colors to the bands of the TM image respectively 红、绿、蓝, since the assigned colors are the same as those of the original bands, an approximate true-color image can be obtained.

假彩色合成: It is the most commonly used synthesis method. For multi-band remote sensing images, 选取其中的任意3个波段，分别赋予the three primary colors of red, green and blue can be used to synthesize color images on the screen. However, the synthesized color image does not represent the real color of ground objects.
The bands selected for false color synthesis should be based on the spectral characteristics of ground features as the starting point, and different band synthesis methods are used to highlight different ground feature information.
In the TM image of LANDSAT,
the band 2 is the green band (0.52-0.60um),
the band 3 is the red band (0.63-0.69), and
the band 4 is the near-infrared band (0.76-0.90), and the false color of color synthesis is assigned
to each The image is called a standard false color image. Similarly, for the MSS image, the standard false color image can be obtained by selecting the bands and assigning colors to them, and the standard false color synthesis scheme of the SPOT image is as follows . In the standard false-color image, features such as vegetation, water bodies, urban and rural areas, mountains, and plains are highlighted. Vegetation is red, water is black or blue, towns are dark, and the type information of ground objects is rich.4、3、2波段红、绿、蓝4、2、1红、绿、蓝3（红）、2（绿）、1（蓝）

模拟真彩色合成: 3 methods
1) The method provided by SPOT IMAGE:
Red is represented by XS2,
green is realized by (XS1+XS2+XS3)/3 band operation, and
blue is replaced by XS1 band;

2) The method in RRDAS IMAGING software:
red is represented by XS2,
green is realized by the band algorithm of (XS1*3+XS3)/4, and
blue is replaced by XS1 band;

3) Uncertain parameter method:
this method introduces the panchromatic band (P)
red is represented by (aP+(1-a)XS3),
green is realized by 2P XS2/(XS1+XS2) band operation, and
blue is realized by 2P XS1/( XS1+XS2) band instead, in order to prevent oversaturation, the coefficient a is set according to the remote sensing image landscape, between 0.1-0.5.

reference

For the details that need to be dealt with in our course assignments, I suggest you refer to this link:
Use ENVI to extract the water range of the area of ​​interest in the SPOT image